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Positively Charged Iridium(III) Triazole Derivatives as Blue Emitters for Light‐Emitting Electrochemical Cells
Advanced Functional Materials
Abstract
Cationic blue-emitting complexes with (2,4-difluoro)phenylpyridine and different 1,2,3-triazole ligands are synthesized with different counterions. The influence of the substituents on the triazole ligand is investigated as well as the influence of the counterions. The substituents do not change the emission energy but, in some cases, slightly modify the excited-state lifetimes and the emission quantum yields. The excited-state lifetimes, in apolar solvents, are slightly dependent on the nature of the counterion. A crystal structure of one of the compounds confirms the geometry and symmetry postulated on the basis of the other spectroscopic data. Light-emitting electrochemical cell devices are prepared and the recorded emission is the bluest with the fastest response time ever reported for iridium complexes.
... Different triazole rings were also employed to replace the pyridine ring in bpy for blue-shifting the emission of cationic iridium(III) complex. With 2-(1H-1,2,3-triazol-4-yl)pyridine (123-trzpy) as the skeleton, several 123-trzpy-type ancillary ligands were prepared (see ligands 123-trzpy-ada, 123-trzpy-bn, 123-trzpy-ph, and 123-trzpy-biph in Figure 4), [104] which showed similar ability to pzpy to stabilize the LUMO and blue-shift the emission of cationic iridium(III) complex. In solution, [Ir(dfppy) 2 (123-trzpy-R)] + A − (A = PF 6 or BF 4 ) showed similar blue emission to [Ir(dfppy) 2 (pzpy)]PF 6 , with the emission peaks located around 452 and 483 nm. ...
... In solution, [Ir(dfppy) 2 (123-trzpy-R)] + A − (A = PF 6 or BF 4 ) showed similar blue emission to [Ir(dfppy) 2 (pzpy)]PF 6 , with the emission peaks located around 452 and 483 nm. [104] The LECs ITO/PEDOT:PSS/ [Ir(dfppy) 2 (123-trzpy-R)] + A − :TBAOAf (molar ratio 1:1) (70 nm)/ Al (TBAOTf is tetrabutylammonium trifluoromethanesulfonate) afforded blue EL peaked around 460 and 480 nm. [104] At 5.0 V, the LECs showed maximum brightness at 14.5−44.9 ...
... [104] The LECs ITO/PEDOT:PSS/ [Ir(dfppy) 2 (123-trzpy-R)] + A − :TBAOAf (molar ratio 1:1) (70 nm)/ Al (TBAOTf is tetrabutylammonium trifluoromethanesulfonate) afforded blue EL peaked around 460 and 480 nm. [104] At 5.0 V, the LECs showed maximum brightness at 14.5−44.9 cd m −2 and half-lifetimes at 3.4−38 min. ...
Light‐emitting electrochemical cells (LECs) are one of the most promising technologies for solid‐sate lighting. Among them, LECs based on phosphorescent iridium(III) complexes have attracted significant research interest in the past 15 years, because of their high efficiency and tunable emission color across the entire visible spectrum. To fabricate white LECs for lighting, high‐performance blue LECs are the first prerequisite. Huge efforts have been devoted to improving the performances of blue LECs based on iridium(III) complexes either by developing new blue‐emitting complexes or by engineering the devices. Nevertheless, blue LECs have still shown much lower performances (brightness, efficiency, stability, etc.) compared to the red, orange‐red, yellow, and green counterpart devices. In particular, a single blue LEC with satisfactory blue‐color purity, high efficiency, and high stability is still missing. Here, the advances in blue‐emitting iridium(III) complexes for LECs and the device engineering on LECs using the complexes are reported. The challenges ahead are discussed, and future prospects are outlined. Blue light‐emitting electrochemical cells (LECs) incorporating iridium(III) complexes have been extensively researched over the past 15 years, for the ultimate goal of fabricating white LECs for solid‐state lighting. The advances in blue‐iridium(III) complexes used for LECs, and the device engineering on LECs using the complexes, are reviewed. The challenges ahead and future prospects are also discussed.
... 25,26 The replacement of one df-ppy ligand in Ir(df-ppy) 3 with the substituted triazolylpyridine ligand (ptb) results in even greater MO stabilisation, more positive redox potentials, and a further blue-shift in luminescence. [26][27][28][29] Despite its lower photoluminescence quantum yield (0.21), 26,27 [Ir(df-ppy) 2 (ptb)] + produces more intense co-reactant ECL with TPrA, 26 and several close analogues have been reported to exhibit greater annihilation ECL efficiencies 28 than Ir(ppy) 3 . ...
... 25,26 The replacement of one df-ppy ligand in Ir(df-ppy) 3 with the substituted triazolylpyridine ligand (ptb) results in even greater MO stabilisation, more positive redox potentials, and a further blue-shift in luminescence. [26][27][28][29] Despite its lower photoluminescence quantum yield (0.21), 26,27 [Ir(df-ppy) 2 (ptb)] + produces more intense co-reactant ECL with TPrA, 26 and several close analogues have been reported to exhibit greater annihilation ECL efficiencies 28 than Ir(ppy) 3 . ...
... The emission spectra of [Ir(df-ppy) 2 (ptb)] + and [Ir(df-ppy-CF 3 ) 2 (ptb)] + show resolved vibronic structure (consistent with other [Ir(C^N) 2 (L)] + complexes in which L is a 1,2,3-triazole ligand) due to some mixing between the 3 MLCT and 3 LC states. 27,29,30,37,41 Upon application of alternating anodic and cathodic potentials at the working electrode that were sufficient to oxidise Ir(ppy) 3 and reduce [Ir(df-ppy-CF 3 ) 2 (ptb)] + (Fig. 8a, Expt (v)), no significant ECL emission was observed (Fig. S9, ESI †). By design, the subsequent reaction of the oxidised and reduced complexes is not sufficiently exergonic to generate the excited state Ir(ppy) 3 * species (unlike eqn (10)). ...
Previously reported annihilation ECL of mixtures of metal complexes have generally comprised Ir(ppy)3 or a close analogue as a higher energy donor/emitter (green/blue light) and [Ru(bpy)3]²⁺ or its derivative as a lower energy acceptor/emitter (red light). In contrast, here we examine Ir(ppy)3 as the lower energy acceptor/emitter, by combining it with a second Ir(III) complex: [Ir(df-ppy)2(ptb)]⁺ (where ptb = 1-benzyl-1,2,3-triazol-4-ylpyridine). The application of potentials sufficient to attain the first single-electron oxidation and reduction products can be exploited to detect Ir(ppy)3 at orders of magnitude lower concentration, or enhance its maximum emission intensity at high concentration far beyond that achievable through conventional annihilation ECL of Ir(ppy)3 involving comproportionation. Moreover, under certain conditions, the colour of the emission can be selected through the applied electrochemical potentials. We have also prepared a novel Ir(III) complex with a sufficiently low reduction potential that the reaction between its reduced form and Ir(ppy)3⁺ cannot populate the excited state of either luminophore. This enabled, for the first time, the exclusive formation of either excited state through the application of higher cathodic or anodic potentials, but in both cases, the ECL was greatly diminished by parasitic dark reactions.
... 25,31 The lower-lying bands in the visible region (>350 nm) can be assigned, according to the bibliography, to spin-allowed metal-to-ligand charge-transfer ( 1 MLCT) transitions and spin-forbidden 3 MLCT transitions (promoted by the strong spin−orbit coupling of the iridium center) with a strong π−π* character. 19,86 In the complexes with ppy ligands, the maximum of this band appears at 375−378 nm for complexes with a N^C: ligand bearing methyl substituents on the pyridine ring; a very small red shift is observed for those derivatives with a methylene bridge in the N^C: ligand (380 nm), while the complexes with the electron-withdrawing nitro substituent exhibit a blue shift of 10 nm. A larger hypsochromic shift (20 nm) is observed for complexes with dfppy as the cyclometalating ligand when compared with similar ppy complexes. ...
... 91 The oxidation therefore takes place in the cyclometalating ligand-Ir fragment and, as stated, these results are in good agreement with the experimental E ox values, which indicated the effect of the cyclometalating ligand and small influence of the ancillary ligand (Table 3). In contrast to results found for [Ir-(C^N) 2 (N^N)] + species, where the LUMO is located mainly on the N^N ligand, 1,16,[18][19][20]69 and similar to that found in analogous complexes with N^C: ligands, 25,28,29 the LUMO in compounds 1, 7, and 8 is located on the phenyl-pyridine or difluorophenyl-pyridine ligands but with a higher participation of the pyridine fragment (especially that of ligand L A , see Figure 1). This latter finding could explain the lower difference in the energy level between the LUMO of the dfppy derivative (8) and the LUMO of the ppy complexes 1 and 7 when compared with the difference in energy of the HOMO of the same compounds. ...
... Elemental analyses were performed with a Thermo Quest FlashEA 1112 microanalyser, and IR spectra were obtained on a Shimadzu IR Prestige-21 infrared spectrometer equipped with a Pike Technologies ATR. The fast atom bombardment (FAB + ) mass spectrometry (MS) measurements were obtained with a Thermo MAT95XP mass spectrophotometer with a magnetic sector. 1 H and 13 C{ 1 H} NMR spectra were recorded on Varian Innova 500 and Varian Unity 400, and the latter was also used for the recording of the 19 F and 31 P{ 1 H} NMR. Shifts (in ppm) are related to tetramethylsilane, Si(CH 3 ) 4 , (for 1 H and 13 C), CFCl 3 ( 19 F), and 85% H 3 PO 4 ( 31 P). 1 H− 1 H COSY spectra: standard pulse sequence with an acquisition time of 0.214 s, pulse width of 10 ms, and relaxation delay of 1 s was used, optimizing the number of scans, width of the window, and number of increments depending on the sample conditions. ...
Precursors of chelate pyridine-N-heterocyclic carbene (N^C:) ligands with methyl- or benzyl-substituted imidazolylidene fragments were synthesized. They were used to obtain 12 iridium bis-cyclometalated complexes of the type [Ir(C^N)2(N^C:)]+ (C^N = 2-(phenyl)pyridinato-C2,N, ppy, 2-(4,6-difluorophenyl)pyridinato-C2,N, dfppy). The ancillary N^C: ligands contain different structural modifications. The aim of the work was to analyze the effect that changes in the two types of ligands have on the photophysical and electrochemical properties and also on the behavior of these materials as photosensitizers. The X-ray crystal structures of five complexes were determined. The complexes emitted in the blue-green region. It was expected that the frontier orbitals and thus the photophysical and electrochemical properties would be controlled by the main C^N ligands, and it was demonstrated that the effect of the modifications in the N^C: ligand, especially the presence of a nitro group in the pyridine ring or the interruption of conjugation between the two rings, also affected these properties. The quenching with O2 and photostability studies were also performed. Density functional theory calculations were used to explain the behavior of some derivatives. The complexes and other previously reported compounds were employed as photosensitizers (PS) in preliminary studies on the production of H2 from water using [Co(bpy)3]Cl2 (bpy = 2,2'-bipyridine) as catalyst and triethanolamine (TEOA) as the sacrificial reductant. The absence of quenching of the PS with TEOA allowed us to propose an oxidative quenching mechanism.
... Most reported efficient blueemitting iTMCs showed sky-blue EL [80,[125][126][127] while saturated blue-emitting iTMCs exhibited moderate EL efficiencies. [128][129][130][131][132] As such, efficient white LECs employing sky-blue-emitting iTMCs commonly exhibited greenish white EL even when saturated red-emitting iTMCs were doped. [85,125,126] In 2012, Su et al. proposed suppressing the green part of EL emission from a sky-blue-emitting iTMC by employing destructive interference from microcavity effect, rendering saturated blue EL from iTMC. ...
... Combining these two filters, both green and red emissions are suppressed, leading to saturated blue EL emission with CIE coordinate of (0.14, 0.22), which is among the bluest reported values for the blue LECs based on iTMCs. [128][129][130][131][132] These results reveal the flexibility in wavelength tuning of the plasmonic filters used to realize saturated blue LECs. ...
Since the first demonstration of light‐emitting electrochemical cells (LECs) in 1995, much effort has been made to develop this technology for display and lighting. A common LEC generally contains a single emissive layer blended with a salt, which provides mobile ions under a bias. Ions accumulated at electrodes facilitate electrochemical doping such that operation voltage is low even when employing high‐work‐function inert electrodes. The superior properties of simple device architecture, low‐voltage operation, and compatibility with inert metal electrode render LECs suitable for cost‐effective light‐emitting sources. In addition to enormous progress in developing novel emissive materials for LECs, optical engineering has been shown to improve device performance of LECs in an alternative way. Light outcoupling enhancement technologies recycle the trapped light and increase the light output from LECs. Techniques to estimate emission zone position provide a powerful tool to study carrier balance of LECs and to optimize device performance. Spectral tailoring of the output emission from LECs based on microcavity effect and localized surface plasmon resonance of metal nanoparticles improves the intrinsic emission properties of emissive materials by optical means. These reported optical techniques are overviewed in this review. Light outcoupling enhancement technologies recycle trapped light and increase the light output from light‐emitting electrochemical cells (LECs). Techniques to estimate emission zone position provide a powerful tool to study carrier balance of LECs for optimizing device performance. Spectral tailoring of the output emission from LECs based on microcavity effect and localized surface plasmon resonance generates desired emission properties.
... [62] De Cola and co-workers introduced pyridine-N-substituted-1,2,3-triazole as the ancillary ligand, which was hoped to further destabilize the LUMOs of the complexes and thus blueshift the emission. [63] The complexes shared the same dfppy cyclometalated ligands and two sorts of counterions, BF 4 − and PF 6 − . In contrast, the pyridine-triazole ligand was substituted with a variety of different groups represented by adamantane and phenyl rings (the complexes are shown in Figure 7; complexes 56-63). ...
... Mater. 2020, 30,1907156 [55][56][57][58][59][60][61][62][63][64][65] www.afm-journal.de www.advancedsciencenews.com device efficiency was made no mention of. ...
Since their emergence in the 1990s, light‐emitting electrochemical cells (LECs) have attracted much attention due to their unique properties and potential for use as an alternative technology for illuminations and displays. After decades of development, however, the performance of LECs remains far from satisfactory for practical applications, in particular for those requiring blue light. Efforts have been made to develop of highly efficient blue‐emitting materials and more advanced device structures, aiming at realizing blueshifted emission, enhancing efficiency, and extending prolonged device lifetimes. A timely review into the current state of blue LECs is deemed imperative, as a full understanding of the molecular and device design strategy and identification of the major challenges that must be addressed to realize practical applications is necessary. A specific summary of recent progress on blue LECs is provided, with the focus placed on design strategies for blue emitters for LECs and device structures with respect to color tuning, efficiency enhancement, and stability improvement. Finally, the direction of development strategies in the future is suggested. Recent progress in blue‐light‐emitting electrochemical cells is summarized. In particular, emitting active materials and device structures are explored in order to provide a comprehensive understanding to researchers in this field.
... Ultrafast transient absorption 28 and emission upconversion 29 data for these and related complexes reveal an initially populated 3 MLCT/ 3 LC state followed by population transfer to the 3 MLCT/ 3 LL′CT state occurring on a picosecond time scale after photoexcitation. Replacement of the bpy ancillary N ∧ N ligand by pytz (4-(pyrid-2-yl)-1,2,3-triazole) in the complexes [Ir(ppy) 2 (pytz)] + and [Ir(dfppy) 2 (pytz)] + results in 3 MLCT/ 3 LC-based emission in room-temperature solutions 30 despite the LUMO in each case still being localized on the N ∧ N ligand, albeit being heavily destabilized with respect to those of their bpycontaining analogues. 31 Thus, the nature of the N ∧ N and C ∧ N ligands and their influence on the topology of the tripletexcited-state potential energy surface leads to fundamental differences in the excited-state dynamics and the resultant steady-state emission character. ...
... (i) First, variation of the ancillary N ∧ N ligand will enable selective tuning of the energy of the 3 MLCT/ 3 LL′CT state with an anticipated minimal impact on the C ∧ Nbased 3 MLCT/ 3 LC state. While the known complexes [Ir(ppy) 2 (pytz)] + (1a) and [Ir(dfppy) 2 (pytz)] + (2a) exhibit 3 MLCT/ 3 LC-based emission 30 despite possessing a pytz π*-based LUMO, ancillary ligands such as 2,2′-bipyrazine are known to be more electron withdrawing and have a lower energy LUMO than bpy which will promote 3 LL′CT-based emission. We therefore designed analogous ancillary ligands to pytz (a) containing progressively more electron withdrawing pyrimidine (pymtz, b) and pyrazine (pyztz, c) rings in place of pyridine. ...
Fundamental insights into the mechanism of triplet-excited-state interligand energy transfer dynamics and the origin of dual emission for phosphorescent iridium(III) complexes are presented. The complexes [Ir(C∧N)2(N∧N)]+ (HC∧N = 2-phenylpyridine (1a-c), 2-(2,4-difluorophenyl)pyridine (2a-c), 1-benzyl-4-phenyl-1,2,3-triazole (3a-c); N∧N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (pytz, a), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (pymtz, b), 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (pyztz, c)) are phosphorescent in room-temperature fluid solutions from triplet metal-to-ligand charge transfer (3MLCT) states admixed with either ligand-centered (3LC) (1a, 2a, and 2b) or ligand-to-ligand charge transfer (3LL'CT) character (1c, 2c, and 3a-c). Particularly striking is the observation that pyrimidine-based complex 1b exhibits dual emission from both 3MLCT/3LC and 3MLCT/3LL'CT states. At 77 K, the 3MLCT/3LL'CT component is lost from the photoluminescence spectra of 1b, with emission exclusively arising from its 3MLCT/3LC state, while for 2c switching from 3MLCT/3LL'CT- to 3MLCT/3LC-based emission is observed. Femtosecond transient absorption data reveal distinct spectral signatures characteristic of the population of 3MLCT/3LC states for 1a, 2a, and 2b which persist throughout the 3 ns time frame of the experiment. These 3MLCT/3LC state signatures are apparent in the transient absorption spectra for 1c and 2c immediately following photoexcitation but rapidly evolve to yield spectral profiles characteristic of their 3MLCT/3LL'CT states. Transient data for 1b reveals intermediate behavior: the spectral features of the initially populated 3MLCT/3LC state also undergo rapid evolution, although to a lesser extent than that observed for 1c and 2c, behavior assigned to the equilibration of the 3MLCT/3LC and 3MLCT/3LL'CT states. Density functional theory (DFT) calculations enabled minima to be optimized for both 3MLCT/3LC and 3MLCT/3LL'CT states of 1a-c and 2a-c. Indeed, two distinct 3MLCT/3LC minima were optimized for 1a, 1b, 2a, and 2b distinguished by upon which of the two C∧N ligands the excited electron resides. The 3MLCT/3LC and 3MLCT/3LL'CT states for 1b are very close in energy, in excellent agreement with experimental data demonstrating dual emission. Calculated vibrationally resolved emission spectra (VRES) for the complexes are in excellent agreement with experimental data, with the overlay of spectral maxima arising from emission from the 3MLCT/3LC and 3MLCT/3LL'CT states of 1b convincingly reproducing the observed experimental spectral features. Analysis of the optimized excited-state geometries enable the key structural differences between the 3MLCT/3LC and 3MLCT/3LL'CT states of the complexes to be identified and quantified. The calculation of interconversion pathways between triplet excited states provides for the first time a through-space mechanism for a photoinduced interligand energy transfer process. Furthermore, examination of structural changes between the possible emitting triplet excited states reveals the key bond vibrations that mediate energy transfer between these states. This work therefore provides for the first time detailed mechanistic insights into the fundamental photophysical processes of this important class of complexes.
... In the work of Zysman-Colman et al. [75] and other groups of researchers [76,77], phosphinoand isopropxantphos-derivatives were used in the preparation of heteroleptic complexes as depicted in structures 56-64 (Scheme 16). The results show that all the complexes gave sky-blue emissions, but had very low photoluminescence quantum yields generally found around λem = 477-510 nm. ...
... The results show that all the complexes gave sky-blue emissions, but had very low photoluminescence quantum yields generally found around λem = 477-510 nm. In the work of Zysman-Colman et al. [75] and other groups of researchers [76,77], phosphino-and isopropxantphos-derivatives were used in the preparation of heteroleptic complexes as depicted in structures 56-64 (Scheme 16). The results show that all the complexes gave sky-blue emissions, but had very low photoluminescence quantum yields generally found around λ em = 477-510 nm. ...
Intrinsic characteristics possessed and exhibited by Ir(III) cyclometalated complexes need to be further examined, understood, and explored for greater value enhancement and potentiation. This work focuses primarily on the comparative studies of the ligand structures, types, and their substituent influence on the photophysical and optoelectronic properties of typical cyclometalated mono- and binuclear iridium(III) complexes in solution or solid states.
... This ligand class exhibits several favourable properties for ECL detection, [22][23][24] including simple 'click chemistry' preparation 25 that provides a versatile point for derivatisation or attachment. 26 De Cola and co-workers have previously explored various [Ir(C^N) 2 (pt-R)] + complexes ( Fig. 2c; where C^N ¼ ppy or df-ppy, and R ¼ methyl, phenyl, benzyl, adamantyl, b-cyclodextrin and other groups) for photoluminescence, 27 light emitting electrochemical cells 28 and ECL 22 applications. The [Ir(df-ppy) 2 (pt-R)] + species exhibited a deeper blue emission than most charged Ir(III) complexes, and intense co-reactant ECL under aprotic and aqueous conditions. ...
... The model luminophores were employed because they were commercially available or readily synthesised and they avoided complications from the reactive peripheral functionality of their labelling derivatives 8 when assessing the properties of the luminophore. The [Ir(C^N) 2 (dm-bpy)] + and [Ir(C^N) 2 (ptb)] + complexes containing piq, ppy and df-ppy ligands have previously been reported, 23,28,38,45 but the two bt analogues were prepared in this study for the rst time. ...
Translation of the highly promising electrogenerated chemiluminescence (ECL) properties of Ir(III) complexes (with tri-n-propylamine (TPrA) as a co-reactant) into a new generation of ECL labels for bioassay necessitates the introduction of functionality suitable for bioconjugation. Modification of the ligands, however, can affect not only the photophysical and electrochemical properties of the complex, but also the reaction pathways available to generate light. Through a combined theoretical and experimental study, we reveal the limitations of conventional approaches to the design of electrochemiluminophores and introduce a new class of ECL label, [Ir(C^N)2(pt-TOxT-Sq)]⁺ (where C^N is a range of possible cyclometalating ligands, and pt-TOxT-Sq is a pyridyltriazole ligand with trioxatridecane chain and squarate amide ethyl ester), which outperformed commercial Ir(III) complex labels in two commonly used assay formats. Predicted limits on the redox potentials and emission wavelengths of Ir(III) complexes capable of generating ECL via the dominant pathway applicable in microbead supported ECL assays were experimentally verified by measuring the ECL intensities of the parent luminophores at different applied potentials, and comparing the ECL responses for the corresponding labels under assay conditions. This study provides a framework to tailor ECL labels for specific assay conditions and a fundamental understanding of the ECL pathways that will underpin exploration of new luminophores and co-reactants.
... [54][55][56][57][58][59][60][61][62][63] Ruthenium(II) polypyridine complexes possess several advantageous properties, such as visible-light absorption, large Stokes shift, long-lived excited states, high thermal, photo, and chemical stabilities, good solubility and stability in aqueous media, and low cytotoxicity. [64][65][66][67][68] Although the photophysical/ chemical properties of d 6 -metal polypyridine complexes containing 1,2,3-triazole ligand have been expansively studied by several research groups to date, [69][70][71][72][73] sensing and bio-imaging using these complexes are rarely explored. [74][75] Recently, a few Ru(II) and Ir(III) based probes of 1,2,3-triazole ligand have been reported by our group for sensing and bio-imaging through CÀ H analyte interaction. ...
A bis‐heteroleptic Ru(II) complex, 1[PF6]2 of a benzimidazole substituted pyridyl‐1,2,3‐triazole ligand (BiPT) for highly selective luminescence turn‐on detection of hypochlorous acid (HOCl) is reported. Detection of HOCl is achieved by the Markovnikov addition of HOCl to the C=C bond of 1,2,3‐triazole and a successive highly specific C(sp²)‐H chlorination at the C5 position of 1,2,3‐triazole. The chlorination at C5 in 1,2,3‐triazole is supported by high‐resolution mass spectrometry and ¹H NMR study. 1[PF6]2 shows high sensitivity towards HOCl in PBS buffer (pH 7.4) containing 5 % acetonitrile with a 37‐fold luminescence light‐up and a detection limit as low as 7.5 μM. HOCl mediated C(sp²)‐H chlorination increases the ³MC‐³MLCT energy gap as well as the population of the ³MLCT excited state and exhibits the radiative decay from the excited state of 1. The probe showed low cytotoxicity and efficiently permeated the cell membrane. The cell‐imaging experiments revealed rapid staining of the HeLa cells in the presence of exogenous HOCl.
... Transition metal III complexes have thermal stability, high emission efficiency, and broad capacity for adjusting optical characteristics through ligand modifications [15][16][17][18]. These characteristics make them promising for use in organic light-emitting diodes (OLEDs) [19,20], particularly red [21], green [22], and blue [23] OLEDs, light-emitting electrochemical cells [24], bio-imaging probes, chemo-sensors [25,26], and optoelectronic elements for future molecular computers [27]. ...
This study fabricates novel tris (2-phenylpyridinato-C2, N] iridium III thin films using an electron beam evaporator and investigates their structure formation, surface morphology, and linear/nonlinear optical properties. The structural features of thin films were examined using Fourier Transform spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscope (SEM). The optical characteristics for various doses of gamma radiation (3 kGy, 6 kGy and 9kGy) were investigated using a UV-Vis-NIR spectrophotometer in the wavelength range from 200 nm to 2500 nm. In addition, the values of fundamental energy gap (Efundamental) values showed a reduction from 2.30 to 1.92 eV and urbach energy increasing from 0.23 to 0.30 when the deposited film irradiated for 9 kGy. The third-order nonlinear susceptibility ( ), the nonlinear absorption coefficient ( ) and the nonlinear refractive index ( ) were determined for all gamma doses. Furthermore, The optical electronegativity ( ), the first moment ( ), the second moments of optical spectra ( ), the oscillator strength (f), the dispersion energy ( ), infinite dielectric constant ( ),oscillator energy ( ), the lattice dielectric constant ( ), and to the effective mass for as-deposited film are calculated as : 1.860, 17.29, 300.20, 0.9960 (eV)2, 4.15 eV, 4.52, 1.18 eV, 5.58, and 8.86 x1059 kg−1 m−3 respectively. The high values of ( ) for as-deposited and irradiated are essential for the creation of low power devices for nonlinear optical applications involving ultrafast switches, optical computers, and ultra-pulsed lasers.
... As predicted, the electron distribution in the Ir(III) complex is primarily spread over both the phenyl part of the ppy ligands and Ir 5d orbitals in the HOMO, while the LUMO is localized over both ppy ligands [7,33,34]. Despite the pyridine-triazole ligand containing a rich nitrogen aromatic ring which raises the LUMO energy level up to 1.87 eV [6,39,40], complexation with Ir metal leads to destabilization of the HOMO by 1. The two-dimensional fingerprint plots for the main intercontacts of Ir(III) complex are shown in Figure 8 and summarized in Table 3. ...
The cyclometallated Ir(III) complex [Ir(2,4-F2ppy)2(pyta)Cl], where ppy and pyta denote 2-phenylpyridine and pyridine-triazole respectively, was successfully synthesized by the reflux reaction of the 2-(1H-1,2,4-triazol-1-yl)pyridine ligand with the Ir(III) dimer [Ir(2,4-F2ppy)2(µ-Cl)]2. The Ir(III) complex were characterized by spectroscopic methods: NMR, FTIR, UV–Vis and LC-QTOF/MS, while the molecular structure was determined by the single crystal X-ray diffraction technique. The X-ray crystallographic study revealed that the Ir(III) ion was coordinated to one pyridine-triazole, one chloro and two difluorophenylpyridine ligands in a distorted octahedral geometry. Steady-state emission spectroscopy demonstrated that the Ir(III) complex emitted blue-green light in dichloromethane solution with an emission maximum at 469 nm due to the admixtures of ³LC and ³MLCT character excited states. DFT calculations on the Ir(III) complex showed that the HOMO was localized predominantly over the cyclometallating ligands and the Ir 5d orbitals, whilst the LUMO was located on both cyclometallating ligands, with the HOMO-LUMO energy gap being 3.86 eV. The intercontacts between different units of the cyclometallated Ir(III) complex were investigated by analyzing the Hirshfeld surface and molecular electrostatic potential surface plotted in the ground and triplet excited states. The X-ray structure of the Ir(III) complex was relatively well reproduced with B3LYP/LANL2DZ level of theory, where the two structures, experimental and theoretical, were well superposed. The calculated ground and triplet excited states geometries showed slight differences.
... So far, state-of-the-art LECs have been reported to exhibit EL emission color ranging from blue-green to yellow. [20][21][22]80] The device efficiencies of deep blue [165,166] and red LECs [23,167] are significantly low. The low emission efficiencies limit the device efficiencies of white LECs, which are essential in lighting applications. ...
Solid‐state white light‐emitting electrochemical cells (LECs) exhibit the following advantages: simple device structures, low operation voltage, and compatibility with inert metal electrodes. LECs have been studied extensively since the first demonstration of white LECs in 1997, due to their potential application in solid‐state lighting. This review provides an overview of recent developments in white LECs, specifically three major aspects thereof, namely, host–guest white LECs, nondoped white LECs, and device engineering of white LECs. Host–guest strategy is widely used in white LECs. Host materials are classified into ionic transition metal complexes, conjugated polymers, and small molecules. Nondoped white LECs are based on intra‐ or intermolecular interactions of emissive and multichromophore materials. New device engineering techniques, such as modifying carrier balance, color downconversion, optical filtering based on microcavity effect and localized surface plasmon resonance, light extraction enhancement, adjusting correlated color temperature of the output electroluminescence spectrum, tandem and/or hybrid devices combining LECs with organic light‐emitting diodes, and quantum‐dot light‐emitting diodes improve the device performance of white LECs by ways other than material‐oriented approaches. Considering the results of the reviewed studies, white LECs have a bright outlook.
... Modifying the output EL spectrumb ym eans of the thicknessdependentm icrocavity effect is effective for white LECs based on iTMCs for achieving whiteE Lw ith CIE coordinates approaching (0.33, 0.33). Saturated deep-blue-emitting iTMCs are scarce [40][41][42][43][44] and the moste fficient blue-emitting iTMCs showed sky-blueE L. [18,35,36,45,46] The reported white LECs using sky-blueemitting iTMCs generally showedg reenish-white EL even if doped with saturated red-emittingi TMCs. [33,35,36,39] Without saturatedd eep-blue-emitting iTMCs, suppressing the green spectral region in EL from sky-blue-emitting iTMCs by using microcavity effect hasb een shown to be an effective way to provide am ore saturated blue EL and thusp urer white emission. ...
The concept of solid-state light-emitting electrochemical cells (LECs) proposed in 1995 opened a new field in display and lighting technologies. The key advantage of this technology is based on a single emissive layer containing an emissive material and an ionic salt. Mobile ions in the emissive layer induce electrochemical doping at electrodes and thus the operation voltage can be reduced even by using air-stable electrodes. Since the first demonstration of LECs, many material-oriented efforts have been made in improving device performance of LECs. However, some difficulties arising from material properties still limit further optimizing device characteristics of LECs. Recently, optical techniques have been shown to achieve better device properties without employing new materials. Light extraction techniques recycle the light trapped in layered device structure and thus enhance device light output and efficiency of LECs. Recombination zone probing technique offers direct evidence of carrier balance in LECs and is helpful in optimizing device performance. Spectral filtering based on microcavity effect and localized surface plasmon resonance from metal nanoparticles show advantages of easy fabrication and compatibility with device processing of LECs. This minireview provides a brief overview of the three categories in recent advances of optical techniques of LECs.
The color-tuning strategies of solid-state light-emitting devices (ss-LEDs) are mainly focused on engineering molecular structures. In this paper, for the first time, we developed a facile strategy for tuning the electroluminescence (EL) color from orange to green through the addition of the ionic additive TBAP (tetrabutylammonium perchlorate). To achieve the active ionic emissive compound for use in a light-emitting electrochemical cell (LEC), the neutral biscyclometalated bromo tetrazole iridium(III) [Ir(ppy)2(BrTz)] was exchanged to its cationic complex, [Ir(ppy)2(BrTz-Me)]ClO4 (ppy = 2-phenyl pyridine, BrTz = 4-bromo-2-pyridine tetrazole, BrTz-Me = 4-bromo-2-pyridine methyl tetrazole) with a new synthetic strategy. This method allows employing neutral Ir-cyclometalated complexes, which are ruled out for use in LECs because of their non-ionic behaviors. In the following, an LEC based on the new cationic [Ir(ppy)2(BrTz-Me)]ClO4 as the emissive layer was fabricated between the FTO (fluorine-doped tin oxide) anode and Ga:In alloy cathode without using any additive or polymers, which makes this configuration the simplest ss-LED so far. By adding the ionic additives, the electroluminescence characteristics of [Ir(ppy)2(BrTz-Me)]ClO4 were dramatically increased, including luminance (L) from 162.8 cd/m2 for the device with an additive to 212.9 and 355.9 cd/m2 for devices containing LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) and TBAP, respectively. In particular, when TBAP was added to the [Ir(ppy)2(BrTz-Me)]ClO4 complex, the irradiance was significantly increased from 166.4 to 220.8 μW/cm2 with an efficacy of 1.78 cd/A and external quantum efficiency (EQE) value of 2.14%. The obtained EL results clearly showed that adding TBAP and LiTFSI significantly improved the electroluminescence characteristics and tuned the electroluminescence color.
The development of low-cost catalysts for the water oxidation reaction (WOR) is important for solving the bottleneck issues in water splitting and benefits the widespread utilization of renewable energy sources. Herein, four cobalt(II) triazolylpyridine complexes, namely [Co(DTE)2(H2O)2](ClO4)2·CH3COCH3 (1), [Co(DTE)2Cl2]·2CH3OH (2) (DTE = (1-(2-acetoxymethyl)-4-(2-pyridyl)1,2,3-triazole), [Co(DTEL)2(CH3OH)2](ClO4)2 (3), and [Co(DTEL)2Cl2]·H2O (4) (DTEL = (1-(2-hydroxy)-4-(2-pyridyl)1,2,3-triazole), were synthesized and characterized. The crystal structures of 1-3 were determined by X-ray single crystal diffraction analysis. The electrocatalytic water oxidation by 1-4 was studied in 0.1 M NaOAc-HOAc solutions. Complexes 1-4 were single-site molecular catalysts for the WOR under near-neutral conditions. The overpotentials for the WOR were 440 mV and 480 mV. The faradaic efficiencies were 77-92%. The rate constants kcat were 0.21-0.96 s-1. The catalytic activities were affected by the pendant groups of DTE and DTEL. Complexes with DTE (1 and 2) showed better activities than those with DTEL (3 and 4). Moreover, complexes 1-4 adsorbed on indium-doped tin oxide (ITO) and glassy carbon electrode surfaces were active for the WOR. A mechanism was proposed for the WOR catalyzed by 1-4.
We present here the synthesis and in‐depth physicochemical characterization of a double hetero[7]helicene fused with four triazole rings at both helical ends. The comparison of this triazole‐fused double helicene with the previously reported all‐carbon and thiadiazole‐fused analogs revealed the huge impact of the embedded aromatic rings on the photophysical features. The small structural variation of the terminal rings from thiadiazole to triazole caused a dramatic change of the photoluminescence quantum yields (PLQYs) from <1 % to 96 %, while the replacement of the terminal benzene rings with triazole rings induced a tenfold enhancement of the circularly polarized luminescence dissymmetry factor. These observations were well corroborated with transient absorption analysis and/or theoretic calculations. In addition, the triazole‐fused double helicene exhibited ambipolar redox behavior, enabling the generation of radical cation and anion species by electrochemical and chemical methods and showing its potential for spin‐related applications.
Generation of a promising antioxidative reagent with superior biocompatibility is urgently needed to remedy spinal cord injuries (SCI), repair the damaged neurons and restrain the secondary injuries caused by inflammation-induced oxidative stress. Inhibitory elements in the injury sites and necessitous inherent neural regeneration ability were major challenges for functional recovery after spinal cord injuries. We here developed a highly bioactive iridium complex (IrFPHtz) with enhanced antioxidative activities and improved SCI therapeutic efficacy. Both in vivo and in vitro, IrFPHtz has exhibited neuroprotective and anti-inflammatory properties. Mechanically, IrFPHtz directly targets SOD1 and upregulates the expression of SOD1 to eliminate the excess ROS production induced by SCI, and thus protecting neuron cells from further damage. As a result, IrFPHtz safeguarded the neurons and myelin sheaths against trauma, lessened glial scar conformations and facilitated the repair of neurons and long axon expansion in the glial scar. Furthermore, IrFPHtz significantly ameliorated the behavioral functions of SCI mice and promoted a satisfactory curative effect. Therefore, this study sheds light on a novel method for SCI treatment using IrFPHtz as a potential drug and implicates the clinical significance of metal complexes in diseases featuring with upregulated ROS species.
Cyclometallated iridium complexes possess fascinating electrochemical and photophysical properties that make them excellent candidates for a variety of photonic and optoelectronic applications. In particular, light-emitting electrochemical cells (LEECs) based on iridium-containing ionic transition-metal complexes (Ir-iTMCs) are a promising alternative to conventional organic light-emitting diodes with several advantages, including a simpler device structure, solution processability, and reduced manufacturing costs. This review aims to provide a comprehensive and systematic overview of the current status of Ir-iTMC-based LEECs using the archetypal complex [Ir(ppy)2(bpy)]PF6 as a reference emitter. After a discussion of the device fundamentals and important photophysical and device parameters, key strategies for tuning the emission characteristics and device stability through LUMO and HOMO stabilization/destabilization are presented using numerous examples from the literature, with a particular focus on ligand modification with hydrophobic, electron-withdrawing, and electron-donating substituents, π-stacking interactions, and alternative ancillary and cyclometalated ligand skeletons. Comprehensive data tables summarizing the photophysical and LEEC properties of the various classes of iridium complexes reported to date are also provided. Finally, in an effort to highlight promising directions for future research, the current champion iridium complexes for fabricating state-of-the-art LEECs are identified, and the merits and limitations of existing approaches are discussed.
Two heteroleptic monocationic Ir(III) complexes bearing 6,6′-bis(7-benzothiazolylfluoren-2-yl)-2,2′-biquinoline as the diimine ligand with different degrees of π-conjugation were synthesized and their photophysics were investigated by spectroscopic techniques and first principle calculations....
The synthesis, photophysics and reverse saturable absorption of two cationic dinuclear Ir(III) complexes bearing fluorenyl-tethered 2-(quinolin-2-yl)quinoxaline (quqo) ligands are reported in this paper. The two complexes possess intense and featureless diimine ligand localized 1ILCT (intraligand charge transfer)/1π,π* absorption bands at ca. 330 and 430 nm, and a weak 1,3MLCT (metal-to-ligand charge transfer)/1,3LLCT (ligand-to-ligand charge transfer) absorption band at >500 nm. Both complexes exhibit weak dual phosphorescence at ca. 590 nm and 710 nm, which are attributed to the 3ILCT/3π,π* and 3MLCT/3LLCT states, respectively. The low-energy 3MLCT/3LLCT state also gives rise to a moderately strong triplet excited-state absorption at 490-800 nm. Because of the stronger triplet excited-state absorption than the ground-state absorption of these complexes at 532 nm, both complexes manifest a moderate reverse saturable absorption (RSA) at 532 nm for ns laser pulses. Expansion of the π-conjugation of the fluorenyl-tethered diimine ligand in Ir-1 causes a slight red-shift of the 1ILCT/1π,π* absorption bands in its UV-vis absorption spectrum and the 3MLCT/3LLCT absorption band in the transient absorption spectrum and slightly enhances the RSA at 532 nm compared to that in Ir-2. This work represents the first report on dinuclear Ir(III) complexes that exhibit RSA at 532 nm.
Green to blue-green-emitting cationic iridium complexes free of sp2 C-F bonds, namely [Ir(CF3-dPhTAZ)2(bpy)]PF6 (1), [Ir(CF3-dPhTAZ)2(dmebpy)]PF6 (2) and [Ir(CF3-dPhTAZ)2(phpyim)]PF6 (3), have been designed and synthesized with 3,4-diphenyl-5-(trifluoromethyl)-4H-1,2,4-triazole (CF3-dPhTAZ) as the cyclometalating ligand (C^N) and 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (dmebpy) or 2-(1-phenyl-1H-imidazol-2-yl)pyridine (phpyim) as the ancillary ligand (N^N). In CH3CN solution, complexes 1-3 afford green to blue-green emission centered at 521, 508 and 498 nm, respectively. The electron-withdrawing CF3 group attached at the triazole ring in CF3-dPhTAZ largely blue-shifts (by over 20 nm) the emission of the complex through stabilizing the highest occupied molecular orbital. In doped films, the complexes afford sky-blue emission with near-unity phosphorescent efficiencies. In neat films, the complexes show largely suppressed phosphorescence concentration-quenching, with phosphorescent efficiencies of up to 0.66. Theoretical calculations reveal that the emission of the complexes can arise from either charge-transfer (Ir → C^N/C^N → N^N) or C^N/N^N-centered 3π-π* states, depending on the local environment of the complexes. Solid-state light-emitting electrochemical cells (LECs) based on the complexes afford green to blue-green electroluminescence centered at 525, 517 and 509 nm, respectively, with high current efficiencies of up to 35.1 cd A-1. The work reveals that CF3-dPhTAZ is a promising C^N ligand free of sp2 C-F bonds for constructing efficient cationic iridium complexes with blue-shifted emission.
The facile synthesis of a bimetallic polymer is demonstrated by a single-step modification of [Ru(bpy)2PVP10]²⁺ (bpy = bipyridine, PVP = poly-4-vinylpyridine), which has been partially photolyzed, with an iridium precursor. This bimetallic polymer possesses three emissive centres: Ir, Ru(N)6, and Ru(N)5. The photophysical, electrochemical and electrochemiluminescent properties of this bimetallic and corresponding monometallic polymers in solution-phase, and when immobilised as a thin layer, are reported. The perceived emission colour can be readily tuned from near-infrared through to green, by varying the ratio of iridium to ruthenium centres in the polymer. Energy transfer from the iridium centre to the Ru(N)5 and Ru(N)6 centres is observed on photoexcitation of the polymers in solution-phase. When the materials are immobilised as a thin layer, energy transfer can be observed following excitation via electrochemiluminescent (ECL) pathways. Mechanistic studies were performed and further investigated through 3D ECL. Dexter-type energy transfer enhances the electrochemiluminescence properties of the bimetallic polymer versus the monometallic polymer, improving the limit of detection of the co-reactant oxalate from 20 μM to 5 μM.
Over the last decade, the ease of preparation of triazoles with desirous substituents and electronic and structural features has accelerated their use for the preparation of metal complexes with a wide array of applications. The presence of three donor N atoms capacitates the triazole rings to act as polydentate ligands, and the heterocycles may act as bridging ligands. The triazole ring could adopt at least five coordination modes for bridging metal ions. Using a range of metals, these coordination possibilities have really been exploited for the designing and preparation of a large variety of organic/inorganic hybrid architectures. Herein, a few recent developments in triazole-based metal complexes have been presented to highlight their notable biological, photoelectronic, and catalytic properties.
In this work, we report three deep-blue emitting cationic iridium complexes Ir1−Ir3 with 2ʹ,6ʹ-difluoro-2,3ʹ-bipyridine cyclometalated ligand and pyrazole-type ancillary ligands. Synthesis, crystal structure, photophysical and electrochemical properties of Ir1−Ir3 are studied in detail. Ir1−Ir3 exhibit efficient phosphorescence emissions at 439, 438 and 437 nm with CIE 1931 coordinates of (0.14, 0.12), (0.14, 0.12) and (0.14, 0.13), and luminescence quantum yields of 0.35, 0.27 and 0.50 in CH2Cl2 solutions, respectively, which are among the highest levels of ever reported cationic iridium(III) complexes emitting deep-blue light. High luminescence quantum yields, excellent color purity and short lifetimes demonstrates the great potential of Ir1−Ir3 for light-emitting electrochemical cells (LECs) and solution-processable organic light-emitting diodes (OLEDs) as efficient blue emitters.
Light-emitting electrochemical cells (LECs) based on ionic transition metal complexes (iTMCs) represent a cost-effective solid-state lighting technology compatible with large-area and industrial-scale manufacturing. To improve the current LEC performance and compete with rivaling light-emitting diode (LED) devices, it is pivotal to design efficient iTMCs/counterion couples that combine high photoluminescence efficiency with optimized ionic and electron carrier transport. Despite the continuous proposal of novel iTMCs, the investigated counterions are typically limited to the traditional ones, including PF6– and BF4–. In this work, we introduce both rigid and flexible LEC architectures based on a novel single active layer of [Ir(ppy)2(phtz)]⁻[Et3NH]⁺ + X (ppy = 2-phenylpyridine, phtz = 5-phenyl-1H-tetrazole and X = lithium bis(trifluoromethane)sulfoneimide (LiTFSI), tetrabutylammonium perchlorate (TBAP), or sodium perchlorate (NaClO4)) sandwiched between a FTO-coated glass or ITO-coated polyethylene terephthalate (PET) anode and Ga:In cathode. Our new Ir-cyclometaled complex with a tetrazole ligand, without salt additives or polymers, shows a bright green electroluminescence emission at 508 nm. The LECs based on the synthesized iTMC and TBAP additive show a current efficiency as high as 1.44 cd/A, a luminance of 503.82 cd/m², and an external quantum efficiency of 1.73% at 3.7 V. By using a dual salt additive made of TBAP:LiTFSI (1:1), the LECs further improve the performance of the single salt-based devices, exhibiting a current efficiency of 1.72 cd/A, a luminance of 603.14 cd/m², and an external quantum efficiency of 2.06% at 3.6 V. Such improvement of the LEC performance is attributed to the combination of the TBAP anion–iTMC cation size matching and the peculiar electrical properties of the LiTFSI-based solid electrolytes (i.e., high TFSI– mobility), leading to a compact space charge region near the electrodes and low turn-on voltage, respectively.
K 2 CO 3 ‐mediated [4+1] annulation reactions of N ‐acetyl hydrazones with bifunctional amino reagents are described, which provide an environmental‐friendly strategy to construct 1,2,3‐triazoles that does not employ metals, azides, organocatalysis, or oxidants. A series of substituted 1,2,3‐triazole derivatives was prepared with good yields.
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A series of white polymer light-emitting diodes (WPLEDs) each with a single emitting layer using ionic iridium complex is fabricated. The white light is obtained via two complementary colors of orange light emitter ionic iridium complexe PF6 (Hnpy: 2-(naphthalen-1-yl)pyridine, c-phen: 1-ethyl-2-(9-(2-ethylhexyl)-9H-carbazol-3-yl)-1H-imidazo phenanthroline) and sky-blue light emitter Firpic (iridium bis(2-(4,6-difluorophenyl)-pyridinato-N,C(2)) picolinate. The emtting layer consists of poly(N-vinylcarbzole) (PVK) as host polymer, 1,3-bis -phenylene (OXD-7) as electron-transporting materials, Firpic and PF6. The structure of the WPLED is indium-tin-oxide/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)(40 nm)/emtting layer (80 nm)/CsF(1.5 nm)/Al(120 nm). When the mass ratio of PVK, OXD-7, Firpic, PF6 is 67 ∶23 ∶10 ∶0.25, the most efficient white light is obtained with a color coordinate of (0.31,0.40), a maximal luminance efficiency of 13.3 cd/A and a maximal luminance of 6032 cd/m2. Meanwhile, the color coordinate is unchanged with current density. The mechanism of the WPLED is discussed.
Tris(2-phenylpyridinato-C2, N] Iridium III, Ir(ppy)3, is experimentally investigated as a novel deposited thin film. Ir(ppy)3 thin films were fabricated by the electron beam evaporator technique. X-ray diffraction (XRD) of Ir(ppy)3 powder is investigated to be polycrystalline with triclinic crystal. XRD pattern of Ir(ppy)3 film and the annealed film is analyzed, and the average of crystallite size slightly increases with thermal annealing from 14 to 40 nm. The linear optical parameters were estimated and found that the annealing effect on lattice dielectric constants, dispersion energy, oscillator energy, and the ratio of carrier concentration to its effective mass. The Urbach energy and optical energy gap are estimated at different thermal annealing. On the other hand, dielectric constants and optical conductivity were estimated and found that the annealing plays a remarkable role in the increasing of their values. The calculated values of third-order susceptibility were increased by thermal annealing. Thus, the thermal annealing can be utilized as a tool to modify the optical properties of Ir(ppy)3 films, which can be used in many important applications such as high capacity communication network.
Synthetic, structural, photophysical, and electrochemical study of [Ir(ppy)2(py)2](BF4) (1(BF4)) and four di‐N–N‐bridged complexes of [Ir(ppy)2(bpa)]2(BF4)2 (2A(BF4)2), [Ir(ppy)2((cis‐bpe))]2(BF4)2 (2B(BF4)2), [Ir(ppy)2(tmp)]2(BF4)2 (2C(BF4)2), and [Ir(ppy)2(bpy)]4(BF4)4 (3(BF4)4) are described with Hppy = 2‐phenylpyridine, py = pyridine, N–N = dipyridyl ligands of 1,2‐bis(4‐pyridyl)ethane (bpa), cis‐1,2‐bis(4‐pyridyl)ethylene (cis‐bpe), 1,3‐di(4‐pyridyl)propane (tmp), and 4,4'‐dipyridine (bpy). Five single‐crystal structures of 1(PF6), 2A(NO3)2, 2A(PF6)2, 2B(PF6)2, and 3(NO3)4 were determined, supporting the dibridged structures and presence of a variety of stereoisomers. Application of four luminescent complexes, 1(BF4), 2A(BF4)2, 2C(BF4)2, and 3(BF4)4, in solid‐state light‐emitting electrochemical cells (LECs) is reported. The work demonstrates an effective approach to realize efficient LECs based on dibridged di‐ and multinuclear cationic transition‐metal complexes with a suitably long alkyl spacer in the bridging ligand.
Three new gold(I) alkynyl complexes (Au-ABTF(0-2)) containing a benzothiazole fluorenyl moiety, with either an organic phosphine or N-heterocyclic carbene as ancillary ligand, have been synthesized and photophysically characterized. All three complexes display highly structured ground-state absorption and luminescence spectra. Dual-luminescence is observed in all three complexes at room temperature in toluene after three freeze-pump-thaw cycles. The phosphine complexes (Au-ABTF(0-1)) exhibit similar photophysics with fluorescent quantum yields ~0.40, triplet-state quantum yields ~0.50, and fluorescent lifetimes ~300 ps. The carbene complex Au-ABTF2 displays different behavior; having a fluorescent quantum yield of 0.23, a triplet-state quantum yield of 0.61, and a fluorescent lifetime near 200 ps, demonstrating that the ancillary ligand alters excited-state dynamics. The compounds exhibit strong (on the order of 105 M-1 cm-1) and positive excited-state absorption in both their singlet and triplet excited states spanning the visible region. Delayed fluorescence resulting from triplet-triplet annihilation is also observed in freeze-pump-thaw deaerated samples of all the complexes in toluene. DFT calculations (both static and time-resolved) agree with the photophysical data where phosphine complexes have slightly larger S1 -T2 energy gaps (0.28 eV and 0.26 eV) relative to the carbene complex (0.21 eV). Comparison of the photophysical properties of Au-ABTF(0-2) to previously published dinuclear gold(I) complexes and mononuclear gold(I) aryl complexes bearing the same benzothiazole-2,7-fluorenyl moiety are made. Structure-property relationships regarding ancillary ligand, bridging moiety, and number of metal centers are drawn.
The [Ir(df‐ppy)2(ptb)]+ complex (where df‐ppy=2‐(2,4‐difluorophenyl)pyridine anion; ptb=1‐benzyl‐1,2,3‐triazol‐4‐ylpyridine) has previously been shown to be a promising blue luminophore for electrogenerated chemiluminescence (ECL). Herein, we examine the ECL of three [Ir(df‐ppy)2(ptb)]+ derivatives (containing df(CF3)‐ppy‐Me, df(CN)‐ppy, or df‐ppy‐CF3 ligands) in comparison with the parent complex. In the annihilation mode, all four complexes exhibited ECL, although the emission from [Ir(df(CN)‐ppy)2(ptb)]+ was weak and red‐shifted from its photoluminescence. The absence of this shift in the corresponding reductive‐oxidation co‐reactant ECL with benzoyl peroxide (BPO), and the very low ECL intensity in oxidative–reductive co‐reactant ECL with tri‐n‐propylamine (TPrA) enables this effect to be ascribed to oxidative degradation. The [Ir(df‐ppy‐CF3)2(ptb)]+ complex gave the greatest ECL intensities of the four [Ir 2(ptb)]+ complexes in the annihilation mode and through both co‐reactant pathways, and shows great potential as a blue electrochemiluminophore. In “mixed annihilation” ECL experiments involving the oxidation of Ir(ppy)3 and the reduction of the [Ir 2(ptb)]+ complexes, only [Ir(df‐ppy)2(ptb)]+ and [Ir(df(CF3)‐ppy‐Me)2(ptb)]+ elicited the green ECL from Ir(ppy)3*, as the electron‐withdrawing substituents on the other two complexes lower the SOMO energy of the reduced complexes below that required to attain the Ir(ppy)3* excited state upon reaction with [Ir(ppy)3]+. Feeling blue: The influence of electron‐withdrawing/donating substituents on the electrogenerated chemiluminescence (ECL) of a benchmark blue luminophore [Ir(df‐ppy)2(ptb)]+ (where df‐ppy=2‐(2,4‐difluorophenyl)‐pyridine anion; ptb=1‐benzyl‐1,2,3‐triazol‐4‐ylpyridine) is explored, providing new insight into the ECL of iridium complexes, and revealing a trifluoromethyl derivative as a superior blue electrochemiluminophore.
The synthesis, crystal structure, and photophysics of a series of neutral cyclometalated iridium(III) complexes bearing substituted N-heterocyclic carbene (NHC) ancillary ligands ((C∧N)2Ir(R-NHC), where C∧N and NHC refer to the cyclometalating ligand benzo[h]quinoline and 1-phenylbenzimidazole, respectively) are reported. The NHC ligands were substituted with electron-withdrawing or -donating groups on C4' of the phenyl ring (R = NO2 (Ir1), CN (Ir2), H (Ir3), OCH3 (Ir4), N(CH3)2 (Ir5)) or C5 of the benzimidazole ring (R = NO2 (Ir6), N(CH3)2 (Ir7)). The configuration of Ir1 was confirmed by a single-crystal X-ray diffraction analysis. The ground- and excited-state properties of Ir1-Ir7 were investigated by both spectroscopic methods and time-dependent density functional theory (TDDFT) calculations. All complexes possessed moderately strong structureless absorption bands at ca. 440 nm that originated from the C∧N ligand based 1π,π*/1CT (charge transfer)/1d,d transitions and very weak spin-forbidden 3MLCT (metal-to-ligand charge transfer)/3LLCT (ligand-to-ligand charge transfer) transitions beyond 500 nm. Electron-withdrawing substituents caused a slight blue shift of the 1π,π*/1CT/1d,d band, while electron-donating substituents induced a red shift of this band in comparison to the unsubstituted complex Ir3. Except for the weakly emissive nitro-substituted complexes Ir1 and Ir6 that had much shorter lifetimes (≤160 ns), the other complexes are highly emissive in organic solutions with microsecond lifetimes at ca. 540-550 nm at room temperature, with the emitting states being predominantly assigned to 3π,π*/3MLCT states. Although the effect of the substituents on the emission energy was insignificant, the effects on the emission quantum yields and lifetimes were drastic. All complexes also exhibited broad triplet excited-state absorption at 460-700 nm with similar spectral features, indicating the similar parentage of the lowest triplet excited states. The highly emissive Ir2 was used as a dopant for organic light-emitting diode (OLED) fabrication. The device displayed a yellow emission with a maximum current efficiency (ηc) of 71.29 cd A-1, a maximum luminance (Lmax) of 32747 cd m-2, and a maximum external quantum efficiency (EQE) of 20.6%. These results suggest the potential of utilizing this type of neutral Ir(III) complex as an efficient yellow phosphorescent emitter.
Complex [Ir(dfppy)2(phca)]PF6 (1) has been synthesized (Scheme 1), which contains an aldehyde group in the N^N ligand phca = 1,10-phenanthroline-4-carbaldehyde, with an aim to explore solvent-driven luminescence modulation/switching in this complex. Complex 1 shows green emission at 514 nm in CH3OH, while orange phosphorescence with the emissions at 516 and 624 nm in CH2Cl2. The solid-state structure of 1 is dependent on the used crystallization solvent, forming red solid 1R in CH2Cl2 while yellow solid 1Y in CHCl3. Neighboring [Ir(dfppy)2(phca)]+ cations in solid 1R are held together by ∙∙∙ stacking interaction, while van der Waals interaction in solid 1Y. The distinct packing structures between 1R and 1Y lead to their significantly different solid-state luminescence, weak orange phosphorescence for 1R (emission at 620 nm, = 3.3%) and strong yellow phosphorescence for 1Y (emissions at 532 and 558 nm, = 46.6%). Both 1R and 1Y show CH2Cl2/CHCl3-driven phosphorescence switching between orange and yellow, due to their structural interconversion through recrystallization. Moreover, the emission color of 1Y can be reversibly switched between yellow and orange through alternately pressing and recrystallization in CHCl3. This work discusses the relationship among solvent, the structure and the luminescence modulation/switching of complex 1.
Four cationic iridium complexes with 5-phenyl-1H-1,2,4-triazole (phtz) type cyclometalating ligands (C^N) and different ancillary ligands (N^N), namely, [Ir(dphtz)2(bpy)]PF6 (1), [Ir(dphtz)2(pzpy)]PF6 (2), [Ir(Mephtz)2(pzpy)]PF6 (3), and [Ir(Mephtz)2(dma-pzpy)]PF6 (4), have been designed, synthesized, and fully characterized (dphtz = 1-(2,6-dimethylphenyl)-3-methyl-5-phenyl-1H-1,2,4-triazole, Mephtz = 1,3-dimethyl-5-phenyl-1H-1,2,4-triazole; bpy = 2,2'-bipyridine, pzpy = 2-(1H-pyrazol-1-yl)pyridine, dma-pzpy = 4-dimethylamino-2-(1H-pyrazol-1-yl) pyridine). In solution, complex 1 emits efficient yellow light (λmax = 547 nm), which is blue-shifted by nearly 40 nm (or by 1187 cm-1) compared with that from the archetypal complex [Ir(ppy)2(bpy)]PF6 (Hppy = 2-phenylpyridine), owing to the stabilization of the highest occupied molecular orbital by the phtz-type C^N ligand. In the lightly doped rigid films, complex 1 emits green light with a high luminescent efficiency of 0.89. Although complexes 2-4 with electron-rich N^N ligands are weakly emissive or nearly nonemissive in the solution, they emit relatively strong deep-blue light peaked around 435 and 461 nm in the lightly doped films, which is among the bluest reported for cationic iridium complexes. Theoretical calculations reveal that for complex 1, the emission always comes from the charge-transfer (CT) (Ir/C^N → N^N) state; for complexes 2 and 3, the 3CT and C^N-centered 3π-π* states lie close in energy and the emission could originate from either or both of them; for complex 4, the emission comes predominantly from the C^N-centered 3π-π* state. For blue-emitting complexes 2-4, metal-centered states play an active role in the nonradiative deactivation of the emitting triplet states. Solid-state light-emitting electrochemical cells (LECs) based on complexes 1-3 show yellow-green, blue, and blue-green electroluminescence, respectively, with the yellow-green LEC affording a peak current efficiency of 21.5 cd A-1.
A simple "click-chemistry" approach was employed in order to functionalize the known antibiotic fragment sulfanilamide with a bidentate pyridyl-triazole pocket, which allowed for the synthesis of ruthenium(II) and rhenium(I) carbonyl chloride complexes. Six new complexes were prepared and comprehensively characterized, including five single crystal X-ray structures, photophysical characterization, and testing for antimicrobial activity. Interestingly, functionalization of the pyridine ring with an ortho-hydroxymethyl group resulted in a greater than 100-fold increase in the rate of ligand release in a dimethylsulfoxide solution. Subsequent studies indicated this process could be further accelerated by irradiation with 265 nm light. Structural characterization of four of the complexes indicates that this is the result of a lengthening and weakening of the Re-NPyridine bond (average (L
tri
) = 2.19 Å vs L
tri
OH = 2.25 Å) due to the steric influence of the hydroxymethyl group. The organometallic rhenium(I) pyridyl-triazole functionality maintains its characteristic fluorescent properties despite the presence of the sulfonamide moiety. Two of the compounds showed modest antimicrobial activity against methicillin-resistant Staphylococcus aureus, whereas the structurally similar sulfamethoxazole alone showed no activity under the same conditions.
Ten biscyclometalated monocationic Ir(III) complexes were synthesized and studied to elucidate the effects of extending π-conjugation of the diimine ligand (N^N = 2,2′-bipyridine in Ir1, 2-(pyridin-2-yl)quinoline in Ir2, 2-(pyridin-2-yl)[6,7]benzoquinoline in Ir3, 2-(pyridin-2-yl)-[7,8]benzoquinoline in Ir4, phenanthroline in Ir5, benzo[f][1,10]phenanthroline in Ir6, naphtho[2,3-f][1,10]phenanthroline in Ir7, 2,2′-bisquinoline in Ir8, 3,3′-biisoquinoline in Ir9, and 1,1′-biisoquinoline in Ir10) via benzannulation at 2,2′-bipyridine on the excited-state properties and reverse saturable absorption (RSA) of these complexes. Either a bathochromic or a hypsochromic shift of the charge-transfer absorption band and emission spectrum was observed depending on the benzannulation site at the 2,2′-bipyridine ligand. Benzannulation at the 3,4-/3′,4′-position or 5,6-/5′,6′-position of 2,2′-bipyridine ligand or at the 6,7-position of the quinoline ring on the N^N ligand caused red-shifted charge-transfer absorption band and emission band for complexes Ir2, Ir8, Ir10 vs Ir1 and Ir3 vs Ir2, while benzannulation at the 4,5-/4′,5′-position of 2,2′-bipyridine ligand or at the 7,8-position of the quinoline ring on the N^N ligand induced a blue shift of the charge-transfer absorption and emission bands for complex Ir9 vs Ir1 and Ir4 vs Ir2. However, benzannulation at the 2,2′,3,3′-position of 2,2′-bipyridine or 5,6-position of phenanthroline ligand had no impact on the energy of the charge-transfer absorption band and emission band of complexes Ir5-Ir7 compared with those of Ir1. The observed phenomenon was explained by the frontier molecular orbital (FMO) symmetry analysis. Site-dependent benzannulation also impacted the spectral feature and intensity of the triplet transient absorption spectra and lifetimes drastically. Consequently, the RSA strength of these complexes varied with a trend of Ir7 > Ir5 Ir6 Ir1 > Ir3 > Ir2 > Ir10 > Ir4 > Ir8 > Ir9 at 532 nm for 4.1 ns laser pulses.
Four new heteroleptic copper(I) complexes bearing either 2-pyridyl-1,2,3-triazole (pytri) or the related triphenylamine (TPA) substituted (TPApytri) ligands and the ancillary ligands 6,6′-dimesityl-2,2′-bipyridine (diMesbpy) or bis[(2-diphenylphosphino)phenyl] ether (POP) were synthesized in good yields (75-95%). All the complexes were extensively characterized using nuclear magnetic resonance (NMR) spectroscopies and electrospray ionization mass spectrometry (ESIMS) and in the case of the two pytri compounds the solid state structures were determined via X-ray crystallography. The pytri complexes showed MLCT absorption bands which shift from 433 nm for the diMesbpy complex to 347 nm for POP. TPA-pytri complexes introduce an ILCT band resulting in improved visible absorption (376 nm, 26400 M⁻¹ cm⁻¹ for [Cu(TPA-pytri)(diMesbpy)](PF6)). Emission from this ILCT state (470 nm, Φ = 0.08) was redshifted compared to the free ligand with negligible effects from ancillary ligands. Band assignments were confirmed with resonance Raman spectroscopy and TD-DFT calculations.
Deep insight into the non-radiative deactivation pathways in phosphorescent cationic iridium complexes is critically important for developing efficient blue-emitting complexes toward advanced applications. Here, we report the synthesis, photophysical and electrochemical characterizations of a blue-green-emitting cationic iridium complex [Ir(ppy)2(bipzpy)]PF6 (Hppy is 2-phenylpyridine and bipzpy is 2,4-di(1H-pyrazol-1-yl)pyridine). The non-radiative deactivation pathways in [Ir(ppy)2(bipzpy)]PF6 have been elucidated through extensive density functional theory calculations. The calculations reveal that the higher-lying charge-transfer (CT) state in [Ir(ppy)2(bipzpy)]PF6, which arises from Ir/ppy→bipzpy transitions, favors non-radiative deactivation because of its large structural distortion compared to the ground state. Both the CT state and the dark metal-centered (3MC) state can be thermally accessed by the lowest-lying emitting triplet state at room temperature, with the former being much more easily accessible, which causes additional non-radiative deactivations for the emitting triplet state. The active roles of the CT and 3MC states in the non-radiative deactivation pathways are, for the first time, confirmed in such blue-emitting complexes with pzpy-type ancillary ligands (pzpy is 2-(1H-pyrazol-1-yl)pyridine).
The preparation and characterization of a series of iridium(III) ionic transition-metal complexes for application in light-emitting electrochemical cells (LECs) are reported. The complexes are of the type [Ir(C^N)2(N^N)][PF6] in which C^N is one of the cyclometallating ligands 2-(3-(tert-butyl)phenyl)pyridine (tppy), 2-phenylbenzo[d]thiazole (pbtz), 1-phenyl-1H-pyrazole (ppz) and 1-phenylisoquninoline (piq), and N^N is 2-(pyridine-2-yl)benzo[d]thiazole (btzpy). The variation in the C^N ligands allows the HOMO energy level to be tuned, leading to HOMO−LUMO gaps in the range 2.76‒3.01 eV and values of "E" _"1/2" ^"ox" of 0.81‒1.11 V. In solution, the complexes are orange to deep-red emitters (λmax in the range 600–660 nm), with quantum yields between 2% for [Ir(tppy)2(btzpy)][PF6] to 41% for [Ir(pbtz)2(btzpy)][PF6]. Similar trends for the emission maxima and photoluminescence quantum yields are observed in the solid state. Density functional theory (DFT) calculations support the charge transfer nature of the emission. Very bright electroluminescence was observed for LECs containing [Ir(pbtz)2(btzpy)][PF6], although the device was not stable under continuous operation; this is attributed to an unbalanced charge distribution and/or to a fast ionic migration. Significantly, LECs fabricated with [Ir(tppy)2(btzpy)][PF6] in the active layer are very stable, produce pure red emission and show no signs of degradation over a period of 5 days of continuous operation
The versatility of the triazole chemistry was exploited to obtain mesoionic carbenes working as chelating or cyclometalating ligands for the preparation of three cationic and one neutral iridium(III) complexes. All complexes emit from ³MLCT or ³LC states. However, the cationic complexes display photoluminescence quantum yields (PLQYs) around 1%, due to thermally accessible ³MC states. On the contrary, this nonradiative deactivation pathway is absent in the neutral complex, which shows PLQYs above 10%.
A new highly luminescent iridium complex, bis(2-phenylpyridine-N,C2′)[2-(2′-tosylaminophenyl)benzoxazole-N,N′]iridium(III) [Ir(ppy)2(TAPBO)] (TAPBO- 2-(2′-tosylaminophenyl)benzoxazole) has been synthesized and its molecular structure determined using single crystal X-ray diffraction analysis. The Ir(III) complex displayed intense yellow photophosphorescence emission that manifested its potential for organic electroluminescence. Photo- and electroluminescent properties of the OLEDs fabricated on the basis of [Ir(ppy)2(TAPBO)] with doping concentration of Ir(ppy)2(TAPBO) varied from 3 to 20 wt% have been investigated. The OLED with 9 wt% Ir(ppy)2(TAPBO) exhibited maximum luminance of 9000 cd m⁻² at 180 mA/cm⁻² and had sufficiently low turn-on voltage of ca. 6 V.
In this study, we report a deep red emissive organic crystal that displays high contrast fluorescence switching under mechanical- and thermal stimulation. Upon mechanical grinding, the pristine red emissive crystals of 1R (λem = 667 nm) transformed to green emissive crystalline powder (λem = 550 nm) with remarkable hypsochromic shift of wavelength, �λ = 117 nm. Melting of 1R leads to green emissive amorphous solid (λem = 555 nm) with wavelength shift of �λ = 112 nm. Upon fuming with different solvents, the amorphous melt solid transform to different polymorphs having distinct emission characters. The structural relationship between different emissive states is investigated with the aid of X-ray diffraction and other spectroscopic studies, which clearly demonstrate the role of ordered molecular packing and intermolecular interaction in determining their diverse optical response.
Ir(III) complexes are widely used in electroluminescent devices because of their appropriate photophysical properties. In the device, they can undergo supramolecular aggregation, which quenches their luminescence, as well as red shifts their emission, therefore downgrading the optical properties of the device. Here, we show that self‐aggregation and red shift can be both prevented by designing new Ir(III) complexes using well‐established blue‐emitting ones. Density Functional Theory (DFT) calculations reveal that the emitting triplet state of blue emitting Ir(III) complexes modified with appropriate substituents do not red shift and their supramolecular aggregation is less favorable than that of the precursor unmodified compounds. These results open up new possibilities to tackle one of the downgrading mechanisms observed in luminescent devices.
The electronic structure and photophysical properties of five iridium(III) complexes have been studied using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The influence of different conjugated structures on their photophysical properties has been explored. Ionization potentials, electron affinities and reorganization energy have also been obtained to evaluate the charge transfer and balance properties between hole and electron. The lowest energy emissions from the CAM-B3LYP level for these complexes are localized at 472, 503, 523, 635 and 699 nm, respectively. The theoretical investigation would be useful to design potential phosphorescent materials for application in the organic light-emitting diodes.
A series of PtII complexes featuring 1,2,3-triazole-derived N∧N∧N-, N∧C∧N- and C∧N∧C-coordinating ligands were studied both experimentally and computationally aiming at the design of new PtII phosphors. By virtue of click chemistry, the new complexes were readily functionalized, e.g., with bulky groups in order to suppress aggregation of the complexes. For a N∧C∧N-type cyclometalated PtII complex, the high energy of the π* orbitals of the 1,2,3-triazole units gave rise to deep-blue phosphorescence; the poor luminescence quantum yield was attributed to an inadequate energy separation between the emissive state and the d–d states. However, when the 1,2,3-triazole donor moiety acted as a spectator/ancillary ligand only, an intense green emission could be achieved (ΦPL = 0.57, τ = 4.6 μs).
A neutral multifunctional dinuclear Ir(III) complex 1 with a Schiff base bridging ligand is shown to combine aggregation-induced emission (AIE), piezochromic luminescence (PCL) and vapochromism. The complex displays a reversible colour change in its phosphorescence in the solid state between faint red and bright orange with high contrast intensity, triggered by high polarity volatile organic compounds (VOCs) or by mechanical grinding within 10 s. Notably, unlike many known vapochromic systems, complex 1 exhibits ultrahigh stability, with the orange colour remaining unchanged in air for several months at room temperature. A simple and efficient monitoring device has been fabricated in which highly polar VOCs act as a switch to “turn on” the device by changing the aggregation state of complex 1.
Based on a cyclometalating ligand 2-naphthalen-1-yl-1H-benzoimidazole (nbiH, Scheme 1), two isomeric [Ir(tpy)(nbi)Cl](PF6) complexes, namely Ir-O and Ir-R, have been synthesized, in which an {Ir(tpy)Cl}2+ unit is chelated by a nbi- ligand using a carbon atom from naphthalene unit and an imidazole nitrogen atom (atoms C2 and N1 in Ir-O, and atoms C8 and N1 in Ir-R, Fig. 1a and 1b), thus their nbi- ligands display five- and six-membered ring chelating mode, respectively. The structural differences between Ir-O and Ir-R result in significantly different luminescence, self-assembly ability and cellular imaging behaviors. Complex Ir-O shows a blue-shifted emission at ~581 nm in CH3CN or PBS solution compared to Ir-R (~612 nm). Complex Ir-O (20 M) in PBS buffer can easily self-assemble into mono-dispersed nanoparticles with diameter of ~ 100 nm, which could be due to intermolecular stacking interactions. In contrast, Ir-R has not shown such self-assembly behavior. Compared to Ir-R, complex Ir-O is more appropriate for cell imaging, showing a high capacity to accumulate and stain the lysosomes of live cells, which could be assigned to its relatively high luminescence quantum yield and molecular self-assembly behavior.
We report measurements and modeling studies of organic light-emitting
diodes (LED's) with mobile ions incorporated into the active polymer
layer, similar in structure to the light-emitting electrochemical cells
(LEC's) reported by Pei et al. We show that movement of the ions, rather
than electrons or holes, is responsible for the Ohmic electrode-polymer
contacts observed in these devices. We show that for typical devices
with polymer film thicknesses of 1000-2000 Å, concentrations of
ions greater than 1020 cm-3 are required for
efficient electroluminescent behavior. We show also that under
steady-state operation, the electric field is very low in the bulk of
the polymer, and that the electron and hole currents are therefore
driven mainly by diffusion. Quantitative modeling of electron-hole
recombination matches observed emission profiles.
Publisher Summary X-ray data can be collected with zero-, one-, and two-dimensional detectors, zero-dimensional (single counter) being the simplest and two-dimensional the most efficient in terms of measuring diffracted X-rays in all directions. To analyze the single-crystal diffraction data collected with these detectors, several computer programs have been developed. Two-dimensional detectors and related software are now predominantly used to measure and integrate diffraction from single crystals of biological macromolecules. Macromolecular crystallography is an iterative process. To monitor the progress, the HKL package provides two tools: (1) statistics, both weighted (χ 2 ) and unweighted (R-merge), where the Bayesian reasoning and multicomponent error model helps obtain proper error estimates and (2) visualization of the process, which helps an operator to confirm that the process of data reduction, including the resulting statistics, is correct and allows the evaluation of the problems for which there are no good statistical criteria. Visualization also provides confidence that the point of diminishing returns in data collection and reduction has been reached. At that point, the effort should be directed to solving the structure. The methods presented in the chapter have been applied to solve a large variety of problems, from inorganic molecules with 5 A unit cell to rotavirus of 700 A diameters crystallized in 700 × 1000 × 1400 A cell.
A blended layer composed of a coil-rod-coil triblock oligomer and LiCF <sub>3</sub> SO <sub>3</sub> was introduced into light-emitting electrochemical cells. The response rate and efficiency of the device were greatly improved, and a low operating voltage was maintained. The device, with a structure of indium tin oxide / PEO-PHP-PEO ( LiCF <sub>3</sub> SO <sub>3</sub>)/[ Ru ( bpy )<sub>3</sub>]( PF <sub>6</sub>)<sub>2</sub>/ Au , showed a turn-on voltage as low as 2.85 V, while its luminance and efficiency were approximately twice those of a single-layer device. The power, luminance, and external quantum efficiency at 1000 cd / m <sup>2</sup> reach 2.1 cd/A, 1.5l m/W, and 2.6%, respectively. We attribute these improvements to the enhancement in the hole injection and electron blocking effect resulting from the blended layer.
We report green emission from a single-layer device based on the ionic transition metal complex [ Ir ( F - mppy )<sub>2</sub>( dtb - bpy )]<sup>+</sup>( PF <sub>6</sub><sup>-</sup>) , where F-mppy is 2-( 4<sup>′</sup> -fluorophenyl)-5-methylpyridine and dtb-bpy is 4,4<sup>′</sup> -di-tert-butyl- 2,2<sup>′</sup> bipyridine. External quantum efficiencies of up to 1.1% are achieved with air-stable contacts, and up to 1.8% with a CsF / Al top contact. Addition of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was found to improve the device response time and cause a bias-dependent shift in the emission spectrum. As a result, electroluminescence was observed at 531 nm (CIE coordinates: 0.3230 and 0.5886), the lowest wavelength reported to date for a device based on ionic transition metal complexes.
The authors demonstrate highly efficient solid-state light-emitting electrochemical cells (LECs) consisting of green-emitting [ Ir ( dFppy )<sub>2</sub>( S B )]<sup>+</sup>( P F <sub>6</sub><sup>-</sup>) as the host and orange-emitting [ Ir ( ppy )<sub>2</sub>( S B )]<sup>+</sup>( P F <sub>6</sub><sup>-</sup>) as the guest [where dFppy is 2-(2,4-difluorophenyl)pyridine, SB is 4,5-diaza-9, 9<sup>′</sup> -spirobifluorene, and ppy is 2-phenylpyridine]. Photophysical studies show that with the optimized host-guest compositions, the emission is mainly from the guest and photoluminescence quantum yields are largely enhanced over those of pure host and guest films due to suppressed intermolecular interactions. Correspondingly, LECs based on such host-guest cationic complex systems show substantially enhanced quantum efficiencies (power efficiencies) of up to 10.4% (36.8 lm / W ) , representing a 1.5 times enhancement compared to those of pure host and guest devices. Such results indicate that the host-guest system is essential and useful for achieving highly efficient solid-state LECs.
We report the synthesis, characterisation, photophysical and electrochemical properties of a series of cationic cyclometallated Ir-III complexes of general formula [Ir(ppy)(2)(phen)]PF6 (ppy = 2-phenylpyridine, phen=a substituted phenanthroline). A feature of these complexes is that the phen ligands are substituted with one or two 9,9-dihexylfluorenyl substituents to provide extended pi conjugation, for example, the 3-[2-(9,9-dihexylfiuorenyl)]phenanthroline and 3,8-bis[2-(9,9-dihexylfluorenyl)]phenanthroline ligands afford complexes 6 and 9, respectively. A single-crystal X-ray diffraction study of a related complex 18 containing the 3,8-bis(4-iodophenyl)phenanthroline ligand, revealed an octahedral coordination of the Ir atom, in which the metallated C atoms of the ppy ligands occupy cis positions. The complexes 6 and 9 displayed reversible oxidation waves in cyclic voltammetric studies (E-1/2(ox)=+1.18 and +1.20V, respectively, versus Ag/Ag+ in CH2Cl2) assigned to the metal-centred Ir-III/Ir-IV couple. The complexes exhibit strong absorption in the UV region in solution spectra, due to spin-allowed ligand-centred (LC) (1)pi-pi* transitions; moderately intense bands occur at approximately 360-390nm which are red-shifted with increased ligand length. The photoluminescence spectra of all the complexes were characterised by a broad band at lambda(max)approximate to 595nm assigned to a combination of (MLCT)-M-3 and (3)pi ->pi* states. The long emission lifetimes (in the microsecond time-scale) are indicative of phosphorescence: the increased ligand conjugation length in complexes 9 and 17 leads to increased lifetimes for the complexes (tau=2.56 and 2.57 mu s in MeCN, respectively) compared to monofluorenyl analogues 6 and 15 (tau=1.43 and 1.39 mu s, respectively). DFT calculations of the geometries and electronic structures of complexes 6', 9' (for both singlet ground state (S-0) and triplet first excited (T-1) states) and 18 have been performed. In the singlet ground state (S-0) HOMO orbitals in the complexes are spread between the Ir atom and benzene rings of the phenylpyridine ligand, whereas the LUMO is mainly located on the phenanthroline ligand. Analysis of orbital localisations for the first excited (T-1) state have been performed and compared with spectroscopic data. Spin-coated light-emitting cells (LECs) have been fabricated with the device structures ITO/PEDOT:PSS/Ir complex/Al, or Ba capped with Al (ITO=indium tin oxide, PEDOT = poly(3,4-ethylenedioxythiophene), PSS = poly(styrene) sulfonate). A maximum brightness efficiency of 9 cd A(-1) has been attained at a bias of 9 V for 17 with a Ba/Al cathode. The devices operated in air with no reduction in efficiency after storage for one week in air.
The structural and spectroscopic properties of new heteroleptic iridium complexes having a biphenyl and two bipyridyl based ligands are reported; DFT calculations reveal that the HOMO is composed of the biphenyl and iridium d orbitals while the LUMO is localized mainly on the two bipyridyl based ligands.
A latent catalyst for the [3+2] cycloaddition reaction of azides and alkynes has been developed in accordance with the principles of Click chemistry.
A least-squares procedure is described for modeling an empirical transmission surface as sampled by multiple symmetry-equivalent and/or azimuth rotation-equivalent intensity measurements. The fitting functions are sums of real spherical harmonic functions of even order, ylm(-u0) + ylm(u1), 2 < or = l = 2n < or = 8. The arguments of the functions are the components of unit direction vectors, -u0 for the reverse incident beam and u1 for the scattered beam, referred to crystal-fixed Cartesian axes. The procedure has been checked by calculations against standard absorption test data.
A novel and general approach to scaling diffraction intensities is presented. The method minimizes the disagreement among multiple measurements of symmetry-related reflections using a stable refinement procedure. The scale factors are described by a flexible exponential function that allows different scaling corrections to be chosen and combined according to the needs of the experiment. The scaling model presented here includes: scale and temperature factor per batch of data; temperature factor as a continuous function of the radiation dose; absorption in the crystal; uneven exposure within a single diffraction image; and corrections for phenomena that depend on the diffraction peak position on the detector. This scaling model can be extended to include additional corrections for various instrumental and data-collection problems.
By simply stirring in water, organic azides and terminal alkynes are readily and cleanly converted into 1,4-disubstituted 1,2,3-triazoles through a highly efficient and regioselective copper(I)-catalyzed process (see scheme for an example).
A device configuration for light emission from electroactive polymers is described. In these light-emitting electrochemical
cells, a p-n junction diode is created in situ through simultaneous p-type and n-type electrochemical doping on opposite sides of a thin film of conjugated polymer that contains added electrolyte to provide
the necessary counterions for doping. Light-emitting devices based on conjugated polymers have been fabricated that operate
by the proposed electrochemical oxidation-reduction mechanism. Blue, green, and orange emission have been obtained with turn-on
voltages close to the band gap of the emissive material.
A ruthenium polypyridyl complex has been synthesized and examined as an emitter material in thin film electroluminescent devices. This material exhibits photoluminescent and electroluminescent effects as well as several reversible one‐electron oxidation and reduction processes. Electroluminescent devices fabricated from this ruthenium complex either via spin coating methods or self‐assembly techniques exhibit relatively high electroluminescent efficiencies and luminance levels in some cases as high as 100 cd/m2.
We report on the synthesis and characterization of bis-cyclometalated iridium(l 11) complexes with 4-plienyl-1H-[1,2,3]triazole, synthesized via a "click"-chemistry approach, as a new type of cyclometalating ligand. The photophysical and electrochemical properties of these complexes are investigated experimentally as well as theoretically by using density functional theory, The properties of these new complexes are compared to their known 2-phenylpyridinato analogues. The emission of the herein described complexes is clearly influenced by the applied ancillary ligand and can be adjusted over a broad range of frequencies. The results indicate that the phenyl-1H-[1,2,3]triazole ligands in general cause a spectral blue shift.
We have fabricated organic LEDs with mobile ions incorporated into the active polymer layer, similar in structure to the electrochemical cells (LECs) reported by Pei et al. We report characteristics for devices with ionic concentrations < 1017 cm−3, which show rectifying characteristics We show that device behaviour can be understood solely in terms of an electrostatic model. The accumulation of ionic space-charge in the vicinity of the two electrodes is shown to permit easier injection of electronic carriers than is possible in a conventional LED. The device characteristics are strongly dependent on ionic concentration. Rectification is predicted at low ionic concentrations, switching to symmetrical behaviour at higher concentrations
Experience with a variety of diffraction data-reduction problems has led to several strategies for dealing with mismeasured outliers in multiply measured data sets. Key features of the schemes employed currently include outlier identification based on the values ymedian = median(|Fi|2), σmedian = median[σ(|Fi|2)], and |Δ|median = median(|Δi|) = median[||Fi|2-median (|Fi|2)|] in samples with i = 1, 2 ..... n and n≥ 2 measurements; and robust/resistant averaging weights based on values of |zi| = |Δi|/max{σmedian, |Δ|median[n/(n−1)]1/2}. For outlier discrimination or down-weighting, sample median values have the advantage of being much less outlier-based than sample mean values would be.
Copper(I) complex employed in organic light-emitting electrochemical cells (OLECs) are reported. During the study we found that the electroluminescence (EL) spectra under forward voltage redshifted compared with the photoluminescence spectra of the film. Moreover, the EL spectra under reverse voltage also redshifted compared with the forward EL spectra. Based on the electric-field theory and the device mechanism of OLECs, we suggest that the spectra shift is ascribed to the polarization effect of molecular orbitals under high electric field in the device. The polarization and radiation models under electric field have been proposed.
The photophysical and electrochemical properties of a series of cationic cyclometalated Ir(III) complexes is reported. The complexes are of general formula [Ir(ppy)2(R,R‘-bpy)]+(1−5; PF6- as counterion) where ppy = 2-phenylpyridinato anion. Complexes 1−3 contain asymmetric bpy ligands with R and R‘ substituents in the 6‘ and 4‘ positions, while complexes 4 and 5 bear bpy ligands symmetrically substituted in the 4 and 4‘ positions. Complex 5 was structurally characterized by single-crystal X-ray crystallography, revealing a cis arrangement of the metalated C atoms of the ppy ligands. All the species exhibit strong absorption in the UV region, due to spin-allowed ligand-centered (LC) transitions, and moderately intense bands in the visible region, due to charge transfer (CT) transitions. Several redox processes have been evidenced in each complex and assigned to specific components. The complexes also exhibit relatively strong and long-lived (from 10-8 to 10-5 s, depending on temperature and matrix) luminescence, in all the experimental conditions used (acetonitrile solution and spin-coated films at 298 K; butyronitrile rigid matrix at 77 K). The substituents of the polypyridine ligands affect in a substantial way the redox and photophysical properties of the compounds. In particular, a phenyl substituent on the polypyridine chelating ligand in the 6‘ position (complexes 1−3) stabilizes oxidation of an orbital which receives significant contributions from the ppy ligands and leads to emission from triplet ligand-to-ligand charge transfer (LLCT) excited states. When such a phenyl is absent in the ligand structure (complexes 4 and 5), the usual triplet metal-to-ligand charge transfer (MLCT) emission predominates.
Thin-film solid-state light-emitting devices have been fabricated by using blends of a trischelated complex of ruthenium(II) with 4,7-diphenyl-1,10-phenanthroline disulfonate ligands and lithium triflate complexed poly(ethylene oxide). Charge injection occurs via an electrochemical redox mechanism and the mechanism of light production is similar to electrogenerated chemiluminescence. Orange-red light is emitted with a turn-on voltage of 2.5−3.0 V. At 6 V, devices reach luminance levels of about 100 cd/m2 with an external quantum efficiency of 0.02% photons/electron. The admixed PEO acts both as a film processing aid, giving uniform, homogeneous, and reproducible devices, and as a polymer electrolyte for ruthenium complex and counterion diffusion. Devices reach about 50% of their maximum luminance within a few seconds, and reach maximum luminance in about a minute. This behavior can be realized without the need of elaborate charging schemes involving the use of elevated temperatures or solvent treatments that enhance ionic conductivity. Devices of this type can be fabricated via conventional processing routes and conditioned to high light ouput with a few simple voltage scans.
The preparation, photophysics, and solid state structures of octahedral organometallic Ir complexes with several different cyclometalated ligands are reported. IrCl3·nH2O cleanly cyclometalates a number of different compounds (i.e., 2-phenylpyridine, 2-(p-tolyl)pyridine, benzoquinoline, 2-phenylbenzothiazole, 2-(1-naphthyl)benzothiazole, and 2-phenylquinoline), forming the corresponding chloride-bridged dimers, CN2Ir(μ-Cl)2IrCN2 (CNis a cyclometalated ligand) in good yield. These chloride-bridged dimers react with acetyl acetone (acacH) and other bidentate, monoanionic ligands such as picolinic acid (picH) and N-methylsalicylimine (salH), to give monomeric CN2Ir(LX) complexes (LX = acac, pic, sal). The emission spectra of these complexes are largely governed by the nature of the cyclometalating ligand, leading to λmax values from 510 to 606 nm for the complexes reported here. The strong spin−orbit coupling of iridium mixes the formally forbidden 3MLCT and 3π−π* transitions with the allowed 1MLCT, leading to a strong phosphorescence with good quantum efficiencies (0.1−0.4) and room temperature lifetimes in the microsecond regime. The emission spectra of the CN2Ir(LX) complexes are surprisingly similar to the fac-IrCN3 complex of the same ligand, even though the structures of the two complexes are markedly different. The crystal structures of two of the CN2Ir(acac) complexes (i.e., CN = ppy and tpy) have been determined. Both complexes show cis-C,C‘, trans-N,N‘ disposition of the two cyclometalated ligands, similar to the structures reported for other complexes with a “CN2Ir” fragment. NMR data (1H and 13C) support a similar structure for all of the CN2Ir(LX) complexes. Close intermolecular contacts in both (ppy)2Ir(acac) and (tpy)2Ir(acac) lead to significantly red shifted emission spectra for crystalline samples of the ppy and tpy complexes relative to their solution spectra.
A number of extensions to the multisolution approach to the crystallographic phase problem are discussed in which the negative quartet relations play an important role. A phase annealing method, related to the simulated annealing approach in other optimization problems, is proposed and it is shown that it can result in an improvement of up to an order of magnitude in the chances of solving large structures at atomic resolution. The ideas presented here are incorporated in the program system SHELX-90; the philosophical and mathematical background to the direct-methods part (SHELXS) of this system is described.
The reduction of self-quenching effect by introduction of sterically hindered spacers in phosphorescence molecules was analyzed for a electrophosphorescence emitting device. The iridium complex of tris-ortho-cycloetalated compound exhibits a strong green phosphorescence emission with a photoluminescence (PL) quantum yield of 0.71 in solutions and a short lifetime in solids. Self-quenching is reduced significantly due to sterically hindered pinene spacers which provides minimum bimolecular interaction.
Using imidazole-type ancillary ligands, a new class of cationic iridium complexes (1–6) is prepared, and photophysical and electrochemical studies and theoretical calculations are performed. Compared with the widely used bpy (2,2′-bipyridine)-type ancillary ligands, imidazole-type ancillary ligands can be prepared and modified with ease, and are capable of blueshifting the emission spectra of cationic iridium complexes. By tuning the conjugation length of the ancillary ligands, blue-green to red emitting cationic iridium complexes are obtained. Single-layer light-emitting electrochemical cells (LECs) based on cationic iridium complexes show blue-green to red electroluminescence. High efficiencies of 8.4, 18.6, and 13.2 cd A−1 are achieved for the blue-green-emitting, yellow-emitting, and orange-emitting devices, respectively. By doping the red-emitting complex into the blue-green LEC, white LECs are realized, which give warm-white light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.42, 0.44) and color-rendering indexes (CRI) of up to 81. The peak external quantum efficiency, current efficiency, and power efficiency of the white LECs reach 5.2%, 11.2 cd A−1, and 10 lm W−1, respectively, which are the highest for white LECs reported so far, and indicate the great potential for the use of these cationic iridium complexes in white LECs.
Tris-(benzyltriazolylmethyl)amine (TBTA), a widely used ligand for the copper-catalyzed azide-alkyne cycloaddition, has been immobilized on a TentaGel resin. Once loaded with copper(I), the resulting air-stable complex acts as an efficient catalyst for the azide-alkyne cycloaddition reaction and prevents contamination of products by copper salts. The immobilized TBTA ligand should find immediate use in the parallel synthesis of compounds for direct screening.
A study was performed on self-assembled electroluminescent polymers derived from terpyridine-based moieties. A class of high-performance Zn-terpyridyl based polymers, which give violet to yellow light emission, was prepared. It was shown that these polymers, which exhibited high luminance and good thermal stabilities, are promising light-emitting materials (LED) for polymeric LED (PLED).
The complexes [Cu(dnbp)(DPEphos)]+(X–) (dnbp and DPEphos are 2,9-di-n-butyl-1,10-phenanthroline and bis[2-(diphenylphosphino)phenyl]ether, respectively, and X– is BF4–, ClO4–, or PF6–) can form high-quality films with photoluminescence quantum yields of up to 71 ± 7 %. Their electroluminescent properties are studied using the device structure indium tin oxide (ITO)/complex/metal cathode. The devices emit green light efficiently, with an emission maximum of 523 nm, and work in the mode of light-emitting electrochemical cells. The response time of the devices greatly depends on the driving voltage, the counterions, and the thickness of the complex film. After pre-biasing at 25 V for 40 s, the devices turn on instantly, with a turn-on voltage of ca. 2.9 V. A current efficiency of 56 cd A–1 and an external quantum efficiency of 16 % are realized with Al as the cathode. Using a low-work-function metal as the cathode can significantly enhance the brightness of the device almost without affecting the turn-on voltage and current efficiency. With a Ca cathode, a brightness of 150 cd m–2 at 6 V and 4100 cd m–2 at 25 V is demonstrated. The electroluminescent performance of these types of complexes is among the best so far for transition metal complexes with counterions.
Two blue-emitting cationic iridium complexes with 2-(1H-pyrazol-1-yl)pyridine (pzpy) as the ancillary ligands, namely, [Ir(ppy)2(pzpy)]PF6 and [Ir(dfppy)2(pzpy)]PF6 (ppy is 2-phenylpyridine, dfppy is 2-(2,4-difluorophenyl) pyridine, and PF6− is hexafluorophosphate), have been prepared, and their photophysical and electrochemical properties have been investigated. In CH3CN solutions, [Ir(ppy)2(pzpy)]PF6 emits blue-green light (475 nm), which is blue-shifted by more than 100 nm with respect to the typical cationic iridium complex [Ir(ppy)2(dtb-bpy)]PF6 (dtb-bpy is 4,4′-di-tert-butyl-2,2′-bipyridine); [Ir(dfppy)2(pzpy)]PF6 with fluorine-substituted cyclometalated ligands shows further blue-shifted light emission (451 nm). Quantum chemical calculations reveal that the emissions are mainly from the ligand-centered 3π–π* states of the cyclometalated ligands (ppy or dfppy). Light-emitting electrochemical cells (LECs) based on [Ir(ppy)2(pzpy)]PF6 gave green-blue electroluminescence (486 nm) and had a relatively high efficiency of 4.3 cd A−1 when an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was added into the light-emitting layer. LECs based on [Ir(dfppy)2(pzpy)]PF6 gave blue electroluminescence (460 nm) with CIE (Commission Internationale de L'Eclairage) coordinates of (0.20, 0.28), which is the bluest light emission for iTMCs-based LECs reported so far. Our work suggests that using diimine ancillary ligands involving electron-donating nitrogen atoms (like pzpy) is an efficient strategy to turn the light emission of cationic iridium complexes to the blue region.
A new, but archetypal compound [Ir(ppy-F2)2Me4phen]PF6, where ppy-F2 is
2-(29,49-fluorophenyl)pyridine and Me4phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, was
synthesized and used to prepare a solid-state light-emitting electrochemical cell (LEEC). This
complex emits blue light with a maximum at 476 nm when photoexcited in a thin film, with a
photoluminescence quantum yield of 52%. It yields an efficient single-component solid-state
electroluminescence device with a current efficiency reaching 5.5 cd A21 and a maximum power
efficiency of 5.8 Lm Watt21. However, the electroluminescence spectrum is shifted with respect to
the photoluminescence spectrum by 80 nm resulting in the emission of green light. We
demonstrate that this unexpected shift in emission spectrum does not originate from the mode
of excitation, nor from the presence of large concentrations of ions, but is related to the
concentration of the ionic transition metal complex in the thin film. The origin of the
concentration-dependent emission is extensively commented on and argued to be related to
the population of either 3LC p–p* or 3MLCT triplet states, in diluted and concentrated films,
respectively. Using quantum chemical calculations we demonstrate that three low-energy triplet
states are present with only 0.1 eV difference in energy and that their associated emission
wavelengths differ by as much as 60 nm from each other.
We demonstrate an improvement in the turn-on time of electroluminescent devices based on the iridium complex [Ir(ppy) 2 (dtb-bpy)] + (PF 6 -), where ppy is 2-phenylpyridine and dtb-bpy is 4,4′-di-tert-butyl-2,2′-dipyridine, by introduction of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate BMIM + (PF 6 -). Addition of 0.46 mol of the ionic liquid per mole of Ir complex reduces the turn-on time from 5 h to 40 min. However, the device lifetime is also reduced by a factor of 3 over this range, suggesting a tradeoff between device speed and stability. These results are discussed within the framework of the electrodynamic model of device operation and are found to be consistent with an increase in the ionic conductivity of the [Ir(ppy) 2 (dtb-bpy)] + (PF 6 -) films upon the addition of ionic liquid.
A study was conducted to demonstrate the preparation and characteristics of a supramolecularly caged ionic iridium(III) complex [Ir(ppy) 2(Hpbpy)][PF6], where ppy is 2-phenylpyridine and Hpbpy is 6-phenyl-2,2'-bipyridine. The second complex was compared with the parent complex, [Ir(ppy)2(Hpbpy)][PF6] during investigations. It was demonstrated that the lifetime of a simple electroluminescent device employing air-stable electrodes and supramolecularly-caged complex, as the active component is more than 3000 hours at an average luminance of 200 cd m-2, while operating at a driving voltage of 3 volts. The large increase in lifetime was obtained, without sacrificing the device turn-on time.
Osmium(II) complexes possessing beta-diketonate, quinolinate, diimine, and C-linked pyridyl azolate chelates reveal interesting structural and photophysical properties. Spectroscopic and dynamic measurements, in combination with theoretical analyses, have provided an important understanding of the electronically excited state properties of these complexes, such as the energy gap and nature of the lower lying states, rate for intersystem crossing, and the efficiency of corresponding radiative decay and nonradiative deactivation processes. This review also reports on the synthetic processes that lead to the neutral Os(II) and Run complexes that possess two trans-substituted phosphane donor ligands together with two anti-parallel, aligned azolate chromophores. Considerable efforts have been made to focus on utilizing these emitting materials as phosphorescent dopants for practical PLED and OLED fabrication. Consequently, the interplay between these emitting materials and device configurations is discussed. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).
Mononuclear Ir(III)-polyimine complexes show outstanding luminescence properties, i.e., high intensities,
lifetimes in the μs time range, and emission wavelengths that can be tuned so as to cover a full
range of visible colors, from blue to red. We discuss the approaches for the use of ligands that afford
control on luminescence features. Emphasis is placed on subfamilies of cyclometalated complexes, whose
recent enormous expansion is motivated by their potential for applications, including that as phosphorescent
dopants in OLEDs fabrication. The interplay of the different excited states associated with the luminescence,
usually of MLCT and/or LC nature, is examined and the possible detrimental role of MC levels toward the
luminescence properties is outlined. Ir(III)-polyimine moieties can be incorporated within multicomponent
arrays where they can play as photoactive and/or electroactive units in photoinduced energy and electron
transfer processes. The field is reviewed with attention to the processes of light collection and conversion
into chemical energy.
Here, the photophysics and performance of single-layer light emitting cells (LECs) based on a series of ionic cyclometalated Ir(III) complexes of formulae [Ir(ppy)(2)(bpy)]+PF6- and [Ir(ppy)(2)(phen)]+PF6- where ppy, bpy, and phen are 2-phenylpyridine, substituted bipyridine and substituted phenanthroline ligands, respectively, are reported. Substitution at the N N Iigand has little effect on the emitting metal-ligand to ligand charge-transfer (MLLCT) states and functionalization at this site of the complex leads to only modest changes in emission color. For the more bulky complexes the increase in intermolecular separation leads to reduced exciton migration, which in turn, by suppressing concentration quenching, significantly increases the lifetime of the excited state. On the other hand, the larger intermolecular separation induced by bulky ligands reduces the charge carrier mobility of the materials, which means that higher bias fields are needed to drive the diodes. A brightness of ca. 1000cd m(-2) at 3 V is obtained for complex 5, which demonstrates a beneficial effect of bulky substituents.
In this work, two ruthenium complexes, [Ru(bpy)(3)](PF6)(2) and [Ru(ph2phcn)(3)](PF6)(2) in poly(inethylinethacrylate) matrix were employed to build single-layer light-emitting electrochemical cells by spin coating on indium tin oxide substrate. In both cases the electroluminescence spectra exhibit a relatively broad band with maxima near to 625 rim and CIE (x, y) color coordinates of (0.64, 0.36), which are comparable with the photoluminescence data in the same medium. The best result was obtained with the [Ru(bpy)(3)](PF6)(2) device where the optical output power approaches 10 mu W at the band maximum with a wall-plug efficiency higher than 0.03%. The lowest driving voltage is about 4 V for an electrical current of 20 mA. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
[reaction: see text] An efficient and improved procedure for the preparation of aromatic azides and their application in the Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition ("click reaction") is described. The synthesis of aromatic azides from the corresponding amines is accomplished under mild conditions with tert-butyl nitrite and azidotrimethylsilane. 1,4-Disubstituted 1,2,3-triazoles were obtained in excellent yields from a variety of aromatic amines without the need for isolation of the azide intermediates.
Novel 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine (pytl) ligands have been prepared by "click chemistry" and used in the preparation of heteroleptic complexes of Ru and Ir with bipyridine (bpy) and phenylpyridine (ppy) ligands, respectively, resulting in [Ru(bpy)(2)(pytl-R)]Cl(2) and [Ir(ppy)(2)(pytl-R)]Cl (R=methyl, adamantane (ada), beta-cyclodextrin (betaCD)). The two diastereoisomers of the Ir complex with the appended beta-cyclodextrin, [Ir(ppy)(2)(pytl-betaCD)]Cl, were separated. The [Ru(bpy)(2)(pytl-R)]Cl(2) (R=Me, ada or betaCD) complexes have lower lifetimes and quantum yields than other polypyridine complexes. In contrast, the cyclometalated Ir complexes display rather long lifetimes and very high emission quantum yields. The emission quantum yield and lifetime (Phi=0.23, tau=1000 ns) of [Ir(ppy)(2)(pytl-ada)]Cl are surprisingly enhanced in [Ir(ppy)(2)(pytl-betaCD)]Cl (Phi=0.54, tau=2800 ns). This behavior is unprecedented for a metal complex and is most likely due to its increased rigidity and protection from water molecules as well as from dioxygen quenching, because of the hydrophobic cavity of the betaCD covalently attached to pytl. The emissive excited state is localized on these cyclometalating ligands, as underlined by the shift to the blue (450 nm) upon substitution with two electron-withdrawing fluorine substituents on the phenyl unit. The significant differences between the quantum yields of the two separate diastereoisomers of [Ir(ppy)(2)(pytl-betaCD)]Cl (0.49 vs. 0.70) are attributed to different interactions of the chiral cyclodextrin substituent with the Delta and Lambda isomers of the metal complex.
A new iridium(III) complex showing intramolecular interligand pi-stacking has been synthesized and used to improve the stability of single-component, solid-state light-emitting electrochemical cell (LEC) devices. The pi-stacking results in the formation of a very stable supramolecularly caged complex. LECs using this complex show extraordinary stabilities (estimated lifetime of 600 h) and luminance values (average luminance of 230 cd m-2) indicating the path toward stable ionic complexes for use in LECs reaching stabilities required for practical applications.
A green-light-emitting iridium(III) complex was prepared that has a photoluminescence quantum yield in a thin-film configuration of almost unity. When used in a simple solid-state single-layer light-emitting electrochemical cell, it yielded an external quantum efficiency of nearly 15% and a power efficiency of 38 Lm/W. We argue that these high external efficiencies are only possible if near-quantitative internal electron-to-photon conversion occurs. This shows that the limiting factor for the efficiency of these devices is the photoluminescence quantum yield in a solid film configuration. The observed efficiencies show the prospect of these simple electroluminescent devices for lighting and signage applications.
A new heterogeneous catalyst composed of copper and nickel oxide particles supported within charcoal has been developed. It catalyzes cross-couplings that traditionally use palladium, nickel, or copper, including Suzuki-Miyaura reactions, Buchwald-Hartwig aminations, vinylalane alkylations, etherifications of aryl halides, aryl halide reductions, asymmetric conjugate reductions of activated olefins, and azide-alkyne "click" reactions.
Polyethyleneimine-functionalized platinum nanoparticles (PtNPs) with excellent electrochemiluminescence (ECL) properties were synthesized and applied to the amplified analysis of biomolecules. These particles were prepared at room temperature, with hyperbranched polyethyleneimine (HBPEI) as the stabilizer. The UV/Vis absorption spectra and transmission electron microscopy images clearly confirmed the formation of monodisperse PtNPs. Such particles proved to possess high stability against salt-induced aggregation, enabling them to be employed even under high-salt conditions. Owing to the existence of many tertiary amine groups, these particles exhibited excellent ECL behavior in the presence of tris(2,2'-bipyridyl)ruthenium(II). An HBPEI-coated particle possessed an ECL activity that was at least 60 times higher than that of a tripropylamine molecule. Furthermore, these particles could be immobilized on the 3-aminopropyltriethoxysilane-treated quartz substrates to amplify the binding sites for carboxyl groups. Through this approach, PtNPs were applied to the amplified analysis of the hemin/G-quadruplex DNAzyme by using the luminol/H(2)O(2) chemiluminescence method.
We report a significant decrease in turn-on times of light-emitting electrochemical cells (LECs) by tethering imidazolium moieties onto a cationic Ir complex. The introduction of two imidazolium groups at the ends of the two alkyl side chains of [Ir(ppy)(2)(dC6-daf)](+)(PF(6))(-) (ppy = 2-phenylpyridine, dC6-daf = 9,9'-dihexyl-4,5-diazafluorene) gave the complex [Ir(ppy)(2)(dC6MIM-daf)](3+)[(PF(6))(-)](3) (dC6MIM-daf = 9,9-bis[6-(3-methylimidazolium)hexyl]-1-yl-4,5-diazafluorene). Both complexes exhibited similar photoluminescent/electrochemical properties and comparable electroluminescent efficiencies. The turn-on times of the LECs based on the latter complex, however, were much lower than those of devices based on the former. The improvement is ascribed to increased concentrations of mobile counterions ((PF(6))(-)) in the neat films and a consequent increase in neat-film ionic conductivity. These results demonstrate that the technique is useful for molecular modifications of ionic transition-metal complexes (ITMCs) to improve the turn-on times of LECs and to realize single-component ITMC LECs compatible with simple driving schemes.
The behavior of light-emitting electrochemical cells (LEC) based on solid films ( approximately 100 nm) of tris(2,2'-bipyridine)ruthenium(II) between an ITO anode and a Ga-In cathode was investigated. The response times were strongly influenced by the nature of the counterion: small anions (BF(4)(-) and ClO(4)(-)) led to relatively fast transients, while large anions (PF(6)(-), AsF(6)(-)) produced a slow time-response. From comparative experiments of cells prepared and tested in a glovebox to those in ambient, mobility of the anions in these films appears to be related to the presence of traces of water from atmospheric moisture. An electrochemical model is proposed to describe the behavior of these LECs. The simulation results agreed well with experimental transients of current and light emission as a function of time and show that the charge injection is asymmetric at the two electrodes. At a small bias, electrons are the major carriers, while for a larger bias the conduction becomes bipolar.
Research on new materials for organic electroluminescence has recently focused strongly on phosphorescent emitters, with the aim of increasing the emission efficiency and stability. Here we report the fabrication of a simple electroluminescent device, based on a semiconducting polymer combined with a phosphorescent complex, that shows fully reversible voltage-dependent switching between green and red light emission. The active material is made of a polyphenylenevinylene (PPV) derivative molecularly doped with a homogeneously dispersed dinuclear ruthenium complex, which fulfils the dual roles of triplet emitter and electron transfer mediator. At forward bias (+4 V), the excited state of the ruthenium compound is populated, and the characteristic red emission of the complex is observed. On reversing the bias (-4 V), the lowest excited singlet state of the polymer host is populated, with subsequent emission of green light. The mechanism for the formation of the excited state of the PPV derivative involves the ruthenium dinuclear complex in a stepwise electron transfer process that finally leads to efficient charge recombination reaction on the polymer.
The factors affecting the operating life of the light-emitting electrochemical cells (LECs) based on films of tris(2,2'-bipyridine)ruthenium(II) both in sandwich (using an ITO anode and a Ga:Sn cathode) and planar (using interdigitated electrode arrays (IDAs)) configurations were investigated. Stability of these devices is greatly improved when they are produced and operated under drybox conditions. The proposed mechanism of the LEC degradation involves formation of a quencher in a small fraction of tris(2,2'-bipyridine)ruthenium(II) film adjacent to the cathode, where light generation occurs, as follows from the observed electroluminescence profile in the LECs constructed on IDAs, showing that the charge injection in such devices is highly asymmetric, favoring hole injection. Bis(2,2'-bipyridine)diaquoruthenium(II) is presumed to be the quencher responsible for the device degradation. A microscopic study of photo- and electroluminescence profiles of planar light-emitting electrochemical cells was shown as a useful approach for studies of charge carrier injection into organic films.
We report on the spectroscopic, electrochemical, and electroluminescent properties of [Ir(ppy)(2)(dtb-bpy)](+)(PF(6))(-) (ppy: 2-phenylpyridine, dtb-bpy: 4,4'-di-tert-butyl-2,2'-dipyridyl). Single-layer devices were fabricated and found to emit yellow light with a brightness that exceeds 300 cd/m(2) and a luminous power efficiency that exceeds 10 Lm/W at just 3 V. The PF(6)(-) space charge was found to dominate the device characteristics.
The synthesis and structural, spectroscopic, and electrochemical properties of a series of trinuclear tridentate cyclometalated platinum(II) complexes tethered by bis(diphenylphosphinomethyl)phenylphosphine (dpmp) have been studied and compared with their mono- and binuclear homologues and a propeller-like congener. The X-ray crystal structures of several derivatives show the presence of a variety of intramolecular Pt.Pt, pi-pi, and C-H...O(crown ether) and intermolecular pi-pi interactions. The trinuclear complexes display strong absorption in the 400-600 nm region and show intense red to near-infrared phosphorescence with microsecond lifetimes in fluid and glassy solutions and in the solid state. These emissions are generally assigned as (3)MMLCT [dsigma-->pi(CNN)] in nature. The close similarities between the emission energies in acetonitrile solution and in the solid state at 298 K indicate that comparable Pt.Pt and pi-pi configurations are maintained in both media, and hence a relationship between the photophysical behavior of these lumophores and their solid-state structural features is proposed. The tendencies of the absorption and emission energies to red-shift from mono- to linearly tethered bi- and trinuclear Pt(II) species are evident. A light-emitting electrochemical cell using a trinuclear Pt(II) derivative as emitter has been demonstrated.
We report a novel color tuning methodology in the electrophosphorescent iridium complex by substituting one cyclometalating ligand to an ancillary ligand as an emitting center. Highly efficient exothermic inter-ligand energy transfer (ILET) from the MLCT3 state produced between iridium and cyclometalating 2-(2,4-difluorophenyl)pyridine to LX3 state of the ancillary ligand offers a chance to access a wider range of color from sky blue (478 nm) to red (666 nm). Characteristic shapes of photoluminescence spectra, strong solvatochromic phenomena as well as DFT calculations gave evidences for this exothermic ILET.