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Serendipitous formation of semiconducting semi-NINDIGO indigoid by degradation of diindolopyrrole
Abstract
We report the serendipitous discovery and synthesis of an indigoid “Semi-Nindigo” (2) via oxidation of a diindolopyrrole (1). Reaction of 2 with BF3Et2O affords the borylated derivate (3). The electronic spectra of 2 and 3 possess intense long wave absorptions near 600 nm and 650 nm. 3 is weakly emissive in the near-infrared. Thin film OFETs fabricated with 1 and 2 both exhibited modest p-type mobilities.
... In recent years the design, synthesis, study and implementation of macromolecules with a π-conjugated system (small molecules [1][2][3] and polymers [4][5][6]) commonly called organic semiconductors [7] in optoelectronic devices [8][9][10] has been of great scientific interest [11][12][13]. The intrinsic optical [14][15][16] and electronic [17][18][19] properties of this type of molecules and their possible modulation [20][21][22][23], coupled with their ease of film processing [24,25] have been quite attractive for their application in devices such as solar cells (OSCs) [26][27][28][29][30], organic semiconductor laser diodes (OSLDs) [31][32][33], in organic field-effect transistors (OFETs) [34][35][36][37], and organic light-emitting diodes (OLEDs) [38][39][40][41]. ...
... In recent decades, interest in the development and research of organic semiconductor materials, such as small molecules [1,2] and conjugated polymers [3,4] has gained great interest in the scientific community [5][6][7]. This is due to the attractive photophysical and processing properties of this type of material, which have been tuned and adapted for their application in optoelectronic devices such as organic light-emitting diodes (OLEDs) [8,9], organic solar cells (OSC) [1,10], organic field-effect transistors OFETs [11,12], perovskite solar cells [13,14], sensors [15][16][17], nonlinear optics materials [18,19], molecular switches [20], optical data storage [21], and others. The optical and electrical properties of organic semiconductors derive from their chemical structure [6], and thanks to the versatility of organic chemical synthesis, it is possible to tune them by molecular design [22], using different acceptor or donor segments to promote and favor intramolecular charge transfer (ICT) [23]. ...
A π-conjugated polymer (PBQT) containing bis-(2-ethylhexyloxy)-benzo [1,2-b’] bithiophene (BDT) units alternated with a quinoline-vinylene trimer was obtained by the Stille reaction. The chemical structure of the polymer was verified by nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FT-IR), and mass spectroscopy (MALDI-TOF). The intrinsic photophysical properties of the solution were evaluated by absorption and (static and dynamic) fluorescence. The polymer PBQT exhibits photochromism with a change in absorption from blue (449 nm) to burgundy (545 nm) and a change in fluorescence emission from green (513 nm) to orange (605 nm) due to conformational photoisomerization from the trans to the cis isomer, which was supported by theoretical calculations DFT and TD-DFT. This optical response can be used in optical sensors, security elements, or optical switches. Furthermore, the polymer forms spin-coated films with absorption properties that cover the entire visible range, with a maximum near the solar emission maximum. The frontier molecular orbitals, HOMO and LUMO, were calculated by cyclic voltammetry, and values of −5.29 eV and −3.69, respectively, and a bandgap of 1.6 eV were obtained, making this material a semiconductor with a good energetic match. These properties could suggest its use in photovoltaic applications.
... By itself, DIP 1 is a p-type OSC which shows a modest hole mobility of 10 À5 cm 2 V À1 s À1 in vacuum deposited films. 54 To our knowledge, there has been no report of OFETs based on compound e. We were able to prepare thin-film OFETs by co-sublimation of the H-bonded complex 1 2 e powder, although efforts to co-sublime complexes of 1 with more volatile acceptors (c and d) led to deposition of the individual acceptor component. ...
We report a detailed investigation of a series of new charge-transfer (CT) complexes assembled via a two-point complementary hydrogen bonding (H-bonding) of diindolopyrrole (DIP) electron donors with o-quinone and diazafluorenone acceptors. Unidirectional polarization through the DD⋯AA type H-bonding leads to a dramatic perturbation of electronic levels of the donor and the acceptor. π-Stacking of the H-bonded pairs results in strong charge-transfer (HOMO–LUMO) interactions in their ground state, manifested in low energy optical absorption. Density functional theory (DFT) calculations predict a H-bonding induced rise of the HOMOD (by up to 0.5 eV) and lowering of the LUMOA (by up to 0.7 eV). As a result, the complexes of relatively weak electron donors and acceptor ability exhibit remarkably low optical energy gaps (down to <0.8 eV), that can be tuned by varying the ionization potential and electron affinity of the individual components. Single crystal X-ray analysis for 6 complexes displayed H-bond lengths between 1.9 and 2.3 Å and short π-stacking distances (≥3.2 Å), in line with strong donor–acceptor interactions. Thin-film transistors of such a H-bonded complex, fabricated by vacuum co-sublimation of PhDIP and pyrenetetraone, showed ambipolar charge transport with unusual ‘double dip’ characteristics.
Organic molecular semiconductors have been paid great attention due to their advantages of low-temperature processability, low fabrication cost, good flexibility, and excellent electronic properties. As a typical example of five-ring-fused organic semiconductors, a single crystal of pentacene shows a high mobility of up to 40 cm2 V-1 s-1, indicating its potential application in organic electronics. However, the photo- and optical instabilities of pentacene make it unsuitable for commercial applications. But, molecular engineering, for both the five-ring-fused building block and side chains, has been performed to improve the stability of materials as well as maintain high mobility. Here, several groups (thiophenes, pyrroles, furans, etc.) are introduced to design and replace one or more benzene rings of pentacene and construct novel five-ring-fused organic semiconductors. In this review article, ∼500 five-ring-fused organic prototype molecules and their derivatives are summarized to provide a general understanding of this catalogue material for application in organic field-effect transistors. The results indicate that many five-ring-fused organic semiconductors can achieve high mobilities of more than 1 cm2 V-1 s-1, and a hole mobility of up to 18.9 cm2 V-1 s-1 can be obtained, while an electron mobility of 27.8 cm2 V-1 s-1 can be achieved in five-ring-fused organic semiconductors. The HOMO-LUMO levels, the synthesis process, the molecular packing, and the side-chain engineering of five-ring-fused organic semiconductors are analyzed. The current problems, conclusions, and perspectives are also provided.
Intense static electric fields can strongly perturb chemical bonds and induce frequency shifts of the molecular vibrations in the so-called vibrational Stark effect. Based on a density functional theory (DFT) approach, here, we report a detailed investigation of the influence of oriented external electric fields (OEEFs) on the dipole moment and infrared (IR) spectrum of the nonpolar centrosymmetric indigo molecule. When an OEEF as intense as ∼0.1 V Å −1 is applied, several modifications in the IR spectrum are observed. Besides the notable frequency shift of some modes, we observe the onset of new bandsforbidden by the selection rules in the zero-field case. Such a neat field-induced modification of the vibrational selection rules, and the subsequent variations of the peaks' intensities in the IR spectrum, paves the way toward the design of smart tools employing centrosymmetric molecules as proxies for mapping local electric fields. In fact, here, we show that the ratio between the IR and the Raman intensities of selected modes is proportional to the square of the local field. This indicator can be used to quantitatively measure local fields, not only in condensed matter systems under standard conditions but also in field-emitting-tip apparatus.
Conventional semiconducting polymer synthesis typically involves transition metal-mediated coupling reactions that link aromatic units with single bonds along the backbone. Rotation around these bonds contributes to conformational and energetic disorder and therefore potentially limits charge delocalisation, whereas the use of transition metals presents difficulties for sustainability and application in biological environments. Here we show that a simple aldol condensation reaction can prepare polymers where double bonds lock-in a rigid backbone conformation, thus eliminating free rotation along the conjugated backbone. This polymerisation route requires neither organometallic monomers nor transition metal catalysts and offers a reliable design strategy to facilitate delocalisation of frontier molecular orbitals, elimination of energetic disorder arising from rotational torsion and allowing closer interchain electronic coupling. These characteristics are desirable for high charge carrier mobilities. Our polymers with a high electron affinity display long wavelength NIR absorption with air stable electron transport in solution processed organic thin film transistors.
Archaeological research has identified the use of cultivated cotton (Gossypium barbadense) in the ancient Andes dating back to at least 7800 years ago. Because of unusual circumstances of preservation, 6000-year-old cotton fabrics from the Preceramic site of Huaca Prieta on the north coast of Peru retained traces of a blue pigment that was analyzed and positively identified as an indigoid dye (indigotin), making it the earliest known use of indigo in the world, derived most likely from Indigofera spp. native to South America. This predates by ~1500 years the earliest reported use of indigo in the Old World, from Fifth Dynasty Egypt [ca. 4400 BP (before present)]. Indigo is one of the most valued and most globally widespread dyes of antiquity and of the present era (it being the blue of blue jeans).
Indigo di- and monoimines can be protonated to form stable salts in which the central C=C bond has isomerized from a trans to cis configuration. Deprotonation of these salts regenerates the neutral trans species. The protonation chemistry of indigo is also explored.
A bio-inspired organic semiconductor 5,5’-diphenylindigo shows excellent and well-balanced ambipolar transistor properties; the hole and electron mobilities are 0.56 and 0.95 cm2 V–1 s–1, respectively. The enhanced performance is attributed to the extended π-π overlap of the phenyl groups as well as the characteristic packing pattern that is a hybrid of the herringbone and brickwork structures. The ambipolar transistor characteristics are analyzed considering operation regions, where a large unipolar saturated region appears due to the difference of the electron and hole threshold voltages.
Reactions of indigo-N,N′-diarylimine (‘Nindigo’) derivatives with BF3·Et2O give mono- or bis-BF2 chelate complexes 2 or 3 respectively. The product distribution between 2 and 3 is sensitive to the auxiliary base and solvent. Although the bis-BF2 complexes 3 are isolable, they gradually decompose in solution to the corresponding mono-BF2 species 2; this process is accelerated by water. The instability of 3 is believed to be due to ring stain effects based on structural analyses of 2. Electrochemical studies of 2 reveal one quasi-reversible oxidation process and two irreversible reductions, whereas derivatives of 3 possess a reversible oxidation and two sequential reversible reductions. The electronic spectra of 2 and 3 contain intense (ε 3 × 104 M−1 cm−1) long-wavelength absorptions near 650 nm and 750 nm respectively. Both series of compounds are weakly emissive in the near-infrared. Time-dependent DFT calculations reveal the electronic transitions to be π–π* in nature.
Ambipolar organic semiconductors enable complementary-like circuits in organic electronics. Here we show promising electron and hole transport properties in the natural pigment Tyrian Purple (6,6’-dibromoindigo). X-ray diffraction of Tyrian Purple films reveals a highly-ordered structure with a single preferential orientation, attributed to intermolecular hydrogen bonding. This material, with a band gap of ∼1.8 eV, demonstrates high hole and electron mobilities of 0.22 cm2∕V·s and 0.03 cm2∕V·s in transistors, respectively; and air-stable operation. Inverters with gains of 250 in the first and third quadrant show the large potential of Tyrian Purple for the development of integrated organic electronic circuits.
Herein we report our recent efforts in employing natural materials and synthetic derivatives of natural molecules for organic field effect transistors (OFETs) and organic photovoltaics (OPVs). We evaluated dyes from the following chemical families: acridones, anthraquinones, carotenoids, and indigoids. These materials have proven effective in organic field effect transistors, with mobilities in the 4 × 10 -4 – 0.2 cm 2 /V·s range, with indigoids showing promising ambipolar behavior. We fabricated complementary-like voltage inverters with high gains using indigoids. The photovoltaic properties of these materials were characterized in metal-insulator-metal (MIM) diodes, as well as in donor-acceptor bilayer devices. Additionally, we have found that indigoids and Quinacridone, show long-range crystalline order due to hydrogen binding, and have considerably higher relative permittivities (ε) compared to typical organic semiconductors. Higher permittivities result in lower exciton binding energies and thus may lead to high photocurrents in photovoltaic devices.
The electronics era is flourishing and morphing itself into Internet of Everything, IoE. At the same time questions arise on the issue of electronic materials employed: especially their natural availability and low cost fabrication, their functional stability in devices, and finally their desired biodegradation at the end of the life cycle. Hydrogen bonded pigments and natural dyes like Indigo, Anthraquinone and Acridone have robustness in functionality and versatility in designing electronics and sensors components, and are bio-origin and biodegradable. With this Perspective Article, we intend to coalesce all the scattered reports on the above mentioned classes of Hydrogen bonded semiconductors, spanning across several disciplines and many active research groups. The article will comprise both published and un-published results, on stability during aging, upon electrical, chemical and thermal stress, and will finish with an outlook section related to biological degradation and biological stability of selected hydrogen bonded molecules employed as semiconductors in organic electronic devices. We demonstrate that when the purity, the long range order and the strength of chemical bond, are considered, then the Hydrogen-bonded organic semiconductors are the privileged class of materials having the potential to compete with inorganic semiconductors. As an experimental historical study of stability, we fabricated and characterized organic transistors from a material batch synthesized in 1932 and compared the results to fresh material batch.
Over the past decade, isoindigo has become a widely used electron‐deficient subunit in donor‐acceptor organic semiconductors, and these isoindigo‐based materials have been widely used in both organic photovoltaic (OPV) devices and organic field effect transistors (OFETs). Shortly after the development of isoindigo‐based semiconductors, researchers began to modify the isoindigo structure in order to change the optoelectronic properties of the resulting materials. This led to the development of many new isoindigo‐inspired compounds; since 2012, the Kelly Research Group has synthesized a number of these isoindigo analogues and produced a variety of new donor‐acceptor semiconductors. In this Personal Account, recent progress in the field is reviewed. We describe how the field has evolved from relatively simple donor‐acceptor small molecules to structurally complex, highly planarized polymer systems. The relevance of these materials in OPV and OFET applications is highlighted, with particular emphasis on structure‐property relationships.
A solution-processable dibromoindigo with an alkyoxyphenyl solubilizing group is developed and used as a new electron acceptor in organic photodiodes. The solution-processed fullerene-free organic photodiodes show an almost spectrally flat response with a high responsivity (0.4 A W(-1) ) and a high detectivity (1 × 10(12) Jones). These values are comparable to silicon-based photodiodes.
5,5’-Diiodoindigo (4) exhibits excellent ambipolar transistor properties with the hole/electron mobilities of µh/µe = 0.42/0.85 cm2 V−1 s−1. The halogen substituted indigos show systematically decreasing energy gaps from F to I due to the spreading highest occupied molecular orbitals, and decreasing tilt angles in the crystals. In addition, the iodine-iodine interaction provides extraordinarily large interchain interaction. However, the X-ray diffraction suggests that the indigo molecules are arranged approximately perpendicular to the substrate in the thin films, probably due to the extra iodine-iodine interaction. The remarkable performance is ascribed to this characteristic supramolecular interaction.
(DAF)Pd(OAc)2 (DAF = 4,5-diazafluorenone) catalyzes aerobic intramolecular aryl C–H amination with N-benzenesulfonyl-2-aminobiphenyl in dioxane to afford the corresponding carbazole product. Mechanistic studies show that the reaction involves in situ generation of peroxide species from 1,4-dioxane and O2, and the reaction further benefits from the presence of glycolic acid, an oxidative decomposition product of dioxane. An induction period observed for the formation of the carbazole product correlates with the formation of 1,4-dioxan-2-hydroperoxide via autoxidation of 1,4-dioxane, and the in situ-generated peroxide is proposed to serve as the reactive oxidant in the reaction. These findings have important implications for palladium-catalyzed aerobic oxidation reactions conducted in ethereal solvents.
Indigo and its derivatives are dyes and pigments with a long and distinguished history in organic chemistry. Recently, applications of this 'old' structure as a functional organic building block for organic electronics applications have renewed interest in these molecules and their remarkable chemical and physical properties. Natural-origin indigos have been processed in fully bio-compatible field effect transistors, operating with ambipolar mobilities up to 0.5 cm(2) /Vs and air-stability. The synthetic derivative isoindigo has emerged as one of the most successful building-blocks for semiconducting polymers for plastic solar cells with efficiencies > 5%. Another isomer of indigo, epindolidione, has also been shown to be one of the best reported organic transistor materials in terms of mobility (∼2 cm(2) /Vs) and stability. This progress report aims to review very recent applications of indigoids in organic electronics, but especially to logically bridge together the hereto independent research directions on indigo, isoindigo, and other materials inspired by historical dye chemistry: a field which was the root of the development of modern chemistry in the first place.
Kinetics of the ground state repopulation and the decay lifetime of the lowest excited singlet state of indigo were measured by the use of picosecond spectroscopy. The photostability of indigo and its ring‐substituted homologues can be reconciled in view of the ultrafast internal conversion from the lowest excited singlet state to the ground state enhanced by the proton transfer in the excited state.
Extensive intramolecular π-conjugation is considered to be requisite in the design of organic semiconductors. Here, two inkjet pigments, epindolidione and quinacridone, that break this design rule are explored. These molecules afford intermolecular π-stacking reinforced by hydrogen-bonding bridges. Air-stable organic field effect transistors are reported that support mobilities up to 1.5 cm(2) /Vs with T(80) lifetimes comparable with the most stable reported organic semiconducting materials.
The ultraviolet and visible absorption spectra of seven purified thioindigo dyes in benzene and in chloroform were determined under several conditions of temperature and illumination. It was concluded that these compounds exist in solution as two forms (cis and trans) in equilibrium. The position of the equilibrium is a function of the temperature and the illumination. The approximate spectral absorption curves were calculated for the two isomers of each dye, and the relative amount of each isomer present at the several equilibrium conditions was computed. The two isomers of thioindigo and of 5,5′-dichloro-4,4′,7,7′-tetramethylthioindigo were separated chromatographically and their absorption spectra were obtained. Definite configurations were assigned to the two isomers of each dye. Correlations between the absorption spectra and the structures of thioindigo dyes are discussed.
Bei der spontanen Polymerisation des Phenylisocyanids bei Raumtemperatur entsteht neben Harzen ein blauer Farbstoff, der isoliert und als Indigo-dianil erkannt wurde. Substituierte und homologe aromatische Isocyanide liefern, wenn überhaupt, nur Spuren analoger Farbstoffe. Der Mechanismus dieser neuen, einfachen Indigo-Synthese wird diskutiert.
Bis-imidoylchlorides of oxalic acid react rapidly with magnesium shreds in dry THF under ultrasonic conditions to give 1,5-naphthyridine derivatives and the isomeric indigodianiles. Using a cross-over experiment
the existence of key intermediates corresponding to dimeric isocyanides could be verified.
Bis-imidoylchloride der Oxalsäure reagieren mit Magnesiumspänen in trockenem THF und unter Ultraschallbedingungen zu den 1,5-Naphthyridinderivaten und den isomeren Indigodianilen. Durch Untersuchungen des
Reaktionsmechanismus konnten Hinweise auf radikalische C2-Schlüsselintermediate vom Typ dimerer Isocyanide erbracht werden.
Millenniums-old natural dye indigo - a "new" ambipolar organic semiconductor. Indigo shows balanced electron and hole mobilities of 1 × 10(-2) cm(2) V(-1) s(-1) and good stability against degradation in air. Inverters with gains of 105 in the first and 110 in the third quadrant are demonstrated. Fabricated entirely from natural and biodegradable compounds, these devices show the large potential of such materials for green organic electronics.
Reactions of indigo with a variety of substituted anilines produce the corresponding indigo diimines ("Nindigos") in good yields. Nindigo coordination complexes are subsequently prepared by reactions of the Nindigo ligands with Pd(hfac)(2). In most cases, binuclear complexes are obtained in which the deprotonated Nindigo bridges two Pd(hfac) moieties in the expected bis-bidentate binding mode. When the Nindigo possesses bulky substituents on the imine (mesityl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, etc.), mononuclear Pf(hfac) complexes are obtained in which the Nindigo core has isomerized from a trans- to a cis-alkene; in these structures, the palladium is bound to the cis-Nindigo ligand at the two indole nitrogen atoms; the remaining proton is bound between the imine nitrogen atoms. The palladium complexes possess intense electronic absorption bands [near 920 nm for the binuclear complexes and 820 nm for the mononuclear cis-Nindigo complexes; extinction coefficients are (1.0-2.0) × 10(4) M(-1) cm(-1)] that are ligand-centered (π-π*) transitions. Cyclic voltammetry investigations reveal multiple redox events that are also ligand-centered in origin. All of the palladium complexes can be reversibly oxidized in two sequential one-electron steps; the binuclear complexes are reduced in a two-electron process whose reversibility depends on the Nindigo ligand substituent; the mononuclear palladium species show two one-electron reductions, only the first of which is quasi-reversible.
Reactions of indigo with anilines provide a simple route to indigo N,N'-diaryldiimines ("Nindigo"), a new binucleating ligand with two beta-diketiminate-type metal binding sites. Bis-palladium complexes have interesting ligand-centred properties such as redox activity and intense near infrared absorption.
Fast and convenient approaches to the indole nucleus from isocyanides are reviewed as a means for the tailored preparation of conveniently functionalized indoles by using the unique reactivity of isocyanides in one-pot multicomponent and cascade reactions.
The spectral and photophysical properties of indigo derivatives with di-, tetra-, and hexa-substitution in their neutral (keto) form are investigated in solution. The study comprises absorption and emission spectra, together with quantitative measurements of quantum yields of fluorescence (phi(F)) and singlet oxygen formation (phi(Delta)) and fluorescence lifetimes. The energy difference between the HOMO and LUMO orbitals is dependent on the degree (number of groups) and relative position of substitution. The phi(F) and phi(Delta) values were found to be very low <or=10(-3). Because of the absence of transient triplet-triplet signal, the intersystem crossing yields (phi(T)) were estimated by assuming that all the triplet states formed give rise to singlet oxygen formation, that is, phi(Delta) approximately phi(T) . It was then possible from phi(IC)=1-phi(F)-phi(T) to estimate the S(1) approximately approximately -->S(0) internal conversion yields and thus, with the other data, to determine the rate constants for all decay processes. From these, several conclusions are drawn. Firstly, the radiationless rate constants, k(NR) , clearly dominate over the radiative rate constants, k(F) , (and processes). Secondly, the main deactivation channel for the compounds in their keto form is the radiationless S(1) approximately approximately -->S(0) internal conversion process. Finally, although the changes are relatively small, internal conversion yield seems to be independent of the overall pattern of substitution. A more detailed investigation of the decay profiles with collection at the blue and red emission of the fluorescence band of indigo and one di-substituted indigo reveals the decays to be bi-exponential and that at longer emission wavelengths these appear to be associated with both rise and decay times indicating that two excited species exist, which is consistent with a keto-excited form giving rise (by fast proton transfer) to the enol-form of indigo. Evidence is presented which supports the idea that intramolecular (and possibly some intermolecular) proton transfer can explain the high efficiency of internal conversion in indigo.