[Show abstract][Hide abstract] ABSTRACT: In this work, the solvent field and temperature are used to explore the mutual transformation dynamic process and mechanism between the α-conformation and β-conformation in Poly(9,9-dioctylfluorene) (PFO) precursor solution. The conformational transformation of PFO chain is researched by UV-vis absorption spectra and the proportions of β-conformation are quantitatively calculated. The corresponding variation trend of aggregation structure is researched by using static and dynamic light scattering (SLS/DLS) method. It is found that the mutual transformation process between α-conformation and β-conformation are reversible in essence. Especially in the transformation processes, the complicated relationship between the β-conformation and aggregation structure is understood, that is the aggregation structure make β-conformation formed under solvent field, then the conformational transformation of β-conformation promotes the dissociation of aggregation structure under temperature. The above results give an insight into the β-conformation and aggregation structure of PFO in theory. Furthermore, under the temperature, we find that both two transformation steps have good linear correlations, which indicates that using temperature can be considered as a good method to accurately control the proportion of β-conformation in actual application, and it will help us to get the desired proportion of β-conformation in PFO precursor solution so as to make the charge carrier mobility of optoelectronic films increased and device performance better.
[Show abstract][Hide abstract] ABSTRACT: In this work, the α-conformation (individual locally separated chain) of conjugated polymer poly(9,9-dioctylfluorene) (PFO) in dilute solution is studied by the following three points: Mark-Houwink exponent a, fractal dimension D and form factor Rg/Rh. From the result of a, α-conformation of PFO is considered to have a semi-rigid chain conformation in dilute solution. We establish the mathematical relationship between Mark-Houwink exponent a and fractal dimension D in dilute solution. To prove the rationality of this mathematical relationship, the classic polymer polystyrene (PS) is used for comparison. According to the result of D, it can be known that α-conformation of PFO has relatively loose and extended chain conformation. Moreover, we use light-scattering to get the form factor Rg/Rh of the PFO solution in which the α-conformation and β-conformation coexist. It is found that Rg/Rh increase with the content of α-conformation, which indicates that α-conformation of PFO has a loose and extended chain conformation, and this result agrees well with the conclusions drawn from a and D. Based on the fact that β-conformation (ordered conformation) and α-conformation of PFO can transform into each other in solution, this work is significant for the control of β-conformation and will have a potential meaning to increase the charge carrier mobility and efficiency from the PFO solution to films.
The Journal of Physical Chemistry B 01/2014; 118(3). DOI:10.1021/jp406598x · 3.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An efficient and controllable approach to prepare cross-linked films from a conjugated polymer precursor by electrochemical deposition (ED) is reported for the first time. A novel polymer precursor with high solubility, high electroactivity, and electron-transport ability has been designed. The electrochemically deposited polymer film shows high thickness, smooth morphology, and high fluorescence. The single-layer pure-blue-emitting ED PLED exhibits a luminous efficiency of 3.8 cd A(-1) .
[Show abstract][Hide abstract] ABSTRACT: In this work, the effects of solvation and desolvation on the β phase of poly(9,9-dioctylfluorene) (PFO) are studied. The content of β phase is approximately calculated for comparison. The content of β phase can be enhanced up to 40% by the solvation effect and become a metastable state; the desolvation effect is a dynamic process and can enhance the content of β phase remarkably by 18%age units. It is found that the contents of β phase are always changing with the aggregation degrees of PFO chains. To fully understand it, the concepts of mesoscopic aggregates and macroscopic aggregates are proposed and well proved by the filtration experiment. In the solution (the ethanol content less than 30%), the mesoscopic aggregates are beneficial to enhance the content of β phase; in the solution (the ethanol content more than 40%), which is close to the condensed state of fabricated optoelectronic film, the macroscopic aggregates can make the content of β phase not only much higher but also stable. The content of β phase can be controlled by changing the aggregation characteristics of PFO chains in solution. This work will be significant in fabricating the optoelectronic devices from solutions to films with high carrier mobility and good stability.
The Journal of Physical Chemistry C 04/2012; 116(14):7993–7999. DOI:10.1021/jp301102t · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bacterial cellulose (BC), produced by Gluconacetobacter xylinum, consists of ribbon-shaped nano-fibers in web-like structures. Polyaniline (PAni) is a conductive polymer, the conductivity of which is related to the synthesis and doping process. In this paper, we report on the in situ nano-assembly of BC nanofibers and PAni to enhance the electronic conductivity. PAni could be synthesized on the surface of BC nano-fibers and assembled into a novel 3D network. The reaction time of polymerization, the types and concentration of doping protonic acids play a major role on the electroconductivity properties of the composites. The electroconductivity of composite hydrogels was enhanced from 10−8 to 10−2 S cm−1, and can be further improved by doping with various protonic acids. The BC-PAni nanofiber composite is an electro-conductive hydrogel that combines the properties of hydrogels and conductive systems, and it may potentially be used for flexible displays, biosensors, and platform substrates to study the effect of electrical signals on cell activity, and to direct desirable cell function for tissue engineering applications.
[Show abstract][Hide abstract] ABSTRACT: In order to further improve the efficiency and stability of luminescent electrochemical polymerization (EP) films and devices, electroactive self-assembled monolayers (SAMs) of carbazolyl alkanethiol are successfully designed and applied to modify Au electrode and covalently graft the deposited EP films. The analysis of the formation and coverage of the SAMs by atomic force microscopy (AFM), cyclic voltammetry (CV), and the theoretical calculation provide consistent results indicating the SAM molecules are densely packed and standing upright (liquid-like) on the Au surface. In addition, ultraviolet photoelectron spectroscopy (UPS), CV, UV, AFM, and sonication treatment reveal that the close-packed electroactive SAMs are effective at enhancing the work function of electrode, increasing the deposition rate of EP precursor as well as elevating the cross-linking efficiency and the adhesive property of subsequent EP films. This is a simple and very efficient method for improving the performance of EP device, which has potential applications in display devices.
[Show abstract][Hide abstract] ABSTRACT: This contribution presents a kind of novel and neutral network films based on EDOT formed by in situ electrocopolymerization (ECP). The ECP films which are neutral and colorless exhibit the conductivity of 0.2-0.5 S·cm(-1), W(F) of 4.79-5.20 eV, and RMS roughness of 3.51-5.26 nm. The electroluminescent devices where ECP films acted as hole-transport layer (HTL) exhibit higher brightness, current density, efficiency (20-30% improvement), and stability than that of PEDOT:PSS HTL device. The ECP films also significantly benefit the stability of neighboring organic layer compared to PEDOT:PSS. This kind of new ECP films affords more opportunities to develop organic light-emitting diodes (OLEDs) with high performances and stability.
[Show abstract][Hide abstract] ABSTRACT: Water-dispersed organic nanoparticles (NPs) constructed by the conjugated molecule 2,5,2',5'-tetra(4'-N,N-diphenylaminostyryl)biphenyl (DPA-TSB) with a high luminescence and large two-photon absorption (TPA) section were fabricated via the reprecipitation method. The average size of the NPs can be controlled from 40 nm to 80 nm by adjusting the reprecipitation conditions. The NPs in water dispersions showed high aggregative and optical stability, which were due to contributions from the special cruciform configuration and amorphous nature of DPA-TSB molecules. The cellular uptake behavior of DPA-TSB NPs was investigated to show their cell staining capabilities as nanoprobes using a confocal microscopy test in vitro. The results demonstrated that DPA-TSB NPs were readily internalized into cytoplasm with no apparent toxicity for up to 24 h, implying excellent imaging capabilities.
[Show abstract][Hide abstract] ABSTRACT: We report a novel multilayer electro-chemical polymerization method and the first color-stable polymer-based multilayer white-emissive device, which exhibited CIE coordinates of (0.35, 0.35), a CRI of 93 and extremely stable white-light emission over a wide range of driving voltages of 8 to 20 V. The multilayer electro-chemical polymerization method affords more opportunities to develop multilayer polymer heterostructures in organic solid-state devices.
[Show abstract][Hide abstract] ABSTRACT: The first white-emissive cross-linked films and devices obtained by electrochemical copolymerization that have significantly improved color stability are reported (see figure). The device exhibited the CIE coordinates of (0.33, 0.35), a CRI of 88, and extremely stable white-light emission over a wide range of driving voltages of 8-22V. This kind of new ECP film afforded more opportunities to develop color-stable white-light-emission.
[Show abstract][Hide abstract] ABSTRACT: The electrochemical polymerization (EP) method to fabricate highly luminescent films and devices is rarely reported. It is typically believed that the organic light-emitting devices (OLEDs) made by EP method behave low performance because of the structural defects, doped electrolytes, and rough morphology in EP films. Here we present a new strategy to fabricate high-quality EP films including the special molecular design for EP precursors and the electrochemical control for EP processes. The resulting EP films exhibit high fluorescence, low doping levels, and smooth surface morphology. The efficiency of EP film devices arrive a level of >10 cd A−1 (green-emission). Moreover, the full-color micropatterned EP films with sharp edge and high resolution have been achieved, demonstrating a new simple method for fabricating micropatterned luminescent polymers and devices compared with currently used techniques.
[Show abstract][Hide abstract] ABSTRACT: An improved method for electrochemical deposition (ED) of a novel precursor (peripheral carbazole substituted 9,9′-spirobifluorene (TCPC)) for fabricating highly efficient luminescent films and devices has been developed. Electrochemical deposition often leaves residual charged ion species within the film. These species can negatively impact the performance of these films in OLED applications. The amount of residual charged species in the films can be reduced by controlling the oxidation and reduction potentials, by using electrolytes with different counter anions, and by washing with solvents. An optimized ED process showed a significant decrease in the doping level; up to 0.07% in ED film. The films prepared under a scan potential range from 0.85 to −0.8 V, using TBAAsF6 as the supporting electrolyte, and washed with solvent mixtures of acetonitrile and CH2Cl2 (V/V = 2/3) demonstrated excellent device performance. Light-emitting devices fabricated by electrochemical deposition achieved deep blue emission (x, y) = (0.16, 0.06) in CIE coordinates. High luminance efficiencies of 2.3 cd A−1 were achieved for single-layer device; luminescence efficiencies of 4.4 cd A−1 were achieved for a double-layer device. Finally, the problem that ED films usually exhibit low electroluminescent efficiency is solved.
[Show abstract][Hide abstract] ABSTRACT: A new kind of peripheral carbazole substituted ruthenium(II) complexes [Ru(bpy)2(tkdp-bpy)(AsF6)2] (4) (bpy = bipyridine, tkdp-bpy = 4,4′-(3,5-bis(6-(9H-carbazol-9-yl)hexyloxy)phenyl)methoxycarbonyl-2,2′-bipyridine) and [Ru(bpy)2 (dkte-bpy)(ClO4)2] (5) (dkte-bpy = bis(4-(9H-carbazol-9-yl)butyl)-2,2′-bipyridine-4,4′-dicarboxylate) were synthesized and their photophysical, electrochemical, as well as electroluminescent (EL) properties were studied. They display intense deep red phosphorescent emission centered at 660 nm and 658 nm, respectively, both in solution and in the solid state at room temperature. The peripheral carbazole in the complexes acts as an electrochemical coupling unit providing the ability to carry out electrochemical deposition (ED) and to form an ED film on an ITO electrode under a positive potential. Highly luminescent ED films are obtained under a carefully controlled ED process, and used as emitting layers in organic light-emitting diodes (OLEDs). The diodes gives out strong pure red emission and a luminous efficiency of 3.9 cd/A. These are the first electropolymerized phosphorescent OLEDs to be reported.
[Show abstract][Hide abstract] ABSTRACT: A facile approach for synthesis of spirobifluorene trimers with peripheral carbazole functional groups by utilizing Suzuki coupling as the key reaction has been developed. These novel compounds exhibit blue emission with high quantum yields in solution and thin films, and excellent spectral stability upon photoirradiation and annealing in air. By the introduction of carbazole groups, the oxidation potentials of spirobifluorene trimers S TCPC-6 and STCPC-4 were significantly lower than that of model compound STHPH without peripheral carbazole groups, which reflect that the title compounds process higher HOMO energy level and better hole-injection ability. Highly luminescent films were obtained by electrochemical coupling between carbazole units. Pure blue-emission single-layer LEDs based on electrochemical deposition films as light emitting layers were achieved.
The Journal of Organic Chemistry 07/2008; 73(11):4212-8. DOI:10.1021/jo8006094 · 4.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Luminescent films electrodeposited (ED) on indium tin oxide glass are considered for application in low-cost luminescent devices. During ED processes, the anions play an important role in the quality of resultant ED films. Three species of supporting electrolytes TBA-X (TBA=n-tetrabutylammonium, X= BF 4-, PF 6-, and AsF 6-) with different size of anions were used for the preparation of ED films from a branched carbazyl luminescent precursor TCPC. Increasing the size of anions (BF 4- < PF 6- < AsF 6-) resulted in an increase of growth rate and improved the morphology of ED films. The ED film prepared using TBA- AsF6 as supporting electrolyte showed strong fluorescence with efficiency of 65%, which was significantly higher than that of ED films from the smaller anions BF 4- and PF 6-. By utilizing the ED films as emitting layer, the light-emitting device also showed improved performance with increasing size of anions in the electrolytes. The origin of observed counter anionic size effects on electrochemical, morphological, and luminescent properties of ED films can be attributed to the difference in interaction between the carbazyl cation and anions, which induced an easier (i.e., for the larger size ions) or difficult (i.e., for the smaller size ions) dedoping process.
Journal of The Electrochemical Society 01/2008; 155(5). DOI:10.1149/1.2844453 · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent studies on electrophosphorescent polymeric devices have demonstrated that charge-trapping-induced direct recombination on the phosphorescent dopant is of crucial importance. In this paper, we show that the electrochemical properties of phosphorescent molecules, which reflect their carrier-trapping ability, may be a basic design criterion for the selection of host and device configuration. The systems, consisting of a red phosphorescent [Ru(4,7-Ph-2-phen)(3)](2+) dopant and two blue hosts 2-biphenyl-4-yl-5-(4-tert-butyl-phenyl)-[1,3,4]oxadiazole (PBD) and poly(vinylcarbazole) (PVK), are intensively studied. The triplet energy level of PVK and PBD is higher than that of the [Ru(4,7-Ph-2-phen)(3)](2+), and both hosts show the ability of efficient energy transfer to the dopant, however, efficient electroluminescence (EL) is only obtained in the PVK-host system. The combined studies of photoluminescence (PL), EL, and electrochemistry for doped films demonstrate that [Ru(4,7-Ph-2-phen)(3)](2+), which undergoes a multielectron trapping process as it is used as a dopant in electron-rich (n-type) hosts, for instance, PBD, may induce an inefficient recombination for the resulting emission. Whereas using a hole-rich (p-type) polymer, such as PVK, as a host and inserting both hole-blocking and electron-transfer layers can effectively increase the efficiency of the corresponding devices up to 8.63 Cd A(-1), because of the reduced probability of multielectron trapping at the [Ru(4,7-Ph-2-phen)(3)](2+) sites.
[Show abstract][Hide abstract] ABSTRACT: This paper describes a simple electrochemical deposition (ED) technique to prepare luminescent and patterned films for light-emitting devices (LEDs). The luminescent films are deposited directly on the patterned ITO (indium tin oxide) electrodes through an oxidation coupling reaction of an electroactive and luminescent precursor. The ED films deposited on the ITO strips (width of 200 µm) exhibit smooth surface morphology (roughness of morphology surface of 3.1 nm), small roughness in electrode edge of 1–2 µm and high fluorescence quantum efficiency (>60%). The LEDs with structure ITO/ED film/Ba/Al show pure blue emission (CIE coordinates of (0.16, 0.07)), high brightness of 3080 cd m−2 and the maximum external quantum efficiency of 0.60%.