高分子电致发光材料研究进展

综述了近几年来国内外关于高分子聚合物在电致发光材料领域的研究进展,重点介绍了聚苯撑乙烯、聚芴类、聚噻吩类聚合物及其衍生物的相关研究成果,并讨论了当前高分子电致发光材料存在的关键问题及应用前景.     

Blue luminescence induced by confinement in self-assembled films

The fabrication and characterization by means of photoluminescence (PL), UV-vis absorption, electro-luminescence (EL) and X-ray reflectivity of multilayer heterostructures consisting of alternate layers of conjugated and non-conjugated polymers have been studied. The heterostructures are prepared by the layer-by-layer self-assembly technique, using two types of polyelectrolytes. The first are precursors of conjugated polymers such as poly(phenylenevinylene) (PPV) and other poly(arylenevinylene) polymers, and the second are non-conjugated polymers such as poly(styrene-4-sulfonate) (SPS), polyacrylic acid (PAA) and poly(allylamine hydrochloride) (PAH). The heterostructures consist of a repeated sequence of bilayers (layer pair) or multilayers, where the conjugated polymer is formed by heat treatment under vacuum. The thickness of each bilayer or multilayer was controlled by changing the non-conjugated polymer layer. Most importantly, we have found that the PL and EL spectral emissions can be ‘tuned’ by a proper ‘design’ of the heterostructure. Particularly, heterostructures in which the bilayer thickness is rather small and the electroluminescent layers are practically in contact show a blue shift upon decreasing the thickness of the assembly for ultrathin assemblies. In contrast, for assemblies where the electroluminescent layers are well separated by one or several non-conjugated layers (polyelectrolyte spacers), the emission is in the blue and independent of the assembly thickness (number of bilayers). We interpret the results as being due to confinement effects. Using this assembly technique, we were able to fabricate light emitting diodes (LEDs) which emit in the blue region.     

几种电致发光聚合物材料的研究进展

介绍了几种典型的电致发光聚合物材料,包括聚(对苯乙烯撑)及其衍生物、聚噻吩及其衍生物、聚芴及其衍生物,对它们的结构、制备方法、特点进行了归纳和讨论。其中最重要的是聚(对苯乙烯撑)(PPV)及其衍生物,目前采用较多的制备方法是前聚物法和强碱诱导的去卤缩合法以及电化学聚合法。在苯环上引入长链烷烃、烷氧基或芳基后的取代PPV,即PPV的衍生物,可溶于很多有机溶剂。可溶性PPV衍生物为制备多层电致发光聚合物器件提供了有效途径。文章还对电致发光聚合物材料存在的问题和发展前景进行了探讨和展望。     

Synthesis and characterization of exfoliated MEH-PPV/clay nanocomposites by in situ polymerization

In this article, we demonstrate the synthesis of a conjugated polymer, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) in the presence of organophilic montmorillonite (OMMT) and the properties of the MEH-PPV/OMMT composites produced herefrom. By controlling the reaction conditions, such as the ratio of monomeric precursors to montmorillonite, exfoliated MEH-PPV/OMMT nanocomposites were synthesized via in situ polymerization. These materials exhibit higher electroluminescent properties and enhanced performance of thermal stability than that of the pure polymer. Additionally, based on the solid-state ¹³C NMR measurement results, the possible origin of the optoelectronic property improvement is discussed from the point of view of segmental mobility.     

新型电磷光咔唑-co-吡啶共聚物的合成与发光性能

用Suzuki缩聚反应制备了一系列新型咔唑-吡啶共轭主链上含有金属铱配合物单元的共聚物. 共聚物发光器件结构为ITO/PEDOT:PSS/polymer＋PBD (w＝30%)/CsF/Al [氧化铟锡/苯磺酸掺杂聚乙烯基二氧噻吩/聚合物＋2,4-二苯-5-4-叔丁基苯-1,3,4-恶二唑(w＝30%)/氟化铯/铝]. 基于共聚物PCzPyIrMppy2的器件在电流密度为20.8 mA/cm2时, 最大外量子效率和流明效率分别达到4.1%和6.1 cd/A. 在电流密度200 mA/cm2时, 器件的最大外量子效率和流明效率仍分别达到3.2%和4.8 cd/A, 器件的发光的最大波长位于570 nm, 最大亮度达到13251 cd/m2. 研究结果表明, 在共轭聚合物主链上引入螯合金属铱配合单元是实现高效、稳定的电致磷光器件的有效方法之一.     

Liquid crystalline conjugated polymers and their applications in organic electronics

This article describes the syntheses and electro‐optical applications of liquid crystalline (LC) conjugated polymers, for example, poly(p‐phenylenevinylene), polyfluorene, polythiophene, and other conjugated polymers. The polymerization involves several mechanisms: the Gilch route, Heck coupling, or Knoevenagel condensation for poly(p‐phenylenevinylene)s, the Suzuki‐ or Yamamoto‐coupling reaction for polyfluorenes, and miscellaneous coupling reactions for other conjugated polymers. These LC conjugated polymers are classified into two types: conjugated main chain polymers with long alkyl side chains, namely main‐chain type LC polymers, and conjugated polymers grafting with mesogenic side groups, namely side‐chain type LC conjugated polymers. In general, the former shows higher transition temperature and only nematic phase; the latter possesses lower transition temperature and more mesophases, for example, smectic and nematic phases, depending on the structure of mesogenic side chains. The fully conjugated main chain promises them as good candidates for polarized electroluminescent or field‐effect devices. The polarized emission can be obtained by surface rubbing or thermal annealing in liquid crystalline phase, with maximum dichroic ratio more than 20. In addition, conjugated oligomers with LC properties are also included and discussed in this article. Several oligo‐fluorene derivatives show outstanding polarized emission properties and potential use in LCD backlight application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2713–2733, 2009     

Tuning the optical properties of a water-soluble cationic poly(p-phenylenevinylene): surfactant complexation with a conjugated polyelectrolyte

In this work, we investigate the emission and absorbance properties of the novel water-soluble cationic conjugated polymer poly{2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene}, denoted here as P2, in the presence of varying amounts of the anionic surfactant sodium dodecylsulfate (SDS). We show that the absolute photoluminescence quantum efficiency (PLQE), the absorption wavelength, and the emission wavelength of an aqueous solution of P2 can be adjusted according to the surfactant/polymer ratio in aqueous solution. In particular, we show that the addition of SDS to P2 increases the polyelectrolyte's PLQE to approximately 40%. An observed red shift in the emission spectra upon addition of the surfactant is attributed to the reduction in electrostatic repulsive interactions between side chains that minimize the benzene ring twisting along the backbone structure. At the surfactant's critical micelle concentration, the P2 chains wrap around the outer surface of the SDS micelles. This work has implications on the development of new stable poly(p-phenylenevinylene)-based photovoltaic and electroluminescent materials with tunable optical properties.     

Controlling layer thickness and photostability of water-soluble cationic poly(p-phenylenevinylene) in multilayer thin films by surfactant complexation

In this work we build on prior studies of the novel water-soluble cationic conjugated polymer known as "P2" (poly{2,5-bis[3-( N, N, N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene}) with a focus on its incorporation into thin films for such applications as photovoltaics or electroluminescent devices. Multilayer assemblies were constructed using P2, the anionic surfactant sodium dodecyl sulfate (SDS), and the polyanion poly(sodium 4-styrene-sulfonate) (PSS) using the technique of layer-by-layer electrostatic self-assembly (LBL-ESA). SDS was observed to affect the layer thicknesses and absorbance characteristics of the films. We show that the optical properties and photo-oxidative resistance can be improved by varying the SDS content in the assemblies. Specifically, the surfactant-complexed poly( p-phenylenevinylene) (PPV) shows an enhanced absorption at longer wavelengths as well as improved photostability. Therefore, our work may have broad implications on the development of stable PPV-based materials in general and their efficient integration into thin films technologies.     

Luminscent graphene quantum dots for organic photovoltaic devices

Recent research in organic photovoltaic (OPV) is largely focused on developing low cost OPV materials such as graphene. However, graphene sheets (GSs) blended conjugated polymers are known to show inferior OPV characteristics as compared to fullerene adduct blended with conjugated polymer. Here, we demonstrate that graphene quantum dots blended with regioregular poly(3-hexylthiophene-2,5-diyl) or poly(2-methoxy-5-(2-ethylhexyloxy)-1,4phenylenevinylene) polymer results in a significant improvement in the OPV characteristics as compared to GSs blended conjugated polymers. This work has implications for inexpensive and efficient solar cells as well as organic light emitting diodes.     

Novel fluorinated block copolymer architectures fuelled by atom transfer radical polymerization

Block copolymers based on poly(pentafluorostyrene), PFS, in various numbers and of different lengths, and polystyrene are prepared by atom transfer radical polymerization (ATRP). Di- and triblock copolymers with varying amounts of PFS were synthesized employing either 1-phenylethylbromide or 1,4-dibromoxylene as initiators for ATRP. Diverse bromo(ester) (macro)initiators were also devised and involved in the formulation of fluorinated pentablock as well as amphiphilic triblock copolymers with a central polyether segment. Amphiphilic star-shaped fluoropolymers, hydrophobic fluorinated nanoparticles, or segmented fluorinated star-shaped block copolymers are further designed by use of different multifunctional initiators. The composition of the novel materials with PFS is determined by combination of SEC and ¹H NMR. Glass transition temperatures and thermal stabilities of the hydrophobic star-shaped PFSs on a six arm dipentaerythritol core are investigated in a wide range of molecular masses and further discussed.     

Coronenes,Benzocoronenes and Beyond: Modern Aspects of Their Syntheses,Properties, and Applications

In recent years, a variety of new designs of coronene-based polycyclic aromatic hydrocarbons (PAHs) with diverse functions have emerged to serve as complementary materials in organic chemistry and materials chemistry. In the present review, we highlight the modern aspects of syntheses related to or different from the strategies used in the early era of coronene research. Systematic extension and expansion of coronene backbones to wide categories of angular PAHs are covered. The substitution and extension of coronene architectures, by incorporating functional groups and by fusing small and large conjugated units, advatangeously enrich their photophysical, electrochemical, self-assembling, and other properties, of which are discussed to demostrate their impact in materials chemistry. While the highly symmetric coronenes, tribenzocoronenes and hexabenzocoronenes conceived wide potential in charge-transporting, electroluminescent, sensing, and other applications, other related derivatives such as dibenzo, tetrabenzo and pentabenzocoronenes also displayed their potentials as exemplified by their use as charge-conduction channel in transistor application.     

Photophysical properties of polymers with a system of conjugated bonds and their use in light energy conversion processes

We consider the photophysical properties of polymers with a system of conjugated bonds and their use in light energy conversion processes. Based on our analysis of literature data we show that conjugated polymers of different classes (capable of exhibiting the properties of a dielectric, a semiconductor, or a metal) are characterized by efficient photoconductivity, photoluminescence, and electroluminescence. We determine the regularities in the dependence of the photophysical characteristics on the nature and structure of the conjugated polymers, their degree of doping, the energy and intensity of the incident light, the temperature, etc. In a series of polymers we show that conjugated polymers can be used in particular as photoconductors, electrophotographic materials, materials for lasers, electroluminescent diodes, and also solid-state photoconverters of light energy etc.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 5, pp. 241–263, September–October, 1994.     

发光性液晶共轭聚合物的研究进展发光性液晶共轭聚合物的研究进展

综述了可用做发光材料的液晶共轭聚合物（LCCPs)的种类及其制备,介绍了LCCPs在制备发光器件中的取向方法,并对其光学性能进行了评述。     

Electrochemical stability and transformations of fluorinated poly(2,6-dimethyl-1,4-phenylene oxide)

Fluorination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) leads to narrowing of its window of electrochemical stability in a cathodic range of potentials. It is found this is connected with appearance of both perfluorinated and incompletely fluorinated units in the polymer. The former units are liable to electrochemical reduction (at potentials <−2.0 V) followed by elimination of fluorine anions and the latter react with basic products (generated at potentials <−1.8 V) of electrochemical reduction of the background solution. In the both cases this results in appearance of conjugated multiple bonds in the fluorinated macromolecules. Quantities of these units in fluorinated PPO were determined with a help of direct and indirect electrochemical reductive degradation techniques.     

High-performance pyrrolidinium-based poly(ionic liquid) binders for Li-ion and Li-air batteries

The role of binders is crucial to achieve high performance and long cycle lifes in next-generation electrodes for lithium batteries. Currently used binders in electrode configurations, such as poly(vinylidene difluoride) (PVDF) are inactive polymers that do not transport lithium ions themselves, causing restrictions for high-power applications. Thus, developing innovative binders with an affinity towards lithium mobility is important for both lithium-ion and lithium-air batteries. In this work, we present for the first time the use of PDADMA poly(ionic liquid)s with fluorinated anions (FSI, TFSI, BETI, and CFSO) as cathode binders in Li-ion and Li-air batteries. The high-voltage NMC 532 cathodes with fluorinated PDADMA binders showed improved cells performances as: capacity values, rate performance, and cycling stability in accelerating aging conditions dedicated for more environmental-friendly mobility applications. Especially, PDADMA-CFSO binder in cathodes shows a cell capacity increase of 26% at 5C (12 min charge), when compared to PVDF one. Moreover, the fluorinated PDADMA binders in cathode improve the discharge capacities in Li–O₂ cells, both with liquid and solid gel polymer electrolytes. Impressively, the Coulombic efficiency improves by 146% and the cycling capacity by 70% in solid-state Li–O₂ cells using PDADMA-CFSO binder in the cathode, instead of common lithiated Nafion. All in all, the proposed fluorinated PDADMA Poly(ionic liquid)s can be a highly competitive alternative to conventional binders used nowadays in Li-ion and Li-air batteries.     

High-efficiency polymer light-emitting diodes using neutral surfactant modified aluminum cathode

High-efficiency polymer light-emitting diodes were fabricated by inserting a layer of nonionic neutral surfactant between the electroluminescent (EL) layer and the high-work-function aluminum cathode via spin coating. It was found that both the poly(ethylene glycol)- and poly(propylene glycol)-based surfactants as well as their copolymers can all demonstrate similar performance enhancement. Device performances comparable to or even better than those of the control devices using calcium as the cathode have been achieved for both poly(p-phenylene)-based and polyfluorene-based conjugated polymers with orange-red, green, and blue emission colors. It is possible that when both surfactant and aluminum are used as the cathode, the abundant hole injection through a hole-transporting layer and hole pile-up at the inner side of the EL/surfactant interface might cause an effective electric field to induce the realignment of the dipole moment of those polar surfactant molecules, thus lowering the barrier for electron injection. In addition, the coordination between the aluminum and oxygen atoms on the surfactant might cause n-type doping in the areas near surfactant in the EL polymer layer that causes the enhancement of electron injection.     

Electroluminescence in polymers

Polymeric materials containing chromophores are promising for electroluminescent (EL) device applications including displays and lighting. We report EL for a series of copolymers containing uniform conjugated chromophores and nonconjugated spacers. The emission color of the copolymers can be varied by adjusting the molecular structure to alter the energy gap between the HOMO and LUMO of the chromophore. The design can also be used to tailor other properties of the polymer, such as the glass transition temperature, by varying the length of the nonconjugated spacers.     

Synthesis and characterization of perfluorinated arylenevinylene polymers

Fully fluorinated arylenevinylene polymers have been synthesized via a methodology based on the Stille cross‐coupling reaction and characterized by FTIR spectroscopy and MALDI‐TOF mass spectrometry. Investigation of thin film properties by cyclic voltammetry and ellipsometry shows that complete substitution of hydrogen atoms with fluorine atoms on the conjugated backbone of the poly(arylenevinylene)s results in a strong increase of the band gap. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 285–291, 2010     

Novel fluorinated poly(aryl ether ketone)s

Two novel fluorinated monomers were prepared and polymerized with biphenols to produce amorphous, thermally stable poly(aryl ether ketone)s. The properties of the fluorinated polymers are compared to those of unfluorinated, amorphous poly(aryl ether ketone)s. The presence of fluorine in the polymers was found to cause a decrease in glass transition temperature and Young's moduli, however, no increase in thermal stability was observed. The fluorinated polymers are soluble in common organic solvents such as chloroform and methylene chloride at room temperature, and also show solubility in solvents containing a ketonic moiety, such as acetone. Evidence of polymer branching through fluorines considered to be unreactive under the polymerization conditions was found. Efforts were made to evaluate the reactivity of fluorine atoms under the polymerization conditions using both molecular modeling and ¹⁹F-NMR to ascertain if such branching could be avoided. © 1995 John Wiley & Sons, Inc.     

Anisotropic optical properties in electroluminescent conjugated polymers based on grazing angle photoluminescence measurements

Grazing angle photoluminescence (GPL) originates from a waveguided light emitted at grazing angle to the substrate due to the total internal reflections, and the light emission is polarized with enhanced intensity at selective mode wavelength. GPL measurements reveal the optical anisotropy of luminescent conjugated polymers, in particular, the alignment of emitting dipoles from which emission occurs, in contrast to spectroscopic ellipsometry measurements that give the anisotropy in the absorption. Based on the GPL emission intensities and spectra, we investigate the anisotropic optical properties in electroluminescent poly(9,9'-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) conjugated polymer thin films of different molecular weights (M(n) = 9-255 kg/mol), both in the pristine and annealed states. The optical anisotropy in F8BT films generally increases with molecular weight, suggesting that higher molecular weight polymers with longer chains are more likely to lie in-plane to the substrate. Upon annealing, high molecular weight F8BT films show even a higher degree of anisotropy, in contrast to low molecular weight F8BT films that become more isotropic. Annealing causes the polymer chains to rearrange and adopt a configuration in which the interchain exciton migration to better ordered low energy (LE) emissive states is strongly suppressed. We observe that the emissive states in F8BT are strongly affected by the local polymer chain arrangement, producing the less ordered high energy (HE) emissive states near the substrate interface where there is a higher degree of chain disorder and the LE states in the bulk of the film. When spin coated onto a quartz substrate precoated with a poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) layer, films of F8BT show severe luminescence quenching near the PEDOT:PSS interface for both the LE and HE emissive states, but a selective quenching of the LE states in the bulk of the film. These observations have important implications for fabricating efficient electronic devices using conjugated polymers as an active material, since the performance of these devices will strongly depend on anisotropic optical properties of electroluminescent conjugated polymers.