A novel mesogen‐jacketed liquid crystalline electroluminescent polymer with both thiophene and oxadiazole in conjugated side chain

Abstract

Mesogen‐jacketed liquid crystalline polymers (MJLCPs) with both electron‐transport oxadiazole and hole‐transport thiophene in the side chain were reported for their promising electroluminescent property. Monomers of 2,5‐bis{5‐[(4‐alkoxyphenyl)‐1,3,4‐oxadiazole]thiophen‐2‐yl}styrene (M‐Cm, m is the number of the carbons in the alkoxy groups, m = 8,10) were synthesized and confirmed by 1H‐NMR, mass spectrometry, and elemental analysis. The corresponding polymers were successfully obtained and characterized by thermal analysis, optical spectroscopy, cyclic voltammetry, electroluminescent analysis, polarized light microscopy (PLM), and wide‐angle X‐ray diffraction (WAXD). The polymers exhibited high decomposition temperatures reaching 382 °C and high Tg's reaching 184 °C. The absorption spectra indicated that both the monomers and polymers had little aggregation in film than that in solution, and the absorption spectra of the polymers showed an obvious blue‐shift compared with those of the monomers. Both the monomers and the polymers had blue‐green emission, and the photoluminescence spectra of the polymers in film suggested the formation of excimer or exciplex. The polymers showed lower HOMO energy levels and LUMO energy levels than those of the MJLCPs containing oxadiazole unit reported before. Electroluminescence study with the device configuration of ITO/PEDOT/PVK/polymer/TPBI/Ca/Ag showed maximum brightness and current efficiency of 541 cd/m2 and 0.10 cd/A, which proved that the introduction of directly connected electron‐ and hole‐transport units could greatly improve the EL property of side‐chain conjugated polymers. The phase structures of the polymers were confirmed to be smectic A phase through the results of PLM and WAXD. The annealed samples emitted polarized photoluminescence at room temperature, which indicated potential utility for practical applications in display. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1502–1515, 2010

Influence of different linkage groups in biphenyl mesogenic core on phase behaviors of mesogen‐jacketed liquid crystalline polymers

“…Since the first evolution of MJLCPs reported by Zhou and coworker, many kinds of MJLCPs with various structures, molecular weight, and properties have been designed and investigated. Furthermore, dependence of the phase behaviors on the chemical structures of the polymer repeated unit and rigidity of the side chain has been investigated in detail. Reports have shown that the phase behaviors of the MJLCPs can be modulated by a few factors such as the shape of the mesogens, the molecular weight, and the terminal alkyl length in the side chain,.…”

Side Chain Liquid Crystalline Polymers: Advances and Applications

“…By hydrosilylation of polymethyl hydrosiloxane with the styrenic monomers, MJLCPs with a polysiloxane main chain were synthesized (Zhang et al 2010). Besides MJLCPs with flexible backbones, the jacketed structure has also been applied to polymers with rigid backbones, such as polyalkynes (Chen et al 2006a, b;Peng et al 2010) and polythiophenes (Yang et al , 2010. In addition, MJLCPs with a polynorbornene backbone and laterally attached 2,5-bis [(4 0 -n-alkoxybenzoyl)oxy] mesogens on side chains, display enantiotropic nematic mesophases (Pugh and Schrock 1992).…”

Progress in side-chain thiophene-containing polymers: synthesis, properties and applications

“…polymeric materials, which are expected to be promising active components in electroluminescent devices for practical lighting and information display applications. Zhou et al [40] synthesized a series of mesogen-jacketed liquid crystalline polymers (MJLCPs) with both electron-transporting oxadiazole and hole-transporting thiophene in the mesogenic side groups by ATRP, as shown in Scheme 2(a). The polymers form smectic A phases, confirmed by polarized light microscopy, 1D WAXD, and 2D WAXD experiments.…”