High-performance photorefractive polymer composites based on poly(9-vinyl-3-carbazolcarboxyaldehyde diphenylhydrazone)

Abstract

Photorefractivity is based on the combined effects of photoconductivity and electro-optic property. Under the illumination of non-uniform light formed by the interference of two coherent laser beams, a spatially oscillating space charge field is formed arising from the generation and the redistribution of photo-induced charges. The refractive index of material is subsequently modulated via an electro-optic effect. The photorefractive materials have potentials applications in the fields such as dynamic holography, 3D display, 3D printer, reversible data storage and information processing. In 1994, remarkable improvement in the performance of PR polymeric material was obtained by using the photoconductive polymer poly(N-vinylcarbazole) (PVK). PVK/2,5DMNPAA/ECZ/TNF=34:50:15:1 wt% composite, showed a large gain coefficient of 220 cm and a diffraction efficiency of nearly 100% at the applied electric field of 90 V/ μm. Many studies have been done since Meerholz and coworkers proposed high-performance photorefractive (PR) polymeric composite. Despite this progress, the search for new photorefractive materials are still required for their widespread utilization in information technologies. In a previous paper, we reported on the synthesis and characterization of a photoconducting poly(siloxane) having pendant diphenylhydrazone. This composite shows a high diffraction efficiency of 81% at an electric field of 40 V/μm. Poly[4-(diphenyl-hydrazonomethyl)-phenyl]-[3-(methoxydimethyl-silanyl)-propyl]-methyl-amine (PSX-HZ) system have advantages including excellent optical quality, long shelf lifetime, the large birefringence, and high diffraction efficiency at low electric field. Despite the various advantages, the PSX-HZ system has suffered from relatively slow PR response time. To solve this problem, we applied the polyvinyl-backbone containing the hole transport moiety that is 9-vinyl-3-carbazolcarboxyaldehyde diphenylhydrazone (CPH). Hydrazone based on aromatic amines and arylaldehyde hydrazone are widely studied as organic hole transport materials due to enhanced hole mobility. Carbazole-containg hydrazone especially, exhibit relatively high hole mobility. We expect the realization of large photoconductivity of new polymer. The chemical structures investigated are shown in Figure 1, although the details of the synthesis and photophysical properties will be published elsewhere. The composition our samples was PVCPH/DB-IP-DC/ BBP/PCBM (54:30:15:1 wt%)-C1 and PVCPH/PDCST/BBP/ PCBM (54:30:15:1 wt%)-C2. Where poly(9-vinyl-3-carbazolcarboxyaldehyde diphenylhydrazone) (PVCPH) are photoconducting material, 2-{3-[(E)-2-(dibutylamino) ethen-1yl]-5,5-dimethylcyclohex-2-enylidene}malononitrile (DBIP-DC) and 2-(4-piperidinobenzylidene)malononitrile (PDCST) are nonlinear optical chromophore, butyl benzyl phthalate (BBP, Tokyo Kasei Kogyo Co.) is plasticizer, phenyl-C61butyric acid methyl ester (PCBM, Solenne Co.) is photosensitizer. The device was prepared by sandwiching the softened composite between two indium tin oxide (ITO) coated glass plates.