Multifunctional Photoresponses in Carbazole Main-Chain Polymers

Abstract

Electronic and optical properties of organic charge-transfer (CT) compounds have attracted a lot of attention from both fundamental science and practical applications. Remarkable progress have been made in development of electroactive CT materials such as organic metals, conducting polymers, and organic photoconductors (OPCs). Among them, OPCs are widely used for electrophotographic applications. Besides photoconductive properties, it has been elucidated experimentally and theoretically that organic inter- and intracharge transfer compounds exhibit large nonlinear optical (NLO) responses. We have investigated the third-order NLO properties of polymeric CT materials based on poly-n-vinylcarbazole (PVK) complexed with 2,4,7-trinitrofluorenone (TNF) in terms of the complex composition.1 The values of χ(3) (-3ω; ω,ω,ω) increased linearly with the content of CT complex in the film. Recently large refractive index changes have been demonstrated in organic photorefractive polymers based on PVK/TNF systems.2 Carbazole compounds play a significant part in electroactive and NLO applications. In order to utilize the unique properties of polymer backbone, acceptor-substituted carbazole moiety was incorporated into the main chain through either 3,6- or 3,9-linkage. In this paper we discuss the multifunctional photoresponses in various carbazole main-chain polymers with shoulder-to-shoulder, head-to-tail, and hyper-branched arrangements as shown in Figure 1.