Modified-PVK-based Photorefractive Three-Component Low-Tg Composites

Two modified poly(N-carbazole), poly(2-carbazolylethyl methacrylate) (PCEMA) and poly(3-carbazolylpropyl methacrylate) (PCPMA), were synthesized. Doped with electro-optic (EO) chromophore 1-n-butoxyl-2,5-dimethyl-4-(4'-nitrophenylazo)benzene and the photosensitizer 2,4,7-trinitro-9-fluorenone, the EO response and photorefractive (PR) effect were studied experimentally. Due to the shorter spacer between the carbazolyl and the main-chain and thus a higher glass-transition-temperature Tg, PCEMA-based composite exhibited an effective EO coefficient as only a quarter as that in PCPMA-based composite. However, a slight higher two-beam coupling coefficient and much faster PR response were observed in the former. It was suggested that both the spacer length and the polymerization degree changed the Tg and the number density of traps, which decided the EO and PR responses.