Poly[bis(triphenylamine) ether]s with low glass transition temperatures as photoconductors in fast photorefractive systems

A series of photoconducting poly(tetraphenyldiaminobiphenylene alkyl ether)s in which tetraphenyldiaminobiphenyl (TPD) units are covalently linked through flexible oligomethylene glycol spacers in the main chain were synthesized and the thermal, optical and electrochemical properties were studied. Due to the introduction of flexible spacers, the polymers are highly soluble and could be obtained as film-forming materials with appreciably high molecular weights. The polymers exhibit glass transition temperatures between 92 °C and 128 °C which is about 100 °C less than those main chain polymeric bis(triphenylamine)s without such spacers. The HOMO value as determined from cyclic voltammetry is about −5.1 eV. The glass transition temperature of the photorefractive composites prepared by mixing the different polymers with an electro-optic chromophore, 1-(2-ethylhexyloxy)-2,5-dimethyl-4-(4-nitrophenylazo)benzene, EHDNPB, could be tuned over a wide range about room temperature by just changing the photoconductor and without the need of any additional amount of plasticizer. Degenerate four-wave mixing and two-beam coupling in composites with the composition, photoconductor ∶ EHDNPB ∶ C60 (60 ∶ 39 ∶ 1 by wt/wt%) results in refractive index modulations of 10−3 with corresponding response time ∼10 ms and a photorefractive gain of Γ = 13 cm−1 for a writing beam intensity of 1 W cm−2 (645 nm) under an external electric field of 60 V µm−1.