Influence of the chromophore ionization potential on speed and magnitude of photorefractive effects in poly(N-vinylcarbazole) based polymer composites

We report on the synthesis of three highly polar chromophores and their use as dopants in poly(N-vinylcarbazole) based photorefractive polymer composites sensitized with (2,4,7-trinitro-9-fluorenylidene)malononitrile. Small alterations in the amino donor group substituents were used to tune the dye's ionization potential (IP) by 0.2 eV. At 780 nm, 5 degrees C above the glass transition temperature (T-g), and with an applied field of 59 V/mu m, we observed complete internal diffraction and a gain coefficient of 167 cm(-1). In this temperature range, diffraction efficiency, gain coefficient, and photorefractive phase shift were found to correlate with the chromophore IP. At 20 degrees C below Tg, the contribution from birefringence to the index modulation is insignificant, and the speed of the photorefractive effect correlates well with the chromophore IP. Analysis of the results suggests that the space-charge field is influenced by the chromophore IP. (C) 2000 American Institute of Physics. [S0021-9606(00)70224-8].