Fine tuning of glass transition temperature in monolithic organic photorefractive material

摘要

In order to study the effect of T_g on the photorefractivity in organic monolithic system, we designed and synthesized photorefractive homopolymer (PCzBO) and organic glass (EHCzBO), consisting of the same monolithic chromophore. Photorefractive polymer composites were prepared by blending them. T_g of PCzBO and EHCzBO were 106 and 29℃, respectively. T_g of polymer composite could be controlled precisely by the compositional ratio of PCzBO and EHCzBO in the range from 29 to 40 ℃. Since both the polymer and the organic glass contained the same chromophore structure, all the samples had nearly the same chromophore concentration even though compositional ratios of them were different, as was confirmed by UV-visible spectroscopy. Frequency-dependent ellipsometric technique showed that the birefringence contribution through the orientation enhancement effect was dominant in the refractive index modulation of our low T_g composites. It was found that the reorientation of chromophore according to the modulated voltage was more limited for the higher T_g composite, which consequently reduced the birefringence contribution. The diffraction efficiency and two beam coupling coefficient were decreased with the increase of T_g.