Characterization of photochromic and photorefractive chromophores

Abstract

Although photorefractive materials are those that exhibit both appreciable electro-optic and photoconductive behavior, the chromophore parameters that lead to large electro-optic coefficients have not so far led to similar photorefractive performance. Recently, it has been shown that the electro- optic contribution is one of two principal contributions to the overall photorefractive behavior, and that it is usually the smaller of the two. The larger factor, first referred to in the literature as an "orientational enhancement," is due to the birefringence of the chromophore: the difference in polarizability parallel to the dipole moment and perpendicular to it. A figure of merit incorporating both effects has been derived, although its determination is more difficult than that for purely electro-optic materials. The polarizability anisotropy is a function of all three components of the diagonalized polarizability tensor. Two expressions for these three parameters can be obtained by index of refraction and light scattering measurements on chromophores in solution. The third must be estimated. Results from this new characterization protocol are presented and compared with the results of photorefractive experiments on materials containing the tested chromophores. Another class of compounds has also been found to be of potential use in holographic storage, in this case write- once applications. These chromophores undergo an irreversible photochromic reaction that is triplet sensitized. A mechanism is proposed for this reaction and supporting data provided. ©2005 Copyright SPIE - The International Society for Optical Engineering.