Photorefractive polymers. 2. Structure design and property characterization

Abstract

To manifest a photorefractive effect, the polymer must possess a photocharge generator, a charge transporter, a charge trapping center, and a nonlinear optical (NLO) chromophore. We have synthesized novel photorefractive polymers which contain the NLO chromophore, the charge generator, and the transporting compound covalently linked to the polymer backbone. The charge generators absorbed strongly in the visible region (550-600 nm), allowing us to excite the species with normal laser sources. The other species had absorptions below 450 nm avoiding spectral overlap of these species with the charge generator. Structural characterizations confirmed that all of the species were incorporated into the polymer chains. These polymers exhibit relatively large electrooptical effects (r33 = 12.2 and 13.0 pm/V for polymers 1 and 2, respectively). A photocurrent of 1.4 μA was observed with a response time of 100 ms. Two beam coupling experiments revealed that the refractive index grating caused by the space charge field with a phase shift of 90° is a major contribution to the optical gain, which is a demonstration of the photorefractive effect.