Synthesis and properties of photorefractive polymers containing indole-based multifunctional chromophore as a pendant group

Novel photorefractive chromophores with indole and nitrobenzene as the push and pull groups, respectively, were synthesized and subsequently reacted with methacryloyl and acryloyl chloride to give multifunctional monomers. Polymers were obtained by copolymerization of these monomers with methyl methacrylate (P1, P2) or butyl acrylate (P3). These polymers were very soluble in organic solvents to be fabricated into optically clear polymer films and showed glass transition (T-g) at ca. 150 degrees C for P1, P2 and at 8 degrees C for P3, respectively. Large nonlinear optical coefficients (d(33) as high as 49 pm/V) and photoconductive sensitivity ton the order of 10(-9) S . cm(-1)/W . cm(-2)) were identified with high T-g polymers P1 and P2. Preliminary investigation of photorefractivity was carried out with low T-g polymer (P3) by two-beam coupling and four-wave mixing experiments. It was observed that P3 doped with 1% TNF showed two-beam coupling gain of 2.2 cm(-1) at 75 V/mu m and diffraction efficiency of 0.44% at 60 V/mu m. When the photoconducting plasticizer (EHCzHy) was added to P3, a net gain of 22 cm(-1) and a diffraction efficiency of 2.41% could be achieved.