A PRELIMINARY-STUDY OF POLY(P-PHENYLENE) BASED NONLINEAR-OPTICAL MATERIALS

This paper describes preliminary work exploring the feasibility of pre paring high-performance nonlinear optical (NLO) materials based on the poly(p-phenylene CPPP) backbone. Three new monomer/N10-phores of the general formula: 4-RSO(2)C(6)H(4)C=C(4-XC(6)H(4)) (where R = 2,5-dichl orophenyl; 2a, X = H; 2b, X = OCH3; 2c, X = N(CH3)(2)) were synthesize d and then homopolymerized using catalytic nickel and stoichiometric z inc to produce the poly(p-phenylenes), 3a-c, respectively, as lowmolec ular-weight materials (number-average molecular weight (M) over bar(n) = 1800-6000). NLO-phores 2b-c and low-molecular-weight oligomers of 3 c were dispersed in a poly(methyl methacrylate) (PMMA) host. Spin-cast films of these guest-host systems were subjected to corona poling abo ve the glass transition temperature T-g. Following poling, both monome r NLO-phore/PMMA guest-host systems displayed optical nonlinearity wit h second-order noniinear optical susceptibility (chi)(2) values of 1.7 pm/V and 0.9 pm/V for 2e and 2b, respectively. Both systems exhibited good temporal stability at room temperature, with about 12% loss in s econd harmonic signal over more than 100 h. However, the oligomeric ma terial 3c dispersed in PMMA showed a smaller NLO signal when poled abo ve T-g. Attempts to induce dipolar asymmetry in the homopolymers 3b an d 3c were unsuccessful. The observed response during poling and the re laxation of the chromophore orientation following poling have been dis cussed in terms of structure and composition of these systems.