A preliminary study of poly(p‐phenylene) based nonlinear optical materials

Abstract

AbstractThis paper describes preliminary work exploring the feasibility of preparing high‐performance nonlinear optical (NLO) materials based on the polyp‐phenylene (PPP) backbone. Three new monomer/NLO‐phores of the general formula: 4‐RSO2C6H4C(4‐XC6H4) (where R = 2,5‐dichlorophenyl; 2a, X = H; 2b, X = OCH3; 2c X = N(CH3)2) were synthesized and then homopolymerized using catalytic nickel and stoichiometric zinc to produce the poly(p‐phenylenes), 3a–c, respectively, as low‐molecular‐weight materials (number‐average molecular weight Mn = 1800–6000). NLO‐phores 2b–c and low‐molecular‐weight oligomers of 3c were dispersed in a poly(methyl methacrylate) (PMMA) host. Spin‐cast films of these guest‐host systems were subjected to corona poling above the glass transition temperature. Tg. Following poling, both monomer NLO‐phore/PMMA guest‐host systems displayed optical nonlinearity with second‐order nonlinear optical susceptibility χ(2) values of 1.7 pm/V and 0.9 pm/V for 2c and 2b, respectively. Both systems exhibited good temporal stability at room temperature, with about 12% loss in second harmonic signal over more than 100h. However, the oligomeric material 3c dispersed in PMMA showed a smaller NLO signal when poled above Tg. Attempts to induce dipolar asymmetry in the homopolymers 3b and 3c were unsuccessful. The observed response during poling and the relaxation of the chromophore orientation following poling, have been discussed in terms of structure and composition of these systems.