Effect of methoxy or benzyloxy groups bound to an amino-benzene donor unit for various nonlinear optical chromophores as studied by hyper-Rayleigh scattering

We report the molecular first hyperpolarizability (β) of a series of nonlinear optical (NLO) chromophores comprising amino-benzene with an additional methoxy or benzyloxy group as the donor units, polyene, phenyl-di-vinylene, or thienyl-di-vinylene as the π-electron bridges, and 2-(dicyanomethylene)-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF), 2-(dicyanomethylene)-3-cyano-4,5-dimethyl-5-trifluoromethyl-2,5-dihydrofuran (CF3–TCF) or 2-(dicyanomethylene)-3-cyano-4-methyl-5-phenyl-5-trifluoromethyl-2,5-dihydrofuran (CF3–phenyl–TCF) as the acceptor units. An improvement in linear and nonlinear optical properties was found in the long π-conjugated NLO chromophores with methoxy or benzyloxy groups compared with benchmark chromophores without these groups. We also discuss a possible mechanism with a contribution for improvement, that is, intra-molecular hydrogen bonding.