FIRST HYPERPOLARIZABILITIES OF SOME PUSH-PULL OLEFINS MEASURED BY THEHYPER-RAYLEIGH SCATTERING TECHNIQUE

First hyperpolarizabilities of a series of donor-acceptor substituted ethylenes and butadienes have been measured using the hyper-Rayleigh s cattering technique. Keeping the donor group fixed as dimethylamino, t he second-order nonlinear coefficient beta in these aliphatic systems has been measured and is shown to increase as a function of the accept or strength with the exception of the cyano group. beta values of the substituted butadienes are correlated with their bond length alternati on parameter [delta r] obtained from semi-empirical calculations. It i s shown that even in these small push-pull olefins, it is possible to generate a variety of ground state structures by choosing a suitable a cceptor with a fixed donor.