First hyperpolarizabilities of some push-pull olefins measured by the hyper-Rayleigh scattering technique

First hyperpolarizabilities of a series of donor-acceptor substituted ethylenes and butadienes have been measured using the hyper-Rayleigh scattering technique. Keeping the donor group fixed as dimethylamino, the second-order nonlinear coefficient β in these aliphatic systems has been measured and is shown to increase as a function of the acceptor strength with the exception of the cyano group, β values of the substituted butadienes are correlated with their bond length alternation parameter 〈δr〉 obtained from semi-empirical calculations. It is shown that even in these small push-pull olefins, it is possible to generate a variety of ground state structures by choosing a suitable acceptor with a fixed donor.