Determination of the First Hyperpolarizabilities of Octupolar Molecular Ions Made from Symmetric Cyanine Dyes

Symmetric cyanine dyes of the kind Me2N+CH(CHCH) n NMe2 normally exhibit no first hyperpolarizabilities β but have relatively long absorption wavelengths. Therefore they are not suitable NLO chromophores for second-order applications. However, if these chromophores are converted into octupolar molecules either by coupling an extra aldiminium group onto the dye molecule or by grafting three vinamidinium units onto a benzene ring, NLO chromophores with considerable first hyperpolarizabilities are obtained. To prove this, the β values of both kinds of octupoles have been determined via hyper-Rayleigh scattering in solution at 1064 nm.