Second-order nonlinear polarizability of "Push-Pull" chromophores. A decade of progress in donor-π-acceptor materials

Fine tuning and switching of nonlinear optical response of ferrocene chromophores has been an area of considerable significance as evidenced by a large number of reports in the current literature. In this personal account, we present linear/nonlinear behavior and structure-activity relationships of several classes of donor-π-acceptor designs using organometallic and organic materials, developed by our research group during the last decade. The results especially the electronic absorption spectral and the hyper-Rayleigh scattering have been supported by theoretical calculations. Exploiting the redox behavior of ferrocene donor, we have demonstrated switching of quadratic nonlinear optical responses with reversible redox chemistry, which is a useful attribute of nonlinear optical materials. Based on the ease in synthesis, structure diversification and structure-based large and switchable second-order optical nonlinearity, these materials are potential candidates for electro-optic applications.