Structure - Second-order polarizability relationship in chromophores incorporating a spacer: A joint experimental and theoretical study

A joint theoretical and experimental study is reported on the structure- polarizability relationship in a novel type of push-pull conjugated system which contains a spacer within the conjugated backbone. The chromophores are based on a dithienyl conjugation pathway, spaced by a keto group, and selectively end-capped by a donor and an acceptor. Four chromophores were synthesized, in which the strength of the acceptor group and the length of the conjugated path were varied. The electronic properties of two model compounds were studied theoretically by means of correlated quantum-chemical calculations. The degree of ground-state polarization was varied in the calculations by the application of an external electric field and varied experimentally by the modification of the dielectric constant of a binary mixture of solvents. The linear and nonlinear optical properties of the compounds (measured in solution by hyper-Rayleigh scattering) are discussed in detail.