Abstract
The first-order hyperpolarizabilities (βvec) of a set of quinonoid derivatives with different donor and acceptor groups in gas-phase and in solution were calculated by the INDO/s method. The variations of βvec with respect to the donor–acceptor strength gave an insight into the effects of donor–acceptor pairs and solvation. The mechanism of the solvent and the dependence of the strength of donor–acceptor pairs on βvec values are interpreted by a two-level model. The results may provide guides on selecting donor and acceptor groups for synthesizing molecules with desired nonlinear optical (NLO) properties.