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.