Valence Bond Charge Transfer Theory for Predicting Nonlinear Optical Properties of Organic Materials

A simple theory (VB-CT) is developed for predicting nonlinear optical properties of organic materials. Application of this theory to donor-acceptor charge-transfer molecules leads to analytic formulae for the absorption frequency, hyperpolarizabilities, and bond length alternation. Derivative relationships between hyperpolarizabilities (with respect to bond length alternation) are derived. Using a continuum description of the solvent in the VB-CT framework leads to the VB-CT-S model which gives results for solvent shifts in good agreement with experiment. To predict the saturation behavior of polarizability and hyperpolarizability with respect to polymer length, we developed the VB-CTE model which is applied to nine polymeric materials.