Maximizing the first hyperpolarizability (beta) of conjugated push-pull charge transfer molecules: Tuning of charge transfer and electron correlationeffects

A two-atom two-orbital Huckel like model has been proposed to predict analy tically the possible variations of the first hyperpolarizability (beta) of intramolecular organic charge transfer systems when the system parameters c hange. The model identifies some parameters which can be tuned to achieve t he maximization of beta. They include donor-acceptor interaction strength ( hopping term), donor and acceptor strength (ionization potential of the don or and electron affinity of the acceptor), state of hybridization of the do nor orbital, etc. A simple modification of the same basic model that includ es electron interaction explicitly throws some light on the possible role o f electron correlation in the emergence of high nonlinear optical response when the other system parameters are favourably tuned.