Hyperpolarizabilities of hetero-cycle based chromophores: A semi-quantitative SOS scheme

The static first- and second-hyperpolarizabilities of isomeric hetero-cycle based chromophores have been calculated by using the CPHF and MP2 methods. A semi-quantitative scheme in the framework of sum-over-state (SOS) has been proposed to explain the variation of hyperpolarizabilities in terms of ground state electric properties. The hyperpolarizabilities calculated using this scheme correlate fairly with the corresponding MP2 values. Electron correlation effect, in general, appreciably enhances the hyperpolarizabilities. The rather larger enhancement of NLO responses of twisted intramolecular charge transfer (TICT) molecule arises from its sudden polarized ground state. Among the chosen hetero-cycles borrole leads to exceptionally large non-linearity.