First hyperpolarizabilities of triazine derivatives.: Ab initio studies and Hammett correlation

First hyperpolarizabilities (beta) of triazine derivatives were studied by the ab initio method (HF/6-31G). The beta values of these molecules increase with a stronger donor and as the conjugation length increases, probably because the electronic charge becomes more delocalized and the HOMO-LUMO energy gap (DeltaE) and the bond length alternation (BLA) decrease with variation of the chromophore structure. Also, the susceptibility of beta to the donor strength is found to be larger for a more elongated substrate. Noteworthy is the excellent linear relationship between beta and BLA and also the gas-phase substituent constants (sigma(gas)(+)). This result may serve as a useful guideline for the design of two-dimensional octupoles with large first hyperpolarizabilities. Copyright (C) 2004 John Wiley Sons, Ltd.