MOLECULAR HYPERPOLARIZABILITY COMPONENTS BETA(ZZZ) AND BETA(ZXX) UNDER DIRECTIONAL EXTENSIONS OF PI-CONJUGATION - MISSING-ORBITAL ANALYSIS AND SIMPLIFIED SUM-OVER-STATES CALCULATIONS

The application of missing-orbital analysis to molecular hyperpolariza bility beta obtained by a simplified sum-over-states calculation, allo ws one to study the effects of the pi conjugation extension on both di agonal beta(zzz) and off-diagonal beta(zxx) components for C-2v molecu les (the z-axis being the principal one). Extension of the z-length in aminonitropolyacetylenes by increasing the number of acetylene units increases beta(zzz) but beta(zxx) remains unchanged. Conversely, beta( zxx) increases significantly with only a slight increase in beta(zzz) if the pi conjugation is extended mainly in the x-direction for 1,3-di amino-4,6-dinitrobenzene by replacing benzene with a fused-ring or ins erting acetylene units between the substituents and benzene. These are ascribable to changes in the charge-transfer structure by the ir exte nsion.