CALCULATION OF THE FREQUENCY-DEPENDENT HYPERPOLARIZABILITY OF DONOR-ACCEPTOR AZABUTADIENES

Calculations are reported on the dipole moments, transition energies, and hyperpolarizabilities of 1-amino-4-nitrobutadiene and its four aza -analogs using a semiempirical sum-over-states method. The results obt ained suggest that the presence of nitrogen in the unsaturated chain c an have a substantial beneficial effect on the molecular hyperpolariza blity provided that it is placed in a position which assists charge tr ansfer from the donor to acceptor group on excitation. The values calc ulated for the 3-azabutadiene are greater than those found for either the simple butadiene or for donor-acceptor aromatics or five-membered heterocycles. The results do not agree with those reported recently us ing an ab initio approach. (C) 1996 John Wiley & Sons, Inc.