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 obtained suggest that the presence of nitrogen in the unsaturated chain can have a substantial beneficial effect on the molecular hyperpolarizability provided that it is placed in a position which assists charge transfer from the donor to acceptor group on excitation. The values calculated 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 using an ab initio approach. © 1996 John Wiley & Sons, Inc.