Theoretical investigation of the electronic properties of donor–acceptor N-benzylideneanilines and related molecules

The dipole moments, transition energies and hyperpolarizabilities of a substituted stilbene, azobenzene and two isomeric–benzylideneanilines containing the 4-dimethylamino-group at one end of the molecule and the 4-nitro-group at the other, have been calculated using a semi-empirical sum-over-states method on structures optimized with the 3-21G basis set. An excellent correlation is found between the calculated and experimental spectra. The azobenzene is predicted to have the largest hyperpolarizability of this series of molecules, followed by the stilbene and N-(nitrobenzylidene)aniline which have comparable values, with the non-planar N-(benzylidene)nitroaniline showing the smallest value.