Conformation of p ‐dimethylaminobenzylidene‐ p ‐nitroaniline, p ‐nitrobenzylidene‐ p ‐dimethylaminoaniline, their stilbene and azobenzene derivatives

PCILO computations have been carried out on the conformation of p ‐dimethylaminobenzylidene‐ p ‐nitroaniline [I(m)], p ‐nitrobenzylidene‐ p ‐dimethylaminoaniline [I(n)] and the corresponding stilbene [II(a)] and azobenzene [II(b)] derivatives. The aniline rings in Im and In are found to be twisted out of the plane containing the central atoms by 60° and 30°, respectively. The two phenyl rings in case of II(a) are twisted out of plane in opposite directions by 30° each. II(b) was found to be planar. The results have been compared with the earlier experimental findings and used as a possible explanation for the visible absorption spectra of the four molecules.