Substituent effects on the UV spectra of extended benzylidene anilines p-X-PhCH=NPhCH=CHPh-p-Y.

Benzylidene anilines with p-substituted styryl groups substituted on the aniline ring, p-X-PhCH=NPhCH=CHPh-p-Y (X=NMe2, OMe, Me, H, Cl, F, CN, or NO2; Y=NMe2, OMe, Me, H, Cl, or CN) have been studied photochemically in ethanol. The substituent effects in the title compounds are more similar to p-X-PhCH=NPh-p-Y than p-X-PhCH=CHPh-p-Y. The introduction of styryl group to XBAY leads to a more planar geometry and a red shift of the maximum absorption wavelength. This can be described as a "styryl conjugation effect". Furthermore, a quantitative model has been established to correlate the UV maximum absorption wavenumbers of the title compounds and substituent parameters. The results help understand the substituent effects of conjugated compounds consisting of both benzylidene aniline and stilbene moieties.