PHOTOCHEMISTRY OF N-BENZYLIDENEANILINIUM CATIONS IN CONCENTRATED SULFURIC-ACID-SOLUTIONS

The photoreversible E reversible arrow Z isomerization of a series of protonated N-benzylideneanilines (X-C6H5CH=NC6H5-Y; X=H, N(CH3)(2); Y= H, NO2) was investigated in concentrated sulphuric acid solution. The UV absorption spectra of the E isomers are practically independent of substituents on benzene rings and suggest a planar conformation for pr otonated N-benzylideneanilines. The UV spectra of Z isomers were obtai ned from photostationary state conditions at two wavelengths. Also the quantum yields of E --> Z and Z --> E photoisomerization are not mark edly affected by the ring substituents and are compatible with a photo reversible process occurring through a common excited state.