SPECTROSCOPIC STUDIES OF THE PHOTOCHROMIC MOLECULE N-(2-HYDROXYBENZYLIDENE)ANILINE AND ITS PHOTOPRODUCT

The structure of N-(2-hydroxybenzylidene)aniline in its crystalline form and in solvents such as hexane, trifluoroethanol, and hexafluoro-2-propanol has been studied by vibrational spectroscopic methods. Band assignments have been facilitated with the help of isotopic 15N and deuterium substitution. The most strongly enhanced Raman band in resonance excitation with the 340-nm electronic band occurs at 1577 cm-1 and is assigned to a vibration involving the HOCCCN part of the molecule. The anil is found to undergo a structural change in polar hydrogen-bonding environments to a zwitterionic form. Increasing amounts of the zwitterion are formed in hexafluoro-2-propanol as compared to trifluoroethanol as evidenced by Raman and N MR spectroscopy. The necessity of a polar hydrogen-bonding environment in the formation of the zwitterionic structure was confirmed by its appearance in the supercages of dehydrated sodium-exchanged zeolite Y. The structures of the photoproduct of the anil and its isotopic forms in the solid state are also investigated by vibrational spectroscopy and are consistent with a trans-quinoid rather than a cis-zwitterionic structure. © 1990 American Chemical Society.