Tautomeric structure of N-salicylideneaniline derivatives studied by soft X-ray absorption spectroscopy and X-ray photoelectron spectroscopy

The tautomeric structures in solid phase were studied by near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for five N-salicylideneaniline derivatives. The observed features in the NEXAFS spectra were assigned by (1) the comparison with the core excitation spectra of reference compounds and (2) ab initio MO calculations of the core-excited states by the improved virtual orbital method. The relative intensity of the observed peaks characteristic of each tautomer enabled us to deduce the tautomeric structures of these compounds. The XPS spectra allowed quantitative estimation of the relative tautomer populations. These structures are consistent with the previous estimation by Xray diffraction. These results demonstrate the usefulness of NEXAFS as well as XPS for studying the tautomerism in hydrogen bonded systems.