VI-Q-4 Soft X-ray Absorption and X-ray Photoelectron Spectroscopic Study of Tautomerism in Intramolecular Hydrogen Bonds of N-Salicylideneaniline Derivatives

Eisuke ITOa, Hiroshi OJIa, Tohru ARAKIb, Kazuyoshi OICHIa, Hisao ISHII, Yukio OUCHIa Toshiaki OHTAc, Nobuhiro KOSUGI, Yusei MARUYAMAd, Toshio NAITOe, Tamotsu INABEe and Kazuhiko SEKIa (aNagoya Univ.y, bKEK, cUniv. Tokyo, d Hosei Univ. and eHokkaido Univ.)

[J. Am. Chem. Soc. 119, 6336 (1997)]

The tautomerism in solid phase was studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the N K- and O K-edges and X-ray photoelectron spectroscopy (XPS) in the N1s and O1s regions for five N-salicylideneaniline derivatives: N,N'-disalicylidene-1,6-pyrenediamine (DSPY), N,N'-disalicylidene-p-phenylenediamine (BSP), N-(2-hydroxy-1-naphthylidene)-1-pyrenylamine (NPY), N,N'-di(2-hydroxy-1-naphthylidene)-p-phenylenediamine (DNP), and the complex between DNP and 7,7,8,8-tetracyanoquinodimethane (DNP-TCNQ). The NEXAFS spectral features 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 using the relaxed Hartree-Fock orbitals. The tautomeric structures were deduced by the intensity of peaks characteristic of the tautomers in OH- and NH-forms. The XPS spectra gave structures consistent with those by NEXAFS, and also allowed quantitative estimation of the relative tautomer populations. The results range from the dominance of the OH-form in DSPY and BSP to comparable mixture of the OH- and NH-forms in DNP and DNP-TCNQ. These structures are consistent with the previous estimation by X-ray diffraction (XD), except for DNP-TCNQ where XD suggested the NH-form dominance. The good correlation of the population by XPS with the C-O bond length by XD supports the present conclusion for DNP-TCNQ. These results demonstrate the usefulness of NEXAFS as well as XPS for studying the tautomerism in hydrogen bonded systems.


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