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

Abstract

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-pphenylenediamine (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 a 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.

Biofunctionalization of a “Clickable” Organic Layer Photochemically Grafted on Titanium Substrates

“…The assignment of the N 1s signals from the triazole ring is supported by the reported XPS data and density functional theory calculation for some aromatic compounds containing sp 2 N atoms bonded to two or three atoms. 40 The ratio of the peak areas was about 1:2:1, consistent with the expected structure of the surface B . The absence of the azido N 1s signal at ~405 eV indicated the absence of physically adsorbed 1a on the surface.…”

Enol-keto tautomerism of aromatic photochromic Schiff base N,N′-bis(salicylidene)-p-phenylenediamine: Ground state equilibrium and excited state deactivation studied by solvatochromic measurements on ultrafast time scale

“…8,12,13,17,18 In nonpolar solvents most or even all molecules are present in its enol form in the ground state. 30 The ratios of the absorbance of the keto form to that of the enol form ͑A K / A E ͒ in different solvents are given in Table I, which also presents parameters describing the solvent prop-erties. The long-wavelength absorption band assigned to the S 1 ← S 0 transition of the keto tautomer was also observed for symmetric Schiff bases.…”

“…This molecule has been studied in the crystal state, in which it shows its thermochromic properties, 29,30 and in solution, showing a photochromic behavior. This molecule has been studied in the crystal state, in which it shows its thermochromic properties, 29,30 and in solution, showing a photochromic behavior.…”

Correlating Infrared and X-ray Absorption Energies for Molecular-Level Insight into Hydrogen Bond Making and Breaking in Solution

“…It was used in particular for the investigation of extended hydrogen-bond networks and their dynamics, 23−31 tautomerism of intramolecular hydrogen bonds 32 and dimerization in solution by hydrogen-bonding, 33 hydrogen bonding in amino acids 34−36 and DNA, 37 and hydrogen-bonding of aromatic molecules in solution 38 and for elucidating the interactions of proteins with salts and the Hofmeister effect. 39 The O or N K-edge absorption bands arise from transitions of O or N core−shell 1s electrons into empty molecular orbitals.…”