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Intramolecular Electron Density Redistribution upon Hydrogen Bond Formation in the Anion Methyl Orange at the Water/1, 2‐Dichloroethane Interface Probed by Phase Interference Second Harmonic Generation
Author(s) -
Rinuy Juliette,
Piron Alexis,
Brevet Pierre Franc˛ois,
BlanchardDesce Mireille,
Girault Hubert H.
Publication year - 2000
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20000915)6:18<3434::aid-chem3434>3.0.co;2-l
Subject(s) - chemistry , hydrogen bond , redistribution (election) , methyl orange , intramolecular force , molecule , density functional theory , hyperpolarizability , crystallography , analytical chemistry (journal) , inorganic chemistry , computational chemistry , stereochemistry , organic chemistry , photocatalysis , politics , political science , law , catalysis , polarizability
Surface second harmonic generation (SSHG) studies of the azobenzene derivative p ‐dimethylaminoazobenzene sulfonate, often referred as Methyl Orange (MO), at the neat water/1,2‐dichloroethane (DCE) interface is reported. The two forms of the anionic MO dye, which are usually observed in bulk solution, with one form being hydrogen bonded to a water molecule through the azo nitrogens (MO/H 2 O) and the other form not being hydrogen bonded (MO) have also been observed at the water/DCE interface. Their equilibrium constant has been compared with the corresponding bulk solution and found to be identical. The adsorption equilibrium of the two forms has been determined and the Gibbs energy of adsorption measured to be −30 kJ mol −1 for both forms. From a light polarisation analysis of the SH signal, the angle of orientation of the MO transition dipole moment was found to be 34±2° for MO and 43±2° for MO/H 2 O under the assumption of a Dirac delta function for the angle distribution, a difference explained by the different solvation properties of the two forms. Furthermore, the wavelength dependence analysis of these data revealed an interference pattern resulting from the electronic density redistribution within the hydrated anionic form occurring upon the formation of the hydrogen bond with a water molecule. This interference pattern was clearly evidenced with the use of another dye at the interface in order to define a phase reference to both forms of Methyl Orange.