Solvent Effects on the Absorption and Fluorescence Spectra of Naphthylamines and Isomeric Aminobenzoic Acids

Abstract

The absorption and fluorescence spectra of naphthylamines and isomeric aminobenzoic acids in various solvents have been measured.From the observed results, the difference in the dipole moments in the fluorescent and ground states respectively, i. e., \overrightarrowΔμ=\overrightarrowμe–\overrightarrowμg, has been estimated for naphthylamines.The effect of hydrogen bonding between solute and solvent molecules on the spectral shifts has been discussed. The hydrogen bonding between alcohol and amino nitrogen exerts a especially remarkable influence on the spectra, and the reorganization of this hydrogen bond during the life time of the excited solute molecule has been concluded from the observed results.The intramolecular hydrogen bond of o-aminobenzoic acid considerably decreases the \overrightarrowΔμ value and the effect of the intermolecular hydrogen bonding on the spectra. This result has been explained as due to the charge transfer through the intramolecular hydrogen bond.The \overrightarrowΔμ values for naphthylamines and naphthols have been calculated using the ASMO CI method and compared with the observed results.This comparison, together with the theoretical interpretation of the characteristics in the spectra of α- and β-isomers, respectively, has indicated that the lowest excited singlet state in the light absorption is 1Lb, whereas the fluorescent state is 1La in the case of α-naph-thylamine and 1Lb is the relevant excited state for both light absorption and fluorescence in the case of β-naphthylamine and naphthols.The mechanism of this level reversal has been discussed as being due to the change in the structure of the amino group during the life time of the excited state.