Spectral characteristics of 2-aminodiphenylamine in different solvents and at various pH values

The absorption and fluorescence spectra of 2-aminodiphenylamine (2ADA) have been studied as a function of solvent polarity and acid concentration. Analysis of solvatochromic and prototropic shifts of 2ADA reveals: (i) the presence of intramolecular hydrogen bonding between imino and amino groups in the ground state, (ii) dual fluorescence (360 and 430 nm) of the monocation (2ADA(+)) formed by the protonation of amino group; and (iii) proton-induced quenching of the monocation (2ADA(+)) fluorescence. In the dual fluorescence of 2ADA(+). the longer wavelength emission at 430 nm is found to be from the twisted form of the monocation. The rate constants of the proton-induced quenching of 2ADA(+) are determined. (C) 2001 Elsevier Science B.V. All rights reserved.