Excited state solvatochromic and prototropic behaviour of 4-aminodiphenylamine and 4,4′-diaminodiphenylamine—A comparative study by electronic spectra

Solvatochromic and prototropic behaviour of 4-aminodiphenylamine (4ADA) and 4,4′-diaminodiphenylamine (DADA) have been investigated in the solvents of different polarity and at various acid–base concentrations in the ground and excited states using absorption and fluorescence spectra. Solvatochromic shifts have been analysed and observed shifts are explained by the hydrogen bonding interactions. The prototropic study reveals that (i) absorption maximum of monocation of DADA is red shifted to its neutral form, and (ii) the fluorescence of 4ADA is red shifted on protonation. The abnormal fluorescence of 4ADA+ is found to be due to large solvent relaxation in polar medium.