Fluorescence quenching of 2,7-diaminoxanthone in alcohols by hydrogen bonding: An experimental and theoretical research

Using methods of stationary and time-resolved femtosecond laser spectroscopy, as well as time-dependent density functional theory, the spectral-kinetic properties of excited electronic states of synthesized 2,7-diaminoxanthone (DAX) have been studied in polar protic and aprotic solvents. The intramolecular charge transfer from amino-groups to the central oxygen-containing moiety manifests itself in appearance of a new intensive long-wavelength absorption band in DAX. Considerable bathochromic Stokes shift observed in DAX fluorescence spectra with increasing aprotic solvents polarity indicates growth of charge transfer degree and, respectively, of transition dipole moment between the ground to the first singlet-excited states. In alcohols, hydrogen bond formation between DAX and solvent results in an increase of Stokes shift and fluorescence quenching. The observed spectral dynamics reflects the solvent relaxations and is well reproduced with the dynamic parameters of the solvents measured and reported elsewhere.