Revisit of 4,4′-Diaminodiphenyl Sulfone Photophysics in Different Solvents

This paper aims at getting the origin of dual emission of 4,4'-diaminodiphenyl sulfone (Dapsone) in various solvents using steady state and time-resolved emission spectroscopy in conjunction with ground and excited state optimized geometry calculations in gaseous phase and in solvents. The dual fluorescence in different solvents and a distinctive bathochromic spectral shift of the low energy band in polar solvents indicate the possibility of intramolecular charge transfer (ICT) from the donor site (-NH2) to the acceptor moiety in the excited state. Time-resolved emission spectra (TRES) and more precisely time-resolved area normalized emission spectra (TRANES) depict the evolution of the dynamics of excited state species and the charge transfer. Hindrance of rotational relaxation in restricted environments causes intensified charge transfer emission quantum yield. A plausible model for excited state deactivation through ICT has been proposed on the basis of both theoretical and experimental findings. The observed results also necessitate to conceive the involvement of a nonradiative deactivation channel in an unrestricted environment which seems to regulate the ICT emission and photophysics of the probe.