Photophysical investigation of a donor-acceptor based Schiff base in solvents of varying polarities

Abstract

The present work reports detailed photophysics of excited state intramolecular charge transfer process in donor-acceptor system, namely, 7-((E)-((E)-3-(4 (dimethylamino)phenyl)allylidene) amino)-4-(trifluoromethyl)-2H-chromen-2-one (DPAATC) by steady state absorption, fluorescence and time resolved spectroscopy in combination with density functional theory calculations. Large fluorescence spectral shift observed in more polar solvents and large calculated excited state dipole moment clearly indicates an efficient charge transfer occurring from the donor group to the acceptor moiety in the excited state compared to the ground state. Effect on addition of acid and pH variation studies on steady state spectral properties further reveals charge transfer character. Fluorescence decay increases with increase in solvent dielectric constant in protic solvents which means the higher the polarity, the more is the stability of the probe. The HOMO and LUMO molecular orbital picture for the optimized ground state, donor twisted and acceptor twisted geometry are obtained at density functional theory level using B3LYP functional and 6-311+g(d,p) basis set which also support excited state intramolecular charge transfer process. The molecular electrostatic potential maps for the optimized ground state, donor twisted and acceptor twisted geometry shed insight on the electrostatic potential and charge distribution in a system which gives information about the reacting site of the probe and nature of the reaction.