Excited state intramolecular proton transfer in 2-(2 '-hydroxyphenyl)-3H-imidazo[4,5-b]pyridine: effect of solvents

Excited state intramolecular proton transfer in 2-(2'-hydroxyphenyl)-3H-imi dazo[4,5-b]pyridine (2-HPIP) in different solvents and mixtures of binary s olvents has been studied by means of UV-Visible absorption, fluorescence, f luorescence excitation and time-correlated fluorescence spectroscopy. Dual fluorescence is observed in all the solvents except ill cyclohexane where o nly large Stokes-shifted emission is noticed. The fluorescence quantum yiel d of the long-wavelength emission decreases, whereas that of the short wave length emission increases, with increase in the polarity and hydrogen bondi ng nature of the solvent. Steady-state fluorescence and fluorescence excita tion spectra and the time-correlated study have clearly established the pre sence of only two distinctly different rotamers in the ground state. Semi-e mpirical quantum mechanical calculations (AM1) have been carried on differe nt isomers, rotamers and tautomers of 2-HPIP to help establish the presence of true species (C) 2001 Elsevier Science B.V. All rights reserved.