Excited state solvation dynamics of 6-methoxyquinoline

Abstract

Steady state and transient studies of 6-methoxyquinoline (6MQ) were undertaken. 6MQ undergoes a large change of dipole moment on excitation. The low energy absorption band L_b does not change in position with solvent polarity whereas the emission maxima shift towards lower frequencies with broadening of the spectra. The edge excitation red shift, which is associated with the time-dependent red shift of emission, is observed in all polar solvents. The fluorescence decay is monoexponential and is dependent on emission wavelength. The data are explained with the help of the Bakhshiev model of solvent relaxation. The solvent relaxation time τ_r and the fluorescence lifetime τ_f increase with the polarity of the solvent. In aqueous solution, 6MQ undergoes a protolytic reaction in the excited state. The rate constant for the proton transfer is 1.2 × 10⁸ s^-1.