Photophysics of quinidine dication in relation to quinine dication and 6-methoxyquinoline monocation

Abstract

Nanosecond time resolved emission spectroscopy was used to investigate the excited state solute-solvent interaction in quinidine dication. The emission spectrum is susceptible to the wavelength of excitation and the viscosity of the medium. The fluorescence lifetime is dependent on the emission wavelength. Spectral relaxation is observed on a nanosecond time scale. The room temperature data have been explained using Bakshiev's formulation of solvent relaxation. However, transient and steady state fluorescence studies from 80 to 290 K reveal that at 160 K, a rapid relaxation process other than the solvent relaxation occurs. A comparison of the photophysical data of protonated quinidine, quinine and 6-methoxyquinoline shows close similarities among these three molecules. The major two relaxation processes in these molecules are solvent relaxation and charge transfer.