Intramolecular Charge Transfer Reaction in Solutions of Low to High Electrolyte Concentrations: Interplay between Friction and Solvation

摘要

Fluorescence emission spectroscopy have been used to investigate the effects of electrolytes on the excited state intramolecular charge transfer (ICT) reaction in 4-(1- azetidinyl)benzonitrile (P4C) in very dilute to concentrated electrolyte solutions of ethyl acetate (EA), acetonitrile (AN) and ethanol (EtOH). In the limit of very low electrolyte concentrations, the reaction rate (= 1/τrxn, τrxn being the reaction time) is found to decrease with increasing electrolyte concentration, the extent of decrease being the maximum in EA and the minimum in AN. At moderate to higher electrolyte concentrations, however, the rate increases upon further addition of electrolyte. The observed non-monotonic electrolyte concentration dependence of rate is believed to occur due to a novel interplay between friction and solvation experienced by the photo-excited reactant in solution. Moreover, the long time decay constant and amplitude of the bi-exponential decay of the time resolved fluorescence emission intensity also show a significant electrolyte concentration dependence which corroborates the relevant steady-state results.