Temperature Effects on the Energy Gap Dependence of Charge Recombination Rates of Ion Pairs Produced by Excitation of Charge-Transfer Complexes Adsorbed on Porous Glass

Abstract

The energy gap dependence of the charge recombination (CR) rate constant (kCR) of geminate ion pairs produced by exciting the ground-state charge-transfer complexes adsorbed on porous glass and temperature effects on it were investigated by means of picosecond laser photolysis. At room temperature, the same energy gap dependence of kCR as observed in polar solutions was found also in the adsorbed systems. This result indicates that not polar solvent dynamic motions but intramolecular high-frequency quantum modes in the ion pair predominate in the CR process of these ion pairs. At 77 K, an energy gap dependence with a somewhat steep slope was obtained. This result indicates that the intra-ion-pair reorganization with low-frequency motion that seems to be frozen at 77 K contributes to the gentle slope in the energy gap dependence at room temperature. By integrating the present results with those obtained in solutions and with theoretical investigations, the factors regulating the charge recombination dynamics of this kind of ion pair are discussed.