Photoinduced Electron Transfer From Carbazole to Halomethanes in a Gas Phase

Abstract

Intermolecular photoinduced electron transfer (PET) in a gas phase was studied using carbazole vapor fluorescence quenching by halomethanes (CHCl3, CH2Br2, CCl4, CHBr3). The fluorescence quenching rate constants k q changing from 2.3·105 sec−1·torr−1 in mixtures with CHCl3 to 4.6·106 sec−1·torr−1 in mixtures with CHBr3 at a constant temperature of 403 K were estimated. The dependence of the carbazole fluorescence decay rates in the presence of halomethanes on the free energy change ΔG during transfer of the electron from carbazole to halomethanes is considered. It is suggested to take into account the influence of the vibrational energy of the carbazole molecule E vib and its temperature changes in estimation of the ΔG values. The differences between PET in the gas and liquid phases were analyzed. It is found that for mixtures with CCl4 and CHBr3 the negative temperature dependence of k q is observed, when the decay rates and efficiencies of the intermolecular PET decreased with temperature increase in the range 403–573 K, i.e. these mixtures the electron transfer is not a barrier-restricted process.