TEMPERATURE-DEPENDENCE OF ULTRAFAST INTERMOLECULAR ELECTRON-TRANSFER FASTER THAN SOLVATION PROCESS

Temperature dependence of intermolecular electron transfer (ET) between oxazine 1 (OX 1) in the excited state and electron donor solvents such-as aniline (AN) and N,N-dimethylaniline (DMA) was studied by observing fluorescence dynamics of OX1. The fluorescence decay of OX1 in DMA showed a single exponential behavior with a time constant of similar to 280 fs which was independent of temperature over the range of 280 to 353 K. In AN, the ET caused nonexponential fluorescence decay whose time constants range from a few hundred femtoseconds to a few picoseconds depending on temperature. The time constants of these ET were smaller than the solvation times obtained by dynamic fluorescence Stokes shift of coumarin 102. This indicates the importance of vibrational nuclear motion in ET. The extended Sumi-Marcus two-dimensional reaction Coordinate model which concerns the effect of high frequency mode was applied to explain the experimental observations. Good agreements Were obtained between the experiments and calculations in terms of necessary parameters such as electronic matrix element and solvent reorganization energy. The difference between the ET of OX1 in DMA and AN can be mainly explained by the free energy difference between the reactant and the product.