Theoretical Investigation On Photo-induced Electron Transfer And Influence Of The Solvent Effect On The Charge-separated Excited State

Theoretical calculations have been performed for the photo-induced electron transfer and the solvent effect on the excited charge-separated states of several complexes by means of ab initio method. Our emphasis has been put on the investigation of the photo-induced electron transfer of the selected isolated donors, acceptors, and donor-acceptor complexes. We have discussed the basis set superposition error (BSSE) produced in calculating the weak interaction of molecular complexes. In the aspect of constructing the complexes, we have considered several representative spatial arrangement fashions as far as possible, so as to find the most stable conformations. For complexes ethylene-tetracyanoethylenec, and tetramethylethylene- tetracyanoethylene, we consider four different spatial arrangements, while three arrangements for complex Vitamin E-benzoquinone. We apply 6-31++G** basis set for the former two systems due to the symmetry existed. Since the latter system has no symmetry, we have to decrease the basis set to 6-3 1G* in order to save the computational cost. Presuming that the inner structure keeps unchanged in the formation of the encounter complexes, we determine the stable conformation of the complex by means of optimizing the center-center distance between the donor and acceptor. Through the construction of the potential energy curve, we find out the energy minimum. The optimization shows that the parallelly stacked conformations are more stable than other stacked ones.We use the complete active space self-consistent field method to investigate the photo-induced charge-separated excited states and the electron transfer transition of the electron donor-acceptor complex in the present work. The optimizations of the ground state S0 and the low-lying excited state S1 of the selected three complexes reveal that photoexcitation can directly produce the charge-separated state. Based on the approximation of spherical cavity and point dipole. the solvation reorganization correction has been made on the charge transfer absorption. The result shows that the theoretical calculation agrees well with the experimental observation. In particular, the steady-state absorption spectra have been experimentally measured with a Shimadzu UV-2100S spectrometer in methanol at room temperature.