A PHOTODYNAMICAL MODEL FOR THE EXCITED-STATE ELECTRON-TRANSFER OF BIANTHRYL AND RELATED MOLECULES

The underlying chemical dynamics of the excited state electron transfer of electronically excited 9,9'-bianthryl in polar solvents is explored via a semi-empirical comprehensive theoretical model for the reaction coordinate energy profile and the dynamics along the reaction coordinate. The predictions of the model are in excellent agreement with new femtosecond fluorescence data on bianthryl, which are presented in this paper. The model is comprised of several key elements, including: (i) an Onsager cavity/semi-empirical treatment for the solvent coordinate; (ii) an electronically adiabatic description of the mixing between the reactant and product zero-order states; (iii) a generalized Langevin equation treatment of the reaction coordinate dynamics where the friction kernel is determined using independent experimental results on solvation dynamics of coumarin probes; and (iv) an empirical solvatochromic/vibronic description for predicting fluorescence and absorption spectra. With a limited amount of parameterization the overall model is able to account in detail for many observables for bianthryl, including the static absorption spectra, the solvent dependence of the static fluorescence spectra, and the time resolved fluorescence spectra. The model supports our previous proposal that the electron transfer kinetics of bianthryl is controlled by polar solvation dynamics.