Quantum dynamics of electron-transfer reactions: photoinduced intermolecular electron transfer in a porphyrin-quinone complex

Photoinduced electron transfer (ET) between a magnesium-porphyrin and benzoquinone in a model molecular complex is investigated employing ab initio multi-configuration electronic-structure calculations combined with quantum dynamical methods. The microscopic parameters controlling the electron-transfer process are obtained using a first-principles diabatization procedure. A model Hamiltonian which includes both linear and quadratic vibronic couplings of all nuclear degrees of freedom of the system is constructed. Quantum dynamical simulations of the ET process are performed employing the multi-layer multi-configuration time-dependent Hartree method. A detailed analysis of the ET dynamics for models of increasing complexity reveals that the dynamics is strongly influenced by resonances associated with vibronically active nuclear modes, leading to significant deviations from the results of classical ET theory. The comparison with results obtained with the simplified spin-boson model reveals the effects related to the Duschinsky rotation of normal modes.