The photoinduced electron-transfer process between a magnesium–porphyrin and a quinone in a model complex has been studied by means of quantum dynamical methods. The microscopic parameters controlling the electron-transfer process have been obtained using ab initio electronic structure calculations. A quantum dynamical simulation for a reduced-dimensionality model, including only the totally symmetric vibrational degrees of freedom of the quinone molecule, shows that the electron-transfer is fast, taking place in a few hundreds of femtoseconds, in agreement with experimental results for similar systems.