Various bimolecular photoinduced electron transfer reactions were investigated in liquid solution using ultrafast electronic and vibrational spectroscopy. In a study about the influence of diffusion on charge separation and recombination, dipolar and ionic liquids were compared and the results explained in the frame of Differential Encounter Theory. Time-resolved infrared spectroscopy was used to monitor the energy dissipation pathway during charge separation at high driving force to confirm the participation of excited radical ions. This result explains the apparent absence of the Marcus Inverted Region for this type of reaction after four decades of discussion. To understand donor acceptor interactions at low driving force, experiments were carried out to differentiate ion pair and exciplex. For the first time, vibrations of an exciplex intermediate have been observed that allowed obtaining information about the structure of the exciplex constituents as well as the competing interplay between ions and exciplex at different solvent polarities.