Recent efforts to develop spectroscopic probes capable of directly examining charge transfer states in organic photovoltaic materials are reviewed. We describe ultrafast solvatochromism assisted vibrational spectroscopy that takes advantage of the sensitivity of vibrational modes to their local molecular environments in order to examine charge transfer states at electron donor/acceptor interfaces. By measuring the formation and subsequent loss of charge transfer states in real time, it is possible to investigate the mechanisms of their formation and to provide insight into how molecular structure affects the rate and efficiency of their dissociation to form separated charges. (C) 2011 Elsevier B.V. All rights reserved.