Time-resolved EPR in artificial photosynthesis

Time-resolved electron paramagnetic resonance (TREPR) methods often play an important role in characterizing artificial photosynthetic systems. The radical pairs and triplet states generated in such systems are spin polarized because of the initial correlation of the electron spins and the spin selectivity of the electronic relaxation and electron transfer. The polarization makes the TREPR signals of the states fundamentally different from those of equilibrium systems and makes it possible to extract information about the geometry of the radical pairs and about the pathway and kinetics of electronic relaxation and electron transfer. In this chapter, we give an overview of the different types of TREPR experiments that can be performed on artificial photosynthetic complexes and the different polarization patterns that are observed. This is followed by a summary of recent results on a several selected systems, which illustrate the strengths and weakness of the technique.