Elucidation of acceptor–acceptor interactions in a Ru(II) supramolecular photosynthetic model complex†

Abstract

The interaction between the two viologen acceptors in a TEMPO-labeled Ru(II) bisviologen photosynthetic model system assembly has been investigated using EPR spectroscopy; the results are consistent with no viologen–viologen spin exchange in water at temperatures above 5 °C, although upon crystallization (⩽2 °C) strong spin exchange is observed; the strong spin exchange interaction results in a single broad line at temperatures below 1 °C, unlike the three broad lines measured for free TEMPO upon solvent freezing; this evidence for the TEMPO-labeled complex indicates that there is no interaction of the two viologen acceptors in the supramolecular Ru(II) bis-viologen structure in solution, thus making it indeed a viable model for the photosynthetic reaction center.