Biomimetic Models of the Photosynthetic Reaction Center Based on Ruthenium−Polypyridine Complexes

Mimicking the fundamental processes of the photosynthetic reaction center is a large field of research over the past decade. We present as biomimetic model systems for electron transfer the mono- and heteroleptic ruthenium complexes 2 − 9 containing differently substituted bipyridazine−glycol ligands. Depending on the number of glycol chains of the complexes 2 − 9, they are divided into three classes: A (2 branches, 2 − 4 ); B (3 branches, 5 − 6 ) and C (6 branches, 7 − 9 ). UV, fluorescence, single-photon counting, and laser flash photolysis were employed as techniques for photophysical characterization. Redox properties were determined using cyclic voltammetry. Detailed steady-state quenching studies of 2 − 9 with MV 2+, OV 2+, and MPVS have shown different supramolecular interactions between sensitizer and acceptor in the case of MV 2+ . These effects may be explained by π−π donor−acceptor attractions as well as hydrophobic interactions. Supporting molecular modeling studies have been done. The suitability as biomimetic model systems was shown by testing the ruthenium complexes 2 − 9 in artificial photosynthesis systems. Two typical reactions were selected: the sacrificial reduction of water and the reduction of CO 2 to CH 4 . The use of 2 − 9 leads to satisfactory hydrogen production from the reduction of water. In the CH 4 /CO 2 system, complexes 7 − 9 worked efficiently.