1/48 The role of the bridging ligand in photocatalytic supramolecular assemblies for the reduction of protons and carbon dioxide Martin Schulz a,** , Michael Karnahl b , Matthias Schwalbe c , Johannes G. Vos a,* a SRC for Solar Energy Conversion, School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Dublin, Ireland. b Department of Photochemistry and Molecular Science, The Ångström Laboratory, Uppsala University, Box 523, 75120 Uppsala, Sweden. c Department of Chemistry, Humboldt Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany. ∗ Corresponding author. E-mail address:han.vos@dcu.ie. ∗∗ Corresponding author. Present address: Pharmaceutical Radiochemistry, Technical University Munich, Walther Meißner-Str. 3, 85748 Garching, Germany; Email adress: martin.schulz@tum.de Content 1. Introduction 2. Complexes for photocatalytic hydrogen production 2.1. Systems with noble metals as catalytic centers (Pd, Pt, Rh and Ir) 2.2. Systems with abundant metals as catalytic centers (like Co) 3. Complexes for photocatalytic CO 2 reduction 3.1. (diimine)Re(CO) 3 X and Ru-Re-systems 3.2. Ru-Co- and Ru-Ni-systems 3.3. Ru-systems 3.4. Rh and Ir-systems 3.5. Miscellaneous 4. Conclusions and perspectives 5. References Abstract Molecular photocatalysts, combining a light absorber and a catalytic active center via a bridging ligand, have received much attention during the last decade. Therefore, many new types of photocatalysts containing novel bridging ligands are reported. The bridging ligand is expected to play an important role and does not only represent the chemical connection between an antenna unit and a catalytically active center, but can also greatly affect the overall catalytic activity and stability of the photocatalysts. Moreover, a well chosen combination of the three parts antenna-bridge- catalyst is expected to yield intramolecular photocatalysts superior over intermolecular systems. This review will discuss the coordination, photophysical, electrochemical and photocatalytic properties of multinuclear metal complexes based on a selection of heterocyclic bridging ligands