We have designed and synthesized a new tris-chelating polypyridine ligand (bpy3Ph) suitable to be used as a bridging ligand (BL) for constructing various supramolecular photocatalysts.

The scientific adventure starting from simple dinuclear ruthenium(II) complexes and leading to the design, preparation, and study of photo-and redox-active polynuclear metal dendrimers capable of performing useful photo-driven processes is reviewed through decades of activity. The recent appli- [a] 3887 cations of luminescent metal dendrimers in the field of artificial photosynthesis -in particular as far as the photochemical water oxidation process is concerned -and their very recently revealed self-aggregating properties, including concentrationdependent photoinduced energy transfer, are also shown. the investigation of intercomponent photoinduced energy and electron-transfer processes. The simultaneous growth of supramolecular photochemistry [11] was indeed significantly powered by such studies, and an evolution towards larger multicomponent assembled systems appeared almost obvious. Scheme 1. Structural formulas of the polypyridine ligands mainly used for the synthesis of the metal dendrimers here described and their representations, used in the following figures.Within such a scenario, our research group started a collaboration with the groups of Vincenzo Balzani in Bologna and of Gianfranco Denti in Pisa, with the aim of building up unprecedented methods toward the synthesis of metal complexes of high nuclearity, having in mind some guidelines for preparing supramolecular assemblies capable of exhibiting made-to-order properties. In particular, photoinduced intramolecular energy transfer and predetermined redox patterns were among the properties we were looking for, since such properties were essential to open the way to artificial antenna systems for light harvesting purposes and for multiple charge storage. After the initial studies, that led us to synthesize and investigate the lumi-Microreview nescence properties and redox behavior of -among othersdinuclear, trinuclear, tetranuclear, hexanuclear, heptanuclear, Sebastiano Campagna received his Laurea in Chemistry from the University of Messina in 1983. Since 1985 to 1997 he worked in the Photochemistry group led by Vincenzo Balzani at the University of Bologna. In 1998 he joined the Faculty of Science of the University of Messina, where he became full professor in 2002. His research interests include photochemistry and photophysics of coordination compounds and supramolecular species, photoinduced electron and energy transfer, and artificial photosynthesis. Giuseppina La Ganga is post-doc student at University of Messina. She received her master degree in 2009 and received her PhD in Chemistry in 2014 from the University of Messina, working in the group of Prof. Sebastiano Campagna on supramolecular photochemistry. Her scientific interest is focused on renewable energies, with particular emphasis on the generation of solar fuels. She has developed and studied in detail various kinds of sensitizer-antenna dyes and multi-electron catalysts for water oxidation. Ambra Cancelliere obtained her Master degree in Chemistry in 2016 from the University of Messina...

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In this review, photoinduced electron transfer processes in specifically designed assembled architectures have been discussed in the light of recent results reported from our laboratories. A convenient and useful way to study these systems is described to understand the rules that drive a light-induced charge-separated states and its subsequent decay to the ground state, also with the aim of offering a tutorial for young researchers. Assembled systems of covalent or supramolecular nature have been presented, and some functional multicomponent systems for the conversion of light energy into chemical energy have been discussed.

Supramolecular photocatalysts, wherein redox photosensitizer (PS) and catalyst (CAT) molecules are connected to each other, have been extensively studied because of their high photocatalytic activity in both homogeneous and heterogeneous environments compared with the corresponding mixed systems of separated PS and CAT. A supramolecular photocatalyst RuC2PhC2Re, wherein [Ru­(diimine)3]2+ redox PS and fac-[Re­(diimine)­(CO)3{OC­(O)­OCH2CH2N­(CH2CH2OH)2}] CAT units were spatially separated by a bridging ligand p(-C2H4)2Ph consisting of 8 C–C bonds including a p-phenylene ring, was developed. Although the rate of intramolecular electron transfer of RuC2PhC2Re from one-electron-reduced Ru unit to the Re unit, which is a critical process of photocatalysis proceeding through the bond mechanism, was slower than that of RuC2Re having shorter bridging ligand with an ethylene chain, it could reduce CO2 to CO with higher durability (TON = 3880) than RuC2Re (TON = 2800). These results clearly suggest that the PS and CAT units can be separated further without lowering photocatalysis of supramolecular photocatalysts because the rate of intramolecular electron transfer is much faster, even in RuC2PhC2Re, than that of the subsequent processes in photocatalytic CO2 reduction.