Photo‐ and Redox‐Active Metal Dendrimers: A Journey from Molecular Design to Applications and Self‐Aggregated Systems

Abstract

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...

Mechanistic Insights into Light‐Activated Catalysis for Water Oxidation

“…To this respect, PSs displaying high triplet yields are typically the best candidates, particularly when a bimolecular reaction is considered. (iii) The potential difference E(EA/EA – ) – E(PS + /*PS) (where the potential E(PS + /*PS) is given by Equation ) has to be positive enough to provide sufficient thermodynamic driving force for Equation 3 to occur. …”

“…If ground‐state association between the Ru(bpy) 3 2+ PS and the Ru 4 POM WOC leads to undesired, detrimental quenching pathways, a different situation is encountered when a tetranuclear ruthenium dendrimer [Ru{(µ‐2,3‐dpp)Ru(bpy) 2 } 3 ] 8+ (µ‐2,3‐dpp = 2,3‐bis(2‐pyridyl)pyrazine), hereafter Ru4, is used as the PS (Figure ) . In this compound, the excited state redox potentials (for Ru4: E PS+/*PS = –0.03 V vs. NHE; E *PS/PS– = +1.38 V vs. NHE; for Ru(bpy) 3 2+ : E PS+/*PS = –0.86 V vs. NHE; E *PS/PS– = +0.84 V vs. NHE) are indeed suitably unbalanced in order to make reductive quenching thermodynamically more favored than a potentially competing oxidative one.…”

Exploring the Effect of the Irradiation Time on Photosensitized Dendrimer-Based Nanoaggregates for Potential Applications in Light-Driven Water Photoreduction

“…According to this approach, macromolecular structures with well-defined architectures and monodispersity emerge as relatively viable and interesting alternatives for the development of viable photoactive systems [24,25,26]. Specifically, the use of dendrimers seems to be an ideal strategy due to their unique chemical structure and properties, such as compact globular shapes and sizes, significant peripheral functionalities, and appropriate stability in diverse chemical environments [27,28,29]. Importantly, the high functionality of polyamidoamine (PAMAM) provides a profitable way to covalently attach photosensitizers onto their numerous peripheral functional groups.…”

New Hybrid Light Harvesting Antenna Based on Silicon Nanowires and Metal Dendrimers

“…These two species belong to the class of supramolecular light‐harvesting antennas featuring both significant absorption throughout a large portion of the visible region and emission in the NIR. [ 48–50 ]…”