Toward Sustainable Energy: Molecular Complexes and Organized Architectures for Solar Harvesting and Conversion

The global energy crisis is one of the most pressing challenges of the 21st century, with the increasing demand for energy exacerbating concerns about the environmental impact of fossil fuels. Solar energy, with its abundance and clean nature, emerges as a promising solution to address this issue. However, the efficient conversion of solar energy into usable forms, particularly chemical energy, remains a critical challenge. This research emphasizes solar-to-chemical energy conversion, a cutting-edge approach that aims to harness sunlight to drive chemical reactions that can store energy in stable, transportable forms, such as hydrogen or other fuels. In the field of artificial photosynthesis, photo-induced water-splitting represents a key process, generally investigated employing a three-component system involving a photosensitizer, a catalyst, and a sacrificial agent. In this context, the aim of this study is to design, synthesize, and optimize an integrated macrocyclic photosensitizer-catalyst complex to enhance the efficiency of photoinduced water oxidation. This system incorporates three [Ru(bda)]-type catalytic subunits (bda = 2,2’-bipyridine-6,6’-dicarboxylate; pic = 4-picoline), held together by three [Ru(bpy)2(bpy-py2)]²⁺ (bpy = 2,2’-bipyridine; py = pyridine) photosensitizer subunits. The photosensitizer complex features a bipyridine ligand with pyridine groups positioned at 5 and 5’, oriented to promote coordination. A key innovation of this system lies in its closed-loop architecture, which not only improve the effective organization of the photocatalytic components but also creates a confined environment capable of trapping water molecules within the macrocycle’s cavity, thereby facilitating the catalytic process. This work further extends to the investigation of the reductive half-reaction of water-splitting, carried out at the University of Montréal. The focus here is on the design, synthesis, and comprehensive photophysical and electrochemical characterization of heteroleptic Ru-based polypyridyl complexes of the type [Ru(bpy)2([bpy]-4,4'-dicarboxamide-L)]2+ (L = 4-amino-pyridine, 3-amino-pyridine, and 3-aminomethyl-pyridine as photosensitizers for the light-driven hydrogen evolution reaction. A promising strategy to enhance the efficiency of this process is the implementation of spatially integrated design, to minimize diffusion-related losses and promote interactions between the photosensitizer and the catalyst, thereby optimizing hydrogen generation. The development of such integrated photoactive systems represents a crucial advancement in the field of artificial photosynthesis. This work provides valuable perspectives for improving robust multi-functional systems that integrate light-harvesting, energy-transfer, and catalytic processes into a single cooperative framework, ultimately enhancing the effectiveness of photocatalytic water-splitting technologies.