STM investigation of molecular architectures of porphyrinoids on a Ag(111) surface

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The functionalization of surfaces on the nanoscale is a captivating and challenging area of science, essential for developing catalysts, sensors, and devices for solar energy conversion. This process relies on the interaction between an active solid surface and another phase, whether liquid or gaseous. Planar transition metal complexes adsorbed on solid supports are promising candidates for novel heterogeneous catalysts. These catalysts feature well-defined and uniform active sites, specifically the coordinated metal centers with vacant axial coordination sites. Metalloporphyrinoids are particularly advantageous as they combine a rigid molecular frame that promotes long-range order with an active site, the coordinated metal ion. Their planar coordination environment allows for two axial coordination sites for additional ligands. When adsorbed on a surface, one axial site is occupied by the substrate, enabling electronic interactions that can be manipulated to tailor the metal center's electronic structure and reactivity. The remaining site can attach molecules for sensor functionality or serve as a reaction center for single-site catalysis. Numerous prototypes exist in nature, notably metallo-tetrapyrrols, which are crucial in significant biological processes, such as iron porphyrins in heme, magnesium porphyrins in chlorophyll, and cobalt corrin in vitamin B12.