STM Investigation of Molecular Architectures of Porphyrinoids on a Ag (111) Surface
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The functionalization of surfaces at the nanoscale is a captivating and challenging area of science, essential for developing catalysts, sensors, and solar energy devices. This process hinges on the interaction between an active solid surface and another phase, whether liquid or gas. For instance, planar transition metal complexes adsorbed on solid supports show promise as novel heterogeneous catalysts. A key advantage of these catalysts over supported metal clusters is the well-defined and uniform nature of their active sites, specifically the coordinated metal centers with vacant axial coordination sites. Metalloporphyrinoids are particularly effective in this context, as they feature a rigid molecular frame that promotes long-range order and an active site with a coordinated metal ion. Their planar coordination leaves two axial sites available for additional ligands. When adsorbed on a surface, one axial site is occupied by the substrate, allowing for tailored electronic interactions that modify the metal center's reactivity. The other site remains available for molecule attachment (sensor functionality) or acts as a reaction center (single-site catalysis). Such structures are prevalent in nature, with metallo-tetrapyrrols playing crucial roles in biological processes, exemplified by iron porphyrins in heme, magnesium porphyrins in chlorophyll, and cobalt corrin in vitamin B12.
