Modular assembly of high-potential zinc porphyrin photosensitizers attached to TiO₂ with a series of anchoring groups

Efforts to improve the ease of assembly and robustness of photoanodes for light-driven water oxidation have led to the development of a modular assembly method for anchoring high-potential zinc porphyrins to TiO₂ via coordination to surface-bound pyridine linkers. It is essential that the anchoring groups provide strong electronic coupling between the molecular dye and metal oxide surface for optimal electron injection and that they are robust under the operating conditions of the system. Here, four linker molecules functionalized with either carboxylate, phosphonate, acetylacetonate, or hydroxamate anchoring groups are compared for their relative water stability on TiO₂. We also report the relative electron injection efficiencies, as measured by terahertz spectroscopy, for high-potential zinc porphyrins coordinated to TiO₂ via pyridyl linkers with the series of anchoring groups.