Substrate Preorganization Within Photoactive Pt12L24 Nanospheres for Accelerated Decarboxylation Catalysis at Low Concentrations

Substrate preorganization is used to overcome the concentration and lifetime constraints of photoredox catalysis. Pt₁₂L₂₄ nanospheres equipped with guanidinium moieties (LGua) are able to preorganize carboxylic acids and act as photocatalysts for the decarboxylative oxygenation reaction. Substrate preorganization accelerates the photochemical rate by two orders of magnitude, which allows efficient photoredox catalysis at 2 µM concentrations.

Photoredox catalysis with short-excited state lifetimes or in dilute conditions is challenging because the photochemical mechanism relies on collisions within the excited state of the photocatalyst. In this work, we use supramolecular substrate preorganization within Pt₁₂L₂₄ nanospheres as strategy to perform photoredox catalysis at low concentrations. We show that Pt₁₂L₂₄ nanospheres are efficient photocatalysts for the decarboxylative oxygenation reaction. Nanospheres with endo-functionalized guanidinium groups (Pt₁₂LGua₂₄) preorganize the substrate, which increases the catalytic turnover frequency by two orders of magnitude. Crucially, this preorganization ensures that Pt₁₂LGua₂₄ retains its photocatalytic activity at extremely low concentrations (2 µM). This strategy thus overcomes the concentration limitations of photoredox catalysis and may be interesting for applications in dilute environments such as water purification and cellular photocatalysis.