Substrate Preorganization Within Photoactive Pt ₁₂ L ₂₄ Nanospheres for Accelerated Decarboxylation Catalysis at Low Concentrations

Abstract 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 Pt 12 L 24 nanospheres as strategy to perform photoredox catalysis at low concentrations. We show that Pt 12 L 24 nanospheres are efficient photocatalysts for the decarboxylative oxygenation reaction. Nanospheres with endo‐functionalized guanidinium groups (Pt 12 LGua 24 ) preorganize the substrate, which increases the catalytic turnover frequency by two orders of magnitude. Crucially, this preorganization ensures that Pt 12 LGua 24 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.