Visible Light Generation of a Microsecond Long-Lived Potent Reducing Agent

Photoexcitation of molecular radicals can produce strong reducing agents; however, the limited lifetimes of the doublet excited states preclude many applications. Herein, we propose and demonstrate a general strategy to translate a highly energetic electron from a doublet excited state to a ZrO₂ insulator, thereby increasing the lifetime by about 6 orders of magnitude while maintaining a reducing potential less than -2.4 V vs SCE. Specifically, red light excitation of a salicylic acid modified perylene diimide radical anion PDI^•- anchored to a ZrO₂ insulator yields a ZrO₂(e^-)|PDI charge separated state with an ∼10 μs lifetime in 23% yield. The ZrO₂(e^-)s were shown to drive CO₂ → CO reduction with a Re catalyst present in micromolar concentrations. More broadly, this strategy provides new opportunities to reduce important reagents and catalysts at low concentrations through diffusional electron transfer.