Direct Quantum Yield Measurement of Non-luminescent Photocatalysts via Cyclic Voltammetry

Electro-photocatalysis (e-PC), the co-localization of photons and electrons on a single reaction center, has emerged as powerful methodology for activating inert bonds. A merger between the fields of molecular electrocatalysis and photoredox catalysis, e-PC methods enable deeply reducing and oxidizing reactions via the generation of highly reactive intermediates. Yet, directing the selectivity of these intermediates remains a challenge due to our poor mechanistic understanding at longer timescales. At present, ultrafast spectroscopy represents the best strategy for understanding excited state dynamics, yet the difference in timescale (pico- to nanosecond) from synthetic experiments (hours to days) makes a truly quantitative mechanistic relationship difficult. Electroanalytical methods, such as cyclic voltammetry (CV), could provide a much-needed connection between these two timescales (and at a fraction of the experimental cost). However, a well-defined molecular picture of CV responses under illumination has yet to arise, and the utility of these experiments remain uncertain.

Here, we provide a straightforward and quantitative interpretation of molecular electro-photocatalysis that yields experimentally useful parameters, such as quantum yield and catalytic rates, directly from CV experiments. With a well-behaved experimental model system and mechanistic support from finite element simulations, we provide a detailed picture on physical concerns and the constraints of light-dependent voltammetry. These efforts represent a significant step towards a molecular understanding of photocatalysis at longer timescales and pave the way towards electrocatalytic control of deeply reducing/oxidizing reactions.