Direct Quantum Yield Measurement of a Ligand-to-Metal Charge Transfer Photocatalyst via Cyclic Voltammetry

Measurements of molecular quantum yields are crucial for understanding and directing photocatalytic activation of inert substrates. However, present methods to study photocatalysts are limited by high costs, disparate measurement and photocatalytic reaction time scales, or poor luminescent behavior. Electroanalytical methods such as cyclic voltammetry (CV) are a promising orthogonal measurement to address these limitations. Here, CV was used to directly measure the molecular quantum yield of a model iron chloride ligand-to-metal charge transfer (LMCT) photocatalyst. Cyclic voltammograms of the LMCT photocatalyst exhibited catalytic currents that were dependent on light intensity. Correlation between light intensity and catalytic current was used to derive a light-dependent plateau equation which enables the direct measurement of quantum yield from CV. Finite element simulations further supported the quantum yield measurements. Control experiments and simulations incorporating photothermal convection indicated minimal thermal interference on the measured quantum yield. We used our quantum yield measurement to extract quantitative information about the follow up C-H activation step via the transient chlorine radical. Overall, these measurements establish cyclic voltammetry as a quantitative method for determining photocatalytic quantum yields. This work enables a rapid, simple, and orthogonal approach to study molecular photocatalysts.