The Dependence of Chemical Quantum Yields of Visible Light Photoredox Catalysis on the Irradiation Power

Despite the great achievements of advanced photoredox catalysis for organic-synthetic reactions, the literature is rather vague with respect to reaction quantum yields – the number of product molecules per absorbed photon. This stands in contrast to the clear and commonly used chemical yield as standard parameter to quantify the efficiency of chemical reactions. We applied an opto-electronic device to measure the reaction quantum yields of a reference reaction in a rapid and facile way, which revealed that this parameter cannot be regarded as a single, isolated value. A so far undescribed strong dependence of the reaction quantum yield on the incident light power and the irradiation time was revealed. The light input even decides on the interplay of the closed photoredox catalytic cycle and the radical chain propagation. The reaction kinetics were modelled in full detail to obtain important insight into the general description of photoredox catalytic mechanisms.