When conducting a photooxidation reaction, the key question is what is the best amount of photocatalyst to be used in the reaction? This work demonstrates a fast and simple method to calculate a reliable concentration of the photocatalyst that will ensure an efficient reaction. The determination is based on shifting the calculation away from the concentration of the compound to be oxidized to utilizing the limitations on the total light dose that can be delivered to the catalyst. These limitations are defined by the photoflow setup, specifically the channel height and the emission peak of the light source. This method was tested and shown to work well for three catalysts with different absorption properties through using LEDs with emission maxima close to the absorption maximum of each catalyst.

The characterization of commercially available Corning ® Lab Photo Reactor by actinometry at different wavelengths (365, 385, 405 and 475 nm) using azobenzene E ↔ Z photoisomerization is reported. By comparison with photon fluxes determined externally using a radiometer, this method based on NMR spectroscopy is rapid, cheap, robust, reproducible and can applied to UVA-visible range, compared to previously described chemical actinometric protocols. Recalculation of isatin N 2 -phenylhydrazone isomerization quantum yield at 405 nm gave almost the same value as the literature data ( Φ = 0.0013) and confirmed the robustness and applicability of this methodology.