A facile strategy to determine photon flux and effective optical path length in intensified continuous-flow photoreactors

Photocatalysis for small molecule activation has seen significant advancements over the past decade, yet its scale-up remains a challenge due to photon attenuation effects. A promising solution lies in harnessing high photonic intensities paired with continuous-flow reactor technology. However, a deep grasp of photon transport is essential, typically demanding resource-intensive experiments. To address this, we introduce an innovative approach to photochemical reactor setup characterization, starting with radiometric light source analysis and progressing to a 3D reactor simulation for photon flux determination. Contrary to conventional techniques that prioritize complete photon absorption, our technique operates optimally when the reaction mixture is unsaturated. This strategy decouples photon flux and path length determination, substantially curtailing the experimental process. The workflow proves versatile across various reactor systems, simplifying intricate light interactions into a single one-dimensional parameter, i.e., the effective optical path length. Combined with the photon flux, this parameter effectively characterizes photochemical setups, irrespective of scale, geometry, light intensity, or photocatalyst concentration. Employing radiometry further offers insights into light source positioning and reactor design, and obviates the need for repeated chemical actinometry measurements due to light source degradation. Additionally, the proposed workflow facilitates experiments at lower concentrations, ensuring optimal reactor operation. In essence, our approach provides a thorough, efficient, and consistent framework for reactor irradiation characterization.