PDI-functionalised glass beads: efficient, metal-free heterogeneous photocatalysts suitable for flow photochemistry

Perylene diimides (PDI) have an extraordinary ability to activate both energy and electron transfer process upon light excitation, however, their extremely low solubility has hindered their wide use as photocatalysts. Here, we show a series of supports developed to anchor PDI and to enable its use as a heterogeneous photocatalyst in diverse reactor set-ups. Inert, easy-to-handle, glass microspheres of various morphological and chemical properties were chemically functionalised with PDI to form an inorganic-organic hybrid material. Using the photo-oxidation of n-butyl sulfide as a benchmark reaction for the synthesis of sulfoxides, we show that immobilised PDI are highly active, outperforming reported homogeneous photosensitisers, and capable of reuse in both batch and flow reactors. Transferring the process from batch to flow resulted in a 10-fold reduction in irradiation time and an increase in the space-time-yield by a factor of 10 (0.04 vs 0.38 mmol-1 h-1 mL-1 batch vs flow). This work combines the remarkable photocatalytic properties of PDI with inert, easy to handle glass beads, producing hybrid materials that are reusable and can be adapted for performing heterogeneous photocatalysis in a range of scalable photochemical reactors.