Photocatalysts heterogenization on silica nanoparticles for the photosensitization of oxygen and photoredox applications

Abstract

Within the last decades, solar energy has attracted much attention as the supply of clean, secure, and sustainable energy and chemicals which is of paramount importance for the future. Chemists therefore try to use light activation to conduct organic transformations through photocatalysis. Ruthenium and iridium polypyridyl complexes dominate this field but their use is limited due to their price, scarcity, and strong ecological impact. Organic dyes and copper complexes have been investigated to replace them, but their low photostability still hamper their implementation. In this context, the strategy of homogeneous silica-supported photocatalysis triggered our attention to design more efficient, photostable, and recyclable photoactive systems. Firstly, we investigated the impact of the morphology of silica nanoparticles onto the photocatalytic generation of singlet oxygen by Rose Bengal that was non-covalently bound to the solids surface. We identified that a Core-shell nanostructure was the best to employ in terms of photophysical properties, activity and recycling of the surface-bound molecules. Next, we designed a covalent anchoring strategy between a benzophenazine and the silica surface, which requires the derivatization of the considered photocatalyst. To determine the best way to anchor it without perturbing its photophysical properties and photoactivity in singlet oxygen generation, we established a structure-activity relationship to identify the best route for immobilization and successfully devised photoactive grafted organic dyes. Finally, heteroleptic and homoleptic copper(I) complexes were anchored onto silica to increase their photostability by limiting their ligand exchange likelihoods. Grafted homoleptic complexes were competent for excited-state electron transfers to diazonium derivatives which generated the corresponding Cu(II) analogue that persisted on the millisecond timescale. Such long-lived analog is promising for photoredox applications. (SC - Sciences) -- UCL, 2023