Herein, we provide an up-to-date overview of metal oxide semiconductors (MOS) as versatile and inexpensive photocatalysts to enable light-driven organic transformations.

The sun is the most sustainable light source available on our planet, therefore the direct use of sunlight for photochemistry is extremely appealing. Demonstrated here, for the first time, is that a diverse set of photon‐driven transformations can be efficiently powered by solar irradiation with the use of solvent‐resistant and cheap luminescent solar concentrator based photomicroreactors. Blue, green, and red reactors can accommodate both homogeneous and multiphase reaction conditions, including photochemical oxidations, photocatalytic trifluoromethylation chemistry, and metallaphotoredox transformations, thus spanning applications over the entire visible‐light spectrum. To further illustrate the efficacy of these novel solar reactors, medicinally relevant molecules, such as ascaridole and an intermediate of artemisinin, were prepared as well.

The importance of discovering the true catalytically active species involved in photocatalytic systems allows for a better and more general understanding of photocatalytic processes, which eventually may help to improve their efficiency. Bi₂O₃ has been used as a heterogeneous photocatalyst and is able to catalyze several synthetically important visible-light-driven organic transformations. However, insight into the operative catalyst involved in the photocatalytic process is hitherto missing. Herein, we show through a combination of theoretical and experimental studies that the perceived heterogeneous photocatalysis with Bi₂O₃ in the presence of alkyl bromides involves a homogeneous Bi_nBr_m species, which is the true photocatalyst operative in the reaction. Hence, Bi₂O₃ can be regarded as a precatalyst which is slowly converted in an active homogeneous photocatalyst. This work can also be of importance to mechanistic studies involving other semiconductor-based photocatalytic processes.

The sun is the most sustainable light source available on our planet, therefore the direct use of sunlight for photochemistry is extremely appealing. Demonstrated here, for the first time, is that a diverse set of photon‐driven transformations can be efficiently powered by solar irradiation with the use of solvent‐resistant and cheap luminescent solar concentrator based photomicroreactors. Blue, green, and red reactors can accommodate both homogeneous and multiphase reaction conditions, including photochemical oxidations, photocatalytic trifluoromethylation chemistry, and metallaphotoredox transformations, thus spanning applications over the entire visible‐light spectrum. To further illustrate the efficacy of these novel solar reactors, medicinally relevant molecules, such as ascaridole and an intermediate of artemisinin, were prepared as well.

Metal oxide semiconductors are widely used in photocatalysis for the sustainable synthesis of fine chemicals and fuels. However, the mechanisms and the actual catalytically active species involved in these photocatalytic processes are not yet fully understood. Herein, we reveal that the addition of certain amines can effectively accelerate the photocatalytic atom transfer radical addition (ATRA) reaction by stabilizing a soluble Bi‐species formed through a reaction between Bi₂O₃ and diethyl bromomalonate using either N, N‐dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) as a solvent. Moreover, thermodynamic calculations revealed that N, N, N’, N’‐tetramethylethylenediamine (TMEDA), and DMF yield the most stable complexes [(κ²‐TMEDA)₂BiBr₃], ultimately accelerating the formation of the targeted ATRA product.