A mild visible‐light‐mediated strategy for cysteine arylation is presented. The method relies on the use of eosin Y as a metal‐free photocatalyst and aryldiazonium salts as arylating agents. The reaction can be significantly accelerated in a microflow reactor, whilst allowing the in situ formation of the required diazonium salts. The batch and flow protocol described herein can be applied to obtain a broad series of arylated cysteine derivatives and arylated cysteine‐containing dipeptides. Moreover, the method was applied to the chemoselective arylation of a model peptide in biocompatible reaction conditions (room temperature, phosphate‐buffered saline (PBS) buffer) within a short reaction time.

Recently, new opportunities have emerged for the synthesis of functional polymers and materials by light-induced controlled radical polymerization techniques. Light-induced polymerization reactions implemented in batch reactors require chromophores as initiators or activators, and with increasing optical pathlength light is successively absorbed, lowering the overall efficiency of the reactions. This typically leads to long reaction times, making the process both inconvenient and costly to upscale. Implementing a continuous flow reactor is hereby advantageous. In here, we describe the visible light induced polymerization of several methacrylates via trithiocarbonate photoiniferter polymerization. In all cases, the method affords polymers with comparatively narrow molecular weight distribution (Đ = 1.20–1.30) even for moderate molar mass values above 10 kg mol⁻¹, whereby full monomer conversions are reached already after 60 min for a variety of monomers. Several diblock and triblock copolymers were synthesized, demonstrating the versatility and good control of the technique. Further, the intensified synthesis of block copolymers is shown by coupling two photoflow reactors into a single continuous process, allowing for block copolymer synthesis without intermediate purification or sample collection.