presents an alternative avenue for functionalization, as depicted in Figure . The recent advancement in photochemical LSF of Dha-enriched peptides has facilitated targeted and chemoselective processes such as alkylation, fluoroalkylation, acylation, and to a more limited degree, arylation. Prior arylation approaches typically demanded aryl bromides as coupling agents, necessitating complex and laborious de novo synthesis to produce a variety of functionalized partners. However, recent studies by the groups of Ritter, Procter, and Alcarazo has highlighted the utility of arylsulfonium salts. These salts enable straightforward preparation routes leading to intricate aryl electrophiles, which are instrumental for both transition metal-catalyzed cross-coupling chemistry and photochemical applications. Building on this, vinyl-sulfonium salts have recently been employed for various polar transformations. Therefore, we were intrigued by the prospect of developing a photocatalytic LSF approach for Dha-containing peptides using the highly versatile and modular arylthianthrenium salts, as illustrated in Figure . This transformation was accomplished by the single electron transfer (SET) reduction of these salts, which generates an exceptionally reactive aryl radical. This radical readily adds to the α,β-unsaturated moiety within the Dha backbone. To guarantee gentle reaction conditions and minimize reaction times-key factors for ensuring broad functional group compatibility and scalability-we also devised a continuous-flow protocol. Notably, our method facilitates the efficient ligation of peptides and their conjugation with various drug scaffolds.