Benzoselenadiazole‐Based Photosensitizers: Effect of Substituent Position on the Electrochemical, Photophysical, and Photochemical Properties

ABSTRACT Selenium‐containing photosensitizers are attracting growing attention for optoelectronic and biomedical applications due to their distinctive redox and photophysical characteristics. Herein, we present a series of novel donor–acceptor benzoselenadiazole derivatives synthesized via Buchwald–Hartwig and Ullmann‐type cross‐coupling reactions. Fine‐tuning of the substitution pattern on the benzoselenadiazole core leads to distinct positive solvatochromism, reflecting strong intramolecular charge‐transfer character. Most of the synthesized compounds exhibited efficient singlet oxygen ( 1 O 2 ) generation, with generation quantum yield values (Φ Δ ) of up to 0.74. Their photocatalytic activity was further demonstrated through the visible light‐driven oxidation of 2‐furoic acid, achieving complete conversion within four hours at a catalyst loading of just 0.05 mol%. The results highlight the potential of benzoselenadiazole‐based chromophores as multifunctional materials for light‐driven applications in photocatalysis, and as promising scaffolds for the future design of photosensitizers.