Eosin Y Catalyzed Photochemical Synthesis of Arylated\nPhenothiazones

In the presence of\nEosin Y (<b>EY</b>), the synthesis of\nsubstituted phenothiazones was carried out efficiently using various\nsubstituted 2-aminothiophenol, diazonium salts, and 1,4-napthaquinones\n(<b>1,4-NQ</b>) at room temperature (RT) (condition: green LED\nof 525 nm, 44 W; reaction time: 8 h, isolated yield: 68–90%).\nA fluorescence quenching experiment and density functional theory\n(DFT) calculations suggested that the triplet photoexcited state of\nEY (EY*; τT = 320 ± 10 ns) converts to EY<sup>+•</sup> via oxidative quenching by ArN<sub>2</sub><sup>+</sup> (−1.11\nV vs SCE for EY* to EY<sup>+•</sup>) initially. Thiyl and aryl\nradicals were captured as TEMPO adducts in high-resolution mass spectroscopy\n(HRMS). The reaction was not inhibited by the addition of a singlet\noxygen quencher such as 1,4-diazobicyclo [2.2.2] octane (DABCO), which\nsuggests that singlet oxygen is not participated.