As the mesityl group-substituted acridinium photocatalyst has an orthogonal structure, the π-systems are not conjugated, leading to the formation of a long-lived electron-transfer state depicted as Acr•-Mes•+ under photoirradiation conditions. Since this excited acridinium salt displayed a strong oxidizing ability (E*1/2=+2.06 V vs. SCE), single-electron oxidation of alkenes and arenes was accomplished. Applying this arene oxidation as key radical initiation protocol, direct C-H amination, cyanation, fluorination of electron-rich arenes and desulfurative [4+2] benzannulation were developed. Moreover, a single-electron reduced TICT state served as photoreductant in reductive dehalogenation of aryl halides and detosylation of N-tosylamines.
