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Redox flow batteries (RFBs) have emerged as significant energy storage systems amid the growing adoption of renewable energy. However, the advancement of all-organic RFBs is hindered by material crossover, limited energy density, and the time-consuming selection of suitable electrolyte partners. To address these challenges, bipolar redox-active organic molecules (BRMs) show promise for charge storage in symmetric organic redox flow batteries (SORFBs), although their development can be complex and tedious. In this study, we report an approach aimed at streamlining the identification of suitable compounds through an examination of the organophotocatalyst literature, illustrated through six acridinium compounds exhibiting stable redox states. These compounds were thoroughly characterized in electrochemical cells and subjected to cycling tests in fully symmetric flow batteries. Notably, a trisubstituted electron-rich acridinium compound emerged as a potential candidate, demonstrating over 20 days of cycling stability. Given the extensive library of organic catalysts and the advantages of SORFB designs, this approach will prove to be essential for developing an innovative electrochemical storage system. 

Chromoselective bond activation has been achieved in organic helicenium (nPr-DMQA+)-based photoredox catalysis. Consequently, control over chromoselective C(sp2)–X bond activation in multihalogenated aromatics has been demonstrated. nPr-DMQA+ can only initiate the halogen atom transfer (XAT) pathway under red light irradiation to activate low-energy-accessible C(sp2)–I bonds. In contrast, blue light irradiation initiates consecutive photoinduced electron transfer (conPET) to activate more challenging C(sp2)–Br bonds. Comparative reaction outcomes have been demonstrated in the α-arylation of cyclic ketones with red and blue lights. Furthermore, red-light-mediated selective C(sp2)–I bonds have been activated in iodobromoarenes to keep the bromo functional handle untouched. Finally, the strength of the chromoselective catalysis has been highlighted with two-fold functionalization using both photo-to-transition metal and photo-to-photocatalyzed transformations. 

Abstract The development of tunable organic photoredox catalysts remains important in the field of photoredox catalysis. A highly modular and tunable family of trianguleniums (azadioxatriangulenium, diazaoxatriangulenium, and triazatriangulenium), and the related [4]helicene quinacridinium have been used as organic photoredox catalysts for photoreductions and photooxidations under visible light irradiation (λ = 518–640 nm). A highlight of this family of photoredox catalysts is their readily tunable redox properties, leading to different reactivities. We report their use as photocatalysts for the aerobic oxidative hydroxylation of arylboronic acids and the aerobic cross-dehydrogenative coupling reaction of N-phenyl-1,2,3,5-tetrahydroisoquinoline with nitromethane through reductive quenching. Furthermore, their potential as photoreduction catalysts has been demonstrated through the catalysis of an intermolecular atom-transfer radical addition via oxidative quenching. These transformations serve as benchmarks to highlight that the easily synthesized trianguleniums, congeners of the acridiniums, are versatile organic photoredox catalysts with applications in both photooxidations and photoreductions.