The photochemical behavior of benzo[a]pyrido[2′,1′:2,3]imidazo[4,5-c]phenazine dyes

• Behavior of benzo[a]pyrido[2′,1′:2,3]imidazo[4,5-c]phenazine dyes were examined.
• Bleaching experiments with onium salts in cyclohexene oxide were measured.
• The quantum yields of dye bleaching under different conditions were calculated.
• Photobleaching mechanism of photoredox pairs was proposed.

The photochemical behavior of benzo[a]pyrido[2′,1′:2,3]imidazo[4,5-c]phenazine dyes was studied in the presence of diphenyliodonium and triarylsulfonium salts that are used in photoredox systems for light-induced cationic polymerization. The fluorescence quenching of these dyes were examined in the presence of the onium salts. Photolysis of the dyes was measured in the presence of onium salts in cyclohexene oxide. The quantum yields of dye bleaching under aerobic and anaerobic conditions were calculated. A mechanism was proposed for this process based on density functional theory calculations and spectroscopic characterization of both the radical cation of benzo[a]pyrido[2′,1′:2,3]imidazo[4,5-c]phenazine dyes and the cation formed after hydrogen abstraction by the radical cation.