Janus-type photo-redox properties and catalytic applications of 5,10-dihydrophenazine derivatives

Inspired by the synthetic potential of organic photoredox catalysts, we synthesised and characterised a series of 5,10-dihydrophenazine derivatives that bear heterocycles as electron-withdrawing groups. Upon exploring their photocatalytic behaviour, we discovered that these compounds exhibit Janus-type reactivity, enabling both oxidative C(sp3)–H cyanation and reductive aryl halide cleavage. We investigated their photophysical and electrochemical properties through cyclic voltammetry (CV), transient absorption spectroscopy (TA) and UV-Vis spectroelectrochemistry (SEC). Time-resolved UV-Vis spectroscopy and electron paramagnetic resonance (EPR) provided valuable information on excited-state dynamics and radical cation formation. This revealed that the catalysts act as effective reductants for C(sp2)–I bond cleavage, generating aryl radicals. Furthermore, the excited-state radical cation facilitates the oxidative C(sp3)–H cyanation of tertiary amines. Our mechanistic studies confirm the dual redox nature of these catalysts, thereby expanding the utility of 5,10-dihydrophenazine derivatives in photoredox catalysis.