Substitution Effects on the Photophysical and Photoredox Properties of Tetraaza[7]helicenes

Helicenes combine an extended aromatic system with a pronounced helical structure. Hence, they show unique properties for photochemical and chiroptical applications. In this study, we synthesized a series of substituted derivatives of a tetraaza[7]helicenes and investigated the influence of the substitution pattern on their photophysical and photoredox-catalytic properties. The separated enantiomers show circularly polarized luminescence (CPL) that is among the brightest reported for [7]helicenes so far. We successfully used the helicenes as photocatalysts in sulfonylation/hetarylation reactions using cyanopyridines as substrates. DFT calculations predict that in the future more strongly oxidizing catalysts can be obtained by introducing electron withdrawing substituents.