Aromaticity-Driven Regioselective Cyclodehydrogenations in Azahelicenes with High-Performance Circularly Polarized Luminescence

While increasing helical length n has been proven-theoretically and experimentally-to amplify circularly polarized luminescence (CPL) performance of [n]helicene derivatives, the highly efficient synthetic approaches and the corresponding reaction mechanism investigation remain limited. In this work, the helical lengths of azahelicenes Aza[n] have been successfully extended from Aza[7] to Aza[9] and Aza[11] via a facile two-step approach by different arylamine precursors. The reaction is proposed to proceed via C-N bond-forming cyclization from a cationic intermediate generated by an in situ-formed hypervalent iodine species, thereby favoring α-selectivity to retain aromaticity. All the helical structures are ambiguously confirmed by single-crystal Xray diffraction. Comprehensive photophysical studies and density functional theory calculations reveal that Aza[11] exhibits outstanding chiroptical properties, achieving high absorption dissymmetry factors (|gabs|max = 3.2×10-2) and luminescence dissymmetry factors (|glum|max = 3.0×10-2) ranking among the highest values reported for organic CPL emitters.