Deciphering Co(III)‐Catalyzed Oxidative C−H/C−H Annulation Towards Maleimide‐Fused Imidazopyridine AEEgens

Abstract A cobalt(III)‐catalyzed dual C(sp 2 )−H/C(sp 2 )−H activation of 2‐arylimidazopyridines and its annulation with N ‐substituted maleimides leads to polycyclic aromatic heterocycles. This sustainable oxidative annulation uses earth‐abundant, less toxic, and cost‐effective cobalt(III) catalyst that complement expensive 2nd and 3rd‐row metals. This oxidative annulation features a broad substrate scope with very good functional group tolerance. These maleimide‐fused imidazopyridines display strong fluorescence in the region of 527− 536 nm with a Stokes shift of 83−87 nm and possess an excited state lifetime of 14.6−16.1 ns. Interestingly, such luminescent compounds show aggregation‐enhanced emission (AEE) behavior in the i Pr‐OH/hexane mixed solvent system. Furthermore, field emission scanning microscopy (FESEM) reveals their spherical nano‐aggregates with an average diameter of ~216.8 nm. They can also be used as cellular‐imaging and picric acid‐sensing probes.