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

A cobalt(III)-catalyzed dual C(sp²)-H/C(sp²)-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 ⁱPr-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.