Sustainable photocatalytic C-H annulation of heteroarenes with sulfoxonium ylides: synthesis and photophysical properties of fused imidazo[1,2-a]pyridine-based molecules

A sustainable visible light-mediated synthetic protocol for the construction of color-tunable fluorescent 6-aryl-derived naphthoimidazo[1,2-a]pyridine- and anthraimidazo[1,2-a]pyridine-based molecules has been achieved via ruthenium-catalyzed sequential multiple C-H activation/annulation between heteroarenes and sulfoxonium ylides. This annulation strategy provides easy access to obtain a library of fused heterocyclic frameworks with significant yields and atom economy. In furthering this protocol to discover new small N-fused heterocyclic fluorophores, we also demonstrate a systematic investigation using a practical and computational analysis of photophysical properties. A conceptual trend is deep-rooted across a series of naphthyl and anthracene fused imidazo[1,2-a]pyridines based on the predicted emission wavelengths and theoretical concepts. Towards the end, we demonstrate an effective method to understand and synthesize color-tunable fluorophores under mild reaction conditions with a broad substrate scope.