Facile approach to benzo[d]imidazole-pyrrolo[1,2-a]pyrazine hybrid structures through double cyclodehydration and aromatization and their unique optical properties with blue emission

A modular approach to polycyclic N-fused heteroaromatics is described. Acid-catalyzed reactions of various 1-(2-oxo-2-arylethyl)-1H-pyrrole-2-carbaldehydes with several o-phenylenediamines provided facile access to a number of new benzo[d]imidazole-pyrrolo[1,2-a]pyrazine hybrid structures through double cyclodehydration and aromatization. Optical characterization of the synthesized compounds revealed unique emission properties, with deep blue emission in the aggregated and solid states, and a dramatic substituent effect was observed. Fusion of an additional benzene ring into the benzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazine scaffold resulted in a remarkable increase in the intensity of blue fluorescence from the solution along with good cell permeability and negligible phototoxicity, indicating the potential for bioimaging applications.