The synthesis, characterization and optical properties of novel pyrido[1,2-a]benzimidazole derivatives

A series of novel, substituted, pyrido[1,2-a]benzimidazole derivatives were synthesized using a novel tandem annulation reaction between 2-acylbenzimidazole derivatives and 4-bromobut-2-enoic esters under mild conditions. The compounds were characterized using IR, 1H NMR, 13C NMR and HRMS; the crystal structure of 2,7,8-trimethyl-3-ethoxycarbonyl-4-phenylpyrido[1,2-a]benzimidazole was determined as orthorhombic. The absorbance and fluorescence spectra of the pyrido[1,2-a]benzimidazoles were measured in dichloromethane; an intense absorption maxima was observed at 250 nm and emission maxima were noted at 460 nm. The absorption spectra and fluorescence characteristics of the pyrido[1,2-a]benzimidazole derivatives revealed that a phenyl and a methyl group attached to the pyrido[1,2-a]benzimidazole ring markedly influenced maximum emission.