One-pot synthesis of highly fluorescent polycyclic benzimidazole derivatives

An efficient one pot synthesis of polycyclic benzimidazole derivatives has been developed (up to 90% yield). The protocol is very mild, metal-free, and not restricted to anhydrous conditions. It also demonstrates an example of preferential electrocyclic reaction over Michael reaction. These new benzimidazole derivatives are highly fluorescent and show a dramatic change with pH; The characteristic bright bluish fluorescence was observed in MeOH (UV-light, 366 nm) but the intensity was totally diminished at pH = 2.5.