Unprecedented intramolecular cyclization of pyridinium to pyrido[1,2-a]benzimidazole: a novel chemodosimeter for fluoride ions

Pyridinium 1a underwent an efficient intramolecular cyclization initiated by fluoride ion to form highly fluorescent 1,3,4-triphenylpyrido[1,2-a]benzimidazole, providing a novel chemodosimeter for fluoride ion detection.