Fluorescence-enhancement sensing of ammonia and hydrazines via disruption of the internal hydrogen bond in a carbazolopyridinophane

A carbazolopyridinophane has been designed and prepared, with an internal NH⋯N hydrogen bond between the carbazole and pyridine rings. This hydrogen bond causes the fluorescence of the carbazole unit to be substantially quenched. In heptane solution, addition of ammonia or simple hydrazines disrupts the internal hydrogen bond and restores fluorescence, within 1–5 min. Signal intensity varies linearly with guest concentration; concentrations of ammonia or hydrazines down to 100 ppb have been measured.