Synthesis of epiminocyclohepta[b]pyrazolo[4,3-e]pyridines from tropinone: Fluorescent “Turn on–off” chemosensors for the sequential detection of Al3+, Cd2+ and Pb2+ in nanomolar concentration

Abstract

The syntheses of hitherto unreported epiminocyclohepta[b]pyrazolo[4,3-e]pyridines have been achieved through a microwave-assisted two-component domino strategy. These bicyclic heterocycles exhibited weak fluorescence under UV in 1:1 dioxane:water mixture. From the metal interference studies it has been observed that addition of Al3+ selectively induced a four-fold increase in the fluorescence intensity of these compounds through chelation-enhanced fluorescence. The regenerative nature of these probes has been evidenced by the successive addition of EDTA and Al3+. Further it has been demonstrated that upon sequential addition of Al3+ followed by either Cd2+ or Pb2+ led to fluorescence “turn on-off” of the epiminocyclohepta[b]pyrazolo[4,3-e]pyridine probes.