A bis-pyrene chalcone based fluorescent material for ratiometric sensing of hydrazine: An acid/base molecular switch and solid-state emitter

In this work, we have designed and synthesized a new fluorescent molecular probe, DPY comprising of pyrene-diacetylpyridine conjugate, which was found to be sensitive to hydrazine as well as protonation. DPY is characterised by a strong emission both in solution (lambda(em) = 530 nm) as well as in solid state (lambda(em) = 610 nm), attributed to intramolecular charge-transfer. The probe responds to hydrazine with a ratiometric fluorescence emission change from yellow to blue, due to chalcone cyclisation reaction of a, b-unsaturated carbonyl group resulting in the pyrazoline compound, DPY-Hy, imparting a strong greenish-blue emission in solution. Further, the strong fluorescence emission of DPY in powder and thin film was quenched upon exposure to TFA, and revived upon exposure to TEA. For developing on-site detection protocol, when DPY was drop-casted on nonfluorescent silica plate a vivid naked-eye colour change from orange-red to dark blue was realized. Interestingly, in the aggregated state, DPY exhibited a broad range emission from green to orange in a mixed solvent system of THF:H2O. A plausible explanation of the photophysical events is substantiated with theoretical calculations. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

A new fluorescent molecular probe, DPY, sensitive to hydrazine and protonation, exhibits ratiometric fluorescent emission changes and different fluorescence properties in various environments. This probe shows strong emission in solution and solid state due to intramolecular charge-transfer, and its fluorescence can be quenched or revived with exposure to different chemicals.