Reversible ratiometric silver ion and pH probe constructed from a quinoline-containing diphenylsulfone derivative with AIEE effect

A novel organic fluorophore, di-4-(2-quinolinylhydrazinyl)diphenyl sulfone (QDPS), was designed and synthesized by hydrazino bridging of quinoline and diphenylsulfone. The fluorophore emits weak blue fluorescence in pure THF and becomes a strong emitter in aggregated state, signifying the aggregation-induced emission enhancement (AIEE) effect. It can selectively bind Ag-ion on an extremely low concentration (LOD = 2.0 × 10⁻⁷ mol/L) with 1:2 binding mode and a binding constant of 1.58 × 10¹⁰ (mol/L)⁻² in the mixture solution of THF/water (V/V = 1/9) as the reversible ratiometric UV and fluorescence chemosensors. After protonation by adding acids, QDPS has an unexpected tunable AIEE effect from blue in pure DMF to green in the aggregated state. Additionally, its emission can be reversibly switched between blue and green by reiterant deprotonation and protonation. This unique ability enables QDPS as a novel reversible ratiometric pH probe, as well as a colorimetric sensor for detecting acidic and basic organic vapors.