Preparation, AIE and ESIPT behaviour, controllable solid-state fluorescence and application of Co 2+ probe based on α -cyanostilbene.

A simple α -cyanostilbene-functioned salicylaldehyde-based Schiff-base probe, which exhibited outstanding 'aggregation-induced emission and excited state intramolecular proton transfer (AIE + ESIPT)' emission in solution, aggregation and solid states, was synthesized in high yield of 87%. Its solid-states with different morphologies emitted different fluorescence after crystallization in EtOH/H 2 O (1/2, v/v) mixtures or pure EtOH solvent. Besides, it exhibited an obvious spectro-photometrical fluorescence quenching for highly selective sensing of Co 2+ in THF/water system (ƒ w = 60%, pH = 7.4), accompanied by an intense green fluorescence turn-off behavior under UV 365nm illumination. The binding stochiometry between the ligand and Co 2+ was found to be 2:1, and the detection limit (DL) was calculated to be 0.41 × 10 -8 M. In addition, it could be applied to detect Co 2+ in real water samples and on silica gel testing strip.