A fluorescent hydrogen-bonded organic framework for highly selective sensing of mono-nitrophenol isomers in water

Hydrogen-bonded organic frameworks (HOFs) have great potential as sensing platforms for specific molecular recognition due to their designable structures, high solution processability, and easy regeneration. However, the exploration of fluorescent HOFs for chemical sensing in water remains a challenge due to the need to combine excellent photoluminescence performance, high water stability, and specific recognition sites simultaneously. Herein, we report an aggregation-induced emission (AIE) active HOF (termed HOF-TPE-CN) built from a cyano-decorated tetraphenylethylene linker for highly fluorescent sensing of mono-nitrophenol isomers. Owing to the effective AIE effect, HOF-TPE-CN shows a notable enhancement in fluorescence emission, wherein the quantum yield of HOF-TPE-CN was notably increased to 21% compared with that of the TPE-CN ligand in DMF solution (2.89%). Most importantly, this HOF exhibits highly efficient fluorescence quenching toward mono-nitrophenol isomers in water, with a remarkably low detection limit of 0.65 μM. Furthermore, HOF-TPE-CN is more responsive and selective toward mono-nitrophenols compared with a series of homologues. Theoretical calculations combined with X-ray photoelectron spectroscopy revealed that there exist multiple van der Waals and hydrogen-bonding interactions between the trapped nitrophenol molecules and the HOF framework, which form ground-state complexation, resulting in fluorescence quenching by efficient photo-induced electron transfer. We designed and realized a water-stable and AIE-active HOF (HOF-TPE-CN) with notably enhanced fluorescence emission for achieving highly sensitive and selective sensing of mono-nitrophenols in water.