Designing one-dimensional covalent organic frameworks: novel post-synthetic modification on hydroxyl groups and ratiometric detection of chemical warfare agent mimics

Abstract

Sulfur mustard (SM) and tabun, being chemical warfare agents, persistently pose a serious threat to the safety of the public. Their high toxicity makes it essential to develop fluorescent sensors to detect them. Herein, a one-dimensional covalent organic framework (1D COF, termed ETTADFP–OH) with red fluorescence was synthesized from tetrakis(4-aminophenyl)ethene (ETTA) and 2,6-diformylphenol (DFP) for the first time. Additionally, a novel covalent post-synthetic modification (PSM) was developed to introduce carboxyl groups, which can coordinate with Tb³⁺, resulting in a dual-emission hybrid material (Tb@ETTADFP–COOH). It is worth noting that 2-chloroethyl ethyl sulfide (2-CEES) and diethyl cyanophosphonate (DCNP), mimics of SM and tabun, can be specifically detected in different responsive modes. Mechanism experiments show that the variation in fluorescence may be caused by the occurrence of nucleophilic reactions and the process of energy transfer, which rarely take place in the fluorescence detection of porous materials. A wearable gas sensor for naked-eye monitoring and warning of 2-CEES was prepared. In summary, this work not only provides a unique esterification strategy of hydroxyl-containing COFs but also offers a potential approach for the detection of SM and tabun.