Thiazole‐2‐Carbaldehyde‐Based Covalent Organic Frameworks

Abstract We first synthesize a novel aldehyde‐substituted benzo[1,2‐d:4,5‐d']bis(thiazole) monomer (BBTC) via a facile method with a high yield, and the BBTC is used for the first time as a building block for synthesis of imine‐linked COFs. By using linkage transformation strategy, we further synthesize an imidazole N‐heterocyclic carbene precursor COF (BBTC‐INP COF) and the imidazole‐2‐thione COF (BBTC‐IT COF). Interestingly, the BBTC‐INP and BBTC‐IT COFs exhibit 2620‐ and 1810‐fold enhancements in photoluminescence quantum yields, respectively, compared to the parent BBTC COF. This linkage transformation not only optimizes the optical performance but also enables effective Hg 2 ⁺ detection through the strategic incorporation of thione (C═S) groups as specific binding sites. In particular, the BBTC‐IT COF presents outstanding selectivity and sensitivity for toxic Hg 2 ⁺ detection, and the limit of detection reaches 60 nM, highlighting the advantage of as‐synthesized BBTC‐IT COFs in fluorescence sensing applications. In short, this work reports a series of novel thiazole‐2‐carbaldehyde‐based COFs, which largely enriches the diversity of COFs and would also stimulate the synthesis of more BBTC‐based COFs for different applications.