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Structural regulation of alkynyl-based covalent organic frameworks for multi-stimulus fluorescence sensing
Xinrui Chen, Wenjian Huang, Xiaoyang Zhao, Songyao Zhang, Xinrui Miao*
https://doi.org/10.1016/j.cjsc.2025.100604
ABSTRACT
Stimuli-responsive two-dimensional (2D) covalent organic frameworks (COFs) with precise structures and permanent porosity have been employed as platforms for sensors. The slight change of the backbones inside the framework leads to different electronic states by external stimuli, such as solvent, pH, and water. Herein, we introduced an alkynyl-based building block (ETBA) with high planarity to synthesize two imine-based alkynyl-COFs (ETBA-TAPE-COF and ETBA-PYTA-COF) with high yield, good crystallinity, and chemical stability. Due to the presence of acetylene bonds, ETBA-TAPE-COF does not adopt the completely overlapping AA stacking mode. Slight interlayer displacement occurs along the parallel direction relative to the acetylene linkages, which facilitates lower configurational energy. Additionally, the introduction of pyrene group contributes to high π-electron mobility of ETBA-PYTA-COF. The interactions between electron-withdrawing group (ETBA) and electron-donating group (PYTA) during processes of protonation and intramolecular charge transfer (ICT) endow ETBA-PYTA-COF with excellent acidochromic and solvatochromic properties, respectively. Based on this, a fluorescence sensor is successfully established, which can be used for rapid response to trace amounts of water in organic solvents. In contrast, ETBA-TAPE-COF does not exhibit these photophysical properties due to its higher HOMO–LUMO gap compared to ETBA-PYTA-COF. This work proposes a new strategy for designing and preparing COFs with unique photophysical properties without introducing additional functional groups.
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