A cationic squaraine-based chemosensor SQM was synthesized and its sensing behaviors towards nucleophiles followed by CO₂ gas were described in detail by interpreting the results from UV-Vis, ESI-MS, and ¹H NMR spectral analysis. The results indicated that there were two different paths for the bleaching of SQM, depending on whether water existed or not when the nucleophilic addition reaction between SQM and a superbase, such as TBD or DBU, occurred. More interestingly, the bleached SQM in MeCN–H₂O (v/v = 90 : 10) could be colorimetrically restored with bubbling CO₂ gas, which enabled it to act as a highly sensitive “naked-eye” CO₂ gas detector in an aqueous medium. However, when treated in the same way, the SQM bleached in MeCN remained unchanged, unexpectedly. Combining theoretical analysis and experimental tests, a plausible sensing mechanism was proposed to illustrate the bleaching of SQM and the response of the bleached SQM to CO₂ gas in an aqueous medium.

中文翻译：

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基于方酸的传感器，通过意想不到的识别机制对水介质中的CO ₂气体进行比色检测：实验和DFT计算†

合成了基于阳离子方酸的化​​学传感器SQM，并通过解释UV-Vis，ESI-MS和¹ H NMR光谱分析的结果，详细描述了其对亲核试剂和CO ₂气体的传感行为。结果表明，取决于SQM与超碱（如TBD或DBU）之间发生亲核加成反应时，是否存在水，有两种不同的SQM漂白途径。更有趣的是，MeCN–H ₂ O（v / v = 90：10）中漂白的SQM可以通过鼓泡的CO ₂气体进行比色还原，从而使其可以用作高度敏感的“裸眼” CO₂在含水介质中的气体检测仪。但是，以同样的方式处理后，MeCN中漂白的SQM意外地保持不变。结合理论分析和实验测试，提出了一种合理的感测机制来说明SQM的漂白以及在水介质中漂白的SQM对CO ₂气体的响应。