Ratiometric detection of pH is always significant in environmental regulation, medical diagnosis, synthetic chemistry, and beyond. The construction of practical ratiometric pH sensors with reusability is still challenging. Herein, by exploiting a multivariate strategy, we first synthesized and reported a series of novel three-component covalent organic frameworks (COF-COOH_X, X = 33, 50, and 67) through Schiff base reaction between 2-hydroxybenzene-1,3,5-tricarbaldehyde (HTA), 4,4′-diamino-3,3′-biphenyldicarboxylic acid (DBA), and 5,5′-diamino-2,2′-bipyridine (BPY) at various molar ratios (X = [DBA]/([BPY] + [DBA]) × 100 = 33, 50, and 67). COF-COOH_X (X = 33, 50, and 67) displayed ratiometric pH sensing performance in acidic conditions with selectivity and repeatability. By tuning the molar ratio of DBA and BPY, the fluorescent properties, linear pH responsive ranges, and pK_a values of COF-COOH_X (X = 33, 50, and 67) can be regulated. Meanwhile, the two-component COF-COOH₀ and COF-COOH₁₀₀ did not exhibit ratiometric pH detection ability. Moreover, the constructed three ratiometric sensors can be applied to detect pH in drug solutions and carbonated drinks with satisfactory results. This work sheds new light on the design and fabrication of innovative ratiometric fluorescent sensors using COFs.

中文翻译：

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基于可调多元共价有机框架的比率荧光 pH 传感器

pH 的比率检测在环境监管、医学诊断、合成化学等领域始终具有重要意义。具有可重复使用性的实用比例 pH 传感器的构建仍然具有挑战性。在此，通过利用多元策略，我们首先通过 2-羟基苯-1,3 之间的席夫碱反应合成并报道了一系列新型三组分共价有机骨架（COF-COOH _X，X = 33、50 和 67）。 ,5-三甲醛 (HTA)、4,4'-二氨基-3,3'-联苯二甲酸 (DBA) 和 5,5'-二氨基-2,2'-联吡啶 (BPY) 以各种摩尔比 ( X = [DBA]/([BPY] + [DBA]) × 100 = 33、50 和 67)。COF-COOH _X ( X= 33、50 和 67）在酸性条件下显示出比率式 pH 传感性能，具有选择性和可重复性。_{通过调节 DBA 和 BPY 的摩尔比，可以调节 COF-COOH X}（X = 33、50 和 67）的荧光特性、线性 pH 响应范围和 p K _a值。同时，双组分COF-COOH ₀和COF-COOH ₁₀₀没有表现出比例pH检测能力。此外，构建的三个比率传感器可用于检测药物溶液和碳酸饮料的pH值，结果令人满意。这项工作为使用 COF 设计和制造创新的比率荧光传感器提供了新的思路。