具有碱性部分的高 CT 荧光团进入 D-A 链作为 pKa 探针,The Journal of Organic Chemistry

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具有碱性部分的高 CT 荧光团进入 D-A 链作为 pKa 探针
The Journal of Organic Chemistry ( IF 3.3 ) Pub Date : 2022-06-07 , DOI: 10.1021/acs.joc.1c03104
Angel H Romero ₁ , Hugo E Cerecetto _{1,

2}

Affiliation

酸度的测定是荧光法中的一项重大挑战，目前尚未成功开发出有效的策略。这归因于这样一个事实，即在激发时酸度趋于增强，通常高估了电离常数 p K _a。在此，我们开发了一种策略，通过使用方便的 p K _a探针N ¹ -aryl-7-methoxy-2-(trifluoromethyl)benzo[ b ][1,8] ，通过荧光法估计溶液中的布朗斯台德酸 p K _a萘啶-4(1 H )-一。它使我们能够获得线性 log K _SV与p K _a相关性源自探针通过与不同布朗斯台德酸相互作用产生的选择性猝灭响应。N ¹ -aryl-7-methoxy-2-(trifluoromethyl)benzo[ b ][1,8]naphthyridin-4(1 H )-one 作为 ap K _a探针的关键点是（i）弱荧光团的供体-受体链中的碱性部分，有利于根据酸的酸度选择性猝灭分子内电荷转移过程，以及（ii）激发时的高 CT 特性，促进更高的猝灭幅度并有利于更广泛的p K _a范围 (19.5p K _a ) 对于 log K _SV与pK相关_性。其他关键原则是将研究限制为纯质子转移和非荧光酸，这允许将淬火响应限制在主要取决于酸碱平衡的过程中。所有这些发现开辟了一个新的视角，作为设计有效荧光 p K _a探针的概念证明。

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High CT-Fluorophore Featuring a Basic Moiety into D–A Chain as a pKa Probe

The determination of acidity represents a significant challenge within fluorometry, and no effective strategy has been developed successfully yet. It is attributed to the fact that acidity tends to be enhanced upon excitation, giving, in general, an overestimation of the ionization constant, pK_a. Herein, we developed a strategy for pK_a estimation of Brønsted acids in solution through fluorometry by using a convenient pK_a probe, N¹-aryl-7-methoxy-2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-one. It allowed us to obtain a linear log K_SVversus pK_a correlation derived from the selective quenching response of the probe by an interaction with different Brønsted acids. The key points of N¹-aryl-7-methoxy-2-(trifluoromethyl)benzo[b][1,8]naphthyridin-4(1H)-one as a pK_a probe were (i) the location of a weak basic moiety in the donor–acceptor chain of the fluorophore, which favors a selective quenching of the intramolecular charge-transfer process according to the acidity of acid, and (ii) the high CT character upon excitation that promotes higher quenching magnitudes and favors a wider pK_a range (19.5pK_a) for the log K_SVversus pK_a correlation. Other key principles were to delimit the study to pure proton transfer and nonfluorescent acids, which allowed restricting the quenching response to a process dependent mainly on the acid–base equilibrium. All these findings open a new perspective as a proof of concept to design effective fluorescent pK_a probes.

更新日期：2022-06-07

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