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Temperature Sensing of Thiolate Addition by Phenolate Merocyanine Dyes: Importance of the Quinone Methide Resonance Structure
The Journal of Organic Chemistry ( IF 3.6 ) Pub Date : 2020-12-24 , DOI: 10.1021/acs.joc.0c02428
Abigail J. Van Riesen 1 , Ryan E. Johnson 1 , M. Sameer Al-Abdul-Wahid 2 , Cristina Liota 1 , Anjelyn Christyanton 1 , Richard A. Manderville 1
Affiliation  

Merocyanine (MC) dyes containing an aromatic donor vinyl linked to a cationic acceptor serve as chemosensors for analyte detection. Their electrophilicity permits anion detection through addition reactions that disrupt dye conjugation. Herein, we demonstrate the temperature influence on thiolate addition to MCs containing the N-methylbenzothiazolium (Btz) acceptor. The zwitterionic phenolate dye (PhOBtz) displays impressive temperature sensitivity to thiolate addition, with the brightly colored phenolate favored upon heating and the colorless thiolate adduct favored upon cooling. In contrast, MC dyes containing neutral donors (PhOMeBtz and PhNMe2Btz) display only moderate temperature sensitivity to thiolate capture and release. Extraction of thermodynamic parameters demonstrates a strong enthalpic driving force for thiolate addition to PhOBtz that is absent for PhOMeBtz and PhNMe2Btz. Variable temperature 1H NMR studies demonstrate that PhOBtz adopts the para-quinone methide (p-QM) resonance structure. Thus, thiolate addition to PhOBtz resembles 1,6-conjugate addition to p-QMs which is accompanied by a large increase in the π-stabilization energy upon adduct formation. Manipulation of PhOBtz electrophilicity by attaching chlorine substituents to the phenolate caused the thiolate adducts to dissipate over time for p-QM regeneration. Our work provides new design ideas for the utility of phenolate MC dyes, given that they are carriers of the p-QM electrophile.

中文翻译:

酚盐花青染料对硫氰酸盐加成的温度感测:醌甲基甲烷共振结构的重要性。

包含与阳离子受体连接的芳族供体乙烯基的花青(MC)染料可作为化学传感器进行分析物检测。它们的亲电子性允许通过破坏染料结合的加成反应检测阴离子。在本文中,我们证明了温度对含有N-甲基苯并噻唑鎓(Btz)受体的MC的硫醇盐添加的影响。两性离子酚盐染料(PhOBtz)对添加硫醇盐显示出令人印象深刻的温度敏感性,加热时偏爱鲜艳的酚盐,冷却时偏爱无色的硫醇盐加合物。相反,含有中性供体的MC染料(PhOMeBtz和PhNMe 2Btz)仅显示对硫醇盐捕获和释放的中等温度敏感性。热力学参数的提取证明了向PhOBtz中添加硫醇盐的强大的焓驱动力,而PhOMeBtz和PhNMe 2 Btz则不存在。可变温度1 H NMR研究表明PhOBtz采用甲基醌(p -QM)共振结构。因此,向PhOBtz的硫醇盐加成类似于向p -QMs的1,6-缀合物加成,这伴随着加合物形成时π-稳定能的大大增加。通过将氯取代基连接到酚盐上来操作PhOBtz亲电性会导致硫醇盐加合物随时间的流逝消散成p-QM再生。我们的工作为酚盐MC染料的实用性提供了新的设计思路,因为它们是p -QM亲电试剂的载体。
更新日期:2021-01-16
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