School of Physics, Shandong University, Jinan 250100, China.
ACS Appl Bio Mater. 2021 Feb 15;4(2):1950-1957. doi: 10.1021/acsabm.0c01579. Epub 2021 Feb 1.
2-(6'-Hydroxy-2'-pyridyl)benzimidazole (BI), having double functional groups donating protons, is investigated theoretically with an aim to determine the excited-state proton transfer (ESPT) mechanism in different solvents. We demonstrate that the ESPT reaction can take place with the assistance of protic solvents (water and ethanol). At the same time, the vitally important role of bridges of water and ethanol for the ESPT reaction is confirmed by the disappearance of the ESPT reaction when we replaced the protic solvent with aprotic solvent acetonitrile (ACN). We regulate the ESPT reaction of BI via solvents successfully. A different ESPT mechanism from the one proposed previously (the proton of BI transfers from benzimidazole NH to pyridyl nitrogen in ethanol) is proposed. Our simulated potential energy barriers indicate that the ESPT reaction of BI can occur only between the hydroxyl proton and pyridyl nitrogen with the assistance of water or ethanol molecules. We further verify that the water- or ethanol-assisted ESPT reaction of BI is stepwise, and the concerted mechanism is unambiguously ruled out. This systematic investigation into the ESPT mechanism of BI is significant in designing and constructing the desirable supramolecular architectures, which can provide potential supramolecular recognition sites and supramolecular inter- or intra-H-bonding interactions.
2-(6'-羟基-2'-吡啶基)苯并咪唑（BI）具有两个供质子的官能团，我们从理论上对其进行了研究，旨在确定不同溶剂中的激发态质子转移（ESPT）机制。我们证明质子溶剂（水和乙醇）可以辅助 ESPT 反应。同时，通过用非质子溶剂乙腈（ACN）取代质子溶剂，确认了水和乙醇桥对 ESPT 反应的至关重要的作用，因为当我们用非质子溶剂取代质子溶剂时，ESPT 反应消失了。我们成功地通过溶剂来调节 BI 的 ESPT 反应。提出了一种与之前提出的（BI 的质子从苯并咪唑 NH 转移到乙醇中的吡啶氮）不同的 ESPT 机制。我们模拟的势能障碍表明，BI 的 ESPT 反应只能在羟基质子和吡啶氮之间在水或乙醇分子的协助下发生。我们进一步验证了 BI 的水或乙醇辅助 ESPT 反应是分步进行的，明确排除了协同机制。对 BI 的 ESPT 机制的系统研究对于设计和构建理想的超分子结构具有重要意义，这些结构可以提供潜在的超分子识别位点和超分子内或超分子间氢键相互作用。
