Fabrication of Supramolecular Chirality from Achiral Molecules at the Liquid/Liquid Interface Studied by Second Harmonic Generation
Fabrication of Supramolecular Chirality from Achiral Molecules at the Liquid/Liquid Interface Studied by Second Harmonic Generation
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通过二次谐波产生研究液/液界面处非手性分子的超分子手性制造
DOI：
10.1021/acs.langmuir.7b04170
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发表时间：
2018
期刊：
影响因子：
3.9
通讯作者：
Liu M.
中科院分区：
文献类型：
--
作者：
Lin L.;Zhang Z.;Guo Y.;Liu M.
采用二次谐波生成（SHG）方法研究了5-十八烷基氧基-2-（2-吡啶偶氮）苯酚（PARC18）在水/1,2-二氯乙烷界面上的超分子手性。我们观察到PARC18分子虽然是非手性分子，但通过在液/液界面的自组装形成了超分子手性。有机相中PARC18的体积浓度对其超分子手性有深远的影响。随着体积浓度的增加，界面处过量的对映体先增大后减小，直至最终消失。进一步分析表明，对映体的过量是由PARC18分子在界面处的扭转角而不是取向角决定的。在较低和较高的体积浓度下，PARC18分子的平均扭转角趋近于零，其组装为非手性的；而在中等体积浓度下，平均扭转角是非零的，因此该组合物表现出超分子手性。我们还估计了PARC18分子在界面上的覆盖率与体积浓度的关系，并将其拟合到Langmuir吸附模型中。结果表明，在半满的单分子结构中，PARC18具有最强的超分子手性。这些发现强调了通过控制体积浓度来精确控制液/液界面超分子手性的机会。
We present the investigation into the supramolecular chirality of 5-octadecyloxy-2-(2-pyridylazo)phenol (PARC18) at water/1,2-dichloroethane interface by second harmonic generation (SHG). We observe that PARC18 molecules form supramolecular chirality through self-assembly at the liquid/liquid interface although they are achiral molecules. The bulk concentration of PARC18 in the organic phase has profound effects on the supramolecular chirality. By increasing bulk concentration, the enantiomeric excess at the interface first grows and then decreases until it eventually vanishes. Further analysis reveals that the enantiomeric excess is determined by the twist angle of PARC18 molecules at the interface rather than their orientational angle. At lower and higher bulk concentrations, the average twist angle of PARC18 molecules approaches zero, and the assemblies are achiral; whereas at medium bulk concentrations, the average twist angle is nonzero, so that the assemblies show supramolecular chirality. We also estimate the coverage of PARC18 molecules at the interface versus the bulk concentration and fit it to Langmuir adsorption model. The result indicates that PARC18 assemblies show strongest supramolecular chirality in a half-full monolayer. These findings highlight the opportunities for precise control of supramolecular chirality at liquid/liquid interfaces by manipulating the bulk concentration.