Lateral dipole moments induced by all-cis-pentafluorocyclohexyl groups cause unanticipated effects in self-assembled monolayers
Lateral dipole moments induced by all-cis-pentafluorocyclohexyl groups cause unanticipated effects in self-assembled monolayers
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DOI：
10.1007/s12274-023-5818-4
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发表时间：
2023-06-26
期刊：
影响因子：
9.9
通讯作者：
Terfort, Andreas
中科院分区：
文献类型：
--
作者：
Fischer, Christian;Das, Saunak;Terfort, Andreas
全顺式六氟环己烷和全顺式五氟环己烷（PFCH）衍生物是新型材料，其结构和性能由高偶极Janus面基序主导。在这里，我们报告了将 PFCH 基团整合到 Au(111) 上链烷硫醇盐的自组装单层 (SAM) 中的影响。具有奇数（十一）和偶数（十二）个亚甲基的单层通过几种补充实验工具进行了详细表征，并得到了理论计算的支持。令人惊讶的是，所有数据都显示出两种单层细胞的高度相似性，几乎缺乏通常观察到的奇偶效应。由于 PFCH 部分体积庞大，这些新的单层的堆积密度比未取代的链烷硫醇盐单层的堆积密度低约 1/3。 PFCH 基团和烷基链的方向可以独立确定，这表明其构象与类似化合物的固态结构中发现的构象相似。尽管在 SAM 中，PFCH 基团稍微偏离表面法线且轴向氟原子指向下方，但该基团的大部分偶极矩仍保持平行于表面的方向，这是 SAM 系统的独特特征。其结果是与其他部分氟化的 SAM 相比，水接触角要低得多，并且功函数值相当适中。尽管这些薄膜的堆积密度较低，但末端 PFCH 部分之间的相互作用导致 PFCH 修饰的 SAM 在与潜在分子取代基发生交换反应时的稳定性增强。
All-cis-hexafluoro- and all-cis-pentafluoro-cyclohexane (PFCH) derivatives are new kinds of materials, the structures and properties of which are dominated by the highly dipolar Janus-face motif. Here, we report on the effects of integrating the PFCH groups into self-assembled monolayers (SAMs) of alkanethiolates on Au(111). Monolayers with an odd (eleven) and even (twelve) number of methylene groups were characterized in detail by several complementary experimental tools, supported by theoretical calculations. Surprisingly, all the data show a high similarity of both kinds of monolayers, nearly lacking the typically observed odd-even effects. These new monolayers have a packing density about 1/3 lower than that of non-substituted alkanethiolate monolayers, caused by the bulkiness of the PFCH moieties. The orientations of the PFCH groups and the alkyl chains could be determined independently, suggesting a conformation similar to the one found in the solid state structure of an analogous compound. Although in the SAMs the PFCH groups are slightly tilted away from the surface normal with the axial fluorine atoms pointing downwards, most of the dipole moments of the group remain oriented parallel to the surface, which is a unique feature for a SAM system. The consequences are much lower water contact angles compared to other partly fluorinated SAMs as well as rather moderate work function values. The interaction between the terminal PFCH moieties results in an enhanced stability of the PFCH-decorated SAMs toward exchange reaction with potential molecular substituents in spite of the lower packing density of these films.