Odd–even effects in aryl-substituted alkanethiolate SAMs: nonsymmetrical attachment of aryl unit and its impact on the SAM structure,Physical Chemistry Chemical Physics

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Odd–even effects in aryl-substituted alkanethiolate SAMs: nonsymmetrical attachment of aryl unit and its impact on the SAM structure
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2024-02-12 , DOI: 10.1039/d4cp00311j
Waleed Azzam ₁ , Abdu Subaihi ₂ , Michael Rohwerder ₃ , Asif Bashir ₄ , Andreas Terfort ₅ , Michael Zharnikov ₆

Affiliation

Aryl-substituted alkanethiolate (AT) self-assembled monolayers (SAMs) exhibit typically so-called odd–even effects, viz. systematic variations in the film structure, packing density, and molecular inclination depending on the parity of the number of the methylene units in the alkyl linker, n. As an exception to this rule, ATs carrying an anthracen-2-yl group (Ant-n) as tail group were reported to have different behavior due the non-symmetric attachment of the anthracene unit to the AT linker, providing additional degree of freedom for the molecular organization and allowing for partial compensation of the odd–even effects. In this context, the structure of SAMs formed by adsorption of anthracene-substituted ATs (Ant-n; n = 1–6) at room temperature on Au(111) substrate was investigated by high-resolution scanning tunnelling microscopy (STM). Most of these SAMs exhibit a coexistence of two different ordered phases, some of which are common for either n = odd or n = even while other vary over the series, showing a broad variety of different structures. The average packing density of the Ant-n SAMs, derived from the analysis of the STM data, varies by 7.5–10% depending on the parity of n, being, as expected, higher for n = odd. The respective extent of the odd–even effects is noticeably lower than that usually observed for other aryl-substituted monolayers (∼25%), which goes in line with the previous findings and emphasizes the impact of the non-symmetric attachment of the aromatic unit.

中文翻译：

芳基取代的烷硫醇 SAM 中的奇偶效应：芳基单元的非对称连接及其对 SAM 结构的影响

芳基取代的烷硫醇（AT）自组装单层（SAM）通常表现出所谓的奇偶效应，即。膜结构、堆积密度和分子倾向的系统变化取决于烷基连接体中亚甲基单元数量的奇偶性， n 。作为该规则的一个例外，据报道，携带蒽-2-基（Ant -n ）作为尾基的 AT 有不同的行为，因为蒽单元与 AT 连接体的非对称连接，提供了额外的自由度用于分子组织并允许部分补偿奇偶效应。在这种情况下，通过高分辨率扫描隧道显微镜（STM）研究了室温下在Au（111）基板上吸附蒽取代的AT（Ant- n ； n = 1-6）形成的SAM的结构。这些 SAM 中的大多数表现出两种不同有序相的共存，其中一些常见为n = 奇数或n = 偶数，而其他则随系列变化，显示出各种各样的不同结构。 Ant -n SAM 的平均堆积密度由 STM 数据分析得出，根据n的奇偶性变化 7.5-10%，正如预期的那样，当n = 奇数时，密度会更高。奇偶效应的各自程度明显低于其他芳基取代的单层通常观察到的程度（~25%），这与之前的发现一致，并强调了芳香单元非对称连接的影响。

更新日期：2024-02-16

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