Odd-even effects in aryl-substituted alkanethiolate SAMs: nonsymmetrical attachment of aryl unit and its impact on the SAM structure

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...

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Published inPhysical chemistry chemical physics : PCCP Vol. 26; no. 9; pp. 7563 - 7572
Main Authors Azzam, Waleed, Subaihi, Abdu, Rohwerder, Michael, Bashir, Asif, Terfort, Andreas, Zharnikov, Michael
Format Journal Article
LanguageEnglish
Published England Royal Society of Chemistry 28.02.2024
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Summary: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. Due to non-symmetric attachment of the anthracene unit to the alkanethiolate linker, the respective monolayers on Au(111) exhibit low extent of the odd-even effects and distinct polymorphism, showing, at the same time, high structural order.
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ISSN:1463-9076
1463-9084
DOI:10.1039/d4cp00311j