Effect of Head‐Group Chemistry on Surface‐Mediated Molecular Self‐Assembly

Abstract

Surface molecular self-assembly is a fast advancing field with broad applications in sensing, patterning, device assembly, and biochemical applications. A vast number of practical systems utilize alkane thiols supported on gold surfaces. Whereas a strong Au-S bond facilitates robust self-assembly, the interaction is so strong that the surface is reconstructed, leaving etch pits that render the monolayers susceptible to degradation. By using different head group elements to adcust the molecule-surface interaction, a vast array of new systems with novel properties may be formed. In this paper we use a carefully chosen set of molecules to make a direct comparison of the self-assembly of thioether, selenoether, and phosphine species on Au(111). Using the herringbone reconstruction of gold as a sensitive readout of molecule-surface interaction strength, we correlate head-group chemistry with monolayer (ML) properties. It is demonstrated that the hard/soft rules of inorganic chemistry can be used to rationalize the observed trend of molecular interaction strengths with the soft gold surface, that is, P>Se>S. We find that the structure of the monolayers can be explained by the geometry of the molecules in terms of dipolar, quadrupolar, or van der Waals interactions between neighboring species driving the assembly of distinct ordered arrays. As this study directly compares one element with another in simple systems, it may serve as a guide for the design of self-assembled monolayers with novel structures and properties.

From the bottom up: dimensional control and characterization in molecular monolayers

“…In addition to the molecules with head groups based on sulfur, discussed above, 1,28,25 many other head groups are available, including isocyanides, 75 Si, 76–78 P, 50,79–81 Se, 29,73,82,83 carboxylic acids, 84,85 and head groups that allow noncovalent π-stacking interactions on highly oriented graphite, such as cyclodextrins, 86–89 pentacene, 90 and peptides. 91–93 While these surface connectors are relatively less explored, comparisons between molecule-substrate systems provide insight into how to translate surface attachment and patterning strategies from one system to another, and will hopefully lead to the identification of new strategies.…”

Asymmetric Thioethers as Building Blocks for Chiral Monolayers

“…DMS arranges in a perpendicular (or ''herringbone'') packing arrangement, which is typical of quadrupolar molecules [42,58]. However, DBS, which is very chemically similar to DMS, packs in linear rows [43,44].…”

“…Our previous studies examining dimethyl sulfide (DMS) and dibutyl sulfide (DBS) on Cu(111) and Au(111) offer evidence that van der Waals attractions play an important role in the assembly of the longer tailed species [42][43][44]58]. DMS arranges in a perpendicular (or ''herringbone'') packing arrangement, which is typical of quadrupolar molecules [42,58].…”

Phthalocyanine Derivatives with Eight Peripheral Long‐Chain n‐Alkylseleno Substituents

“…The work presented here was stimulated by the results of recent studies comparing SAMs fabricated from thiols, disulfides or thioethers on gold with those obtained with the respective selenium homologues. It was found that the replacement of the sulfur anchor atom by selenium frequently leads to SAMs of better order and/or higher thermal stability, because the molecular interactions with the gold surface tend to be stronger for the selenium adsorbates . These findings prompted us to target the selenium homologues of phthalocyanine derivatives used in our previous work.…”