Olefin-Bridged Bidentate Adsorbates for Generating Self-Assembled Monolayers on Gold

Abstract

A series of custom-designed olefin-bridged bidentate adsorbates composed of an olefin group linking symmetrical hydrocarbon moieties of varying chain lengths was synthesized and used for the preparation of self-assembled monolayers (SAMs) on gold. The structures of the adsorbates are in the form Z-[CH3(CH2) m ]2(CC)­[CH2SH]2 (OBCnSH) where m = 12–15 and n = m + 3 (OBC15SH, OBC16SH, OBC17SH, and OBC18SH). The influence of the olefin linker on the structural and interfacial properties of the SAMs was investigated and compared to SAMs formed from analogous n-alkanethiols. Characterization techniques included ellipsometry, X-ray photoelectron spectroscopy (XPS), polarization modulation-infrared reflection–adsorption spectroscopy (PM-IRRAS), and contact angle measurements. The OBCnSH SAMs exhibited ellipsometric thicknesses that were similar to their monodentate counterparts, suggesting that the new olefin-bridged adsorbates pack similarly to the monodentate analogs. Characterization by PM-IRRAS revealed that the OBCnSH SAMs were as conformationally ordered as those derived from the reference n-alkanethiols with the exception of the adsorbate with the shortest chain length OBC15SH, which exhibited low coverage and a liquid-like structure. Unlike the SAMs derived from the n-alkanethiols, the OBCnSH SAMs failed to exhibit “odd–even” effects. However, the OBCnSH SAMs displayed similar hexadecane contact angles as their n-alkanethiol counterparts with the exception of OBC15SH, which exhibited markedly diminished hexadecane contact angles. The similar structural and interfacial properties of the OBCnSH SAMs, when compared to analogous n-alkanethiol SAMs, render the molecular architecture of the olefin-bridged dithiol as a robust platform for the synthesis of adsorbates with two chemically distinct tailgroups for use in the preparation and study of phase-incompatible “conflicted” interfaces.

Functionalized N-Heterocyclic Carbene Monolayers on Gold for Surface-Initiated Polymerizations

“…31,35 In the NHC15OH SAMs, the alkyl chains on the benzimidazole moieties help to maximize interchain van der Waals interactions, allowing the molecules within these SAMs to have an upright orientation, and insufficient chain−chain interactions lead to more flat-lying adsorbate structures on the substrate. 53 Polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) is a useful technique that can be used to evaluate the conformational order or crystallinity of alkyl chains in SAMs. 15,49,54 Specifically, the positions of the asymmetric methylene C−H stretching vibration (ν a CH 2 ) bands provide insight into the intermolecular environment of the alkyl chains in organic thin films.…”

Self-Assembled Monolayers Derived from Positively Charged Adsorbates on Plasmonic Substrates for MicroRNA Delivery: A Review

“…For gold and related noble metal substrates, thiol headgroups are typically used [13,16,20]. The second component of the adsorbate is a spacer, composed of an alkyl chain that dictates the packing of the resulting films through van der Waals (vdW) interactions [21]. The last major component of the adsorbate is a terminal group.…”

Sum frequency generation spectroscopy of fluorinated organic material-based interfaces: a tutorial review

“…[4][5][6][7] Numerous surface analytical techniques including ellipsometry, contact angle goniometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy, such as polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) 6,8 have been used to investigate properties of various organic-based surfaces, such as their basic structural orientations, wettability, and chemical compositions at interfaces. 4,5,9 Additionally, atomic force microscopy (AFM) has also been utilized to obtain detailed information about the nanometric lateral resolution of such surfaces. [10][11][12] This technique, however, is limited in its ability to provide an advanced understanding of buried surfaces, such as the direction and interaction of different types of liquids in contact with solid interfaces, or the tilt angle and conformational features at solid-air and solid-liquid interfaces.…”