Self-Assembled Monolayer Films Derived from Tridentate Cyclohexyl Adsorbates with Alkyl Tailgroups of Increasing Chain Length

Tridentate cyclohexyl-based alkanethiolate SAMs generated from a series of adsorbates of the form R₃C₆H₆(CH₂SH)₃, where R = −(CH₂)_<i>n</i>H and <i>n</i> = 3, 8, and 13 (<b>3CnCyTSH</b>), were examined. Characterization of the SAMs by X-ray photoelectron spectroscopy (XPS) revealed that all sulfur atoms of the tridentate adsorbates were bound to the surface of gold, and that the tailgroups were in general less densely packed than the SAM derived from octadecanethiol (<b>C18SH</b>). For each of the SAMs, the relative molecular coverage on the surface was estimated from the XPS-derived C_1s/Au_4f ratios. The trend in conformational order for these SAMs as determined by the surface interactions with contacting liquids and the relative crystallinity of the alkyl chains as revealed by the PM-IRRAS spectra were found to decrease as follows: <b>C18SH</b> ≫ <b>3C13CyTSH</b> > <b>3C8CyTSH</b> > <b>3C3CyTSH</b>. A preliminary study of the thermal stability of the SAMs as evaluated by XPS indicates that the SAM generated from the cyclohexyl-based adsorbate with the longest alkyl chain, <b>3C13CyTSH</b>, is markedly more stable than the SAM generated from <b>C18SH</b>. Overall, the results suggest that the stability of the SAMs are influenced by both the length of the alkyl chains and the chelate effect associated with the tridentate adsorbates