Self-Assembled Monolayers of Aromatic ω-Aminothiols on Gold: Surface Chemistry and Reactivity

Amino-terminated self-assembled monolayers on gold substrates were studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption Fine structure (NEXAFS) measurements,and atomic force microscopy (AFM). Two different omega-amino-4,4'-terphenyl substituted alkanethiols of the general structure H2N-(C6H4)(3)-(CH2)(n)-SH (ATPn) were used: 2-(4 ''-amino-1,1':4',1 ''-terphenyl-4-yl)ethane-1-thiol (n = 2, ATP2) and 3-(4 ''-amino-1,1':4',1 ''-terphenyl-4yl)propane-1-thiol (n = 3, ATP3). Moreover, the addressability of amino groups within the films was investigated by chemical derivatization of ATPn SAMs with 3,5-bis(trifluoromethyl) phenyl isothiocyanate (ITC) forming fluorinated thiourea ATPn-F Films. Evaluation of high-resolution C Is and N Is XPS data revealed successful derivatization of at least 50% of surface amino species. Furthermore, it could be demonstrated by angle-resolved NEXAFS spectroscopy that chemical derivatization with ITC has no noticeable influence on the preferential upright orientation of the molecules in the SAMs.