Reactivity of self-assembled monolayers: formation of organized amino functionalities

The reactivity of self-assembled monolayers (SAMs) of mercaptodocosanol (MD O) on gold has been screened by a variety of wet chemical reactions. Change s in thickness and composition were monitored using X-ray photoelectron spe ctroscopy (XPS). The order and tilt angles were studied using near-edge X-r ay absorption fine structure spectroscopy (NEXAFS). Sulfonyl chlorides coul d not be reacted to form sulfonates, and p-toluenesulfonyl chloride (TosCl) at longer reaction times even resulted in a partial desorption of the alka nethiol film. A coupling reaction of silanes to the hydrophilic surface was very much dependent on the reagent. Whereas chlorodimethylphenylsilane (CP S) at elongated reaction times leads to an almost complete removal of the m onolayer, p-aminophenyltrimethoxysilane (APTS) attaches to the OH terminate d surface. From the orientation analysis a broad distribution of tilt angle s of the aromatic moiety is concluded. Attachment of the APTS moieties indu ces disorder in the thiol layer. The average tilt angle of the hydrocarbon chains of the MDO layer changes from 30 degrees for the unperturbed, well-o rdered layer to 44 degrees for the reacted film and indicates an increasing number of gauche conformations.