New Approach on the Synthesis of Functionalized Alkanethiols and the Structural Characterization of Their Self-Assembled Monolayers

A simple and general method fro synthesizing functionalized alkanethiols is reported. The synthesis started from carboxylic acid, RCOOH, which was selectively condensed with the amino group of 2-aminoethanethiol, thus giving the targetting thiol compounds. A series of thiol compounds having a structure of RC(O)NHCH2CH2SH, where R was azobenzene derivatives, dicetylene derivatives and n-akanes, respectively, have been synthesized using this method. The self-assembled monolayers(SAMs) of these species were characterized by wettability measurement, electrochemistry and grazing incidence reflectance infrared spectroscopy (GIR-IR). The SAM from 4-((N-(2'-mercapto-ethyl)amino)carbonyl) azobenzene showed clearcut electrochemical reactivity in aqueous solution, in which the surface coverage was evaluated to be 4.21 x 10(-10) mol.cm(-2). On the other hand, for the thiols of R being n-alkanes, the packing structures became gradually improved with increasing the alkyl chain length. For CH3(CH2)(6)C(O)NHCH2CH2SH SAM, GIR-IR data indicate that the C=O and N-H groups are parallel with the substrate surface while the whole molecular axis is perpendicular to the surface.