MIXED MONOLAYERS FORMED BY THE SELF-ASSEMBLY ON GOLD OF THIOL-FUNCTIONALIZED ANTHRAQUINONES AND 1-ALKANETHIOLS

The self-assembly and electrochemical properties of a series of thiol-functionalized anthraquinone derivatives were studied on gold by cyclic voltammetry. The compounds were 1,8-bis(1,7-dithia-4-oxaheptyl)-anthracene-9,10-dione (1), 1,8-bis(4,7-dioxa-1,10-dithiadecyl)anthracene-9,10-dione (2), and 1-(4,7-dioxa-1,10-dithiadecyl)anthracene-9,10-dione (3). Compounds 1-3 formed self-assembled monolayers on gold with surface coverages of 2.7 x 10(-10), 2.5 x 10(-10), and 2.9 x 10(-10) mol/cm2, respectively. All monolayers showed voltammetric responses in 0.1 M KOH that corresponded to the two-electron reduction of the anthraquinone subunit. However, the voltammetric response was not reversible, exhibiting large pear-to-peak potential splittings (60-80 mV at a scan rate of 0.1 V/s) and other distortions. The voltammetric reversibility increased substantially in mixed monolayers prepared by the competitive self-assembly of one of the anthraquinone derivatives and a 1-alkanethiol (C-10 to C18). Interestingly, the anthraquinone derivatives competed quite effectively with alkanethiols for adsorption sites on the gold surface. Compound 2 was found to be optimum in this regard because it has two thiol-terminated chains that may serve as anchoring points to the gold surface.