Orthogonal Self-Assembly of Redox Active Molecules on Pt and Au: Selective Reaction of Disulfide with Au and Isonitrile with Pt

Surfaces of platinum and gold adsorb ferrocenyl-12-dodecyl isocyanide, I, and di(10-ferrocenecarbonyl-decyl) disulfide, II, and yield self-assembled, redox active monolayers incorporating ferrocene groups. The values of E 1/2 for alkyl ferrocenyl centers from I are approximately 300 mV more negative than acyl ferrocenyl centers from II. This difference allows easy electrochemical measurement of surface concentrations of ferrocene centers from I and II on Pt or Au. I adsorbs selectively on Pt or Au compared to II, but with different degrees of selectivity. Further, for Pt the selectivity depends on the surface pretreatment. The affinity of II for a Pt surface first exposed to an O2 plasma (oxidized Pt) is lower than that for a Pt surface exposed first to an O2 plasma and then to a H2 plasma (reduced Pt). The same two plasma treatments of Pt do not affect the binding of I on Pt. Thus, the selectivity of Pt for I vs. II is higher for the oxidized Pt approximately (200:1) compared to that for the reduced Pt approximately (20:1). The two plasma treatments of Au do not influence the selectivity for binding I vs. II; the selectivity for binding I vs II. on Au is approximately 8.1. By using the O2 plasma pretreatment and a 40:1 solution of II:I, orthogonal self-assembly of II onto Au and I onto Pt can be effected when the two samples are derivatized in the same solution.