Redox-Stable SAMs in Water (pH 0-12) from 1,1′-Biferrocenylene-Terminated Thiols on Gold

Redox-active alkyl and acyl SAMs (self-assembled monolayers) on gold prepared from BFD-terminated thiols (BFD = bis(fulvalene)diiron, 1,1'-biferrocenylene) have been investigated in aqueous buffered solutions at various pH values by electroanalytical methods, and their redox potentials were determined at pH 7. Excellent redox stability over the whole range from pH 0 to 12, far superior to that of the corresponding ferrocene-terminated SAMs, is established by oxidizing alkanethiol BFD-SAMs to alkanethiol BFD+-SAMs for more than 1 h without any significant decomposition (<3%). The high stability and full reversibility suggests profitable use for diverse redox applications in aqueous solution. As a proof of concept, the utility of alkanethiol BFD SAMs for controlling surface wetting properties is demonstrated in contact angle changes of 25 degrees by triggering the BFD/BFD+ redox process.