Mie Lillethorup, Kyoko Shimizu, Nicolas Plumeré, Steen U. Pedersen, and Kim Daasbjerg
Novel types of dual-functional surface-attached polymer brushes were developed by post-polymerization modification of poly(glycidyl methacrylate) brushes on glassy carbon substrates. Azide and alcohol groups were initially introduced by epoxide ring-openings of the side chains. These polymer brushes represent an attractive chemical platform to deliberately introduce other molecular units at specific sites. In this work, ferrocene and nitrobenzene redox units were immobilized through the two groups to create redox polymers. In-depth analysis by infrared reflection–absorption spectroscopy and X-ray photoelectron spectroscopy revealed an almost quantitative conversion of the modification reactions. The electrochemical activity of the ferrocenyl part of this diode-like system was fully expressed with an electron transfer rate constant = 1.2 s–1 and surface density = 0.19 nmol cm–2 per nm section of the film, independent of its thickness. In contrast, for the nitrobenzene moieties diffusion of counterions (i.e., tetraalkylammonium) easily becomes the rate-controlling step, thereby leaving a substantial fraction of them electrochemically inactive.