Submicrosecond Electron Transfer to Monolayer-Bound Redox Species on Gold Electrodes at Large Overpotentials

Chronoamperometry with microscopic line electrodes was used to measure rates of electron transfer between gold electrodes and monolayer-bound ferrocenes for a variety of short chain lengths (5 to 13 methylenes) and at overpotentials exceeding 1 V. The rates vary from 102 s-1 to 3 × 107 s-1 and show an exponential chain-length dependence with a decay constant of 1.1 per CH2 over the measured overpotential range. The potential dependence of the rates for these short chain lengths follows the predictions of the Marcus−Levich model of interfacial electron transfer. The reorganization energy is near the value of 0.8 eV previously reported for similar systems. A thorough understanding of this system is likely to be an important foundation in the broader understanding of electron transport through organic materials, which is facilitated by access to fast rates over wide potential ranges.