Single-Molecule Spectroelectrochemistry (SMS-EC)

We introduce single-molecule spectroelectrochemistry (SMS-EC), a powerful new technique for studying electrochemical kinetics in highly heterogeneous systems. This technique uses fluorescence single-molecule spectroscopy to indirectly measure electrochemical kinetics one molecule at a time, offering for the first time the distribution of key electrochemical variables, such as the half-wave potential, <i>E</i><sub>1/2</sub>, not just the ensemble averages. In SMS-EC, the potential of the working electrode of an electrochemical cell is linearly scanned while simultaneously measuring the florescence intensity, <i>I</i><sub>fl</sub>(<i>t</i>), of individual single molecules as a function of time in a wide-field microscope. SMS-EC is used herein to study the oxidation at an indium tin oxide (ITO) electrode of single molecules of the organic conjugated polymer F8BT. The results reveal both excited singlet state and ground state oxidation of F8BT. The latter process occurs over a narrow distribution of single-molecule half-wave potential values, indicating a relatively uniform electrochemical potential at the electrode.