Poster: "Spectroelectrochemical studies of conjugated polymer nanoparticles"

PALACIOS, RODRIGO E.; FAN, FU-REN F.; BARD, ALLEN J.; BARBARA, PAUL F.

Austin, Texas, EE.UU.

Conferencia; The Best Little Nano Conference in Texas; 2007

Texas Academy of Medicine, Engineering and Science

We describe an approach to the determination of the thermodynamics and kinetics of electron transfer (eT) to single immobilized molecules based on single molecule spectroelectrochemistry (JACS, 2006, 128(28), 9028). Such eT reactions are of interest in solar cells, flat-panel displays and chemical sensors. The extreme heterogeneity of inorganic/organic interfaces has been a key obstacle to developing a quantitative, molecular-level understanding of such device. Here we introduce a powerful new technique for studying eT processes at highly heterogeneous interfaces, SMS-EC measures electrochemical behavior one molecule at a time, offering for the first time the distribution of key electrochemical variables (e.g. the half-wave potential) not just the ensemble average. In this work SMS-EC is used to study the oxidation at an indium tin oxide (ITO) electrode of single molecules and nanoparticles of the widely used organic conjugated polymer poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT). In the case of single molecules, the results reveal both excited singlet state and ground state oxidation of F8BT. The latter process occurs over a narrow distribution of single-molecule values indicating a relatively uniform electrochemical potential at the electrode. In the case of F8BT nanoparticles two main processes have been observed: an irreversible chemical reaction on the surface of the oxidized F8BT nanoparticles and a reversible hole-injection charging process. The latter occurs primarily by initial injection of shallow (untrapped) holes, but soon after the injection, a small fraction of the holes becomes deeply trapped. Support: This work was supported by the National Science Foundation, AFOSR, and the Welch Foundation, and by the Basic Energy Sciences Program of the Department of Energy.