Detailed single-molecule spectroelectrochemical studies of the oxidation of conjugated polymers.
Single-particle fluorescence spectroelectrochemistry was used to investigate the electrochemical oxidation of isolated, immobilized particles of the conjugated polymers BEH-PPV and MEH-PPV at an indium tin oxide (ITO) electrode immersed in an electrolyte solution. Two types of particles were investigated: (i) polymer single molecules (SM) and (ii) nanoparticle (NP) aggregates of multiple polymer single molecules. For the BEH-PPV polymer, the observation of nearly identical lowest oxidation potentials for different SM in the ensemble is evidence for effective electrostatic screening by the surrounding electrolyte solution. A combination of Monte Carlo simulations and application of Poisson-Boltzmann solvers were used to model the charging of polymer single molecules and nanoparticles in the electrochemical environment. The results indicate that the penetration of electrolyte anions into the polymer nanoparticles is necessary to produce the observed narrow fluorescence quenching vs oxidation potential curves. Finally, fluorescence-lifetime single-molecule spectroelectrochemical (SMS-EC) data revealed that at low potential an excited state reduction process (i.e., electron transfer from ITO to the polymer) is probably the dominant fluorescence quenching process.
Department of Chemistry and Biochemistry and the Center for Nano- and Molecular Science and Technology, University of Texas at Austin, Austin, Texas 78712, USA.
Rodrigo E
RE
Palacios
Wei-Shun
WS
Chang
John K
JK
Grey
Ya-Lan
YL
Chang
William L
WL
Miller
Chun-Yaung
CY
Lu
Graeme
G
Henkelman
Danny
D
Zepeda
John
J
Ferraris
Paul F
PF
Barbara