Presentación Oral: "Single molecule techniques to study charge transfer at electrode interfaces”

PALACIOS, RODRIGO E.

La Serena, Chile

Congreso; X Encuentro Latinoamericano de Fotoquímica y Fotobiología (ELAFOT); 2010

ELAFOT

I will discuss new approaches to study electron transfer processes at highly heterogeneous interfaces using the recently developed technique, Single Molecule Spectroelectrochemistry (SMS-EC). The technique uses florescence spectroscopy to measure the electrochemical behavior of single molecules and nanoparticles (NPs), one at a time. This unique ability was used to uncover, for the first time, the distribution of single molecule oxidation potentials in conjugated polymers, a novel class of organic electronic materials used in promising strategies for solar cells, flat-panel displays, and chemical sensors. Several conjugated polymers -including F8BT, MEH-PPV, and BEH-PPV- were studied at the single molecule and NP level. In the case of single molecules, the results reveal both excited singlet state and ground state oxidation. In the case of NPs two main processes have been observed: an irreversible chemical reaction (occurring when the particle is highly oxidized) and a reversible hole-injection charging process. The latter seems to occur primarily by initial injection of shallow (untrapped) holes (positive charge carriers), but soon after the injection a small fraction of the holes becomes deeply trapped. In a different application SMS-EC was used to demonstrate, for the first time, the Electrogenerated Chemiluminescence (ECL) of single conjugated polymer NPs. In this case SMS-EC allowed the study of the dynamics of the ECL process. Thus, in addition to the usual advantage of single particle studies of obtaining information about particle environments, this approach may also provide dynamic information not seen in ensembles. Moreover, because of high sensitivity, low background, and relatively high spatial and temporal resolution of ECL, this new method could be useful as a sensitive analytical technique. Lastly, a variation of SMS-EC and ECL was used to study the spatial evolution of electrochemical oxidation in thin conjugated polymer films.