Single Molecule Spectroscopy of Semiconductor Nanoparticles in a Device Environment

So-Jung Park

Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104

Photoluminescence (PL) intensity fluctuations of single conjugated polymers have been studied by single molecule spectroscopy combined with a charge injection device.  This technique allows for the direct correlation of photochemistry, photobleaching, and charge carrier effects for the same nanometer scale region (i.e. isolated single molecule) with controlled hole/electron injection.  The PL of isolated MEH-PPV conjugated polymer molecules was observed to exhibit diverse environment and electrical bias effects: (1) fluorescence quenching due to holes in the hole-transport layer; (2) fluorescence quenching due to chemical defects generated by photooxidation; and (3) reductive “repair” of the photooxidation-induced quenching by charge carrier injection.  These results demonstrate a very different mechanism for photobleaching of organic conjugated materials than is generally assumed to operate, and furthermore suggest an intimate relationship between photobleaching, charge transport, and persistent photoconductivity in organic materials.