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Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

Copyright 2004 by Marcel Dekker, Inc. All Rights Reserved.

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Figure 10 Transmission electron microscope images of blends of MEH–PPV with 5-nm-diameter CdSe nanocrystals at concentrations of 5%, 20%, and 65% <strong>by</strong> weight:(a) pyridine-treated nanocrystals; (b) TOPO-coated nanocrystals. Distinct aggregationcan be seen in the blends containing pyridine-treated nanocrystals.mer backbone increases the electron affinity of the polymer <strong>by</strong> roughly 0.5 eV.[73]. Nevertheless, all sizes of CdSe nanocrystals studied quenched the fluorescenceof MEH–CN–PPV to nearly the same degree as they had quenchedthe emission of MEH–PPV. On the other hand, DHeO–CN–PPV, withHOMO and LUMO levels similar to those of MEH–CN–PPV, did not exhibitfluorescence quenching in the presence of the nanocrystals. Ultimately weattributed this difference to the fact that the symmetric alkyl side chains ofDHeO–CN–PPV provide an insulating spacer between the nanocrystals andthe conjugated polymer core, which prevents rapid electron transfer.In the same article [27], we also used photoinduced absorption (PIA)spectroscopy to provide direct evidence for the presence or absence of photo-<strong>Copyright</strong> <strong>2004</strong> <strong>by</strong> <strong>Marcel</strong> <strong>Dekker</strong>, <strong>Inc</strong>. <strong>All</strong> <strong>Rights</strong> <strong>Reserved</strong>.

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