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Journal of the American Chemical Society 03/2008; 130(8):2384-5. · 9.91 Impact Factor
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ABSTRACT: Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems.
The Journal of Physical Chemistry B 08/2006; 110(29):14167-71. · 3.70 Impact Factor
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ABSTRACT: Fluorescence intermittency, or “blinking” in quantum dot systems has been the subject of great interest since the first observation of this phenomenon nearly 10 years ago. The stability of quantum dot fluorescence emission is especially important in the context of photovoltaic, optoelectronic, and biological applications, where device performance, or the ability to track labeled particles, is affected adversely by fluorescence intermittency. Single-molecule spectroscopy combined with atomic force microscopy measurements reveal that CdSe quantum dots functionalized with oligo(phenylene vinylene), OPV, ligands exhibit modified optical properties such as suppression of blinking when compared to conventional TOPO covered or ZnS-capped CdSe quantum dots. The blinking suppression is shown to be highly sensitive to the degree of ligand coverage on the quantum dot surface and this effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. This direct surface derivatization of quantum dots with organic ligands also enables a “tunable” quantum dot surface that allows dispersion of quantum dots in a variety of polymer supported thin films without phase segregation. This facilitates straightforward inclusion of these new hybrid materials into solid state formats and suggests exciting new applications of composite quantum dot/organic systems in optoelectronic systems.
MRS Proceedings. 12/2005; 959.
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ABSTRACT: Fluorescence intensity fluctuations from individual CdSe quantum dots coordinated with oligo(phenylenevi-nylene) ligands (CdSe-OPV) have been previously observed to be qualitatively different from conventional capped CdSe quantum dots. In particular, the high degree of blinking suppression observed in these (inherently multichromophoric) systems was suggestive of multichromophoric emission. In this paper we describe results of second-order fluorescence intensity correlation function g (2) (τ) measurements from individual CdSe-OPV nanostructures to definitively assess the multiexcitonic character of the emission from these species. Our results point to a weak multiexcitonic character (g (2) (0) ≈ 0.2) under 405 nm excitation where both the organic ligand and quantum dot absorb. Using 514.5 nm excitation, where the ligand absorption is negligible, the quantum dot emission is completely antibunched (g (2) (0) ≈ 0.05), similar to that of ZnS-capped CdSe control samples. These results provide new insights into to the mechanism of intensity flickering and electronic interactions in composite quantum dot/conjugated organic composite systems.
