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Distance-dependent Fluorescence Quenching and Binding of CdSe Quantum Dots by Functionalized Nitroxide Radicals.

Authors
  • C, Tansakul
  • E, Lilie
  • Ed, Walter
  • 3rd, Rivera F
  • A, Wolcott
  • Jz, Zhang
  • Glenn Millhauser
  • R, Braslau
Type
Published Article
Journal
The Journal of Physical Chemistry C
Publisher
American Chemical Society
Publication Date
Apr 25, 2010
Volume
114
Issue
17
Pages
7793–7805
Identifiers
DOI: 10.1021/jp1005023
Source
UCSC Aging biomedical-ucsc
License
Green

Abstract

Quantum dot (QD) fluorescence is effectively quenched at low concentration by nitroxides bearing amine or carboxylic acid ligands. The association constants and fluorescence quenching of CdSe QDs with these derivatized nitroxides have been examined using electron paramagnetic resonance (EPR) and fluorescence spectroscopy. The EPR spectra in the non-protic solvent toluene are extremely sensitive to intermolecular and intramolecular hydrogen bonding of the functionalized nitroxides. Fluorescence measurements show that quenching of QD luminescence is nonlinear, with a strong dependence on the distance between the radical and the QD. The quenched fluorescence is restored when the surface-bound nitroxides are converted to hydroxylamines by mild reducing agents, or trapped by carbon radicals to form alkoxyamines. EPR studies indicate that photoreduction of the nitroxide occurs in toluene solution upon photoexcitation at 365 nm. However, photolysis in benzene solution gives no photoreduction, suggesting that photoreduction in toluene is independent of the quenching mechanism. The fluorescence quenching of QDs by nitroxide binding is a reversible process.

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