Simultaneous determination of the adsorption constant and the photoinduced electron transfer rate for a Cds quantum dot - Viologen Complex

Adam J. Morris-Cohen, Matthew T. Frederick, Laura C. Cass, Emily A. Weiss

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Transient absorption (TA) spectroscopy of solution-phase mixtures of colloidal CdS quantum dots (QDs) with acid-derivatized viologen molecules, N-[1-heptyl],N′-[3-carboxypropyl]-4,4′-bipyridinium dihexafluorophosphate (V2+), indicates electron transfer occurs from the conduction band of the QD to the LUMO of V2+ after photoexcitation of a band-edge exciton in the QD. Analysis of the magnitude of the ground state bleach of the QD as a function of the molar ratio QD:V 2+ yields the QD - ligand adsorption constant, Ka (4.4 × 104 M-1) for V2+ ligands adsorbed in geometries conducive to electron transfer. The value of Ka, together with the measured rates of (i) formation of the V+• electron transfer product and (ii) recovery of the ground state bleach of the QD, enables determination of the intrinsic rate constant for charge separation, k CS,int ∼ 1.7 × 1010 s-1, the rate for a single QD - V2+ donor - acceptor pair. This analysis confirms previous reports that the number of ligands adsorbed to each QD is well-described by a Poisson distribution. This is the first report where the QD - ligand charge transfer and binding equilibria are quantitatively investigated simultaneously with a single technique.

Original languageEnglish
Pages (from-to)10146-10154
Number of pages9
JournalJournal of the American Chemical Society
Issue number26
Publication statusPublished - Jul 6 2011


ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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