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In-Depth Information
support the above discussed model [
178
], namely that we observe (see Fig.
4.34
)
a variation of the PL decay rates across the PL emission wavelength but without a
corresponding built-up component for PL (of, e.g., traps) with a time corresponding
to the PL decay time of energetically higher states [
118
]. More PL wavelength-
related experiments will be needed to definitely decide in favor of one of the models
or a combination of them. Nevertheless, both approaches are in agreement with
most of our findings related to various aspects of non-FRET quenching not only for
QD-Dye nanoassemblies but in general with related PL properties of QDs such as
blinking, non-exponential PL decay, influence of temperature, surfactant shell, and
environment.
Finally we would like to point out that properties of “QD-Dye” nanoassemblies
are not only interesting in themselves but also provide a valuable tool to study
surface-related phenomena in QDs on an extremely low level of surface modifica-
tion. Instead of investigating ligand dynamics directly, e.g. by NMR, we suggest to
make use of QD PL quenching in combination with appropriately functionalized dye
molecules. In contrast to NMR, this approach allows to investigate ligand dynamics
at extremely low modifications of surface properties.
Note added in proof
: In addition, recently, based on the combination of X-ray
absorption spectroscopy and ab initio calculations it has been demonstrated that
overcoating CdSe QDs with ligands of distinct end group functionalities manifests
itself in specific changes in the unoccupied electronic structure, particularly near
the bottom of the conduction band [
179
]. It should be noted that the ligands being
used in this study primarily affect unoccupied electronic states
3 eV above the
absorption edge rather than in the gap, as one might have predicted for surface
states. The calculated spectra indicate that the differences in absorbance associated
with changes in surface geometry and chemistry arise primarily due to variations in
the unoccupied surface states with
d
character.
>
Acknowledgments
This work was supported by Volkswagen Foundation (Priority Program
“Physics, Chemistry and Biology with Single Molecules”), DFG GRK 829/3 (“Accumulation
of single molecules to nanostructures”), German Academic Exchange Service (DAAD, grant
№
A/08/08573, EZ), Belarussian Foundation for Basic Research (grant
-005), Belarussian
State Program for Scientific Research “Convergence 3.2.08—Photophysics of Bioconjugates,
Semiconductor and Metallic Nanostructures and Supramolecular Complexes and Their Biomedical
Applications.”
Prof. E. Zenkevich thanks B.I. Stepanov Institute of Physics NAS, Minsk, Belarus and the
DFG FOR877 (“From local constraints to macroscopic transport”) for financial support.
The first experiments in 2002 have only been possible by providing CdSe/ZnS QDs by Dr.
A. Rogach (Ludwig-Maximilians-University Munich, Germany) and Dr. D. Talapin (University
of Hamburg, Germany) which are gratefully acknowledged. We also thank Dr. A. Shulga (B.I.
Stepanov Institute of Physics NAS, Minsk, Belarus) for the synthesis of all tetrapyrrole compounds
including monomers and chemical dimers and Prof. F. Wuerthner (Wuerzburg University) for
supplying all perylene diimide dyes.
We t hank
Dr. Habil. E. Sagun, Dr. A. Stupak, Dr. V. Knyukshto, Dr. V. Galievsky, A. Stasheuski, and
A. Yarovoi (B.I. Stepanov Institute of Physics NAS, Minsk, Belarus), who have performed many
experiments in Minsk or in Chemnitz,
№
·
10
´±
