Plenarvorträge - DPG-Tagungen

Chemische Physik und Polymerphysik Dienstag
ize the resulting material. A commercial FCS system has been modified
to permit FCS measurements in volatile organic solvents. FCS was used
to determine the molecular weight dependence of the diffusion coefficient
of 10 nM solutions of end-labelled polystyrenes in toluene. The data is
ultilized to establish a calibration procedure for FCS measurements in
organic solvents.
CPP 16.33 Di 17:00 B
Confocal Raman Spectroscopy of Ruthenium Dyes and their
Application in Organic Solar Cells — •Carmen Pérez León 1 ,
Lothar Kador 1 , Bin Peng 2 , and Mukundan Thelakkat 2 —
1 University of Bayreuth, Institute of Physics and Bayreuther Institut
für Makromolekülforschung (BIMF), 95440 Bayreuth — 2 University
of Bayreuth, Makromolekulare Chemie I and Bayreuther Institut für
Makromolekülforschung (BIMF), 95440 Bayreuth
With confocal Raman spectroscopy we investigated a new Ru dye (Ru-
TPA2) and compared it with a similar commercial compound (N179).
We measured the spectra of the dyes in powder, in solution, and in a
solution containing silver nanoparticles to obtain surface enhancement
effects (SERS). Since we are interested in the performance of the dyes in
solid-state organic solar cells, we recorded their signals when they were
chemisorbed on TiO2 nanoparticles and contained in the complete photovoltaic
cells. In the latter case, to identify characteristic Raman lines
and assign them to specific compounds, we also measured the spectra of
cells, in which only part of the constituents were present. The spectra
show some peaks which indicate the formation of new chemical bonds
between the constituents.
CPP 16.34 Di 17:00 B
Fluorescence Lifetime Investigations of DNA mediated
Dye/Gold Nanoparticle Conjugates — •M. Ringler 1 , E.
Dulkeith 1 , T. Niedereichholz 1 , T. A. Klar 1 , and J. Feldmann
1 , A. Munoz-Javier 2 , and W. J. Parak 2 — 1 Photonics and
Optoelectronics Group, University of Munich — 2 CeNS, University of
Munich
Gold nanoparticles have been shown to be extremely efficient quenchers
of luminescence from dye molecules attached to their surface [1]. In the
present study we investigated how the quenching efficiency depends on
the distance between the dye molecule and the nanoparticle using carbon
chain spacers of different lengths. An increase of the fluorescence lifetime
with spacer length is observed.
In a subsequent experiment we replaced the carbon spacers with single
stranded oligonucleotides (ssDNA). We can spectroscopically determine
the number of ssDNA bound to a nanoparticle. Varying the degree
of ssDNA coverage we observe that the fluorescence lifetime becomes
significantly longer when the number of ssDNA per nanoparticle is increased.
This gives evidence that the conformation of DNA bound to
gold nanoparticles changes from wrapped to stretched when the surface
coverage is increased [2].
[1] E. Dulkeith et al., Phys. Rev. Lett. 89, 203002 (2002)
[2] W. J. Parak et al., Nano Letters 3, 33-36 (2003)
CPP 16.35 Di 17:00 B
Optical microresonators formed by cholesteric liquid crystals —
•Jürgen Schmidtke 1 , Werner Stille 1 , and Heino Finkelmann 2
— 1 Physikalisches Inst., Albert-Ludwig-Universität, Freiburg — 2 Inst.
für Makromolekulare Chemie, Albert-Ludwig-Universität, Freiburg
Due to the periodic helical order of the mesogens, cholesteric liquid
crystals (CLCs) act as polarization-sensitive, one dimensional photonic
crystals. Indeed, modified fluorescence as well as photonic band edge lasing
of dye doped CLCs has been repeatedly demonstrated.
In an analytical treatment[1], we discuss different ways to realize
cholesteric optical microresonators by introducing artficial defects in the
helical molecular order. A conventional defect can be realized, if one interrupts
the cholesteric helix by an optically isotropic defect layer: the defect
layer acts as the resonator cavity, which is sandwiched between dielectric
mirrors formed by the cholesteric medium. A unique photonic defect can
be realized in a CLC by an abrupt phase jump in the cholesteric helix
(‘twist defect’[2]). A combination of defect layer and twist defect allows
for an independent tuning of resonance frequency and resonator quality.
We discuss the optics of these defects and the drastic effect of a finite
sample thickness on the polarization properties of the resonant modes,
and compare our findings with experimental results on the twist defect
mode laser emission[3] of a polymeric CLC film.
[1] J. Schmidtke and W. Stille, Eur. Phys. J. E (in press)
[2] V. I. Kopp and A. Z. Genack, PRL 89, 083902 (2002)
[3] J. Schmidtke, W. Stille, and H. Finkelmann, PRL 90, 083902 (2003)
CPP 16.36 Di 17:00 B
13 C-Knight-Verschiebung in Di- Naphthalin-Hexafluoroarsenat
(NA)2AsF6 — •A. Kaiser — Physikalisches Institut, Universität
Karlsruhe (TH), D-76128 Karlsruhe
Mit magnetischen Kernspinresonanzmessungen an 13 C-Kernen werden
Eigenschaften der Leitungselektronen im Radikalkationensalz (NA)2AsF6
charakterisiert. Die Leitungselektronen bewegen sich in diesem quasieindimensionalen
Leiter auf den Stapeln aus Naphthalinmolekülen
(C10H8). Messungen an den 13 C-Kernen der Naphthalinmoleküle zeigen
aufgrund der Hyperfeinwechselwirkung zwischen den Kernspins und den
Leitungselektronenspins in den Frequenzspektren Linien, die eine Knight-
Verschiebung aufweisen. Um eine Hochauflösung der 13 C- Festkörperspektren
zu erzielen, wurde als Messmethode eine Kombination aus der
Rotation unter dem magischen Winkel und einem Doppelresonanzverfahren
verwendet. Die Knight-Verschiebung der 13 C- Linien wurde bei
verschiedenen Temperaturen gemessen. Die auftretenden Linien im Frequenzspektrum
werden durch einen Vergleich mit theoretisch berechneten
Knight- Verschiebungen und durch eine Doppelresonanzmessung
mit verzögerter Entkopplung den einzelnen Kohlenstoffplätzen auf dem
Naphthalinmolekül eindeutig zugeordnet. Aus der Temperaturabhängigkeit
der Knight- Verschiebungen werden zusammen mit der ”lokalen” Leitungselektronensuszeptibilität
die Hyperfeinwechselwirkungskonstanten
bestimmt. Aus diesen lassen sich die Spindichten der Leitungselektronen
am Ort der Kohlenstoffatome ermitteln und somit kann die vollständige
Spindichteverteilung auf einem Naphthalinmolekül bestimmt werden.