Plenarvorträge - DPG-Tagungen

Symposium Organic and Hybrid Systems for Future Electronics Donnerstag
SYOH 5.87 Do 18:00 B
Photophysical properties of core substitution at perylene
derivates — Harald Graaf 1 , Christine Mattheus 2 , Derck
Schlettwein 2 , Gottfried Heinrich Bauer 1 , •Harald Graaf 1 ,
Christine Matth eus 2 , Derck Schlettwein 2 , and Gottfried
Heinrich Bauer 1 — 1 Inst. of Physics, CvO University Oldenburg —
2 Dept. of Pure and Applied Chemistry, CvO University Oldenburg
Chemical substitution in bay-position at perylene tetra carboxylic acid
derivates (PTCD) e.g. by chlorine substitution leads to a twisting of the
aromatic core and as a consequence influences the photophysical properties
especially in the solid state. Unlike the unsubstituted PTCD, however,
thin films (≈ 30nm) of the bay-chlorinated Cl4PTCD showed almost
no chromophore coupling, directly measured by optical absorption
spectroscopy. The formation of excimers is prevented so that an emission
from uncoupled monomers could be found in a quantum efficiency
comparable to that in solution. Also the arrangement of the molecules
in the film is influenced by the hindered coupling which was seen in an
unstructured morphological configuration measured by AFM. In thicker
films (≥ 100nm) a slow ordering process was observed and an excimer
formation could be obtained. More over we have prepared monolayers of
substituted molecules by covalent bounding at a modified glass surface
in order to study two- dimensional intermolecular interactions.
SYOH 5.88 Do 18:00 B
Structural and Optoelectronic Properties of Different Phases
of the Electroluminescent Material Alq3 — •Michael Cölle 1 ,
Christoph Gärditz 1 , Jürgen Gmeiner 1 , Stefan Forero 1 , and
Wolfgang Brütting 1,2 — 1 Experimental Physics II, University of
Bayreuth, 95440 Bayreuth, Germany — 2 Experimental Physics IV, University
of Augsburg, 86135 Augsburg, Germany
Tris(8-hydroxyquinolinato)aluminium(III) (Alq3) stands as one of the
most successful materials used in OLEDs for display applications. Although
the partly nanocrystalline character of evaporated films used in
these applications is known, so far comparatively few investigations have
been devoted to the crystalline state of this material. Another still unresolved
issue concerns the isomery of the Alq3 molecule. From theory
is well-known that Alq3 can occur in two different geometrical isomers:
meridional and facial. However, until recently all existing phases ( α, β
and γ) have been found to consist of the meridional isomer. Recently we
have reported a new crystalline phase of Alq3 (δ-Alq3) exhibiting strongly
blue-shifted fluorescence. Its significantly different optical properties have
been tentatively discussed in terms of the isomery of the Alq3 molecule.
In this contribution we will present an in-depth characterisation of the
different phases of Alq3 by combining thermal, structural and vibrational
analysis. These data provide the first unambigous evidence for the existence
of the facial isomer in the blue-luminescent δ-phase of Alq3. These
results will be correlated to the optoelectronic properties of Alq3 and
Alq3-based thin film electroluminescent devices.
SYOH 5.89 Do 18:00 B
EPR spectroscopy on different phases of electroluminescent
Alq3 — •A. Mirea 1,2 , M. N. Grecu 2 , M. Cölle 1 , and M.
Schwoerer 1 — 1 Experimentalphysik II, Universität Bayreuth,
D-95440 Bayreuth — 2 National Institute for Materials Physics, R-76900
Bucharest, Romania
Tris(8-hydroxyquinolino)aluminum (Alq3) is one of the most extensive
used electron conductor and emitting layer material in organic lightemitting
devices (OLED’s). We report on X- and Q-band temperature
dependence EPR experiments on different crystalline Alq3 phases formed
by using the train sublimation method. The room temperature X-band
EPR spectra show two types of signals centered at g=2 and g=4 whose
relative intensity are dependent on the crystalline phase nature. The g=2
signal is of a very particular nature - its intensity is temperature independent
between 10-300 K for all phases, and increases of 4-6 times under
room temperature e − - or γ-irradiation. By choosing appropriate annealing
conditions (663-673 K temperature range, inert atmosphere) of as
prepared Alq3 phases, new features in the Q-band EPR spectra appear.
Their simulation and analysis based on a spin Hamiltonian appropriate
to a high spin system (S =1, S=3/2) is in good agreement with the existence
of triplet and quartet spin states in annealed Alq3. The D and
E zero field parameters are evaluated. The EPR results, correlated with
others investigation methods, are discussed in terms of different molecular
models.
SYOH 5.90 Do 18:00 B
Origin of delayed fluorescence in conjugated polymers — •Dirk
Hertel 1 and Chan Im 2 — 1 Institute of Physical Chemistry, University
of Cologne, Luxemburger Str. 116, 50939 Cologne, Germany — 2 Max-
Planck Institute for Polymer Research, Ackermannweg 10, 55021 Mainz,
Germany
We report on measurements of phosphorescence (Ph) and delayed
fluorescence (DF) in poly(2,7-(9,9-bis(2-ethylhexyl)fluorene)) (PF2/6)
present as dilute solid solution as well as in bulk films. From combined
experimental investigations of the time and intensity dependence of DF
and Ph as well as the temperature dependence of DF we are able to show
that DF in PF2/6 both in solution and film is dominated by triplet-triplet
annihilation (TTA). As a consequence of the intra-chain diffusion and,
hence, relaxation of triplets, the kinetics of the bimolecular reaction show
a turn-over from dispersive to non-dispersive regime as borne out by the
DF decay. This in accord with theoretical predictions of TTA in disordered
solids.
The dominance of TTA as source of DF in PF2/6 films is in marked
contrast to the DF in MeLPPP, although the chemical structures of the
materials are similar. In MeLPPP geminate pair recombination is responsible
for DF. In order to understand the relation between chemical
structure and routes of DF generation we have investigated the delayed
fluorescence on the electron-accepting poly(9,9-dioctylfluorene-cobenzothiadiazole)
F8BT present as film and solid solution.
SYOH 6 Single Molecules and Molecular Clusters
Zeit: Freitag 10:15–11:15 Raum: H1
Hauptvortrag SYOH 6.1 Fr 10:15 H1
Growth control and optics of organic nanoaggregates — •Horst-
Günter Rubahn — Fysisk Institut, Syddansk Universitet, DK-5230
Odense M, Danmark
Nanoaggregates and ultrathin films made of organic molecules might
become integral parts of new electronic and optoelectronic devices due to
their interesting optical properties as well as their chemical and mechanical
flexibility. We present a new way to generate by a combination of
external control and self assembled growth well ordered, crystalline nanoscaled
structures (nanofibers and rings) of highly luminescent organic
materials (1). It is shown that microscopic growth control results in low
defect densities and thus strongly improved optical properties of these
aggregates. Since the nanofibers possess macroscopic lengths but nanoscaled
widths and heights they are ideal model systems for investigating
limitations and possibilities of optics on the nanoscale. This aspect is
exploited in the present talk via a combination of structural and morphological
sensitive methods such as low energy electron scattering and
atomic force microscopy with optical methods such as epifluorescence
microscopy, scanning near field microscopy and two-photon femtosecond
resolved spectroscopy. 1: F. Balzer and H.-G.Rubahn, Optics and Pho-
tonics News, 14(12), Dec.2003.
Hauptvortrag SYOH 6.2 Fr 10:45 H1
Electronic transport through single molecules — •H. v.
Löhneysen 1,2 , F. Heinrich 3 , M. M. Kappes 3 , R. Krupke 3 , M.
Major 3 , J. Reichert 3 , and H. B. Weber 3 — 1 Physikalisches
Institut, Universität Karlsruhe, 76128 Karlsruhe — 2 Forschungszentrum
Karlsruhe, Institut für Festkörperphysik, 76344 Karlsruhe —
3 Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76344
Karlsruhe
Electronic transport measurements through single π-conjugated
molecules can be realized using mechanically controlled break junctions
to couple thiol end groups of the molecules to two gold electrodes. We
have investigated transport through π-conjugated molecules which differ
by their spatial symmetry and π-conjugated connectivity. The current
voltage characteristics (IV s) of the metal-molecule-metal system reflect
the spatial symmetry and topology of the molecules with respect to the
direction of current flow indicating that transport occurs indeed through
single molecules [1]. Fluctuations in the IV s are a manifestation of the
variation of level spacings of the system, which depend crucially on the