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Struktur und Dynamik Poster: Mi., 14:00–16:30 M-P144
Time-Resolved Structural Investigation of Excimer Evolution in Organic
Molecules
Henrik Till Lemke 1 , Tine Ejdrup 1 , Nerijus Rusteika 1 , Peter Hammershøj 1 ,
Theis Ivan Sølling 1 , Niels Harrit 1 , Klaus Bechgaard 1 , Robert
Feidenhans’l 1 , Martin Meedom Nielsen 1
1 Centre for Molecular Movies, Niels Bohr Institute, University of Copenhagen, Universitetsparken
5, DK-2100 Copenhagen Ø, Denmark
Excited aromatic molecules like pyrene, perylene and pentacene can relax to a short
lived (≈100 ps) excited dimer state (excimer) that decays radiatively. Although this
state is well characterised by time resolved optical spectroscopy the structural change
upon dimerization remains unknown. We employ pump laser probe X-ray experiments
in order to investigate structural changes during excimer evolution. X-ray pulses are
either obtained from Kα secondary radiation from a plasma source or as synchrotron radiation
from individual electron bunches at the ESRF. Using grazing incidence diffraction
on polycrystalline thin films we can achieve a high excitation density within the
probed volume and thus enhance the scattering signal. We have demonstrated a preferential
uniaxial alignment of crystallites along the substrate surface, resembling a
2D-powder, as well as bi-axial alignment on substrates with friction deposited PTFE
alignment layers. This enables us to take advantage of the grazing incidence scattering
geometry to enhance the scattering signal. Results for this first time-resolved structural
observations of transient excimers are reported.