Dresden 2009 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 44: Organic semiconductors I
HL 44.4: Talk
Thursday, March 26, 2009, 11:30–11:45, POT 51
Electronic Spectroscopy of Organic Semiconductors in Helium Nanodroplets — •Matthieu Dvorak1, Oliver Bünermann1, Frank Stienkemeier1, and Alexander Eisfeld2 — 1Physikalisches Institut, Universität Freiburg, Hermann-Herder Str. 3, D-79104 Freiburg — 2MPI-PKS, Nöthnitzer Str. 38, D-01187 Dresden
Spectroscopy of molecules or molecular complexes embedded in helium nanodroplets is an outstanding tool to characterize electronic and geometric structures. Due to the unique properties of the superfluid droplets, helium nanodroplets isolation (HENDI) spectroscopy reaches far better spectral resolution than usually obtained in organic solvents or on thin films.
We applied HENDI to investigate the absorption and emission spectra of the PTCDA molecule and its complexes. The PTCDA monomer shows sharp vibronic lines (<1 cm-1) that can be assigned to different internal vibration modes as well as overtones and combination modes. PTCDA complexes show different spectral features. Sharp lines, red shifted compared to the monomer absorptions are assigned to T-structured dimers. Additionally, very broad absorption lines are observed. These are assigned to complexes forming sandwich structures [1]. Recent theoretical calculations can reproduce the spectra and support this interpretation. Furthermore, in comparison to absorption spectra, emission intensities allow to study the amount of internal relaxation before emitting a photon, giving further insight into the involved processes.
[1] M. Wewer and F. Stienkemeier, Phys. Rev. B 67, 125201, 2003