Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 5: Organic Thin Films
DS 5.4: Vortrag
Montag, 25. Februar 2008, 18:30–18:45, H 2013
Exciton-phonon coupling in rubrene thin films — •Milan Kytka1,2, Linus Gisslen3, Alexander Gerlach1, Jaroslav Kováč2, Reinhard Scholz3, and Frank Schreiber1 — 1Institut für Angewandte Physik, Auf der Morgenstelle 10, 72076 Tübingen — 2Faculty of Electrical Engineering and Information Technology, Slovak University of Technology in Bratislava — 3Walter Schottky Institut, Technische Universität München
We investigate the absorption spectra of amorphous rubrene thin films (thickness ∼30 nm) and rubrene molecules in solution using spectroscopic ellipsometry and UV-VIS spectroscopy, respectively. We evaporated purified rubrene material under UHV conditions and measured the optical constants n+ik in-situ. Both for the solution and the thin films, we find a well-defined vibronic progression of the S0–S1 transition of rubrene, because of the small orbital overlap of the π-electrons in the tetracene backbone with the four phenyl groups. We present a detailed data analysis for the progression of the vibronic transitions in the thin film and in the solution. Employing the model of displaced harmonic oscillator we obtain the characteristic parameters of the first absorption band. Using B3LYP/DZ (DFT) calculations we find good agreement with the experimental data. We find that the variation of the electronic and vibrational energy as well as the slightly higher electron-phonon coupling may be assigned not only to intermolecular interactions, but also to a different conformation of the molecule in the thin film phase.