Regensburg 2004 – scientific programme

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HL: Halbleiterphysik

HL 23: Organische Halbleiter

HL 23.8: Talk

Tuesday, March 9, 2004, 18:30–18:45, H13

Ultrafast Relaxation between Davydov Components in Crystalline N-N’-dimethyl-perylene-3,4,9,10-dicarboximide (MePTCDI) — •Marco Koschorreck, Egbert Engel, Karl Leo, and Michael Hoffmann — Institut für Angewandte Photophysik, TU Dresden, 01062 Dresden, Germany, www.iapp.de

We investigated polarization anisotropies in polycrystalline films of the organic semiconductor N-N’-dimethyl-perylene-3,4,9,10-dicarboximide (MePTCDI) by means of pump-probe and time-resolved luminescence measurements. The timescale of the observed processes range from tens of femtoseconds to several picoseconds.

On the shorter timescale (50 fs), the equilibration process of the initially differently populated Davydov components was observed. The textbook model for polarization anisotropies was extended to the case of two coupled Davydov components. Through this it is possible to predict the remaining anisotropy after this very fast relaxation process. The experimental results agreed well with the theoretical values. The behavior at longer timescales (100 ps) could be explained by exciton diffusion between randomly oriented crystallites. While crossing the crystallite boundaries, the excitons lose their polarization memory and the polarization anisotropy goes to zero. Temperature dependent measurements indicate an incoherent thermally activated hopping process.