Dresden 2006 – scientific programme

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HL: Halbleiterphysik

HL 31: Organic semiconductors

HL 31.2: Talk

Wednesday, March 29, 2006, 14:45–15:00, POT 51

Investigation of Frenkel and charge transfer (CT) states in PTCDA and MePTCDI crystals — •L. Gisslén, M. Schreiber, and R. Scholz — Institut für Physik, Technische Universität Chemnitz

In perylene derivatives like N,N^′-dimethyl-perylene-3,4,9,10-di-carboximide (DiMePTCDI) and 3,4,9,10-perylene tetracarboxylic dian-hydride (PTCDA), neutral molecular excitations and inter-molecular charge transfer occur in the same energetic range. Their mixing via electron and hole transfer has a strong impact on the photophysical properties, including e.g. the absorption lineshape, the minima of the excited state potential landscape resulting in various kinds of photoluminescence (PL) [1], and the decay routes between absorption and PL.
The optical transition energies and the transfer matrix elements are determined with Hartree-Fock-based methods and with time-dependent DFT applied to molecular dimers in a geometry compatible with the crystalline phase [2]. In mixed Frenkel-CT models for the photophysical properties, the degree of mixing between Frenkel and CT states can be related to their different energetic ordering in PTCDA and DiMePTCDI. The present approach is compared to a pure Frenkel exciton model [3] and a one-dimensional model for Frenkel-CT mixing [4].

[1] A. Yu. Kobitski, R. Scholz, H.P. Wagner, and D. R. T. Zahn, Phys. Rev. B 68, 155201 (2003).

[2] R. Scholz, A. Yu. Kobitski, D. R. T. Zahn, and M. Schreiber, Phys. Rev. B (2005) accepted.

[3] I. Vragović and R. Scholz, Phys. Rev. B 68, 155202 (2003).

[4] M. Hoffmann and Z. G. Soos, Phys. Rev. B 66, 024305 (2002).