Dresden 2011 – scientific programme

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MO: Fachverband Molekülphysik

MO 11: Poster: Transport and Spectroscopy in Molecular Nanostructures (Intersectional Session with CPP)

MO 11.1: Poster

Tuesday, March 15, 2011, 18:00–20:00, P1

Structure and Spectroscopy of Perylene Bisimide Aggregates — David Ambrosek, •Sergey Bokarev, and Oliver Kühn — Institut für Physik, Universität Rostock, Germany

Perylene bisimides (PBIs) are excellent dyes and versatile building blocks for supramolecular structures. Only recently have PBIs been shown to depict absorption characteristics specific to J-aggregates. In contrast to the exciton trapping observed in H-aggregates, these systems could potentially be used in transferring energy captured from the sunlight to artificial reaction centers. We apply electronic structure calculations to investigate monomeric and aggregate geometries as well as electronic properties in gas phase.

The PBI monomeric excitation spectrum has been assigned based on time-dependent Density Functional Theory (DFT) calculations for the geometry-optimized electronic ground state structure. The two lowest π−π^* type transition at 582 nm and 453 nm are found to be in excellent agreement with experiment. A shoulder in the experimental spectrum around 550 nm is assigned to result from a vibrational progression involving several vibrational normal modes. The electronic coupling within a dimer is analyzed in terms of a supermolecule approach, paying attention to the influence of charge transfer states, as well as using monomeric transition densities. Dimer and hexamer structures are also discussed on the basis of the dispersion-corrected tight-binding DFT method.