Excitonic and vibronic couplings in weakly bound molecular aggregates

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The theretical description of molecular aggregates often relies on the use of the individual components and their interactions. For large systems this is often the only viable approach which can, however, for smaller systems be complemented by a supermolecular approach, where the aggregate is considered as a whole. In the first funding period this combined strategy has been successfully employed to analyse - in cooperation with the experimental group of Prof. S. Leutwyler, Univ. Bern - the so-called quenching of the excitonic energy splitting in a series of hydrogen-bonded molecular dimers. In addition, for two systems the excitation spectra could be well reproduced in the whole spectral range. In the new funding period the investigations are to be extended to other systems with different types of interaction to explore the generality of the methods applied. This comprises systems with lower symmetry in the electronic ground or excited state and furthermore partially deuterated dimers where the overall symmetry is broken by the asymmetric distribution of the nuclear masses. As a new focus of the work, the impact of the quenching and vibronic interactions (vibrational excitation) on the transfer of the electronic excitation energy is to be investigated. This is expected to be slowed down by the quenching effect in question and also should exhibit a more complex time dependence owing to the simultaneous vibrational excitation. Both is to be confirmed and made more quantitative. Finally and if time permits, an extension to larger aggregates, especially trimers, shall be attempted.