Münster 1999 – wissenschaftliches Programm

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CP: Chemische Physik

CP 33: Poster: Dynamik molekularer Systeme

CP 33.1: Poster

Montag, 22. März 1999, 18:00–20:00, R52/R72

Solvent induced crossover of electron transfer mechanism in porphyrin complexes — •D. Kilin, U. Kleinekathöfer, and M. Schreiber — Institut für Physik, Technische Universität, D-09107 Chemnitz

Photoinduced processes in a supermolecular complex are calculated within the framework of the reduced density matrix theory. The complex consists of a zinc-porphyrin dimer (ZD) which is connected to a free-base porphyrin (FB) on one side and to an electron acceptor on another side. The optically created excitation of the ZD relaxes quickly to the FB and then decays by fluorescence to the ground state or, by an alternative reaction channel, with charge transfer (CT) back to the ZD and further to the acceptor. The equations of motion for these processes are solved numerically and approximately analytically. We obtain the the full kinetics of the system especially charge transfer rates as well as final populations which allow to characterize the quenching of the FB fluorescence and in this way to clarify the presence of CT. It is shown that moderate lowering the energy of the bridge molecule induced by altering the solvent (e. g. cyclohexane) gives only a quantitative change of reaction rates. By adding a more polar solvent (e. g. acetone) a crossover of the electron transfer mechanism from superexchange to a sequential one can be induced. In addition a strong polar solvent opens a new channel of decay to the ground state through a CT state of FB.