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CPP: Chemische Physik und Polymerphysik

CPP 18: Physics of polymers II

CPP 18.5: Vortrag

Dienstag, 8. März 2005, 12:15–12:30, TU C130

Optical absorption spectra of linear and cyclic thiophenes, selection rules manifestation — •Mariusz Bednarz and Peter Reineker — Abteilung Theoretische Physik, Universität Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany

Recently a series of oligothiophenes with well defined chain lengths have been synthesized and chain lengths up to 96 thiophene units have been achieved by the stepwise addition of definite repeat units. Such materials are not polydisperse and a strong dependence of the electronic properties on the chain length is observed. In addition a series of fully conjugated macrocyclic structures, based on the same repeat units, have been synthesized: cyclo[n]thiophenes and cyclo(oligothiophenediacetylenes). The absorption spectra for the oligothiophenes and the cyclothiophenes show a systematic redshift with increasing number of thiophene units. Also the absorption line position of a given oligothiophene corresponds to the line position of the cyclothiophene with the doubled number of repeat units. In our theoretical approach we consider the local ground and the relevant local excited state of a repeat unit as a local two level system. The electronic excitations are described as Frenkel excitons. The conjugation between the units is taken into account by transfer integrals. From the corresponding model Hamiltonian we derive the redshift mentioned above and by taking into account selection rules the relation between the spectra of the oligothiophenes and cyclothiophenes is explained [1]. [1] M. Bednarz, P. Reineker, E. Mena-Osteritz, and P. Bäuerle, J. Lumin., in press.