Regensburg 2019 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 37: Poster Session III

CPP 37.32: Poster

Mittwoch, 3. April 2019, 11:00–13:00, Poster B1

Polarisation anisotropy in organic guest-host systems — •Felix Höhnle, Thomas Morgenstern, and Wolfgang Brütting — Institute of Physics, University of Augsburg, 86135 Augsburg, Germany

Exciting dye molecules with linearly polarised light leads to an anisotropic excited state population of the emitters’ transition dipole moments (TDMs). Depending on different depolarisation effects before light emission –such as rotational diffusion (mostly in solutions), intra- and intermolecular exciton migration or conformational changes of molecules– the emitted light can also be partly polarised. The extent of the latter is quantified by the anisotropy value r. It relates the intensities emitted with polarisation parallel and perpendicular with respect to the polarisation of the exciting light.

In this work we probed thin solid films of commonly used organic emitters doped into a matrix. It could be shown that polarisation anisotropy can be increased by decreasing the dye concentration in the guest-host system, which must be due to reduced intermolecular exciton transfer since no other processes should be present in a solid film. Depending on the exact material, values close to the theoretical maximum of r=0.4 were reached. Additionally, we see that excess energy of excitons affects the migration process and thus the anisotropy.

The above effect can also influence TDM orientation measurements which aim to improve device efficiencies. At low dye concentrations, the hindered equilibration of excitons to all orientations upon light emission can lead to erroneous (pseudo-horizontal) orientation values.