Berlin 2008 – scientific programme

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 4: Organic Devices II

SYSA 4.5: Talk

Tuesday, February 26, 2008, 17:45–18:00, H 2013

Magnetic field effects on the triplet-polaron quenching in Ir(III)-complexes — Alex Thiessen, •Dirk Hertel, and Klaus Meerholz — Institute of Physical Chemistry, University of Cologne, Luxemburger Str. 116, 50939 Cologne, Germany

Recently [1], we reported a study of phosphorescence quenching in polyspirobifluorene doped with the phosphorescent emitter platinum-porphyrin (PtOEP). It was shown that the phosphorescence reduction is due to the interaction of triplet excitons with charges (polarons) in a unipolar diode structure. The rate constant for triplet-polaron interaction has been evaluated to be 10-13 cm3/s leading to an interaction radius of 0.2 nm. In our current work we have used the methodology [1] to elucidate the role of this process in materials relevant to phosphorescent OLEDs. We have studied a red-emitting Ir(III)-complex doped into low molecular weight materials and in polymers. It will be shown, that the efficiency of triplet-polaron annihilation depends mostly on the nature of the matrix and not on the structure of the heavy-metal complex. The results give insight to a possible origin of the magneto-resistance effects in organic materials [2]. Recently [3], it has been proposed that triplet-polaron annihilation might play a crucial role. We will discuss the influence of magnetic fields on the triplet-polaron annihilation for our model system.

References [1] Hertel, D.; et al. J. Phys. Chem. B 2007, 111, 12075. [2] Mermer, O.; et al. Phys. Rev. B 2005, 72, 202202. [3] Desai, P.; et al. Phys. Rev. B 2007, 75, 094423.