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CPP: Chemische Physik und Polymerphysik
CPP 4: SYMPOSIUM Materials for Molecular Electronics
CPP 4.3: Talk
Monday, March 24, 2003, 15:30–16:00, ZEU/160
Emissive defects in conjugated polymers: From exciton trapping to efficient electrophosphorescence — •John Lupton1, Alexander Pogantsch2, Thomas Piok2, Emil List2, Satish Patil3, and Ulli Scherf3 — 1Sektion Physik, Uni Muenchen — 2Uni Graz — 3Uni Wuppertal
On-chain chemical defects in conjugated polymers have previously been associated with luminescence quenching. Recently, however, it was demonstrated that oxidative defects in polyfluorene act as exciton traps and give rise to a broad emission red-shifted from the polymer backbone emission and characteristic of a fluorenone moiety. Using gated fluorescence spectroscopy this emission was clearly identified on isolated chains of pristine fluorene polymers and oligomers, suggesting that the previous assignment to an intermolecular excited state is inappropriate. Gated electroluminescence (EL) was also used to study the dynamics of charge trapping and delayed recombination on these defects. A further highly significant class of defects we have identified in conjugated polymers relate to metal impurities. We find that contamination of the polymer backbone with 80 ppm of covalently bound palladium atoms is sufficient to enable efficient room temperature electrophosphorescence. The diffusion of triplets to these sites also gives rise to extremely fast phosphorescence observable under optical excitation, without modifying the electronic structure or intersystem crossing of the material. Using time resolved EL spectroscopy with different bias offsets we can distinguish between delayed emission resulting from long lived neutral excitations and delayed pair recombination.