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Faculty for Biology, Chemistry, and Earth Sciences

Macromolecular Chemistry I:

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Hoffmann, S.; Koenen, J.-M.; Scherf, U.; Bauer, I.; Strohriegl, P.; Bässler, H.; Köhler, A.: Triplet-Triplet Annihilation in a Series of Poly(p-phenylene) Derivatives, Journal of Physical Chemistry B, 115(26), 8417-8423 (2011) -- DOI: 10.1021/jp202763e
We have studied the temperature dependence of phosphorescence (Ph) and delayed fluorescence (DF) in two series of poly(p-phenylene) derivatives within a temperature range from 10 to 300 K under quasi-stationary conditions. One set of materials consists of the dimer, trimer, and polymer of ethylhexyl-substituted poly(fluorene) (PF2/6) and thus allows US to assess the effects of oligomer length. The second series addresses the influence of energetic disorder and conjugation length by being composed of the polymers alkoxy-substituted poly(p-phenylene) (DOO-PPP), poly(indenofluorene) (PIP), and ladder-type poly(p-phenylene) (MeLPPP). Under low light intensities, the DF features a maximum at a certain temperature T(max). For the dimer and trimer, the T(max) coincides with the temperature at which the phosphorescence has decayed to 1/2 of the value at 10 K, while T(max) shifts to lower temperature values along the series DOO-PPP, PIP, and MeLPPP and approaches T = 0 K for MeLPPP. By applying conventional kinetic equations we show that the occurrence of a maximum in the DF intensity is the consequence of generalized thermally activated triplet exciton transport toward quenching sites. We find the quenching rates at OK to be in the range of 1 s(-1) for the polymers, while they are more than an order of magnitude lower for the oligomers.
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