title: Triplet-triplet annihilation in a series of poly(p-phenylene) derivatives.
abstract: 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) (PIF), 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, PIF, 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 0 K 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.
authors.affiliation: Experimental Physics II, University of Bayreuth, Bayreuth, Germany.
authors.forename: Sebastian T
authors.initials: ST
authors.lastname: Hoffmann
authors.forename: Jan-Moritz
authors.initials: JM
authors.lastname: Koenen
authors.forename: Ullrich
authors.initials: U
authors.lastname: Scherf
authors.forename: Irene
authors.initials: I
authors.lastname: Bauer
authors.forename: Peter
authors.initials: P
authors.lastname: Strohriegl
authors.forename: Heinz
authors.initials: H
authors.lastname: Bässler
authors.forename: Anna
authors.initials: A
authors.lastname: Köhler