Non-approximative Kinetics of Triplet-Triplet Annihilation at Room Temperature: Solvent Effects on Delayed Fluorescence

The molecular processes taking place during triplet-triplet annihilation (TTA) in solvents at room temperature are examined in detail. Special attention is paid to modelling of the nonlinear kinetic reactions. Using time- and spectrally resolved spectroscopy of DPA and Pt/Pd-OEP based sensitizer and annihilators, it is shown how the kinetic of parameters, such as the triplet energy transfer (TET) and TTA of the rate-reactions, can be simulated, measured and fitted, without approximations, using a numerical scheme. Studies of DPA in the solvents DMSO, THF and toluene at room temperature revealed that viscosity/diffusion together with the excited triplet lifetime of the annihilator are the most crucial parameters for high TTA induced delayed fluorescence. From an analysis of the experimentally determined rates an efficiency of 16-40 % was determined for the combined TET and TTA processes using THF, DMSO and toluene as solvents. (DPA=9,10-diphenylanthracene, OEP=2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin)