Temperature dependence of the exciton dynamics in DCM2:Alq3

We study the temperature dependence of the triplet and singlet exciton dynamics in the archetype small molecule fluorescent guest-host system tris(8-hydroxyquinolinato) aluminum (Alq3) doped with 4-(dicyanomethylene)-2methyl- 6-julolidyl-9-enyl-4H-pyran (DCM2). We develop a comprehensive model of the exciton dynamics, and use it to fit the transient photoluminescence under different pulsed optical pumping in the temperature range of 80 < T < 295 K. The triplet decay has a significantly different temperature dependence than that of singlets. From 295 to 80 K, the triplet-triplet annihilation (TTA) rate decreases by two orders of magnitude, whereas the singlet-triplet annihilation rate decreases by < 50%, primarily a result of the different energy transfer mechanisms of singlets and triplets. The temperature dependence of the TTA rate reveals two regimes separated by a transition at 180 K from Marcus to Miller-Abrahams transfer. This work deepens our understanding of exciton dynamics and energy transfer in small molecule organic materials.