The research that will be presented will discuss how exciton dynamics in tetracene depend on crystal morphology with an emphasis on the singlet fission processes. Two different sample types are studied using time-resolved photoluminescence, single crystals and polycrystalline thin films. The single crystal samples exhibit photoluminescence decays that range from 130 to 300ps depending on the sample. Polycrystalline thin films show decays which are on the order of 70-90ps. Along with this change in fluorescence dynamics at room temperature, we found that the decay of the single crystals show an activation energy of ~450cm<sup>-1</sup> over the temperature range of 200-400K whereas the polycrystalline sample’s decay only has an activation energy of ~50cm<sup>-1</sup>. We observe more pronounced oscillations in the photoluminescence decay of the single crystal, which are attributed to triplet pair spin coherences. Thin-films also exhibit a red-shifted excimer-like emission which the single crystal does not show. We found that it was possible to recover the behavior of single-crystal samples by annealing the thin films at ~350K for 30minutes. We hypothesize that the different dynamics arise from the ability of singlet excitons in the thin films to sample regions with defects or packing motifs that accelerate singlet fission.

How singlet fission depends on crystal morphology

251st National Meeting (2016)

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