Piland Geoffrey B, Bardeen Christopher J
Department of Chemistry, University of California, Riverside, Riverside, California 92506, United States.
J Phys Chem Lett. 2015 May 21;6(10):1841-6. doi: 10.1021/acs.jpclett.5b00569. Epub 2015 May 5.
The dependence of exciton dynamics on the crystalline morphology of tetracene is investigated using time-resolved photoluminescence. Single crystals exhibit relatively slow singlet decays with times that range from 130 to 300 ps depending on the sample. This decay has an activation energy of ∼450 cm(-1) over the temperature range of 200-400 K. Single-crystal samples also exhibit more pronounced quantum beats due to the triplet pair spin coherences. Polycrystalline thin films grown by thermal evaporation have singlet decay times on the order of 70-90 ps with a much weaker temperature dependence. Many thin-film samples also exhibit a red-shifted excimer-like emission. When a polycrystalline thin film is thermally annealed to produce larger crystal domains, single-crystal behavior is recovered. 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.
利用时间分辨光致发光研究了激子动力学对并四苯晶体形态的依赖性。单晶表现出相对较慢的单线态衰减，根据样品不同，衰减时间范围为130至300皮秒。在200 - 400 K的温度范围内，这种衰减的活化能约为450厘米−1。由于三重态对自旋相干性，单晶样品还表现出更明显的量子拍。通过热蒸发生长的多晶薄膜的单线态衰减时间约为70 - 90皮秒，温度依赖性要弱得多。许多薄膜样品还表现出红移的准分子样发射。当多晶薄膜进行热退火以产生更大的晶域时，会恢复单晶行为。我们推测，不同的动力学源于薄膜中单线态激子能够对具有加速单线态裂变的缺陷或堆积图案的区域进行采样。
