Bayliss Sam L, Kraffert Felix, Wang Rui, Zhang Chunfeng, Bittl Robert, Behrends Jan
Berlin Joint EPR Lab, Fachbereich Physik , Freie Universität Berlin , D-14195 Berlin , Germany.
National Laboratory of Solid State Microstructures, School of Physics , Nanjing University , Nanjing 210093 , China.
J Phys Chem Lett. 2019 Apr 18;10(8):1908-1913. doi: 10.1021/acs.jpclett.9b00356. Epub 2019 Apr 5.
Tetracene is an archetypal material undergoing singlet fission-the generation of a pair of triplet excitons from one singlet exciton. Here, using time-resolved electron spin resonance, we show how the spin dynamics in tetracene crystals are influenced by temperature and morphology. Upon cooling from 300 to 200 K, we observe a switch between singlet fission and intersystem crossing generated triplets, manifesting as an inversion in transient spin polarization. We extract a spin dephasing time of approximately 40 ns for fission-generated triplets at room temperature, nearly 100 times shorter than the dephasing time that we measure for triplets localized on isolated tetracene molecules. These results highlight the importance of morphology and thermal activation in singlet fission systems.
并四苯是一种典型的经历单重态裂变的材料，即从一个单重态激子产生一对三重态激子。在此，我们利用时间分辨电子自旋共振，展示了并四苯晶体中的自旋动力学如何受到温度和形态的影响。从300 K冷却至200 K时，我们观察到单重态裂变和系间窜越产生的三重态之间的转换，表现为瞬态自旋极化的反转。我们测得室温下裂变产生的三重态的自旋退相时间约为40 ns，比我们测量的孤立并四苯分子上的三重态的退相时间短近100倍。这些结果突出了形态和热激活在单重态裂变系统中的重要性。
