Steady-state and time-resolved photophysical studies are performed with freshly prepared nanoaggregates (Bi-An NA) and vapor-deposited thin films (Bi-An TF) of 9,9′-bianthracene (Bi-An) for the comparative study of excitonic processes. It is monitored that the Bi-An NA sample possesses broad emission, having contribution from the excitonic and long-lived excimeric states, while the Bi-An TF sample shows an emission feature dominated by singlet excitonic states. The ultrafast transient absorption studies carried out for both the nanoaggregate and thin film show excitation intensity-dependent decay kinetics for the initial delay time (<25 ps). The flounce-dependent decay kinetics were fitted to extract the excitonic diffusion parameters. It is observed that the thin film has more packing irregularity, resulting in slow exciton diffusion and shorter exciton diffusion length as compared to that of the nanoaggregate. The flounce-dependent transient absorption measurements also show the signature of triplet exciton formation as an auxiliary product of the singlet–singlet exciton annihilation process for both the samples. It is the first report to show such a phenomenon and deserves ample attention of the scientific community dealing with fast triplet exciton formation via the singlet exciton fission process.

中文翻译：

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9,9'-联蒽纳米聚集体和薄膜中激子动力学的比较研究：单线态-单线态湮没介导的三线态激子形成的观察

使用新制备的纳米聚集体 (Bi-An NA) 和 9,9'-联蒽 (Bi-An) 的气相沉积薄膜 (Bi-An TF) 进行稳态和时间分辨光物理研究，以比较研究激子过程。据监测，Bi-An NA 样品具有广泛的发射，受激子和长寿命准分子态的贡献，而 Bi-An TF 样品显示出以单重激子态为主的发射特征。对纳米聚集体和薄膜进行的超快瞬态吸收研究显示了初始延迟时间 (<25 ps) 的激发强度依赖性衰减动力学。拟合绒毛依赖衰减动力学以提取激子扩散参数。观察到薄膜具有更多的堆积不规则性，与纳米聚集体相比，激子扩散速度慢，激子扩散长度更短。与绒毛相关的瞬态吸收测量还显示了三重态激子形成的特征，作为两个样品的单重态 - 单重态激子湮灭过程的辅助产物。这是第一个显示这种现象的报告，值得科学界充分关注通过单重态激子裂变过程处理快速三重态激子形成。