Photosciences and Photonics Section, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, Kerala 695 019, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India.
J Phys Chem B. 2022 Feb 10;126(5):1054-1062. doi: 10.1021/acs.jpcb.1c07951. Epub 2022 Feb 2.
The role of excimer formation in inhibiting or enhancing the efficiency of the intramolecular singlet fission (iSF) process has been a subject of recent debate. Here, we investigated the effect of excimer formation on iSF dynamics by modifying its configuration by connecting pentacenes at various positions. Hence, pentacene dimers having slip-stacked (, J-type), oblique (), and facial (, H-type) configurations were synthesized by covalently linking pentacenes at positions 2,2', 2,6', and 6,6', respectively, with an ethynyl bridge, and their ultrafast excited-state relaxation dynamics were characterized. Femtosecond time-resolved transient absorption spectra revealed that the efficiency of iSF dynamics decreased from slip-stacked (182%) to oblique configuration (97%),whereas in the with facial configuration, strong electronic coupling led to the formation of excimers that decayed nonradiatively without formation of correlated triplet pairs. These studies reveal the formation of excimers by strong intrapentacene electronic coupling upon ultrafast excitation, preventing the efficient iSF process.
激基缔合物的形成在抑制或增强分子内单重态裂变（iSF）过程的效率方面的作用一直是最近争论的主题。在这里，我们通过连接五并苯在不同位置来改变其构型，研究了激基缔合物形成对 iSF 动力学的影响。因此，通过在位置 2、2'、2、6'和 6、6'处用乙炔桥键将五并苯共价连接，合成了具有滑移堆积（，J 型）、斜交（）和面对面（，H 型）构型的五并苯二聚体，并对其超快激发态弛豫动力学进行了表征。飞秒时间分辨瞬态吸收光谱表明，iSF 动力学的效率从滑移堆积（182%）降低到斜交构型（97%），而在具有面对面构型的 中，强的分子内电子耦合导致激基缔合物的形成，而没有形成相关的三重态对，激基缔合物通过超快激发形成非辐射衰减。这些研究揭示了激基缔合物的形成通过五并苯内的强电子耦合来阻止有效的 iSF 过程。
