使用结构上定义良好的去甲酰基桥连的蒽二聚体来绘制单线态Fission中相关三重态形成的机理图
Using Structurally Well-Defined Norbornyl-Bridged Acene Dimers to Map a Mechanistic Landscape for Correlated Triplet Formation in Singlet Fission
摘要：
结构明确的TIPS-乙炔取代的并四苯（TIPS BT 1 '）和并五苯（TIPS BP 1'）二聚体利用[2.2.1]双环庚二酰基桥已被研究-主要使用时间分辨光谱方法-揭示有关单线态裂变的主要步骤的机制细节，导致形成双激子1 TT态以及衰变途径的基态。对于TIPS BP 1 '，在室温甲苯中，1 TT形成是快速和完全的，在4.4 ps内发生。在100 ns内衰减到基态是该系统中1 TT的主要损耗途径。对于TIPS BT 1 ′，也观察到1 TT快速形成（时间常数为5 ps），但在这种情况下，它与单重态激子S1在高于基态2.3 eV的能量处的激发态平衡（K~1）的建立相一致。平衡态存活36 ns，并通过辐射和非辐射途径通过S1和非辐射途径通过1 TT损失到基态。TIPS BT 1 '中1 TT形成的速度乍一看令人惊讶。然而，我们的分析表明，马库斯理论的几个参数的速率常数表达式解释了一组系统中的个人和比较结果，从而建立了非绝热耦合和重组所需的能量有效的1 TT形成的基准。最后，比较TIPS BT 1 '与以前的结果得到的一个密切的宪法异构体（TIPS-BT 1）不同的TIPS-乙炔侧基的位置表明，在相关的三重态歧管的交换相互作用的大小起着至关重要的作用，决定1 TT产率在tetracenic系统。
英文摘要：
Structurally well-defined TIPS-acetylene substituted tetracene (TIPS BT1') and pentacene (TIPS BP1') dimers utilizing a [2.2.1] bicyclic norbornyl bridge have been studied -primarily using time-resolved spectroscopic methods - to uncover mechanistic details about primary steps in singlet fission leading to formation of the biexcitonic 1TT state as well as decay pathways to the ground state. For TIPS BP1' in room temperature toluene, 1TT formation is rapid and complete, occurring in 4.4 ps. Decay to the ground state in 100 ns is the primary loss pathway for 1TT in this system. For TIPS BT1', the 1TT is also observed to form rapidly (with a time constant of 5 ps) but in this case it occurs in concert with establishment of an excited state equilibrium (K~1) with the singlet exciton state S1 at an energy of 2.3 eV above the ground state. The equilibrated states survive for 36 ns and are lost to ground state through both radiative and non-radiative pathways via the S1 and non-radiative pathways via the 1TT. The rapidity of 1TT formation in TIPS BT1' is at first glance surprising. However, our analysis suggests that the few-parameter rate constant expression of Marcus theory explains both individual and comparative findings in the set of systems, thus establishing benchmarks for diabatic coupling and reorganization energy needed for efficient 1TT formation. Finally, a comparison of TIPS BT1' with previous results obtained for a close constitutional isomer (TIPS-BT1) differing in the placement of TIPS-acetylene side groups suggests that the magnitude of exchange interaction in the correlated triplet manifold plays a critical role dictating 1TT yield in the tetracenic systems.
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