Using Structurally Well-Defined Norbornyl-Bridged Acene Dimers to Map a Mechanistic Landscape for Correlated Triplet Formation in Singlet Fission
Using Structurally Well-Defined Norbornyl-Bridged Acene Dimers to Map a Mechanistic Landscape for Correlated Triplet Formation in Singlet Fission
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DOI：
10.1021/jacs.9b00904
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发表时间：
2019-04-10
影响因子：
15
通讯作者：
Damrauer, Niels H.
中科院分区：
文献类型：
--
作者：
Gilligan, Alexander T.;Miller, Ethan G.;Damrauer, Niels H.
利用[2.2.1]双环庚二酰基桥的结构明确的TIPS-乙炔取代的TIPS并四苯（TIPS-BT 1 '）和并五苯（TIPS-BP 1'）二聚体已经被研究-主要使用时间分辨光谱方法-以揭示导致双激子（TT）-T-1态形成的单线态裂变的主要步骤以及到基态的衰变途径的机理细节。对于室温甲苯中的TIPS-BP 1 '，（TT）-T-1形成是快速和完全的，在4.4ps内发生。在100 ns内衰减到基态是（TT）-T-1在该系统中的主要损耗途径。对于TIPS-BT 1 ′，也观察到（TT）-T-1迅速形成（时间常数为5 ps），但在这种情况下，它与在基态以上2.3eV的能量下与单重激子态S-1建立激发态平衡（K类似于1）一致地发生。平衡态存活36 ns，并通过辐射和非辐射途径通过S-1和非辐射途径通过（TT）-T-1丢失到基态。在TIPS-BT 1 ′中（TT）-T-1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（TT）-T-1形成的基准。最后，比较的TIPS-BT 1 '与以前的结果获得的一个接近的宪法异构体（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决定（TT）-T-1产率在tetracenic系统的关键作用。
Structurally well-defined TIPS-acetylene substituted TIPS 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 (TT)-T-1 state as well as decay pathways to the ground state. For TIPS-BP1' in room-temperature toluene, (TT)-T-1 formation is rapid and complete, occurring in 4.4 ps. Decay to the ground state in 100 ns is the primary loss pathway for (TT)-T-1 in this system. For TIPS-BT1', the (TT)-T-1 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 similar to 1) with the singlet exciton state S-1 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 nonradiative pathways via the S-1 and nonradiative pathways via the (TT)-T-1. The rapidity of (TT)-T-1 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 (TT)-T-1 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 (TT)-T-1 yield in the tetracenic systems.