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Solvent-Controlled Branching of Localized versus Delocalized Singlet Exciton States and Equilibration with Charge Transfer in a Structurally Well-Defined Tetracene Dimer
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2017-11-21 00:00:00 , DOI: 10.1021/acs.jpca.7b09458 Jasper D. Cook 1 , Thomas J. Carey 1 , Dylan H. Arias 2 , Justin C. Johnson 2 , Niels H. Damrauer 1
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2017-11-21 00:00:00 , DOI: 10.1021/acs.jpca.7b09458 Jasper D. Cook 1 , Thomas J. Carey 1 , Dylan H. Arias 2 , Justin C. Johnson 2 , Niels H. Damrauer 1
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A detailed photophysical picture is elaborated for a structurally well-defined and symmetrical bis-tetracene dimer in solution. The molecule was designed for interrogation of the initial photophysical steps (S1 → 1TT) in intramolecular singlet fission (SF). (Triisopropylsilyl)acetylene substituents on the dimer TIPS-BT1 as well as a monomer model TIPS-Tc enable a comparison of photophysical properties, including transient absorption dynamics, as solvent polarity is varied. In nonpolar toluene solutions, TIPS-BT1 decays via radiative and nonradiative pathways to the ground state with no evidence for dynamics related to the initial stages of SF. This contrasts with the behavior of the previously reported unsubstituted dimer BT1 and is likely a consequence of energetic perturbations to the singlet excited-state manifold of TIPS-BT1 by the (trialkylsilyl)acetylene substituents. In polar benzonitrile, two key findings emerge. First, photoexcited TIPS-BT1 shows a bifurcation into both arm-localized (S1-loc) and dimer-delocalized (S1-dim) singlet exciton states. The S1-loc decays to the ground state, and weak temperature dependence of its emissive signatures suggests that once it is formed, it is isolated from S1-dim. Emissive signatures of the S1-dim state, on the other hand, are strongly temperature-dependent, and transient absorption dynamics show that S1-dim equilibrates with an intramolecular charge-transfer state in 50 ps at room temperature. This equilibrium decays to the ground state with little evidence for formation of long-lived triplets nor 1TT. These detailed studies spectrally characterize many of the key states in intramolecular SF in this class of dimers but highlight the need to tune electronic coupling and energetics for the S1 → 1TT photoreaction.
中文翻译：
结构良好定义的四烷二聚体中溶剂控制的局域化和解域化单重态激子状态的分支以及电荷转移的平衡
详细阐述了溶液中结构清晰，对称的双并四聚体的详细光物理图像。该分子设计用于询问初始的光物理步骤（S 1 → 1TT）在分子内单峰裂变（SF）中。二聚体TIPS-BT1上的（三异丙基甲硅烷基）乙炔基取代基以及单体模型TIPS-Tc能够比较光物理性质，包括瞬态吸收动力学，因为溶剂极性变化。在非极性甲苯溶液中，TIPS-BT1通过辐射和非辐射途径衰减到基态，没有证据表明与SF初始阶段有关的动力学。这与先前报道的未取代的二聚体BT1的行为相反，并且可能是（三烷基甲硅烷基）乙炔基取代基对TIPS-BT1的单线态激发态歧管的能量扰动的结果。在极性苄腈中，出现了两个关键发现。首先，受光激发的TIPS-BT1在两臂上均分叉（S 1loc）和二聚体离域（S 1-dim）单重态激子态。S 1-loc衰减至基态，其发射标记的温度依赖性较弱，这表明它一旦形成，便与S 1-dim隔离了。另一方面，S 1-dim状态的发射信号强烈依赖于温度，瞬态吸收动力学表明，在室温下，S 1-dim在50 ps时与分子内电荷转移状态相平衡。这种平衡衰减到基态，几乎没有形成长寿命三胞胎的证据，也没有1TT。这些详细的研究从光谱上表征了此类二聚体中分子内SF的许多关键状态，但强调了需要调整S 1 → 1 TT光反应的电子耦合和高能学。
更新日期：2017-11-21
中文翻译：
结构良好定义的四烷二聚体中溶剂控制的局域化和解域化单重态激子状态的分支以及电荷转移的平衡
详细阐述了溶液中结构清晰，对称的双并四聚体的详细光物理图像。该分子设计用于询问初始的光物理步骤（S 1 → 1TT）在分子内单峰裂变（SF）中。二聚体TIPS-BT1上的（三异丙基甲硅烷基）乙炔基取代基以及单体模型TIPS-Tc能够比较光物理性质，包括瞬态吸收动力学，因为溶剂极性变化。在非极性甲苯溶液中，TIPS-BT1通过辐射和非辐射途径衰减到基态，没有证据表明与SF初始阶段有关的动力学。这与先前报道的未取代的二聚体BT1的行为相反，并且可能是（三烷基甲硅烷基）乙炔基取代基对TIPS-BT1的单线态激发态歧管的能量扰动的结果。在极性苄腈中，出现了两个关键发现。首先，受光激发的TIPS-BT1在两臂上均分叉（S 1loc）和二聚体离域（S 1-dim）单重态激子态。S 1-loc衰减至基态，其发射标记的温度依赖性较弱，这表明它一旦形成，便与S 1-dim隔离了。另一方面，S 1-dim状态的发射信号强烈依赖于温度，瞬态吸收动力学表明，在室温下，S 1-dim在50 ps时与分子内电荷转移状态相平衡。这种平衡衰减到基态，几乎没有形成长寿命三胞胎的证据，也没有1TT。这些详细的研究从光谱上表征了此类二聚体中分子内SF的许多关键状态，但强调了需要调整S 1 → 1 TT光反应的电子耦合和高能学。
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