Excitonic Coupling in Fluorene-Based Bichromophoric Systems: Vibrational Quenching and the Transition from Weak to Intermediate Coupling
Excitonic Coupling in Fluorene-Based Bichromophoric Systems: Vibrational Quenching and the Transition from Weak to Intermediate Coupling
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芴基双色体系中的激子耦合：振动淬火和从弱耦合到中耦合的转变
DOI：
10.1021/acs.jpca.3c03511
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发表时间：
2023
期刊：
影响因子：
--
通讯作者：
Reid, Scott A.
中科院分区：
文献类型：
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作者：
Kokkin, Damian L.;Reilly, Neil J.;Ivanov, Maxim;Rathore, Rajendra;Reid, Scott A.
准分子系统（即，激发的二聚体）已经很好地用作研究弱相互作用发色团上电子能量离域的模型化合物。然而，仍然有相对较少的孤立系统中，这种相互作用可以在实验上研究的水平，提供详细的比较与理论。在这篇文章中，我们研究了一系列共价和非共价连接的芴二聚体，作为一个模型的芳香族发色团，其中的准分子的形成需要一个π-堆叠，共面取向在货车德瓦尔斯接触。基于一系列开创性的先前研究，研究了货车德瓦耳斯二聚体中激发相互作用的振动猝灭，我们试图解决的关键问题是，一个单一的猝灭因子是否可以在一系列由相同发色团构建的共价和非共价连接的双发色团系统中重现实验激子分裂。在比较实验测量的激子分裂与用含时密度泛函方法计算的静态分裂时，我们发现所有系统都在斜率为0.080（8）的线上保留了一个下降，反映了大约1个数量级的振动猝灭。异常值，这表明显着降低的淬灭因子，代表一个环芳连接的系统，其中的芴部分被限制在共面排列。我们认为，该系统的证据从弱到中等耦合制度的过渡。
Excimeric systems (i.e., excited dimers) have well served as model compounds for the study of the delocalization of electronic energy over weakly interacting chromophores. However, there remain relatively few isolated systems in which such interactions can be studied experimentally at a level to afford detailed comparisons with theory. In this Article, we examine a series of covalently and noncovalently linked dimers of fluorene, as a model aromatic chromophore, where the formation of excimers requires a π-stacked, cofacial orientation at van der Waals contact. Building upon a series of seminal prior studies that examined vibronic quenching of the excitation interaction in van der Waals dimers, the key question that we sought to address here is whether a single quenching factor could reproduce experimental excitonic splittings across a series of covalently and noncovalently linked bichromophoric systems built from the same chromophore. In comparing experimentally measured excitonic splittings with calculated static splittings using time-dependent density functional methods, we find that all systems save one fall on a line with a slope of 0.080(8), reflecting a vibrational quenching of roughly 1 order of magnitude. The outlier, which shows a significantly reduced quenching factor, represents a cyclophane-linked system where the fluorene moieties are constrained in a cofacial arrangement. We argue that this system evidences the transition from the weak to intermediate coupling regime.