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.

中文翻译：

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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

准分子系统（即激发二聚体）很好地充当了研究弱相互作用发色团上电子能离域的模型化合物。然而，仍然存在相对较少的孤立系统，可以在一定程度上对这种相互作用进行实验研究，以提供与理论的详细比较。在本文中，我们研究了一系列共价和非共价连接的芴二聚体，作为芳香族发色团模型，其中准分子的形成需要范德华接触处的π堆积、共面取向。基于一系列开创性的先前研究，检查了范德华二聚体中激发相互作用的振动猝灭，我们在这里寻求解决的关键问题是，单个猝灭因子是否可以在一系列共价和非共价连接中重现实验激子分裂。由相同发色团构建的双发色系统。在将实验测量的激子分裂与使用时间相关密度泛函方法计算的静态分裂进行比较时，我们发现所有系统都在斜率为 0.080(8) 的线上保存了一次跌落，反映了大约 1 个数量级的振动猝灭。异常值显示出显着降低的猝灭因子，代表环芳连接的系统，其中芴部分被限制在共面排列中。我们认为该系统证明了从弱耦合状态到中间耦合状态的转变。