Bressan Giovanni, Penty Samuel E, Green Dale, Heisler Ismael A, Jones Garth A, Barendt Timothy A, Meech Stephen R
School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.
School of Chemistry, University of Birmingham, Birmingham, B15 2TT, UK.
Angew Chem Int Ed Engl. 2024 Sep 23;63(39):e202407242. doi: 10.1002/anie.202407242. Epub 2024 Aug 22.
Perylene diimide (PDI) dimers and higher aggregates are key components in organic molecular photonics and photovoltaic devices, supporting singlet fission and symmetry breaking charge separation. Detailed understanding of their excited states is thus important. This has proven challenging because interchromophoric coupling is a strong function of dimer architecture. Recently, a macrocyclic PDI dimer was reported in which excitonic coupling could be turned on and off simply by changing the solvent. This presents a useful case where coupling is modified without synthetic changes to tune supramolecular structure. Here we present a detailed study of solvent dependent excited state dynamics in this dimer by means of coherent multidimensional spectroscopy. Spectral analysis resolves the different coupling strengths, which are consistent with solvent dependent changes in dimer conformation. The strongly coupled conformer forms an excimer within 300 fs. The low-frequency Raman active modes recovered from two-dimensional electronic spectra reveal frequencies characteristic of exciton coupling. These are assigned to modes modulating the coupling from the corresponding DFT calculations. Further analysis reveals a time dependent frequency during excimer formation. Analysis of two-dimensional "beatmaps" reveals features in the coupled dimer which are not predicted by the displaced harmonic oscillator model and are assigned to vibronic coupling.
苝二酰亚胺（PDI）二聚体及更高聚集体是有机分子光子学和光伏器件中的关键组分，可支持单线态裂变和对称性破缺电荷分离。因此，详细了解它们的激发态很重要。事实证明，这颇具挑战性，因为发色团间耦合强烈依赖于二聚体结构。最近，有报道称一种大环PDI二聚体，其中激子耦合可通过简单改变溶剂来开启和关闭。这提供了一个有用的案例，即无需通过合成变化来调整超分子结构就能改变耦合。在此，我们借助相干多维光谱对该二聚体中溶剂依赖的激发态动力学进行了详细研究。光谱分析解析了不同的耦合强度，这与二聚体构象随溶剂的变化一致。强耦合构象体在300飞秒内形成激基缔合物。从二维电子光谱中恢复的低频拉曼活性模式揭示了激子耦合的特征频率。这些频率被指定为通过相应密度泛函理论计算来调制耦合的模式。进一步分析揭示了激基缔合物形成过程中频率随时间的变化。对二维“拍频图”的分析揭示了耦合二聚体中的特征，这些特征无法由位移谐振子模型预测，并被归因于振转耦合。
