Kaufmann Christina, Bialas David, Stolte Matthias, Würthner Frank
Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany.
Center for Nanosystems Chemistry , Universität Würzburg , Theodor-Boveri-Weg , 97074 Würzburg , Germany.
J Am Chem Soc. 2018 Aug 8;140(31):9986-9995. doi: 10.1021/jacs.8b05490. Epub 2018 Jul 27.
Four well-defined π-stacks of perylene bisimide (PBI) dyes were obtained in solution by covalent linkage of two chromophores with spacer units of different length and sterical demand. Structural elucidation of the folda-dimers by in-depth nuclear magnetic resonance studies and geometry optimization at the level of density functional theory suggest different, but highly defined molecular arrangements of the two chromophores in the folded state enforced by the various spacer moieties. Remarkably, the dye stacks exhibit considerably different optical properties as investigated by UV/vis absorption and fluorescence spectroscopy, despite only slightly different chromophore arrangements. The distinct absorption properties can be rationalized by an interplay of long- and short-range exciton coupling resulting in optical signatures ranging from conventional H-type to monomer like absorption features with low and appreciably high fluorescence quantum yields, respectively. To the best of our knowledge, we present the first experimental proof of a PBI-based "null-aggregate", in which long- and short-range exciton coupling fully compensate each other, giving rise to monomer-like absorption features for a stack of two PBI chromophores. Hence, our insights pinpoint the importance of charge-transfer mediated short-range coupling that can significantly influence the optical properties of PBI π-stacks.
通过将两个发色团与具有不同长度和空间需求的间隔单元共价连接，在溶液中获得了四个结构明确的苝二酰亚胺（PBI）染料π堆积。通过深入的核磁共振研究和密度泛函理论水平的几何优化对折叠二聚体进行结构解析，结果表明，在折叠状态下，两个发色团的分子排列不同，但高度明确，这是由各种间隔部分所强制形成的。值得注意的是，尽管发色团排列仅有细微差异，但通过紫外/可见吸收光谱和荧光光谱研究发现，染料堆积表现出显著不同的光学性质。长程和短程激子耦合的相互作用可以解释不同的吸收特性，从而产生从传统H型到具有低和相当高荧光量子产率的类似单体吸收特征的光学信号。据我们所知，我们首次通过实验证明了基于PBI的“零聚集体”，其中长程和短程激子耦合相互完全补偿，使得两个PBI发色团堆叠产生类似单体的吸收特征。因此，我们的研究结果指出了电荷转移介导的短程耦合的重要性，它可以显著影响PBI π堆积的光学性质。
