Universität Würzburg , Institut für Organische Chemie & Center for Nanosystems Chemistry , Am Hubland , 97074 Würzburg , Germany.
Department of Chemistry and Spectroscopy Laboratory for Functional π-Electronic Systems , Yonsei University , Seoul 03722 , Korea.
J Am Chem Soc. 2018 Mar 28;140(12):4253-4258. doi: 10.1021/jacs.7b11571. Epub 2018 Mar 14.
An adequately designed, bay-tethered perylene bisimide (PBI) dimer Bis-PBI was synthesized by Pd/Cu-catalyzed Glaser-type oxidative homocoupling of the respective PBI building block. This newly synthesized PBI dimer self-assembles exclusively and with high binding constants of up to 10 M into a discrete π-stack of four chromophores. Steady-state absorption and emission spectra show the signatures of H-type excitonic coupling among the dye units. Broadband fluorescence upconversion spectroscopy (FLUPS) reveals an ultrafast dynamics in the optically excited state. An initially coherent Frenkel exciton state that is delocalized over the whole quadruple stack rapidly (τ = ∼200 fs) loses its coherence and relaxes into an excimer state. Comparison with Frenkel exciton dynamics in PBI dimeric and oligomeric H-aggregates demonstrates that in the quadruple stack coherent exciton propagation is absent due to its short length of aggregates, thereby it has only one relaxation pathway to the excimer state. Furthermore, the absence of pump-power dependence in transient absorption experiments suggests that multiexciton cannot be generated in the quadruple stack, which is in line with time-resolved fluorescence measurements.
通过 Pd/Cu 催化的各自 PBI 构筑块的 Glaser 型氧化同偶联，成功设计并合成了具有 Bay 键合的并苯二酰亚胺（PBI）二聚体 Bis-PBI。这种新合成的 PBI 二聚体通过自身偏好，以高达 10 M 的高结合常数，高度专一性地自组装成四个发色团的离散 π-堆叠。稳态吸收和发射光谱显示了染料单元之间 H 型激子耦合的特征。宽带荧光上转换光谱（FLUPS）揭示了光激发态中的超快动力学。最初在整个四重堆栈上离域的相干 Frenkel 激子态迅速（τ = ∼200 fs）失去相干性，并弛豫到激子态。与 PBI 二聚体和低聚物 H-聚集体中的 Frenkel 激子动力学的比较表明，在四重堆栈中，由于其聚集体的长度较短，相干激子传播不存在，因此它只有一条弛豫途径到激子态。此外，瞬态吸收实验中不存在泵浦功率依赖性表明，四重堆栈中不能产生多激子，这与时间分辨荧光测量结果一致。
