Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul, 120-749, Korea.
ACS Nano. 2013 Jun 25;7(6):5064-76. doi: 10.1021/nn400616u. Epub 2013 May 14.
Properties of a series of acetylene-linked perylene bisimide (PBI) macrocycles with different ring size composed of three to six PBI dyes were investigated by atomic force microscopy (AFM) and single-molecule fluorescence spectroscopy in a condensed phase. It was demonstrated that the structures of PBI cyclic arrays (CNs, N = 3, 4, 5, and 6) become distorted with increasing the ring size through molecular dynamics (MD) simulations (PM6-DH2 method) and AFM height images of CNs on highly ordered pyrolytic graphite (HOPG) surface. The MD simulations showed that only C5 and C6 rings are highly flexible molecules whose planarization goes along with a significant energetic penalty. Accordingly, both molecules did not show ordered adlayers on a HOPG surface. In contrast, C3 and C4 are far more rigid molecules leading to well-ordered hexagonal (C3) and rectangular (C4) 2D lattices. At the single-molecule level, we showed that the fluorescence properties of single CNs are affected by the structural changes. The fluorescence lifetimes of CNs became shorter and their distributions became broader due to the structural distortions with increasing the ring size. Furthermore, the CNs of smaller ring size exhibit a higher photostability and an efficient excitation energy transfer (EET) due to the more well-defined and planar structures compared to the larger CNs. Consequently, these observations provide evidence that not only PBI macrocycles are promising candidates for artificial light-harvesting systems, but also the photophysical properties of CNs are strongly related to the structural rigidity of CNs.
一系列不同环大小的乙炔键连接的苝二酰亚胺（PBI）大环（由三个到六个 PBI 染料组成）的性质通过原子力显微镜（AFM）和凝聚相中单分子荧光光谱进行了研究。通过分子动力学（MD）模拟（PM6-DH2 方法）和 PBI 环阵列（CN，N = 3、4、5 和 6）在高取向热解石墨（HOPG）表面的 AFM 高度图像，证明了随着环尺寸的增加，PBI 环阵列的结构变得扭曲。MD 模拟表明，只有 C5 和 C6 环是高度灵活的分子，其平面化伴随着显著的能量惩罚。因此，这两种分子在 HOPG 表面上没有表现出有序的吸附层。相比之下，C3 和 C4 是更刚性的分子，导致形成有序的六边形（C3）和矩形（C4）二维晶格。在单分子水平上，我们表明单个 CN 的荧光性质受到结构变化的影响。随着环尺寸的增加，由于结构变形，CN 的荧光寿命变短，分布变宽。此外，由于更明确和更规则的结构，较小环尺寸的 CN 表现出更高的光稳定性和有效的激发能量转移（EET）。因此，这些观察结果表明，PBI 大环不仅是人工光捕获系统的有前途的候选物，而且 CN 的光物理性质与 CN 的结构刚性密切相关。
