Photomodulation of Two-Dimensional Self-Assembly of Azobenzene–Hexa-<i>peri</i>-hexabenzocoronene–Azobenzene Triads
作者:Ian Cheng-Yi Hou、Valentin Diez-Cabanes、Agostino Galanti、Michal Valášek、Marcel Mayor、Jérôme Cornil、Akimitsu Narita、Paolo Samorì、Klaus Müllen
DOI:10.1021/acs.chemmater.9b01535
日期:2019.9.10
Achieving exquisite control over self-assembly of functional polycyclic aromatic hydrocarbons (PAH) and nanographene (NG) is essential for their exploitation as active elements in (nano)technological applications. In the framework of our effort to leverage their functional complexity, we designed and synthesized two hexa-peri-hexabenzocoronene (HBC) triads, pAHA and oAHA, decorated with two light-responsive azobenzene moieties at the pseudo-para and ortho positions, respectively. Their photoisomerization in solution is demonstrated by UV–vis absorption. 1H NMR measurements of oAHA suggested 23% of Z-form can be obtained at a photostationary state with UV irradiation (366 nm). Scanning tunneling microscopy imaging revealed that the self-assembly of pAHA and oAHA at the solid–liquid interface between highly oriented pyrolytic graphite (HOPG) and their solution in 1,2,4-trichlorobenzene can be modulated upon light irradiation. This is in contrast to our previous work using HBC bearing a single azobenzene moiety, which did not show such photomodulation of the self-assembled structure. Upon E-Z isomerization both pAHA and oAHA displayed an increased packing density on the surface of graphite. Moreover, pAHA revealed a change of self-assembled pattern from an oblique unit cell to a dimer row rectangular crystal lattice whereas the assembly of oAHA retained a dimer row structure before and after light irradiation, yet with a modification of the inter-row molecular orientation. Molecular mechanics/molecular dynamics simulations validated the self-assembly patterns of pAHA and oAHA, comprising azobenzenes in their Z-forms. These results pave the way toward use of suitably functionalized large PAHs, as well as NGs, to develop photoswitchable devices.
要将功能性多环芳烃(PAH)和纳米石墨烯(NG)用作(纳米)技术应用中的活性元素,实现对其自组装的精密控制至关重要。为了充分利用它们的功能复杂性,我们设计并合成了两种六全六苯并硼烯(HBC)三元体 pAHA 和 oAHA,它们分别在假对位和正位上装饰有两个光响应偶氮苯分子。紫外-可见吸收证明了它们在溶液中的光异构化。oAHA 的 1H NMR 测量结果表明,在紫外线照射(366 纳米)下,可以获得 23% 的 Z 形光静止态。扫描隧道显微镜成像显示,pAHA 和 oAHA 在高取向热解石墨(HOPG)与它们在 1,2,4- 三氯苯中的溶液之间的固液界面上的自组装可以在光照射下进行调节。这与我们之前使用含有单一偶氮苯分子的 HBC 所做的工作形成了鲜明对比,后者没有显示出自组装结构的这种光调节作用。E-Z 异构化后,pAHA 和 oAHA 在石墨表面的堆积密度都有所增加。此外,pAHA 的自组装模式从斜向单元格转变为二聚体行矩形晶格,而 oAHA 的组装在光照射前后都保留了二聚体行结构,但分子行间取向发生了改变。分子力学/分子动力学模拟验证了 pAHA 和 oAHA 的自组装模式,包括 Z 型偶氮苯。这些结果为利用适当官能化的大型多环芳烃和 NG 开发光开关器件铺平了道路。