Materials and Process Simulation Center, California Institute of Technology , Pasadena, California 91125, United States.
Department of Chemistry, Faculty of Science, King Abdulaziz University , Jeddah 22254, Saudi Arabia.
J Am Chem Soc. 2017 Mar 22;139(11):4107-4116. doi: 10.1021/jacs.6b13223. Epub 2017 Mar 10.
Molecules capable of performing highly efficient energy transfer and ultrafast photoinduced electron transfer in well-defined multichromophoric structures are indispensable to the development of artificial photofunctional systems. Herein, we report on the synthesis, characterization, and photophysical properties of a rationally designed multichromophoric tetracationic cyclophane, DAPPBox, containing a diazaperopyrenium (DAPP) unit and an extended viologen (ExBIPY) unit, which are linked together by two p-xylylene bridges. Both H NMR spectroscopy and single-crystal X-ray diffraction analysis confirm the formation of an asymmetric, rigid, box-like cyclophane, DAPPBox. The solid-state superstructure of this cyclophane reveals a herringbone-type packing motif, leading to two types of π···π interactions: (i) between the ExBIPY unit and the DAPP unit (π···π distance of 3.7 Å) in the adjacent parallel cyclophane, as well as (ii) between the ExBIPY unit (π···π distance of 3.2 Å) and phenylene ring in the closest orthogonal cyclophane. Moreover, the solution-phase photophysical properties of this cyclophane have been investigated by both steady-state and time-resolved absorption and emission spectroscopies. Upon photoexcitation of DAPPBox at 330 nm, rapid and quantitative intramolecular energy transfer occurs from the ExBIPY unit to the DAPP unit in 0.5 ps to yield DAPP. The same excitation wavelength simultaneously populates a higher excited state of DAPP which then undergoes ultrafast intramolecular electron transfer from DAPP to ExBIPY to yield the DAPP-ExBIPY radical ion pair in τ = 1.5 ps. Selective excitation of DAPP at 505 nm populates a lower excited state where electron transfer is kinetically unfavorable.
在定义明确的多发色团结构中，能够进行高效能量转移和超快光诱导电子转移的分子对于人工光功能系统的发展是必不可少的。在此，我们报告了一种合理设计的多发色团四阳离子环番，DAPPBox 的合成、表征和光物理性质，该环番含有一个二氮杂并[3,4-f]吡咯𬭩(DAPP)单元和一个扩展的二价联吡啶(BIPY)单元，它们通过两个对二甲撑桥连接在一起。H NMR 光谱和单晶 X 射线衍射分析都证实了不对称、刚性、盒状环番 DAPPBox 的形成。该环番的固态超结构显示出一种鱼骨型堆积模式，导致两种类型的π···π相互作用：(i) 在相邻平行环番中，ExBIPY 单元和 DAPP 单元之间(π···π 距离为 3.7 Å)，以及(ii) 在最接近的正交环番中，ExBIPY 单元(π···π 距离为 3.2 Å)和苯环之间。此外，还通过稳态和时间分辨吸收和发射光谱研究了该环番在溶液相中的光物理性质。在 330nm 处光激发 DAPPBox 时，ExBIPY 单元到 DAPP 单元的快速和定量分子内能量转移在 0.5ps 内发生，生成 DAPP。相同的激发波长同时使 DAPP 的较高激发态达到激发态，然后在 1.5ps 内发生超快分子内电子转移，从 DAPP 到 ExBIPY 生成 DAPP-ExBIPY 自由基离子对。在 505nm 处选择性激发 DAPP 会使电子转移在动力学上不利的低激发态达到激发态。
