Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
J Am Chem Soc. 2021 May 12;143(18):7059-7068. doi: 10.1021/jacs.1c01693. Epub 2021 Apr 29.
The ability to dynamically control chirality remains a grand challenge in chemistry. Although many molecules possess chiral isomers, lacking their isolation, for instance during photoisomerization, results in racemic mixtures with suppressed enantiospecific chiral properties. Here, we present a nanoporous solid in which chirality and enantioselective enrichment is induced by circularly polarized light (CPL). The material is based on photoswitchable fluorinated azobenzenes attached to the scaffold of a crystalline metal-organic framework (MOF). The azobenzene undergoes -to--photoisomerization upon irradiation with green light and reverts back to upon violet light. While each moiety in conformation is chiral, we show the isomer also possesses a nonplanar, chiral conformation. During photoisomerization with unpolarized light, no enantiomeric enrichment is observed and both isomers, - and - as well as and -, respectively, are formed in identical quantities. In contrast, CPL causes chiral photoresolution, resulting in an optically active material. Right-CPL selectively excites - and - enantiomers, producing a MOF with enriched -enantiomers, and . The induction of optical activity is reversible and only depends on the light-handedness. As shown by first-principle DFT calculations, while both, and , are stabilized in nonplanar, chiral conformations in the MOF, the isomer adopts a planar, achiral form in solution, as verified experimentally. This shows that the chiral photoresolution is enabled by the linker reticulation in the MOF. Our study demonstrates the induction of chirality and optical activity in solid materials by CPL and opens new opportunities for chiral resolution and information storage with CPL.
动态控制手性仍然是化学领域的一大挑战。尽管许多分子都具有手性异构体，但如果无法将它们分离出来，例如在光异构化过程中，就会得到外消旋混合物，从而抑制了对映体特异性的手性性质。在这里，我们提出了一种纳米多孔固体，其中手性和对映体富集是由圆偏振光（CPL）诱导的。该材料基于光致变色的氟化偶氮苯与结晶金属有机骨架（MOF）的支架相连。偶氮苯在绿光照射下发生顺-反光异构化，在紫光照射下恢复为反式。虽然 构象中的每个部分都是手性的，但我们表明该异构体也具有非平面手性构象。在非偏振光照射下进行光异构化时，没有观察到对映体富集，并且分别形成等量的-和-异构体以及-和-异构体。相比之下，CPL 引起手性光分辨率，导致产生光学活性材料。右 CPL 选择性激发-和-对映体，产生富含-对映体的 MOF 和 。光活性的诱导是可逆的，仅取决于光的手性。正如第一性原理 DFT 计算所示，尽管 和 都在 MOF 中以非平面手性构象稳定，但在溶液中 异构体采用平面非手性形式，实验上得到验证。这表明手性光分辨率是由 MOF 中的连接剂交联实现的。我们的研究表明，CPL 可以在手性固体材料中诱导手性和光活性，并为 CPL 下的手性分辨率和信息存储开辟了新的机会。
