Control on Dimensions and Supramolecular Chirality of Self-Assemblies through Light and Metal Ions

Precise control over helical chirality and dimensions of molecular self-assemblies, a remaining challenge for both chemists and materials scientists, is the key to manipulate the property and performance of supramolecular materials. Herein, we report that a cholesterol-azopyridine conjugate could self-assemble into organogels with photocontrollable dimensional transition from 2D microbelts to 1D nanotubes and finally to 0D nanoparticles. The E/Z-Photoisomerization of the 4-azopyridine unit is the major driving force for the dimensional transformation. Furthermore, the self-assembled structures were observed to exhibit metal ion-mediated helicity inversion through the metal coordination. These observations were collectively confirmed by several techniques including scanning electron microscopy, atomic force microscopy, circular dichroism, and X-ray crystallography. The rational design of building blocks for the construction of dimension and chirality controllable self-assembly systems may lead to versatile applications in smart display, advanced optoelectronic device, and supramolecular asymmetric catalysis.对分子自组装体的螺旋手性与尺寸进行精准调控，既是当前化学家与材料科学家尚未攻克的共同难题，亦是调控超分子材料物性与性能的核心所在。本文报道一种胆固醇-偶氮吡啶缀合物可自组装形成有机凝胶，其组装体尺寸可通过光控实现从二维微带（2D microbelts）到一维纳米管（1D nanotubes），最终转变为零维纳米颗粒（0D nanoparticles）的动态转变过程。4-偶氮吡啶单元的E/Z光异构化是该尺寸转变的核心驱动力。此外，研究发现该自组装结构可通过金属配位作用，实现金属离子介导的螺旋手性反转。上述实验结果通过扫描电子显微镜（scanning electron microscopy）、原子力显微镜（atomic force microscopy）、圆二色谱（circular dichroism）以及X射线晶体学（X-ray crystallography）等多种表征手段得到了全面验证。通过合理设计构筑单元以构建尺寸与手性可控的自组装体系，有望在智能显示、先进光电器件以及超分子不对称催化等领域实现多元应用。