The Institute of Chemistry of the Chinese Academy of Sciences has made important progress in the field of multi-level chiral self-assembly

On November 4, 2022, Beijing time, Liu Minghua’s research team at the Institute of Chemistry of the Chinese Academy of Sciences published a research paper entitled “Hierarchically self-assembled homochiral helical microtoroids” in the journal Nature Nanotechnology.

The research team developed a new strategy of solution-interface combined multi-stage self-assembly, realized cross-scale transfer and precise control of chirality from the molecular level to the micron level, constructed a large-area monodisperse chiral helical spiral microring structure, revealed the structure-activity relationship between circular dichroism and circularly polarized luminescence performance of chiral modulation of microstructure, and provided a new way for understanding the chiral transport mechanism of self-assembly and developing multi-level chiral microstructure and optical function system.

The corresponding authors of the paper are Liu Minghua and Ou Yangguanghui; The first authors are Chung Du and Li Zujian.

Chirality refers to the asymmetric feature that does not coincide with its mirror image, which is a common phenomenon in nature. In the process of the emergence and evolution of life, chiral molecules, as an important basic unit and building factor to control multi-level biological structures such as double helix DNA and α-helical protein, play a vital role in living systems. On the other hand, chiral substances can rotate the polarization surface of light to produce special optical properties, so chiral modulated functional molecules and materials have attracted more and more attention from the scientific community, and gradually demonstrated their application potential in the fields of medicine, pesticides, information, biology and optoelectronic functional materials. In the construction of advanced structures and materials from small molecules to polymers, supramolecules, and larger nanometers and microns, the topological morphology and cross-scale chiral control of multi-level chiral substances play a crucial role in understanding the origin of chirality in nature and modulating chiral functions.

Self-assembly chemistry based on weak interactions between molecules is an important way to construct chiral substances above the molecular level. However, compared with the precise asymmetric synthesis of chiral molecules, chiral self-assembled structures with nano, micron or even larger scales are often difficult to construct accurately, which is reflected in the difficult control of multi-level chirality, structural defects, and poor size dispersion. Therefore, the precise construction of monodisperse chiral nanostructures from molecular assembly has always been one of the problems in the field of chiral science and self-assembly chemistry.

Figure 1: Solution-interface multistage self-assembly strategy and construction of isochiral spiral microring structure.

Recently, with the support of the major project of the National Natural Science Foundation of China and the relevant research projects of the Chinese Academy of Sciences, the research group of researcher Liu Minghua of the Institute of Chemistry, Chinese Academy of Sciences, based on the research of solution chiral self-assembly chemistry, has developed a new solution-interface multi-stage self-assembly strategy, integrated the self-assembly of the solution system and the surface confinement effect of the di-wiki bottom, realized the precise construction of micron-scale monodisperse chiral spiral microrings and the application of circular polarization luminescence, and in order to understand the chiral transport mechanism of self-assembly, The development of multi-level chiral nanostructure and new chiral functional system provides a new idea.

The research group designed and synthesized a series of amphiphilic binaphthalene chiral biurea assembly motifs, and optimized the effects of alkyl tail chain length and intramolecular hydrogen bonding of biurea groups on self-assembly by synthesizing control molecules. Through programmed cooling control, the supersaturated solution of biurea bibiurea bienazile first formed a nanoscale colloidal dispersion phase, which was supported by cryo-EM and dynamic light scattering data and a series of in situ spectral data. These nanoaggregates were further transferred to the dioctane bottom, driven by solvent evaporation, controlled by interfacial tension and chiral interaction between preaggregates, and further fused and reassembled to form a micron-scale chiral spiral ring structure with good monodispersity.

By coating or spin coating, this solution-interface multistage assembly strategy can prepare isochiral spiral microrings over a wide range of substrates such as silicon wafers, quartz, mica, and glass. Based on experimental data such as variable temperature spectroscopy, single crystal diffraction and electron microscopy, as well as theoretical analysis results such as density functional calculation and molecular dynamics simulation, they proposed a hierarchical assembly mechanism of aggregation-cyclization. The structure-activity relationship study shows that the interfacial microring structure plays an important role in mediating self-assembled circular polarization luminescence. By doping chiral receptor dyes in helical microrings, they further prepared a novel chiral light-harvesting antenna model with both ring and circularly polarized luminescence characteristics. This work provides a new idea for the precise construction of multi-level chiral assembly structures, which is expected to promote the development of chiral self-assembly technology in the fields of supramolecular functional materials and nanotopology.

Figure 2: Single crystal structure analysis and molecular dynamics simulation.

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Fig. 3: Chiral structure-activity relationship of microstructure and model of new chiral light-harvesting antenna.(Source: Web of Science)

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