Chirality is widely present in nature and is one of the fundamental characteristics of life systems. Studying the chirality sources, multi chirality, chiral chemistry, and cluster chemistry of chiral clusters at the atomic level is of great significance. However, chiral metal organic clusters account for only 7.8% of chiral crystalline compounds, concentrated in precious metals, rare earths, and transition metals. Recently, Fang Weihui, a researcher at the Fujian Institute of Material Structure, Chinese Academy of Sciences, used the coordinated synthesis strategy to build the first type of chiral alumina clusters (cAlOCs) and applied them to circularly polarized luminescence.

In nature, the molecular chirality of amino acids determines the helical chirality of proteins, ultimately manifested as the macroscopic chirality of multi-scale biomolecules. This type of cAlOCs Al5 cluster system, stabilized by chiral amino acids and auxiliary chelating ligands 2,6 pyridine dicarboxylic acid, integrates the chirality of cluster molecules, DNA like chiral double helix, and chiral hydrogen bonding topology. Based on weak hydrogen bonding interactions between clusters, this study achieves chiral transfer and amplification between clusters, and provides a new topology method for assembling chiral topologies with four connected clusters as nodes. In addition, this collaborative coordination synthesis strategy has good universality and can be extended to different isomorphic ligands and different counter ions. This type of cAlOCs material can achieve gram level amplification synthesis, with good stability and high BET specific surface area.

In addition, this study applies this type of cAlOCs material in chiral optics. Due to the existence of one-dimensional channels with a diameter of about 1 nanometer in the supramolecular structure of clusters and the substitutability of cluster counteranions, the study investigated the organic dye molecule CF3512- loaded with anions through nanoscale spiral pores. Extensive characterization has demonstrated the successful doping and uniform distribution of dye molecules in crystals, while molecular simulation calculations further confirm that fluorescent dye anions bind to positively charged Al5 clusters through electrostatic and hydrogen bonding interactions. The chiral transfer between chiral spiral channels and fluorescent anionic dye molecules results in a significant circularly polarized luminescence (CPL) signal in the doped material, with signal intensity equivalent to the CPL of some chiral precious metals. This material can be further prepared into flexible, transparent, and inexpensive CPL films, demonstrating potential application value.

The above research provides an effective method for the synthesis of chiral aluminum oxide clusters and a new approach for the synthesis of low-cost CPL materials. The relevant research results are published in the Journal of the American Chemical Society.

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Multiple chirality of compounds and schematic diagram for preparing flexible CPL films