Low‐Symmetry molecular assemblies formed through self‐assembly: A discovery by Nagasaki University, the University of Tokyo, and others

A research group led by Professor Keisuke Umakoshi from Nagasaki University's Graduate School of Engineering, Lecturer Shinnosuke Horiuchi from the University of Tokyo's Graduate School of Arts and Sciences, and Associate Professor Takumi Yamaguchi from the Japan Advanced Institute of Science and Technology (JAIST) Division of Advanced Science and Technology's Bioscience, Biotechnology, and Biomedical Engineering research area have made a significant finding. By simply mixing organic molecules and coordination complexes, the team discovered that molecular assemblies with the lowest molecular symmetry, C₁ symmetry, can be formed. The research group has also clarified how low‐symmetry molecules produced through self‐assembly affect the optical properties of the materials.

Enzymes and DNA form self‐assembled structures through the cooperative action of weak association forces such as hydrogen bonds and molecular interactions. The research team investigated the creation of novel molecular assemblies by incorporating weak association forces into the self‐assembly process. They discovered that by combining organic molecules with hydrogen bonding capabilities and cationic coordination complexes, they could produce molecular assemblies with the rare C₁ molecular symmetry, which is challenging to achieve through conventional self‐assembly methods.

Additionally, the team found that the molecular self‐assembly process significantly modified the physical properties of the coordination complexes. When coordination complexes form molecular assemblies with organic molecules, it leads to significantly improved luminescent properties, including higher energy, increased efficiency, and longer lifespan.

Next, the team focused on its observation that the coordination complexes used were composed of two different optical isomers and examined the impact of the low‐symmetry molecular assembly structure on the chiral optical properties. It found that molecular self‐assembly‐based low symmetrization enhances the anisotropic factor glum value of circularly polarized luminescence observed in chiral coordination complexes. The unchanged glum value in similar coordination complexes without low symmetrization led to the conclusion that the enhancement in the glum value results from the altered physical properties brought about by the low symmetric structure.

Horiuchi said, 'By harnessing the power of self‐assembly found in nature, we have produced molecular assemblies with the elusive C₁ symmetry, which was challenging to obtain through traditional methods. While it remains to be seen if this approach can be widely adopted, if a molecular assembly system based on this research is developed, it will bring about a revolutionary shift in the field of molecular self‐assembly. It would pave the way for creating innovative functional molecular materials.'

Coordination complex / cationic coordination complex: Broad terms that refer to compounds where transition metal ions and organic compounds become composite bodies through coordination bonds. Positively charged ones are called cationic.

Journal Information
Publication: Nature Communications
Title: Symmetry‐Breaking Host‐guest Assembly in a Hydrogen‐bonded Supramolecular System
DOI: 10.1038/s41467‐023‐35850‐4