Breakthrough Unveiled in Dynamic Materials' Molecular Origami

Abstract

Origami, known as paper folding has become a fascinating research topic recently. Origami-inspired materials often establish mechanical properties that are difficult to achieve in conventional materials. However, the materials based on origami tessellation at the molecular level have been significantly underexplored. Herein, we report a two-dimensional (2D) porphyrinic metal-organic framework (MOF), self-assembled from Zn nodes and flexible porphyrin linkers, displaying folding motions based on origami tessellation. A combined experimental and theoretical investigation demonstrated the origami mechanism of the 2D porphyrinic MOF, whereby the flexible linker acts as a pivoting point. The discovery of the 2D tessellation hidden in the 2D MOF unveils origami mechanics at the molecular level.

Origami, traditionally associated with paper folding, has transcended its craft origins to influence a diverse range of fields, including art, science, engineering, and architecture. Recently, origami principles have extended to technology, with applications spanning solar cells to biomedical devices. While origami-inspired materials have been explored at various scales, the challenge of creating molecular materials based on origami tessellations has remained. Addressing this challenge, a team of researchers, led by Professor Wonyoung Choe in the Department of Chemistry at UNIST, has unveiled a remarkable breakthrough in the form of a two-dimensional (2D) Metal Organic Framework (MOF) that showcases unprecedented origami-like movement at the molecular level.

Metal-Organic Frameworks (MOFs) have long been recognized for their structural flexibility, making them an ideal platform for origami tessellation-based materials. However, their application in this context is still in its early stages. Through the development of a 2D MOF based on the origami tessellation, the research team has achieved a significant milestone. The researchers utilized temperature-dependent synchrotron single-crystal X-ray diffraction to demonstrate the origami-like folding behavior of the 2D MOF in response to temperature changes. This behavior showcases negative thermal expansion and reveals a unique origami tessellation pattern, previously unseen at the molecular level.

The key to this breakthrough lies in the choice of MOFs, which incorporate flexible structural building blocks. The inherent flexibility enables the origami-like movement, observed in the 2D MOF. The study highlights the deformable net topology of the materials. Additionally, the role of solvents in maintaining the packing between 2D framework in MOFs is emphasized, as it directly affects the degree of folding.

"This groundbreaking research opens new avenues for origami-inspired materials at the molecular level, introducing the concept of origamic MOFs. The findings not only contribute to the understanding of dynamic behavior in MOFs, but also offer potential applications in mechanical metamaterials," noted Professor Choe. He further highlighted the potential of molecular level control over origami movement, as a platform for designing advanced materials with unique mechanical properties. The study also suggests exciting possibilities for tailoring origamic MOFs for specific applications, including advancements in molecular quantum computing.

The findings of this research have been published in Nature Communications, a sister journal to Nature, on December 01, 2023. This study has been supported by the National Research Foundation (NRF) of Korea via the Mid-Career Researcher Program, Hydrogen Energy Innovation Technology Development Project, Science Research Center (SRC), and Global Ph.D. Fellowship (GPF), as well as Korea Environment Industry & Technology Institute (KEITI) through Public Technology Program based on Environmental Policy Program, funded by the Korean Ministry of Environment (MOE).

Journal Reference

Eunji Jin, In Seong Lee, D. ChangMo Yang, et al., "Origamic metal-organic framework toward mechanical metamaterial," Nat. Commun., (2023).