Supramolecular assembly opens a new route to building quantum materials

A joint research team fabricated a two-dimensional structure that exhibits properties of both the honeycomb and Kagome lattices using organic molecules. They discovered that edge states specific to topological materials (states that exist only at the edges and are distinct from those in the interior) appear in this structure. The team included researchers from NIMS, Toyota Kosen (National Institute of Technology, Toyota College), Saga University, Nara Women's University, Kiel University (Germany) and other institutions.

While organic molecules allow for flexible structural design, it is difficult to bind the molecules together strongly through electronic coupling. Therefore, inorganic materials had mainly been used to synthesize topological materials. The team's success in realizing unique electronic states in an assembly of organic molecules (a supramolecular structure) paves the way for a new approach to designing quantum materials using organic molecules. This research was published in Nano Letters on Sept. 2, 2026.

Design flexibility meets weak electronic coupling

While quantum technology is expected to fundamentally transform society, its future advancement relies on the development of quantum materials, which serve as its foundation. However, most previously known quantum materials were composed of inorganic materials and had significant limitations in design and synthesis flexibility.

By contrast, supramolecular structures formed by assembling organic molecules allow for flexible design. Nevertheless, since supramolecules generally have weak electronic coupling between their constituent units, they were not suitable for use as quantum materials. Therefore, there had been a call for a new method for designing quantum materials based on organic molecules.

Combining honeycomb and Kagome lattices

In this study, the research team created a two-dimensional structure that exhibits the properties of both the honeycomb and Kagome lattices (a diatomic Kagome lattice) by assembling molecules derived from triptycene as building blocks.

The honeycomb lattice has a structure resembling bees' honeycomb, as the name suggests, and is found in graphene (a single layer of graphite), while the Kagome lattice has a structure resembling the lattice pattern of a traditional Japanese Kagome craft basket. Due to their unique electronic states, these lattices have been studied actively in recent years. However, very few studies have created a diatomic Kagome lattice, which can be described as a hybrid of these two lattices, in an actual material.

Topological edge states emerge

When the research team observed the prepared sample using a scanning tunneling microscope, they discovered a unique electronic state that exists only in the boundary (edge) region between the two-dimensional structure of the organic molecules and its exterior. They conducted a detailed theoretical analysis and found that this state is a topological edge state derived from its mathematical structure (technically called topology). This demonstrates the sample's properties as a quantum material.

The structure exhibits such a state despite being composed of organic molecules because the molecules are strongly bonded to each other. This stems from the fact that the three planes constituting the triptycene derivative are arranged in a three-dimensional propeller-like configuration, with adjacent planes in contact with one another (the coupling is denoted as t₁). The team's ability to design and synthesize this unique molecular structure and assemble the molecules into a supramolecular structure was key to achieving this result.

Based on this result, we will accelerate the development of materials for quantum technology applications. For example, by using such a unique lattice structure, it may become possible to switch between a high-mobility semiconductor-like state and a superconducting state, achieve ultrahigh-speed, ultralow-power optical switching, and even enable lossless energy transport at room temperature. We will also work to realize a variety of quantum materials by taking advantage of the design flexibility of organic molecules.