Futuristic Nanomaterials: Molecular Christmas Trees

When we observe the natural world, we are all captivated by phenomena that are extremely important to life, such as photosynthesis and respiration. Life first emerged in the sea, where many kinds of metal ions existed. This led to the natural formation of substances incorporating metals, which over long periods evolved into the life forms of today, capable of expressing advanced biological functions. In these substances, many different types of metals are precisely arranged within a polymer skeleton. The polymers and metals work together to carry out the complex and ingenious functions of life.

We were the first in the world to develop "new metallopolymer materials" in which the number and position of metals can be precisely controlled and arranged [Nature, 415, 509 (2002)]. These polymers have an interesting shape, branching like a tree and round like a marimo moss ball. Their diameter is only a few nanometers, tens of thousands of times smaller than a human hair. Like a tree, one branch splits into two, and these further split into two more. This regular, exponential branching from the center results in a dendritic, spherical structure. We were able to freely decorate this molecular tree with metal ions, much like a Christmas tree. These molecular Christmas trees are gaining attention as new nanomaterials originating from Keio University, with potential applications in next-generation thin-film displays, thin-film solar cells, new therapeutic drugs, and batteries for electric vehicles.

As is clear from history, the creation of new materials such as nylon and semiconductors has greatly contributed to improving our quality of life. We expect that the discovery of such new substances will have a ripple effect, becoming foundational materials for nanotechnology and science, and will support the fields of electronics, biotechnology, and energy in the near future, heralding a new era.