Topics that shape the future
- Closer look at research results -

Another feature of "Rare Earth Elements" that you should pay attention to is that the belly band does not completely surround the rare earths, but is interrupted in the middle. This interruption makes it easier to dissolve in the medium. Not only is it easy to dissolve, but it also maintains its structure and remains in a stable state, making it easy to control the properties and dimensionality mentioned earlier, expanding the possibilities for various applications. It was very difficult to stabilize the optical functions and molecular structure, and it took more than 10 years from the time the structure was proposed to the time it was published in a paper, and about 12 years if you include the time from the idea to planning and starting the experiments. Really, all we can do is fight with a positive attitude and perseverance.

We never thought about giving up halfway through. We never even considered giving up. It wasn't like we wanted to be the best in this research field or amaze the world, but rather we wanted to take on the challenge precisely because it was something that no one had done before. We wanted to cherish the feeling that we would be the first in the world to demonstrate the concept through experiments. It was fun to be the first to do something that no one had achieved before, and we spent every day repeating trial and error, trying to find ways to improve the stability and create a structure that could be used in more places. That feeling hasn't changed since our first paper on helical rare earth complexes was published.
This molecular design was actually arrived at after a certain failure. The mechanism by which rare earths emit light is by converting ultraviolet light into the visible range, so the experiment is carried out under ultraviolet light. However, although the rare earth complexes previously used were stable under the gentle light of ultraviolet lamps, they were destroyed by the ultraviolet laser light used to interpret the spectra in detail, and the data and the substance were no longer in a state where they could be discussed. From this experience, we realized the need for molecules that would not be destroyed by laser light, and we began to develop them.
The concept is simple. If you want to prevent a child swimming in the ocean from being swept away by the waves, it is better to connect with both hands than with one hand, as this makes them less likely to be swept away and more stable. In the same way, molecules become more stable if many hands are connected together. This is the principle that has been known for 100 years as the "chelating" effect of the crab claws mentioned earlier. We thought that by utilizing this principle, we could increase the number of connections as much as possible to stabilize both the molecules and their luminescence function.
Furthermore, rare earth elements need an energy "receptacle" to receive ultraviolet energy and convert it into visible light, and this receptacle is determined by the type of rare earth. For example, the rare earth element europium (Eu) only has receptacles that glow red. When we increased the number of connecting places to stabilize the system, the energy received by each "receptacle" decreased, and we encountered a problem in that it could only receive weaker energy than the red light. Therefore, we devised a way to connect the elements in a way that would allow for a stable structure while still allowing for a good exchange of energy. Thanks to the synthesis technology of Dr. Hideki Otsu, who was an assistant professor at the time (now an associate professor at Toyama University), we were able to realize my concept. In other words, we arrived at a structure that could exchange energy while maintaining the stability of the rare earth complex. Although it took time, I think that it was because of this repeated trial and error that we were able to create something highly original.

The slits in the belly band I mentioned earlier, and the number of claws, are not something I arrived at by chance. I like to think about it based on principles, set up hypotheses, and confirm them, rather than just going by chance. This is also the result of many years of research and learning. I designed it boldly based on principles, repeated experiments, verified the results, and then reflected on the molecular design, revised it, and conducted experiments repeatedly, and I think I arrived at the results I expected. This type of research is positioned as material development and principle elucidation through molecular design. In particular, the incorporation of the "chelating" effect was a major factor in realizing the concept. The ideal is to reflect the accumulated knowledge and small results and failures in the molecular design at each stage of the experiment, and build a better path to the desired results. Because I was able to create a groundbreaking molecular structure, I still receive happy comments from researchers not only in Japan but also overseas when I meet them, such as "I know your paper," or "I thought that's how it came about!" Through persistent research and working with students to synthesize many modified versions of this molecule, the number of papers we published increased to the point that it caused a massive traffic jam (laughs). However, the first report was brilliantly published by the Royal Society of Chemistry in the UK in 2014, and we continued to publish papers on new luminescence phenomena of derivatives at a rapid pace, which spurred on collaborative research and co-authored papers both domestically and internationally.