Chemistry of Soft Two-dimensional Materials
from Keio's Faculty of Science and Technology The search for flexible material design that moves and attributes function to molecules

The pursuit for functional and soft 2D material structures

Throughout the research world, unexpected discoveries are often described as “serendipitous.” Chemistry is no exception, with results from failed experiments sometimes leading to unexpected findings and useful data. Oaki of the Department of Applied Chemistry showed us a blackened sample bottle (Fig. 1, left) he says led to an “unexpected discovery” 10 years prior, explaining “I have been doing research for about 20 years, and have had an experience that I could call serendipitous on two occasions.”
In university laboratories, students conduct research under the guidance of faculty members such as professors and associate professors. The faculty and students discuss and decide the direction and method of research together, but it is the students who carry out the experiments. Oaki likes to communicate with (or something like that...) how his students conduct their experiments and the results of their collected samples and then engage students in discussion. On one particular occasion, his attention was drawn by a student who was conducting an experiment to coat the surface of a dendritic crystal of iron nitrate with a conductive polymer in order to apply it to an electrical circuit. The student, thinking he had failed in his attempt, proceeded to dump the blackened sample bottle into the disposal bin for experimental waste.
“I instructed the student to reuse the bottle, given that normal grime can be removed from glass when washed. The student replied that it wouldn’t come off,” Oaki recalls. “I knew intuitively that something interesting was afoot as a coating on a glass bottle so black, even, and strong, should not have been produced by the planned experiment.”
Following his instincts, he examined the black substance. The polypyrrole film they expected to form on the crystal surface of the iron nitrate had also adhered to the entire inner wall of the bottle. "Polypyrrole, which is a series of pyrroles (see the figure), is a ‘conjugated polymer’ in which double bonds and single bonds are alternately linked. They are incapable of mixing with solvent due to their rigid chemical structure. In other words, it should not be possible for them to form a paint-like coating. This means that while many conjugated polymers are highly functional in terms of conductivity, heat resistance, and redox activity, applying the substance can prove quite a challenge.
However, this failed experiment showed that conjugated polymers could easily be coated on various substrates and substrate surfaces," Oaki explained, emphasizing that the black sample bottle was a discovery, not a failure.

Fig. 1: Two serendipities

Upper row, lower left: Reproduction of interaction with student at the time of the first “unexpected discovery,” which is used when giving lectures on the topic. The student attached iron nitrate crystals to the lid of the sample bottle, added the monomer liquid which serves as the base of the coating, and closed the lid. It was thought that when this was allowed to stand at 60°C, the monomer liquid would evaporate and a polypyrrole coating would form solely on the surface of the iron nitrate crystals. In reality, the monomer vapor reacted with the iron nitrate, filling the bottle and creating a solid coating.

Lower right: The second “unexpected discovery.” A network structure is formed from a reaction between pyrrole with benzoquinone (middle). This could be easily delaminated (photo), and the produced nanosheets had the property of acting as a hydrogen-generating electrocatalyst.

The “coatability” of polypyrrole film is not the only factor to its viability; its quality also comes into question. At first the film was not sufficiently conductive to be used, but this problem was solved by changing the strength of the oxidant (a benzoquinone derivative) combined with pyrrole during its formation. “With that I thought that my research had reached its ending point, until one of my students said that they would attempt to synthesize the film by means of combining pyrrole and benzoquinone without substituents. Drawing from my own chemical knowledge, I warned the student that the reaction would not be feasible due to insufficient oxidizing power, but they proceeded with experiment anyway,” Oaki remembers.
Their effort succeeded, resulting in the creation of a new polymer material consisting of a loosely stacked random network formed of pyrrole and benzoquinone (Fig. 1, right). Not only was it easily peeled off to produce thin nanosheets, but it was also found that the nanosheets function as a catalyst to electrochemically convert protons (H⁺) into hydrogen (H₂). At present, hydrogen is of interest to researchers because it is an energy source that does not generate carbon dioxide. However, in general, since hydrogen production requires a platinum catalyst, there are inevitable cost and resource complications. This nanosheet has received a large amount of interest because it may present a possible alternative as a metal-free organic compound.
While Oaki claims that these two incidents were serendipitous, the story hints at Oaki’s deep insight, chemical expertise, attentive ear when interacting with students, and ability to ignore “common sense” when pursuing an interesting lead that was necessary to capitalize on the fortunate turn of events.

This is how Oaki’s research focusing on conjugated polymers began. His methodology is to give flexibility (molecular mobility) to generally rigid conjugated polymers by various chemical methods, creating two-dimensional materials such as layered structures and nanosheets, and then explore their functionalities. Oaki’s mindset is that “it is important to first enjoy creating substances; figuring out the new material’s specific characteristics comes later.” In the aforementioned case of a two-dimensional material made from polypyrrole and benzoquinone, “creating” was the important part of the process—its ability to catalyze hydrogen was a coincidental byproduct.
Oaki is also developing sensor materials that quantitatively detect heat, light, and force (Fig. 2, top) using a similar research methodology. When the diacetylene molecules arranged in layers are irradiated with ultraviolet light, the triple bond moieties polymerize with each other and turn blue. When this polydiacetylene is stimulated with heat, force, light, etc., the molecular chain is twisted and other subtle changes occur in the structure, causing the color to change. By manipulating what guest ions and molecules are inserted between the layers, scientists can adjust the material’s responsiveness to external stimuli.
One of the materials developed using this process changes color depending on the frictional force created when brushing teeth. This then can be used to create a sensor that can gauge, based on color, an appropriate level of strength when using a toothbrush.

Oaki due to his enjoyment of making new materials, has been incorporating “materials informatics (MI)” into his research since 2016 (Fig. 2, bottom). MI is said to accelerate research and development by utilizing informatics for material research. Specifically, he feeds the artificial intelligence a large amount of data about materials, and tasks it with finding possible factors necessary to discover new substances and improve their performance. However, in many cases, it is difficult to interpret exactly what the AI has done after processing the data.
Oaki is trying to prevent his AI from becoming a “black box” (an AI system that gives no view of its inner workings) by judging whether the computer-generated factors are important or correct based on his own chemical knowledge. “It is important for researchers to know when to take the lead,” he says, “But artificial intelligence can also accomplish a large number of tasks, so it is our job is to make good use of it.”
I am looking forward to the next "unexpected discovery," and how AI innovation will aid in sharpening Oaki's insight.

I don’t have a strong recollection of when I was little. So much so that I’m learning about it now, mildly surprised to find comments written on elementary school report cards unearthed while cleaning my parents’ home saying that I was “restless.”
I remember playing the flute in brass band during junior high school and high school. It may have also been due the influence of my mother who was involved in music, but I became totally absorbed in band. Even though I hated being forced to play piano when I was little, I think I was able to try my best with flute because it was something I chose by myself.
I have such fond memories of grueling practices with my band mates as we tried to get into the Kanto regional championships. In retrospect I think it was a bit of the Showa-era die-hard spirit, but it made me mentally tough. My music teacher was incredibly strict, but I am grateful for the lessons they taught me about etiquette, navigating relationships, and teamwork. For the longest time since graduating I have thought about visiting my teacher to say hello... But if I went now, I feel like I would be met with an angry “Took you long enough!” [laughs].

There were times when I really wasn’t sure about it. Actually, I had trouble deciding between physics, chemistry, and mechanical engineering when it was time to take the university entrance exams. The reason I chose Keio University was because students weren’t required to declare a major until starting their second year. Before settling on chemistry, I even considered entering the School of Medicine and there was a time during the second year of my master’s program when I thought about joining the corporate workforce. However, when it came time to search for a job, I started to feel like I was leaving my research incomplete. That was the turning point for me when I decided to pursue a PhD. After constantly being told to “aim higher” by my junior and high school brass band music teacher, I couldn’t stomach graduating without finishing everything that I had set out to accomplish.

When I return to my office I sometimes drop in on the students. They probably find it annoying, but for me to see students conducting experiments and their samples is just as fun as conducting experiments myself. On a more serious note, as a faculty member, I need to pay attention to whether experimental data are collected correctly, whether there are any issues, and whether experiments are conducted safely. To that end, I find it is crucial to monitor on-site experiments as much as possible.
I consider my students to be colleagues who share in our collective goal of “enjoying the best research in the world.” So I’m able to be frank with them. When I don’t know something, I tell them “I don’t know.” When I think something is off I tell them “I think this is off.” And, when someone puts in a good effort, I compliment them on a job well done. We talk about things that have nothing to do with research as well, having normal interactions that don’t enforce a strict teacher-student hierarchy.
Above all, I want them to personally invest in and enjoy their research. In order to get there, I believe it is a teacher’s role to help students have their “lightbulb moment.” Every student is different in what leads them to that moment, but once they light up, their progress always exceeds my expectations.

As I mentioned during my research introduction, my current exploration of conjugated polymers began following an incident in which one of my students threw away a blackened sample vial. Similarly, we discovered a new material after my students conducted an experiment I had advised them was pointless. I am always learning from my students, and together we have come across quite the variety of “unexpected discoveries.” As a result of these outcomes, I decided about 10 years ago to change my research to focus on such discoveries.
By telling the students of these past happenings, they feel compelled to come and show me samples when something unusual occurs during an experiment. “Unexpected discoveries” are not so common, but we find something interesting in about one in 20 reports. Humans naturally tend to treat things as failures when they don’t go as expected. In those moments, in addition to asking my students to think about what could be done to make the original experiment a success, I want them to consider the possibility that a change of perspective might lead to something new and to challenge the notion of what is “expected” in the first place. I am always so excited when we make “unexpected discoveries” because in that moment we may be the only ones in the world with that new piece of knowledge.
There was another reason I changed my research. It was right around that time when I was told by fellow researchers that there was “nothing of interest in your research lately,” that “you should change your research so that it differs from your PhD,” and other statements along the lines of “you should focus on things that you’re actually capable of.” This is what got me to think I actually should pursue an independent course of research, blaze new trails in research based on my own discoveries, synthesize unique materials, and aim to develop special uses for them.

You understand when you look at the number and content of published papers, but the sense among those in the field is that the research and development capabilities of China and other countries are increasing with tremendous speed and power. I personally feel concerned that if Japan follows its current trajectory it will left far behind. My hope is that the field will be revitalized as more people, regardless of age or occupation, will come to know the joy of chemistry.

I would agree, though I haven’t done anything special myself. That’s mostly because I consider research and education to be the same thing, though others hold varying opinions on the subject. If you are doing research alongside students, it will naturally become an educational experience.
In recent years, interdisciplinary and joint research projects that involve other fields have increased, so solitary research that I do all alone has given away to a more collaborative approach with co-researchers. I first want my students to learn how to interact with researchers from other fields who don’t speak in the same technical language, how to enjoy while collaborating to obtain the best results, and how to communicate not only as a researcher but also as a well-rounded human being.

While you can’t say that Keio’s faculties are particularly large-scale, I would say that they are appropriately sized. I used to think that the bigger the university, the better, but at some point, after conversing with teachers in the School of Medicine, I realized that what makes it so easy to communicate with teachers in other disciplines is that the university isn’t too big. There is also a sense of unity and community at Keio.
I hope that myself and others able to use this great advantage while conducting research here.

In a variety of fields there is a growing demand for the development of visual indicators for stimuli such as light, heat, and force. I’ve taken over research handed down from upperclassmen on materials that change color from external stimuli. The main reason that I chose to study with Professor Oaki was that the research felt very future-oriented, but another decisive factor in choosing his laboratory was the welcoming atmosphere. Here, students from different academic backgrounds share knowledge and push each other while enjoying their research. After completing my Master’s degree I plan to enter the work force, but I will cherish the research and communication skills I learned here and intend to use them to expand my horizons. (1st-year master’s student)