What research are you engaged in?

Fig. 1: Examples of light-emitting metal complex crystals

My specialization is coordination chemistry, that is, the chemistry of metal complexes. Do you know metal complexes? The term “complex” means a complicated compound and a typical form of metal complexes is constructed by a metal ion and a set of inorganic and/or organic substances called ligands. Thus, coordination chemistry is the field in which a wide range of elements can be freely combined to produce an infinite number of materials. You can see many “complexes” in your surroundings which have peculiar properties and exhibit some special function. Red blood cells, for example, which carry oxygen to the extremities of our body via the blood, function mainly because of an iron complex with an organic substance known as porphyrin. I am particularly interested in complexes that exhibit photofunctionality and luminescence properties, and am engaged in research in these areas (Fig. 1). To date, I have created various luminescence chromic complexes that change color in response to stimuli, which includes temperature, pressure, solvents, vapor and light. For example, there exist platinum complexes that switch their light emissions on and off in response to alcohol vapors, or switch through a wide range of colors depending on their environment (Fig. 2).

How is your research related to our day-to-day lives?

Fig. 2: Crystal structure of a light-emitting platinum complex that changes color depending on its environment

Light-emitting metal complexes have been garnering a lot of attention recently, as they are used as organic electroluminescence (EL) materials in the currently popular flat-panel displays. Iridium complexes and platinum complexes have been used to create highly efficient organic EL materials. In addition, there is currently a large amount of research being conducted on the use of visible light by a type of solar cells known as “dye-sensitized solar cells”, which can be achieved through the use of ruthenium complex, among others. Substances that exhibit luminescence color changes are also used in environmental sensors. The metal complexes used in these applications are also the subject of basic research, as they are compounds that demonstrate interesting properties in and of themselves. It is important that we continually seek new substances and materials – after all, the potential number of combinations of elements is infinite. 

What sort of equipment do you use in your research?

Fig. 3: Light emissions spectrum of a platinum complex demonstrating changing light colors depending on solvent composition

Once you have decided what sort of complex you want, you first have to conduct synthesis experiments. We use a lot of classic glassware such as flasks and beakers, but for chemical synthesis you may also need to create a special atmosphere, such as an atmosphere with no oxygen, so we use vacuum lines, evaporators to achieve efficient distillation of solvents, and stirrers to achieve efficient mixing of reactive solutions, among other essential equipment. Once you have achieved synthesis, you have to examine what it is you have created. For this, we need a range of analytical devices and spectrum analysis equipment. Furthermore, it is extremely important to clarify the three-dimensional structure of the complex, to understand its attributes and functions, and in order to do this, we spend a lot of time and energy in crystallizing the sample. Once it has been crystallized, we use X-rays to conduct structural analyses. The structural diagram in Fig. 2 is based on the results of X-ray structural analysis. Once we have achieved the complex we were aiming for (or perhaps something unexpected), we look at its properties. For example, in order to clarify the sort of light-emitting properties it has, we use a range of devices (fluorospectrometers, fluorescence lifetime measurement systems and quantum yield measurement devices) to measure the wavelength, strength, timing, etc. of its light emissions (Fig. 3). In addition, it is important for us to perform thermal analysis and measure the UV/visible/infra-red absorption spectrum, in order to establish the state of the sample and any structural changes.

What is interesting about your research?

The interesting thing about university research is that you can follow what you are interested in and try out new things to your heart’s content. Of course, a lot of experiments do not turn out the way you expect, but when you suddenly see a crystal glittering in the solution, or detect light emitting from a sample under the microscope, or when you succeed in structural analysis and the molecular structure appears on the computer… there are many moments of happiness in this sort of research. As researchers, though, in addition to the pursuit of knowledge, we have to constantly remind ourselves of our responsibility to contribute to humanity.

What are you aiming for?

I am aiming for the creation of photofunctional materials which exhibit outstanding properties such as extremely intense luminescence, highly sensitive chromic behavior, and superior photosensitizing ability. I hope materials and scientific findings obtained in my laboratory will contribute to the development of the science and technology, and better human life and happiness. In order to do this, I feel it will be important to continue basic research much more into the utilization of light and the elements.