Research

Creation of new elemental materials

Organic and polymeric materials have been used in our daily lives, and modern electronic devices as well. However, conventional materials consist of a limited number of elements, such as carbon, hydrogen, oxygen, and nitrogen. We think that advanced materials having superior properties would be obtained by employing elements that have not been used in conventional materials. Based on this idea, we aim to develop optoelectronic materials, catalysts, and sensors with unique elemental functions. Furthermore, we expect that new characters of elements can be revealed from the results. The discovery of fundamental properties of elements and applications for practical materials are our motivation for exploring.

Various types of element materials have been developed. For example, we recently found that some elemental complexes can exhibit intense emission in solid where conventional organic dyes commonly show poor luminescence. Moreover, by adding external stimuli, luminescent color changes were induced. From the mechanistic analyses, we showed that elements should play a critical role in such unique optical behaviors. On the basis of these stimuli-responsive and environment-sensitive solid-state luminescent properties, chemical sensors and bioprobes have been developed such as for monitoring trace amounts of harmful chemicals and real-time sensing on skin surfaces. These technologies are applicable for creating advanced sensing systems.

By homogeneously mixing organic and inorganic components at a nanometer scale, organic-inorganic hybrid materials can be obtained. Owing to the high thermal stability of inorganic species, hybridization is regarded as one of the facile strategies for reinforcing the durability of organic materials. Furthermore, by using cubic silica molecules as a scaffold, we can obtain designable hybrids. Based on the preprogrammed designs, we can obtain stimuli-responsive hybrid materials, such as luminescent chromic hybrid rubbers for detecting distortion, electric conductive flexible hybrids which can monitor the degree of external forces, and thermally stable liquid crystals. In particular, nano-plastics in water dispersion were detected by luminescence color changes with hybrid gels. These future sensing materials would be helpful for establishing precise environmental assessment.

Discovery of new element periodic table

Since the establishment of the element periodic table by Mendeleev 150 years ago, we use the table for estimating material properties. In contrast, we have found curious element properties which do not correspond to the preliminary estimation. After photo-excitation, some element complexes show individually different behaviors even with the same element group. We are interested in the roles of elements in the excited state in material properties. By introducing another bond into the central element of elemental complexes, we can form hyper-valent states of the element. Recently, we can obtain stable hyper-valent complexes and find that unique environmental sensitivity appears to originate from extraordinary atomic valences. These new properties are promising platforms for designing the next generation of sensing technologies. By obtaining new insight, we can expect the establishment of a “new element periodic table”.