Prof. Takashi Kato has presented original concept and methods to organize molecules and functionalize molecular assemblies and has been widely recognized to open a new field, that is, functional molecular chemistry. He has developed supramolecular liquid crystals, functional molecular assemblies, and organic/inorganic fusion materials, which provide a new perspective to molecular materials.
1. Construction of supramolecular liquid crystals through control of intermolecular interactions
He has developed supramolecular liquid crystals for the first time. In particular, the concept building supramolecular structures through the formation between carboxylic acids and pyridyl moieties has been used by many researchers. He also prepared side-chain LC polymers and LC networks that change their structures through the association and dissociation of the dynamic H bonds. These are the pioneering findings on supramolecular materials and polymers. Throughout these works, he established a novel research field of dynamic functional materials utilizing intermolecular interactions such as hydrogen bonding, ionic interactions, and charge-transfer interactions.
In addition, he has developed mechanochromic luminescent liquid crystals by using structural change of these molecular assemblies in response to external stimuli. Combination of mechanical and thermal stimuli was found to generate tricolored luminescence for the first time. He has further studied redox-responsive LC materials by aligning LC rotaxanes that exhibit mechanical movement induced by redox stimuli.
His research has made a significant impact on the world and led to the development of a new field combining mechano-chemistry and photochemistry.
2. Development of functional transport materials forming nanosegregated LC structures
He has developed transport materials showing anisotropic and efficient transport of ions, electrons, and molecules by using nanosegregated structures of liquid crystals. He established anisotropic ion-conductive materials forming layered smectic LC structures and columnar LC structures through self-assembly of block molecules consisting of ionic and non-ionic moieties. In particular, ionic moieties or oxyethylene chains were combined with rod- or fan-shaped hydrocarbon moieties to form functional nanosegregated structures. He demonstrated, for the first time, one-dimensional and two-dimensional anisotropic ion transport by controlling the orientation of these materials. He also constructed LC materials exhibiting bicontinuous cubic phases with three-dimensional networks, which have been rarely reported earlier. Furthermore, he succeeded in the preparation of nanostructured films by in situ polymerization of monomers forming LC nanostructures. He also demonstrated the applications of nanostructured ion-conductive liquid crystals as electrolytes for lithium batteries and solar cells, and as water treatment membranes.
Thus, he provided new directions to the functionalization of liquid crystals and molecular assemblies through the construction of LC nanostructures.
3. Development of LC physical gels
He demonstrated for the first time gelation of liquid crystals with low molecular weight gelators from his unique viewpoint, and developed a new concept of functional materials named "LC physical gels". The characteristics of LC physical gels are to preserve dynamic properties of liquid crystals even in the soft solid state. As for the responses to electric fields, LC physical gels were found to show faster responses with lower driving voltages than the liquid crystals alone. This was explained by the formation of microphase-separated structures of liquid crystals and one-dimensional molecular aggregates, resulting in the tuning of interactions at the interface between these two components. Furthermore, he developed photo-functional devices that efficiently switch light transmission and scattering through the control of the composite structures consisting of one-dimensional fibers and liquid crystals. Thus, he provided new aspects for the design of molecular assembled materials through the utilization of phase-separated structures, hierarchical structures, and aligned structures.
4. Biomineralization-inspired organic/inorganic Fusion Materials
He has led new fields of materials inspired by biomineralization processes that form organic/inorganic composites such as the nacre of shell, bones, and teeth. He found that thin-film hybrids comprising of calcium carbonates are formed on chitin or chitosan matrix in the presence of acidic macromolecules. This discovery was highly appreciated by international communities. He also prepared the calcium carbonate-based hybrids with a variety of morphologies. For example, periodically patterned hybrids have been obtained using polymer gels as the matrix. Based on this method, not only calcium carbonate-based hybrids but also hybrids comprising of hydroxyapatite and zinc oxides with various morphologies have been developed. He also succeeded in the preparation of amorphous calcium carbonate (ACC) using acidic macromolecules. Moreover, new composite materials of ACC with cellulose nanofibers have also been developed.
As mentioned above, Professor Kato has established new advancement in the field of materials chemistry. He has shown new design of functional self-assembled materials. Thus, He has been internationally recognized to be a leader. The Chemical Society of Japan (CSJ) has recognized Professor Kato to deserve the CSJ Award.