Today, our world is facing the quite large and common problem to find the way for overcoming the limitation of the energy and other resources.
For achieving continuous and sustainable development, it is the key to realize the materials which can convert the infinite light energy into various forms such as chemicals, electricity, magnetic response and mechanical energies with high efficiency.
In addition, it is also the essential and common problem for the field of telecommunication and photonic computation, because such materials are also expected to show ultrafast photonic response such as dramatic color change to external stimulations by weak light.
To realize such photonic materials showing chemical, electronic and photonic responses to weak light excitation with ultrafast response time, it is a key to utilize interactions among constituents. The purpose of our research laboratory is to contribute into physical and chemical foundations of cooperative phenomena triggered by photo-excitation.
This class of exotic photo-effect can be named as a photo-induced phase transition (PIPT) and is analogous to the domino effect as shown in Fig.1.
The very recent progress in the study on electronic (spin)-structural transformations in molecular systems has stressed the importance of cooperativity among constituents of materials. This opens the way for controlling the switching by external field (light, magnetic,...) between different states and/or phases by virtue of cooperative interactions.
Therefore it becomes an attractive and realistic target for materials science to search for multistable organic and inorganic systems accompanied with the changes in structural, magnetic, transport, optical, dielectric properties which can be controlled by light stimulations.
In addition, the dynamics and kinetics of the phase transformation in this class of material is important not only for materials science and its application but also for the basic research on the (nonequilibrium) statistical physics and chemistry.
We are also devoting our efforts for developing the facilities to probe the structural changes induced by light excitation in atomic and molecular scales with pico(10-12) and femto(10-15) second time resolution under collaboration with big facilities such as synchrotron (SR).