Molecules in the electronic excited state take important roles in various photo-functional processes, such as photo-energy and photo-material conversions. For molecules in condensed phase, however, three general restrictions limit the efficient utilization of light energies. First, molecules in higher excited states usually very rapidly relax to lower electronic states (Kasha's rule) and some portion of the absorbed photon energy is diminished in this relaxation. Second, a large number of the molecules excited in assemblies undergo fast annihilation and only a small number of excited state molecules can remain, leading to the loss of the number of photons absorbed in the system. In addition, the electronic state accessible through the one-photon absorption is limited by the optical selection rule and we cannot access various dark electronic excited states of molecules.
The purpose of the present project is to develop and advance excitation methods and molecules/molecular assemblies that can overcome these three restrictions, by exploring methods beyond the conventional paradigm, "one-photon and one-molecule outcomes"; such as multiple excitation, multiphoton absorption, strong modulation of electronic states, coherent and cooperative responses of molecules, and rational design of molecular assemblies. By integrating these investigations, we aim to acquire general principles on "photosynergetics" enabling more effective utilization of the light energy in molecular systems.
Hiroshi Miyasaka (Osaka University)