Controlling excited-state proton transfer dynamics using nanocavity engineering

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Controlling excited-state characters of molecules is of great importance for developing novel photofunctional materials. Encapsulation of a molecule is one of the promising methods by coupling with rapid development of novel porous materials such as metal organic frameworks. Nevertheless, there is little information on excited characters in a small cavity due to experimental and theoretical difficulties. We developed the handling methods of molecules in a various nano- and micro-cavities and combined with our ultrafast spectroscopic techniques. As a result, we found that the emissive character of a prototypical emissive molecule, benzophenone, is dramatically changed when it is encapsuled in a nanocavity of mesoporous material, MCM-41. Aiming at applications of this novel phenomenon to luminescent devices, we also investigated encapsulation effects on emissive materials for organic light emitting diode (OLED), and found that the encapsulation highly improves their thermally activated fluorescence (TADF) activities. Recently, TADF activities have attracted much attention for applications not only to the emissive materials for OLED but also to the harvesting of long-lived triplet-states in various photofunctional materials. Thus, this new finding would be contributed to developments of novel highly efficient photofunctional devices. Moreover, we discovered that light irradiation accelerates encapsulation process for a certain type of emissive materials. This finding would open a new world such as light control of encapsulation and decapsulation of photofunctional molecules.