多重励起分光による高位励起状態における化学反応の探究

抄録

Electronic excited states play a central role in photo-energy and photo-material conversion processes such as photosynthesis, photovoltaics and photocatalysis. Although molecules inherently possess diverse excited states at a higher energy level, such excited states are rapidly deactivated into the lowest excited state via ultrafast internal conversion. Thus, electronic excited states we can utilize for creation of novel photoresponses and photofunctions are limited to be the lowest excited state in a given spin multiplicity, as advocated as Kasha's rule. However, recent studies have reported exceptional reaction behavior in higher excited states not only for classical examples such as porphyrin and azulene but also for emergent molecular systems playing a key role in materials science and biology. In this context, excited states lying at the higher energy level are one of frontier left in molecular science. In this article, we introduce recent advances in our studies on photochemical reactions such as isomerization, ionization, and electron transfer in the higher excited state revealed by multiple excitation spectroscopy. In addition, we describe exciton diffusion dynamics in molecular aggregates which involve more diverse electronic states and show more elaborate photophysical properties and functions than single-molecule level.