Probing and creating photoinduced charge-separated states using multiple excitation techniques

Abstract

Photoinduced charge-separated (CS) states play a crucial role in photo-energy and photo-material conversion such as natural/artificial photosynthesis, photovoltaics and photoredox catalysis. For their effective utilization, CS states are required to have a large formation rate, high energy level and long lifetime, and a multiphoton/multiple excitation method is a promising approach for creating high-quality CS states, as represented by the Z-scheme in natural photosynthesis. Also from the viewpoint of time-resolved spectroscopy, multiple excitation techniques provide detailed information on ultrafast dynamics in the higher excited state, which is difficult to obtain using conventional transient absorption measurements. In this context, we will introduce formation of high-quality CS states using two-photon ionization beyond the traditional framework of electron transfer. In addition, signal-enhanced pump-repump-probe spectroscopy was developed and applied to detection of spatiotemporal evolution of electron-cation pairs in the solution phase.