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Ultrafast capture of electrons ejected by photoionization leading to the formation of a charge-separated state at a high energy level

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Abstract

Electron transfer reactions driven by two-photon ionization in the higher excited state were investigated via transient absorption spectroscopy, with the aim to develop a method for creating the charge-separated (CS) state with a large formation rate, high energy level, and long lifetime. In the proof-in-principle experiments using pyrene and biphenyl as a model system, femtosecond transient absorption spectroscopy revealed that intense irradiation of an ultraviolet laser pulse at 355 nm efficiently pumps up pyrene into a higher excited state via a stepwise two-photon absorption, and then an ionization process takes place. An electron ejected from pyrene is directly captured by biphenyl with a time constant of 200 fs without the diffusion process of the electron in solution. The energy level of the CS state (Py+–Bp) thus formed was estimated to be higher than that of the S1 state of pyrene by 0.53 eV. In addition, the subsequent ionic dissociation without a remarkable geminate recombination in the sub-nanosecond to nanosecond time region effectively avoids the quantity loss of the CS state. By applying the two-photon excitation method, we experimentally achieved ultrafast formation of the long-lived CS state at a high energy beyond the traditional framework of electron transfer reactions.

Graphical abstract: Ultrafast capture of electrons ejected by photoionization leading to the formation of a charge-separated state at a high energy level

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Article information


Submitted
15 Apr 2020
Accepted
08 Jun 2020
First published
08 Jun 2020

Phys. Chem. Chem. Phys., 2020, Advance Article
Article type
Paper

Ultrafast capture of electrons ejected by photoionization leading to the formation of a charge-separated state at a high energy level

T. Kawakami, M. Koga, H. Sotome and H. Miyasaka, Phys. Chem. Chem. Phys., 2020, Advance Article , DOI: 10.1039/D0CP02029J

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