Photoexcitation and One-Electron Reduction Processes of a CO 2 Photoreduction Dyad Catalyst Having a Zinc(II) Porphyrin Photosensitizer

• Published in: Inorganic chemistry 2024-12, Vol.63 (50), p.23524
• Main Authors: Honda, Teruyuki, Ehara, Takumi, Sato, Ren, Ogawa, Tomohiro, Kuramochi, Yusuke, Satake, Akiharu, Miyata, Kiyoshi, Onda, Ken
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.4c02271

We have explored the photophysical properties and one-electron reduction process in the dyad photocatalyst for CO photoreduction, , in which the catalyst of -[Re(1,10-phenanthoroline)(CO) Br] is directly connected with the photosensitizer of zinc(II) porphyrin ( ), using time-resolved infrared spectroscopy, transient absorption spectroscopy, and quantum chemical calculations. We revealed the following photophysical properties: (1) the intersystem crossing occurs with a time constant of ∼20 ps, which is much faster than that of a single unit, and (2) the charge density in the excited singlet and triplet states is mainly localized on , which means that the excited state is assignable to the π-π* transition in . The one-electron reduction by 1,3-dimethyl-2-phenyl-2,3-dihydro-1 -benzo[ ]imidazole occurs via the triplet excited state with the time constant of ∼100 ns and directly from the ground state with the time constant of ∼3 μs. The charge in the one-electron reduction species spans and the phenanthroline ligand, and the dihedral angle between and the phenanthroline ligand is rotated by ∼24° with respect to that in the ground state, which presumably offers an advantage for proceeding to the next CO reduction process. These insights could guide the new design of dyad photocatalysts with porphyrin photosensitizers.