Charge Transfer Dynamics in Dye-Sensitized Photocatalysts Using Metal Complex Sensitizers with Long-Wavelength Visible Light Absorption Based on Singlet–Triplet Excitation

Yamamoto, Haruka; Tanaka, Toshiya; Oura, Masahito; Kopera, Kelly M.; Okazaki, Megumi; Onda, Ken; Mallouk, Thomas E.; Maeda, Kazuhiko

doi:10.1021/acscatal.5c06687

Charge Transfer Dynamics in Dye-Sensitized Photocatalysts Using Metal Complex Sensitizers with Long-Wavelength Visible Light Absorption Based on Singlet–Triplet Excitation

Journal Article · Fri Dec 05 00:00:00 EST 2025 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.5c06687· OSTI ID:3009717

Yamamoto, Haruka ^[1]; Tanaka, Toshiya ^[1]; Oura, Masahito ^[2]; Kopera, Kelly M. ^[3]; ^[1]; ^[2]; ^[3]; ^[1]

Institute of Science Tokyo (Japan)
Kyushu University, Fukuoka (Japan)
University of Pennsylvania, Philadelphia, PA (United States)

An Os(II) polypyridyl complex was applied as a photosensitizer in dye-sensitized photocatalyst systems based on Pt-intercalated HCa₂Nb₃O₁₀ and Pt-loaded TiO₂. The Os(II) complex exhibits a spin-forbidden but partially allowed triplet metal-to-ligand charge transfer (³MLCT) transition, enabling broad visible light absorption up to 800 nm, which surpasses that of conventional Ru(II)-based dyes. Despite its shorter excited-state lifetime compared to Ru(II) complexes, efficient electron injection from the excited Os(II) dye into the semiconductor was confirmed. Under visible-light irradiation, the Os(II)- sensitized photocatalysts showed higher H₂ evolution activity than the Ru(II)-sensitized photocatalysts when sodium ascorbate was used as an electron donor, demonstrating effective utilization of long-wavelength visible light. In contrast, negligible H₂ evolution was observed when NaI was employed as a redox mediator for Z-scheme water splitting. Transient absorption spectroscopy revealed that the lack of activity stemmed from inefficient electron transfer from I⁻ to oxidized Os(II). These findings highlight the importance of selecting appropriate redox mediators to fully exploit long-wavelength dyes for overall water splitting under visible light.

View Accepted Manuscript (DOE)

Research Organization:: US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Basic Energy Sciences (BES)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division (CSGB)

Grant/Contract Number:: SC0019781

OSTI ID:: 3009717

Journal Information:: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 24 Vol. 15; ISSN 2155-5435

Publisher:: American Chemical Society (ACS)Copyright Statement

Country of Publication:: United States

Language:: English

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