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Two Excited State Collaboration of Heteroleptic Ir(III)-Coumarin Complexes for H-2 Evolution Dye-Sensitized Photocatalysts

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Title: Two Excited State Collaboration of Heteroleptic Ir(III)-Coumarin Complexes for H-2 Evolution Dye-Sensitized Photocatalysts
Authors: Kobayashi, Atsushi Browse this author →KAKEN DB
Muramatsu, Eiichirou Browse this author
Yoshida, Masaki Browse this author
Kato, Masako Browse this author
Keywords: photocatalysis
water splitting
Ir(III) complex
dye sensitization
Issue Date: May-2021
Publisher: MDPI
Journal Title: Energies
Volume: 14
Issue: 9
Start Page: 2425
Publisher DOI: 10.3390/en14092425
Abstract: Interfacial electron injection from a photoexcited surface-immobilized dye to a semiconductor substrate is a key reaction for dye-sensitized photocatalysts. We previously reported that the molecular orientation of heteroleptic Ir(III) photosensitizer on the TiO2 nanoparticle surface was important for efficient interfacial electron injection. In this work, to overcome the weak light absorption ability of heteroleptic Ir(III) photosensitizer and to improve the photoinduced charge-separation efficiency at the dye-semiconductor interface, we synthesized two heteroleptic Ir(III) complexes with different coumarin dyes, [Ir(C6)(2)(H(4)CPbpy)]Cl and [Ir(C30)(2)(H(4)CPbpy)]Cl [Ir-CX; X = 6 or 30; HC6 = 3-(2-enzothiazolyl)-7-(diethylamino)coumarin, HC30 = 3-(2-N-methylbenzimidazolyl)-7-N,N-diethylaminocoumarin, H(4)CPbpy = 4,4 '-bis(methylphosphonic acid)-2,2 '-bipyridine], as the cyclometalated ligands and immobilized them on the surface of Pt-cocatalyst-loaded TiO2 nanoparticles. Ultraviolet-visible absorption and emission spectroscopy revealed that the singlet ligand-centered ((LC)-L-1) absorption and triplet (LC)-L-3 emission bands of Ir-C30 occurred at shorter wavelengths than those of Ir-C6, while time-dependent density-functional-theory data suggested that the ligand-to-ligand charge transfer (LLCT) excited states of the two complexes were comparable. The photocatalytic H-2 evolution activity of the Ir-C6-sensitized Pt-TiO2 nanoparticles (Ir-C6@Pt-TiO2) under visible light irradiation (lambda > 420 nm) was higher than that of Ir-C30@Pt-TiO2. In contrast, their activities were comparable under irradiation with monochromatic light (lambda = 450 +/- 10 nm), which is absorbed comparably by both Ir-CX complexes. These results suggest that the internal conversion from the higher-lying LC state to the LLCT state effectively occurs in both Ir-CX complexes to trigger electron injection to TiO2.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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