Two Excited State Collaboration of Heteroleptic Ir(III)-Coumarin Complexes for H2 Evolution Dye-Sensitized Photocatalysts
Two Excited State Collaboration of Heteroleptic Ir(III)-Coumarin Complexes for H2 Evolution Dye-Sensitized Photocatalysts
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DOI：
10.3390/en14092425
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发表时间：
2021-04
期刊：
影响因子：
3.2
通讯作者：
A. Kobayashi;Eiichirou Muramatsu;Masaki Yoshida;Masako Kato
中科院分区：
文献类型：
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作者：
A. Kobayashi;Eiichirou Muramatsu;Masaki Yoshida;Masako Kato
从光激发的表面固定染料到半导体基底的界面电子注入是染料敏化光催化剂的关键反应。我们之前报道过，异配体铱（III）光敏剂在二氧化钛纳米颗粒表面的分子取向对于高效的界面电子注入非常重要。在这项工作中，为了克服异配体铱（III）光敏剂吸光能力弱的问题，并提高染料 - 半导体界面的光致电荷分离效率，我们合成了两种带有不同香豆素染料的异配体铱（III）配合物，[Ir(C6)2(H4CPbpy)]Cl和[Ir(C30)2(H4CPbpy)]Cl [Ir - CX；X = 6或30；HC6 = 3 - (2 - 苯并噻唑基) - 7 - (二乙氨基)香豆素，HC30 = 3 - (2 - N - 甲基苯并咪唑基) - 7 - N,N - 二乙氨基香豆素，H4CPbpy = 4,4′ - 双(甲基膦酸) - 2,2′ - 联吡啶]，作为环金属化配体，并将它们固定在负载铂助催化剂的二氧化钛纳米颗粒表面。紫外 - 可见吸收和发射光谱表明，Ir - C30的单重态以配体为中心（1LC）的吸收和三重态3LC发射带比Ir - C6出现在更短的波长处，而含时密度泛函理论数据表明这两种配合物的配体 - 配体电荷转移（LLCT）激发态相当。在可见光照射（λ> 420 nm）下，Ir - C6敏化的Pt - TiO2纳米颗粒（Ir - C6@Pt - TiO2）的光催化产氢活性高于Ir - C30@Pt - TiO2。相反，在单色光（λ = 450 ± 10 nm）照射下，它们的活性相当，因为两种Ir - CX配合物对该单色光的吸收相当。这些结果表明，在两种Ir - CX配合物中，从较高的LC态到LLCT态的内转换都能有效发生，从而触发向TiO2的电子注入。
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(H4CPbpy)]Cl and [Ir(C30)2(H4CPbpy)]Cl [Ir-CX; X = 6 or 30; HC6 = 3-(2-enzothiazolyl)-7-(diethylamino)coumarin, HC30 = 3-(2-N-methylbenzimidazolyl)-7-N,N-diethylaminocoumarin, H4CPbpy = 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 (1LC) absorption and triplet 3LC 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 H2 evolution activity of the Ir-C6-sensitized Pt-TiO2 nanoparticles (Ir-C6@Pt-TiO2) under visible light irradiation (λ > 420 nm) was higher than that of Ir-C30@Pt-TiO2. In contrast, their activities were comparable under irradiation with monochromatic light (λ = 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.