Light-induced charge separation and photocatalytic hydrogen evolution from water using RuIIPtII-based molecular devices: Effects of introducing additional donor and/or acceptor sites
Light-induced charge separation and photocatalytic hydrogen evolution from water using RuIIPtII-based molecular devices: Effects of introducing additional donor and/or acceptor sites
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DOI：
10.1039/c0dt01673j
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发表时间：
2011-01-01
影响因子：
4
通讯作者：
Sakai, Ken
中科院分区：
文献类型：
--
作者：
Ajayakumar, Gopalakrishnan;Kobayashi, Masayuki;Sakai, Ken
为了提高光解氢分子器件的光催化效率，一些新的二元组和三元组拥有光敏Ru(bpy)(phen)(2)(2+)（或Ru(phen)(3)(2+))发色团（缩写为Ru-II），连接到吩噻嗪部分（缩写为Phz）和/或H-2-演化分子合成了PtCl2(bpy)单元（缩写为Pt），例如Phz-Ru-II-Pt2（三元组）、Ru-II-Pt2（二元组）和Ru-II-Pt3（二元组），并详细研究了它们的基本性质以及光析氢特性。由于高效的光诱导电子转移 (PET)，这些系统中 RuII 部分的 (MLCT)-M-3 磷光基本上被猝灭。根据电化学研究，PET的驱动力对于Phz-Ru-II-Pt2估计为-0.07 eV，对于Ru-II-Pt2为-0.24 eV，对于Ru-II-Pt3为-0.22 eV，揭示了PET在这些系统中的放能特性。发光寿命研究揭示了两种以上衰变成分的存在，表明溶液中至少存在两种不同的构象异构体，从而导致了多种 PET 过程的贡献。混合体系的主要发光衰变成分[乙腈中的 tau(1) = 6.5 ns (Ru-II-Pt2) 和 tau(1) = 1.04 ns (Phz-Ru-II-Pt2)] 比不含 Phz/不含 Pt 的 Ru(bpy)(phen)(2)(2+) 衍生物短得多。一个重要的发现是，三元组 Phz-Ru-II-Pt2 提供了相当长寿命的电荷分离 (CS) 态 (tau(CS) = 43 ns)，表示为 Phz(+中心点)-Ru-Red-Pt2，这是由于束缚 Phz 部分对 Ru(bpy)(phen)(2)(2+) 三重激发态的还原猝灭的结果，其中 Ru-Red 表示Ru(bpy)(phen)(2)(+)。此外，观察到Phz(+中心点)-Ru-Red-Pt2的寿命比Phz(+中心点)-Ru-Red长得多。在含有 4-19% 二甲基亚砜（增溶剂）的醋酸盐缓冲水溶液（pH 5.0）中，在 EDTA 作为牺牲电子供体的情况下，对这些系统驱动的水光催化 H-2 放出进行了检测。与我们小组迄今为止开发的异双核 Ru-Pt 二价体相比，Ru-II-Pt2 和 Ru-II-Pt3 二价体被发现表现出改进的光析氢活性。另一方面，尽管形成了强还原性Ru-Red位点（Phz（+中心点）-Ru-Red-Pt2），但几乎没有观察到Phz-Ru-II-Pt2的催化活性，这表明从光生Ru-Red单元到PtCl2（bpy）单元的电子转移不有利，可能是由于Marcus反转区域的电子转移速率较慢。
In our hopes to improve the photocatalytic efficiency of photo-hydrogen-evolving molecular devices, several new dyads and triads possessing a photosensitizing Ru(bpy)(phen)(2)(2+) (or Ru(phen)(3)(2+)) chromophore (abbreviated as Ru-II) attached to both/either a phenothiazine moiety (abbreviated as Phz) and/or H-2-evolving PtCl2(bpy) units (abbreviated as Pt), such as Phz-Ru-II-Pt2 (triad), Ru-II-Pt2 (dyad), and Ru-II-Pt3 (dyad), were synthesized and their basic properties together with the photo-hydrogen-evolving characteristics were investigated in detail. The (MLCT)-M-3 phosphorescence from the RuII moiety in these systems is substantially quenched due to the highly efficient photoinduced electron transfer (PET). Based on the electrochemical studies, the driving forces for the PET were estimated as -0.07 eV for Phz-Ru-II-Pt2, -0.24 eV for Ru-II-Pt2, and -0.22 eV for Ru-II-Pt3, revealing the exergonic character of the PET in these systems. Luminescence lifetime studies revealed the existence of more than two decay components, indicative of a contribution of multiple PET processes arising from the presence of at least two different conformers in solution. The major luminescence decay components of the hybrid systems [tau(1) = 6.5 ns (Ru-II-Pt2) and tau(1) = 1.04 ns (Phz-Ru-II-Pt2) in acetonitrile] are much shorter than those of Phz-free/Pt-free Ru(bpy)(phen)(2)(2+) derivatives. An important finding is that the triad Phz-Ru-II-Pt2 affords a quite long-lived charge separated (CS) state (tau(CS) = 43 ns), denoted as Phz(+center dot)-Ru-Red-Pt2, as a result of reductive quenching of the triplet excited state of Ru(bpy)(phen)(2)(2+) by the tethering Phz moiety, where Ru-Red denotes Ru(bpy)(phen)(2)(+). Moreover, the lifetime of Phz(+center dot)-Ru-Red-Pt2 was observed to be much longer than that of Phz(+center dot)-Ru-Red. The photocatalytic H-2 evolution from water driven by these systems was examined in an aqueous acetate buffer solution (pH 5.0) containing 4-19% dimethylsulfoxide (solubilising reagent) in the presence of EDTA as a sacrificial electron donor. Dyads Ru-II-Pt2 and Ru-II-Pt3 were found to exhibit improved photo-hydrogen-evolving activity compared to the heterodinuclear Ru-Pt dyads developed so far in our group. On the other hand, almost no catalytic activity was observed for Phz-Ru-II-Pt2 in spite of the formation of a strongly reducing Ru-Red site (Phz(+center dot)-Ru-Red-Pt2), indicating that the electron transfer from the photogenerated Ru-Red unit to the PtCl2(bpy) unit is not favoured presumably due to the slow electron transfer rate in the Marcus inverted region.