xcited state , reductive quenching , and intramolecular electron transfer of Ru ( II ) – Re ( I ) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements †
xcited state , reductive quenching , and intramolecular electron transfer of Ru ( II ) – Re ( I ) supramolecular photocatalysts for CO 2 reduction using time-resolved IR measurements †
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使用时间分辨红外测量进行 CO 2 还原的 Ru (II) – Re (I) 超分子光催化剂的激发态、还原猝灭和分子内电子转移 †
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发表时间：
2018
期刊：
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通讯作者：
O. Ishitani
中科院分区：
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作者：
K. Koike;D. Grills;Yusuke Tamaki;E. Fujita;K. Okubo;Y. Yamazaki;Masaki Saigo;Tatsuhiko Mukuta;Ken Ondad;O. Ishitani
其中Ru（II）光敏剂和Re（I）催化剂单元通过乙烯连接体彼此连接的超分子光催化剂是用于CO2还原的最知名、最有效和最耐用的光催化体系之一。在本文中，我们报告，为第一次，时间分辨红外（TRIR）光谱的三个这些双核配合物，以揭示为什么催化剂的功能如此有效。选择性激发的Ru单元与532 nm的激光脉冲诱导缓慢的分子内电子转移从MLCT激发态的Ru单元的Re单元，与速率常数为（1.0-1.1）10 s-1作为主要成分和（3.5-4.3）10 s-1作为次要成分，在乙腈中。产生的电荷分离态具有长寿命，电荷复合速率常数仅为（6.5-8.4）10 s。因此，虽然它具有大的驱动力（DGCR 2.6 eV），但该过程处于马库斯反转区。另一方面，在1-苄基-1，4-二氢烟酰胺（BNAH）的存在下，激发的Ru单元的还原猝灭比上述分子内氧化猝灭进行得更快（kq[BNAH（0.2 M）] 1⁄4（3.5-3.8）10 s），产生Ru单元的单电子还原物质（OERS）。纳秒TRIR数据清楚地表明，从Ru单元的OERS到Re单元的分子内电子转移（kET > 2 10 s）比从Ru单元的激发态快得多，并且它也比由BNAH激发的Ru单元的还原猝灭过程快。为了测量kET的精确值，使用皮秒TRIR光谱和更强的还原剂。因此，在3种双核配合物中，分子内电子转移最快的是三（对氟苯基）膦配体（RuRe（FPh））的双核配合物，在1，3-二甲基-2-苯基-2，3-二氢-1H-苯并[d]咪唑（BIH）存在下，kET的测定结果为kET 1/4（1.4 0.1）10 s。这清楚地表明，在这些RuRe双核超分子光催化剂中的分子内电子转移不是CO2光催化还原的速率决定过程，这是它们如此有效地工作的主要原因之一。
Supramolecular photocatalysts in which Ru(II) photosensitizer and Re(I) catalyst units are connected to each other by an ethylene linker are among the best known, most effective and durable photocatalytic systems for CO2 reduction. In this paper we report, for the first time, time-resolved infrared (TRIR) spectra of three of these binuclear complexes to uncover why the catalysts function so efficiently. Selective excitation of the Ru unit with a 532 nm laser pulse induces slow intramolecular electron transfer from the MLCT excited state of the Ru unit to the Re unit, with rate constants of (1.0–1.1) 10 s 1 as a major component and (3.5–4.3) 10 s 1 as a minor component, in acetonitrile. The produced charge-separated state has a long lifetime, with charge recombination rate constants of only (6.5–8.4) 10 s . Thus, although it has a large driving force ( DGCR 2.6 eV), this process is in the Marcus inverted region. On the other hand, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH), reductive quenching of the excited Ru unit proceeds much faster (kq[BNAH (0.2 M)] 1⁄4 (3.5–3.8) 10 s ) than the abovementioned intramolecular oxidative quenching, producing the one-electron-reduced species (OERS) of the Ru unit. Nanosecond TRIR data clearly show that intramolecular electron transfer from the OERS of the Ru unit to the Re unit (kET > 2 10 s ) is much faster than from the excited state of the Ru unit, and that it is also faster than the reductive quenching process of the excited Ru unit by BNAH. To measure the exact value of kET, picosecond TRIR spectroscopy and a stronger reductant were used. Thus, in the case of the binuclear complex with tri(p-fluorophenyl)phosphine ligands (RuRe(FPh)), for which intramolecular electron transfer is expected to be the fastest among the three binuclear complexes, in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), kET was measured as kET 1⁄4 (1.4 0.1) 10 s . This clearly shows that intramolecular electron transfer in these RuRe binuclear supramolecular photocatalysts is not the rate-determining process in the photocatalytic reduction of CO2, which is one of the main reasons why they work so efficiently.