Li Ping, Amirjalayer Saeed, Hartl František, Lutz Martin, de Bruin Bas, Becker René, Woutersen Sander, Reek Joost N H
Homogeneous & Supramolecular Catalysis, van 't Hoff Institute for Molecular Sciences, University of Amsterdam , Science Park 904, 1098 XH Amsterdam, The Netherlands.
Inorg Chem. 2014 May 19;53(10):5373-83. doi: 10.1021/ic500777d. Epub 2014 Apr 26.
A pyridyl-functionalized diiron dithiolate complex, [μ-(4-pyCH2-NMI-S2)Fe2(CO)6] (3, py = pyridine (ligand), NMI = naphthalene monoimide) was synthesized and fully characterized. In the presence of zinc tetraphenylporphyrin (ZnTPP), a self-assembled 3·ZnTPP complex was readily formed in CH2Cl2 by the coordination of the pyridyl nitrogen to the porphyrin zinc center. Ultrafast photoinduced electron transfer from excited ZnTPP to complex 3 in the supramolecular assembly was observed in real time by monitoring the ν(C≡O) and ν(C═O)NMI spectral changes with femtosecond time-resolved infrared (TRIR) spectroscopy. We have confirmed that photoinduced charge separation produced the monoreduced species by comparing the time-resolved IR spectra with the conventional IR spectra of 3(•-) generated by reversible electrochemical reduction. The lifetimes for the charge separation and charge recombination processes were found to be τCS = 40 ± 3 ps and τCR = 205 ± 14 ps, respectively. The charge recombination is much slower than that in an analogous covalent complex, demonstrating the potential of a supramolecular approach to extend the lifetime of the charge-separated state in photocatalytic complexes. The observed vibrational frequency shifts provide a very sensitive probe of the delocalization of the electron-spin density over the different parts of the Fe2S2 complex. The TR and spectro-electrochemical IR spectra, electron paramagnetic resonance spectra, and density functional theory calculations all show that the spin density in 3(•-) is delocalized over the diiron core and the NMI bridge. This delocalization explains why the complex exhibits low catalytic dihydrogen production even though it features a very efficient photoinduced electron transfer. The ultrafast porphyrin-to-NMI-S2-Fe2(CO)6 photoinduced electron transfer is the first reported example of a supramolecular Fe2S2-hydrogenase model studied by femtosecond TRIR spectroscopy. Our results show that TRIR spectroscopy is a powerful tool to investigate photoinduced electron transfer in potential dihydrogen-producing catalytic complexes, and that way to optimize their performance by rational approaches.
合成并全面表征了一种吡啶基官能化的二铁二硫醇配合物[μ-(4-pyCH2-NMI-S2)Fe2(CO)6]（3，py = 吡啶（配体），NMI = 萘单酰亚胺）。在四苯基卟啉锌（ZnTPP）存在下，吡啶基氮与卟啉锌中心配位，在二氯甲烷中很容易形成自组装的3·ZnTPP配合物。通过飞秒时间分辨红外（TRIR）光谱监测ν(C≡O)和ν(C═O)NMI光谱变化，实时观察到超分子组装体中从激发态ZnTPP到配合物3的超快光致电子转移。通过将时间分辨红外光谱与可逆电化学还原产生的3(•-)的常规红外光谱进行比较，我们证实了光致电荷分离产生了单还原物种。发现电荷分离和电荷复合过程的寿命分别为τCS = 40 ± 3 ps和τCR = 205 ± 14 ps。电荷复合比类似的共价配合物慢得多，这表明超分子方法在延长光催化配合物中电荷分离态寿命方面的潜力。观察到的振动频率变化为电子自旋密度在Fe2S2配合物不同部分的离域提供了非常灵敏的探针。TR和光谱电化学红外光谱、电子顺磁共振光谱以及密度泛函理论计算均表明，3(•-)中的自旋密度在二铁核心和NMI桥上离域。这种离域解释了为什么该配合物尽管具有非常有效的光致电子转移，但催化产氢效率却很低。超快的卟啉到NMI-S2-Fe2(CO)6光致电子转移是首次报道的通过飞秒TRIR光谱研究的超分子Fe2S2-氢化酶模型的例子。我们的结果表明，TRIR光谱是研究潜在产氢催化配合物中光致电子转移的有力工具，也是通过合理方法优化其性能的途径。
