Solvent exchange in preformed photocatalyst-donor precursor complexes determines efficiency†,Chemical Science

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Solvent exchange in preformed photocatalyst-donor precursor complexes determines efficiency†
Chemical Science ( IF 7.6 ) Pub Date : 2017-12-21 00:00:00 , DOI: 10.1039/c7sc04533f
Laura M Kiefer ₁ , Kevin J Kubarych ₁

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In homogeneous photocatalytic reduction of CO₂, it is widely assumed that the primary electron transfer from the sacrificial donor to the catalyst is diffusion controlled, thus little attention has been paid to optimizing this step. We present spectroscopic evidence that the precursor complex is preformed, driven by preferential solvation, and two-dimensional infrared spectroscopy reveals triethanolamine (donor)/tetrahydrofuran (solvent) exchange in the photocatalyst's solvation shell, reaching greatest magnitude at the known optimal concentration (∼20% v/v TEOA in THF) for catalytically reducing CO₂ to CO. Transient infrared absorption shows the appearance of the singly reduced catalyst on an ultrafast (<70 ps) time scale, consistent with non-diffusion controlled electron transfer within the preformed precursor complex. Identification of preferential catalyst–cosolvent interactions suggests a revised paradigm for the primary electron transfer, while illuminating the pivotal importance of solvent exchange in determining the overall efficiency of the photocycle.

中文翻译：

预制光催化剂-供体前体复合物中的溶剂交换决定效率†

在CO ₂的均相光催化还原中，人们普遍认为从牺牲供体到催化剂的初级电子转移是扩散控制的，因此很少有人关注优化该步骤。我们提出了光谱证据，表明前体复合物是在优先溶剂化的驱动下预先形成的，二维红外光谱揭示了光催化剂溶剂化壳中的三乙醇胺（供体）/四氢呋喃（溶剂）交换，在已知的最佳浓度（∼20 % v/v TEOA in THF)，用于将 CO ₂催化还原为 CO。瞬态红外吸收显示在超快 (<70 ps) 时间尺度上单一还原的催化剂的出现，与预制前体内的非扩散控制电子转移一致复杂的。优先催化剂-共溶剂相互作用的识别提出了一次电子转移的修订范例，同时阐明了溶剂交换在确定光循环整体效率方面的关键重要性。

更新日期：2017-12-21

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