Ultrafast Structural Dynamics of Cu(I)-Bicinchoninic Acid and Their Implications for Solar Energy Applications
Ultrafast Structural Dynamics of Cu(I)-Bicinchoninic Acid and Their Implications for Solar Energy Applications
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DOI：
10.1021/jp504294j
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发表时间：
2014-11-13
影响因子：
2.9
通讯作者：
Chen, Lin X.
中科院分区：
文献类型：
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作者：
Fransted, Kelly A.;Jackson, Nicholas E.;Chen, Lin X.
在这项研究中，超快光学瞬态吸收和X射线瞬态吸收（XTA）光谱用于探测二辛可宁酸铜（I）（[Cu(I)(BCA)(2)](+)）的激发态动力学和结构演化，与菲咯啉基配合物相比，它具有相似但研究较少的联喹啉基配体。在一系列极性质子溶剂中对该配合物进行的光学瞬态吸收测量表明，激发寿命具有很强的溶剂依赖性，其范围从水中的约 40 ps 到 2-甲氧基乙醇中的超过 300 ps。 XTA 实验显示，激发态 X 射线吸收近边结构 (XANES) 光谱中突出的 1s -> 4pz 边缘峰减少，这表明与第五配体（最有可能是溶剂）发生相互作用。扩展 X 射线吸收精细结构 (EXAFS) 光谱的分析表明，激发态下的金属-配体键缩短，并且 Cu(II) 金属中心的配位数增加。 DFT 计算支持扁平结构，该计算表明系统松弛为具有最低能量三重态的扁平几何结构，该几何结构具有偶极禁止跃迁到基态。虽然相对于之前研究的 Cu(I) 二亚胺络合物较短的激发态寿命可能归因于这种暗三重态，但 XTA 数据中强溶剂依赖性和 1s -> 4pz 峰的减少表明溶剂相互作用也可能发挥作用。这项对不同溶剂中动力学的详细研究为通过溶剂可及性等结构因素调节激发态路径和寿命提供了指导，以满足高效光捕获和电子注入的激发态特性要求。
In this study, ultrafast optical transient absorption and X-ray transient absorption (XTA) spectroscopy are used to probe the excited-state dynamics and structural evolution of copper(I) bicinchoninic acid ([Cu(I)(BCA)(2)](+)), which has similar but less frequently studied biquinoline-based ligands compared to phenanthroline-based complexes. The optical transient absorption measurements performed on the complex in a series of polar protic solvents demonstrate a strong solvent dependency for the excited lifetime, which ranges from approximately 40 ps in water to over 300 ps in 2-methoxyethanol. The XTA experiments showed a reduction of the prominent 1s -> 4pz edge peak in the excited-state X-ray absorption near-edge structure (XANES) spectrum, which is indicative of an interaction with a fifth ligand, most likely the solvent. Analysis of the extended X-ray absorption fine structure (EXAFS) spectrum shows a shortening of the metal-ligand bond in the excited state and an increase in the coordination number for the Cu(II) metal center. A flattened structure is supported by DFT calculations that show that the system relaxes into a flattened geometry with a lowest-energy triplet state that has a dipole-forbidden transition to the ground state. While the short excited-state lifetime relative to previously studied Cu(I) diimine complexes could be attributed to this dark triplet state, the strong solvent dependency and the reduction of the 1s -> 4pz peak in the XTA data suggest that solvent interaction could also play a role. This detailed study of the dynamics in different solvents provides guidance for modulating excited-state pathways and lifetimes through structural factors such as solvent accessibility to fulfill the excited-state property requirements for efficient light harvesting and electron injection.