Department of Chemistry and Center for Photochemical Sciences, Bowling Green State University , Bowling Green, Ohio 43403, United States.
J Am Chem Soc. 2016 Feb 10;138(5):1536-42. doi: 10.1021/jacs.5b10253. Epub 2016 Feb 2.
Fundamental understanding of the energetic coupling properties of a molecule-semiconductor interface is of great importance. The changes in molecular conformations and vibrational modes can have significant impact on the interfacial charge transfer reactions. Here, we have probed the change in the interface properties of alizarin-TiO2 system as a result of the externally applied electric field using single-hot spot microscopic surface-enhanced Raman spectroscopy (SMSERS) and provided a theoretical understanding of our experimental results by density functional theory (DFT) calculations. The perturbation, caused by the external potential, has been observed as a shift and splitting of the 648 cm(-1) peak, typical indicator of the strong coupling between alizarin and TiO2, at SMSERS. On the basis of our experimental results and DFT calculations, we suggest that electric field has significant effects on vibrational coupling at the molecule-TiO2 interface. The presence of perturbed alizarin-TiO2 coupling under interfacial electric potential may lead to changes in the interfacial electron transfer dynamics. Additionally, heterogeneously distributed dye molecules at the interface on nanometer length scale and different chromophore-semiconductor binding interactions under charge accumulation associated interfacial electric field changes create intrinsically inhomogeneous interfacial ET dynamics associated with both static and dynamic disorders.
深入理解分子-半导体界面的能量偶联性质具有重要意义。分子构象和振动模式的变化会对界面电荷转移反应产生重大影响。在这里，我们使用单热点微观表面增强拉曼光谱（SMSERS）探测了茜素-TiO2 体系由于外加电场引起的界面性质的变化，并通过密度泛函理论（DFT）计算对我们的实验结果提供了理论理解。在外加电位的作用下，观察到了 648cm(-1)峰的位移和分裂，这是茜素与 TiO2 之间强耦合的典型标志，在 SMSERS 中也是如此。基于我们的实验结果和 DFT 计算，我们提出电场对分子-TiO2 界面的振动耦合有显著影响。界面电势下受扰的茜素-TiO2 偶联可能导致界面电子转移动力学的变化。此外，界面处纳米尺度上不均匀分布的染料分子和电荷积累相关界面电场变化下不同的生色团-半导体结合相互作用会产生与静态和动态无序相关的固有不均匀界面 ET 动力学。
