Dieringer Jon A, Wustholz Kristin L, Masiello David J, Camden Jon P, Kleinman Samuel L, Schatz George C, Van Duyne Richard P
Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
J Am Chem Soc. 2009 Jan 21;131(2):849-54. doi: 10.1021/ja8080154.
The surface-enhanced Raman excitation profiles (REPs) of rhodamine 6G (R6G) on Ag surfaces are studied using a tunable optical parametric oscillator excitation source and versatile detection scheme. These experiments afford the ability to finely tune the excitation wavelength near the molecular resonance of R6G (i.e., approximately 500-575 nm) and perform wavelength-scanned surface-enhanced Raman excitation measurements of a single molecule. The ensemble-averaged surface-enhanced REPs are measured for collections of molecules on Ag island films. The relative contributions of the 0-0 and 0-1 vibronic transitions to the surface-enhanced REPs vary with vibrational frequency. These results highlight the role of excitation energy in determining the resonance Raman intensities for R6G on surface-enhancing nanostructures. Single-molecule measurements are obtained from individual molecules of R6G on Ag colloidal aggregates, where single-molecule junctions are located using the isotope-edited approach. Overall, single-molecule surface-enhanced REPs are narrow in comparison to the ensemble-averaged excitation profiles due to a reduction in inhomogeneous broadening. This work describes the first Raman excitation spectroscopy studies of a single molecule, revealing new information previously obscured by the ensemble.
利用可调谐光学参量振荡器激发源和通用检测方案，研究了罗丹明6G（R6G）在银表面的表面增强拉曼激发谱（REPs）。这些实验能够在R6G分子共振附近（即约500 - 575 nm）精细调节激发波长，并对单个分子进行波长扫描表面增强拉曼激发测量。对银岛膜上的分子集合测量了系综平均表面增强REPs。0 - 0和0 - 1振动跃迁对表面增强REPs的相对贡献随振动频率而变化。这些结果突出了激发能量在确定R6G在表面增强纳米结构上的共振拉曼强度中的作用。通过银胶体聚集体上R6G的单个分子获得单分子测量结果，其中使用同位素编辑方法定位单分子结。总体而言，由于非均匀展宽的减少，单分子表面增强REPs与系综平均激发谱相比更窄。这项工作描述了首个单分子的拉曼激发光谱研究，揭示了以前被系综掩盖的新信息。
