Department of Chemistry, Faculty of Science, University of Zagreb, Zagreb, Croatia.
Spectrochim Acta A Mol Biomol Spectrosc. 2010 Mar;75(3):1008-12. doi: 10.1016/j.saa.2009.12.032. Epub 2009 Dec 14.
Surface-enhanced Raman scattering (SERS) of the cationic and the neutral form of rhodamine 19 octadecylamide (R19OA) has been studied in the silver citrate colloid using NIR excitation at 1064 nm. Cationic molecules readily adsorb onto negatively charged silver nanoparticles through a positively charged xanthene part of the molecules resulting in surface enhancement of Raman scattering. Due to a lack of the positive charge in molecular structure, SERS spectrum of neutral molecules is not observed. Nevertheless, a broad band appearing at 1240 cm(-1) in the spectrum of the cationic form indicates conversion of the cationic into the neutral species occurring close to the silver surface. The observed band most likely arises from a vibration of the ring formed in the molecular structure after conversion, but before complete desorption of the neutral molecules from the metal surface. Upon addition of HCl and NaOH in the silver sol, equilibrium is shifted toward the cationic and the neutral form of R19OA, respectively, followed by corresponding changes in the Raman spectrum. In addition, FT-SERS spectra of two rhodamine dyes, rhodamine 19 (R19) and rhodamine 6G (R6G), that are structurally related to R19OA, have been studied under the same experimental conditions for comparison.
已在使用 1064nm 的近红外激发的银柠檬酸胶体中研究了罗丹明 19 十八酰胺（R19OA）的阳离子和中性形式的表面增强拉曼散射（SERS）。阳离子分子通过分子中带正电荷的香豆素部分容易吸附到带负电荷的银纳米颗粒上，从而导致拉曼散射的表面增强。由于分子结构中缺乏正电荷，因此未观察到中性分子的 SERS 光谱。然而，阳离子形式光谱中出现在 1240cm(-1)处的宽带表明，阳离子向靠近银表面的中性物质的转化。观察到的带很可能是由于分子结构在转化后形成的环的振动，但在中性分子从金属表面完全解吸之前。在银溶胶中加入 HCl 和 NaOH 后，平衡分别向 R19OA 的阳离子和中性形式移动，随后拉曼光谱也发生相应变化。此外，还在相同的实验条件下研究了结构上与 R19OA 相关的两种罗丹明染料罗丹明 19（R19）和罗丹明 6G（R6G）的 FT-SERS 光谱，以作比较。
