Muniz-Miranda Francesco, Pedone Alfonso, Menziani Maria Cristina, Muniz-Miranda Maurizio
Department and Geological Sciences (DSCG), University of Modena and Reggio Emilia, Via Campi 103, 41125 Modena, Italy.
Department of Chemistry "Ugo Schiff" (DiCUS), University of Florence, Via Lastruccia 3, 50019 Sesto Fiorentino, Italy.
Nanomaterials (Basel). 2022 Aug 24;12(17):2907. doi: 10.3390/nano12172907.
The surface-enhanced Raman scattering (SERS) spectra of piperidine adsorbed on silver/chloride colloids were studied by a combined density functional theory (DFT)/time dependent DFT (TD-DFT) approach. The mechanism of chemical enhancement on the Raman signals is due to at least two contributions: the first comes from the changes in the molecular force constants and the dynamic polarizabilities of the normal modes, when the molecule is chemisorbed. DFT calculations satisfactorily reproduce the SERS spectra of piperidine adsorbed on silver, showing that the species formed on the silver particle is a complex formed by a deprotonated piperidine linked to a silver cation. A second contribution to the SERS chemical enhancement is due to a resonance Raman effect occurring when the wavelength of the Raman excitation falls within the electronic excitation band of the molecule/metal complex. Actually, the SERS spectra of piperidine show a significant dependence on the wavelength of the laser excitation, with a marked enhancement in the green-light region. TD-DFT calculations on the most-probable complex explain this behavior, because a strong excitation band of the complex is calculated in the green spectral region. This pinpoints that a resonance between the exciting radiation and the absorption band of this complex is responsible for this enhancement effect.
采用密度泛函理论（DFT）/含时密度泛函理论（TD-DFT）相结合的方法，研究了吸附在银/氯化物胶体上的哌啶的表面增强拉曼散射（SERS）光谱。拉曼信号化学增强的机制至少有两种贡献：第一种来自分子化学吸附时分子力常数和正常模式动态极化率的变化。DFT计算令人满意地再现了吸附在银上的哌啶的SERS光谱，表明在银颗粒上形成的物种是由与银阳离子相连的去质子化哌啶形成的络合物。SERS化学增强的第二种贡献是由于当拉曼激发波长落在分子/金属络合物的电子激发带内时发生的共振拉曼效应。实际上，哌啶的SERS光谱对激光激发波长有显著依赖性，在绿光区域有明显增强。对最可能的络合物进行的TD-DFT计算解释了这种行为，因为在绿色光谱区域计算出了该络合物的强激发带。这表明激发辐射与该络合物吸收带之间的共振是这种增强效应的原因。
