Department of Chemistry, College of Chemistry and Chemical Engineering, State Key Laboratory of Physical Chemistry of Solid Surfaces and Collaborative Innovation Center for Energy Materials Chemistry, Xiamen University, Xiamen 361005, Fujian Province, P. R. China
Surface-enhanced Raman spectroscopy (SERS) is one of the most powerful techniques for obtaining fingerprint information on molecules adsorbed on coinage metal surfaces. Its detection sensitivity has reached the single-molecule level. On the basis of density functional theoretical (DFT) calculations and Raman scattering theory, we investigated the normal Raman spectra of two isomers and surface-enhanced Raman scattering (SERS) spectra of 4-mercaptopyridine (4MPY) adsorbed on silver. The results aided us in uncovering the relationships between normal Raman spectra and SERS spectra and adsorption configuration, tautomerization, protonation, and hydrogen bonding interactions as well as low-lying excited states. First, we compared the relative stability and normal Raman spectra of two isomers of 4MPY in the gas phase and aqueous solution with a solvent model similar to the solvation model of density (SMD). We then studied the Raman spectra of 4MPY interacting with silver clusters. Our results indicate that the Raman spectra were not dependent on the size of the silver clusters, owing to the formation of strong Ag-S bonds. We also considered two cases of Nend interaction in the 4MPY-Ag5 complex. (1) For the hydrogen bond interaction between the nitrogen in 4MPY and water clusters or hydrated proton clusters, the theoretical results indicated that the vibrational frequencies of the pyridine ring increase. (2) For the interaction of the 4MPY-Ag5 complex with a silver cluster Ag4 through the lone-paired orbital in nitrogen of the pyridine ring, the theoretical results further revealed that the vibrational frequency shift is in good agreement with SERS peaks reported in the literature. Finally, our calculated results focused on the relationship between the Raman spectra and the charge transfer mechanism when the excitation photonic energy matches the transition energy of low-lying excited states in single-end and double-end adsorption configuration. Particularly for the case of the double-end adsorption configuration, the charge transfer states from the excitation from the silver cluster binding to the pyridine ring not only enhance the Raman signals of v12, v1, and v8a modes, but also selectively enhance the Raman signal of the v9a mode associated with the symmetric C-H in-plane bending vibration.
Received: 02 August 2016
Published: 21 November 2016
Yuan-Fei WU,Ming-Xue LI,Jian-Zhang ZHOU,De-Yin WU,Zhong-Qun TIAN. Density Functional Theoretical Study on SERS Chemical Enhancement Mechanism of 4-Mercaptopyridine Adsorbed on Silver. Acta Physico-Chimica Sinca, 2017, 33(3): 530-538.
Fig 1 (A) Equilibrium of protonation, deprotonation, isomerization of 4MPY as well as (B) structure modelings of 4MPY-silver clusters of 4MPY adsorbed on silver nanostructures
Table 1Relative energies and relative Gibbs free energies calculated at the UB3LYP/6-311+G** level
Fig 2 Simulated Raman spectra in gas phase (weak curve) and the solvation model (strong curve) calculated at the B3LYP/6-311+G** level (A) PYSH, (B) PYSNH. The Raman bands are expanded by using the Lorentzian line shape with a line width of 10 cm-1 at the excitation wavelength 632.8 nm. color online
Fig 3 Optimized structures (A) and simulated Raman spectra (B) of dimer, tetramer, pentamer, and hexamer of PYSNH calculated at the B3LYP/6-311+G** level The Raman bands are expanded by using the Lorentzian line shape with a line width of 10 cm-1. color online
Fig 4 Simulated Raman spectra of PyS-Agn complexes calculated at the B3LYP/6-311+G**/LANL2DZ level (A) Ag3-S-PyN; (B) Ag5-S-PyN; (C) Ag7-S-PyN; (D) Ag9-S-PyN. The Raman intensity is estimated by differential Raman scattering cross section. It is expanded according to the Lorentzian line shape with the line width about 10 cm-1.
Fig 5 Simulated Raman spectra of complexes calculated at the B3LYP/6-311+G**/Lanl2DZ level (A) Ag5-SPYN-(H2O)8; (B) Ag5-SPYNH-(H2O)4. The excitation wavelength is 632.8 nm. The Raman intensity is estimated according to differential Raman scattering cross sections expanded in the Lorentzian line shape with the line width about 10 cm-1.
Fig 6 Simulated Raman spectra of Ag4-N-PyS-Ag5 calculated at the B3LYP/6-311+G**/Lanl2DZ level (A) gas phase; (B) SMD model. The excitation wavelength is 632.8 nm.
Fig 7 Frequency-dependent Raman spectra of 4MPY with a silver cluster in (A) a single-end configuration Py-S-Ag5 at 488.5 nm and (B) a two-end configuration Ag5-S-PYSN-N-Ag4 at 550.0 nm calculated by combining the B3LYP/6-311+G**/LANL2DZ method and Raman intensity theory The Raman spectra are drawn by using differential Raman scattering cross section according to the Lorentzian line shape with the line width about 10 cm-1.
Wilson E. B. ; Decius J. C. ; Cross P. C. Molecular Vibrations: The Theory of Infrared and Raman Vibrational Spectra New York: Dover, 1955.
Wang Z. J. ; Rothberg L. J. J.Phys. Chem. B 2005, 109, 3387.
Wu D. Y. ; Li J. F. ; Ren B. ; Tian Z. Q. Chem. Soc. Rev. 2008, 37, 1025.
Wu D. Y. ; Zhang M. ; Zhao L. B. ; Huang Y. F. ; Ren B. ; Tian Z. Q. Sci. China-Chem. 2015, 58, 574.
Wu D. Y. ; Liu X. M. ; Duan S. ; Xu X. ; Ren B. ; Lin S. H. ; Tian Z. Q. J.Phys. Chem. C 2008, 112, 4195.
Su S. ; Huang R. ; Zhao L. B. ; Wu D. Y. ; Tian Z. Q. Acta Phys.-Chim. Sin. 2011, 27, 781.
苏抒; 黄荣; 赵刘斌; 吴德印田中群. 物理化学学报, 2011, 27, 781.
Gui J. Y. ; Lu F. ; Stern D. A. ; Hubbard A. T. J.Electroanal.Chem. 1990, 292, 245.
Hu J.W. ; Zhao B. ; Xu W. Q. ; Li B. F. ; Fan Y. G. Spectrochimica Acta A 2002, 58, 2827.
Singh P. ; Deckert V. Chem. Commun. 2014, 50, 11204.
Latorre F. ; Kupfer S. ; Bocklitz T. ; Kinzel D. ; Trautmann S. ; Graefe S. ; Deckert V. Nanoscale 2016, 8, 10229.
Carron K. T. ; Hurley L. G. J.Phys. Chem. 1991, 95, 9979.
Bron M. ; Holze R. J.Solid State Electrochem. 2015, 19, 2673.
Shegai T. ; Vaskevich A. ; Rubinstein I. ; Haran G. J.Am.Chem. Soc. 2009, 131, 14390.
Chao Y.W. ; Zhou Q. ; Li Y. ; Yan Y. R. ; Wu Y. ; Zheng J.W. J. Phys. Chem. C 2007, 111, 16990.
Zheng X. S. ; Hu P. ; Zhong J. H. ; Zong C. ; Wang X. ; Liu B.J. ; Ren B. J.Phys. Chem. C 2014, 118, 3750.
Yu H. Z. ; Xia N. ; Liu Z. F. Anal. Chem. 1999, 71, 1354.
Wang Y. ; Yu Z. ; Ji W. ; Tanaka Y. ; Sui H. ; Zhao B. ; Ozaki Y. Angew. Chem.-Int. Edit. 2014, 53, 13866.
Respondek I. ; Benoit D. M. J.Chem. Phys. 2009, 131, 054109.
Sun L. ; Bai F. Q. ; Zhang H. X. Acta Phys.-Chim. Sin. 2011, 27, 1335.
孙磊; 白福全张红星. 物理化学学报, 2011, 27, 1335.
Birke R. L. ; Lombardi J. R. J.Optics 2015, 17, 114004.
Liu L. ; Chen D. ; Ma H. ; Liang W. J.Phys. Chem. C 2015, 119, 27609.
Iida K. ; Noda M. ; Nobusada K. J.Chem. Phys. 2014, 141, 124124.
Wu D. Y. ; Liu X. M. ; Huang Y. F. ; Ren B. ; Xu X. ; Tian Z. Q. J. Phys. Chem. C 2009, 113, 18212.
Jung H. S. ; Kim K. ; Kim M. S. J.Mol. Struct. 1997, 407, 139.
Guo H. ; Ding L. ; Mo Y. J. J.Mol. Struct. 2011, 991, 103.
Zhang L. ; Bai Y. ; Shang Z. G. ; Zhang Y. K. ; Mo Y. J. J. Raman Spectrosc. 2007, 38, 1106.
Etter M. C. ; Macdonald J. C. ; Wanke R. A. J.Phys. Org.Chem. 1992, 5, 191.
Flakus H. T. ; Tyl A. ; Jones P. G. Spectroc. Acta Pt. A-Molec.Biomolec. Spectr. 2002, 58, 299.
Muthu S. ; Vittal J. J. Cryst. Growth Des. 2004, 4, 1181.
Baldwin J. ; Schuhler N. ; Butler I. S. ; Andrews M. P. Langmuir 1996, 12, 6389.
Baldwin J. A. ; Vlckova B. ; Andrews M. P. ; Butler I. S. Langmuir 1997, 13, 3744.
Schlucker S. ; Singh R. K. ; Asthana B. P. ; Popp J. ; Kiefer W. J. Phys. Chem. A 2001, 105, 9983.
Wu D. Y. ; Ren B. ; Jiang Y. X. ; Xu X. ; Tian Z. Q. J.Phys.Chem. A 2002, 106, 9042.
Wu D. Y. ; Hayashi M. ; Shiu Y. J. ; Liang K. K. ; Chang C. H. ; Yeh Y. L. ; Lin S. H. J.Phys. Chem. A 2003, 107, 9658.