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Quantum Chemical Study of Raman Spectroscopy of Substituted Benzene Derivatives Adsorbed on Metal Surfaces De-Yin Wu, Zhong-Qun Tian Department of Chemistry.

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Presentation on theme: "Quantum Chemical Study of Raman Spectroscopy of Substituted Benzene Derivatives Adsorbed on Metal Surfaces De-Yin Wu, Zhong-Qun Tian Department of Chemistry."— Presentation transcript:

1 Quantum Chemical Study of Raman Spectroscopy of Substituted Benzene Derivatives Adsorbed on Metal Surfaces De-Yin Wu, Zhong-Qun Tian Department of Chemistry in College of Chemistry and Chemical Engineering & State Key Laboratory of Physical Chemistry for Solid Surfaces Xiamen University Ohio, 2010.6.24

2 Studies on solution/metal electrodes High detection sensitivity High Resolution Energy Space Time 2-20 Å Surface-enhanced Raman spectroscopy : SERS Surface plasmon resonance Chemical property

3 Our Research Pathway : 1.Assignment of vibrational Raman bands. 2.To find the insight of vibrational frequency shift. 3.To understand the change of Raman intensity To determine the dependence between structures and molecular spectra, to infer structures and reaction of adsorbed molecules on metal surfaces. 11

4 Molecules/Metallic cluster model Adsorption models of different molecules

5 Computational details Cluster Model: M n – Molecule – M n (M = Au, Ag; n =2,3, 4…13) DFT: B3LYP, PW91PW91, … Basis set: LANL2DZ (Ag)/ Optimized structure 6-311+G(d,p)(C,N,H,S) Bonding analysis Scaled Quantum Mechanics force field method (SQMF)] Calculations of Raman Intensity : Non-resonance, pre-resonance, and resonance cases

6 (1)Simulated Raman spectra of Benzene Derivatives Vibrational coupling existing

7 ( 2 ) Thiophenol (TP) and Benzenedithiol (BDT)/Au SERS J. H. Tian, et al., JACS, 2006,128,14748. Bridge site Hollow site Au 5 -BDT-Au 5 Not sensitive to adsorption site Thiol

8 (3) Aniline and Benzenediamine (BDA)/Au SERS Amino

9 (4) Questions in SERS of PATP/Ag Osawa M., et al. J. Phys. Chem. 1994, 98, 12702. Abnormal: 1142, 1391, 1440 cm -1 CT mechanism on b 2 modes of PATP Is it a real story? PATP/Ag PATP solid Weak Strong HS- -NH 2 1142 1391 1440

10 B3LYP/6-311+G**(C,N,S,H)/ Lanl2DZ(Ag) PATP binding to different sites, such as top, bridge, hollow, and bi-end configurations ( 4 ) Simulated Raman Spectra of PATP/Ag Fingerprint region: ( 1 ) Weak in intensity ( 2 ) No fundamental band

11 Hollow site

12 (4) Simulated Raman spectra of PATP/Au

13 (4) Beyond supposed mechanisms for PATP? & ? (1) Charge Transfer ( HT vibronic term ) N. Matsuda, et al., Chem. Lett. 1992,7,1385 M. Osawa, et al., J. Phys. Chem. 1994, 98, 12702 (2) Isomerization of Aromatic and Quinonoidic W. Hill, B. Wehling, J. Phys. Chem., 1993, 97, 9451 (3) Charge tunneling in metal/PATP/metal nanogap Au/ - SC 6 H 4 NH 2 + /Ag Q. Zhou, et al. Angew. Chem. 2006, 45, 397 1064 nm514.5 nm 790 nm SERS Solid Acidic aromatic Alkaline quinonoidic Theoretical Study

14 (4) A new mechanism: 2 * PATP/M  DMAB/M a.Electrochemical anodic oxidation of aniline; Y. Matsuda, et al. Bull Chem. Jap., 1971, 44, 2960-2963. b. Optically catalytic Oxidation (hv/Alkaline/silver; hv/Ag + /TiO 2 ) H. Park, et al., J. Phys. Chem., 1990, 94, 7576. (P-aminobenzoic acid/Silver Electrode) DMAB reversibly decomposes DMAB yields DMAB: p,p´-dimercaptoazobenzene

15 (4) Ag 5 /DMAB and Ag 5 /DMAB/Ag 5 B3LYPPW91PW91 Free Molecule Singe-end Double-end vC-N b C-H vN=N AgAg

16 (4) Simulated Raman spectra of azobenzene

17 (4 ) Comparison of Structural parameters We find B3LYP overestimates the N=N bond, resulting in the blue shift of the v N=N stretching frequency; PW91PW91 and BP86 are more reliable to describe the N=N bond.

18 JPCC2009,113,18212 × ×× ×

19 SERS of DMAB and pATP on Ag NPs Prof. Hongping Zhu JACS2010,132,9244 Direct evidence

20 4. Conclusion (1) The amino group is more chemical activity than the thiol group on coinage metal surfaces. (2) PATP may undergo surface catalytic coupling reaction to form azobenzene derivative, yielding the intense Raman bands at 1140, 1390, and 1440 cm -1 。 (3) PW91PW91 and BP86 is better to describe the N=N double bond than B3LYP. (4) Quantum chemical calculation is helpful to understand the observed phenomenon in the view of nature.

21 Acknowledgement : Collaborators: Prof. Bin Ren (Xiamen University) Prof. Xin Xu (Fudan University) Prof. S. H. Lin (IAMS, Taipei) Prof. Yi-Jin Yan (HKUST, Hong Kong) Doctoral and Master students : Xiu-Min Liu, Yi-Fan Huang , Liu-Bin Zhao , Rong Huang , Wen-Li Luo Fund: Chinese NSF, 973 (2007CB815303, 2009CB930703) Thanks for your attention!

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23 (4) pH effect: Reversibility of Raman spectra of PATP W. Hill, B. Wheling, J. Phys. Chem., 1993, 97, 9451 Na 2 S 2 pH = 2.0 Acidic Alkaline Acidic ---good Basic ----bad


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