Theoretical Study on SERS of Wagging Vibrations of Benzyl ...

De-Yin Wu, Yan-Li Chen, Zhong-Qun Tian

ISMS71 ---RJ12

Theoretical Study on SERS of Wagging Vibrations of Benzyl Radical Adsorbed

on Silver Electrodes

College of Chemistry and Chemical Engineering

& State Key Laboratory of Physical Chemistry for Solid Surfaces

2016.6.23

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

EC-SERS (Metal NPs + Molecule + Light)

KE

Ag AgAg Ag

633 nm laser

SH

H2N

SilverGold

CopperRough

electrode surfaces

Nanostructures

a. 1010 cm-1; d. 1215 cm-1

b. 1036 cm-1; e. 1594 cm-1

c. 3056 cm-1; f. 623 cm-1

Potential-Intensity Profiles dependent on Laser Lines

DY Wu, JF Li, B Ren, ZQ Tian, Chem. Soc. Rev. 2008, 37, 1025

At the open circuit potential At the peak potential of the ring breathing mode

Electrochemical Surface-Enhanced Raman Spectroscopy of Pyridine

Pyridine N-Metal Interaction: Pt > Au, Cu > Ag

DY Wu, JF Li, B Ren, ZQ Tian, Chem. Soc. Rev. 2008, 37, 1025

Electrochemical CV and SERS of Benzyl Chloride on Silver Electrodes

Cyclic voltammetry of PhCH2Cl, 5 mM in 0.1 M TEAP + CH3CN, at a Ag electrode (2 mm diameter) and a scan rate of 0.2 Vs-1.

Potential dependent SERS spectra of PhCH2Cl on Ag electrode, excited by

633 nm

J. Am. Chem. Soc. 2010, 132, 9534-9536.

Computational details

Cluster Model: Molecule-Mn; Mn – Molecule – Mn (M = TM)

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：

( )( ) ( )

42 20

2 45 78 45 1 exp

R ii i i

i i B

v vhIcv hcv k T

α γπ

−′ ′= ⋅ +

− −

Non-resonance, pre-resonance, and resonance cases

C

C

C

C

CN

H

H

H

H H

M

M

M M MM

MMM

Y

Z

Metallic Cluster Modeling: Size effect

M = Cu, Ag, Au, TM

Small Large

22

745

+

=

kkk dQ

ddQdS γα

( ) 144

2

~exp1

45

~~2~8

−

−−

−=

Ω

∝

kThc

Sch

ddI

kk

ki

k

kRaman

νννπνπ

σ

M-m

Qi

E M+-m-

hv

SERS Intensity: Raman scattering processes

Raman Intensity：

0 00

13

yyxx zz

Q Q Qαα αα

∂ ∂ ∂′ = + + ∂ ∂ ∂ 22 2 2 22

2

0 0 00 0 000 0

1 62

yy yy yz xyxx xx xzzz zz

Q Q Q Q Q Q Q Q Qα α α αα α αα α

γ ∂ ∂ ∂ ∂ ∂ ∂ ∂∂ ∂ ′ = − + − + − + + + ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂ ∂

Schrödinger Equation: H = T + V, V=V(R) Vibrational peaks

∑≠

Γ++−

+Γ+−−

=FIK KFKKIK iEE

FKKIiEEFKKI

, 00, ω

µµωµµ

α σρρσσρ

Kramers-Heisenberg-Dirac Dispersion Equation

Qi

E

M-m

M+-m-

SERS Intensity: Resonance Raman Scattering

D. Wu, et al., Spectrochim. Acta A, 2004, 60, 137;J. Chem, Phys. 2005, 122, 094719

( )

2 2

,1 ,

22 1

nn

CEfb v

Q

ρσρ σ

α

α==

∂+ ∂

∑∑~10 - 103

( ) ( ) ( )

( )( ) ( )

( ) ( )

22

1 , 0

2

0

, 1 ,

2 2 1

1

1 /

1exp 02

i i

i

i

ia a app i am ma

i i

i i i i

m n m n app i ii i

I V s M M

edt

e

et it a V G th

λ

λ

ββ β

β β β β

ω ω ω

′−∞

′−

′= ′+

−

′ ′+ − +×

× −Γ + + + +

∫

∑ ∏

D.Y. Wu*, et al., Spectrochim. Acta. A, 2004, 60, 137.

D. Y. Wu*, et al., J. Phys. Chem. C, 2008, 112, 4195.

Experiments

950 1000 1050 1100

% (v1 and v12 resonance)Γv1

= 3 cm-1

Γv12 = 2 cm-1

ΓCT = 1880 cm-1

Wavenumber (cm-1)

Energy matching between photon and the CT state

Charge transfer mechanism of pyridine/Ag

Theory

No CT

sp2 sp3 hybridization

Wagging Vibrations of Amino Group in Adsorbed Aniline

J. Phys. Chem. C, 2011,115, 4174

Aniline Benzyl species

J. Phys. Chem. C, 2011,115, 4174

Wagging Vibrations of Amino group in Adsorbed Aniline

Simulated Raman Spectra of PATP/Ag or Au

J. Phys. Chem. C, 2011,115,4174-4183

J. Phys. Chem. C, 2009,113,18212-182212

p -Aminobenzoic acid at Ag electrode

Aniline/Ag Electrode

Aniline/AgNP

Benzidine/Ag

Wagging Vibrations of Aniline and its derivatives/Ag

Tian, et al, Acta Phys. Chem. Sinica, 1987, 3, 178.Li, et al, Environment Sci. & Tech., 2011, 45,4046Kim, et al., J. Phys. Chem., 1990, 94,7576

Benzyl and Amino Groups Adsorbed on Silver Electrodes

yy

xxzz

zz

xx

yy

Free state

Adsorption

Amino Benzyl radical

S. Tao, et al., J. Phys. Chem. C., 2013, 117, 18891

-0.30

-0.25

-0.20

-0.15

-0.10

-0.05

-1.0 -0.5 0.0 0.5 1.0

LOMO

E(a.

u)

Normal coordinate

HOMO

(A)

sp2

-0.20

-0.15

-0.10

-0.05

0.00

0.05

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

LUMO

E(a.

u)

Normal coordinate

HOMO

(B)

sp2

J. Phys. Chem. C, 2013,117,18891

Wagging Vibrations of Aniline and Benzyl/Ag

Three factors:1. Binding strength2. p-π3. sp2-sp3

SERS spectra of Benzyl adsorbed on silver electrodes J. Am. Chem. Soc. 2010, 132, 9534-9536.

Wagging Vibrations of Benzyl/Ag and Aniline/Ag Nanopart.

Chemical enhancement factor from chemical bonding

10~500 fold

Summary

(1) Chemical enhancement effect is significantly influenced by charge transfer and chemical binding interaction on metal electrode surfaces.

(2) The p-π conjugation effect, hybridization effect, and the strength of the binding interaction influence on the surface Raman bands of wagging vibrations (Vibrationalfrequency and Raman intensity).

(3) Quantum chemical calculation is helpful to understand the observed phenomena in surface Raman spectra in Electrochemical interfaces. EC-SERS + QC

Acknowledgements：

Collaborators:

Prof. Zhong-Qun Tian (Xiamen University) EC-SERS Expt

Prof. Bin Ren (Xiamen University) EC-SERS Expt

Prof. Zhi-Lin Yang (Xiamen University) SERS-Surface Plasmon

Prof. S. H. Lin (IAMS, Taipei) Molecular Spectroscopy

Students：

Song-Yuan Ding, Xiu-Min Liu, Yi-Fan Huang, Ran Pang, Liu-Bin Zhao, Rong Huang, Xi Jin, Wen-Li Luo, Sha Tao, Li-Juan Yu, Zi-Feng Liu

Fund: NSF of China, Basic Research Project of MOST

Thanks for your attention!

D.Y. Wu*, et al., Spectrochim. Acta. A, 2004, 60, 137.

D. Y. Wu*, et al., J. Phys. Chem. C, 2008, 112, 4195.

Experiments

16

950 1000 1050 1100

% (v1 and v12 resonance)Γv1

= 3 cm-1

Γv12 = 2 cm-1

ΓCT = 1880 cm-1

Wavenumber (cm-1)

Theory

Energy matching between photon and charge transfer state

Charge transfer mechanism of pyridine/Ag

Charge Transfer Enhancement for Pyridine/Ag

950 1000 1050 1100

v1 and v12 resonanceΓv1

= 3 cm-1

Γv12 = 2 cm-1

ΓCT = 1880 cm-1

Wavenumber (cm-1)

~100 fold

17