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 Chemistr

y for Solid Surfaces

Xiamen University

Ohio, 2010.6.24

Studies on solution/metal electrodes

High detection sensitivityHigh detection sensitivity

High ResolutionHigh Resolution

EnergyEnergy

SpaceSpace

TimeTime

2-20 Å

Surface-enhanced Raman spectroscopy ： SERS

Surface plasmon resonance

Chemical property

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.

C

C

C

C

C

N

H

H

H

H H

M

M

M M MM

MMM

Y

Z

H H

HH

H H

N

H H

H

H H

1 1

Molecules/Metallic cluster model

C1

C6

C5

C4

C3

C2

X2

X1

SH

SH

SH

NH2

NH2

NH2

NH2 SH

AN TP

BDA

DSB

pMA

x1, x2= -NH2x2= -SH

x1, x2= -SHx1 = -NH2

BDT

Adsorption models of different molecules

Computational details

Cluster Model: Mn – Molecule – Mn (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 ：

4

2 202

45 78 45 1 exp

R ii i i

i i B

v vhI

cv hcv k T

Non-resonance, pre-resonance, and resonance cases

0.00

0.04

0.08

Aniline

0.00

0.08

0.16

BDT

0.00

0.08

0.16R

aman

Inte

nsity

Benzene

400 600 800 1000 1200 1400 1600 1800

0.00

0.04

0.08

Thiophenol

400 600 800 1000 1200 1400 1600 1800

0.00

0.04

0.08

pMA

0.00

0.08

0.16

Raman Shift/cm-1

BDA

(1)Simulated Raman spectra of Benzene Derivatives

H

H

H

H

H

H

SH

H

H

H

H

H

NH2

H

H

H

H

H

SH

SH

H

H

H

H

NH2

NH2

H

H

H

H

SH

NH2

H

H

H

H

Vibrational coupling existing

（ 2 ） Thiophenol (TP) and Benzenedithiol (BDT)/Au SERS

0.00

0.25

0.50

Raman Shift/cm-1

TP-Au5

Ram

an

In

ten

sity

(X1

0-3

0 cm

2 /mo

l)

400 600 800 1000 1200 1400 1600 1800

0.00

0.50

1.00TP-Au

13

J. H. Tian, et al., JACS, 2006,128,14748.

Bridge site

Hollow site

Au5-BDT-Au5

SH

H

H

H

H

H

Not sensitive to adsorption site

SH

SH

H

H

H

H

Thiol

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

400 600 800 1000 1200 1400 1600 1800

0.0

0.2

0.4 AN-Au2

Ram

an In

tensi

ty

Raman Shift/cm-1

0.0

0.2

0.4 AN-Au4

0.0

1.0

2.0

BDA-Au2

0.0

1.0

2.0

3.0

Au2-BDA-Au2

400 600 800 1000 1200 1400 1600 1800

0.0

1.0

2.0

Ram

an Int

ensi

ty(X

10-3

0 c

m2/m

ol)

Raman Shift

BDA-Au4

400 600 800 1000 1200 1400 1600 1800

0.0

1.0

2.0

3.0

Au4-BDA-Au4

400 600 800 1000 1200 1400 1600 1800

0.0

1.0

2.0

Au4-cis-BDA-Au4R

am

an Inte

nsi

ty(X

10-30 c

m2 /m

ol)

Raman Shift/cm-1

Amino

NH2

H

H

H

H

H

NH2

NH2

H

H

H

H

(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 b2 modes of PATP

Is it a real story?

PATP/Ag

PATP solid

Weak

Strong

HS- -NH2

1142

13911440

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

Hollow site

(4) Simulated Raman spectra of PATP/Au

400 600 800 1000 1200 1400 1600 1800

01020

Au3-PATP-Au

2

0.01.02.0

Ram

an In

tens

ity (X

10-3

0 c

m2 /m

ol) Au

5-PATP

0.01.02.0 Au

5-PATP

0.01.02.0 Au

5-PATP

0.01.02.0

Raman Shift /cm-1

Au5-PATP-Au

6

(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/-SC6H4NH2+

/Ag

Q. Zhou, et al. Angew. Chem. 2006, 45, 397

1064 nm514.5 nm

790 nm

790 nm

SERS

Solid

Acidic

aromatic

Alkaline quinonoidic

Theoretical Study

(4) A new mechanism: 2 * PATP/M DMAB/M

N

N SH

HS

N

N SH

HS

NH2

H2N SH

HS

H

H

2H+

2H+

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+/TiO2)

H. Park, et al., J. Phys. Chem., 1990, 94, 7576. (P-aminobenzoic acid/Silver Electrode)

DMAB reversibly decomposesDMAB yields

DMAB: p,p´-dimercaptoazobenzene

(4) Ag5/DMAB and Ag5/DMAB/Ag5

B3LYP PW91PW91

Free Molecule

Singe-end

Double-end vC-N C-H

vN=N

Ag

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

Raman shift(cm-1)

Inte

nsi

ty

PW91PW91

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

B3LYP

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

PBE1PBE

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

B3PW91

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

MPW1PW91

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

B3P86

600 800 1000 1200 1400 1600 1800

0

2

4

6

8

10

12

BP86

(4) Simulated Raman spectra of azobenzene

(4) Comparison of Structural parameters

We find B3LYP overestimates the N=N bond, resulting in the blue shift of the vN=N stretching frequency; PW91PW91 and BP86 are more reliable to describe the N=N bond.

1000 1200 1400 1600 1800Raman Shift(cm-1)

S

NH2

Ag

S

NH2

Ag

S

NH

Au

Ag

S

N

Ag

N

SH

Ag

+ e-

hv

? ? ?!!!

+ e-

+

-

The nature of SERS?Surface catalytic coupling reaction

JPCC2009,113,18212

× × ×JPCC2009,113,18212

×

1000 2000 3000Raman Shift /cm-1

900 1200 1500Raman Shift /cm-1

NH2HS

N NHS SH

SERS of DMAB and pATP on Ag NPs

Prof. Hongping Zhu JACS2010,132,9244

NH2HS N NHS SH

Direct evidence

4. Conclusion

(1) The amino group is more chemical activity than the thiol grou

p on coinage metal surfaces.

(2) PATP may undergo surface catalytic coupling reaction to for

m azobenzene derivative, yielding the intense Raman bands a

t 1140, 1390, and 1440 cm-1 。

(3) PW91PW91 and BP86 is better to describe the N=N double b

ond than B3LYP.

(4) Quantum chemical calculation is helpful to understand the ob

served phenomenon in the view of nature.

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!

Thanks for your attention!

(4) pH effect: Reversibility of Raman spectra of PATP

W. Hill, B. Wheling, J. Phys. Chem., 1993, 97, 9451

Na2S2

pH = 2.0

Acidic

Alkaline

Acidic ---good

Basic ----bad