sers roundtable 2007 ellenz-poltersdorf, october 03 – 05, 2007 1 of 21 spectroelectrochemistry of...

SERS Roundtable 2007

Ellenz-Poltersdorf, October 03 – 05, 2007

1 of 21

Spectroelectrochemistry of Self Assembled Monolayers of Biphenyl Ethynyl Thiols on Gold Electrodes

Abdel Aziz Jbarah, Katrin Rößler, Heinrich Lang and Rudolf Holze

Institut für Chemie, Technische Universität Chemnitz, D-09107 Chemnitz



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S

R

S

R

S

R

S

R

S

R

S

R

S

R

S

R



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C SC(H3C)3Si

C SCH

C SHC(H3C)3Si

C

C

O

CH3

O

CH3

1

2

3

4-Trimethylsilylethinyl-1,1'-biphenyl-4'-thiol

4-Ethinyl-4'-thiomethylester-1,1'-biphenyl

4-Trimethylsilylethinyl-4'-thiomethylester-1,1'-biphenyl



4 of 21



5 of 21

Nyquist-plots of a gold electrode, 1: 3a/Au, 3: 3b/Au, 2: 4/Au und 21/Au, 0.01 M (NH4)2Fe(SO4)2/0.01 M (NH4)Fe(SO4)2 in 1

M HClO4



6 of 21

C SC( H 3 C ) 3 S i C

O

C H 3

R C T /

Ω

C D L / μ F l / n m

o f R S -

A u 3 3 0 1 0 . 0 -

( 1 ) / A u 2 7 1 2 1 . 9 9 1 . 5 0 3

( 2 ) / A u 2 4 3 4 3 . 0 2 1 . 2 5 2

( 3 ) / A u 2 9 3 8 1 . 0 8 1 . 5 0 3

C SCH C

O

C H 3

C S HC( H 3 C ) 3 S i

0.01 M (NH4)2Fe(SO4)2/0.01 M (NH4)Fe(SO4)2 in 1 M HClO4

Assumption: 2 and 3 should yield the same SAM after S-R-cleavage



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d

AC ro

Au

Assuming: 3 stands upright and 1 is tilted → α ≈ 60°

31

3 1

DL

DL

dC

C d 1cos

d

l

31

3 1cos DL

DL

Cd

d C



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Cyclic voltammogram of: 3: 3a/Au und 2: 4/Au in 0.01 M (NH4)2Fe(SO4)2/ 0.01 M (NH4)Fe(SO4)2 in 1 M HClO4.

4 3a

-0,25

-0,2

-0,15

-0,1

-0,05

0

0,05

0,1

0,15

0,2

0,25

-0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8

E / V

I / µ

A



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UV-Vis spectra of 10-5 mM of 1 in THF (a), 10-5 mM of 2 in THF (b) and 10-5 mM of 3 in THF (c), 5.0 mm cell,

resolution 0.1 nm.

300 400 500 600 700 800 900

0.0

0.5

1.0

2, max

= 285 nm

1, max

= 293 nm

3, max

= 288 nm

Wavelength / nm

Ab

sorp

tion

/ -



10 of 21

500 1000 1500 2000

0

2000

4000

Calculated Raman spectrum of 1

Raman shift / cm-1

Ram

an In

tens

ity /

a.u.

500 1000 1500 2000

0

200

400

600

Abso

rptio

n / a

.uWavenumbers / cm-1

Calculated infrared spectrum of 1



11 of 21

500 1000 1500 2000

0

1000

2000

3000


Raman shift / cm-1

Ram

an In

tens

ity /

a.u.

500 1000 1500 2000

0

100

200

300

400

500

Wavenumbers / cm-1

Abso

rptio

n / a

.u




12 of 21

500 1000 1500 2000

0

2000

4000

6000


Raman shift / cm-1

Ram

an In

tens

ity /

a.u.

500 1000 1500 2000

0

200

400

600

Abso

rptio

n / a

.u

Wavenumbers / cm-1




13 of 21

C

C

Si(CH3)3

S

Me

CC

Si(CH3)3

S

Me

C C Si(CH3)3S

Me

3



14 of 21

500 1000 1500 2000

30

40

50

60

70

1: SERS

ERHE

=

800 mV

700 mV

500 mV

300 mV

100 mV

Ra

ma

n in

ten

sity

/ s

-1

Raman shift / cm-1



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Tilted orientation, weaker Au-S interaction than with 3

1



16 of 21

5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

1 0 0

2 0 0

3 0 0

4 0 02 : N R

Ra

ma

n in

ten

sity

/ s

-1

R a m a n s h i f t / c m - 1

5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

0 . 5

1 . 0

1 . 52 : I R

W a v e n u m b e r s / c m - 1

Ab

sorp

tion

/ -

500 1000 1500 2000

50

100

150 2: SERS

ERHE

=

900 mV

700 mV

500 mV

300 mV

100 mV

Ra

ma

n in

ten

sity

/ s

-1

Raman shift / cm-1



17 of 21

Assignment of vibrational modes of 2 in a solid form and the SER-spectra of a gold electrode coated with a monolayer of 2 in a solution of 1.0 M HClO4 at various electrode potential.

SERS in 1.0 M HClO4 Assignment

Wilson mode #

IR, Fig. 6a

NRAS, Fig. 6b ERHE=

100 mV ERHE=

300 mV ERHE=

500 mV ERHE=

700 mV ERHE=

900 mV νAu? S - - - - 190 178 177 δCH 9b - 416 414 413 412 414 415 δring 6a 452 459 - - 468 - 473 n.a. - 518 - - - - - - γring 16b 537 - - - - - - n.a. - 561 - - - - - - νCS - 628 636 - 636 635 635 632 n.a. - 661 - - - - - - n.a. - 677 - - - - - - δring 12 740 742 - - - - - νring

1 - 800 - - - - - 10a 819 - - - - - -

γCH 17b 854 - - - - - -

γCH 17a 943 - 940 939 939 939 939 n.a. - 1003 - - - - - -

18a 1016 1026 1017 1017 1017 1019 1017 δCH 18b 1098 1099 1086 1085 1086 1086 1085 n.a. - 1112 1108 - - - - - n.a. - 1126 - - - - - -

1188 1183 1183 1186 1188 1186 δCH 9a -

1195 1193 1196 1193 - - 7a 1254 1249 - - - 1233 1231

νCH 13 - 1292 1289 1290 1288 1292 1290

δCH 3 1309 - - - - - - methyl def. 1352 - - - - - -

19b 1388 - - - - - - 19a 1480 - - - - - - 8b - 1602 1592 1594 1587 1592 1591

νring

8a - 1612 - - - 1602 1606 νCO - 1694 - - - - - -

ν: stretch mode; def.: deformation mode; δ: in-plane deformation mode; γ: out-of-plane deformation mode; βas: rocking mode.

More tilted or even flat orientation – fits with CDL, very weak Au-S interaction, presum-ably R-S-R intact with corresponding orienta-tion

2



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5 0 0 1 0 0 0 1 5 0 0 2 0 0 0

0 . 4

0 . 6

0 . 8

1 . 0

1 . 23 : I R

W a v e n u m b e r s / c m - 1

Ab

sorp

tion

/ -

5 0 0 1 0 0 0 1 5 0 0 2 0 0 03 0

4 0

5 0

6 0

7 0

8 03 : N R

Ra

ma

n in

ten

sity

/ s

-1

R a m a n s h i f t / c m - 1

500 1000 1500 2000

20

30

40

3: SERS

ERHE

=

900 mV

700 mV

500 mV

300 mV

100 mV

Ra

ma

n in

ten

sity

/ s

-1

Raman shift / cm-1



19 of 21

Assignment of vibrational modes of 3 in a solid form and the SER-spectra of a gold electrode coated with a monolyer of 3 in a solution of 1.0 M HClO4 at various

electrode potentials. SERS in 1.0 M HClO4

Assignment Wilson mode #

IR, Fig. 7a

NRAS, Fig. 7b ERHE=

100 mV ERHE=

300 mV ERHE=

500 mV ERHE=

700 mV ERHE=

900 mV n.a. - - - 166 168 164 162 165 νAu? S

- - - 264 267 266 265 265 γring 6a - - 372 374 371 371 374 δCH 9b - - 410 411 413 412 409 n.a. - - - 471 473 471 469 470 γring 16b 512 - 499 499 501 501 504 n.a. - 554 - - - - - - νCS - 617 625 621 621 622 622 621 δring 12 659 - 663 664 663 664 664 γring 4 698 - 713 717 715 718 715 βas, methyl - 759 - 754 753 754 754 754

10a 812 - - - - - - γCH

17b 843 - 832 830 831 834 827 βas, methyl - 867 - 870 869 872 - - γCH 17a - - 940 940 940 940 940 n.a. - 1003 - - - - 1006 1008

18a 1014 - 1019 1019 1020 1020 1019 18b 1103 1113 1085 1087 1085 1086 1085 δCH 9a 1140 - - - - - -

n.a. - 1201 1208 1195 1198 1199 1198 1200 νCH 7a 1244 1242 - - - - - n.a. - 1253 - - - - - - νCH 13 - 1287 1290 1289 1289 1289 1291 δCH 3 1317 - - - - - - methyl def. - 1396 - - - - - -

19b 1460 - - - - - - 19a 1484 - 1484 1485 1483 1483 1483 8b 1594 - 1591 1592 1591 1590 1590

νring

8a - 1604 1609 1609 1609 1609 1609 νC?C 2157 2167 2171 2169 2170 2170 2170

ν: stretch mode; def.: deformation mode; δ: in-plane deformation mode; γ: out-of-plane deformation mode; βas: rocking mode.

Au-S-mode typical of thiolate

3



20 of 21

Take home:

•SAMs are formed

•different compactness/thickness

•Some are tilted with respect to surface normal

•Various strengths of Au-S-interaction



21 of 21

C

S-

C

Si(CH3)3

C

S

C

H

C

S-

C

Si(CH3)3

CCH3O

123

sers roundtable 2007 ellenz-poltersdorf, october 03 – 05, 2007 1 of 21 spectroelectrochemistry of...

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