Effect of the Molecule-Metal Interface on the Surface Enhanced ...
Supporting Information
Effect of the Molecule-Metal Interface on the Surface
Enhanced
Raman
Scattering
of
1,4-Benzenedithiol
Sho Suzuki, Satoshi Kaneko*, Shintaro Fujii, Santiago Marqués-González, Tomoaki Nishino, Manabu Kiguchi*
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 W4-10 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
1
1. Vibrational assignment of BDT and ABT Assignment of the vibrational modes of both BDT and ABT was based in previously reported studies assuming a C2v symmetry.1-4 Wilson’s notation was used throughout. Vibrational modes: ν (stretch); δ and γ (bend); π (wagging). Relative intensity: s (strong); m (medium); w (weak); vw (very weak). Table S1. Vibrational assignment of BDT. No.
Raman Bulk (cm-1)
1
290 w
2
329 m
SERS (cm-1) Rough
Sphere-Plane
Assignment πCH, 10b (b2)
345 s
350 s
νCS + γCCC, 6a (a1)
3
400 vw
400 vw
τCC, 16a (a2)
5
480 w
495 w
γCCC, 16b (b2)
6
530 vw
510 vw
20a
630 vw
630 vw
6b
690 vw
690 vw
πCH + πCS +πCC, 4 (b1)
750 m
750 m
νCS, 7a (a1)
810 vw
810 vw
17b (b2)
7
630 w
9 10
750 m
11 13
900 w
β (SH)
14
1000 vw
18a
15
1050 w
νCH + νCS + νCC, 1 (a1)
16
1087 s
1060 s
1060 s
νCH + νCS + νCC, 1 (a1)
17
1200 w
1200 w
1200 w
δCH, 9a (a1)
19
1250 vw
1250 vw
νCC +δCH, 14(b2)
20
1300 vw
1300 vw
δCH + νCC, 3 (b2)
21
1400 vw
1400 vw
νCC + δCH, 19b (b2)
1450 vw
19a
1550 s
νCC, 8a (a1)
22 25
1566 s
1555 s
β (SH) indicates a vibrational mode of a thiol group. One of the two bands of ν1 arises from an overtone or a combination band such as 6a + 7a, in Fermi resonance with the ν1 fundamental.2
2
Table S2. Vibrational assignment of ABT. No.
Raman Bulk (cm-1)
1
300 m
3
400 w
4
500 s
5 6
SERS (cm-1) Rough
Sphere-Plane
δCH +δCS, 18b (b2) 400 m
400 m
τCC, 16a (a2) νCS + γCCC, 6a (a1)
550 vw
550 vw
600 w
7
Assignment
γCCC, 16b (b1) γCCC, 12 (a1)
700 vw
700 vw
πCH +πCS +πCC, 4 (b1)
800 vw
800 vw
πCH, 10a (a2)
9
800 m
10
900 vw
12
1000 vw
1000 w
1000 w
γCC +γCCC, 18a (a1)
13
1081 s
1075 s
1070 s
νCS, 7a (a1)
1140 m
1130 m
δCH, 9b (b2)
1200 w
1200 w
δCH, 9a (a1)
14 15
1200 w
18
1250 vw
δSH
νCH, 7a’ (a1)
19
1300 w
1300 w
νCC +δCH, 14 (b2)
20
1400 vw
1400 vw
δCH + νCC, 3 (b2)
21
1430 m
1420 m
νCC + δCH, 19b (b2)
22
1500 vw
1500 vw
1500 vw
νCC + δCH, 19a (a1)
23
1585 s
1580 s
1570 s
νCC, 8a (a1)
24
1600 vw
δNH
2. Calculated Raman spectra of BDT Density functional theory (DFT) calculations were performed to investigate the spectroscopic features of molecular junctions using Gaussian 09 software.5 The B3LYP/ 6-31G* and LANL2DZ basis sets were used for C, S, and H, and Au, respectively. A series of structural relaxation calculations were performed in order to find the global potential energy minima. Initial atomic positions were selected from lowest-energy conformers obtained by structural optimization using a semi-empirical method. To simulate the Raman spectra of BDT, Gaussian 09 was used to calculate the molecular 3
Raman activities that were subsequently converted into relative vibrational intensities. A scaling factor of 0.961 was used for the analysis of the vibrational energies. The Au electrode was modeled using a single Au atom. Figure S1 and Table S3 show the calculated Raman and energies of BDT ν6a (deformation-coupled C-S stretching mode), ν8a (ring breathing mode) and ν1 (C=C stretching mode) together with the experimentally observed values. The calculated values were found to adequately fit the experimental data. The trend in vibrational energies were preserved for all vibrational modes i.e. bulk BDT > Au−BDT (rough Au substrate) > Au−BDT−Au (sphere-plane configuration) for ν8a and ν1, and inversely for ν6a. The comparatively small energy shift observed for the calculated values of the ν6a mode can be attributed to the use of a streamlined model.
Figure S1. Schematic representation and calculated Raman spectra of (a) bulk BDT, (b) Au−BDT (rough Au substrate), and (c) Au−BDT−Au (sphere-plane configuration).
4
Table S3. Calculated and experimentally observed energies of ν6a, ν1 and ν8a vibrational modes in bulk BDT, Au−BDT, and Au−BDT−Au.
ν6a (cm-1) Calc. Exp.
ν1 (cm-1) Calc.
Exp.
ν8a (cm-1) Calc.
Exp.
Bulk BDT
327
329 1066 1087 1581 1566
Au−BDT
327
345 1051 1060 1565 1555
Au−BDT−Au
329
350 1043 1060 1552 1550
References (1) Joo, S. W.; Han, S. W.; Kim, K. Adsorption of 1,4-Benzenedithiol on Gold and Silver Surfaces: Surface-Enhanced Raman Scattering Study. J. Colloid Interface Sci.
2001, 240, 391-399. (2) Cho, S. H.; Han, H. S.; Jang, D.-J.; Kim, K.; Kim, M. S. Raman Spectroscopic Study of 1,4-Benzenedithiol Adsorbed on Silver. J. Phys. Chem. 1995, 99, 10594-10599. (3) Osawa, M.; Matsuda, N.; Yoshii, K.; Uchida, I. Charge Transfer Resonance Raman Process in Surface-Enhanced Raman Scattering from p-Aminothiophenol Adsorbed on Silver: Herzberg-Teller Contribution. J. Phys. Chem. 1994, 98, 12702-12707. (4) Kim, K.; Shin, D.; Choi, J.-Y.; Kim, K. L.; Shin, K. S. Surface-Enhanced Raman Scattering Characteristics of 4-Aminobenzenethiol Derivatives Adsorbed on Silver. J. Phys. Chem. C 2011, 115, 24960-24966. (5) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Gaussian, Inc.: Wallingford, CT, USA, 2009.
5
Effect of the Molecule-Metal Interface on the Surface
Enhanced
Raman
Scattering
of
1,4-Benzenedithiol
Sho Suzuki, Satoshi Kaneko*, Shintaro Fujii, Santiago Marqués-González, Tomoaki Nishino, Manabu Kiguchi*
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 W4-10 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
1
1. Vibrational assignment of BDT and ABT Assignment of the vibrational modes of both BDT and ABT was based in previously reported studies assuming a C2v symmetry.1-4 Wilson’s notation was used throughout. Vibrational modes: ν (stretch); δ and γ (bend); π (wagging). Relative intensity: s (strong); m (medium); w (weak); vw (very weak). Table S1. Vibrational assignment of BDT. No.
Raman Bulk (cm-1)
1
290 w
2
329 m
SERS (cm-1) Rough
Sphere-Plane
Assignment πCH, 10b (b2)
345 s
350 s
νCS + γCCC, 6a (a1)
3
400 vw
400 vw
τCC, 16a (a2)
5
480 w
495 w
γCCC, 16b (b2)
6
530 vw
510 vw
20a
630 vw
630 vw
6b
690 vw
690 vw
πCH + πCS +πCC, 4 (b1)
750 m
750 m
νCS, 7a (a1)
810 vw
810 vw
17b (b2)
7
630 w
9 10
750 m
11 13
900 w
β (SH)
14
1000 vw
18a
15
1050 w
νCH + νCS + νCC, 1 (a1)
16
1087 s
1060 s
1060 s
νCH + νCS + νCC, 1 (a1)
17
1200 w
1200 w
1200 w
δCH, 9a (a1)
19
1250 vw
1250 vw
νCC +δCH, 14(b2)
20
1300 vw
1300 vw
δCH + νCC, 3 (b2)
21
1400 vw
1400 vw
νCC + δCH, 19b (b2)
1450 vw
19a
1550 s
νCC, 8a (a1)
22 25
1566 s
1555 s
β (SH) indicates a vibrational mode of a thiol group. One of the two bands of ν1 arises from an overtone or a combination band such as 6a + 7a, in Fermi resonance with the ν1 fundamental.2
2
Table S2. Vibrational assignment of ABT. No.
Raman Bulk (cm-1)
1
300 m
3
400 w
4
500 s
5 6
SERS (cm-1) Rough
Sphere-Plane
δCH +δCS, 18b (b2) 400 m
400 m
τCC, 16a (a2) νCS + γCCC, 6a (a1)
550 vw
550 vw
600 w
7
Assignment
γCCC, 16b (b1) γCCC, 12 (a1)
700 vw
700 vw
πCH +πCS +πCC, 4 (b1)
800 vw
800 vw
πCH, 10a (a2)
9
800 m
10
900 vw
12
1000 vw
1000 w
1000 w
γCC +γCCC, 18a (a1)
13
1081 s
1075 s
1070 s
νCS, 7a (a1)
1140 m
1130 m
δCH, 9b (b2)
1200 w
1200 w
δCH, 9a (a1)
14 15
1200 w
18
1250 vw
δSH
νCH, 7a’ (a1)
19
1300 w
1300 w
νCC +δCH, 14 (b2)
20
1400 vw
1400 vw
δCH + νCC, 3 (b2)
21
1430 m
1420 m
νCC + δCH, 19b (b2)
22
1500 vw
1500 vw
1500 vw
νCC + δCH, 19a (a1)
23
1585 s
1580 s
1570 s
νCC, 8a (a1)
24
1600 vw
δNH
2. Calculated Raman spectra of BDT Density functional theory (DFT) calculations were performed to investigate the spectroscopic features of molecular junctions using Gaussian 09 software.5 The B3LYP/ 6-31G* and LANL2DZ basis sets were used for C, S, and H, and Au, respectively. A series of structural relaxation calculations were performed in order to find the global potential energy minima. Initial atomic positions were selected from lowest-energy conformers obtained by structural optimization using a semi-empirical method. To simulate the Raman spectra of BDT, Gaussian 09 was used to calculate the molecular 3
Raman activities that were subsequently converted into relative vibrational intensities. A scaling factor of 0.961 was used for the analysis of the vibrational energies. The Au electrode was modeled using a single Au atom. Figure S1 and Table S3 show the calculated Raman and energies of BDT ν6a (deformation-coupled C-S stretching mode), ν8a (ring breathing mode) and ν1 (C=C stretching mode) together with the experimentally observed values. The calculated values were found to adequately fit the experimental data. The trend in vibrational energies were preserved for all vibrational modes i.e. bulk BDT > Au−BDT (rough Au substrate) > Au−BDT−Au (sphere-plane configuration) for ν8a and ν1, and inversely for ν6a. The comparatively small energy shift observed for the calculated values of the ν6a mode can be attributed to the use of a streamlined model.
Figure S1. Schematic representation and calculated Raman spectra of (a) bulk BDT, (b) Au−BDT (rough Au substrate), and (c) Au−BDT−Au (sphere-plane configuration).
4
Table S3. Calculated and experimentally observed energies of ν6a, ν1 and ν8a vibrational modes in bulk BDT, Au−BDT, and Au−BDT−Au.
ν6a (cm-1) Calc. Exp.
ν1 (cm-1) Calc.
Exp.
ν8a (cm-1) Calc.
Exp.
Bulk BDT
327
329 1066 1087 1581 1566
Au−BDT
327
345 1051 1060 1565 1555
Au−BDT−Au
329
350 1043 1060 1552 1550
References (1) Joo, S. W.; Han, S. W.; Kim, K. Adsorption of 1,4-Benzenedithiol on Gold and Silver Surfaces: Surface-Enhanced Raman Scattering Study. J. Colloid Interface Sci.
2001, 240, 391-399. (2) Cho, S. H.; Han, H. S.; Jang, D.-J.; Kim, K.; Kim, M. S. Raman Spectroscopic Study of 1,4-Benzenedithiol Adsorbed on Silver. J. Phys. Chem. 1995, 99, 10594-10599. (3) Osawa, M.; Matsuda, N.; Yoshii, K.; Uchida, I. Charge Transfer Resonance Raman Process in Surface-Enhanced Raman Scattering from p-Aminothiophenol Adsorbed on Silver: Herzberg-Teller Contribution. J. Phys. Chem. 1994, 98, 12702-12707. (4) Kim, K.; Shin, D.; Choi, J.-Y.; Kim, K. L.; Shin, K. S. Surface-Enhanced Raman Scattering Characteristics of 4-Aminobenzenethiol Derivatives Adsorbed on Silver. J. Phys. Chem. C 2011, 115, 24960-24966. (5) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A., et al. Gaussian 09, Gaussian, Inc.: Wallingford, CT, USA, 2009.
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