Effect of the Molecule-Metal Interface on the Surface Enhanced Raman Scattering of 1,4-Benzenedithiol

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1 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, W4-10 Ookayama, Meguro-ku, Tokyo , Japan 1

2 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 C 2v 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 SERS (cm -1 ) (cm -1 ) Rough Sphere-Plane Assignment w πch, 10b (b 2 ) m 345 s 350 s νcs + γccc, 6a (a 1 ) vw 400 vw τcc, 16a (a 2 ) w 495 w γccc, 16b (b 2 ) vw 510 vw 20a w 630 vw 630 vw 6b vw 690 vw πch + πcs +πcc, 4 (b 1 ) m 750 m 750 m νcs, 7a (a 1 ) vw 810 vw 17b (b 2 ) w β (SH) vw 18a w νch + νcs + νcc, 1 (a 1 ) s 1060 s 1060 s νch + νcs + νcc, 1 (a 1 ) w 1200 w 1200 w δch, 9a (a 1 ) vw 1250 vw νcc +δch, 14(b 2 ) vw 1300 vw δch + νcc, 3 (b 2 ) vw 1400 vw νcc + δch, 19b (b 2 ) vw 19a s 1555 s 1550 s νcc, 8a (a 1 ) β (SH) indicates a vibrational mode of a thiol group. One of the two bands of ν 1 arises from an overtone or a combination band such as 6a + 7a, in Fermi resonance with the ν 1 fundamental. 2 2

3 Table S2. Vibrational assignment of ABT. No. Raman Bulk SERS (cm -1 ) (cm -1 ) Rough Sphere-Plane Assignment m δch +δcs, 18b (b 2 ) w 400 m 400 m τcc, 16a (a 2 ) s νcs + γccc, 6a (a 1 ) vw 550 vw γccc, 16b (b 1 ) w γccc, 12 (a 1 ) vw 700 vw πch +πcs +πcc, 4 (b 1 ) m 800 vw 800 vw πch, 10a (a 2 ) vw δsh vw 1000 w 1000 w γcc +γccc, 18a (a 1 ) s 1075 s 1070 s νcs, 7a (a 1 ) m 1130 m δch, 9b (b 2 ) w 1200 w 1200 w δch, 9a (a 1 ) vw νch, 7a (a 1 ) w 1300 w νcc +δch, 14 (b 2 ) vw 1400 vw δch + νcc, 3 (b 2 ) m 1420 m νcc + δch, 19b (b 2 ) vw 1500 vw 1500 vw νcc + δch, 19a (a 1 ) s 1580 s 1570 s νcc, 8a (a 1 ) 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

4 Raman activities that were subsequently converted into relative vibrational intensities. A scaling factor of 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 ν 6a (deformation-coupled C-S stretching mode), ν 8a (ring breathing mode) and ν 1 (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 ν 8a and ν 1, and inversely for ν 6a. The comparatively small energy shift observed for the calculated values of the ν 6a 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

5 Table S3. Calculated and experimentally observed energies of ν 6a, ν 1 and ν 8a vibrational modes in bulk BDT, Au BDT, and Au BDT Au. ν 6a (cm -1 ) ν 1 (cm -1 ) ν 8a (cm -1 ) Calc. Exp. Calc. Exp. Calc. Exp. Bulk BDT Au BDT Au BDT Au 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, (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, (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, (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, (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,