Raman spectral vibrational frequencies are used to probe the local chemical environment surrounding molecules in solution and adsorbed to gold nanostars. Herein, the impacts of functional group protonation on monosubstituted benzene derivatives with amine, carboxylic acid, or hydroxide are evaluated. Changes in binding affinity and orientation are apparent by evaluating systematic variations in vibrational frequencies. Notably, the electron donating abilities of these functional groups influence the vibrational frequency of the ring breathing mode, thus leading to improved spectral interpretation. Furthermore, gold nanostars are used to investigate the impact of molecular protonation on the adsorption of benzoic acid/benzoate to gold. The changes in molecular protonation are measured using zeta potential and the surface-sensitive technique, surface-enhanced Raman scattering. These methods reveal that pH variations induce carboxylate protonation and electron redistribution that weaken molecular affinity, thereby causing the molecule to adopt a perpendicular to parallel orientation with respect to the nanostar surface. Functional group identity influences the ring breathing mode frequency as a function of changes in electron donation from the functional group to the ring in solution as well as molecular affinity to and orientation on gold. This exploitation of vibrational frequencies facilitates the elucidation of molecule behavior in complex systems.
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14 November 2020
Research Article|
November 11 2020
Elucidation of pH impacts on monosubstituted benzene derivatives using normal Raman and surface-enhanced Raman scattering
Special Collection:
Spectroscopy and Microscopy of Plasmonic Systems
Wenjing Xi
;
Wenjing Xi
Chemistry Department, University of Iowa
, Iowa City, Iowa 52242, USA
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Amanda J. Haes
Amanda J. Haes
a)
Chemistry Department, University of Iowa
, Iowa City, Iowa 52242, USA
a)Author to whom correspondence should be addressed: amanda-haes@uiowa.edu
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a)Author to whom correspondence should be addressed: amanda-haes@uiowa.edu
Note: This paper is part of the JCP Special Topic on Spectroscopy and Microscopy of Plasmonic Systems.
J. Chem. Phys. 153, 184707 (2020)
Article history
Received:
September 12 2020
Accepted:
October 25 2020
Citation
Wenjing Xi, Amanda J. Haes; Elucidation of pH impacts on monosubstituted benzene derivatives using normal Raman and surface-enhanced Raman scattering. J. Chem. Phys. 14 November 2020; 153 (18): 184707. https://doi.org/10.1063/5.0029445
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