Surface‐enhanced Raman scattering properties of Lewis acid–base complexes ofp‐hydroxybenzoic andp‐mercaptobenzoic acids with CO₂in the presence of silver

Abstract

Effects of local environment on the sensitivity of surface‐enhanced Raman scattering have been recently considered as an important issue in experiments involving charge‐transfer mechanism between the adsorbed molecules and the metal surface. To theoretically investigate this issue, we consider the complexation of p‐hydroxybenzoic acid (PHBA) and p‐mercaptobenzoic acid (PMBA) with carbon dioxide (CO2), and in contact with silver (Ag), by means of ab initio calculations. Within the Møller–Plesset perturbation theory, it is demonstrated that the carboxylic group of PHBA or PMBA can act as an electron‐donating site, binding the electron‐deficient carbon atom of CO2, via a Lewis acid–base (LA–LB) interaction. Changes in the vibrational spectra of these molecules are carefully determined and attributed to both LA–LB complexation with CO2 and interaction with Ag. Calculated Raman scattering shifts for the complexes also indicate that the chemical nature of the substituent group at para position of the aromatic ring can dramatically alter the signal of typical shifts expected for LA–LB complexes, as well as affect surface‐enhanced Raman scattering intensities. The LA–LB complexation is also reinforced by the ultraviolet–visible absorption spectra for the complexes, calculated within time‐dependent density functional theory and combined with the polarizable continuum model, employed to simulate the local environment dielectric constant. It is demonstrated that the lowest singlet π–π* excitation of both LA–LB complexes, PHBA and PMBA weakly bound to CO2, is significantly red shifted, which gives evidence for such a complexation. Copyright © 2016 John Wiley & Sons, Ltd.

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“…Filho, Cunha, and Rivelino studied the SERS properties of the Lewis acid‐base (LA‐LB) complexes of p‐hydroxybenzoic and p‐mercaptobenzoic acids with CO 2 in the presence of silver. Their work demonstrated that the lowest singlet π‐π* excitation of both LA‐LB complexes is significantly red‐shifted, which gives evidence for such a complexation with CO 2 . Kitahama et al described the analysis of blinking from multicolored SERS‐active Ag colloidal nanoaggregates with poly‐L‐lysine by means of a truncated power law.…”