Revealing the effects of molecular orientations on the azo-coupling reaction of nitro compounds driven by surface plasmonic resonances. Issue 38 (22nd September 2021)

• Record Type: Journal Article
• Authors: Shiu, Ying-Jen; Hayashi, Michitoshi; Lai, Ying-Huang; Jeng, U-Ser
• Is Part Of: Physical chemistry chemical physics. Volume 23:Issue 38(2021)
• Page Start: 21748
• Page End: 21756
• Publication Date: 2021-09-22
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp03041h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Simulated SERS from the preferred molecular orientations of 4NTP and the azo product 4NB15C–4NTP at the bridge site and in parallel with the facets of an adsorbed silver cluster. Abstract : A recent report on the azo coupling of 4-nitrobenzo-15-crown-ether (4NB15C) and 4-nitrothiophenol (4NTP) indicated that the reaction barrier could be reduced greatly with surface plasmonic effects on silver dendritic nanostructures in aqueous solution. Accordingly, an azo coupling reaction mechanism was proposed based on one or two SERS peaks. Toward a profound understanding of this azo coupling reaction mechanism, it is crucial to scrutinize the origin of the full SERS spectrum. Here, we construct a molecular model consisting of 4NTP and 4NB15C on an Ag7 cluster that simulates a silver dendritic nanostructure, and investigate the SERS spectra of the azo coupling of these two molecules. We propose five different adsorption sites and 13 different orientations of 4NTP on the Ag7 cluster and optimize the geometries of the five configurations. With each optimized configuration of 4NTP adsorbed on Ag7, we further consider the azo coupling product with a 4NB15C molecule and simulate the corresponding Raman spectra. Comparing the measured Raman spectra and model analysis, we conclude that the azo coupling reaction depends decisively on a parallel molecular orientation of the adsorbed 4NTP relative to the facets of Ag7, the orientation of which further directs the subsequent reaction for the product of 4NB15C–4NTP.