Surface-enhanced Raman scattering and quantum chemical studies of 2-trifluoroacetylpyrrole chemisorbed on colloidal silver and gold nanoparticles: A comparative study

Surface-enhanced Raman scattering (SERS) studies of 2-trifluoroacetylpyrrole (TFAP) molecule adsorbed on synthesized colloidal silver nanoparticles (SNPs) and gold nanopartides (GNPs) were reported and compared to the normal Raman spectra (nRs) of TFAP molecule in solid and liquid states. The experimental results were validated with the simulated nRs and SERS spectra of the molecule using density functional theory (DFT) calculations. The structures of the TFAP, TFAP-Ag-3 and TFAP-Au-4 molecular systems were optimized at different level of basis sets. HR-TEM analysis reveals that the colloidal SNPs and GNPs were monodispersed in spherical shape with average particle size were predicted as similar to 20 and similar to 25 nm, respectively. The observed red shift and decreased intensity behavior in the UV-visible spectral analysis confirm that the TFAP molecule chemisorbed on the colloidal SNPs and GNPs surface. Frontier molecular orbitals (FMOs) analysis points out the charge transfer from silver cluster to molecule and gold cluster to molecule in the TFAP-Ag-3 and TFAP-Au-4 molecular systems, respectively. The molecular electrostatic potential surface and Fukui functions analysis further validated the charge transfer interaction in the molecular systems. SERS spectral analysis confirms that the TFAP molecule was adsorbed on colloidal SNPs and GNPs surface with tilted orientation through the lone pair electrons on oxygen atom in the C=O group, pyrrole ring pi electrons and lone pair electrons on fluorine atom in the trifluoro group. Moreover, the calculated SERS enhancement factor values indicate that the title molecule chemisorbed on colloidal GNPs surface with higher affinity than that of colloidal SNPs surface. Hence, the present study paves the way for the designing of SERS active colloidal silver and gold substrates, which will be useful for the development of pyrrole related biosensors. (C) 2019 Elsevier B.V. All rights reserved.