Raman, Infrared, and Surface-Enhanced Raman Spectroscopy in Combination with ab Initio and Density Functional Theory Calculations on 10-Isopropyl-10<i>H</i>-phenothiazine-5-oxide

Abstract

Raman, infrared, and surface-enhanced Raman spectroscopies were applied to the vibrational characterization of the most stable conformer of the 10-isopropyl-10H-phenothiazine-5-oxide derivative. To find the optimized structure and the computed vibrational wavenumbers of the title compound, ab initio calculations at the Hartree−Fock level of theory and density functional theory calculations at the BPW91 and B3LYP levels of theory were performed. The comparison of the surface-enhanced Raman (SER) spectra, obtained only on activated silver colloids, with the corresponding Raman spectra reveals small shifts (Δν ≤ 5 cm-1) and proves the partial chemisorption of the molecules on the silver surface via the lone pair electrons of the oxygen atom; the electromagnetic mechanism is the main mechanism of the enhancement. Variations of the SER spectra with the change of pH were attributed to the orientational changes of the adsorbed molecules with respect to the silver surface.