Study on Surface‐Enhanced Raman Scattering Spectra of Malachite Green on Silver Surface Based on Density Functional Theory

ABSTRACT Density functional theory (DFT) at the PBE0‐D 3 hybrid functional and 6‐311G + (d,p) basis set levels was employed to optimize the ground state of malachite green (MG). The optimized MG molecule has a nonplanar structure. The electrical properties and densities were calculated for MG by the natural population analysis (NPA) method at the same level. GaussView and Multiwfn software were used to draw a Fukui function electron density isosurface coloring map and an electrostatic potential coloring map of the MG molecular surface. We found that the region near the two N atoms in MG was most susceptible to an electrophilic reaction. Time‐dependent density functional theory (TD‐DFT) was used to calculate the electronic excitation data of MG and draw the UV–Vis spectrum of MG at the same level. By comparing the experimental UV–Vis spectrum with the calculated UV–Vis spectrum, it was found that the UV–Vis spectrum of MG has three peaks, of which the maximum peak is 616 nm (calculated as 586 nm). The structure of the MG‐Ag 4 complex was optimized by using DFT. The resonance surface‐enhanced Raman scattering (SERS) spectrum excited with 633‐nm laser light was calculated and compared with the experimental results, and there was a high similarity in the characteristic peak positions between them. Further analysis showed that MG combined with the silver plane by the adsorption orientation of one of the N,N‐dimethylaniline skeleton planes was almost perpendicular to the silver plane in SERS detection. One of the N atoms in N,N‐dimethylaniline is combined with Ag and then adsorbed onto the silver substrate to form a special surface‐bound compound.