Theoretical SERS study of the strength and suitability of Cu12 nanostar for SERS: Complete theoretical studies, coinage metal SM12 comparisons, benzothiazole (BTH) adsorbent

Abstract

Theoretical calculations were used to optimize molecular structures which help determine binding energies, and elucidate electronic properties of unsubstituted benzothiazole (BTH) adsorption on metal star models, SM12 (M = Ag/Au/Cu). BTH tends to connect via its donor nitrogen and sulfur heteroatoms as well as the pi-conjugated carbon atoms; adsorption is onto the bare metal atoms of the nanostar, a single 12-membered ring, involving increasingly stable adsorption energies of-3.25/-5.71/-17.57 kcal mol-1 for BTH-Ag12/Au12/Cu12 complexes as one ascends the Group 11 triad. From the electrophilicity values, it is clear that the outermost electrons of the system will be able to travel (injected) from the chemically adsorbed BTH unit into the adsorbent SM12 within the structure of the complex. The values for changes in enthalpy and entropy for all complexes studied herein show that the motion of the atoms is constrained due to the presence of the BTH; the adsorption of BTH onto the investigated SM12 adsorbents is spontaneous. The increase of dipole moments for the complexes in aqueous media support potential for molecular recognition; drug delivery-oriented applications of the complexes are predicted to undergo dissolution in polar media such as water, offering the possibility for drug molecule recognition applications. Raman inactive modes of BTH become active within the BTH-metal complexes and experience enhancement in intensity. Adsorption behavior and thermodynamics parameters also indicate that the Cu12 cluster has the strongest interaction with maximum adsorption energy of-17.6 kcal mol-1. Density of states spectral analysis supports the charge transfer, adsorption behavior, and other thermodynamic parameters. In conclusion, density functional theory (DFT) has helped to determine electronic characteristics of SM12 clusters which have been demonstrated to be highly sensitive to the presence of BTH; these findings can allow for the molecular pairs to be used in (bio) sensor devices and to potentially trace the drug in the human body via spectrophotometry.