Probing the adsorption and orientation of 2,3-dichloro-5,8-dimethoxy-1,4-naphthoquinone on gold nano-rods: A SERS and XPS study

2, 3-Dichloro-5,8-dimethoxy-1,4-naphthoquinone (DDNQ) is a synthetic naphthaquinone which has shown reduced chemotoxicity and enhanced chemotherapeutic activity in in vitro studies. The ability of DDNQ to serve as a chemical dopant of graphene resulting improved performance of graphene by tuning its band gap is also being explored. In this report surface enhanced Raman scattering (SERS) spectroscopy was utilized to probe the adsorption/orientation of DDNQ on gold nano-rods. Interpretation of the SERS data required a complete assignment of the vibrational modes of DDNQ and this was performed with DFT calculations using BP86/6-31G (d, p), B3LYP/6-31G (d) basis sets, and potential energy distribution (PED) calculations. Surface selection rules and relative band enhancement factors were utilized to propose an orientation and mode of interaction for DDNQ adsorbed on Au nanosurfaces. XPS data supported the conclusions obtained from the SERS data.