Surface Modification of Au Nanoparticles with Heteroleptic Cu(I) Diimine Complexes

Gold colloidal nanoparticles (NPs) were functionalized in acetonitrile with a Cu(I) complex consisting of one 2,2'-bipyridine ligand possessing a lipoic acid moiety and one 2,9-dimesitylene-1,10-phenanthroline. UV electronic absorption, inductively coupled plasma-atomic emission spectroscopy, and scanning transmission electron microscopy with energy-dispersive X-ray analysis specifically targeting the Cu element were employed to confirm the grafting of the metallic complex on the Au NPs via Au-S bond formation and to probe its surface distribution and surface coverage. At the highest coverage achieved while retaining nanoparticle dispersibility, we estimate the molecular footprint of the complex at 0.71 nm(2), corresponding to similar to 7000 molecules over a 40 nm spherical particle. This is only four time less than what is reported for much smaller alkanethiols forming a compact self-assembled monolayer on similar gold nanoparticles. In the surface-enhanced Raman spectra (SERS), we underline a convenient marker band at similar to 1000 cm(-1); its frequency position is indicative of the complexation state of the surface-bound bipyridine molecules. From the analysis of the normal Raman spectra of the powders and the SERS data, the anchored tetrahedral complex is presumed to orient with the two polycyclic ligands predominantly normal to the surface and the most cumbersome substituted phenanthroline more peripherally placed.