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 nm2, corresponding 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 ∼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.