Using SERS To Understand the Binding of N-Heterocyclic Carbenes to Gold Surfaces

Abstract

Surface functionalization is an essential component of most applications of noble-metal surfaces. Thiols and amines are traditionally employed to attach molecules to noble-metal surfaces, but they have limitations. A growing body of research, however, suggests that N-heterocyclic carbenes (NHCs) can be readily employed for surface functionalization with superior chemical stability compared with thiols. We demonstrate the power of surface-enhanced Raman scattering combined with theory to present a comprehensive picture of NHC binding to gold surfaces. In particular, we synthesize a library of NHC isotopologues and use surface-enhanced Raman scattering to record the vibrational spectra of these NHCs while bound to gold surfaces. Our experimental data are compared with first-principles theory, yielding numerous new insights into the binding of NHCs to gold surfaces. In addition to these insights, we expect our approach to be a general method for probing the local surface properties of NHC-functionalized surfaces for their expanding use in sensing applications.

A Benchtop Method for Appending Protic Functional Groups to N‐Heterocyclic Carbene Protected Gold Nanoparticles

“…The NHC binding to the AuNP was confirmed using SERS (Figure ), XPS (Figure S51), and TGA (Figure S55) and the particle morphology was measured with TEM. The resulting SERS spectra are consistent with those obtained from NHC surfaces created using the NHC–CO 2 adduct method (Figure S36) . Peaks at 1296 cm −1 and 1403 cm −1 correspond to the isopropyl and aryl stretching frequencies .…”

“…We previously employed CO 2 ‐protected NHCs to make SERS‐active NHC‐functionalized gold film‐over‐nanospheres (AuFONs); however, this method of deposition is not effective for nanoparticles, except with very small atomic gold clusters . The AuFONs NHCs were deposited on gold surfaces by heating the solid NHC–CO 2 compound in vacuum; therefore, this method cannot be transferred to an aqueous environment for Au nanoparticles . Instead, we hypothesized that gold(I) complexes might transfer the NHC to the gold surface (Figure ).…”

“…Peaks at 1296 cm −1 and 1403 cm −1 correspond to the isopropyl and aryl stretching frequencies . These SERS peaks are red‐shifted approximately 20 cm −1 relative to the Raman spectra, indicating binding to the gold surface . Several variations of our procedure all yielded 1‐AuNP : water/dichloromethane (Method 1); water/acetonitrile (Method 2); using the mono‐NHC ligated gold(I) complex 2‐Cl with biphasic water/dichloromethane (Method 3).…”

A Semi‐quantitative method for the detection of fentanyl using surface‐enhanced Raman scattering (SERS) with a handheld Raman instrument

“…This monolayer is critical in SERS detection—EM enhancement decays exponentially from the surface, so any fentanyl additional to this monolayer (i.e., fentanyl in subsequent layers) will have a significantly lower contribution to the observed signal, and a non‐linear relationship would be expected (Table 2). Further enhancement occurs via interaction of the junctions (or “hotspots”) between aggregated nanoparticles, hence the need to add an aggregating solution prior to measurement [34–38]. Another factor may be that nanoparticles display different sorption kinetics in diluted samples compared to more concentrated ones, resulting in more rapid molecule desorption/exchange from the nanoparticles [36,39], which may explain the variation observed with higher concentrations.…”

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…Moreover, a spectroscopic investigation of the spatial orientation and coordination mode of NHC moieties on different metallic surfaces will provide useful insights to modulate the reactivity of the organic/inorganic interface towards CO 2 RR. [458][459][460][461][462]…”