Surface-enhanced Raman spectroscopy (SERS) underpins a wide range of commercial and fundamental applications. SERS often relies on ligands, usually thiols, bound to a noble metal surface. The difficulty of straightforward thiol synthesis combined with their instability on surfaces highlights the need for alternative ligand design. We present the first example of SERS utilizing N-heterocyclic carbene ligands. A general three step synthesis is presented for functionalized NHC-CO adducts. These ligands are deposited on SERS-active gold film-over-nanosphere substrates (AuFONs) in solvent-free and base-free conditions, which prevents fouling. The resulting films are found to be robust and capable of postsynthetic modifications.

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.

The remarkable resilience of N-heterocyclic carbene (NHC) gold bonds has quickly made NHCs the ligand of choice when functionalizing gold surfaces.D espite rapid progress using deposition from free or CO 2 -protected NHCs, synthetic challenges hinder the functionalization of NHC surfaces with protic functional groups,s uch as alcohols and amines,p articularly on larger nanoparticles.H ere,w es ynthe-sizeN HC-functionalized gold surfaces from gold(I) NHC complexes and aqueous nanoparticles without the need for additional reagents,e nabling otherwise difficult functional groups to be appended to the carbene.T he resilience of the NHC À Au bond allows for multi-step post-synthetic modification. Beginning with the nitro-NHC,w ef orm an amine-NHC terminated surface,w hichf urther undergoes amide coupling with carboxylic acids.T he simplicity of this approach, its compatibility with aqueous nanoparticle solutions,a nd its ability to yield protic functionality,g reatly expands the potential of NHC-functionalized noble metal surfaces.

Three five-coordinate iron(IV) imide complexes have been synthesized and characterized.T hese novel structures have disparate spin states on the iron as afunction of the R-group attached to the imide,w ith alkylg roups leading to low-spin diamagnetic (S = 0) complexes and an aryl group leading to an intermediate-spin (S = 1) complex. The different spin states lead to significant differences in the bonding about the iron center as well as the spectroscopic properties of these complexes.M çssbauer spectroscopyc onfirmed that all three imide complexes are in the iron(IV) oxidation state.T he combination of diamagnetism and 15 Nlabeling allowed for the first 15 NN MR resonance recorded on an iron imide.M ultireference calculations corroborate the experimental structural findings and suggest how the bonding is distinctly different on the imide ligand between the two spin states.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

A new photoacid that reversibly changes from a weak to a strong acid under visible light was designed and synthesized. Irradiation generated a metastable state with high CH acidity due to high stability of a trifluoromethyl-phenyl-tricyano-furan (CF3 PhTCF) carbanion. This long-lived metastable state allows a large proton concentration to be reversibly produced with moderate light intensity. Reversible pH change of about one unit was demonstrated by using a 0.1 mM solution of the photoacid in 95 % ethanol. The quantum yield was calculated to be as high as 0.24. Kinetics of the reverse process can be fitted well to a second-order-rate equation with k=9.78×10(2)  M(-1)  s(-1) . Response to visible light, high quantum yield, good reversibility, large photoinduced proton concentration under moderate light intensity, and good compatibility with organic media make this photoacid a promising material for macroscopic control of proton-transfer processes in organic systems.