Our group has an ongoing collaboration with the Camden group at the University of Notre Dame for the development of highly robust ligands for surface enhanced Raman spectroscopy (SERS). SERS detection commonly relies on thiol and amine ligands, which are unfortunately susceptible to oxidative degradation, to bind to the metal surface. We are employing N-heterocyclic carbenes (NHCs, Figure 1) to form highly stable functionalized gold surfaces. Our group is responsible for the synthesis of the air stable precursors, known as NHC-CO2 adducts, which are sent to the Camden group to functionalize surfaces.
In addition, our group has synthesized a set of six deuterated isotopologues of both imidazolium and benzimidazolium NHC-CO2 adducts. Deuteration of the various aromatic and alkyl groups on the complexes, alongside theoretical calculations by the Jensen group at Pennsylvania State University, gave us insight to assigning key signals in the Raman spectra, assessing the binding of the NHC to the Au surface, as well as the positions of the N-substituents in relation to the surface (Figure 2). These studies represent the first examples of utilizing NHCs for SERS.
Currently we are pursuing new avenues for the synthesis of NHC functionalized gold surfaces. Alongside the Camden and Jensen groups, we have worked on synthesizing bis-NHC Au(I) complexes to achieve SERS-active NHC functionalized gold nanoparticles for applications in aqueous media. This approach has allowed for the synthesis of protic functionalized nanoparticles, which has not been easily achieved through traditional approaches. Our group is also focusing on synthesizing non-standard NHCs in attempts to further functionalize surfaces and to access the potentially greater stability of such NHC ligands on gold. 
Figure 1: Synthesis of functionalized Au surfaces
Figure 2: SERS spectra demonstrating key functional group signals (left) and dominating vibrational modes (right).
Notable Publications
N-Heterocyclic Carbenes as a Robust Platform for Surface-Enhanced Raman Spectroscopy, DeJesus, Joseph F.; Trujillo, Michael, J.; Camden, Jon P.; Jenkins, David M. J. Am. Chem. Soc. 2018, 140, 1247-1250.
Using SERS to Understand the Binding of N-Heterocyclic Carbenes to Gold Surfaces, Trujillo, Michael J.; Strausser, Shelby L.; Becca, Jeffrey C.; DeJesus,Joseph F.; Jensen, Lasse; Jenkins, David M.; Camden, Jon P. J. Phys. Chem. Lett. 2018, 9, 6779-6785.
A Benchtop Method for Appending Protic Functional Groups to N-Heterocyclic Carbene Protected Gold Nanoparticles, DeJesus, Joseph F.; Sherman, Lindy M.; Yohannan, Darius J.; Becca, Jeffrey C.; Strausser, Shelby L.; Karger, Leonhard F. P.; Jensen, Lasse; Jenkins, David M.; Camden, Jon P. Angew. Chem. Int. Ed. 2020, 59, 7585-7590.