N-Heterocyclic Carbene as Self-Assembled Monolayers on Gold and Carbon
N-Heterocyclic carbenes (NHCs) have been shown to be exceptional ligands for molecular coordination chemistry due to their ability to form strong carbon-metal bonds. Only recent, our group and others have demonstrated that the strong carbon-metal bonding properties of NHCs can be leveraged for materials chemistry. In 2014, Crudden and co-workers showed that self-assembled monolayers (SAMs) derived from NHCs on gold surfaces were significantly more stable than thiolate SAMs; which, for decades, have been considered the state-of-the-art in SAM chemistry. Since then, our group has continued to advance the field by incorporating unique functionalities to NHCs and new methods of SAM formation. In addition, stability of NHCs in different chemical and electrochemical conditions was critical to determine NHCs use in biological and industrial applications. In this thesis, I will present the use of electrochemical measurement of NHCs in phosphate buffer are discussed to confirm the prospective use of NHC-based SAMs in biological applications. The electrochemical stability of NHC-based SAMs at different levels of applied potential will also be presented. This study is crucial to employ NHC-based SAMs in electrochemical devices such as fuel cells, sensors, and catalysts. For both projects, 5-((6-ferrocenohexyl)oxy)-1,3-diisopropyl-1H-benzo[d]imidazole-3-ium bicarbonate (2-8•H2CO3) and 2-(6-(4-anthraquinyl)-1H-1,2,3-triazol-1-yl)hexyloxy)-1,3-diisopropyl-1H-benzo[d]imidazole-3-ium bicarbonate (8-4•H2CO3) were synthesized as a new NHC-based electrochemical tag molecules to compare with the known NHC 5-((12-(4-(ferrocenyl)-1H-1,2,3-triazol-1-yl)dodecyl)oxy)-1,3-diisopropyl-1H-benzo[d]imidazole-3-ium bicarbonate (1-20•H2CO3) which was previously used in the Crudden lab for electrochemical analysis. The capability of 3-6-ethyl-1,3-diisopropyl-1H-benzo[d]imidazole-5-carboxylate trifluorosulfonate (2-18•OTf) as a measles biosensor will be discussed. The mechanisms of SAM formation with NHCs will be discussed using free carbenes and their precursor bicarbonate and triflate salts. Finally, the first example of NHC depositions on Vulcan xc-72 carbon will be presented, and the effect of different oxidative treatments of carbon to facilitate NHC deposition will be discussed.