CAREER: Stable Carbenes as Surface Anchoring Groups

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Professor Jeremiah A. Johnson at the Massachusetts Institute of Technology is supported by an award from the Macromolecular, Supramolecular and Nanochemistry Program to chemically modify the surfaces of several-nanometer-sized particles (nanoparticles) in order to make them more useful for different functions. A broad range of modern technologies, e.g., electronics, diagnostic systems, sensors, drug delivery agents, etc., rely on controlled, robust coating of the nanoparticle surface with layers of molecules that will react in particular ways with other molecules; this is called surface functionalization. It is quite surprising that chemical methods for surface functionalization are relatively few in number, involving only a handful of reactions for most applications, and each of these methods has limitations. As a result, new approaches to produce and use single layers of functional monolayers could drastically impact a wide range of technologies. The research in this project focuses on the development of particular carbene families (reactive carbon compounds) as a new way of making single-layer surface modifications of nanoparticles. This carbene chemistry offers a potentially ideal combination of strong surface bonding and synthetic versatility with the potential to be the ideal platform for different modern nanoparticle technologies. The research encompasses fundamental studies of NHC-layer formation, as well as applications of this technology to electronics and drug delivery. This CAREER proposal research is being integrated with an outreach program focused on the development of a Nanoscience Day and science fair at an elementary and high school. This proposal seeks to develop addressable N-heterocyclic carbenes (ANHCs) as versatile ligands for the fabrication of novel metal-organic interfaces. This goal is being pursued through three research thrusts: (1) a library of ANHCs with varied steric bulk and reactivity is being synthesized and studied in the context of film formation on various substrates; (2) the scope of surface-initiated polymerization from ANHC surfaces is being expanded to include a variety of semiconducting polymers and other polymeric nanostructures; (3) the electronic properties of bis-NHCs and metal-organic ANHC wires is being studied using the scanning tunneling microscopy break junction (STMBJ) technique. The synthetic diversity of the proposed ANHCs, the ability to form ANHC monolayers on a wide array of substrates and subsequently functionalize those monolayers, and the potential to form conductive ANHC-metal interfaces makes the proposed research a platform technology for a variety of surface modification applications. Furthermore, the results of this research are being integrated with a comprehensive education plan that includes course development within MIT and extramural graduate, undergraduate, high school, and elementary education.