Research in the Gilliard Laboratory is multidisciplinary and combines various aspects of organic, inorganic, main-group, and materials chemistry. We develop novel synthetic methods to access molecules that are important for solving problems related to the design of stimuli-responsive materials and fluorescent probes, the discovery of new main-group element chemical synthons, the activation of energy-relevant small-molecules such as carbon dioxide, and fundamental investigations into unusual polycyclic aromatic hydrocarbons. Our research is currently supported by research grants from the National Science Foundation (NSF), National Institutes of Health (NIH), Packard Foundation, Beckman Foundation, Research Corporation for Science Advancement, among others granting agencies.
Boron-Incorporated Organic Materials and Fluorescent Dyes
Boron-Incorporated Organic Materials and Fluorescent Dyes: We are interested in the design and synthesis of luminescent organic materials and stimuli-responsive or “smart” materials, a broad class of materials that respond to triggers such as mechanical force, light, or heat. These types of materials are important because they change their chemical and/or physical properties based on their environment, without the need for external additives. Thermochromic materials have a wide range of practical applications, particularly with regard to fabrics/coatings, devices, and industrial packaging, where the temperature of a substance needs to be tracked. For example, one can envision camouflage combat uniforms that adapt to different temperatures or terrains during war (e.g., desert vs. jungle), reducing the amount of equipment soldiers need to carry. We recently developed the first examples of thermoluminescent borafluorenium and borepinium ions, which are air-stable and selectively emit across the visible spectrum under temperature control. We expanded this cationic molecular approach to luminescent azabora-anthracenes and -tetracenes with high quantum efficiencies. Recently, we began building a program in the design and synthesis new types of far-red and near-infrared absorbing/emitting boracycles for biomedical applications in photothermal and photodynamic therapies.
Nanographenes and Graphene Nanoribbons
We recently began to focus on developing synthetic protocols for the design and synthesis of boron-doped nanographenes and graphene nanoribbons. Graphene is an allotrope of carbon consisting of a single sheet of atoms arranged in a hexagonal lattice nanostructure resembling that of a honeycomb. Graphene can become conductive when external voltage is applied (like in transistors) or light shines on them (like in photovoltaic cells). As such, it is a very useful material for potential use in solar cells, LED screens, and other applications that utilize the conversion of electricity into light and vice versa. In this project, smaller aromatic compounds containing the chemical element boron are synthesized and stitched together using Scholl reaction methodologies or other oxidative cyclodehydrogenation methods. We place a strong emphasis on the chemical and electrochemical characterization, photophysical measurements, and studies of the supramolecular assemblies of these unique materials.
Energy-Relevant Small Molecule Activation
Our laboratory is interested in the synthesis and reactivity of main-group element chemical synthons that react with small molecules [e.g., dihydrogen (H2), dinitrogen (N2), carbon dioxide (CO2), carbon monoxide (CO)]. We are also concerned with the mechanisms of how these small-molecules are released from main-group element molecules. We have a specific interest in the design of systems for CO2 sequestration, activation, and functionalization and collaborate with the MIT Climate and Sustainability Consortium (MCSC). In recent years, we have studied how pre-activated forms of CO2 undergo chemical and electrochemical redox chemistry, which resulted in the formation of CO and CO3– among other carbon-containing products. We have also designed borafluorene compounds which activate CO2 to form new heterocycles which serve as carbon monoxide releasing molecules (CORMs).
Boron-Doped Radicals/Anions and Borylenes
Polycyclic aromatic hydrocarbon (PAH) materials are well-known as molecular vehicles for energy conversion and storage (e.g., sensors, electronics, solar energy). Our group seeks to understand the impact main-group heteroatoms have on traditional organic PAH materials. Boron, possessing an empty pz orbital, facilitates facile electronic structure modulation, leading to properties that are vastly different from their all-carbon analogues. Redox-active radicals possess energetically accessible electrons and are key compounds in charge transport and storage (e.g., batteries). While neutral, boron-doped PAHs are common, reduced complexes are rare, and we recently isolated stable borafluorene/borepin radicals and anions. We are also investigating these reduced boron-centered molecules as chemical synthons for the activation of a range of small gas molecules. Recently, we have prepared carbene-boron-N2 compounds that release N2 to form reactive borylenes. These transient borylene molecules have diverse reactivity including serving as a means to arrive at new boron-incorporated heterocycles.
Bond Activation by Low-Coordinate Heavy Pnictogens
Bismuth is a component of several drugs, including the well-known Pepto Bismol. When bismuth is reduced to lower oxidation states or rendered cationic its complexes typically become more reactive, and thus suitable for bond activation chemistry. Recent studies have shown that in some cases antimony compounds can be less toxic than the comparable bismuth reagents. While the low-valent and cationic chemistry of lighter group 15 elements (e.g., phosphorus, non-metal) has thrived for decades, the analogous antimony and bismuth (metal, non-toxic) chemistry has proven to be extremely challenging. However, in the last few years, heavy group 15 element redox and Lewis acid-promoted chemistry has received increased attention. We recently synthesized stibaalkeene and bismaalkene cations with rare C=Sb/Bi multiple bonds. We have used these types of cationic antimony and bismuth compounds for energy-relevant transformations of small molecules, including C-H activation. In a recent study, we prepared distibene and dibismuthene dications that undergo novel cycloaddition chemistry with alkenes and alkynes.