Stimuli-Responsive Boron Cation-Doped Materials

We are interested in the design and synthesis of 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 ions, which are air-stable and selectively emit across the visible spectrum under temperature control.

Redox-Active Boron-Doped Heterocycles

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 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 (e.g., CO2, CO, and H2). In addition to our work with single-site boron compounds, we are currently investigating the optical and electronic properties of PAHs with extended conjugated networks, including nanographenes and linear acenes (e.g., bora-tetracenes and -pentacenes).

Alkaline Earth Metal Redox Chemistry

The chemistry that governs the development of new catalysts, molecules, and materials often involve redox reactions where a metal center undergoes a change in oxidation state. While this redox behavior is well-established for transition metals [e.g., Pd(0)/Pd(II)], it is difficult to elicit from main-group elements due to differences in the frontier molecular orbitals of their complexes. As alkaline earth metals are some of the most abundant and cost-effective elements in the toolbox of synthetic chemists, there is a renewed interest in understanding the reactivity of Lewis acidic and low-oxidation state molecules which feature group 2 metals in an unusual coordination environment. Recent studies by our lab have shown that alkaline earth complexes possess redox- and coordination-state flexibility to a degree that was not previously apparent. In this research area we have explored the synthesis and reactivity of beryllium and magnesium compounds that are important for the use of these elements in new redox processes for bond activation.

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. While the low-valent and cationic chemistry of lighter group 15 elements (e.g., phosphorus, non-metal) has thrived for decades, the analogous bismuth (metal, non-toxic) chemistry has proven to be extremely challenging. However, in the last few years, bismuth redox and Lewis acid-promoted chemistry has received increased attention. We synthesized the first carbene-bismuthinidene, isolated bismuth-phosphaketenes, and prepared bismaalkene cations with rare C=Bi multiple bonds. We are now engaged in the synthesis of new types of bismuth and antimony compounds for energy-relevant transformations of small molecules, including C-H activation.