Research

We are interested in using the tools of organic synthesis, physical organic chemistry, and materials science to design, construct, and study relatively large (nanoscale) organic molecules with properties relevant to electronics, molecular recognition, and catalysis.

We are particularly interested in compounds that exhibit unusual conformational behavior, self-assembly into more-complex architectures, or functional electronic structures, and those that only exist away from equilibrium. Typically, the molecules we target are synthetically challenging, often because of the very structural features we hope to exploit. Consequently, much of our time is spent on synthetic chemistry. However, every compound we target is chosen for functional properties which we then characterize by various spectroscopies and other techniques. Further characterization of our materials is done in collaboration with other groups at Miami and elsewhere.

Although the methods we employ vary by project, all students in the group get extensive training in organic synthesis, including the execution of oxygen- and moisture-sensitive reactions; structure elucidation by spectroscopic techniques (e.g., NMR); and basic UV–vis and fluorescence spectroscopy. In addition, our group also studies chemical kinetics and makes use of polarized microscopy and differential scanning calorimetry (for liquid crystals); gel permeation chromatography; and computational chemistry.

ortho-Phenylenes

oP12_helix_p_bThe focus of this project is the development of ortho-phenylenes as a new and unusual class of conjugated oligomers. These compounds, just chains of aromatic rings connected through the ortho positions, represent a fundamental class of polyphenylenes but have received very little attention.

Our work on the ortho-phenylenes has principally focused on the folding behavior of short oligomers. We have been using a method based on the combination of NMR spectroscopy and DFT calculations. Recently, we have developed a model that semi-quantitatively explains the folding of ortho-phenylenes. On the basis of this model, we have shown that substituent effects on aromatic stacking interactions can be used to give o-phenylenes with essentially perfect folding (as judged by NMR spectroscopy).

More recently, we have begun taking advantage of the nice features of ortho-phenylenes to construct compounds of increased complexity with multiple folded subunits.

Dissipative covalent chemistry

One of the defining features of biological chemical systems is that they are typically not at equilibrium, dissipating energy to their environments. It is clear from nature’s example that these sorts of systems offer functions and complexity that cannot be achieved otherwise. The design of abiotic nonequilibrium chemical systems that follow this example is, however, in its infancy.

We are interested in identifying chemical fuels that can be used to “power” out-of-equilibrium covalent bond formation: that is, compounds that would behave by analogy with ATP in biochemistry. The formation of temporary bonds offers a simple framework to think about designing out-of-equilibrium assemblies and chemically fueled “molecular machines”. We are currently focusing on the use of carbodiimides (common reagents) to generate transient carboxylic acid anhydrides.

Board-shaped liquid crystals

We are working to develop new types of compounds with board-like shapes that exhibit new liquid crystal phases. We are specifically interested in compounds derived formally from the planarization of o-phenylenes. We recently demonstrated liquid crystallinity in our first series of compounds, alkoxy dibenzo[fg,op]naphthacenes. These materials exhibit phases similar to those of rod-like compounds (calamitics)—and not those of discotics—but with important differences we ascribe to their board-like aspect ratios.