ORGANIC CHEMISTRY: CARBON-RICH MOLECULES AND MATERIALS
Research in the Goroff group focuses on the synthesis and properties of unnatural organic compounds and materials, especially highly conjugated carbon-rich structures. Conjugated organic molecules and polymers have attracted increasing attention from material scientists as semiconducting materials. Ideally, organic semiconductors will be lighter in weight, more easily modifiable, and less expensive than their inorganic counterparts. These properties make conjugated organics attractive, for example, as components in large-area displays, light-emitting diodes, chemical sensors, and even high-tech pigments. Demand has never been higher for new cost-effective conjugated molecules with desirable electronic and optical properties.

Work in the Goroff group focuses on finding new conjugated molecules with unusual electronic and optical properties.  Our research involves organic synthesis and standard characterization techniques; in some cases, we also use computer modeling or low-temperature spectroscopy. Collaborations with other groups allow us to study our compounds with state-of-the-art physical and analytical techniques. 

Halocarbon Chemistry for New Materials
One focus of our research is the chemistry of conjugated halocarbons, including iodoalkynes and halogenated cumulenes.  We have prepared compounds 1-6, most of which were previously unknown.  The simplicity of these molecules conceals their interesting chemistry.

Compounds 1-3 contain strongly Lewis-acidic iodine atoms.  We can use these acidic sites to guide self-assembly of macromolecular systems.  Some avenues we are pursuing include polymerizing diiodopolyynes to form novel conjugated polymers, using compounds like 1-3 as rods to create “molecular squares” and other two and three-dimensional supramolecular assemblies, and adsorbing iodoalkynes onto graphite or metal surfaces to form monolayers which can then undergo polymerization.

We have also developed methods for preparing tetrahalobutatrienes 4-6 by halogenation of appropriate diynes.  We are now exploring these perhalo compounds as synthetic precursors to larger cumulenic pi systems via Suzuki and Sonagashira couplings.  In addition, we are examining ways to extend our halogenation methodology to make other dihalocumulenes, which we can use as solution-phase precursors to polydiacetylenes.

Figure 1.  Halocarbon compounds 1-6 have all been prepared and studied in the Goroff lab.

Conjugated Molecular Belts
The other major project in the Goroff lab centers on preparing tube-shaped cylindrically conjugated molecules, using cyclodextrins as the scaffolding for construction. These compounds (e.g., Figure 2) represent a previously unreachable class of organic materials for electronics applications.

Figure 2.  A conjugated aromatic belt.

Similar to fullerenes and carbon nanotubes, these “buckybelts” will have a p system formed from adjacent benzene rings linked together into a cylinder.  However, unlike fullerenes or nanotubes, the belts will have open edges that can be functionalized to alter the structures' physical, electronic, and chemical properties.  In addition, the edges will allow for reversible binding of cations or small molecules inside the cylindrical cavity.  This binding, which is impossible under ambient conditions for closed-cage fullerenes, make the belts potential components for nanoscale switches.

This project takes advantage of the well-developed and relatively inexpensive chemistry of cyclodextrins, cyclic oligomers of glucose.  Using a cyclodextrin as scaffolding, we will align several aromatic groups, as shown in Figure 3, and couple them to form the desired molecular belts.  This template-directed approach will provide the conjugated belts in a small number of steps.  In addition, the overall route is quite flexible:  we can modify the cyclodextrin scaffold, the aromatic groups, or the tethers that connect the two, allowing us to make different members of this class of compounds and to optimize the overall synthetic route.

Figure 3.  Building a conjugated belt on a cyclodextrin scaffold.