The Organic and Macromolecular Chemistry Program in the Chemistry Division at the National Science Foundation supports Professor Nancy Goroff of SUNY Stony Brook who will seek effective routes from one-dimensional conjugated materials (e.g., polyynes) to graphitic nanostructures. The first experiments will center on the pseudo-1-dimensional polymer poly(diiododiacetylene), or PIDA. PIDA, recently prepared in the Goroff lab, is the first reported ordered polydiacetylene with only single-atom side groups. The simplicity of the PIDA structure allows the individual polymer strands to aggregate in much greater proximity than other well studied conjugated materials. The proposed research will include studies of PIDA co-crystals and aggregates, including conductivity, magnetoresistivity, optical absorptions and the chemistry that transforms PIDA into new materials. In addition, preliminary results suggest that aggregates of one-dimensional conjugated systems with limited side groups may be uniquely facile graphitization substrates. Professor Goroff will therefore examine aggregates of polyyne rods themselves, as sources of graphitic nano-wires. Polyynes containing 3-6 adjacent triple bonds and a diverse selection of side groups will be synthesized. The aggregation behavior of each of these polyynes will be examined, as well as their polymerization behavior. Methods will be sought for making well-defined ordered materials, with complete characterization of the products' structural, optical, electronic, and chemical properties.
Research by Professor Goroff offers new methods for preparing conjugated materials with unique structures. Because of their electronic and optical properties, these materials will have applications as semi-conductors and as non-linear optical absorbers. In addition to the direct impact of the research, the proposed work will offer other benefits. A major component of this proposal involves collaborative research. The proposed projects bring together scientists from many different fields, each with different expertise and research focus, increasing communication across disciplinary boundaries. The proposed research also offers significant educational benefits. The graduate students and undergraduates supported by this grant will gain experience in modern organic synthesis, computational modeling, spectroscopy, and polymer characterization methods. Professor Goroff also participates in outreach activities, including activities in the local elementary and junior high schools. For example, she recently created, with a colleague, a hands-on workshop on the Chemistry of Perfumes, which was held for three classes of 21 students each as part of a local elementary school Career Lab Day, and will be repeated in the coming years. In addition, she has developed a freshman seminar course for 20 students on the Chemistry of Cooking. These activities are designed to attract students to chemistry who might otherwise not consider chemistry as a career.
The goal of this project has been to prepare new carbon-rich and all-carbon materials, with molecular structures that are significantly different from materials that had been made before. The targets are organic (i.e., carbon-based) semi-conductors. Practical applications for these materials include organic light emitting diodes (OLEDs), thin-film solar cells, and large-area displays. Carbon-based semiconductors have benefits over inorganic materials because they are likely to be less dense, more processible, and made from renewable materials. However, there are many different hypothetical semi-conducting polymer structures, and only a relatively small number have been explored. This project aimed to prepare new polymers (molecules made from repeating molecular units, like beads on a string) with fundamentally different structures from what was already known, so that we can better understand the chemistry of carbon and to access materials that may be beneficial for electronic devices. This project has used the approach of preparing linear carbon chains called polyynes, and then examining them as precursors to more complex semi-conducting structures. Polyynes are rod-shaped molecules that have multiple carbon atoms connected together by alternating single and triple bonds. As part of the work of this proposal, we developed a new method for preparing polyynes which is more efficient, especially for chains of 8-12 carbon atoms (4-6 triple bonds), than previously existing methods. This work will help chemists who want to access such molecules for a variety of synthetic and materials chemistry projects. During this grant period, we also examined the chemistry of the polymer poly(diiododiacetylene), or PIDA, which was first synthesized under previous NSF funding. This polymer, made from the small molecule monomer diiodobutadiyne (C4I2), contains just carbon and iodine. During this grant period, we demonstrated that the iodine atoms of the polymer PIDA can be removed by a number of different mild methods, including heat, laser irradiation, and reaction with some small molecules. Removing the iodine atoms makes it possible to use PIDA as a precursor to all-carbon materials. We have shown that reaction with bases such as the solvent pyrrolidine removes some of the iodine from PIDA and makes a new material which has significantly increased conductivity compared to the starting polymer. Future studies will examine the applications of both PIDA and this new material for solar cells and other electronic devices. In addition, as part of this project, we developed synthetic routes to two new semi-conducting polymers, one starting from the monomer dibromobutadiyne (C4Br2) and one from the monomer diiodohexatriyne (C6I2). The synthetic approaches here depend on lining up the small molecules in a crystal, so that the desired polymerization is the only reaction that can take place. We mix the monomer in solution with another compound that helps it form crystals with the right geometry, and then evaporate off the solvent to grow the desired crystals. After polymerization, the second co-crystallizing compound can be rinsed away to leave just the polymer. The new carbon-bromine polymer (poly(dibromodiacetylene), or PBDA) is much more stable than PIDA, even though the monomer C4Br2 is much less stable than C4I2. In fact, the monomer explodes when left at room temperature, so the crystals are grown at -18 °C. The polymer, however, can withstand mild heat and exposure to bases. Future work will therefore examine the chemistry of PBDA and explore whether it can be used as a precursor to other polymers that cannot otherwise be made. In addition, the grant had broader impact by supporting seven graduate students and 3 undergraduates who received training in organic synthesis, computational modeling, and spectroscopic characterization of molecules and materials. The research was highly collaborative, involving researchers at Oak Ridge National Lab, Brookhaven National Lab, and in the Chemistry, Geosciences, and Materials Science departments at Stony Brook. Students therefore had opportunities to learn how to communicate with scientists of different backgrounds, and to work together in teams, an important skill for modern science research. Students also participated in classes from the Alan Alda Center for Communicating Science, at Stony Brook, where they improved their skills in communicating with non-technical audiences. The Principle Investigator for this grant serves on the Steering Committee of the Alda Center, and has participated in many different informal science education projects, often including graduate students in those efforts. Overall, the studies funded by this grant have given us access to new carbon-rich and all-carbon materials which are interesting for their fundamental properties, possible applications in organic electronics, and potential as precursors to other new materials. It also helped with training the next generation of scientists, giving them the technical skills and experience in collaboration and communication which will be critical for success in the future.
