In a project entitled "Metal-Catalyzed Diradical Reactivity: From Fundamental Thermal- and Photo-Chemistry to Novel Nanomaterials," the Chemical Catalysis (CAT) program supports Professor Jeffrey M. Zaleski at Indiana University to probe the geometric and electronic factors that control metal-catalyzed and photochemical diradical generation by the Bergman cyclization. Three primary structure types are investigated: 1) combined sigma/pi complexes where activation is geometrically controlled through the sigma bonds and electronically via the pi-system. Structures in this theme examination of catalytic Bergman vs. Myers-Saito cyclization pathways that are important to radical-mediated chemical transformations; 2) construction of large chromophoric assemblies that use thermal and photochemical Bergman cyclizations to fuse ring systems catalytically to form optically responsive molecules; and 3) incorporation of these reactive ligand sets into large nanoassemblies that can be activated to form all carbon frameworks by template vaporization. These three architectural classes carry both a fundamental research question to be addressed as well as a potential broader impact from the final architectures and reactions. Thermal reaction pathways are evaluated using standard synthetic methodology such as NMR, crystallography, and spectroscopic characterization of reaction intermediates. Optical properties of chromophoric products are examined using nanosecond and ultrafast lifetime and transient absorption methods, while characterization of nanoarchitectures is conducted mainly using electron microscopy.
This research impacts chemical catalysis methodology for constructing new molecules using metal/radical mediated reactions, which is a fundamental need in the chemical community. The chromophore assembly component of the work builds new constructs that can be used as chemical sensors, or for light harvesting in solar energy conversion. The nanomaterial aspect of the project generates reactions on nanoscale surfaces to create new, higher-order assemblies that have potential applications in molecular electronics and ultralight pure carbon electronic arrays. From an educational perspective, the research helps to train students in a combined fundamental science/application approach to chemistry that spans synthesis and high-tech measurements. Students at all levels from undergraduate to postdoctoral, including those from underrepresented minorities programs at IU, benefit from exposure to a range of research challenges and diversities of solution. Some of the work is outreached to local schools to entice young minds to pursue degrees in science.
