Very High-Spin Polyradicals and Chiral Pi-Conjugated Systems

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

This research comprises two research projects directed at the design, synthesis and characterization of very high-spin polyradicals and chiral pi-conjugated systems The objectives of the first project, the characterization of high-spin polyradicals, are (1) to prepare organic polyradicals with the highest possible spin quantum numbers and minimum spin polydispersity, (2) to synthesis and study high-spin and/or switchable polyradicals with stability at ambient conditions. Modern synthetic methodologies will be employed to obtain the proposed polyradicals. For nanometer-sized molecules (polyradicals and its derivatives), molecular sizes and shapes will be determined by small angle neutron scattering, in conjunction with the Monte Carlo conformational searches. Magnetic properties will be characterized using SQUID magnetometry. For stable polyradicals, X-ray crystallography, ESR spectroscopy, and SQUID magnetometry will be the primary characterization techniques. The objectives of the second project, characterization of chiral pi-conjugated systems, are (1) to develop new approaches to optimize interactions between pi-conjugated systems in three-dimensions, using tetra-o-phenylenes and thiophene-based chiral carbon-sulfur mixed allotropes and (2) to develop asymmetric synthesis and/or optical resolutions for pi-conjugated helices (and double helices) and to characterize their redox states, including barriers for racemization. This project will rely on the development of new synthetic methods. The primary characterization for chiral molecules (their radical ions and polyions) in solution will be circular dichroism (CD); a CD spectropolarimeter will be setup with its sample compartment accessible from an inert atmosphere glovebox. The solid state characterization will include X-ray crystallography and electrical conductivity measurements. Graduate and postdoctoral students carrying out the experiments will be trained in the synthesis of molecules of mesoscopic dimensions, and the experimental and theoretical characterization of their electronic properties. With this award, the Organic and Macromolecular Chemistry Program support the educational and research activities of Dr. Andrzej Rajca of the Chemistry Department at the University of Nebraska. His work promises advances in the production and understanding of two kinds of materials: organic magnets and chiral conjugated oligomers. The research should be significant in a number of fields: chemical synthesis, the physics of magnetic materials, and the physics of conductors.