Very High-Spin Polyradicals and Chiral Pi-Conjugated Systems

本研究包括两个研究项目，针对高自旋多自由基和手性共轭体系的设计、合成和表征。第一个项目，高自旋多自由基的表征，目标是：(1)制备具有最高可能自旋量子数和最小自旋多分散性的有机多自由基，(2)合成和研究具有环境条件稳定性的高自旋和/或可切换多自由基。将采用现代合成方法来获得所提出的多自由基。对于纳米大小的分子（多自由基及其衍生物），分子的大小和形状将由小角度中子散射确定，并结合蒙特卡罗构象搜索。磁性能将使用SQUID磁强计进行表征。对于稳定的多自由基，x射线晶体学、ESR光谱和SQUID磁强计将是主要的表征技术。第二个项目，手性pi共轭体系的表征，目标是：(1)开发新的方法来优化pi共轭体系之间的三维相互作用，使用四邻苯和噻吩基手性碳-硫混合同素异形体；(2)开发pi共轭螺旋（和双螺旋）的不对称合成和/或光学分辨率，并表征它们的氧化还原态，包括外消旋化障碍。这个项目将依赖于新的合成方法的发展。溶液中手性分子（其自由基离子和多离子）的主要表征是圆二色性（CD）；将安装一台CD分光偏振仪，其样品室可从惰性气氛手套箱中进入。固态表征将包括x射线晶体学和电导率测量。进行实验的研究生和博士后将接受介观尺度分子的合成以及其电子性质的实验和理论表征的训练。通过这个奖项，有机和大分子化学项目支持了内布拉斯加州大学化学系的Andrzej Rajca博士的教育和研究活动。他的工作有望在两种材料的生产和理解方面取得进展：有机磁铁和手性共轭低聚物。这项研究在化学合成、磁性材料物理学和导体物理学等许多领域都具有重要意义。

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.