Nitrogen-Centered Radicals

以氮为中心的自由基

• 批准号: 1362454
• 负责人: Andrzej Rajca
• 金额: $ 46.33万
• 依托单位: University of Nebraska-Lincoln
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1362454&HistoricalAwards=false
• 关键词: Nitrogen; Centered; Radicals

In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professor Andrzej Rajca of the Department of Chemistry at the University of Nebraska-Lincoln will investigate structure and property relationships of organic molecules and macromolecules that are relevant to the development of novel magnetic and optical technology. The goal of this research is to synthesize and study high-spin nitrogen-centered radicals (aminyls) and chiral helical radical cations. The aminyls with strong through-bond ferromagnetic coupling and with persistence at room temperature are important to the development of lightweight, soft organic magnets. In addition, such organic radicals could benefit the development of metal-free paramagnetic contrast agents for magnetic resonance imaging (MRI), agents for paramagnetic relaxation enhancement nuclear magnetic resonance (NMR) spectroscopy, as well as materials for spintronics. The helical radical cations, which possess an unpaired electron confined to a helix, could facilitate the discovery of new organic magneto-optic materials and devices. This interdisciplinary research project involves multi-step organic synthesis, diverse physical characterization of organic molecules, and computations, and is therefore well suited to the education of scientists at all levels, with exceptional opportunities to gain a broad education as well as to develop a wide range of skills. This group is also well-positioned to provide the highest level of education and training for students underrepresented in science. The proposed aminyls are high-spin radicals based upon annelated pi-systems of nitrogen-centered radicals that are made persistent by steric shielding of radical centers and isotopic substitution to prevent decay of radicals. The proposed radicals will be prepared by modern organic synthetic methodologies and characterized by electron spin resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) magnetometry, as well as computations. Aminyl diradicals with very strong pairwise ferromagnetic coupling between electron spins and persistence at room temperature, with half-life that would permit isolation of the radicals, will be investigated and compared to analogous nitroxide diradicals, to provide an insight into the degree of spin delocalization in the pi-system. Aminyl triradical will be prepared and extended to the synthesis of aminyl polyradical polymers with very large magnetic moment. The proposed chiral helical radical cations are based on nitrogen-centered radical cations of helical pi-systems, which would be configurationally persistent at room temperature. Helical radical cations are intriguing molecules with a combination of chiral pi-systems and paramagnetism. Helical, ladder-type pi-systems of n ortho-annelated aromatic rings, such as [n]helicenes, are among molecules with the strongest chiral properties. Paramagnetism of radical cations within the three-dimensional helical pi-system would render unique properties, a combination of helicene chirality and delocalized electronic spin, for development of novel paramagnetic materials with inherently strong chiral properties. Radical cations of aza-thio-[7]helicene and conjoined [5]helicene will be prepared and studied by electrochemistry, UV-vis-NIR, circular dichroism (CD), EPR spectroscopies, as well as computations.

在本项目中，内布拉斯加大学林肯分校化学系的Andrzej Rajca教授将研究与新型磁性和光学技术开发相关的有机分子和高分子的结构和性质关系，该项目由化学系的化学结构，动力学机制B计划资助。 本研究的目的是合成和研究高自旋氮中心自由基（胺基）和手性螺旋自由基阳离子。 胺基化合物具有较强的穿键铁磁耦合和室温下的持久性，对开发轻质、柔软的有机磁体具有重要意义。 此外，这样的有机自由基可以有利于开发用于磁共振成像（MRI）的无金属顺磁造影剂、用于顺磁弛豫增强核磁共振（NMR）光谱的试剂以及用于自旋电子学的材料。 螺旋自由基阳离子具有一个限制在螺旋中的未成对电子，可以促进新的有机磁光材料和器件的发现。 这个跨学科的研究项目涉及多步有机合成，有机分子的各种物理特性和计算，因此非常适合各级科学家的教育，有特殊的机会获得广泛的教育以及发展广泛的技能。 该小组也有能力为科学领域代表性不足的学生提供最高水平的教育和培训。 所提出的胺基是基于氮中心自由基的稠合π系统的高自旋自由基，其通过自由基中心的空间屏蔽和同位素取代而持久化以防止自由基的衰变。 拟议的自由基将通过现代有机合成方法制备，并通过电子自旋共振（EPR）光谱，超导量子干涉仪（SQUID）磁力测量以及计算进行表征。 氨基双自由基与电子自旋和持久性之间的非常强的成对铁磁耦合，在室温下，与半衰期，将允许隔离的自由基，将被调查和比较类似的氮氧双自由基，提供一个洞察到的π-系统中的自旋离域的程度。 胺基三自由基的合成将被推广到具有超大磁矩的胺基聚合物的合成。 所提出的手性螺旋自由基阳离子是基于螺旋π系统的氮中心自由基阳离子，其在室温下将是构型持久的。 螺旋自由基阳离子是一类有趣的分子，具有顺磁性和手性π系统。 n个邻位稠合芳环的螺旋、梯形π-体系，例如[n]螺烯，是具有最强手性性质的分子之一。 三维螺旋π系统内自由基阳离子的顺磁性将呈现独特的性质，螺旋烯手性和离域电子自旋的组合，用于开发具有固有强手性性质的新型顺磁性材料。 制备了氮杂硫代[7]螺烯和联体[5]螺烯的自由基阳离子，并通过电化学、UV-vis-NIR、圆二色谱（CD）、EPR光谱以及计算对其进行了研究。

项目成果

Thermally and Magnetically Robust Triplet Ground State Diradical

• DOI: 10.1021/jacs.9b00558
• 发表时间: 2019-03-20
• 期刊: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
• 影响因子: 15
• 作者: Gallagher, Nolan;Zhang, Hui;Rajca, Andrzej
• 通讯作者: Rajca, Andrzej