以喹啉为耦合单元双自由基体系的理论研究

Theory study on biradical systems with quinoline as coupling unit

设计用4种自由基自旋中心连接在耦合单元喹啉的不同位置上的双自由基体系,用AM1-CI方法计算的结果表明:双自由基连接的位置不同对体系耦合作用的影响符合双自由基之间磁性耦合的拓扑规则,即共轭体系中,两个自由基之间以偶数个C(或N)原子耦合,体系具有低自旋基态,表现反铁磁耦合;两个自由基之间以奇数个C(或N)原子耦合,体系具有高自旋基态,表现铁磁耦合.当双自由基连接在喹啉的相邻奇数个C或N原子位置时,体系具有高自旋基态,表现铁磁耦合.

Spin coupling rules of ground state of quinoline as coupling unit and four radicals as spin centers have been studied by AM1-CI methods. It is proved that there are topological rules in magnetic coupling between radicals of conjugated systems：In conjugated system, the effective exchange integrals of radical sites through the even number of carbons with π-electron network are negative in sign,i, e. , all the molecules corresponded to antiferromagnetic coupling and possessed low-spin ground states, while those through odd carbon atoms are positive in sign, i. e. ,all the molecules corresponded to ferromagnetic coupling and possessed high-spin ground states. When two radicals are linked to the even number of carbons or nitrogens site of the quinoline, all the molecules corresponded to ferromagnetic coupling and possessed high-spin ground states.