Synthesis of poly(6-azulenylethynyl)benzene derivatives as a multielectron redox system with liquid crystalline behavior
Synthesis of poly(6-azulenylethynyl)benzene derivatives as a multielectron redox system with liquid crystalline behavior
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DOI：
10.1021/ja0209262
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发表时间：
2003-02-12
影响因子：
15
通讯作者：
Imafuku, K
中科院分区：
文献类型：
--
作者：
Ito, S;Inabe, H;Imafuku, K
在Sonogashira-Hagihara条件下，通过钯催化卤代芳烃与取代6-乙炔基偶氮唑烯和/或取代6-溴代芳烃的简单一锅反应，合成了一系列在1，3-位取代6-己氧基羰基的聚(6-氮烯乙炔)苯，即六，1，2，5-四-，1，3，5-三和1，4-双(6-氮丙基)苯衍生物。用循环伏安法(CV)研究了这些新型聚(6-偶氮乙炔)苯衍生物的氧化还原行为，揭示了其可能的多电子氧化还原性质。化合物4b在循环伏安曲线上呈现一步两电子还原波，表明在电化学还原条件下形成了由两个6-偶氮烯乙炔基团稳定的双阴离子。苯环上1，2，4，5四个6-偶氮乙炔取代基由于形成了稳定的闭壳双阴离子结构而提高了电子接受性能，而3在较负的还原电位下被还原。与化合物2的多步氧化还原行为不同，化合物1在-1.28V的循环伏安下被一步还原。化合物1的柱状中间相(Col(Ho)和Col(Ro))的温度范围很宽，从77.3℃到270℃左右的分解温度。化合物2、3和4b表现为柱状介晶(Col(Ro))，其中2为晶型，3为异常的三重熔融行为，4b为双重熔融行为和柱状介晶(Col(Ho))。因此，所研究的体系体现了具有液晶性质的多电子氧化还原行为的新原理。
A series of poly(6-azulenylethynyl)benzenes substituted with n-hexyloxycarbonyl chains at 1,3-positions in azulene rings, i.e., hexakis-, 1,2,4,5-tetrakis-, 1,3,5-tris-, and 1,4-bis(6-azulenylethynyl)benzene derivatives 1, 2, 3, and 4b, have been prepared by a simple one-pot reaction involving repeated Pd-catalyzed alkynylation of halogenated arenes with substituted 6-ethynylazulene and/or ethynylated arenes with substituted 6-bromoazulene under Sonogashira-Hagihara conditions. The redox behavior of these novel poly(6-azulenylethynyl)benzene derivatives was examined by cyclic voltammetry (CV), which revealed the presumed multielectron redox properties. Compound 4b exhibited a one-step, two-electron reduction wave upon CV, which revealed the formation of the dianion stabilized by two 6-azulenylethynyl substituents under electrochemical reduction conditions. Four 6-azulenylethynyl substituents on a benzene ring in a 1,2,4,5 relationship increased the electron-accepting properties because of the formation of a stabilized closed-shell dianionic structure, whereas 3 was reduced at more negative reduction potentials. In contrast to the multistep redox behavior of 2, compound 1 was reduced in one step at -1.28 V upon CV. Compound 1 showed a wide temperature range of columnar mesophases (Col(ho) and Col(ro)) from 77.3 degreesC to the decomposition temperature at ca. 270 degreesC. Compounds 2, 3, and 4b exhibited columnar mesomorphism (Col(ro)) with crystalline polymorphs for 2, unusual triple-melting behavior for 3, and both double-melting behavior and columnar mesomorphism (Col(ho)) for 4b. Therefore, the investigated systems exemplify a new principle for multielectron redox behavior with liquid crystalline properties.