5,5′-Bis-(alkylpyridinyl)-2,2′-bithiophenes: synthesis, liquid crystalline behaviour and charge transport
作者:Yulia A. Getmanenko、Shin-Woong Kang、Naresh Shakya、Chandra Pokhrel、Scott D. Bunge、Satyendra Kumar、Brett D. Ellman、Robert J. Twieg
DOI:10.1039/c3tc31522c
日期:——
Liquid crystalline materials with 5,5â²-bis-(alkylpyridinyl)-2,2â²-bithiophene structures with different positions of the nitrogen atoms in the aromatic core were synthesized, characterized by differential scanning calorimetry, polarized optical microscopy and, in some cases, by synchrotron X-ray diffraction analysis and single crystal X-ray analysis. The molecular planarity and liquid crystalline (LC) behaviour of these materials are strongly influenced by the location of the nitrogens in the aromatic core, and LC behaviour is more complex than the mesomorphic behaviour of the known structurally related 5,5â²-bis-(alkylphenyl)-2,2â²-bithiophene LCs. Single crystal X-ray structural analysis of 5,5â²-bis-(5-alkylpyridin-2-yl)-2,2â²-bithiophenes 2 reveals that the aromatic core is nearly planar with s-cis conformation of the thiophene and pyridine rings and s-trans conformation of the thiophene rings of the central 2,2â²-bithiophene unit. The length of the alkyl chains has a pronounced effect on the molecular planarity and the packing motifs. A preliminary study of the charge-transporting properties of 5,5â²-bis-(5-alkylpyridin-2-yl)-2,2â²-bithiophenes 2d and 2e with n-nonyl and n-decyl alkyl chains, respectively, by the time-of-flight technique shows that the hole mobility is temperature independent, electric field dependent and with a magnitude of â¼1.5 Ã 10â4 cm2 Vâ1 sâ1 in the unidentified S2/Cr2 phase.
具有不同氮原子位置的芳香核结构的5,5'-双-(烷基吡啶基)-2,2'-联噻吩液晶材料被合成,并通过差示扫描量热法、偏光显微镜进行表征,在某些情况下还通过同步X射线衍射分析和单晶X射线分析进行表征。这些材料的分子平面性和液晶行为受芳香核中氮原子的位置影响较大,且其液晶行为比已知的结构相关的5,5'-双-(烷基苯基)-2,2'-联噻吩液晶的介晶行为更加复杂。对5,5'-双-(5-烷基吡啶-2-基)-2,2'-联噻吩2的单晶X射线结构分析揭示了其芳香核几乎呈平面结构,且噻吩和吡啶环为s-顺式构型,中心2,2'-联噻吩单元的噻吩环为s-反式构型。烷基链的长度对分子平面性和堆叠模式有显著影响。通过飞行时间技术对5,5'-双-(5-烷基吡啶-2-基)-2,2'-联噻吩2d和2e的电荷传输性质的初步研究表明,其空穴迁移率与温度无关,受电场影响,在未确定的S2/Cr2相中约为1.5×10-4 cm2 V-1 s-1。