Wöhrle Tobias, Gündemir Rafet, Frey Wolfgang, Knecht Friederike, Köhn Andreas, Laschat Sabine
Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
Chemistry. 2017 Mar 23;23(17):4149-4159. doi: 10.1002/chem.201605648. Epub 2017 Feb 28.
A series of MIDA (N-methylimino diacetic acid) boronates carrying 4-alkoxy, 3,4-bisalkoxy, or 3,4,5-trisalkoxyphenyl substituents were synthesized and their mesomorphic properties characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques such as small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). Most derivatives were liquid crystalline. In the case of mono- and bisalkoxy-substituted derivatives, C chains already induced smectic A (SmA) mesophases despite the bulky MIDA head group. With increasing chain length, columnar hexagonal (Col ) phases replaced SmA phases in the disubstituted series. Quantum chemical calculations on a series of MIDA boronates show that the B-N bond is a dative bond with a positive charge on the boron atom and negative charges on the nitrogen and oxygen atoms. In addition, no π-interaction between the aryl moiety and B-N bond was found, thus the mesogenic unit is electronically decoupled from the MIDA head group. These theoretical findings were supported by IR and Raman spectra as well as by asingle crystal structure analysis of 4-ethoxyphenyl MIDA boronate. Calculations of the electrostatic potential of the MIDA boronate reveal a special polarity pattern that can support the formation of a two-dimensional network and is likely to explain the liquid crystalline self-assembly. The absence of any electronic cross-talk between the MIDA head group and B-aryl or B-alkyl substituents allows the efficient tailoring of the mesophase type through variation of the substituents.
合成了一系列带有4-烷氧基、3,4-双烷氧基或3,4,5-三烷氧基苯基取代基的MIDA（N-甲基亚氨基二乙酸）硼酸酯，并通过差示扫描量热法（DSC）、偏光显微镜（POM）以及小角和广角X射线散射（分别为SAXS和WAXS）等X射线衍射（XRD）技术对其介晶性质进行了表征。大多数衍生物具有液晶性。对于单烷氧基和双烷氧基取代的衍生物，尽管MIDA头部基团体积较大，但C链已诱导出近晶A（SmA）中间相。随着链长增加，在二取代系列中柱状六方（Col ）相取代了SmA相。对一系列MIDA硼酸酯进行的量子化学计算表明，B-N键是一种配位键，硼原子带正电荷，氮原子和氧原子带负电荷。此外，未发现芳基部分与B-N键之间存在π相互作用，因此介晶单元在电子上与MIDA头部基团解耦。这些理论发现得到了红外光谱和拉曼光谱以及4-乙氧基苯基MIDA硼酸酯单晶结构分析的支持。MIDA硼酸酯静电势的计算揭示了一种特殊的极性模式，该模式可以支持二维网络的形成，并可能解释液晶的自组装。MIDA头部基团与B-芳基或B-烷基取代基之间不存在任何电子串扰，这使得通过改变取代基能够有效地调整中间相类型。
