Configuration effects of H-bonded sites and rigid core lengths on h-bonded banana-shaped liquid crystalline supramolecules consisting of symmetric trimers and asymmetric heterodimers.
Configuration effects of H-bonded sites and rigid core lengths on h-bonded banana-shaped liquid crystalline supramolecules consisting of symmetric trimers and asymmetric heterodimers.
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DOI：
10.1021/jp907360c
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发表时间：
2009-10
期刊：
影响因子：
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通讯作者：
Ling-yung Wang;I. Chiang;Po-Jen Yang;Wan-Sheung Li;I. Chao;Hong‐Cheu Lin
中科院分区：
文献类型：
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作者：
Ling-yung Wang;I. Chiang;Po-Jen Yang;Wan-Sheung Li;I. Chao;Hong‐Cheu Lin
通过选择合适的质子给体(H给体)和受体(H受体)的摩尔比，合成了一系列新型香蕉形氢键对称三聚体(含两个氢键)和不对称杂二聚体(含一个氢键)。计算和理论分析了氢键连接位置和芳环数目(刚性核中4~8个芳环)和链长(柔性部分分别为n、m=12或16)对弯核超分子介晶性和开关行为的影响。除了具有较长刚性核或较短柔性链的具有矩形柱状(Col(R)或B1)相的超分子结构外，大多数超分子不对称二聚体都存在SMC(A)P(A)相，并通过外加电场转变为SMC(S)P(F)相。除了核心中心外，具有氢键中心的C相以近晶C相为主。有趣的是，在氢键中心附近的氢键非对称二聚体中观察到了SMA和向列相，这从理论上证明了在最低能量的氢键构象中，由于不利于弯曲角度(小于110度的下限)，极性近晶C相是不利的。与完全共价键合的类似物相比，具有极性近晶C相的氢键不对称二聚体具有较低的转变温度和阈值电压。在分子模拟理论计算的基础上，证明了不对称杂二聚体的极性近晶C相极性开关行为的存在与其具有较高的偶极矩和合适的弯曲角的构型有关。此外，超分子对称三聚体缺乏极性开关行为，表现出规则的SMC相，具有较弱的电稳定性，这与它们的偶极矩较小的构型有关，并得到了理论计算的证实。
Several series of novel banana-shaped H-bonded symmetric trimers (with two H-bonds) and asymmetric heterodimers (with one H-bond) were self-assembled by appropriate molar ratios of proton donors (H-donors) and acceptors (H-acceptors). The influences of H-bonded linking positions and aromatic ring numbers (4-8 aromatic rings in the rigid cores) as well as the chain lengths (n, m = 12 or 16, respectively, in the flexible parts) on the mesomorphism and the switching behavior of the bent-core supramolecules were evaluated and theoretically analyzed. Except for the supramolecular structures with longer rigid cores or shorter flexible chains possessing the rectangular columnar (Col(r) or B1) phase, the SmC(A)P(A) phase was revealed in most supramolecular asymmetric heterodimers and switched to the SmC(S)P(F) phase by applying electric fields. The polar smectic C phase was dominated for those with H-bonded sites apart from the core center. Interestingly, the SmA and nematic phases were observed in H-bonded asymmetric dimers with H-bonded sites close to the core center, which theoretically proved that the polar smectic C phase was disfavored due to an unfavorable bend angle (smaller than the lower limit of 110 degrees ) in the lowest-energy H-bonded conformer. Compared with the fully covalently bonded analogue, lower transition temperatures and lower threshold voltages were developed in the H-bonded asymmetric dimers with the polar smectic C phase. On the basis of the theoretical calculations of molecular modeling, the existence of polar switching behavior in the polar smectic C phase of asymmetric heterodimers was proven to be associated with their configurations with higher dipole moments and suitable bend angles. Furthermore, the lack of polar switching behavior in supramolecular symmetric trimers, which exhibited the regular SmC phase with weak electrical stabilities, was related to their configurations with smaller dipole moments and confirmed by theoretical calculations.