三个新的基于氨基-s-三嗪的树突,1a,1b,1c,以72-81%的产率制备在树枝状骨架中含有芳基-CN部分(1a:R1=-N(n-C8H17)2,R2=n-OC8H17,1b:R1=R2=-N(n-C8H17)2,1c:R1=-N(n-C8H17)2,R2=-N(n-C4H9)2)。带有N(n-C8H17)2和n-OC8H17外围取代基的树枝1a,令人惊讶的是,在热过程中没有显示任何介晶相。然而,通过消除由烷氧基取代基产生的外围偶极,可以将非介晶1a转化为介晶1b或1c;仅包含相同N(n-C8H17)2外围基团的树突1b在加热时显示出〜25°C的介晶范围,在冷却时显示出〜108°C的介晶范围。相比之下,树突1c具有不同的N(n-CmH2m1)2(m=8对m=4)外围单元,具有与1b类似的堆叠,在热处理时表现出柱状相,但它的介晶范围(加热和冷却时的~9℃和~66℃,分别)比1b窄得多,归因于树枝外围部分1c的柔性较低的烷基链。在外围骨架中具有烷氧基取代基的Dendron1a,相应地产生额外的偶极子,因此,导致树枝状分子具有非介晶堆叠。没有分子间并排相互作用的外围偶极子,由于外围烷基链的振动,树突1b和1c在热处理时表现出柱状相。
Three new amino-s-triazine-based dendrons, 1a, 1b, and 1c, containing an aryl-CN moiety in the dendritic skeleton were prepared in 72-81% yields (1a: R1 = - N(n-C8H17)2, R2 = n-OC8H17, 1b: R1 = R2 = - N(n-C8H17)2, 1c: R1 = - N(n-C8H17)2, R2 = - N(n-C4H9)2). Dendrons 1a with N(n-C8H17)2 and n-OC8H17 peripheral substituents, surprisingly, did not show any mesogenic phase during the thermal process. However, non-mesogenic 1a can be converted to mesogenic 1b or 1c by eliminating the peripheral dipole arising from the alkoxy substituent;
dendron 1b only comprising the same N(n-C8H17)2 peripheral groups showed a ~25 °C mesogenic range on heating and ~108 °C mesogenic range on cooling. In contrast,
dendron 1c possessing different N(n-CmH2m+1)2 (m = 8 versus m = 4) peripheral units, having similar stacking as 1b, exhibited a columnar phase on thermal treatment, but its mesogenic range (~9 and ~66 °C on heating and cooling, respectively) was much narrower than that of 1b, attributed to 1c\'s less flexible alkyl chains in the peripheral part of
dendron.
Dendron 1a with the alkoxy substituent in the peripheral skeleton, creating additional dipole correspondingly, thus, leads to the dendritic molecules having a non-mesogenic stacking. Without the peripheral dipole for intermolecular side-by-side interaction, dendrons 1b and 1c exhibit a columnar phase on thermal treatment because of the vibration from the peripheral alkyl chain.