Converting Non-Mesogenic to Mesogenic Stacking of Amino--Triazine-Based Dendrons with -CN Phenyl Unit by Eliminating Peripheral Dipole

Three new amino--triazine-based dendrons, , , and , containing an aryl-CN moiety in the dendritic skeleton were prepared in 72-81% yields (: R = - N(-CH), R = -OCH, : R = R = - N(-CH), : R = - N(-CH), R = - N(-CH)). Dendrons with N(-CH) and -OCH peripheral substituents, surprisingly, did not show any mesogenic phase during the thermal process. However, non-mesogenic can be converted to mesogenic or by eliminating the peripheral dipole arising from the alkoxy substituent; dendron only comprising the same N(-CH) peripheral groups showed a ~25 °C mesogenic range on heating and ~108 °C mesogenic range on cooling. In contrast, dendron possessing different N(-CH) (m = 8 versus m = 4) peripheral units, having similar stacking as , 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 attributed to 's less flexible alkyl chains in the peripheral part of dendron. Dendron 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 and exhibit a columnar phase on thermal treatment because of the vibration from the peripheral alkyl chain.