Both increasing the Iso-to-Col transition and lowering the solidifying temperatures of a triazine-based dendrimer by introducing CN polar groups in the dendritic core

Abstract

Two new triazine-based dendrimers 1a and 1b, containing –NY(CH₂)₃NY– linkers between two G₃ dendrons (1a: Y = Bz, 1b: Y = 4-cyanoBz; Bz = benzyl), were successfully prepared in ∼32 and ∼34% yields, respectively. Compared with dendrimer 1c that contains –NH(CH₂)₃NH– linkers between two G₃ dendrons, dendrimer 1a exhibits a similar mesogenic range to 1c, but 1b possesses a broader mesophase-temperature range than 1c. Surprisingly, dendrimer 1b not only increases the isotropic-phase-to-columnar-mesophase (Iso-to-Col) transition temperature but also lowers the solidifying temperature on cooling. It is believed that the CN groups in the dendritic linker of 1b increase both the molecular interaction between dendrimers, leading to its increasing Iso-to-Col transition temperature, and dendritic distances within columns, leading to its decreasing solidifying temperature.