Synthesis and mesomorphic properties of bent liquid crystals containing triazole mesogenic unit with terminal flexible alkyl chain and laterally ethoxy substituted Schiff base

A new series of bent-shaped liquid crystals containing a triazole ring were synthesised and characterised at ambient and elevated temperatures. The triazole-cored and bent liquid crystals possess a flexible alkyl chain at one terminal, while the other side of the core is connected by a laterally ethoxy Schiff base consisting of a CN-biphenyl moiety. The evaluation on optical and thermal properties was carried out by polarising optical microscope and differential scanning microscope which revealed the length of the alkyl chain, -CnH2n + 1, that influenced the mesophase and the related clearing temperatures (T-c). Whilst the compounds with higher number of n possess lower T-c points, the presence of SmA phase seemed to be more favourable for the compounds in which the alkyl chain length was n >= 12. This observation can be associated with its bending angle and charge distributions along the two arms of which the interaction between the opposite counterparts of both arms in these bent-liquid crystals would promote the formation of SmA phase. The computational calculations based on density functional theory were performed to further support the transition from non-mesomorphic to SmA phases upon the increase in alkyl chain length (n), dipole moment and polarity which contribute to its stability.

Automated summary

A series of bent-shaped liquid crystals containing a triazole ring were synthesized and characterized. The study showed that the length of the alkyl chain influenced the mesophase and clearing temperatures, and the presence of SmA phase was more favorable for compounds with longer alkyl chains. Computational calculations further supported the transition to SmA phase with increasing alkyl chain length.