Effect of Functional Group Positional Isomerization on the Mesomorphic Properties and Thermal Stability of Biphenyl Ester Liquid Crystals

Abstract

AbstractIntermolecular interactions and molecular configurations are of great significance for the formation of liquid crystals. During this study, a series of isomer compounds with biphenyl esters as rigid cores were synthesized, and their mesomorphic properties and thermal stability were investigated. Based on the same rigid core, compounds heptyl 4′‐methoxy‐[1,1′‐biphenyl]‐4‐carboxylate (1OBE7), propyl 4′‐(pentyloxy)‐[1,1′‐biphenyl]‐4‐carboxylate (5OBE3), ethyl 4′‐(hexyloxy)‐[1,1′‐biphenyl]‐4‐carboxylate (6OBE2) and methyl 4′‐(heptyloxy)‐[1,1′‐biphenyl]‐4‐carboxylate (7OBE1) have no mesophase, while compounds hexyl 4′‐ethoxy‐[1,1′‐biphenyl]‐4‐carboxylate (2OBE6), pentyl 4′‐propoxy‐[1,1′‐biphenyl]‐4‐carboxylate (3OBE5) and butyl 4′‐butoxy‐[1,1′‐biphenyl]‐4‐carboxylate (4OBE4) have multiple smectic mesophases, whereas the production of the smectic mesophase is due to the microphase separation between aromatic cores and the alkyl chains. Compound 3OBE5 exhibiting good thermal stability (The value of T5% is 258.3 °C). In addition, with the right shift of the functional group position, compound 4OBE4 formed the widest smectic mesophase. The results show that the mesophase properties and thermal stability of liquid crystals are related to the position of the functional group.