Adjacent functional group effects on the assembly of columnar liquid crystals

Carson O Zellman,Danielle Vu,Vance E Williams

doi:10.1139/cjc-2020-0060

Abstract

Although the impact of individual functional groups on the self-assembly of columnar liquid crystal phases has been widely studied, the effect of varying multiple substituents has received much less attention. Herein, we report a series of dibenzo[a,c]phenazines containing an alcohol or ether adjacent to an electron-withdrawing ester or acid. With one exception, these difunctional mesogens form columnar phases. The phase behavior appeared to be dominated by the electron-withdrawing substituent; transition temperatures were similar to derivatives with these groups in isolation. In most instances, the addition of an electron-donating group ortho to an ester or acid suppressed the melting temperature and elevated the clearing temperature, leading to broader liquid crystal thermal ranges. This effect was more pronounced for derivatives functionalized with longer chain hexyloxy groups. These results suggest a potential strategy for controlling the phase ranges of columnar liquid crystals and achieving room temperature mesophases.

Highlights

James Wuest has asserted that understanding molecular crystallization is one of the “great unmet challenges of contemporary science.”[1]
It is in this context that we have been examining the structure– property relations of columnar liquid crystals formed from discshaped molecules (“discotic mesogens”)
Functional groups that engage in specific interactions such as hydrogen bonding further alter the stability of the liquid crystal (LC) phase; the clearing point of the carboxylic acid D(CA,H) is 60 °C higher than that of the corresponding methyl ester D(MeE,H).[31]

Summary

Introduction

James Wuest has asserted that understanding molecular crystallization is one of the “great unmet challenges of contemporary science.”[1]. Before discussing the effects of adjacent functional groups, it is first worth examining the phase behaviour of the six derivatives, D(CA,H), D(MeE,H), D(HxE,H), D(H,OH), D(H,OMe), and D(H,OHx), that bear each of these functional groups in isolation.

Results

Conclusion