Broadening the temperature range of blue phases using $azo$ compounds of various molecular geometries assembled from modular "LEGO" molecular units

TL;DR

This study demonstrates that the temperature range of blue phases in liquid crystals can be significantly broadened by using specially designed azo compounds with varied molecular geometries and photo-isomerization properties.

Contribution

It introduces a modular molecular design approach to control blue phase temperature stability through azo compound engineering and UV-induced isomerization effects.

Findings

Azo compounds with different geometries effectively broadened BP temperature range.

Cis-isomers have a stronger impact on BP stability than trans-isomers.

Molecular engineering combined with photo-isomerization allows precise control of blue phase temperatures.

Abstract

The temperature range of the blue phases (BPs) formed in highly chiral mixtures based on cholesteryl oleyl carbonate (COC) and the nematic liquid crystal E7 was studied in the presence of various chemical structures. The $azo$ compounds used were of both chiral and achiral nature, and their molecular geometry was modified by substitution of modular "LEGO" molecular units of varying alkyl chain lengths and types of bridging groups, which could substantially affect the mesomorphic properties of the matrix mixture. It was shown that in many cases these dopants effectively broadened the BP temperature range. This effect depends on both the variation in the molecular geometry of the $azo$ compounds and the increase in the $cis$-isomer concentration under UV irradiation. The presence of the $cis$-isomers formed have a stronger impact on broadening the BP temperature range than the initial $trans$-isomers. These results demonstrate that the temperature range of BPs can be precisely controlled via a combination of molecular engineering and $trans$-$cis$ photo-isomerization.