Phase and optical behaviours of chiral-azo liquid crystal polymethylsiloxanes with isosorbide units

ABSTRACT

In this study, we synthesised two series of cholesteric liquid crystal polymers CPQ and CPZ series. First, we prepared four different monomers ML₁ containing a cholesteryl group, ML₂ containing a cyano group, ML₃ containing a phenolic hydroxyl group and ML₄ containing isosorbide with azo groups. With the polymethylsiloxanes as the main chain, CPQ series were then synthesised by copolymerisation among the monomers ML₁, ML₂ and ML₃ and CPZ series were synthesised by esterification between the CPQ series and the monomer ML₄. ¹HNMR and FT-IR spectra confirmed the chemical structures of all the monomers and polymers. The mesomorphic behaviours and thermal properties were investigated by TGA, DSC, POM and XRD. Both the CPQ and CPZ series exhibited excellent thermal stability and reversible phase transitions, as well as interesting Grandjean textures under POM. CPZ series showed higher optical activity than CPQ series due to the introduction of the isosorbide group and the azo group, which could tune the pitch to make Bragg selective reflection appear more easily. UV–Vis spectra investigated the photoresponse behaviours of CPZ series thoroughly.

Graphical Abstract

KEYWORDS:

• Cholesteric liquid crystal polymers
• azo
• optical activity
• selective reflection
• photoresponse behaviours

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

1. Joint fund of National Natural Science Fund [U1708258]. 2. National Nature Science Foundation of China [31560268]. 3. Fundamental Research Funds for the Central Universities [N180705004].