Cross-linkable cholesteric fluorescent liquid crystal polymers with reversible thermochromic and photoluminescent properties

In order to synthesise a fluorescent liquid crystal polymer (PL) with thermochromic effect at lower temperatures, allyl glycidyl ether (ME) was graft copolymerised with a fluorescent monomer (FM), a cholesteric monomer (M1), and a nematic monomer (M2) onto a polymethylhydrosiloxane (PMHS) backbone. This PL polymer was subsequently crosslinked with 4,4’-oxydianiline (MF), yielding a fluorescent liquid crystal elastomer (CPL) which exhibits a more ordered arrangement of the liquid-crystal molecules. The molecular structures and mesophase behaviours of the monomers and polymers were characterised by conventional methods, and all polymers were confirmed to meet the design requirements. The liquid-crystalline properties of the polymers before and after crosslinking were established as cholesteric phase by polarised optical microscopy (POM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), which also revealed excellent thermal stability, mesophase behaviour and thermal properties. Fluorescence spectroscopic analysis and imaging revealed that the polymer’s emission intensity is highly temperature-dependent. The cholesteric liquid crystal polymers exhibit different fluorescence intensities under UV irradiation at different temperatures, and the fluorescence is temperature-reversible. The two series polymer shows the expected dual effects of fluorescence and selective reflection at low temperatures, which have been fully verified experimentally.