Large-area preparation of rainbow cholesteric liquid crystal polymer network films using a photoisomerizable chiral dopant

Since the cholesteric liquid crystal polymer network (CLCN) films with a structural colour have been applied for decoration, those with colourful patterns become more attractive. They have been successfully prepared using photochromic cholesteric liquid crystals with the addition of photoisomerizable chiral dopants. Herein, two isosorbide derivatives with benzoate and cinnamate groups were synthesised using isomannide through chirality inversion and without using protecting groups. CLCN films were prepared using these two isomers as the chiral dopants. The structural colour of the films can be tuned by the photoisomerisation of the chiral dopants. Colourful patterns were also prepared using photomasks, which were suitably applied for decoration and anti-counterfeiting. Although the isomer with a higher melting point tended to induce the crystallisation of the CLC mixtures, the CLC mixtures prepared using the isomer with a lower melting point were stable at room temperature. Rainbow CLCN films were prepared using photomasks on a coating line.