Composition-dependent emission colors for biomass-based main-chain luminescent liquid crystalline copolyesters with excellent tensile properties†

Abstract

Liquid crystalline polymers with multicolor emission have attracted great attention in view of their great potential applications such as light-emitting diodes and information storage devices. However, luminescent liquid crystalline polymers (LLCPs) still have disadvantages involving single emission color, low solid-state emission efficiency, and poor mechanical properties. Herein, a series of main-chain LLCPs were obtained by the melt polycondensation of biobased dimethyl 2,2′-bifuran-5,5′-dicarboxylate (BFDCE), AIE-active α-cyanostilbene (Z-CS), and 1,6-hexanediol. Based on the Förster resonance energy transfer (FRET) effect between bifuran and Z-CS moieties, the emission colors of these LLCPs can be continuously tuned from blue to cyan, and then to green by changing the feed molar ratio of BFDCE and Z-CS, which can be applied in the visualization of latent fingerprints. Owing to the introduction of the rigid bifuran, the melt-pressed thin films from these main-chain LLCPs exhibit excellent tensile ductility (233%–332%), tensile strength (25.7–45.0 MPa), and medium Young's modulus (329–1028 MPa). Under 365 nm UV irradiation, the Z-CS chromophores in the main chain can undergo an irreversible [2 + 2] cyclization in the film state. Accordingly, the ‘QR code’ information and fluorescence pattern can be directly printed on the melt-pressed films instead of employing the common supporting substrates such as quartz and poly(ethylene terephthalate), paving a way for the development of anti-counterfeiting and information storage technologies.