Positional Isomerism-Mediated Copolymerization Realizing the Continuous Luminescence Color-Tuning of Liquid-Crystalline Polymers

Abstract

Liquid crystals with color-tunable light emission are important for a variety of applications; however, achieving multicolor light-emitting liquid crystals whose emission colors can be fine-tuned remains challenging because the limited derivatization of mesogenic fluorophores disfavors the diversity of the emission. Here, we present a positional isomerism-mediated copolymerization strategy to obtain liquid-crystalline polymers with continuous luminescence color-tuning ability. The introduced α–/β-cyanostilbene positional isomers possess very similar molecular structures, thus reducing the risk of assembly heterogeneity and facilitating the formation of a homogeneous and consistent liquid crystal mesophase. Meanwhile, a significant electronic effect was caused for fluorophores with positional isomerization, allowing the efficient tuning of emission colors via copolymerization. Especially with a gradual change in the composition of the copolymers, the emission color shift behaved in a continuous manner from blue to green. These cyanostilbene-based liquid-crystalline polymers also showed reversible photochromic fluorescence switching ability. This approach highlights the value of positional isomers to prepare color-tunable solid-state light-emitting materials, allowing control and fine-tuning of the emission property while maintaining the ordered assembly ability.