Photo-responsive near-infrared circularly polarized luminescent liquid crystal copolymers†

Near-infrared circularly polarized luminescent (NIR-CPL) materials hold great promise for applications in biomedical diagnostics and treatments, optical displays, and information storage. However, the range of reported intrinsic NIR-CPL polymers is still limited. Moreover, integrating stimulus responsiveness into these materials to develop stimulus-responsive intrinsic NIR-CPL polymers remains a significant challenge. This paper presents a new approach to prepare photo-responsive intrinsic NIR-CPL polymers by incorporating photo-responsive near-infrared luminescent groups into chiral liquid crystals. We copolymerize chiral cholesterol monomer M6Chol with the spiropyrane photo-responsive near-infrared luminescent monomer MSP, forming copolymers poly(M6Chol(x)-co-MSP(y)). Research reveals that by changing the composition, the aggregation structure and photo-physical properties of copolymers can be modulated. As the content of PMSP component increases, poly(M6Chol(x)-co-MSP(y)) gradually transforms into a twist grain boundary smectic-A phase, and then further transitions into an amorphous polymer. Meanwhile, the luminescence asymmetry factors (g_lum) first increases and then decreases, accompanied by a continuous redshift of the emission wavelength to 710 nm, exhibiting efficient NIR-CPL. Interestingly, the CPL properties of the copolymers can be effectively tuned via light exposure. For poly(M6Chol(0.95)-co-MSP(0.05)), after exposure to 365 nm light, the g_lum value increases from 2.0 × 10⁻² to 3.0 × 10⁻². Moreover, this photo-responsive behavior also demonstrates excellent reversibility and fatigue resistance.