Pyrrolopyrrole cyanine dye doping liquid crystals with thermal sensing and polarized near-infrared luminescent properties

Near-infrared (NIR) luminescent liquid crystals (LLCs) have garnered great academic interest because of their potential applications in liquid-crystal displays, thermal sensing, and smart devices. However, the development of NIR LLCs is currently limited by the scarcity of NIR dyes with adequate compatibility with liquid crystals and high luminous efficiency. Pyrrolopyrrole cyanine (PPCy) is a class of dye with good photostability and high fluorescence quantum yield in the NIR spectral region, but has not used for LLCs. In this study, we designed and synthesized two novel PPCy compounds with high solubility and luminous efficiency, namely PDPB and PDPBF, and prepared efficient and stable NIR LLCs by incorporating PDPBF into commercially available liquid crystals (8OCB and E7). The LC mixture PDPBF-8OCB shows both high quantum yield (QY) of 49.8 % and high dichroic ratio ( N ) of 4.11 by rubbing alignment in its nematic LC phase. This study presents a feasible method for obtaining stable NIR LLCs, addressing the challenges of efficiency, stability and compatibility of NIR LLCs. • Highly soluble and stable PDPB and PDPBF NIR dyes were synthesized. • PDPBF possessed an ordered columnar mesophase over a wide thermal range, including room temperature. • Quantum yield of the mixture of PDPBF and liquid crystals possessed unique temperature dependent characteristic. • PDPBF doped liquid crystals achieved the improvement of solid-state fluorescence quantum yield . • The mixture of PDPBF and liquid crystal exhibited linearly polarized fluorescence.