A Discotic Mesogenic near-infrared absorbing dye and its application in photo-responsive liquid crystal elastomers

Abstract

Near-infrared (NIR) light-responsive liquid crystal elastomers (LCEs) doped with organic small-molecule photothermal agents have garnered scientific attention. However, the challenge remains in designing and synthesizing mesogenic photothermal dyes with absorption wavelengths greater than 800 nm. In this research, we design a novel discotic mesogenic NIR absorbing dye, namely the nickel bis(dithiolene) complex YHD868, and prepare NIR-responsive LCE/YHD868 composite films. The discotic mesogenic molecule YHD868 possesses a columnar hexagonal mesophase and exhibits intense NIR absorption at 868 nm, with a photothermal conversion efficiency of about 27 % and a molar extinction coefficient of approximately 30000 M−1·cm−1. Due to the strong NIR absorption of YHD868, combined with its excellent photothermal stability, the LCE/YHD868 composite films exhibit remarkable photoresponse and mechanical properties. Even at a low doping concentration of 0.2 wt%, the composite film can achieve a tensile strength of 9.8 MPa and an elongation at break of 165 %. Under 880 nm NIR irradiation (3.3 W·cm−2), the film can complete reversible photo-induced shrinking deformation in just 2 s, with a shrinkage ratio of about 64 %. This work offers a new approach for the development of photo-responsive smart soft materials.