Langmuir, Vol.35, No.43, 14031-14041, 2019
Highly Miscible Hybrid Liquid-Crystal Systems Containing Fluorescent Excited-State Intramolecular Proton Transfer Molecules
Doping of luminescent molecules in a nematic liquid-crystal (LC) host is a convenient approach to develop light-emitting LC diSplays that would be a promising alternative to conventional LC displays. The requirements for the luminescent guest molecules include high miscibility in the host LC, high-order parameters in the host LC media to show anisotropic luminescence, lack of self-absorption, transparency in the visible region, and a large photo-luminescence quantum yield independent of its concentration. To address these issues, here, we newly synthesize a highly miscible and fluorescent excited-state intramolecular proton transfer molecule, C-4-CF C-HBT, based on 2-(2-hydroxyphenyl)benzothiazole (HBT). This compound is highly miscible in a conventional room-temperature nematic LC 4-pentyl-4'-cyano biphenyl (5CB) up to 14 wt % (similar to 12 mol %) and exhibits a large photoluminescence quantum yield of Phi(FL) = 0.32 in the 5CB host, both of which were achieved by the introduction of an alkynyl group into the HBT core. C-4-CC HBT possesses a high-order parameter of S = 0.46 in 5CB, and the C-4-C C-HBT/5CB mixtures show anisotropic fluorescence whose intensity is controlled by the applied electric field. A patterned image is demonstrated, which is not visible under an ambient environment but is readable upon UV illumination, relying on the orientational differences of ordered C-4-C C-HBT molecules.