Probing a Local Viscosity Change at the Nematic-Isotropic Liquid Crystal Phase Transition by a Ratiometric Flapping Fluorophore


Local viscosity change in the thermal phase transition of a nematic liquid crystal, 5CB, has been analyzed by doping fluorescent viscosity probes, flapping fluorophores (FLAP) as well as a molecular rotor BODIPY-C12. As a result, only flapping anthraceneimide has successfully monitored a small viscosity change (corresponding to a few cP (centipoise) change in shear viscosity around 25 cP) in the nematic-to-isotropic phase transition by ratiometric spectroscopy. In addition, analysis of fluorescence anisotropy indicates that the emissive species (planarized flapping anthraceneimides) are aligned parallel to the director of 5CB in the nematic phase.