Thermally Invertible Full-Color Circularly Polarized Luminescence with High Dissymmetry Factors and High Quantum Yields in Fluorene Derivatives with Induced Chirality Generated in Chiral Liquid Crystals
Keita Horie, Yuki Fujita, Kosuke Kaneko, Tomonori Hanasaki, Kazuo Akagi
Abstract
Deliberately targeted emission wavelengths, high quantum yields (QYs), and high luminescence dissymmetry factors ( g lum ) are essential for chiral materials exhibiting circularly polarized luminescence (CPL). The addition of achiral luminophores to chiral nematic liquid crystals (N*-LCs) is a promising way to generate CPLs. We aimed to generate red–green–blue (RGB)- and white-colored CPLs by adding each of three types of fluorene-based luminescent molecules and their mixtures to N*-LCs. Herein, achiral fluorene-based derivatives with RGB emission colors were synthesized and added to N*-LCs containing alkylcyanobiphenyl- and alkylcyanoterphenyl-based N-LCs and an axially chiral binaphthyl dopant. A mixture of the RGB fluorene derivatives was subsequently prepared at an optimum mixing ratio and added to the N*-LCs. The fluorene-based derivatives dissolved in the N*-LCs exhibited induced CPLs of RGB and white colors with QY values of 60–90% and g lum values of 0.5–1.0. The g lum value of 1.0 is the highest among white CPLs reported thus far, and there are no examples that simultaneously exhibit both high QY and high g lum . Furthermore, a mixture of the RGB fluorene derivatives was added to a temperature-responsive N*-LC containing a thermally invertible chiral compound, resulting in reversible thermal inversion of white CPL.