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

Deliberately targeted emission wavelengths,
high quantum yields
(QYs), and high luminescence dissymmetry factors (glum) 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 glum values
of 0.5–1.0. The glum 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 glum. 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.