Highly Fluorescent Bipyrrole‐Based Tetra‐BF<sub>2</sub> Flag‐Hinge Chromophores: Achieving Multicolor and Circularly Polarized Luminescence
Luxia Cui, Hyuga Shinjo, Takafumi Ichiki, Koichi Deyama, Takunori Harada, Kohei Ishibashi, Takumi Ehara, Kiyoshi Miyata, Ken Onda, Yoshio Hisaeda, Toshikazu Ono
Abstract
Abstract This study reports the facile syntheses of tetra‐boron difluoride (tetra‐BF 2 ) complexes, flag‐hinge‐like molecules that exhibit intense green‐to‐orange luminescence in solution and yellow‐to‐red emission in the solid states. Single‐crystal structure analysis and density functional theory calculations suggested a bent structure of this series of compounds. The complexes also exhibited excellent optical properties, with quantum yields reaching 100 % and a large Stokes shift. These properties were attributed to the altered bending angle of the molecule in the S 1 excited state. As the rotational motion was suppressed around the 2,2′‐bipyrrole axis, atropisomers with axial chirality were formed, which are optically resolvable into ( R ) and ( S )‐enantiomers through a chiral column. The atropisomers thus function as circularly polarized luminescent (CPL) materials, in which the color (green, green‐yellow, and yellow) can be varied by controlling the aggregation state. This rational design of multi‐BF 2 complexes can potentially realize novel photofunctional materials.