ABSTRACT
Invited for this month's cover picture is the groups of Professor Hirotsugu Kikuchi and Dr. Yasushi Okumura at the Institute for Materials Chemistry and Engineering at Kyushu University (Japan). External dynamic control of molecular self-organized superstructures with unique features has been researched, as these structures are applicable to chiral molecular devices. The cover picture shows photocontrol of selective reflection color that originated from the self-organized helical structure of chiral nematic liquid crystals (N*LCs) using closed-/open-type dopants. The drastic structure changes of the dopants by light stimuli enable reversible broad-spectrum control of selective reflections of N*LCs with opposite helical sign. Read the full text of the Full Paper at 10.1002/open.201700121.
ABSTRACT
We demonstrate reversible RGB-color photocontrol of a chiral nematic liquid crystal (N*LC) by using newly synthesized closed- and open-type chiral dopants. The photoswitching elements in the dopants are azobenzene units on axially chiral binaphthyl cores. Owing to cis-trans photoisomerization of the azobenzene units, both closed- and open-type compounds showed higher solubility, larger helical twisting power (HTP), and larger changes in HTP than conventional chiral dopants in host LCs. Thus, even at very low dopant concentrations, we successfully controlled the chirality of the induced helical structure of the N*LCs. Consequently, the N*LCs reflected right- and left-handed circularly polarized light (CPL) under a light stimulus. In the N*LCs with closed-type chiral dopants, the RGB-color reflection was reversibly controlled within several seconds. Interestingly, the open-type chiral dopant reversibly inverted CPL with opposite handedness in the near and short-wave IR regions. These novel materials are expected to realize new applications and perspectives in color information and similar technologies.
