Reversible Broad‐Spectrum Control of Selective Reflections of Chiral Nematic Phases by Closed‐/Open‐Type Axially Chiral Azo Dopants

• Published in: ChemistryOpen (Weinheim) Vol. 6; no. 6; pp. 710 - 720
• Main Authors: Nishikawa, Hiroya, Mochizuki, Daigou, Higuchi, Hiroki, Okumura, Yasushi, Kikuchi, Hirotsugu
• Format: Journal Article
• Language: English
• Published: Germany John Wiley & Sons, Inc 01.12.2017; John Wiley and Sons Inc
• Subjects: azo compounds; binaphthyl; Chirality; Color; Dopants; Handedness; isomerization; Liquid crystals; Nematic crystals; Polarized light; selective reflection; Twisting; binaphthyl; liquid crystals; chirality; isomerization; selective reflection; azo compounds
• ISSN: 2191-1363; 2191-1363
• DOI: 10.1002/open.201700121

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. High‐chirality photocontrol: The reversible broad‐spectrum control of selective reflections of opposite‐handed chiral nematics by using new chiral dopants is demonstrated. Quick reversible RGB color switching is achieved by using closed types, whereas open types provide broad reflection spectrum changes across the whole visible and NIR/SWIR ranges (see figure).