Remote-Controllable Molecular Knob in the Mesomorphic Helical Superstructures

• Published in: Advanced functional materials Vol. 26; no. 24; pp. 4242 - 4251
• Main Authors: Kim, Dae-Yoon, Lee, Sang-A, Park, Minwook, Choi, Yu-Jin, Yoon, Won-Jin, Kim, Jin Soo, Yu, Yeon-Tae, Jeong, Kwang-Un
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 27.06.2016
• Subjects: Doping; Helical; helical superstructure; Knobs; layer structure; light-responsive; liquid crystal; Liquid crystals; Molecular structure; Nematic; self-assembly; Superstructures; Tuning
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201505342

A programed light‐responsive chiral liquid crystal (LC) containing four photochromic azobenzene moieties covalently connected to a central bicyclic chiral core (abbreviated as AZ4ICD) is newly designed, precisely synthesized, and efficiently applied as a remote‐controllable molecular knob for the optically tunable thin film. First of all, phase evolutions and ordered structures of AZ4ICD are systematically investigated by a combination of thermal, microscopic, scattering, and simulation techniques. Wide‐angle X‐ray diffractions of oriented AZ4ICD samples indicate that the AZ4ICD molecule itself basically forms layer structures: one is a low‐ordered chiral smectic A LC phase (SmA*) with 5.61 nm layer periodicity at high temperatures, and two highly ordered smectic crystal (SmCr1 and SmCr2) phases are subsequently formed at lower temperatures with the anticlinically tilted molecular packing structures. The helical superstructures of chiral nematic LC phase (N*) can be spontaneously constructed by doping AZ4ICD chiral agents into the achiral nematic molecules. Due to the bent conformational geometry of AZ4ICD, the thermal window of blue LC phase (BP) is expanded by stabilizing the double twisted cylindrical building blocks. Remote‐controllable phase transformations in the mesomorphic helical superstructures are demonstrated by tuning the wavelength of light. By taking intramolecular conformations and intermolecular interactions into account, a photochromic chiral liquid crystal is synthesized that functions as a remote‐controllable molecular knob for tuning the mesomorphic helical superstructures.