Liquid crystalline amorphous blue phase and its large electrooptical Kerr effect Khoa V. Le, a Satoshi Aya, a Yuji Sasaki, b Hyunhee Choi, a Fumito Araoka, a Kenji Ema, b Jozef Mieczkowski, c Antal Jakli, d Ken Ishikawa a and Hideo Takezoe * a Received 19th November 2010, Accepted 7th January 2011 DOI: 10.1039/c0jm04009f An amorphous blue phase III with low and wide thermal range (20  C) including room temperature is induced by doping a bent-core nematic with a strong chiral material. We confirm that the elec- trooptical response is due to the Kerr effect, with the Kerr constant being up to two orders of magnitude larger than conventional Kerr materials such as nitrobenzene. Blue phases (BPs) are thermodynamically stable mesophases that appear between the isotropic (Iso) and the helical cholesteric (Ch) phases. Although they have no birefringence, they can show colorful selective reflection which is due to Bragg reflection of circularly polarized visible light. The molecules organize into double-twist cylinders and depending on how the cylinders assemble themselves in space, there can be 3 different types; BPI and BPII are characterized by the body-centered cubic and simple cubic structures, respectively, while BPIII is believed to be amorphous by most observations to date. 1 For many years, BPs used to be only of academic interest since their available temperature range was limited in one Kelvin or less. 2,3 Nevertheless, some efforts to expand it have been successfully made 4–7 and thereby BPs have drawn the attention of researchers again from the standpoint of practical applications. Recently Karatairi et al. doped some chiral liquid crystals (LCs) with surface-functionalized CdSe nanoparticles and succeeded in expanding the temperature range of BPIII over nearly 20 K, although the concentration of nanoparticles was still quite high. 8 On the other hand, Iwamochi et al. synthesized a T-shaped compound that exhibited BPIII with a temperature range of about 30 K including room temperature, but the switching in this system was considerably slow. 9 Meanwhile, recently we have also shown an amorphous BP over a wide temperature range by simply doping achiral bent-core (BC) nematics (Ns) (BCNs) with a few percentages of a certain chiral dopant. This effect is seemingly general for all bent-core molecules. 10 The low bend/splay elastic ratio of bent-core molecules 11 might account for the wide stability of the BP, as suggested by a theoretical study several years ago. 12 In addition, similar to T-shaped molecules, 6,9 only BPIII was stabilized in our study and such phenomenon was explained by the broad-temperature range smectic nano-clusters that inhibit the development of long-range order of the double twisted helical structures of BPI or BPII. 13–16 In this communication, we demonstrate a material with BPIII which covers room temperature and can be switched between dark and bright states with an electric field. For the first time, the electrooptical switching in BPIII is also confirmed to be due to the Kerr effect 17 with a large Kerr constant (up to two orders of magnitude larger than conventional Kerr mate- rials, such as nitrobenzene). This promises unprecedented optoelec- tronic and photonic applications making use of amorphous BP. We have studied a mixture made by doping a BCN LC with 3.9 wt% the same high twisting power chiral dopant BDH1281 (Merck Chemicals) used in ref. 5 and 10. Fig. 1a depicts the molecular structure of the host BCN (compound M12). The detailed synthetic scheme has been reported elsewhere. 18 M12 exhibits monotropic nematic (N) phase at 45  C upon cooling from the isotropic fluid as Fig. 1 (a) Molecular structure of compound M12 used in the experi- ments; (b) texture of the BPIII mixture (left) observed at 25  C under a polarizing optical microscope. This view is slightly brighter than in the air region. a Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8552, Japan. E-mail: takezoe.h.aa@m.titech.ac.jp b Department of Physics, Tokyo Institute of Technology, 2-12-1 O- okayama, Meguro-ku, Tokyo, 152-8551, Japan c Chemistry Department, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland d Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio, 44242, USA This journal is ª The Royal Society of Chemistry 2011 J. Mater. Chem., 2011, 21, 2855–2857 | 2855 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. Chem., 2011, 21, 2855 www.rsc.org/materials COMMUNICATION Downloaded by KENT STATE UNIVERSITY on 13 July 2012 Published on 27 January 2011 on http://pubs.rsc.org | doi:10.1039/C0JM04009F View Online / Journal Homepage / Table of Contents for this issue