title: Reversible Isothermal Twist-Bend Nematic-Nematic Phase Transition Driven by the Photoisomerization of an Azobenzene-Based Nonsymmetric Liquid Crystal Dimer.
abstract: The liquid crystal nonsymmetric dimer, 1-(4-butoxyazobenzene-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl) hexane (CB6OABOBu), shows enantiotropic twist-bend nematic, NTB, and nematic, N, phases. The NTB phase has been confirmed using polarized light microscopy, freeze fracture transmission electron microscopy, and X-ray diffraction. The helicoidal pitch in the NTB phase is 18 nm. The NTB-N (TNTBN) and N-I (TNI) transition temperatures are reduced upon UV light irradiation, with the reduction in TNTBN being much larger than that in TNI. An isothermal, reversible NTB-N transition may be driven photochemically. These observations are attributed to a trans-cis photoisomerization of the azobenzene fragment on UV irradiation, with the cis isomers stabilizing the standard nematic phase and the trans isomers stabilizing the NTB phase. The dramatic changes in TNTBN provide evidence that the transition between the normal nematic and twist-bend nematic with spontaneous breaking of chiral symmetry is crucially dependent on the shape of molecular dimers, which changes greatly during the trans-cis isomerization.
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen , Meston Building, Old Aberdeen AB24 3UE, United Kingdom.|Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Paterson
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Jie
authors.initials: J
authors.lastname: Xiang
authors.affiliation: Department of Physics, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Gautam
authors.initials: G
authors.lastname: Singh
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen , Meston Building, Old Aberdeen AB24 3UE, United Kingdom.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Walker
authors.affiliation: Department of Physics, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Deña M
authors.initials: DM
authors.lastname: Agra-Kooijman
authors.affiliation: School of Engineering, University of Aberdeen, King's College , Aberdeen AB24 3UE, United Kingdom.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Martı́nez-Felipe
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Min
authors.initials: M
authors.lastname: Gao
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen , Meston Building, Old Aberdeen AB24 3UE, United Kingdom.
authors.forename: John M D
authors.initials: JM
authors.lastname: Storey
authors.affiliation: Department of Physics, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Satyendra
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University , Kent, Ohio 44242, United States.
authors.forename: Oleg D
authors.initials: OD
authors.lastname: Lavrentovich
authors.affiliation: Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen , Meston Building, Old Aberdeen AB24 3UE, United Kingdom.
authors.forename: Corrie T
authors.initials: CT
authors.lastname: Imrie