1225283-67-9Relevant academic research and scientific papers
The design of smectic liquid crystals with an axially chiral biphenyl core: In search of a proper ferroelectric liquid crystal phase
Ahmed, Ziauddin,Müller, Carsten,Holzwarth, Marcel,Haege, Christian,Giesselmann, Frank,Lemieux, Robert P.
, p. 1562 - 1566 (2018)
We report the results of a study in which we introduce a tricarbosilane end-group in a mesogenic scaffold derived from an axially chiral biphenyl with a large transverse dipole moment. This structural modification is intended to promote the formation of a chiral smectic C (SmC?) phase, with the aim of discovering a mesogen with a virtual transition temperature to a proper ferroelectric phase (To) that approaches the crystal-SmC? melting point. We show herein that the combination of a 4-pentylbicyclo[2.2.2]octane-1-carboxylate chain and a tricarbosilane-terminated 4-alkoxybenzoate chain gives a mesogen (R,S)-WL43 forming an enantiotropic orthogonal smectic A (SmA) phase and a higher order tilted smectic phase. Substitution of the 4-pentylbicyclo[2.2.2]octane-1-carboxylate group with a trans-4-pentylcyclohexane-1-carboxylate group gives a mesogen (R,S)-WL45 forming monotropic SmA and SmC phases. The SmC? phase formed by the enantiomerically pure (R)-WL45 exhibits Goldstone-mode switching characteristic of a surface-stabilized FLC, but its spontaneous polarization PS is too low to be measured by conventional methods.
Polar Order and Symmetry Breaking at the Boundary between Bent-Core and Rodlike Molecular Forms: When 4-Cyanoresorcinol Meets the Carbosilane End Group
Westphal, Eduard,Gallardo, Hugo,Caramori, Giovanni Finoto,Sebastián, Nerea,Tamba, Maria-Gabriela,Eremin, Alexey,Kawauchi, Susumu,Prehm, Marko,Tschierske, Carsten
, p. 8181 - 8197 (2016/06/14)
Two isomeric achiral bent-core liquid crystals involving a 4-cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid-crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result. For the compound with larger dipole moment (CN1) segregation of the carbosilane units is suppressed, and this compound forms paraelectric SmA and SmC phases; polar order is only achieved after transition to a new LC phase, namely, the ferroelectric leaning phase (SmCLsPS) with the unique feature that tilt direction and polar direction coincide. The isomeric compound CN2 with a smaller dipole moment forms separate layers of the carbosilane groups and shows a randomized polar SmA phase (SmAPAR) and ferroelectric polydomain SmCsPSphases with orthogonal combination of tilt and polar direction and much higher polarizations. Thus, surprisingly, the compound with the smaller molecular dipole moment shows increased polar order in the LC phases. Besides ferroelectricity, mirror-symmetry breaking with formation of a conglomerate of macroscopic chiral domains was observed in one of the SmC phases of CN1. These investigations contribute to the general understanding of the development of polar order and chirality in soft matter. The power of an ester group: Reversing one COO group in a bent-core mesogen leads to very different dipole moments, gives rise to distinct segregation of the carbosilane end groups from the aliphatic and aromatic segments, and thus modifies the mode of self-assembly, the coherence length of polar order, and the capability of mirror-symmetry breaking. One of the isomers forms a new leaning-type liquid-crystalline (LC) phase in which the tilt coincides with the polar direction, whereas the other forms a ferroelectric LC in which the tilt is perpendicular to the polar direction (see figure).
Topological ferroelectric bistability in a polarization-modulated orthogonal smectic liquid crystal
Zhu, Chenhui,Shao, Renfan,Reddy, R. Amaranatha,Chen, Dong,Shen, Yongqiang,Gong, Tao,Glaser, Matthew A.,Korblova, Eva,Rudquist, Per,MacLennan, Joseph E.,Walba, David M.,Clark, Noel A.
supporting information; experimental part, p. 9681 - 9687 (2012/07/14)
We report a bent-core liquid crystal (LC) compound exhibiting two fluid smectic phases in which two-dimensional, polar, orthorhombic layers order into three-dimensional ferroelectric states. The lower-temperature phase has a uniform polarization field which responds in an analog fashion to applied electric field. The higher-temperature phase is a new smectic state with periodic undulation of the polarization, structurally modulated layers, and a bistable response to applied electric field which originates in the periodically splay-modulated bulk of the LC rather than by surface stabilization at the cell boundaries.
