Does Introduction of a Bent Tail Stabilize Biaxiality and Lateral

Subscriber access provided by UNIV OF LOUISIANA

B: Fluid Interfaces, Colloids, Polymers, Soft Matter, Surfactants, and Glassy Materials

Does Introduction of a Bent Tail Stabilize Biaxiality and Lateral Switching Behavior of Smectic A Liquid Crystal Phases of Rodlike Molecules? Chiharu Koga, Michinari Kohri, Tatsuo Taniguchi, and Keiki Kishikawa J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.9b00589 • Publication Date (Web): 24 Apr 2019 Downloaded from http://pubs.acs.org on April 30, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Does Introduction of a Bent Tail Stabilize Biaxiality and Lateral Switching Behavior of Smectic A Liquid Crystal Phases of Rodlike Molecules? Chiharu Koga,† Michinari Kohri,† Tatsuo Taniguchi,† Keiki Kishikawa*,†,‡ †

Department of Applied Chemistry and Biotechnology, Graduate School of Science and

Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan ‡

Molecular Chirality Research Centre, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-

8522, Japan *Corresponding Author. E-mail: [email protected], Phone: +81-43-290-3238.

ABSTRACT

By introducing an oleyl group at the end of the straight rod-like molecule, the effect of the tail shape on the liquid crystallinity, biaxiality, and lateral switching behavior of the smectic A phase was investigated. Three types of molecules possessing a fluorinated phenyl (pentafluorophenyl, 2,3,4-trifluorophenyl, or 2,3-difluorophenyl) group and a cis-octadec-9-enyl group were synthesized, and their liquid crystallinities were compared with the corresponding molecules with a straight alkyl (trans-octadec-9-enyl or n-octadecanyl) group. In switching experiments,

1 ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 33

the molecules with a bent terminal chain showed higher spontaneous polarization (Ps) values than those with a straight terminal chain. Further, the directional changes of the long molecular axes were suppressed for the molecules possessing a bent terminal chain. These results show that the introduction of a bent terminal chain is highly effective for stabilizing ferroelectric switching behaviors.

INTRODUCTION Uniaxial nematic (Nu) liquid crystal (LC) phases in which rod-like molecules only have one directional order are widely used in current LC displays (LCDs); the directions of the molecular long axes in these molecules are changed by an applied electric field in each of the LC switching cells (Figure 1a). Due to collision with the surrounding molecules, the switching movement of each molecule is not smooth, which suppresses a sufficient electro-response in LCDs. In this respect, recently, concern regarding biaxial nematic (Nb) and biaxial smectic A (SmAb) LC phases has increased.1-7 Nb and SmAb LC phases have a lateral directional order in addition to the directional order parallel to the molecular long axis. If each of the molecules has a lateral polarity, each molecule can respond to an applied electric field and switch its short axis directions around the molecular long axis (Figure 1b).1,2,8 The molecular rotational motion of these molecules is expected to be rapid compared with that of the Nu LC phases because of their smaller excluded volume during switching.1,2,9 Studies regarding switching in the Nb and SmAb LC phases are mostly limited to those of bentcore molecules,10-37 disc-like molecules,38-40 and mixtures of these molecules with rod-like molecules,41-47 which are known to be effective. However, these core shape-assisted approaches have the problem of low electro-responsiveness due to the large excluded volume during


Page 3 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


molecular rotation. On the other hand, we previously reported an interaction-assisted approach using a straight rod-like core, and our molecules showed a rapid switching response.48 However, our rod-like molecules had problems such as a high LC temperature range (102-178 ℃) and a low spontaneous polarization (Ps), which was approximately 80 nC∙cm-2 due to the low molecular ordering. Considering the application of biaxial LC molecules to LCDs, it is necessary that the molecules exhibit liquid crystallinity at a lower temperature and have a higher Ps value. In this paper, we describe the stabilization of biaxiality in SmA phases of rod-like molecules by introduction of a bent tail (= oleyl group) and realization of ferroelectrically switchable SmAb phases. To the best of our knowledge, few studies have been conducted that realize biaxiality by effectively using flexible bent terminal chains. We expected the bent tail to lower the LC temperature range and stabilize the molecular biaxiality to increase the Ps value.49,50

Figure 1. Schematic representation of the molecular motions for switching in (a) a uniaxial phase of axially polar molecules and (b) a biaxial phase of laterally polar molecules. The red arrows indicate the molecular dipoles.



Page 4 of 33

Figure 2. Molecular packing models in our concept: molecules in (a) the uniaxial SmA phase, (b) unstable biaxial SmA phase generated by the introduction of PFA-A interaction, (c) biaxial SmA phase stabilized by the introduction of both PFA-A interaction and bent chains, and (d) polarityswitchable biaxial SmA phase realized by introducing a lateral polarity (the red arrow indicates the molecular lateral dipole). In our concept (Figure 2), to realize ferroelectrically switchable SmAb phases of rod-like molecules, the molecules have the following two features; (1) the core has fluorinated benzoyl and biphenyl groups, and (2) the terminal chain is bent. The first feature is necessary to generate strong intermolecular perfluoroarene-arene (PFA-A) interactions51-74 that change the monoaxial SmA phase (Figure 2a) to the SmAb phase (Figure 2b). Regarding the second feature, the introduction of the bent terminal chain was expected to suppress the tight molecular packing to


Page 5 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


shift the LC temperature range to lower values49,50 and simultaneously stabilize the biaxiality and ferroelectricity due to the increase in the excluded volume of the spin and slide molecular movement (Figure 2c). The tri- and di-fluorinated benzoyl groups play an important role for generating a lateral polarity (Figure 2d),75-78 which is necessary for realizing the polarityswitchable SmAb phase. Based on our concept, we designed simple molecules F5-BB-C18(c), F3-BB-C18(c), and F2BB-C18(c) (Scheme 1) consisting of a fluorinated benzoyl group, a biphenyl moiety, and an oleyl group. Compound F0-BB-C18(c) with no fluorine atoms was synthesized to evaluate the influence of fluorine atoms on the liquid crystallinity. Further, compounds F5-BB-C18(t), F3BB-C18(t), and F2-BB-C18(t) with a trans-double bond and compounds F5-BB-C18(n), F3BB-C18(n), and F2-BB-C18(n) with a normal alkyl chain were synthesized to evaluate the influence of the geometries of the double bond and the existence of the double bond, respectively.

Scheme 1. Molecular structures of the compounds synthesized in this study.



Page 6 of 33

RESULTS AND DISCUSSIONS Compounds F5-BB-C18(c), F3-BB-C18(c), F2-BB-C18(c), F5-BB-C18(t), F3-BBC18(t), F2-BB-C18(t), F5-BB-C18(n), F3-BB-C18(n), and F2-BB-C18(n) were synthesized as follows (Figure S1). Oleyl alcohol ((Z)-octadec-9-en-1-ol), (E)-octadec-9en-1-ol,

and

1-octadecanol

were

brominated

by

carbon

triphenylphosphine to produce the corresponding alkyl bromides.

tetrabromide

and

Each of the alkyl

bromides obtained was reacted with 4,4’-biphenol to obtain 4-alkoxy-4’-hydroxybiphenyl. Condensation of the corresponding fluorinated benzoic acid with the monoalkylated biphenols produced the compounds. The phase transition behaviors are shown in Table 1 and their DSC charts are shown in Figures S2-S4. The phases were identified by polarized light optical microscopy (POM). The micrographs are shown in Figure 3. Compounds F5-BB-C18(c) and F3-BB-C18(c) exhibited the SmA phase (Figures 3a and 3b), and F2-BB-C18(c) exhibited the SmA and SmCA (Figure 3c) phases. In all these SmA phases, the homeotropic texture in POM appeared to be slightly clouded because of light scattering.(Figure S5) In SmCA phases, the molecules are tilt alternately in opposite directions from layer to layer. During the SmA-SmCA transition (Figure S6), the extinction brushes of the focal conic texture keeps their perpendicular and horizontal directions, though the homeotropic textures change from dark to schlieren textures. Further, two-brush defects are observed in its schlieren textures (Figure S7). These features are consistent with those of the SmCA phase.79,80 These mesophases were observed upon both heating and cooling. In contrast, compound F0-BBC18(c) exhibited the SmA (Figure3d) and SmCA phases only upon cooling. This result indicates that the introduction of the fluorine atoms greatly stabilizes the LC states.


Page 7 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Phase transition behaviors of the compoundsa

a

The transition temperatures (°C) and transition enthalpies (kcal mol−1) were determined by DSC (5 °C min−1) and are given above and below the arrows. Cr, SmA, SmCA, and Iso indicate the crystal, smectic A, smectic CA, and isotropic liquid phases, respectively. b The temperature was measured by POM because the temperature was not observed in the DSC experiment.



Page 8 of 33

Figure 3. Polarized optical micrographs of (a) F5-BB-C18(c) at 116 ℃ (SmA), (b) F3-BBC18(c) at 104 ℃ (SmA), (c) F2-BB-C18(c) at 88 ℃ (SmCA), (d) F0-BB-C18(c) at 98 ℃ (SmA), (e) F5-BB-C18(t) at 100 ℃ (SmA), (f) F3-BB-C18(t) at 109 ℃ (SmA), (g) F2-BB-C18(t) at 84 ℃ (SmCA), (h) F5-BB-C18(n) at 111 ℃ (SmA), (i) F3-BB-C18(n) at 107 ℃ (SmA), and (j) F2-BB-C18(n) at 110 ℃ (SmA).


Page 9 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To investigate the influence of the bent terminal chain on the liquid crystallinities, the phase transition behaviors of F5-BB- C18(t), F3-BB-C18(t), F2-BB-C18(t), F5-BB-C18(n), F3-BBC18(n), and F2-BB-C18(n) were compared with those of F5-BB-C18(c), F3-BB-C18(c), and F2-BB-C18(c).

Consequently, the corresponding derivatives showed the similar phase

transitions. F5-BB-C18(t), F3-BB-C18(t), F5-BB-C18(n), F3-BB-C18(n), and F2-BB-C18(n) exhibited a SmA phase (Figures 3e, 3f, 3h, 3i and 3j), and F2-BB-C18(t) showed a SmCA phase (Figure 3g). The orders of the Cr-SmA (or SmCA) transition temperatures are, from the lowest to the highest, F5-BB-C18(c) < F5-BB-C18(t) < F5-BB-C18(n) for the pentafluorobenzoate esters, F3-BB-C18(c) < F3-BB-C18(t) < F3-BB-C18(n) for the trifluorobenzoate esters, and F2-BBC18(c) < F2-BB-C18(t) < F2-BB-C18(n) for the difluorobenzoate esters. The orders of the compounds possessing the cis-octadecenyl, trans-octadecenyl, and n-octadecyl groups can be explained by the difference in the packing tightness of the terminal chains in the crystal states. In this respect, the bent terminal chain, the oleyl group, is the most effective for lowering the melting points of these series of LC compounds. On the other hand, the orders of the SmA-Iso transition temperatures are, from the lowest to the highest, F5-BB-C18(t) < F5-BB-C18(c) < F5BB-C18(n) for the pentafluorobenzoate esters and F3-BB-C18(t) < F3-BB-C18(c) < F3-BBC18(n) for the trifluorobenzoate esters. The order of the SmA-Iso transition temperature in the difluorobenzoate esters is, from the lowest to the highest, F2-BB-C18(c) < F2-BB-C18(t) < F2BB-C18(n). These results suggest that the compounds with the normal alkyl chain have the highest SmA-Iso transition temperatures of each series due to the tight packing structure in the LC phase. However, it is difficult to explain the order of the compounds possessing the cis- and trans-octadecenyl groups. These results may occur because the attractive electronic interactions between the cis-double bonds with weak polarities are stronger than those between the non-polar



Page 10 of 33

trans-double bonds, though the trans-alkenyl groups are assumed to stabilize the LC states more than the cis-alkenyl groups due to their tight packing.81 To investigate the molecular-packing structures in the LC phases of all the compounds, their one-dimensional and two-dimensional X-ray diffraction (1D-XRD and 2D-XRD) profiles were measured. XRD could not be performed on F0-BB-C18(c) and F2-BB-C18(n) due to their LC temperature ranges observed only on cooling. We attempted to measure the XRD profiles of the SmA phases of F0-BB-C18(c) and F2-BB-C18(n), but only their LC phases were not observed, because their recrystallization occurred. Figure 4 shows the 1D-XRD profiles of F5-BB-C18(c) (SmA), F3-BB-C18(c) (SmA), and F2-BB-C18(c) (SmCA). Three sharp peaks corresponding to d(100), d(200) and d(300) were observed at even intervals in all of these compounds, which are indicative of smectic phases. The broad peaks at 4.1 Å and 4.6 Å are derived from the distance between the cores and that between the molten alkyl chains, respectively. We carefully checked the bilayer periodicity about twice the d(100) in the XRD profiles, but no bilayer periodicity was observed.

In each of the XRD profiles of F5-BB-C18(c) (SmA) and F3-BB-C18(c) (SmA)

(Figures 4a and 4b), a broad peak of about 11 Å, which includes both the repeat distance at which fluorinated and non-fluorinated benzene rings pile up and the repeat distance at which the two different benzene rings contact side by side, is observed. The 1D-XRD profiles of F5-BBC18(t), F3-BB-C18(t), F2-BB-C18(t), F5-BB-C18(n), and F3-BB-C18(n) are shown in Figure S8. Further, F2-BB-C18(c) and F2-BB-C18(t) exhibiting SmA-SmCA phase sequence showed the a slight change (about 1.5 Å) in the layer distance was observed at the SmA-SmCA transition.


Page 11 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. 1D-XRD profiles of (a) F5-BBC18(c) at 100 °C (SmA), (b) F3-BB-C18(c) at 110 °C (SmA), and (c) F2-BB-C18(c) at 86 °C (SmCA).

The XRD profile was

obtained at each temperature during heating process.



Page 12 of 33

Figure 5. 2D-XRD profiles of (a) F5-BB-C18(c) at 100 °C (SmA), (b) F3-BB-C18(c) at 135 °C (SmA), (c) F2-BB-C18(c) at 98 °C (SmA), and (d) F2-BB-C18(c) at 85 °C (SmCA, the broken lines indicate the direction of the center of the halo). The white arrows indicate the direction of the magnetic field. The layer normal and parallel directions are indicated by solid lines. The enlarged central part was added to the right of each XRD profile. The XRD profile was obtained at each temperature during heating process.


Page 13 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5 shows the 2D-XRD profiles of F5-BB-C18(c), F3-BB-C18(c), and F2-BB-C18(c). Each of the samples in the Iso state in a glass capillary tube (diameter: 1.5 mm) was slowly cooled to the smectic phase to obtain a single crystal of the smectic phase under an applied magnetic field (3000 Gauss). The layer normal of the smectic crystals did not always coincide with the magnetic field direction due to the influence of the capillary glass surface. To facilitate the understanding of the packing structures, in each of the profiles, the layer normal and parallel directions are indicated with solid lines. For the F5-BB-C18(c) (Figure 5a), F3-BB-C18(c) (Figure 5b), and F2-BB-C18(c) (Figure 5c), two kinds of halos (11 and 4-4.5 Å) in the lateral direction of the molecule were observed at the equator of the profile, and their layer distances d(100) were observed on the meridian, indicating a SmA phase. From the scattering homeotropic textures in POM and these lateral repeat distances in XRD, it is assumed that these SmA phases locally have biaxiality, though the phases do not show dark schlieren textures like the SmAb phases reported.18,82-84 The directions of the molecular widths of F2-BB-C18(c) (Figure 5d) at a low LC temperature range were inclined to the equator line by 24º, indicating smectic SmCA phase. These XRD results agreed with the aforementioned POM results. The 2D-XRD profiles of F5-BB-C18(t) (SmA), F3-BB-C18(t) (SmA), F2-BB-C18(t) (SmCA), F5-BB-C18(n) (SmA), and F3-BB-C18(n) (SmA) are shown in Figure S9. The molecular packing structures of SmA and SmCA phases were postulated from the 1D- and 2D-XRD results, as shown in Figure 6. Figure 6a indicates the molecular model for F5-BBC18(c), F3-BB-C18(c), and F2-BB-C18(c). Figure 6b shows the molecular packing structure of the SmA phases. The cores have PFA-A interaction between the fluorinated and non-fluorinated benzene rings. In order not to lower the packing density, the bent alkyl chains interdigitate



Page 14 of 33

between the layers so as to direct their bending directions in one direction. Figure 6c indicates the structure of the SmCA phases. The cores are tilt alternately in opposite directions layer to layer. Because the interlayer distance and the molecular length were almost the same, these core parts were considered to have formed a layer by using the PFA-A interaction to self-organize the adjacent molecules anti-parallel each other.

Figure 6. Estimated molecular packing structures; (a) molecular model for F5-BB-C18(c), F3BB-C18(c) and F2-BB-C18(c), (b) front view of the SmA phase of F5-BB-C18(c), F3-BBC18(c), and F2-BB-C18(c) and (c) front and side views of the SmCA phase of F2-BB-C18(c).


Page 15 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


To investigate the ferroelectric switching behaviors of the molecules, electro-optic measurements were conducted. The samples were sandwiched between two glass plates that were coated with indium-tin-oxide (ITO) and polyimide (anti-parallel rubbing to align the molecules homogeneously). The size of the ITO area was 10 mm × 10 mm, and the cell gap was 5 μm. A triangular wave voltage was applied to the cell while the textures of the sample in the cell were observed by POM. Figure 7 shows the switching current response traces obtained in the LC phases of F5-BB-C18(c), F3-BB-C18(c), and F2-BB-C18(c) under the application of a triangular-wave electric field at 4 Hz (200 Vpp). The peak top voltage is not 0 V under applying the triangular wave voltage at 4 Hz, but each switching peak starts around 0 V. This means that the induced polarity is not be maintained after removal of the voltage. Therefore, we think that this switching should be distinguished from that of general ferroelectric LC phases. As shown in Figures 7a-c, switching current peaks were observed in the LC phases of F5-BB-C18(c), F3-BBC18(c), and F2-BB-C18(c). In addition, these samples responded to an approximately 10-15 Hz triangular voltage. Sharp peaks were observed for F5-BB-C18(c) and F3-BB-C18(c), but the peaks were broad for F2-BB-C18(c).

F5-BB-C18(c) has few lateral polarizations in the

pentafluorophenyl group; the ester groups are assumed to change their polar directions cooperatively under the application of a triangular wave voltage. Moreover, the Ps of F5-BBC18(c) was similar to that of F3-BB-C18(c) (Table 2). Therefore, presumably the sharp peaks of F5-BB-C18(c) and F3-BB-C18(c) are derived from the polarization reversal of the ester group, and the broad peaks of F2-BB-C18(c) are derived from the polarization reversal of both the ester and fluorinated phenyl groups. Accordingly, the PFA-A interaction in F3-BB-C18(c) is assumed to be so strong that the trifluorophenyl group cannot reverse. As shown in Table 2, the order of the Ps values are, from the lowest to highest, F5-BB-C18(n) < F5-BB-C18(t) < F5-BB-



Page 16 of 33

C18(c) for the pentafluorobenzoate esters, F3-BB-C18(n) < F3-BB-C18(t) < F3-BB-C18(c) for the trifluorobenzoate esters, and F2-BB-C18(t) < F2-BB-C18(c) for the difluorobenzoate esters. Since no switching peaks were observed in their Iso states (Figure S12), it is clear that the peaks are related to the smectic layer structures.

The orders of the compounds possessing n-

octadecanyl, trans-octadecenyl and cis-octadecenyl groups can be explained by the difference in the degree of intermolecular steric interaction between the terminal chains in the polarization reversal. Accordingly, the introduction of an oleyl group is most effective for generating high Ps values in these series of LC compounds.


Page 17 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Switching current response traces obtained by applying a triangular-wave voltage; (a) F5-BB-C18(c) in the SmA phase (100 °C, 4 Hz, 200 Vpp), (b) F3-BB-C18(c) in the SmA phase (120 °C, 4 Hz, 200 Vpp) and (c) F2-BB-C18(c) in the SmA phase (95 °C, 4 Hz, 200 Vpp). Black arrows indicated the switching current peaks.

Table 2. Comparison of the Ps values of compounds possessing a (Z)-dodec-9-enyl, (E)dodec-9-enyl and dodecanyl groups Compound

Ps (nC∙cm-2)(temp(℃))

F5-BB-C18(c)

176 (100)

F3-BB-C18(c)

164 (120)

F2-BB-C18(c)

287 (95)

F0-BB-C18(c)

−a

F5-BB-C18(t)

119 (100)

F3-BB-C18(t)

135 (120)

F2-BB-C18(t)

166 (95)

F5-BB-C18(n)

20 (115)

F3-BB-C18(n)

78 (120)

F2-BB-C18(n)

−a

a

Not measurable due to the narrow liquid crystal range.



Page 18 of 33

Figure 8. Change of textures in POM before and after voltage application; (a)(b) F5-BB-C18(c) (100 °C, 4 Hz, 200 Vpp), (c)(d) F5-BB-C18(t) (100 °C, 4 Hz, 200 Vpp), and (e)(f) F5-BB-C18(n) (115 °C, 4 Hz, 200 Vpp). Furthermore, the electro-responsive behaviors of pentafluorobenzoyl esters F5-BB-C18(c), F5-BB-C18(t), and F5-BB-C18(n) in the SmA phase were observed by POM under applying the triangular-wave voltage (Figure 8). In F5-BB-C18(c) (Figures 8a (0 V) and 8b (+100 V)), although the brightness slightly changes, the homogeneous texture remains during the voltage application. This result means that each molecule changed its molecular short axis direction around the molecular long axis under the applied electric field (Figure 9a).85 It is thought that this change in brightness includes those due to increase and decrease in orientation order. In comparison with this result, the textures of F5-BB-C18(t) and F5-BB-C18(n) (Figures 8c, 8d, 8e, and 8f) became dark from the application of the voltage (0 V→+100 V) and after removal of the


Page 19 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


voltage (+100 V→0V) their textures appeared again; each molecule changed the direction of its molecular long axis due to the applied electric field (Figure 9b). It is thought that the direction of the molecule has changed due to the influence of the dielectric anisotropy and the molecular dipole to the applied electric field. The DFT calculation (B3LYP6-31G(d)) showed that all these molecules had similar core shape and molecular dipole direction (Figure S13).

However, the

oleyl group suppresses the directional change of the molecular long axis during the switching process. Accordingly, it is clear that the introduction of an oleyl group stabilizes the lateral switching behavior.

Figure 9. Schematic representation of molecular movements under the application of the triangular wave voltage; (a) directional change of the molecular short axes of the F5-BB-C18(c)



Page 20 of 33

molecules around their long axes and (b) directional change of molecular long axes of F5-BBC18(t) and F5-BB-C18(n) around their short axes. CONCLUSIONS We synthesized rod-like LC compounds possessing a fluorinated benzoyl group and an alkyl chain and confirmed their ferroelectric switching behaviors. In this study, we found that the introduction of a bent terminal chain was effective not only for lowering the LC temperature ranges but also for increasing the Ps values in switching. These results are surprising because these long alkyl groups are highly flexible compared to the mesogenic cores in the LC temperature ranges. We believe that these results make an important contribution to the study of LC science and the design of LC molecules.

ASSOCIATED CONTENT Supporting Information Figure S1 presents the synthetic routes of the compounds. Their synthetic procedures and spectral data are described. Figures S2-S4 presents their DSC charts. Figure S5 shows microphotographs of slightly clouded homeotropic textures of the SmA phases. Figures S6 and S7 present microphotographs of F2-BB-C18(c) in SmCA phase. Figure S8 shows 1D-XRD profiles of F5-BB-C18(t) (SmA), F3-BB-C18(t) (SmA), F2-BB-C18(t) (SmCA), F5-BB-C18(n) (SmA), and F3-BB-C18(n) (SmA). Figure S9 shows the 2D-XRD profiles of F5-BB-C18(t) (SmA), F3-BB-C18(t) (SmA), F2-BB-C18(t) (SmCA), F5-BB-C18(n) (SmA), and F3-BB-C18(n) (SmA). Figure S10 shows 2D-XRD profiles of F5-BB-C18(t) (SmA), F3-BB-C18(t) (SmA), F2BB-C18(t) (SmCA), F5-BB-C18(n) (SmA) and F3-BB-C18(n) (SmA). Figure S11 shows azimuthal plots of F2-BB-C18(c) (SmCA) and F2-BB-C18(t) (SmCA). Figure S12 shows


Page 21 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


switching current response trace in the Iso state of F5-BB-C18(c) at 140 °C, 4 Hz, 200 Vpp. Figure S13 presents the most stable conformers of F5-BB-C18(c), F3-BB-C18(c), F2-BBC18(c), F5-BB-C18(t), F3-BB-C18(t), F2-BB-C18(t), F5-BB-C18(n), F3-BB-C18(n), and F2BB-C18(n) obtained by DFT (B3LYP6-31G(d)) calculation.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] ORCID identifier 0000-0002-7539-568X Notes There are no conflicts to declare. The manuscript was written through contributions of all authors.

ACKOWLEDGEMENTS This work was ﬁnancially supported by Japan Society for the Promotion of Science KAKENHI Grant Numbers 17H03035, 25288088. We thank Dr. H. Ozaki who saved KK’s life by an operation for brain hemorrhage five years ago.

REFERENCES (1)

Tschierske, C.; Photinos, D. J. Biaxial nematic phases. J. Mater. Chem., 2010, 20, 42634294.

(2)

Lehmann, M. Biaxial nematics from their prediction to the materials and the vicious circle of molecular design. Liq. Cryst., 2011, 38, 1389-1405.



(3)

Page 22 of 33

Solodkov, N. V.; Nagaraj, M.; Jones, J. C. Effects of monoclinic symmetry on the properties of biaxial liquid crystals. Phys. Rev. E, 2018, 97, 042702.

(4)

Berardi, R.; Muccioli, L.; Orlandi, S.; Ricci, M.; Zannoni, C. Computer simulations of biaxial nematics. J. Phys. Condens. Matter, 2008, 20, 463101.

(5)

Saha, J. Soft ellipsoid potential for biaxial molecules. Molecular Simulation, 2016, 42, 1437-1443.

(6)

Izzoa, D.; de Oliveira, M. J. Landau theory for uniaxial nematic, biaxial nematic, uniaxial smectic-A, and biaxial smectic-A phases. Liq. Cryst., 2016, 43, 1230-1236.

(7)

Dussi, S.; Tasios, N.; Drwenski, T.; Van Roij, R.; Dijkstra, M. Hard competition: stabilizing the elusive biaxial nematic phase in suspensions of colloidal particles with extreme lengths. Phys. Rev. Lett., 2018, 120, 177801.

(8)

Shimbo, Y.; Gorecka, E.; Pociecha, D.; Araoka, F.; Goto, M.; Takanishi, Y.; Ishikawa, K.; Mieczkowski, J.; Gomola, K.; Takezoe, H. Electric-field-induced polar biaxial order in a nontilted smectic phase of an asymmetric bent-core liquid crystal. Phys. Rev. Lett., 2006, 97, 113901.

(9)

Luckhurst, G. R. Biaxial nematic liquid crystals: fact or fiction? Thin Solid Films, 2001, 393, 40-52.

(10) Acharya, B. R.; Primak, A.; Kumar, S. Biaxial nematic phase in bent-core thermotropic mesogens. Phys. Rev. Lett., 2004, 92, 145506. (11) Francescangeli, O.; Stanic, V.; Torgova, S. I.; Strigazzi, A.; Scaramuzza, N.; Ferrero, C.; Dolbnya, I. P.; Weiss, T. M.; Berardi, R.; Muccioli, L.; Orlandi, S.; Zannoni, C.


Page 23 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ferroelectric response and induced biaxiality in the nematic phase of bent-core mesogens. Adv. Funct. Mater., 2009, 19, 2592-2600. (12) Sebastián, N.; Belau, S.; Eremin, A.; Alaasar, M.; Prehm, M.; Tschierske, C. Emergence of polar order and tilt in terephthalate based bent-core liquid crystals. Phys. Chem. Chem. Phys., 2017, 19, 5895-5905. (13) Keith, C.; Lehmann, A.; Baumeister, U.; Prehm, M.; Tschierske, C. Nematic phases of bent-core mesogens. Soft Matter, 2010, 6, 1704-1721. (14) Hegde, R. S.; Kumar, J.; Prasad, V.; Monika, M. The first examples of V-shaped compounds exhibiting a B5 mesophase and a direct transition from the isotropic to a polar biaxial smectic A mesophase. J. Mol. Liq., 2018, 249, 97-105. (15) Kaur, S. Elastic properties of bent-core nematic liquid crystals: the role of the bend angle. Liq. Cryst., 2016, 43, 2277-2284. (16) Madsen, L. A.; Dingemans, T. J.; Nakata, M.; Samulski, E. T. Thermotropic biaxial nematic liquid crystals. Phys. Rev. Lett., 2004, 92, 145505. (17) Luckhurst, G. R. V-shaped molecules: new contenders for the biaxial nematic phase. Angew. Chem. Int. Ed., 2005, 44, 2834-2836. (18) Sadashiva, B. K.; Reddy, R. A.; Pratibha, R.; Madhusudana, N. V. Biaxial smectic A liquid crystal in a pure compound. Chem. Commun., 2001, 2140-2141. (19) Schröder, M. W.; Diele, S.; Pancenko, N.; Weissflog, W.; Pelzl, G. Evidence for a polar biaxial SmA phase (CPA) in the sequence SmA-CPA-B2. J. Mater. Chem., 2002, 12, 13311334.



Page 24 of 33

(20) Yelamaggad, C. V.; Krishna Prasad, S.; Nair, G. G.; Shashikala, I. S.; Shankar Rao, D. S.; Lobo, C. V.; Chandrasekhar, S. A low-molar-mass, monodispersive, bent-rod dimer exhibiting biaxial nematic and smectic A phases. Angew. Chem. Int. Ed., 2004, 43, 34293432. (21) Yelamaggad, C. V.; Shashikala, I. S.; Rao, D. S. S.; Nair, G. G.; Prasad, S. K. The biaxial smectic (SmAb) phase in nonsymmetric liquid crystal dimers comprising two rodlike anisometric segments: an unusual behavior. J. Mater. Chem., 2006, 16, 4099-4102. (22) Shanker, G.; Nagaraj, M.; Kocot, A.; Vij, J. K.; Prehm, M.; Tschierske, C. Nematic phases in 1, 2, 4-Oxadiazole-based bent-core liquid crystals: is there a ferroelectric switching? Adv. Funct. Mater., 2012, 22, 1671-1683. (23) Vita, F. Search for nematic biaxiality in bent-core mesogens: an X-ray diffraction perspective. Liq. Cryst., 2016, 43, 2254-2276. (24) Liu, J.; Guan, R.; Dong, X.; Dong, Y. Molecular properties of a bent-core nematic liquid crystal A131 by multi-level theory simulations. Molecular Simulation, 2018, 44, 15391543. (25) Vaghela, A.; Teixeira, P. I.; Terentjev, E. M. Emergence of biaxial nematic phases in solutions of semiflexible dimers. Phys. Rev., 2017, 96, 042703. (26) Tomczyk, W.; Pająk, G.; Longa, L. Twist-bend nematic phases of bent-shaped biaxial molecules. Soft Matter, 2016, 12, 7445-7452. (27) Alaasar, M.; Prehm, M.; Poppe, S.; Tschierske, C. Development of polar order by liquidcrystal self-assembly of weakly bent molecules. Chem. Eur. J., 2017, 23, 5541-5556.


Page 25 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Aliev, M. A.; Kuzminyh, N. Y.; Ugolkova, E. A. Phase behavior of the thermotropic melt of asymmetric V-shaped molecules. Phys. Rev. E, 2017, 95, 042703. (29) Peroukidis, S. D.; Vanakaras, A. G.; Photinos, D. J. Molecular simulation study of polar order in orthogonal bent-core smectic liquid crystals. Phys. Rev. E, 2015, 91, 062501. (30) Hegguilustoy, C. M.; Darda, M. B.; Montani, R. S.; Heinrich, B.; Donnio, B.; Guillon, D.; Garay, R. O. Symmetric bent-shaped liquid crystal dimers showing transitions between optically uniaxial and biaxial smectic phases. Liq. Cryst., 2015, 42, 1013-1023. (31) Güzeller, D.; Ocak, H.; Bilgin-Eran, B.; Prehm, M.; Tschierske, C. Development of tilt, biaxiality and polar order in bent-core liquid crystals derived from 4’-hydroxybiphenyl-3carboxylic acid. J. Mater. Chem. C, 2015, 3, 4269-4282. (32) Drwenski, T.; van Roij, R. The effect of flexibility and bend angle on the phase diagram of hard colloidal boomerangs. Mol. Phys., 2018, 116, 2812-2822. (33) Patranabish, S.; Mohiuddin, G.; Begum, N.; Laskar, A. R.; Pal, S. K.; Rao, N. V.; Sinha, A. Cybotactic nematic phase of achiral unsymmetrical bent-core liquid crystals-Quelling of polar ordering and the influence of terminal substituent moiety. J. Mol. Liq., 2018, 249, 144-154. (34) Xu, J.; Zhang, P. Calculating elastic constants of bent-core molecules from Onsagertheory-based tensor model. Liq. Cryst., 2018, 45, 22-31. (35) Kumar, J.; Prasad, V. Ferroelectric nematic and ferrielectric smectic mesophases in an achiral bent-core azo compound. J. Phys. Chem. B, 2018, 122, 2998-3007.



Page 26 of 33

(36) Monika, M.; Roy, A.; Prasad, V. Smectic nanoclusters in the nematic mesophases of dimeric compounds composed of rod-like azo moieties with lateral substituents. New J. Chem., 2017, 41, 11576-11583. (37) Jeong, K. U.; Jing, A. J.; Mansdorf, B.; Graham, M. J.; Yang, D. K.; Harris, F. W.; Cheng, S. Z. Biaxial molecular arrangement of rod-disc molecule under an electric field. Chem. Mater., 2007, 19, 2921-2923. (38) Braga, W. S.; Santos, O. R.; Luders, D. D.; Kimura, N. M.; Sampaio, A. R.; Simões, M.; Palangana, A. J. Refractive index measurements in uniaxial and biaxial lyotropic nematic phases. J. Mol. Liq., 2016, 213, 186-190. (39) Salamończyk, M.; Pociecha, D.; Nowak-Król, A.; Koszelewski, D.; Gryko, D. T.; Górecka, E. Liquid-crystalline properties of trans-A2B2-porphyrins with extended π -electron systems. Chem. Eur. J., 2015, 21, 7384-7388. (40) Hunt, J. J.; Date, R. W.; Timimi, B. A.; Luckhurst, G. R.; Bruce, D. W. Toward the biaxial nematic phase of low molar mass thermotropic mesogens: Substantial molecular biaxiality in covalently linked rod-disk dimers. J. Am. Chem. Soc., 2001, 123, 10115-10116. (41) Cuetos, A.; Galindo, A.; Jackson, G. Thermotropic biaxial liquid crystalline phases in a mixture of attractive uniaxial rod and disk particles. Phys. Rev. Lett., 2008, 101, 237802. (42) Vanakaras, A. G.; Terzis, A. F.; Photinos, D. J. On the molecular requirements for the stabilisation of thermotropic biaxial ordering in rod-plate nematics. Mol. Cryst. Liq. Cryst., 2001, 362, 67-78.


Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(43) Yu, M.; Jiang, Y.; Shin, Y.; Jiang, J.; Yang, H.; Zhang, H.; Jiuzhi Xue, J.; Li. Q.; Yang, D. K. Effect of biaxiality on chirality in chiral nematic liquid crystals. Soft Matter, 2018, 14, 6530-6536. (44) Patti, A.; Cuetos, A. Monte Carlo simulation of binary mixtures of hard colloidal cuboids. Molecular Simulation, 2018, 44, 516-522. (45) Henriques, E. F.; Bohomoletz Henriques, V.; Krebs, P. R. Bimodal form distribution from modelling biaxial lyotropic liquid crystal solutions through a polydisperse Maier-Saupe model. Liq. Cryst., 2017, 44, 510-525. (46) Querciagrossa, L.; Ricci, M.; Berardi, R.; Zannoni, C. Can multi-biaxial mesogenic mixtures favour biaxial nematics? A computer simulation study. Phys. Chem. Chem. Phys., 2017, 19, 2383-2391. (47) Santos, O. R.; Braga, W. S.; Kimura, N. M.; Palangana, A. J.; Amaral, L. Q. Uniaxial and biaxial nematic phases in sodium dodecyl sulphate-decanol-D2O mixtures. An optical conoscopy study. Mol. Cryst. Liq. Cryst., 2015, 615, 19-25. (48) Kishikawa, K.; Inoue, T.; Hasegawa, N.; Takahashi, M.; Kohri, M.; Taniguchi, T.; Kohmoto, S.; Achiral straight-rod liquid crystals indicating local biaxiality and ferroelectric switching behavior in the smectic A and nematic phases. J. Mater. Chem. C., 2015, 3, 3574-3581. (49) Kelly, S. M. The effect of the position and configuration of carbon-carbon double bonds on the mesomorphism of thermotropic, non-amphiphilic liquid crystals. Liq. Cryst., 1996, 20, 493-515.



Page 28 of 33

(50) Jankowiak, A.; Ringstrand, B.; Januszko, A.; Kaszynski, P.; Wand, M. D. Liquid crystals with negative dielectric anisotropy: the effect of unsaturation in the terminal chain on thermal and electro-optical properties. Liq. Cryst., 2013, 40, 605-615. (51) Thompson, M.; Carkner, C.; Mosey, N. J.; Kapernaum, N.; Lemieux, R. P. Tuning the mesomorphic properties of phenoxy-terminated smectic liquid crystals: the effect of fluoro substitution. Soft Matter, 2015, 11, 3860-3868. (52) Patrick, C. R.; Prosser, G. S. A molecular complex of benzene and hexafluorobenzene. Nature, 1960, 187, 1021. (53) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Dougherty, D. A.; Grubbs, R. H. Phenylperfluorophenyl stacking interactions: a new strategy for supermolecule construction. Angew. Chem. Int. Ed. Engl., 1997, 36, 248-251. (54) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Ziller, J. W.; Lobkovsky, E. B.; Grubbs, R. H. Phenyl-perfluorophenyl stacking interactions: topochemical [2+2] photodimerization and photopolymerization of olefinic compounds. J. Am. Chem. Soc., 1998, 120, 3641-3649. (55) Raut, P.; Swanson, N.; Kulkarni, A.; Pugh, C.; Jana, S. C. Exploiting arene-perfluoroarene interactions for dispersion of carbon black in rubber compounds. Polymer, 2018, 148, 247258. (56) Sharber, S.; Shih, K. C.; Mann, A.; Frausto, F.; Haas, T. E.; Nieh, M. P.; Thomas, S. Reversible mechanofluorochromism of aniline-terminated phenylene ethynylenes. Chem. Sci., 2018, 9, 5415-5426.


Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(57) Bhandary, S.; Gonde, S.; Chopra, D. Dissecting the conformational and interaction topological landscape of N-ethynylphenylbenzamide by the device of polymorphic diversity. Cryst. Growth Des., 2018, 18, 3027-3036. (58) Hung, K. E.; Tsai, C. E.; Chang, S. L.; Lai, Y. Y.; Jeng, U. S.; Cao, F. Y.; Hsu, C. S.; Su, C. J.; Cheng, Y. J. Bispentafluorophenyl-containing additive: eEnhancing efficiency and morphological stability of polymer solar cells via hand-grabbing-like supramolecular pentafluorophenyl-fullerene interactions. ACS Appl. Mater. Interfaces, 2017, 9, 4386143870. (59) Kishikawa, K.; Aikyo, S.; Akiyama, S.; Inoue, T.; Takahashi, M.; Yagai, S.; Aonuma, H; Kohmoto, S. Realization of a lateral directional order in nematic and smectic A phases of rodlike molecules by using perfluoroarene-arene interactions. Soft Matter, 2011, 7, 51765187. (60) Morisue, M.; Ueno, I.; Shimizu, M.; Yumura, T.; Ikeda, N. Porphyrins sheathed in quadrupolar solvation spheres of hexafluorobenzene: solvation-induced fluorescence enhancement and conformational confinement. J. Phys. Chem. C, 2017, 121, 19407-19413. (61) Colombo, V.; Presti, L. L.; Gavezzotti, A. Two-component organic crystals without hydrogen bonding: structure and intermolecular interactions in bimolecular stacking. Cryst. Eng. Comm., 2017, 19, 2413-2423. (62) Sharber, S. A.; Baral, R. N.; Frausto, F.; Haas, T. E.; Müller, P.; Thomas III, S. W. Substituent effects that control conjugated oligomer conformation through non-covalent interactions. J. Am. Chem. Soc., 2017, 139, 5164-5174.



Page 30 of 33

(63) Feng, Y.; Chen, H.; Liu, Z. X.; He, Y. M.; Fan, Q. H. A pronounced halogen effect on the organogelation properties of peripherally halogen functionalized poly (benzyl ether) dendrons. Chem. Eur. J., 2016, 22, 4980-4990. (64) Liu, Z. X.; Sun, Y.; Feng, Y.; Chen, H.; He, Y. M.; Fan, Q. H. Halogen-bonding for visual chloride ion sensing: a case study using supramolecular poly (aryl ether) dendritic organogel systems. Chem. Commun., 2016, 52, 2269-2272. (65) Hori, A.; Takeda, H.; Premkumar, J. R.; Sastry, G. N. 1: 1 and 2: 1 cocrystallizations of alkoxy-substituted naphthalene derivatives with octafluoronaphthalene through areneperfluoroarene interactions. Journal of Fluorine Chemistry, 2014, 168, 193-197. (66) Kishikawa, K.; Inoue, T.; Sasaki, Y.; Aikyo, S.; Takahashi, M.; Kohmoto, S. Generation of biaxiality in smectic A phases by introduction of intermolecular perfluoroarene-arene and C-H/F interactions, and the non-odd-even effect of the molecules in their transition temperatures and layer distances. Soft Matter, 2011, 7, 7532-7538. (67) Reichenbächer, K.; Süss, H. I.; Hulliger, J. Fluorine in crystal engineering-“the little atom that could”. Chem. Soc. Rev., 2005, 34, 22-30. (68) Williams, J. H. The molecular electric quadrupole moment and solid-state architecture. Acc. Chem. Res., 1993, 26, 593-598. (69) Kishikawa, K. Utilization of the perfluoroarene-arene interaction for stabilization of liquid crystal phases. Isr. J. Chem., 2012, 52, 800-808. (70) Meyer, E. A.; Castellano, R. K.; Diederich, F. Interactions with aromatic rings in chemical and biological recognition. Angew. Chem. Int. Ed., 2003, 42, 1210-1250.


Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(71) Lee, H.; Knobler, C. B.; Hawthorne, M. F. Supramolecular self-assembly directed by carborane C-H⋯F interactions. Chem. Commun., 2000, 2485-2486. (72) Kishikawa, K.; Oda, K.; Aikyo, S.; Kohmoto, S. Columnar superstructures of non-discshaped molecules generated by arene-perfluoroarene face-to-face interactions. Angew. Chem. Int. Ed., 2007, 46, 764–768. (73) Horiguchi, M.; Okuhara, S.; Shimano, E.; Fujimoto, D.; Takahashi, H.; Tsue, H.; Tamura, R. Control of the mode of polymorphic transition inducing preferential enrichment by modifying the molecular structure or adding seed crystals: significant influence of CH/F hydrogen bonds. Cryst. Growth Des., 2008, 8, 540-548. (74) Lozman, O. R.; Bushby, R. J.; Vinter, J. G. Complementary polytopic interactions (CPI) as revealed by molecular modelling using the XED force field. J. Chem. Soc., Perkin Trans. 2, 2001, 0, 1446-1452. (75) Dasgupta, P.; Pramanik, A.; Das, M. K.; Das, B. Comparative study of the mesomorphic properties of several laterally fluorinated liquid crystalline materials. Liq. Cryst., 2015, 42, 1083-1094. (76) Matharu, A. S.; Cowling, S. J.; Wright, G. Laterally fluorinated liquid crystals containing the 2, 2’-bithiophene moiety. Liq. Cryst., 2007, 34, 489-506. (77) Zhang, H.; Cao, H.; Chen, M.; Zhang, L.; Jiang, T.; Chen, H.; Li, F.; Zhu, S.; Yang, H. Effects of the fluorinated liquid crystal molecules on the electro-optical properties of polymer dispersed liquid crystal films. Liq. Cryst., 2017, 44, 2301-2310.



Page 32 of 33

(78) Jiang, Y.; An, Z.; Chen, P.; Chen, X.; Zheng, M. Synthesis and mesomorphic properties of but-3-enyl-based fluorinated biphenyl liquid crystals. Liq. Cryst., 2012, 39, 457-465. (79) Takanishi, Y.; Takezoe, H.; Fukuda, A.; Watanabe, J. Visual observation of dispirations in liquid crystals. Phys. Rev. B, 1992, 45, 7684-7689. (80) Takezoe, H.; Gorecka, E.; Čepič, M. Antiferroelectric liquid crystals: interplay of simplicity and complexity. Rev. Mod. Phys., 2010, 82, 897-937. (81) Belaissaoui, A.; Cowling, S. J.; Goodby, J. W. Mesogenic properties of two 1,3,4oxadiazolebased bent-core geometrical isomers. Liq. Cryst., 2013, 40, 421-427. (82) Hegmann, T.; Kain, J.; Diele, S.; Pelzl, G.; Tschierske, C. Evidence for the existence of the McMillan Phase in a binary system of a metallomesogen and 2,4,7-trinitrofluorenone. Angew. Chem. Int. Ed., 2001, 40, 887-890. (83) Yelamaggad, C. V.; Tamilenthi, V. P.; Rao, D. S. S.; Nair, G. G.; Prasad, S. K. A new thermotropic reentrant behaviour in a chiral liquid crystal dimer: the occurrence of SmA– SmAb–SmA phase sequence. J. Mater. Chem., 2009, 19, 2906-2908. (84) Padmini, V.; Babu, P. N.; Nair, G. G.; Rao, D. S. S.; Yelamaggad, C. V. Optically biaxial, re-entrant and frustrated mesophases in chiral, non-symmetric liquid crystal dimers and binary mixtures. Chem. Asian J., 2016, 11, 2897-2910. (85) Sreenilayam, S.; Nagaraj, M.; Panarin, Y. P.; Vij, J. K.; Lehmann, A.; Tschierske, C. Properties of non-tilted bent-core orthogonal smectic liquid crystal. Mol. Cryst. Liq. Cryst., 2012, 553, 140-146.


Page 33 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic


Does Introduction of a Bent Tail Stabilize Biaxiality and Lateral

Recommend Documents