Smectic Mesophase Behavior of Dimeric Compounds Showing Antiferroelectricity, Frustration and Chirality

Izumi, Tatsuya; Kang, Sungmin; Niori, Teruki; Takanishi, Yoichi; Takezoe, Hideo; Watanabe, Junji

doi:10.1143/jjap.45.1506

Cited by 28 publications

(44 citation statements)

References 30 publications

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“…The chemical structures of each component are shown in Scheme . We used two bent‐core compounds that show the B4 but no N phase: 1,3‐phenylenebis[4‐(4‐8‐alkoxyphenyliminomethyl)‐benzoates] (P8‐O‐PIMB; Iso–B2–B3–B4)27 and α,ω‐bis(4‐alkoxyazobenzene‐4′‐carbonyloxy)alkene (12OAzo5AzoO12; Iso–SmC A –B4) 28. For rod‐like compounds, we used n ‐pentylcyanobiphenyl (5CB; Iso–N–Cryst), 4′‐cyano‐(1,1′‐biphenyl)‐4‐yl‐4‐pentylbenzoate (5PCB; Iso–N–Cryst), and ZLI‐2293 (a cyano‐type nematic mixture from Merck; Iso–N).…”

Section: Methodsmentioning

confidence: 99%

A General Method for the Enantioselective Formation of Helical Nanofilaments

et al. 2013

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Chirality has been an important subject in chemistry since Pasteur demonstrated the existence of molecules that were mirror images of each other. [1] Indeed, chirality has proven to be important in the fields of biology and pharmacy as well. [2] In the past, single enantiomers have been made by using asymmetric catalysis [3,4] and enantiomeric separation. [5] However, almost all methods rely on the use of chiral molecules. Recently, the development of asymmetric reactions that do not use chiral molecules is attracting lot of attention. In this respect, bent-core liquid crystals (BCLCs) [6][7][8] are very interesting because layer chirality occurs in nonchiral molecular systems as a result of the tilt of polar-ordered molecules from the normal of the smectic layer, [9] and is coupled with conformational molecular chirality. [10] Moreover spontaneous deracemization to give large chiral domains occurs particularly in the helical nanofilament (HNF) B4 phase because of negative splay elastic constants. [7][8][9][10][11][12] Each macroscopic chiral domain consisting of HNFs exhibits high optical activity. [11,[13][14][15] The formation of a helical structure in the B4 phase suggests that the chirality can be controlled, because in many other organic systems the handedness of the helical structure has been controlled by external chiral sources, such as circularly polarized light, [16,17] vortex flow, [18][19][20] and helicity memory induced by chiral molecules. [21] Previously, we used five different methods to control the chirality of the B4 phase and successfully obtained almost 100 % ee with some of them. These methods are: 1) the introduction of chiral analogues, [22] 2) the use of a chiral surface, [23] 3) irradiation of photoisomerizable molecules with circularly polarized ultraviolet (UV) light, [24] 4) the use of twisted nematic (TN) director orientation, [25] and 5) growth from a chiral phospholipid layer. [26] Methods 2 and 5 both involve the use of a chiral surface, however, with the former only 10 % ee was attained, whereas with the latter almost 100 % ee was attained. The difference originates from the absence (method 2) and presence (method 5) of a temperature gradient. Contrary to the use of chiral dopants in method 1 and chiral surfaces in methods 2 and 5, methods 3 and 4 do not require any chiral species and have the added advantage that they work on bulk samples. However, the phase sequences of the compounds used for methods 3 and 4 are restricted by necessary phase sequences, that is, a fluid smectic phase (method 3) and a nematic (N) phase (method 4) that occur at higher temperatures to the B4 phase. Namely, a gradual phase transition from fluid smectic phases to the B4 phase under circularly polarized UV irradiation triggers repeated photoisomerization, whereas UV irradiation in the B4 phase is not an effective method to control chirality. Only one example of method 4 is known [25]

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Section: Methodsmentioning

confidence: 99%

A General Method for the Enantioselective Formation of Helical Nanofilaments

et al. 2013

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“…It is also important to know that one of such twin dimers, called 12AM5AM12, in which two Schiff's base (azomethine) mesogenic groups are linked by COO‐(CH 2 ) 5 ‐OCO, was found to exhibit the SmAP phase and show an antiferroelectric switching soon after the discovery of polar switching in a bent‐core mesogen, P‐8‐PIMB . Another important fact to be noted is some twin dimers, for example, 14OAM5AMO14 and 12OAz5AzO12, exhibit a phase with chirality resolution. Compound 12OAz5AzO12 was assigned to the B4 phase in the literature, but it seems to be the DC phase, according to our recent studies based on SEM, AFM and XRD results .…”

Section: Hierarchical Chiral Superstructuresmentioning

confidence: 99%

Chiral Superstructure Mesophases of Achiral Bent‐Shaped Molecules – Hierarchical Chirality Amplification and Physical Properties

Takezoe

Araoka

2016

Advanced Materials

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Chiral mesophases in achiral bent-shaped molecules have attracted particular attention since their discovery in the middle 1990s, not only because of their homochirality and polarity, but also due to their unique physical/physicochemical properties. Here, the most intriguing results in the studies of such symmetry-broken states, mainly helical-nanofilament (HNF) and dark-conglomerate (DC) phases, are reviewed. Firstly, basic information on the typical appearance and optical activity in these phases is introduced. In the following section, the formation of mesoscopic chiral superstructures in the HNF and DC phases is discussed in terms of hierarchical chirality. Nanoscale phase segregation in mixture systems and gelation ability in the HNF phase are also described. In addition, some other related chiral phases of bent-shaped molecules are shown. Recent attempts to control such mesoscopic chiral structure and the alignment/confinement of HNFs are also discussed, along with several examples of their fascinating advanced physical properties, i.e. huge enhancement of circular dichroism, electro- and photo-tunable optical activities, chirality-induced nonlinear optics (second-harmonic-generation circular difference and electrogyration effect), enhanced hydrophobicity through the dual-scale surface morphological modulation, and photoconductivity in the HNF/fullerene binary system. Future prospects from basic science and application viewpoints are also indicated in the concluding section.

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“…It should be pointed out here, that polar banana phases have only been formed by bent molecules up until now. Although a bent conformation is also exhibited by dimesogens due to the presence of odd-parity central spacer, they do not spontaneously form polar banana phases [ 6 – 7 ].…”

Section: Introductionmentioning

confidence: 99%

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

Findeisen-Tandel¹,

Weißflog²,

Baumeister³

et al. 2012

Beilstein J. Org. Chem.

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SummaryBent-core mesogens have gained considerable importance due to their ability to form new mesophases with unusual properties. Relationships between the chemical structure of bent-core molecules and the type and physical properties of the formed mesophases are relatively unknown in detail and differ strongly from those known for calamitic liquid crystals. In this paper symmetric and nonsymmetric five-ring salicylideneaniline-based bent-core mesogens are presented, and the effect of lateral substituents attached at the outer phenyl rings (F, Cl, Br) or the central phenyl ring (CH3) on the liquid-crystalline behaviour and on the physical properties is studied. Corresponding benzylideneaniline-based compounds were additionally prepared in order to study the influence of the intramolecular hydrogen bond. The occurring mesophases were investigated by differential scanning calorimetry, polarising microscopy, X-ray diffraction and dielectric and electro-optical measurements. The paper reports on new findings with respect to the structure–property relationships of bent-core mesogens. On one hand, the disruptive effect of laterally substituted halogen atoms, F, Cl and Br, on the mesophase behaviour of three isomeric series was much lower than expected. On the other hand, an increase of the clearing temperature by 34 K was observed, caused by small lateral substituents. The electro-optical behaviour, especially the type of polar switching and corresponding molecular movements, is sensitive to variations in the molecular structure.

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Smectic Mesophase Behavior of Dimeric Compounds Showing Antiferroelectricity, Frustration and Chirality

Cited by 28 publications

References 30 publications

A General Method for the Enantioselective Formation of Helical Nanofilaments

A General Method for the Enantioselective Formation of Helical Nanofilaments

Chiral Superstructure Mesophases of Achiral Bent‐Shaped Molecules – Hierarchical Chirality Amplification and Physical Properties

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

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