Fluorinated twist-bend nematogens: the role of intermolecular interaction

Knežević, Anamarija; Dokli, Irena; Novak, Jurica; Kontrec, Darko; Lesac, Andreja

doi:10.1080/02678292.2020.1817585

Cited by 12 publications

(3 citation statements)

References 45 publications

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“…These consist of molecules containing two mesogenic groups connected by a spacer having an odd number of atoms (see, for example, ref. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] although other structures such as higher oligomers, [30][31][32][33][34][35][36] semi-rigid bent core liquid crystals, 37,38 and hydrogen-bonded systems [39][40][41][42][43] are also known to support the formation of the N TB phase. The search for the twist-bend smectic phases has also been focussed on bent mesogenic dimers, but in order to drive smectic phase formation, the molecular design must also incorporate molecular inhomogeneity.…”

Section: Introductionmentioning

confidence: 99%

New patterns of twist-bend liquid crystal phase behaviour: the synthesis and characterisation of the 1-(4-cyanobiphenyl-4′-yl)-10-(4-alkylaniline-benzylidene-4′-oxy)decanes (CB10O·m)

et al. 2022

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Section: Introductionmentioning

confidence: 99%

New patterns of twist-bend liquid crystal phase behaviour: the synthesis and characterisation of the 1-(4-cyanobiphenyl-4′-yl)-10-(4-alkylaniline-benzylidene-4′-oxy)decanes (CB10O·m)

et al. 2022

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“…In addition, odd-membered ether-linked dimers were also shown to exhibit the NTB phase [39] and led to the reassignment of smectic phases as NTB phases as shown, for example, in Figure 9 for the CBO5O.m series [18,40]. There is now a large collection of odd-membered dimers known to exhibit the NTB phase, and structure-property studies have focussed on the nature of the link between the spacer and mesogenic units [41][42][43][44][45][46][47][48][49], the length and parity of the spacer [39,[50][51][52][53], the structure of the mesogenic units [54][55][56][57][58][59][60][61][62][63][64], and the chemical nature of the terminal groups [65][66][67][68]. Although the majority of twist-bend nematogens are odd-membered dimers, other examples include trimers and higher oligomers [69][70][71][72][73][74], hydrogen-bonded supramolecular systems [75][76][77][78]…”

Section: The Twist Bend Nematic Phasementioning

confidence: 99%

Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend

et al. 2022

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In this review we consider the relationships between molecular structure and the tendency of liquid crystal dimers to exhibit smectic phases, and show how our application of these led to the recent discovery of the twist-bend, heliconical smectic phases. Liquid crystal dimers consist of molecules containing two mesogenic groups linked through a flexible spacer, and even- and odd-membered dimers differ in terms of their average molecular shapes. The former tend to be linear whereas the latter are bent, and this difference in shape drives very different smectic behaviour. For symmetric dimers, in which the two mesogenic groups are identical, smectic phase formation may be understood in terms of a microphase separation into distinct sublayers consisting of terminal chains, mesogenic units and spacers, and monolayer smectic phases are observed. By contrast, intercalated smectic phases were discovered for nonsymmetric dimers in which the two mesogenic units differ. In these phases, the ratio of the layer spacing to the molecular length is typically around 0.5 indicating that unlike segments of the molecules overlap. The formation of intercalated phases is driven by a favourable interaction between the different liquid crystal groups. If an odd-membered dimer possesses sufficient molecular curvature, then the twist-bend nematic phase may be seen in which spontaneous chirality is observed for a system consisting of achiral molecules. Combining the empirical relationships developed for smectogenic dimers, and more recently for twist-bend nematogenic dimers, we show how dimers were designed to show the new twist-bend, heliconical smectic phases. These have been designated SmCTB phases in which the director is tilted with respect to the layer plane, and the tilt direction describes a helix on passing between layers. We describe three variants of the SmCTB phase, and in each the origin of the symmetry breaking is attributed to the anomalously low-bend elastic constant arising from the bent molecular structures.

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“…Intensive studies have confirmed that many LC dimers [ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ] and some oligomers [ 50 , 51 , 52 , 53 , 54 ], polymers [ 55 ], and bent-core molecules [ 56 , 57 ] exhibit the N TB phase. Higher oligomers that have more mesogenic units are less likely to form an N TB phase [ 55 ].…”

Section: Introductionmentioning

confidence: 99%

Thioether-Linked Liquid Crystal Trimers: Odd–Even Effects of Spacers and the Influence of Thioether Bonds on Phase Behavior

et al. 2022

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We report the synthesis, phase-transition behavior, and mesophase structures of the first homologous series of thioether-linked liquid crystal (LC) trimers, 4,4′-bis[ω-(4-cyanobiphenyl-4′-ylthio)alkoxy]biphenyls (CBSnOBOnSCB with a wide range of spacer carbon numbers, n = 3–11). All CBSnOBOnSCB homologs exhibited LC phases. Interestingly, even-n and odd-n homologs showed monotropic layered smectic A (SmA) and pseudo-layered twist-bend nematic (NTB) phases, respectively, below a nematic (N) phase. This alternate formation, which depends on spacer chain parity, is attributed to different average molecular shapes, which are associated with the relative orientations of the biphenyl moieties: linear and bent shapes for even-n and odd-n homologs, respectively. In addition, X-ray diffraction analysis indicated a strong cybotactic N phase tendency, with a triply intercalated structure. The phase-transition behavior and LC phase structures of thioether-linked CBSnOBOnSCB were compared with those of the all-ether-linked classic LC trimers CBOnOBOnOCB. Overall, thioether linkages endowed CBSnOBOnSCB with a monotropic LC tendency and lowered phase-transition temperatures, compared to those of CBOnOBOnOCB, for the same n. This is attributed to enhanced flexibility and bending (less molecular anisotropy) of the molecules, caused by the greater bond flexibility and smaller inner bond angles of the C–S–C bonds, compared to those of the C–O–C bonds.

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Fluorinated twist-bend nematogens: the role of intermolecular interaction

Cited by 12 publications

References 45 publications

New patterns of twist-bend liquid crystal phase behaviour: the synthesis and characterisation of the 1-(4-cyanobiphenyl-4′-yl)-10-(4-alkylaniline-benzylidene-4′-oxy)decanes (CB10O·m)

New patterns of twist-bend liquid crystal phase behaviour: the synthesis and characterisation of the 1-(4-cyanobiphenyl-4′-yl)-10-(4-alkylaniline-benzylidene-4′-oxy)decanes (CB10O·m)

Liquid Crystal Dimers and Smectic Phases from the Intercalated to the Twist-Bend

Thioether-Linked Liquid Crystal Trimers: Odd–Even Effects of Spacers and the Influence of Thioether Bonds on Phase Behavior

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