Methylene- and thioether-linked cyanobiphenyl-based liquid crystal dimers CBnSCB exhibiting room temperature twist-bend nematic phases and glasses

Abstract

The twist-bend nematic (NTB) phase is a new heliconical liquid crystal (LC) phase that is associated with spontaneous symmetry breaking for achiral bent LC molecules. Herein, we demonstrate a homologous...

Effects of alkylthio groups on phase transitions of organic molecules and liquid crystals: a comparative study with alkyl and alkoxy groups

“…1. Besides its smaller anisotropy imposed by the longer bond length and smaller bond angle of C-S-C, these effective flexibility and bulkiness (or stronger bend) often cause the rotating alkylthio groups to occupy large space, hindering molecular orientations and packings for LC formation as well as bringing about a decrease in phase transition temperatures [11][12][13][14][15][16][17][18][19][20][21][22][23] and often supercooling LC and Iso phases 18,20,23,26 for lowmolecular-weight organic molecules. Accordingly, it is typical that the alkylthio-based molecules tend to exhibit no LC phase, or even if it does, their LC phases are usually monotropic and occur at narrower or lower temperature compared with the alkyl-and alkoxy-based LC analogues.…”

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

“…For bent LC dimers, the thioether linkage causes the LC phases to be significantly supercooled and vitrified. This is a consequence of the synergy between the enhanced bent shape of the entire molecule and the flexibility of the C−S−C bond, which prevents crystallization [ 68 , 70 , 71 , 72 , 73 , 74 ]. However, such supercooling effects on LC phases were not observed for the thioether-linked trimers in this study, which all crystallized.…”

“…This generally reduces the ability of calamitic molecules to form LCs, by providing greater conformational and steric bulkiness [ 62 , 63 , 64 , 65 , 66 , 67 ]. In contrast, the smaller bond angle of the flexible C–S–C bond synergistically contributes to N TB phase induction and stabilization [ 62 , 63 , 68 , 69 , 70 , 71 , 72 , 73 , 74 ] by enhancing the bent shape and flexibility of LC oligomers with odd- n spacers, as shown in Figure 1 . This is also the case for the higher chalcogen selenoether C–Se–C bond [ 75 ].…”

All Structures Great and Small: Nanoscale Modulations in Nematic Liquid Crystals

“…In recent years there have been impressive developments in the synthesis and characterization of a large number of mesogens that combine molecular flexibility with a bent-core shape while exhibiting nematic phases with nanoscale modulations of the orientational order [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. In attempts to rationalize this nano-scale modulation, some authors simply “miniaturized” known continuum macrostructures insinuating that the twisted structure in the N X is driven by nematic elasticity (a brief review can be found in ref.…”

“…The necessity for the formation of domains in the N SB model was pointed out in the original work. The N X phase: The name is reserved for the experimentally-identified , low- temperature nematic phase, first found in certain classes of achiral, mesogenic dimers [ 1 ] and subsequently in a variety of compounds combining mesogenic features with an overall bent-core (banana-shaped) molecular architecture, see for instance refs [ 8 , 23 ]. For the last decade this phase has often been termed N TB , although its experimentally determined nanoscale modulation features clearly could not stem from twist and/or bend elastic deformations of a uniaxial nematic medium as originally envisaged by R.B.…”