Photonic Bandgap in Achiral Liquid Crystals—A Twist on a Twist

Abstract

Achiral mesogenic molecules are shown to be able to spontaneously assemble into liquid crystalline smectic phases having either simple or double‐helical structures. At the transition between these phases, the double‐helical structure unwinds. As a consequence, in some temperature range, the pitch of the helix becomes comparable to the wavelength of visible light and the selective reflection of light in the visible range is observed. The photonic bandgap phenomenon is reported for achiral liquid crystals.

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)

“…In a cell treated for planar alignment, faint lines appeared on cooling the smectic A phase which became stronger on further cooling. These changes on cooling from the homeotropic SmA texture to a dynamic schlieren texture and back to a homeotropic texture suggests a sequence of SmC TB phases similar to that we have recently described for CB6O· m homologues having long terminal chains, 10 and shown schematically in Fig. 13.…”

“…8,9 It appears that a range of variants of this phase, similar to the SmC* subphases observed for chiral molecules, are possible. 10 The key structural requirement for the observation of the N TB phase is a bent molecular structure and this is most often realised using odd-membered liquid crystal dimers. These consist of molecules containing two mesogenic groups connected by a spacer having an odd number of atoms (see, for example, ref.…”

“…8,9 It appears that a range of variants of this phase, similar to the SmC* subphases observed for chiral molecules, are possible. 10…”

“…1, with n = 6 and m = 10–12, 14, 16, and 18. 7,10,49 For terminal chain lengths with m < 10, twist-bend and conventional nematic phases are observed but no smectic behaviour is seen. By analogy with other non-symmetric dimer series, 50 if the terminal chain in a CB n O· m series was significantly shorter than the spacer length then smectic behaviour should emerge, and to investigate this intriguing possibility here we report the synthesis and characterisation of the 1-(4-cyanobiphenyl-4′-yl)-10-(4-alkylanilinebenzylidene-4′-oxy)decanes (Fig.…”

Bent-Structure Liquid Crystalline Dimers Containing a Cholesteryl Group Exhibiting Blue Phases

“…3−7 Significantly, Imrie has discovered a chiral liquid crystal system composed of achiral bent-structure dimeric liquid crystal molecules, bringing about widespread attention in the field of soft materials, 8 and recently, the double helical structures in an achiral smectic liquid crystal system have also been reported. 9,10 As for the chiral bent-structure liquid crystals, many of them were synthesized containing a cholesteryl group, since the cholesterol could be linked as a liquid crystal core, which is easy to obtain and provide great liquid crystal properties. 11 The mesophase behaviors of the chiral bent-structure liquid crystals are more complex than those of the achiral ones.…”