Distinct twist-bend nematic phase behaviors associated with the ester-linkage direction of thioether-linked liquid crystal dimers

Yuki Arakawa,Chenhui Zhu,Kenta Komatsu,Jun Feng,Hideto Tsuji

doi:10.1039/d0ma00746c

Abstract

Two homologous series of thioether-linked liquid crystal dimers with oppositely directed esters,viz.CBCOOnSCB and CBOCOnSCB, exhibit largely different helical pitches in the NTBphase, which are ascribed to their molecular bend or biaxiality.

Highlights

The N–NTB phase-transition peak was identified as a first-order-like transition with a DSNNTB/R value of 0.54, which differs from the second-order-like transition behavior typically observed for twist-bend nematogens
The NTB phase of CBCOO8SCB crystallized at 76 1C and the dimer bearing the longest spacer (i.e., CBCOO10SCB) exhibited the NTB phase, but underwent crystallization at approximately 90 1C, as can be seen from the differential scanning calorimetry (DSC) curves (Fig. S11 and S12, Electronic supplementary information (ESI)†); the NTB phases could be 262 | Mater
We found that CBOCO4SCB exhibited the usual optical texture of the NTB phase with clear stripes [Fig. 4(c)], which is distinct from the obscure thin stripes found in CBCOO4SCB [Fig. 4(a)]

Summary

Introduction

PaperTo date, a number of bent LC dimers composed of two mesogenic structures connected with an odd-numbered oligomethylene spacer have been shown to exhibit the NTB phase.[36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57] In addition, several LC oligomers (e.g., trimers,[53,58,59,60,61,62,63] tetramers,[58,59,64] a hexamer,[65] and other types of oligomers66–69), polymers,[70] and bent-core molecules[71,72] have been identified as twist-bend nematogens. CBOCO6SCB exhibited a remarkably stable NTB phase when supercooled to room temperature, with vitrification taking place at 14 1C to form the NTBG phase; this behavior is similar to that of CBOCO4SCB.[53] the N–NTB phase transition at 94.9 1C is similar to the secondorder-like phase-transition typically observed for the majority of twist-bend nematogens.

Results

Conclusion