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

Abstract

The effects of the alkylthio groups on the phase transition behavior of organic liquid crystal molecules were examined by comparing them with the effects of alkyl and alkoxy groups.

Alkylthio-based asymmetric liquid crystals: unravelling the substituent effects and intercalated cybotactic nematic and smectic phases

“…These contacts are ascribable to the CQOÁ Á ÁH hydrogen bonds, which are typically observed in phenyl benzoates. 36,65,66 A similar half-slide packing structure was also observed in PBB-1 [Fig. 8(b)].…”

“…When n is increased to 2, the enhanced and significant conformational flexibility and steric bulkiness effects of the alkylthio groups could facilitate crystal melting for SS2 and lower its T m below that of SS1, which in turn masks the steric odd-even n effect on the phase transition temperatures for short alkylthio-containing homologs (n = 1-3). 36 Consequently, the T m of SSn gradually and monotonically decreases when n is increased from 1 to 8.…”

“…Nonetheless, in the case of SS1 which also show a similar SmA phase, 34 PBB-core and methylthio moieties are clearly segregated into each domain in its crystalline state rather than such half-shifted packing. 36 This microphase separation was interpreted by the large dispersion forces and enhanced affinities between more polarizable core p-systems, afforded by the sulfur atoms. This is also likely to be linked to that the influences of those attractive interactions from the sulfur atoms become more pronounced in denser states such as Cr phases.…”

“…As a result, compared to their alkyl-and alkoxy-based counterparts, alkylthio-containing rod-like molecules usually exhibit LC phases monotropically, only across a narrow temperature range, or not at all. [1][2][3][4][5]29,[34][35][36] On the other hand, enantiotropic LC phases were observed from some types of alkylthio-based calamitic molecules. [4][5][6][7][8][29][30][31][32][33][34][35][36][37][38][39][40] However, there has been no report of covalent-bonded homologous series in which all members exhibit enantiotropic LC phases, while only one such hydrogen-bonded homologous series is known.…”

“…[1][2][3][4][5]29,[34][35][36] On the other hand, enantiotropic LC phases were observed from some types of alkylthio-based calamitic molecules. [4][5][6][7][8][29][30][31][32][33][34][35][36][37][38][39][40] However, there has been no report of covalent-bonded homologous series in which all members exhibit enantiotropic LC phases, while only one such hydrogen-bonded homologous series is known. 35 The lack of dataset of more versatile covalent-bonded homologous series showing the enantiotropic LC phases allowed us only to infer the effects of alkylthio groups on LC behaviours based on few of its homologous series.…”