Chalcogen bonding and liquid crystallinity: Understanding the anomalous behaviour of the 4′-(alkylthio)[1,1′-biphenyl]-4-carbonitriles (nSCB)

4′-Alkylseleno-4-cyanobiphenyls, nSeCB: synthesis and substituent effects on the phase-transition and liquid crystalline behaviors

“…As described in section 3, the short n SeCB homologs ( n = 1–6) exhibited a monotropic N phase without any layered Sm phases, and no LC phase was observed in the long n SeCB homologs ( n = 7 and 8). On the other hand, it is known that all previously reported n CB (3 < n ) 29–31 and n OCB ( n = 1–12) 29–32 homologs exhibit enantiotropic or monotropic N and/or smectic A (SmA) phases, whereas all n SCB homologs ( n = 1–11) exhibit exclusively monotropic LC (N or SmA) phases, 33,34 for which the layered SmA phases were observed in their long-chain homologs because of microphase separation facilitated by long alkyl chains. The comparison of the phase-transition behaviors of the four CB homologous series, i.e.…”

“…Table 1 Melting temperature (T m ), crystallization temperature (T c ), isotropic (Iso)-to-nematic (N) phase-transition temperature (T IN ), and the associated entropy changes (ΔS) scaled by the gas constant (R) at T m and T c (ΔS m /R and ΔS c /R) of nSeCB determined by the thermal data obtained from the first cooling and second heating stages at a heating/cooling rate of 10 °C min − long nSeCB homologs (n = 7 and 8). On the other hand, it is known that all previously reported nCB (3 < n) [29][30][31] and nOCB (n = 1-12) [29][30][31][32] homologs exhibit enantiotropic or monotropic N and/or smectic A (SmA) phases, whereas all nSCB homologs (n = 1-11) exhibit exclusively monotropic LC (N or SmA) phases, 33,34 for which the layered SmA phases were observed in their long-chain homologs because of microphase separation facilitated by long alkyl chains. The comparison of the phase-transition behaviors of the four CB homologous series, i.e., nSeCB, nCB, nOCB, and nSCB, revealed that the series with heavy chalcogen atoms led to monotropic or no LC phases for rod-like molecules.…”

“…Therefore, cyanobiphenyls have been used in wide-ranging scientific studies. The alkyl, alkoxy, and alkylthio analogs (nCB, [29][30][31] nOCB, [29][30][31][32] and nSCB, 33,34 respectively) of cyanobiphenyls have been previously reported. However, a homologous series of selenium-containing analogs, that is, 4-alkylseleno-based cyanobiphenyls (nSeCB, Fig.…”

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

“…For relatively small mesogenic core structures, the formation of a highly ordered Sm phase is facilitated by the alkylthio groups. 4,30,33,40,58,59 3.2. Liquid crystal phase structures 3.2.1.…”

The effects of alkylthio chains on the properties of symmetric liquid crystal dimers

“…30,31 At a fundamental level, the inclusion of sulfur provides a demanding challenge to our understanding of structure-property relationships in low molar mass liquid crystals. 5,8,10,11,32,33 Conventional low molar mass calamitic liquid crystalline materials consist of molecules that contain a single rod-like mesogenic unit, which are attached to one or two terminal alkyl chains. In essence the interactions between the semi-rigid mesogenic cores give rise to the liquid crystalline behaviour and the terminal chains lower the melting point.…”