TY - JOUR
T1 - Cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase
AU - Paterson, Daniel A
AU - Abberley, Jordan P
AU - Harrison, William T A
AU - Storey, John
AU - Imrie, Corrie T
PY - 2017
Y1 - 2017
N2 - The synthesis and characterisation of several members of the 1,ω-bis(4-cyanobiphenyl-4′-yl) alkane (CBnCB) and the 1-(4-cyanobiphenyl-4′-yloxy)-ω-(4-cyanobiphenyl-4′-yl) alkane (CBnOCB) homologous series are reported. The new odd members described CB5CB, CB13CB, CB4OCB, CB8OCB and CB10OCB all exhibit twist-bend nematic and nematic phases. The members of these series already reported in literature, CB7CB, CB9CB, CB11CB and CB6OCB, were also prepared in order to allow for a direct comparison of their transitional properties. The properties of these dimers are also compared to those of the corresponding members of the 1,ω-bis(4-cyanobiphenyl-4,-yloxy) alkanes (CBOnOCB). For any given total spacer length, for odd members of these series, the nematic–isotropic transition temperatures and associated entropy changes are greatest for the CBOnOCB dimer and lowest for the CBnCB dimer. These trends are understood in terms of molecular shape. For short spacer lengths, the twist-bend nematic–nematic transition temperature (TNTB N ) is higher for the CBnOCB series than for the CBnCB series but this is reversed as the spacer length increases. Of the CBOnOCB dimers, a virtual value of TNTB N was estimated for CBO3OCB and TNTB N was measured for CBO5OCB. These values are considerably lower than those observed for the corresponding members of the CBnCB or CBnOCB series. The dependence of TNTB N on molecular structure is discussed not only in terms of the molecular curvature but also in the ability of the molecules to pack efficiently. As the temperature range of the preceding nematic phase increases, so the twist-bend nematic–nematic transition entropy change decreases and the transition approaches second order for the longer spacers. For comparative purposes, the transitional behaviour of the even-membered dimers CB6CB, CB5OCB and CBO4OCB is reported and differences accounted for in terms of molecular shape.
AB - The synthesis and characterisation of several members of the 1,ω-bis(4-cyanobiphenyl-4′-yl) alkane (CBnCB) and the 1-(4-cyanobiphenyl-4′-yloxy)-ω-(4-cyanobiphenyl-4′-yl) alkane (CBnOCB) homologous series are reported. The new odd members described CB5CB, CB13CB, CB4OCB, CB8OCB and CB10OCB all exhibit twist-bend nematic and nematic phases. The members of these series already reported in literature, CB7CB, CB9CB, CB11CB and CB6OCB, were also prepared in order to allow for a direct comparison of their transitional properties. The properties of these dimers are also compared to those of the corresponding members of the 1,ω-bis(4-cyanobiphenyl-4,-yloxy) alkanes (CBOnOCB). For any given total spacer length, for odd members of these series, the nematic–isotropic transition temperatures and associated entropy changes are greatest for the CBOnOCB dimer and lowest for the CBnCB dimer. These trends are understood in terms of molecular shape. For short spacer lengths, the twist-bend nematic–nematic transition temperature (TNTB N ) is higher for the CBnOCB series than for the CBnCB series but this is reversed as the spacer length increases. Of the CBOnOCB dimers, a virtual value of TNTB N was estimated for CBO3OCB and TNTB N was measured for CBO5OCB. These values are considerably lower than those observed for the corresponding members of the CBnCB or CBnOCB series. The dependence of TNTB N on molecular structure is discussed not only in terms of the molecular curvature but also in the ability of the molecules to pack efficiently. As the temperature range of the preceding nematic phase increases, so the twist-bend nematic–nematic transition entropy change decreases and the transition approaches second order for the longer spacers. For comparative purposes, the transitional behaviour of the even-membered dimers CB6CB, CB5OCB and CBO4OCB is reported and differences accounted for in terms of molecular shape.
KW - cyanobiphenyl
KW - liquid crystal dimers
KW - molecular modelling
KW - twist-bend nematic phase
UR - http://www.scopus.com/inward/record.url?scp=85010700162&partnerID=8YFLogxK
U2 - 10.1080/02678292.2016.1274293
DO - 10.1080/02678292.2016.1274293
M3 - Article
AN - SCOPUS:85010700162
SN - 0267-8292
VL - 44
SP - 127
EP - 146
JO - Liquid Crystals
JF - Liquid Crystals
IS - 1
ER -