https://orcid.org/0000-0001-5167-7183
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ABSTRACT
The synthesis and characterisation of two homologous series of non-symmetric dimers are reported, the 1-(4-methoxybiphenyl-4ʹ-yl)-6-(4-alkylanilinebenzylidene-4ʹ-oxy)hexanes (MeOB6O.m, m = 1–10) and 1-(4-methoxybiphenyl-4ʹ-yl)-6-(4-alkyloxyanilinebenzylidene-4ʹ-oxy)hexanes (MeOB6O.Om, m = 1–9). All 10 members of the MeOB6O.m series exhibit the conventional nematic phase. At lower temperatures, the members with m = 1–7 formed the twist-bend nematic phase, NTB, whereas for m = 8–10 smectic behaviour replaced the NTB phase. All nine members of the MeOB6O.Om series also show the conventional nematic phase and for m = 1–3, a strongly monotropic NTB phase is also observed. The alkyloxy terminated dimers show the higher values of TNI and TNTBN. For both series, the values of TNI and TNTBN show a modest alternation and in the same sense as m is increased. These observations suggest that the spatial uniformity of molecular curvature is important in driving the formation of the NTB phase. The observation of smectic behaviour is attributed to the molecular inhomogeneity arising from the long terminal alkyl chain driving microphase separation. The transitional behaviour of these series is compared to those of the corresponding cyanobiphenyl-based series and overarching observations discussed.
Graphical Abstract
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