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With mandelic acid (MA) as the chiral core, two series of non-symmetric liquid crystal (LC) dimers have been synthesised by changing the rigidity of the side-arms, namely the DBM-nC2B series and the DBBM-nC2B series. In the DBM-nC2B series, one side-arm is the same, while the length of the flexible tail of the other side-arm increases from 0 to 4. The same is true of the DBBM-nC2B series. Chemical structures and LC properties of the two series LC dimers were characterised by FT-IR, 1H NMR, 13C NMR, DSC, TGA and POM. The results show that the DBM-nC2B series LC dimers display the nematic phase (N), and the DBBM-nC2B series LC dimers exhibit the chiral nematic phase (N*). It shows that the side-arm should have sufficient rigidity for MA to induce the N* phase. In the same series, when the length of the flexible tails of the side-arm increases from 0 to 4, it does not change the mesophase, while it has some effect on the melting temperature (Tm), the clearing temperature (TN(*)I), and mesophase range of the dimers. The molecular length-width ratio (l/w) and dipole moment (μ) were used to explain the variation of Tm and (TN(*)I) of LC dimer. [ABSTRACT FROM AUTHOR]

Two series of symmetric liquid crystal dimers, namely 1F and 3F, have been synthesised by varying the length of the flexible odd spacer. The melting temperatures and clear points of the 3F series are higher than those of the 1F series. The 1F series only exhibits nematic phase, while the 3F series displays both smectic A and nematic phases. As the length of the flexible spacer increases, the dominance of the smectic phase becomes more pronounced. This phenomenon may be attributed to the combined effect by the polar end group CF3 and the long flexible spacer on the molecular conformation. [ABSTRACT FROM AUTHOR]