Odd–even effect in biphenyl‐based symmetrical dimers with methylene spacer – evidence of the B4 phase

Abstract

A series of 4-decyloxy-49-hydroxybiphenyl esters of a,v-alkanedicarboxylic acids containing two mesogenic units connected by a methylene spacer was synthesized. The mesogenic properties of the compounds were investigated by polarising optical microscopy, differential scanning calorimetry and X-ray diffraction methods. A strong influence of the spacer length and its parity on the mesomorphic properties was found. A dramatic odd-even effect was observed for the clearing temperatures and entropies. Compounds with an even number of carbon atoms in the methylene spacer formed tilted smectic phases, whereas compounds with an odd number of carbon atoms in the spacer exhibited the B4 phase, characteristic of bent-shaped molecules.

From Sponges to Nanotubes: A Change of Nanocrystal Morphology for Acute‐Angle Bent‐Core Molecules

“…The signals are significantly broadened due to the finite size of the nanocrystallites, as usually observed for the B 4 phase . The commensurability of the low‐angle diffraction signals confirms a lamellar‐type local crystallographic structure with the layer thickness d (for compound n20 d ≈4.4 nm, for n16 d ≈3.9 nm, and for n8 d ≈2.8 nm) corresponding roughly to the molecular length measured from the naphthalene apex to the end of the alkyl chain, or to the distance between the ends of the alkyl chains for the molecules with a 50–60° opening angle between the arms.…”

Banana-calamitic dimers: unexpected mesophase behaviour by variation of the direction of ester linking groups in the bent-core unit

“…In the meantime Takezoe et al [14,15] have proved that simple odd-numbered calamitic dimers are able to form a polar smectic phase if a special ratio between the length of the terminal aliphatic chains and the spacer is fixed, that means a short spacer and long terminal hydrocarbon groups. Bialecka-Florjanczyk et al [16] reported an odd-even effect in a series of dimers: only the homologues having an odd-numbered spacer are able to form the banana phase B 4 . For a dimer with a relatively long even-numbered spacer, a slightly bent molecular shape has been predicted in a smectic phase to explain properties which are strongly reminiscent of B 7 phases formed by banana-shaped molecules [17].…”

Symmetric bent-shaped liquid crystal dimers showing transitions between optically uniaxial and biaxial smectic phases

“…[14][15][16] Likewise, columnar structures may be formed if core-core interactions are dominant. [17] Even in-plane smectic helicoidal structures have been described [18] and, more recently, twist-bend nematic phases. [19,20] However, regardless of their particularities, all these mesophases formed by bent dimers share the tilted nature of their constituent layers or layer fragments which springs from the conformational characteristics of the oddmembered spacer.…”