Mesomorphic behaviour of carbazole-N-hexyl acrylate liquid crystal and non-reactive analogues

A novel carbazole-N-hexyl acrylate liquid crystal monomer was synthesised to compare its mesomorphic behaviour with several of its non-polymerisable analogues. The compounds exhibit nematic liquid crystalline properties driven by their core-driven molecular anisotropy, incorporating a rigid, highly conjugated molecular core with flexible aliphatic terminal groups. A hexyl chain was strategically incorporated at a lateral position to induce high solubility in organic solvents and lower the phase transition temperatures. Upon cooling, the photopolymerisable acrylate monomer transforms into a nematic phase at 95°C. Owing to a thermodynamically slow crystallisation process governed by high supercooling viscosity kinetics, the material enters an extensive phase coexistence regime below 46°C, where the marble texture and crystalline domains coexist down to −20°C. DSC analysis reveals a prominent cold crystallisation exotherm and a significant melting endotherm during the second heating cycle, with no observable exothermic peaks during the cooling scans. This behaviour contrasts sharply with its non-polymerisable analogues, which display conventional monotropic mesomorphism featuring a sharp melting peak upon heating, followed by distinct isotropic-to-nematic and nematic-to-crystalline exotherms upon cooling. The delayed crystallisation behaviour of the acrylate monomer may be attributed to suppressed crystal nucleation kinetics caused by molecular entanglement of the bulky terminal acrylate groups.