Oligomeric odd-even effect in liquid crystals

Odd-even effects, oscillations in properties of materials comprised of an odd or even number of connected repeating units, are well-known phenomena in materials science. In organic materials, they are usually associated with the number of methyl groups in aliphatic chains. In this work, we unveil multiple signatures of a new odd-even effect in liquid crystals that occurs at the larger scale of molecular moieties that by themselves express liquid crystalline behavior. We demonstrate that oligomeric liquid crystals, with n=1-4 number of rigid mesogenic segments connected by flexible aliphatic chains with an odd number of methyl groups, produce an odd-even effect in optical anisotropy and the bend elastic constant of the liquid crystal oligomer. This effect is different from the usual odd-even effects with respect to the parity of carbon atoms in an aliphatic chain and can be understood in term of the average molecular shape and the associations between n-mers based on the packing of these shapes. We also show that, in spite of the fact that there is no long-range electron density modulation, careful analysis of synchrotron SAXS results can provide important information about the molecular associations in the N and NTB phases that other techniques cannot access. This novel odd-even effect opens up a new mode to optimize phase and optical behavior.