Orientational Order in Nematic and Smectic A Phases of Three Closely Related Compounds 4 4-di-n-Heptylazobenzene 4 4-di-n-Heptyl- and 4 4-di-n-Octylazoxybenzene

Abstract

The orientational ordering in the three related compounds 4,4-di-n-heptyl-d₂-azobenzene-d, (HB-d₁₂), 4,4′-di-n-heptyl-d₂-azoxybenzene-d, (HAB-d₁₂) and 4,4-di-n-octyl-d₂-azoxybenzene-d₈ (OAB-d₁₂) has been monitored using deuteron N.M.R. spectroscopy. In these non-rigid molecules it is possible to obtain only the elements of local order matrices. For the aromatic rings these are found to be axially symmetric within the precision of our measurements. The temperature dependences of the local order parameters for the aromatic rings are compared with those predicted by McMillan's theory of smectic A phases.