Molecular Structure, Conformation and Orientational Order of Para-Azoxy-Anisole (PAA) in the Nematic Phase, and Their Temperature Dependence: Results from a Deuterium and Proton Magnetic Resonance Study

Abstract Deuterium and proton magnetic resonance data of fully deuterated, partially deuterated on the rings and on the methyl groups, and fully protonated nematic para-azoxy-anisole (PAA) are analysed self-consistently in terms of molecular structure, conformation and orientational order using a single order parameter model. The values and temperature dependences of the nematic order parameter and of some conformational averages are deduced. These results are discussed in the light of results obtained by other methods: X-ray diffraction, quantum chemistry calculations, macroscopic measurements. The influence of partial deuteration, density and temperature on molecular properties is discussed in detail. A simple picture for the nematic phase is proposed. A method and simple relations are given to analyse NMR data of PAA dissolved in fluid anisotropic media.