Deuterium spin relaxation and spectral densities in the liquid crystal 4-n-pentyloxybenzylidene-4′-n-heptylaniline-2, 3, 5, 6,-d4

Abstract

We report on the measurements of the deuterium Zeeman and quadrupolar spin‐lattice relaxation times and the deuterium spin–spin relaxation time in the nematic, smectic A and C phases of a ring‐deuterated 4‐n‐pentyloxybenzylidene‐4’‐n‐heptylaniline. The spectral densities of motion J₀(0), J₁(ω₀), and J₂(2ω₀) at ω₀/2π=14.73 MHz were separated from the above relaxation times. A simple ‘‘rotational diffusion in a cone’’ model was used to account for the observed increase in J₁(ω₀) and the decrease in J₂(2ω₀) in the nematic phase as the temperature was decreased. The model of rotational diffusion in a restoring potential was also examined. Our data can be understood qualitatively using the strong collision model or semiquantitatively using the cone model. The restricted rotational diffusion in a cone model supports the molecular reorientations being in the intermediate motion regime (ω₀τ≂1). Additional information on J_p(ω) such as its frequency dependence are required to check the various assumptions used in the above motional models.