Investigation of the dynamics of two chiral smectogens by means of H-2 NMR

In this article we report a dynamics investigation of two chiral smectogens, 1-methylheptyl 4′-(4′′-n- decyloxybenzoyloxy)biphenyl-4-carboxylate (10B1M7) and [4-(2-methylbutyloxycarbonyl) phenyl] 4-n-heptyl- biphenyl carboxylate (MBHB), whose structural and ordering properties were studied previously by our group. The deuterium Zeeman (T1Z) and quadrupolar (T1Q) spin-lattice relaxation times of two differently deuterated isotopomers of 10B1M7 and one of MBHB have been measured across the whole mesophasic range by means of the broadband Jeener-Broekaert pulse sequence. The trends against temperature of the spectral densities obtained from the relaxation times have been discussed qualitatively in the phases in which the molecules do not align along the external magnetic field, whereas a quantitative interpretation in terms of diffusion coefficients of internal and overall molecular motions has been attempted for the smectic phases for which theoretical models were available. The results obtained for the two smectogens are discussed and compared with those of other smectogens reported in the literature