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 (10B1 M7) and [4-(2-methylbutyloxycarbonyl)phenyl] 4-n-heptyl-biphenyl carboxylat e (MBHB), whose structural and ordering properties were studied previously by our group. The deuterium Zeeman (T-1Z) and quadrupolar (T-1Q) spin-latti ce 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 temper ature of the spectral densities obtained from the relaxation times have bee n discussed qualitatively in the phases in which the molecules do not align along the external magnetic field, whereas a quantitative interpretation i n terms of diffusion coefficients of internal and overall molecular motions has been attempted for the smectic phases for which theoretical models wer e available. The results obtained for the two smectogens are discussed and compared with those of other smectogens reported in the literature.