NMR-STUDY OF THE T(1) RELAXATION DISPERSION IN THE SMECTIC MESOPHASE OF 4-CHLOROPHENYL 4-UNDECYLOXYBENZOATE

An experimental study of the Larmor frequency dependence of the proton spin-lattice relaxation time [T1(nu(L))] was carried out in the range of nu(L) = 7 to 30 MHz. Two relaxation times describing the evolution of the longitudinal magnetization have been found to have different behaviors. One of them has been assigned to the relaxation of the protons belonging to the alkyl chain-T1alkyl(nu(L))-. The T1alkyl(nu(L)) dispersion behaves normally without signs of H-1-Cl-35 cross relaxation. The second one, called T(a-c), has a partial contribution from the protons bonded to the molecular core and those of the alkyl chain. Well defined H-1-Cl-35 quadrupole dips (QD) have been observed in the T(a-c)(nu) dispersion curve, due to a cross-relaxation process between the core protons and the chlorine nucleus of the molecule. The shape of the dips are not symmetric, and cannot be fitted by Gaussian or Lorentzian functions. Computer simulations with asymmetric functions previously used in line shape analysis of incommensurate systems and organic glasses are discussed.