Nuclear spin-lattice relaxation rate dispersion study of H-1 and F-19 in the isotropic phase of a singly fluorinated liquid crystal 4'-butoxy-3-fluoro-4-isothiocyantotolane (4OTOLFo) points to their differing relaxation pathways and hence sensitivity to qualitatively different time modulations. In particular fluorine nuclear spins, with strong lattice coupling (larger by two orders) extending to very low frequencies, detect slowly relaxing local structures via the spin-rotation interaction. The field-cycling technique used to carry out these very low frequency measurements, provides for level crossing of the two nuclear species at low enough jump fields, facilitating an additional mechanism of cross-relaxation in the strong coupling limit. (C) 2012 Elsevier B.V. All rights reserved.