1H NMR study of hydrogen bonding and molecular dynamics of 5CB confined to molecular sieves

Abstract It has been found that the main mechanism of 1 H protons spin–lattice relaxation of bulk 5CB at 200 MHz is its intramolecular motion, namely, the reorientation of CH 2 and CH 3 groups of its alkyl chain. Activation parameters of such motions have been estimated. Drastic decrease in proton spin–lattice relaxation times at the nematic-to-isotropic phase transition can be explained by the activation of molecular translational diffusion and reorientations around long and short molecular axes of bulk 5CB. Our NMR analysis revealed the slowing-down of molecular dynamics of confined 5CB molecules and their fragments. This can be explained by the interaction of some part of 5CB molecules with the surface active Si(Al)–OH centers of MCM matrix via hydrogen bonds of Si(Al)–OH⋯N≡C-type.