H-1 Nuclear Magnetic Resonance Study of an Incommensurate-Commensurate Phase Transition in a Dimesogenic Liquid Crystal

Abstract

H-1 nuclear magnetic resonance (NMR) was employed in order to probe an incommensuratecommensurate phase transition in a dimesogenic liquid crystal, N-[4-(6-cholesteryloxycarbonyl) pentyloxy]-4-n-butylazobenzene (KI5A). The recrystallization and the isotropic phase transitions exhibited a discontinuous first-order nature in the H-1 NMR spin-lattice (T (1)) and in the spin-spin relaxation time (T (2E) ) measurements, and an incommensurate smectic A (S (Ainc)) to commensurate helical smectic C (S* (C) ) liquid crystalline phase transition was marked by a discontinuity in the NMR line splitting representing the orientational order. Furthermore, T (1) and T (2E) showed distinct temperature dependencies in the S (Ainc) phase and in the S* (C) phase.