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

1H 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 1H NMR spin-lattice (T1) and in the spin-spin relaxation time (T2E) measurements, and an incommensurate smectic A (SAinc) 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, T1 and T2E showed distinct temperature dependencies in the SAinc phase and in the S ∗ C phase.