14N NMR studies on an optically isotropic liquid crystalline D phase of 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acids (ANBC)

Abstract

14 N nuclear magnetic resonance ( NMR) measurements have been carried out for three members of 4¾ -n-alkoxy-3¾ -nitrobiphenyl-4-carboxylic acids (ANBC-n, where the number of carbon atoms in the alkoxy group, n, is 14, 16, and 22) in the temperature range 400± 500 K. ANBC-16 and -22 show an optically isotropic D phase. The 14 N NMR spectrum of the D phase showed a single peak, which may result from isotropically averaged quadrupole interactions around the 14 N nucleus. Relaxation time measurements indicate the existence of two relaxational processes, faster anisotropic and slower isotropic motions, and suggest that in both cases ANBC molecules act as a dimer. The present 14 N NMR results may be interpreted in the framework of the IPJR model, indicating that the structure of the D phase is a three-dimensional network continuous over the unit lattice.

Phase Transitions of 4‘-n-Hexacosyloxy-3‘-nitrobiphenyl-4-carboxylic Acid (ANBC-26): Two Types of Thermotropic Cubic Phases

“…11,13,19,21,22,24,25,48 For example, Goodby et al 48 tried to explain this phase in terms of "lattice melting"; they considered that the CubD phase is made up of spherical micelles and leaves the remnants of the CubD lattice or clusters of ANBC-n molecules in the next I 1 phase before the complete melting. The possibility of the existence of such weak organization in the I 1 phase was supported by the XRD studies, which were first carried out by Gray et al for n ) 16 13 and recently by us for n ) 15, [18][19][20]22, and 26 also. 30 The XRD photos exhibit a sharp diffraction ring at a small angle, corresponding to a spacing ∼30% shorter than the length of ANBC-n dimer, together with a diffuse ring at a wide angle.…”

“…9,10,14,16,18,23,28,30 For the n ) 16 and 18 homologues, the structure type of the CubD phase has been already identified as space group Ia3d. 10,18,23 By aid of other physical measurements such as NMR 15,22 or dynamic viscoelastic measurements, 20,26 it is now accepted that the structure of the CubD phase is a bicontinuous type, where the rod micelles are connected 3-by-3 to form two sets of interwoven networks, according to Luzzati and Spect's rod-connectors scheme 33 (see the upper part of Figure 6). A somewhat surprising fact 23 is that a 3′-cyano analogue with n ) 18 (4′-n-octadecyloxy-3′-cyanobiphenyl-4-carboxylic acid, ACBC-18) shows a different type of structure with space group Im3m, and the cubic structure is severely dependent on its molecular structure.…”

Structural Studies of 4‘-n-Alkoxy-3‘-nitrobiphenyl-4-carboxylic Acids by Infrared Spectroscopic Analysis

“…Very recently, we found that the D phase exists in all the higher ANBC homologues from n ) 15 to n ) 22, where the molecular length changes from ∼2.9 to ∼3.8 nm. 18 This finding initiated us into more systematic studies on the D phase, 19,20 and in the dynamic viscoelastic measurements for ANBC-16 and -22, we found that the D phase has a very large modulus of ∼10 7 dyn/ cm 2 ()10 6 Pa), which strongly suggests the existence of a threedimensional network structure. 19 In the present work, we first investigated the molecular structure in the D phase of ANBC homologues by use of infrared (IR) spectroscopy.…”

Direct detection of nitrogen-14 in solid-state NMR spectroscopy

“…The above publications spurred an increase in the use of 14 N NMR as a probe of LCs, lipid bilayers and related systems, with a number of reports studying 14 N linewidths and relaxation [180][181][182][183][184][185][186][187][188][189][190][191], and others investigating quadrupolar splittings [192][193][194][195][196][197][198][199][200][201][202][203][204][205][206][207][208][209][210].…”