On the nematic-nematic phase transition in mixtures composed of sheet-shaped palladium organyls and apolar organic solvents

Abstract

The three sheet-shaped palladium organyls la-c exhibit lyotropic nematic properties in apolar organic solvents. The occurrence of two nematic lyomesophases was verified by the investigation of the orientational properties of these liquid crystalline systems. In cells with obliquely deposited SiO, layers, the director of the high temperature phase N2 is aligned in a homogeneous, planar manner. In the low temperature phase N,, a different orientational pattern is observed. The specific pattern type depends on the deposition conditions of the SiO, layers. In samples homeotropically aligned in the N, phase, the director is tilted away from the cell normal after the transition into the N, phase. These changes of orientation are reversible. The experimental observations presented here support our proposed model for the structural change at the nematic-nematic phase transition.

Effect of Slow Cooling on a Discotic Nematic Liquid Crystal: Evidences for Nematic–Nematic Transitions

“…Such a nematic-nematic transition involving tilting of the molecules with respect to the columnar axis is reported for a FIGURE 9 Comparison of lateral peaks of N 1 , N 2 , and N 3 phases. 22 D. Vijayaraghavan and S. Kumar lyotropic nematic system consisting of sheet-shaped palladium organyls [23]. The proposed model [23] also involves stacking of the sheet-like molecules to give rise to short column-like aggregates without any intra-and intercolumnar molecular order between the aggregates.…”

“…22 D. Vijayaraghavan and S. Kumar lyotropic nematic system consisting of sheet-shaped palladium organyls [23]. The proposed model [23] also involves stacking of the sheet-like molecules to give rise to short column-like aggregates without any intra-and intercolumnar molecular order between the aggregates. In our case, the correlation length (n) in the columnar direction can be calculated from the width of the columnar XRD reflections by using the relation n ¼ 2p=Dq, where Dq ¼ q 1 À q 2 : q 1 ¼ 4p sin h 1 =k; q 2 ¼4p sin h 2 =k : h 1 and h 2 are the h values corresponding to the columnar peak at full width at half maximum (FWHM).…”

Thermotropic Liquid-Crystalline Materials Based on Supramolecular Coordination Complexes

“…In the case of the chloro-and bromobridged metalla-cycles (Figure 1), the nematic phase was stabilized upon addition of 2,4,7trinitrofluorenone (TNF), suggesting intercalation of TNF between the disk-shaped columnar stacks. Following this initial study, analogous systems built from either palladium or platinum metal centers were prepared and their liquid-crystalline properties examined [21][22][23][24][25], showing similar organization in the lyotropic mesophases. Later on, analogous platinum Schiff base pyridyl type metalla-cycles were synthesized by MacLachlan and his coworkers [26].…”

Amphotropic Properties of Multi-Palladium and -Platinum Liquid Crystals [1]

“…This is in contrast to the usual observation of increasing thermal fluctuations with increasing temperature. The two phases are also indicated by orientational [31,32], electro-optical [31,32] and spectroscopic [16,33] studies.…”