Hydrogen‐Bonded Complexes between 4‐Alkoxystilbazoles and Fluorophenols: Solid‐State Structures and Liquid Crystallinity

Abstract

48 new hydrogen-bonded complexes have been prepared by combining 16 fluorophenols of general formula C(6)F(n)H(5-n)OH with three different alkoxystilbazoles (butyloxy-, octyloxy- and dodecyloxy-). Single-crystal X-ray structures were obtained for 10 of the 16 complexes of octyloxystilbazole from which it was found that most of the structures could be collected into one of two groups according to both the motif shown by the complex and by the solid-state packing. Because all but one crystallised in the P1 space group, meaningful comparisons could be drawn and it was observed that six structures were extremely close in nature so that significant molecular overlap was found. On this basis, doubt is cast on the significance of some of the weaker intermolecular contacts found in the solid state. 40 of the new complexes showed liquid-crystal properties and it was found that although complexes of butyloxystilbazole were all nematic, almost all of those with dodecyloxystilbazole showed a smectic A (SmA) phase. Complexes of octyloxystilbazole showed a mixture of both. Structure/property correlations showed that clearing points were independent of the pK(a) of the phenol. The most stable mesophases were found when the fluorophenol contained a fluorine at the 2-position, which was interpreted in terms of the formation of an intramolecular H⋅⋅⋅F hydrogen bond to give a six-membered ring linking the two components into a stable, coplanar conformation. The least stable mesophases were found when no such ring formation was possible and the phenol was relatively free to move.

Polymorphism of hydrogen-bonded star mesogens – a combinatorial DFT-D and FT-IR spectroscopy study

“…[56][57][58][59][60][61][62][63][64] In contrast to these binding motifs, the interaction between phenol (PH) and pyridine (pyr) is signicantly weaker leading to a higher exibility and enhances structural diversity. 46,[65][66][67] In order to nd a suitable starting geometry for our study, we initially investigated the PH/pyr interaction by conformational analysis (details see ESI, Chapter 3 †). Hereby, we obtained 121 optimized conformer geometries, which differ in their energies (zero point energy ZPE and Gibbs free energy G; ESI Fig.…”

Halogen‐ and Hydrogen‐Bonded Salts and Co‐crystals Formed from 4‐Halo‐2,3,5,6‐tetrafluorophenol and Cyclic Secondary and Tertiary Amines: Orthogonal and Non‐orthogonal Halogen and Hydrogen Bonding, and Synthetic Analogues of Halogen‐Bonded Biological Systems

“…Solvents and anti-solvents are given in Table 2. Single-crystal X-ray structures were determined as described elsewhere; [37] CCDC deposition numbers are given in Table S1.…”

Hydrogen Bonding for Supramolecular Liquid Crystals

“…The stability of liquid crystalline phases of these complexes is 22-n < 24 < 25-n < 23-n, this would suggest that p-C 6 F 4 -I is a more effective terminal group than p-C 6 F 4 -F for phase stabilization, probably due to the large polarizability anisotropy. Hydrogen bonded complexes between fluorophenols 27-31 and different alkoxy stilbazoles 26 were also studied [45], nematic and smectic A phases were found in these complexes by the formation of H···N and H···F hydrogen bonds. The most stable mesophases were found when the fluorophenol contained a fluorine at the 2-position, which was interpreted in terms of the formation of an intramolecular H···F hydrogen bond to give a six-membered ring linking the two components into a stable, coplanar conformation.…”