Liquid crystals, halogen-bonded

Mukai, T. and Nishikawa, K., Syntheses and crystal structures of two ionic liquids with halogen-bonding groups 4,5-dibromo- and 4,5-diiodo-l-butyl-3-methylimidazolium trifluoromethanesulfonates. Solid State Sci. 12 (5), 783-788 (2010). 

Bruce DW (2007) Halogen-bonded Liquid Crystals. 126 161-180 Buddhudu S, see Morita M (2004) 107 115-144... 

Prasang C, Whitwood AC, Bruce DW (2008) Spontaneous symmetry-breaking in halogen-bonded, bent-core liquid crystals observation of a chemically driven Iso-N-N phase sequence. Chem Commun 2008 2137-2139... 

Supramolecular liquid crystals have also been reported based on more unusual supramolecular interactions such as halogen bonding (Section 1.8.9).12 Neither of the components in 13.17 are mesomorphic by themselves but the presence of the highly activated iodine atom in pentafluoroiodo-benzene results in a strong N---I interaction (N---I distance 2.81 A by X-ray crystallography). These... 

Both hydrogen bonding and halogen bonding can be used to realize new liquid crystals. Bruce and coworker have first reported that complex 22-n formed by a 4-alkoxy stilbazole and iodopentafluorobenzene showed SmA phases with a mesophase range from 81 to 84 °C. Recently, they also reported trimeric new liquid... 

Given the work that we had carried out with hydrogen-bonded liquid crystals, when we became aware of the possibilities offered by halogen bonding, we considered how it might best be exploited and this led us to prepare and report the first examples of halogen-bonded liquid crystals in 2004. However, before discussing the mesomorphism and structure-function relationships in these systems, there are some important features that need to be considered. 

Introductory Aspects. Relaxation in Molecules or Ions with Covalently Bonded Halogens. Shielding Effects in Covalent Halogen Compounds. Scalar Spin Couplings. Relaxation of Chloride, Bromide and Iodide Ions. Shielding of Halide Ions. Quadru-pole Splittings in Liquid Crystals. Halide Ions in Biological Systems. Studies of the Perchlorate Ion. 

Nguyen HL, Horton PN, Hursthouse MB, Legon AC, Bruce DW (2004) Halogen bonding a new interaction for liquid crystal formation. J Am Chem Soc 126 16-17... 

In the past 2 years or so, halogen-bond-based supramolecular materials have emerged in the context of aU the aforementioned phenomena. No matter whether dealing with photoactive polymers, liquid crystals, or crystals, the directionality of the halogen bond is the key to its success. Its tunability, on the other hand, provides unprecedented possibilities to carry out fundamental studies on light-induced motions unrelated to other types of material systems. The road is wide open, and the first steps taken are presented in the following sections. 

The first example of halogen-bonded liquid crystal with additional functional properties appeared in 2012 when an azobenzene-based system capable of combining a high degree of photoinduced anisotropy and exceptionally efficient SRG formation was reported [12]. The structure of the complex is shown in Fig. 7. The design is rather unusual because of the lack of flexible alkyl chains, which have been reported to suppress the formation of SRGs in LC polymers [56]. 

As weak non-covalent interactions are best observed in crystal structures, it is not surprising that halogen bonding was at first mainly explored in the sohd state, where it now constitutes a reliable design principle for crystal engineering [26, 29, 58-61]. In contrast, applications in solution have been relatively sparse until a few years ago, with one notable exception being the work of Sandorfy in the 1970s [62]. In recent years, however, the number of applications in the liquid phase has seen a steady increase [63, 64]. This especially concerns the development of... 

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