Incompatibility-Driven Self-Organization in Polycatenar Liquid Crystals Bearing Both Hydrocarbon and Fluorocarbon Chains

The synthesis and liquid crystal properties are reported for tri-and tetra-catenar mesogens in which both hydrocarbon and semiperfluorocarbon chains have been incorporated. In the tricatenar mesogens, the lamellar spacing in the smectic C phase of the all-hydrocarbon mesogen almost doubles when the isolated hydrocarbon chain is replaced by a semiperfluorinated chain on account of the localized segregation in different sublayers between the two chain types. In the tetracatenar materials, the replacement of at least one hydrocarbon chain by semiperfluorocarbon chains is sufficient to promote columnar phase formation, but when the molecule has two hydrocarbon chains at one end and two semiperfluorocarbon chains at the other, the requirement for localized phase segregation leads to the formation of a rectangular phase with very large lattice parameters. The juxtaposition of terminal chains of different nature within the same molecular structure thus leads to a reduction in mesophase symmetry and the emergence of more complex supramolecular organization

"Smart" molecular engineering of metallomesogens based on Pt(II) terpyridine coordination complexes

A series of ionic tetracoordinated Pt(II) complexes based on terpyridine ligand were synthesized and characterized. Their chemical structures were engineered by using counterions of different coordination strengths and dimensions, namely non-coordinating BF4, weakly coordinating bulky gallate units, and small and strongly coordinating chlorine (Cl). The complexes containing lipophilic gallate units exhibit low temperature liquid crystalline properties. The mesomorphic properties were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction studies (SWAXS). Photophysical properties were determined in solution and condensed states

Emissive Zn(II) metallomesogen based on tridentate terpyridine ligand

A low temperature liquid crystal based on luminescent terpyridine Zn(II) complex is presented. The induction of the mesomorphic properties was achieved using a lipophilic gallate unit as ancillary ligands. The mesomorphic properties were investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TA) and X-ray scattering (SWAXS) of bulk materials, while the optical properties of the complex were investigated in solution and in condensed liquid crystalline states

Comparative Analysis of Self-Aggregation of Liquid Crystalline Pt(II) Complexes in Solution and in Neat Films

Two novel cycloplatinated complexes that differ by the presence/absence of a lateral fused cyclopenteno ring, respectively, were prepared. Although contributing to only a few percentage of the whole molecular volume, the presence of this aliphatic protuberance appears to be essential for the emergence of liquid crystalline behaviour. This pair of two similar compounds, non-mesomorphic complex and mesomorphic complex, was prepared as a model to assess the possible link of the self-aggregation in solution with the appearance of the liquid crystallinity in molten state. NMR dilution studies in CDCl3 solution and X-ray diffusion study in neat films show qualitative similarity of the aggregated structures formed by liquid crystalline complex. Solution studies may therefore be a useful additional tool to the characterization of the liquid crystalline properties and other self-association processes of Pt(II) complexes. © 2021We thank Northumbria University, CNRS, University of Strasbourg and Russian Foundation for Basic Research (project No. 18-03-00232A ) for the support of this work

Controlling the lateral aggregation of perfluoroalkylated hexa-peri-hexabenzocoronenes

The investigation of two hexa-peri-hexabenzocoronene (HBC) derivatives carrying linear or branched perfluoroalkylated side chains is reported. Polycondensed aromatic hydrocarbons (PAH) such as HBC derivatives are well known to self-organize to form highly ordered monomolecular stacks, which in turn show a concentration- and solvent-dependent lateral aggregation. However, possible applications of self-assembled HBC derivatives require linear, laterally non-aggregated columnar structures. According to powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC), HBC derivatives with linear perfluoroalkylated side chains show liquid crystalline (LC) properties whereas those with branched perfluoroalkylated side chains have an amorphous structure. The stacking behaviour and the lateral aggregation are found to be greatly influenced by changes in the medium, as shown by fluorescence spectroscopy and cryo-scanning electron microscopy (cryo-SEM)

Green-blue light-emitting platinum(II) complexes of cyclometallated 4,6-difluoro-1,3-dipyridylbenzenes showing mesophase organisation

Blue-green light-emitting phosphorescent Pt-II complexes of 1,3-bis(2-pyridyl) benzene are reported that incorporate hexadecyl-containing fragments in the 5-position of the pyridine rings. Along with the more classical half disc-shaped hexacatenar molecule with six pendant alkoxy chains, which shows an R (3) over barm mesophase, the simpler complex functionalised by just two alkoxy chains, one at each pyridyl 5-position, was also found to be mesomorphic. The luminescence of pure films obtained from these complexes is orange-red, dominated by the excimer-like emission, and is independent of the thermal history of the film. The mesophases of the complexes are three-dimensional and columnar in nature - all are based on a two-dimensional hexagonal arrangement extended into the third dimension

Comparative analysis of self-aggregation of liquid crystalline Pt(II) complexes in solution and in neat films

Two novel cycloplatinated complexes that differ by the presence/absence of a lateral fused cyclopenteno ring, respectively, were prepared. Although contributing to only a few percentage of the whole molecular volume, the presence of this aliphatic protuberance appears to be essential for the emergence of liquid crystalline behaviour. This pair of two similar compounds, non-mesomorphic complex and mesomorphic complex, was prepared as a model to assess the possible link of the self-aggregation in solution with the appearance of the liquid crystallinity in molten state. NMR dilution studies in CDCl3 solution and X-ray diffusion study in neat films show qualitative similarity of the aggregated structures formed by liquid crystalline complex. Solution studies may therefore be a useful additional tool to the characterization of the liquid crystalline properties and other self-association processes of Pt(II) complexes