On the thermodynamics of aggregation toward phosphorescent metallomesogens:From electronic tuning to supramolecular design

Two series with three Pt(II)complexes each(PtLPh-n,PtLFpy-n)bearing asymmet-ric tetradentate ligands as dianionic luminophores with variable alkyl chain lengths were synthesized.Hence,each ligand series is distinguished by one of its cyclomet-allating rings(phenyl vs.2,6-difluoropyrid-3-yl).Steady-state and time-resolved photoluminescence spectroscopic studies in diluted solutions at room temperature and in glassy matrices at 77 K show that the emissive state is mainly centered on the invariantly electron-rich cyclometalated side while the second ring regulates the admixture of ligand-centered and metal-to-ligand charge-transfer character.Hence,the radiative rates can be controlled,as indicated by quantum-mechanical calcula-tions,which also explain the temperature-dependent trend in the phosphorescence rate constants.Studies in condensed phases(single-crystal X-ray diffractometry,polarized optical microscopy,differential scanning calorimetry,steady-state and time-resolved photoluminescence micro(spectro)scopy)showed the development of a smectic A mesophase for thefluorinated species bearing the two longest alkyl chains.Nuclear magnetic resonance-based studies on the thermodynamics of aggre-gation in solution confirm the marked enthalpic stabilization of aggregates mediated by the polar 2,6-difluoropyrid-3-yl moiety(and to a lesser extent by dispersive forces between the alkyl chains).On the other hand,the negative entropy of aggregation is dominated by the restriction of degrees of freedom involving the peripheral alkyl moieties upon stacking,which becomes increasingly relevant for longer chains.All these factors control coupling,a crucial interaction for the design of Pt⋅⋅⋅Ptphotofunctional mesogens based on Pt(II)complexes.

Water-soluble hollow nanocrystals from self-assembly of AIEEactive Pt(II)metallomesogens

Luminescent hollow micro-and nanocrystals have been successfully obtained taking advantage of the self-assembly behavior and the aggregation-induced emission enhancement properties of several bispyrazolate Pt(II)metallomesogens decorated with four terminal alkyl chains.Oil-in-water droplets have been used to confine the Pt(II)compounds and drive them to be self-assembled via intermolecular Pt…Pt interactions into spherical aggregates of about 200 or 50 nm.Evaporation of the oil phase generates highly-stable aqueous dispersions of nanocrystals that emit a bright orange light as a result of the existence of^(3)MMLCT excited states.Different methods and conditions have been tested for studying the effect of several parameters such as the temperature and the stirring speed in the final particle size and in the polydispersity index.Moreover,the micro-and nanocrystals are able to entrap hydrophobic drugs between the alkyl chains of the compounds,forming stable dispersions of drug-loaded capsules in water.The droplet method is applied in the area of metallomesogens for the first time to synthesize self-assembled Pt(II)nanocapsules,which opens a new field of study that could allow the use of these liquid crystal materials in biomedical applications.

Investigation of Intermetallic Compound Formed from Rapid Solidification of Al-Ti-RE Alloy

Al-Ti alloy containing rare earth elements can produce fine, uniform dispersion intermetallic phase through rapid solidification (RS) technology. RS Al-Ti-RE alloy can be designed for applications at elevated-temperature since the intermetallic compound has good thermal stability. A transmission electron microscopy investigation shows the intermetallic phase has a diamond cubic structure (a=1.47736 nm), with space group Fd3m. The chemical stoichiometry is Al_(20)Ti_2La. The particle is formed from the melting directly, prior to other phases, and the nucleus is formed from icosahedrons composed with twenty tetrahedrons. Twin crystal structure plays an important role in the nucleation stage.

Synthesis and Thermal Behaviour of Lanthanide Complexes of 4′[（Cholesteryloxy）Carbonyl]—Benzo—15—Crown—5

Lanthanide complexes of a steroid-substituted benzocrown ether were synthesised. The metal-to-ligand ratio of all the metal complexes is 1∶1. The ligand 4′-[(cholesteryloxy)carbonyl]-benzo-15-crown-5 is a monotropic liquid crystal, displaying a cholesteric mesophase. The lanthanide complexes with nitrate counter-ions form a highly viscous mesophase, decomposing at the clearing point. The transition temperatures change as a function of the lanthanide ion. The corresponding lanthanide complexes with dodecylsulphate (DOS) counter-ions do not form a mesophase. In both cases, the metal complexes have a much lower melting point than the parent ligand.

Solid State Structure and Lyotropic Mesomorphism of Rare-Earth Trisdode cylsulphates in the Water-Ethylene Glycol System

The phase behaviour of lanthanide(Ⅲ) dodecylsulphates, Ln(C 12 H 25 SO 4) 3, by thermo optical microscopy using Lawrence penetration technique was investigated. The lyotropic phase behaviour of lanthanide(Ⅲ) dodecylsulphates in ethylene glycol water in mixtures hereof, depends on the composition of the solvent. For pure ethylene glycol and mixtures of ethylene glycol and water three different mesophases are formed, i.e. a lamellar, a cubic and a hexagonal phase, whereas when water is used as solvent no cubic phase is formed. The size of the lanthanide ion has no influence on the mesomorphism of these metallomesogens, although the smaller the lanthanide ion the lower the solubility.

Mesomorphism of Lanthanide(Ⅲ) 4-Hexyloxybenzoates

The 4-alkoxybenzoic acids are well-known liquid crystals showing several mesophases (nematic, smectic C phase or both) depending on the alkoxy chain length and whereby the rigid core of the mesogen is formed by intermolecular hydrogen bonds. In this paper it is shown that the thermal behaviour of lanthanide salts of 4-hexyloxybenzoic acids depends on the lanthanide ion (Ln=La, Pr, Nd, Sm, Eu). The lanthanum(Ⅲ) and praseodymium(Ⅲ) 4-hexyloxybenzoates exhibit a smectic A mesophase. No mesophase is found for the corresponding compounds of heavier lanthanides. The thermal properties of the lanthanide(Ⅲ) 4-hexyloxybenzoates were investigated by differential scanning calorimetry (DSC), polarising thermo-optical microscopy and synchrotron X-ray radiation.

Mesomorphic Studies on a Series of Nickel (II) Centered Aromatic Complexes Displaying Liquid Crystalline Phases

Two new series (A & B) of three materials each based on the aroyl hydrazinato-nickel (II) complex were synthesized and characterized. The core molecule in these series consists of two 4-benzoyloxy benzylidene moieties and two benzene rings attached at the azomethine moiety. These latter benzene rings have one or two alkoxy chains comprised of either 10, 12, 16 or 18 carbon atoms. The characterization of these two series by polarized optical microscopy and differential scanning calorimetry is described herein. Upon cooling from the Isotropic phase, three of the six materials display a monophasic columnar phase and the other three possess a biphasic nematic and columnar phases. Upon heating, all six materials have a clearance point at high temperatures without displaying mesomorphic behavior. In series B mesogens, it was observed that the longer the hydrocarbon tail length, the lower the clearance point.