Molecular Orientation Behavior of Lyotropic Liquid Crystal-Carbon Dot Hybrids in Microfluidic Confinement.

Lyotropic liquid crystals represent an important class of anisotropic colloid systems. Their integration with optically active nanoparticles can provide us with responsive luminescent media that offer new fundamental and applied solutions for biomedicine. This paper analyzes the molecular-level behavior of such composites represented by tetraethylene glycol monododecyl ether and nanoscale carbon dots in microfluidic channels. Microfluidic confinement allows for simultaneously applying multiple factors, such as flow dynamics, wall effects, and temperature, for the precise control of the molecular arrangement in such composites and their resulting optical properties. The microfluidic behavior of composites was characterized by a set of analytical and modeling tools such as polarized and fluorescent microscopy, dynamic light scattering, and fluorescent spectroscopy, as well as image processing in Matlab. The composites were shown to form tunable anisotropic intermolecular structures in microchannels with several levels of molecular ordering. A predominant lamellar structure of the composites was found to undergo additional ordering with respect to the microchannel axis and walls. Such an alignment was controlled by applying shear and temperature factors to the microfluidic environment. The revealed molecular behavior of the composite may contribute to the synthesis of hybrid organized media capable of polarized luminescence for on-chip diagnostics and biomimetics.

Effect of Magnetic and Electric Field on the Orientation of Rare-Earth-Containing Nematics.

We report rare-earth-containing metallomesogens with newly synthesized ligands represented by the ß-diketone 1-(4-(4-propylcyclohexyl)phenyl)octane-1,3-dione (CPDk3-5) and the Lewis base 5,5'-bis(heptadecyl)-2,2'-bipyridine (bpy17-17). The stoichiometry of the complexes is [Ln(CPDk3-5)3bpy17-17], where Ln is a trivalent rare-earth ion (La, Sm, Eu, Gd, Tb, Dy, Ho, Tm, and Yb). Although the ligands themselves do not form any mesophase, the respective metal complexes produce nematic and smectic A phases. The mesogenic rare-earth complexes were characterized by NMR, MS, POM, DSC, X-ray diffraction, magnetic susceptibility measurements, and dielectric spectroscopy. The metal complexes display a remarkably large magnetic anisotropy in the mesophase. These nematic liquid crystals can, therefore, be easily aligned by an external low-threshold magnetic field.

Optical and structural characteristics of PMMA films doped with a new anisometric EuIII complex.

A new film material capable of transforming UV radiation into visible light was obtained from a highly anisometric EuIII complex with organic ligands in a polymethylmethacrylate (PMMA) matrix and then structurally characterized. An important advantage of the synthesized complex is its good solubility in organic solvents such as dichloromethane, chloroform, THF, toluene, etc. The ligand environment (flexible alkyl and cyclohexyl substituents) of the EuIII complex was selected to prevent crystallization, to inhibit the formation of defects in the structure of films and to provide its uniform distribution in the polymer during polymerization. As a result we obtain an EuIII complex of the film with remarkable thermal behavior: the complex melts to isotropic liquid without decomposition, it supercools at ambient temperature and it forms a stable amorphous material at low (up to -30°C) temperatures. The films were prepared by two methods: bulk polymerization and spin coating. A comparison of the differences of luminescent and optical characteristics of micro- and nanosized PMMA films doped with the anisometric EuIII complex is given. Based on X-ray powder diffraction and small-angle scattering data, it has been supposed that the association of EuIII complex molecules occurs in the voids of the PMMA matrix and is accompanied by the formation of a nanocrystalline phase. For films obtained by spin coating, a deeper microphase separation is demonstrated than by bulk polymerization. The dimensional characteristics of the nano-associates were determined and a correlation between the method of preparation and the type of distribution of the EuIII complex in the PMMA matrix is established.

Influence of Eu(III) Complexes Structural Anisotropy on Luminescence of Doped Conjugated Polymer Blends.

Europium(III) complexes that are the anisometric analogues of a well-known Eu(DBM)3Phen (DBM = dibenzoylmethane; Phen = 1,10-phenanthroline) complex were synthesized. Quantum-chemical calculations of the excited states of new Eu(III) complexes and some conjugated polymers showed that poly(N-vinylcarbazole) provides the most efficient energy transfer in polymer films doped with synthesized Eu(III) complexes. These new composite films were prepared, and their luminescence properties were studied. The results of experimental data confirmed theoretical prediction about significant influence introduced in molecular structure long terminal alkyl chains and cyclohexane on the luminescence efficiency of "Ln(III)-polymer" composite. As the result a substantial contribution of complex anisometry to the luminescence efficiency of composite was revealed due to the increase of the complex limit concentration before self-quenching more than twofold.

Influence of structural anisotropy on mesogenity of Eu(III) adducts and optical properties of vitrified films formed on their base.

A new series of europium adducts with the general formula Eu(CPDk3-CnH2n+1)3Phen, where CPDk3-CnH2n+1 denotes ß-diketones and Phen is 1,10-phenanthroline, was synthesized. The obtained mesogenic complexes were heated to the temperatures of the isotropic liquid state and then cooled. The complexes having short CH3 and C2H5 substituents crystallized upon cooling, and the complexes with longer substituents from C3H7 to C6H13 underwent a glass transition with the formation of optically transparent amorphous films. Inside the series the complexes with C7H15 and C8H17 substituents exhibited a unusual smectic C mesomorphism for lanthanidomesogens. On the basis of quantum-chemical simulations and the results of small-angle X-ray scattering the dependence between the anisotropy of Eu(III) complexes with various ligand environments and their supramolecular organization was found. The synthesized Eu(III) complexes in the solid state show intense red photoluminescence upon irradiation by ultraviolet light (λmax - 337 nm).