Larisa G. Klapshina

FERROUS TRIS( TRIMETHYLSILYL) SILANOLATES : SYNTHESIS, STRUCTURE, REACTIVITY AND THERMAL DECOMPOSITION

Abstract Reaction of FeBr2 with 3 equiv. of sodium tris(trimethylsilyl)silanolate (1) in DME affords the ate-complex {(Me3Si)3SiOFe[μ-OSi(SiMe3)]2Na(DME)} (2). X-ray studies have shown the Fe atom in 2 is bonded to three O atoms of OSi(SiMe3)3 groups, two O atoms are connecting as a μ-bridge the Fe[OSi(SiMe3)3]3] unit with the Na(DME) group. The FeO3 core is slightly non-planar: the deviation of the Fe atom from the O3 plane is 0.08A. The four-member Fe(μ-O)2Na cycle is also non-planar: the dihedral angle between the Fe(μ-O)2 and the (μ-O)2Na planes is 31.0°. The bridging and terminal FeO distances are 1.840(2) and 1.894(2), 1.910(2) A, respectively. The average SiSi and SiC distances are 2.358(8) A and 1.873(8) A. Interaction of FeBr2 with two equiv. of 1 in THF followed by treatment with pyridine yields the adduct, [(Me3Si)3SiO]2Fe(Py)2 (3). The Mossbauer spectrum of complex 2 at 295 K consists of a single doublet with isomer shift 0.60(1) mm/s and quadrupole splitting 0.90(3) mm/s. The corresponding parameters of 3 are as follows: isomer shift, 1.08(1) mm/s, and quadrupole splitting, 2.12(2) mm/s. Molecular oxygen is easily incorporated into the SiSi bonds of compounds 2 and 3 by activation at the iron (II) center. Reaction of 2 with 1 equiv. of tetracyanoethylene leads to iron (III) silanolate, [(Me3Si)3SiO]3Fe (4) and the anion-radical salt, Na +TCNE−. Slow thermolysis of 2 and 3 yields (Me3Si)2SiOSiMe3 and (Me3Si)4Si as well as polyferrsiloxane with MW ∼ 3500. Fast thermolysis results in formation of α-Fe and a complicated mixture of oligosiloxanes.

N-Ethylcarbazole as a structure-directing agent in poly[(ethynediyl)(arylene)(ethynediyl)silylene]–poly(phenylsilsesquioxane) hybrid nanomaterials exhibiting photorefraction at telecommunication wavelengths

Self-organisation through π-stacking occurs in poly[(ethynediyl)(arylene)(ethynediyl)silylene]–N-ethylcarbazole–poly(phenylsilsesquioxane) compositions giving rise to nanostructured hybrid layered materials exhibiting photorefraction at telecommunication wavelengths. To our knowledge, this is the first such material to be reported the poly[(ethynediyl)(arylene)(ethynediyl)silylene] acting as an optical chromophore, charge generator and conductor. The absorption band tails into the near-IR hence providing charge generation at 1500 nm excitation. The photorefractive response was investigated by using a two-beam coupling technique. The gain of the probe beam intensity, delivered from the pumping beam, reached 40 cm−1 with an electric field strength of 650 kV cm−1 thus confirming the photorefractive nature of the grating. The gain exceeded the absorption (30 cm−1) hence showing the high potential of this material for practical applications.

Novel metal-template assembled highly-functionalized cyanoporphyrazine ytterbium and vanadium complexes for potential photonic and optoelectronic applications

A novel facile synthetic route to the metal-template assembly of a tetrapyrrollic framework from tetracyanoethylene (TCNE) and tricyanovinylbenzene (TCNVB) structural units through reaction of TCNE and TCNVB with metal π-sandwich complexes has been developed. The reactions occur under extremely mild conditions, the porphyrazine macrocycles being assembled in high yield from TCNE and TCNVB building-blocks by VO2+ or Yb3+-template synthesis. The redox behaviour of the novel complexes has been investigated. The vanadyl octacyanoporphyrazine complex was found to be a rare example of a highly-absorbing dye combining significant electron-acceptor properties with a band gap unusually narrow for an organic semiconductor (ca. 1.1 eV). The preparation is described of a novel highly emissive ytterbium complex with a proposed unusual structure obtained by reaction of TCNVB with bis(indenyl)ytterbium(II) in THF. The analytical, spectral and electrochemical investigations of the obtained ytterbium complex indicate it to be a binuclear adduct with Yb(TCNVB)3 species in which a single doubly-reduced TCNVB molecule bridges two Yb3+ cations. The formation of a disordered polynuclear coordination polymer network including a macrocyclic structure and metal cations bridged through the nitrile nitrogen atoms is proposed. The complex is readily soluble and is compatible with a variety of polymeric matrices giving doped polymeric glasses and films which are highly luminescent in the biologically relevant optical window covering the visible and near-infrared (NIR) range (640–1000 nm). In addition, doped polymeric glasses and films highly emissive at the telecommunication wavelength (1540 nm), including a composition consisting of the novel ytterbium complex and an equimolar ratio of the novel ytterbium complex and a per se non-luminescent erbium chelate, have been obtained. The complex is found to be an extraordinarily strong sensitizer of NIR Er3+ emission.

Imaging tumor microscopic viscosity in vivo using molecular rotors

The microscopic viscosity plays an essential role in cellular biophysics by controlling the rates of diffusion and bimolecular reactions within the cell interior. While several approaches have emerged that have allowed the measurement of viscosity and diffusion on a single cell level in vitro, the in vivo viscosity monitoring has not yet been realized. Here we report the use of fluorescent molecular rotors in combination with Fluorescence Lifetime Imaging Microscopy (FLIM) to image microscopic viscosity in vivo, both on a single cell level and in connecting tissues of subcutaneous tumors in mice. We find that viscosities recorded from single tumor cells in vivo correlate well with the in vitro values from the same cancer cell line. Importantly, our new method allows both imaging and dynamic monitoring of viscosity changes in real time in live animals and thus it is particularly suitable for diagnostics and monitoring of the progress of treatments that might be accompanied by changes in microscopic viscosity.

Novel materials from bis(arene)metal-containing polyacrylonitrile

Novel bis(arene)metal-containing polyacrylonitrile materials have been prepared by the polycyanoethylation reaction between acrylonitrile and (arene) 2 M (M = Cr or V; arene = PhH, C 6 H 4 Et 2 or mesitylene) in the absence of solvent. The resulting star-shaped molecules consist of a central (arene) 2 M species with up to four polyacrylonitrile arms covalently bonded to the arene ligands. The materials are readily soluble and films can be cast from solutions in acetonitrile. The IR and solid state 13 C NMR spectra (or EPR spectrum for the oxidized chromium-containing polymer) are consistent with the presence of a metal-arene bond and confirm the persistence of the sandwich structure. The properties of the thermolysed materials are consistent with the formation of conjugated naphthyridine-type structures. The value of |n 2 | determined by the degenerate four-wave mixing technique at 1064 nm with a 6 ns pulse duration for a solution in conc. H 2 SO 4 (1 g l -1 ) of the chromium-containing polymer pyrolysed at 350 °C was found to be 0.8 × 10 -13 cm 2 W -1 corresponding to |Re X (3) | = 0.4 x 10 -11 esu.

Chromium-containing organometallic nanomaterials for non-linear optics

Novel non-linear optical polymeric film-producing nanocomposites based on bis(arene)chromium complexes incorporated into a CN-containing matrix have been developed. Polymeric nanocomposite precursors were prepared by the reaction of Cr(EtnC6H6−n)2 (n = 1,2,3) with CN-containing vinyl monomers (acrylonitrile, crotononitrile or ethyl 2-cyanopropenoate). Extraordinarily high third-order non-linear optical susceptibilities of the ultra-fast electronic type have been demonstrated at various wavelengths for polymer films prepared from these composites by using the Z-scan technique and the spectrally-resolved two-beam coupling method. A notable electro-optical response of the composite with an essential contribution of orientational effects was established. The electron-diffraction pattern in films and the presence of a non-zero electro-optical coefficient in the absence of an external poling field indicate the formation of self-organized structures. In CrPAN and [CrPAN]+TCNE−, a single Cr–C distance was found in the EXAFS data refinement, showing that the arene rings are parallel and symmetric as in bis(benzene)chromium. The Cr–C distances in these two materials are very similar to the 2.13 A in bis(benzene)chromium. In [CrPAN]+OH−, more than one metal–carbon distance was resolved, showing either that the two arene rings are at different distances from the metal, or that they are tilted rather than parallel.

Photorefractive properties of new polymer composites incorporating poly[ethynediyl-arylene-ethynediyl-silylene]s

The photorefractive properties of low glass transition temperature, Tg, composites based on oligomeric poly[ethynediyl-arylene-ethynediyl-silylene]s as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N-ethylcarbazole and phenyltrimethoxysilane as plasticizer, and fullerenes as charge generators have been investigated. The nonlinear optical effects, including four-wave mixing and two-beam coupling were studied at 633 nm. The photorefractive origin of the refractive index changes was confirmed by the achievement of a two-beam gain as high as 67 cm−1 under an externally applied electric field (E0 = 16 V µm−1). Refractive index gratings affording two-beam gains up to 51 cm−1 can also be written under zero-field conditions. A possible explanation for this unique property of the materials is that chromophore orientation asymmetry can be induced by the longitudinal intensity gradient.

Effective delivery of porphyrazine photosensitizers to cancer cells by polymer brush nanocontainers

Efficient drug delivery can be assigned to tasks that attract the most acute attention of researchers in the field of anticancer drug design. We have reported the first case of using amphiphilic polymer brushes as nanocontainers for photosensitizer delivery to cancer cells. Regular graft-copolymers of hydrophobic polyimides with hydrophilic polymethacrylic acid side chains were loaded with photosensitive dye tetra(4-fluorophenyl)tetracyanoporphyrazine (Pz) providing a sufficiently stable homogeneous fraction of fluorescent Pz-loaded nanoparticles with a size of 100-150 nm. Pz-loaded polymer brushes were substantially more efficient for Pz delivery into cells compared with other types of particles examined, Pz-polyethyleneglycol and Pz-methylcellulose. In vivo, an efficient Pz delivery to tumor can also be expected since the Pz-PB particle size is in the optimal range for passive targeting. Pz-PB showed pronounced photodynamic activity, while, that is important, in the absence of irradiation the PB carrier itself was significantly less toxic than the dye itself. Summing up, water-soluble polymer brushes with polyimide backbones and polymethacrylic acid side chains can be regarded as a novel type of nanocontainers providing efficient intracellular drug delivery for photodynamic therapy of cancers.

Metal template assembly of highly functionalized octacyanoporphyrazine framework from TCNE structural units.

A new route to the octacyanoporphyrazine framework based on the interaction of metal sandwich pi-complexes with TCNE has been developed.

Chromium-containing Organometallic Self-organized Materials for Nanophotonics

Novel non-linear optical polymeric film-producing nanocomposites based on bis(arene)chromium complexes incorporated into CN-containing matrices have been developed. Measurements by the spectrally resolved two-beam coupling method with a femtosecond range of pulse widths (central wavelength 795-800 nm) confirmed that the test composites exhibited a significant cubic nonlinear optical susceptibility of the ultra-fast electronic type. An open aperture Z-scan of the polymer film at 1550 nm showed a value of 9 x 10-19 cm3 W-2 for the three- photon absorption coefficient. The electro-optical measurements of the polymer composite showed a high electro-optical response (r33.n3 = 4.245 pm V-1 at modulation frequency 210 Hz and poling DC voltage 2.16 V). A significant enhancement of the signals with a decrease in modulation frequency was observed consistent with an essential contribution of orientation effects to the electro- optical response. The measurements in the absence of external electrical fields showed a natural anisotropy resulting from self- organization taking place during the film formation process as confirmed by electron diffraction studies. A single Cr-C distance was found in the EXAFS data refinement, showing that the arene rings are parallel and symmetric as in bis(benzene)chromium.