Adsorption-induced Fermi level pinning

The adsorption-induced Fermi level pinning is shown to occur at the coverages Θ* corresponding to a shallow extremum or saturation of the work function of the system. Equations for Θ* are derived within a modified Anderson-Newns adsorption model. Experimental data on the adsorption of atoms of alkali, alkaline-earth (Ba), and rare-earth metals and hydrogen on semiconductors (silicon, gallium arsenide, and titanium dioxide) are analyzed. The position of the Fermi level on the surface of a semiconductor is estimated.     

Chemical and Phase Transformations during the Synthesis of Cs[MgR<Subscript>0.5</Subscript>P<Subscript>1.5</Subscript>O<Subscript>6</Subscript>] (R = B,Al, Fe) Complex Oxides from Metal Chlorides

Cesium-containing complex oxides Cs[MgR_0.5P_1.5O₆] (R = B, Al, Fe) are prepared from solutions containing H₃BO₃, metal chlorides, and H₃PO₄/NH₄H₂PO₄. The chemical and phase transformations that occur during the synthesis are elucidated by differential thermal analysis (DTA) and X-ray powder diffraction (XRD). Optimal synthesis parameters are determined. The oxides where R = B or Fe are formed at 800°C, those where R = Al are formed at 1100°C. All compounds crystallize in the pollucite-type structure (cubic system, space group I4₁32).     

Facile synthesis of isomerically pure fullerenols C60(OH)5Br and 1,4-C60(OH)2 from chlorofullerene C60Cl6

The chlorofullerene C₆₀Cl₆ was demonstrated as a versatile precursor for the synthesis of two isomerically pure fullerenols via tetrabutylammonium bromide promoted reactions with water. Performing the synthesis in wet chlorobenzene produced 1,4-C₆₀(OH)₂ as the only isolable product along with substantial amounts of non-functionalized C₆₀. However, the addition of DMSO as a co-solvent altered the reaction pathway, leading to the formation of C₆₀(OH)₅Br as the main product. Both isolated compounds were novel and their molecular compositions and structures were confirmed by mass spectrometry and NMR spectroscopy. The fullerenol C₆₀(OH)₅Br, which was formed in a moderate yield, represents the first isomerically pure polyhydroxylated fullerene available on a large scale.     

New pyrrolidine and pyrroline derivatives of fullerenes: from the synthesis to the use in light-converting systems

The results of the authors’ studies on the [2+3] cycloaddition of azomethine and nitrile ylides generated from picolylamine and benzylamine derivatives to fullerenes are systematized and new experimental data are considered. Catalysts and microwave radiation promoting the formation of ylides and their addition to fullerenes were successfully used for the first time. A large series of new pyrrolidine and pyrroline derivatives of fullerenes C₆₀ and C₇₀ were synthesized and characterized. The proposed procedures afford the reaction products in yields twice as high (80–85%) as those attained by the classical Prato reaction. The reactions proceed with virtually complete regio- (in the case of C₇₀) and stereoselectivity to afford only cis-2′,5′-disubstituted and trans-1′,2′,5′-trisubstituted pyrrolidinofullerenes. Pyridyl-substituted pyrrolidinofullerenes react with metalloporphyrins and phthalocyanines to form self-ordered coordination complexes. The latter are analogs of natural photosynthetic antenna systems due to photoinduced charge separation that occurs in these complexes upon exposure to light. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 873–898, May, 2008.     

Calculation of parameters of diffraction polarizers

The results of calculations of two types of reflective polarizers made up of thin-film diffraction grating formed by birefringent plane-parallel elements are presented. One of the two orthogonal linear polarizations can be separated almost without any losses because of a strong zero-order reflection. A polarizer of the first type represents a grating formed by asperities of a dielectric coating with a columnar structure produced upon oblique deposition of the dielectric. The second polarizer represents a thin mica plate grating. In this case, comparison with previous experiments can be performed.     

Note on inconsistency of unitarity saturation and maximal odderon

It is shown that regime of elastic scattering with maximal odderon contribution is not compatible with unitarity and black disk limits saturation.     

Photoaddition of N-substituted piperazines to C60: an efficient approach to the synthesis of water-soluble fullerene derivatives

An oxidative radical photoaddition of mono N-substituted piperazines to [60]fullerene was systematically investigated. Reactions of C60 with piperazines bearing bulky electron-withdrawing groups (2-pyridyl, 2-pyrimidinyl) were found to be the most selective and yielded C60(amine)4O as major products along with small amounts of C60(amine)2. In contrast, interactions of fullerene with N-methylpiperazine and N-(tert-butoxycarbonyl)piperazine were found to have low selectivity due to different side reactions. Tetraaminofullerene derivative C60(N-(2-pyridyl)piperazine)4O was found to react readily with organic and inorganic acids to yield highly water-soluble salts (solubility approximately 150 mg mL(-1)). In contrast, C60(N-(2-pyrimidinyl)piperazine)4O undergoes hydrolysis under the same conditions and results in a complex mixture of compounds with an average composition of C60(N-(2-pyrimidinyl)piperazine)2(OH)2O. Radical photoaddition of N-(2-pyridyl)piperazine to fullerene derivatives can be used as a facile route for their transformation into water-soluble compounds. Two model fullerene cycloadducts (a methanofullerene and a pyrrolidinofullerene) were easily converted into mixtures of regioisomers of A=C60(N-(2-pyridyl)piperazine)4O (A=cyclic addend) that give highly water-soluble salts under acid treatment.     

Molecular and ionic complexes of pyrrolidinofullerene bearing chelating 3-pyridyl units

Molecular and ionic complexes of cis-2',5'-di(pyridin-3-yl)pyrrolidino[3',4':1,9](C(60)-I(h))[5,6]fullerene DP3FP with chlorobenzene (C(6)H(5)Cl), manganese(II) tetraphenylporphyrin (Mn(II)TPP) and tetrakis(dimethylamino)ethylene (TDAE) have been obtained for the first time. X-ray single crystal structure determination for the crystalline DP3FP·C(6)H(5)Cl (1) solvate proved unambiguously its molecular structure with the cis-arrangement of chelating 3-pyridyl groups. It has been demonstrated that DP3FP easily forms self-assembled photoactive complexes with metallated porphyrins. For example, the formation of a 1 : 1 complex between DP3FP and zinc (II) tetraphenylporphyrin (Zn(II)TPP) in cyclohexane solution (2) was evidenced using absorption spectroscopy. A successful X-ray single crystal structure determination was performed for a self-assembled triad composed of a DP3FP molecule linked with two Mn(II)TPP molecules in {DP3FP·(Mn(II)TPP)(2)}·(C(6)H(4)Cl(2))(3) (3). A strong organic donor TDAE reduces DP3FP to the radical anion state thus forming an ionic complex (TDAE˙(+))·(DP3FP˙(-))·(C(6)H(4)Cl(2))(1.6) (4). Optical, electronic and magnetic properties of 4 were investigated in detail. The performed studies strongly suggest that pyrrolidinofullerene DP3FP can be used as a building block in the design of various organic materials with advanced optoelectronic and/or magnetic properties.     

Facile preparation of amine and amino acid adducts of [60]fullerene using chlorofullerene C60Cl6 as a precursor

We report a general synthetic approach to the preparation of highly functionalized amine and amino acid derivatives of [60]fullerene starting from readily available chlorofullerene C(60)Cl(6). The synthesized water-soluble amino acid derivative of C(60) demonstrated pronounced antiviral activity, while the cationic amine-based compound showed strong antibacterial action in vitro.