Showing papers by "Sergey Sergeyev published in 2009"

Homeotropic and Planar Alignment of Discotic Liquid Crystals: The Role of the Columnar Mesophase

Abstract: Blends of two metal-free phthalocyanine mesogens exhibiting different mesophases (Colr phase from room temperature to isotropization for the first one, and Colr at room temperature then Colh from around 60 °C to isotropization for the second one) have been studied in order to determine the relationship between the type of mesophase and the alignment behavior. The phase diagram of this system has been built and evidence of full solid-state miscibility of the two pure constituents in all proportions and temperatures is presented. Investigation of phase alternation at room temperature as a function of composition revealed that border compositions exhibit Colr phases similar to the pure constituents, whereas Colh mesophase was stabilized for intermediate compositions. Combined polarized optical microscopy observations and X-ray diffraction measurements showed that homeotropic alignment is adopted only for mixed samples exhibiting Colh mesophase, thus demonstrating that the presence of a Colh mesophase is a ne...

Synthesis of mesogenic phthalocyanine-C60 donor-acceptor dyads designed for molecular heterojunction photovoltaic devices.

Abstract: A series of phthalocyanine-C60 dyads 2a–d was synthesized. Key steps in their synthesis are preparation of the low symmetry phthalocyanine intermediate by the statistical condensation of two phthalonitriles, and the final esterification of the fullerene derivative bearing a free COOH group. Structural characterization of the molecules in solution was performed by NMR spectroscopy, UV–vis spectroscopy and cyclic voltammetry. Preliminary studies suggest formation of liquid crystalline (LC) mesophases for some of the prepared dyads. To the best of our knowledge, this is the first example of LC phthalocyanine-C60 dyads.

Metal-Free Phthalocyanines Bearing Eight Alkylsulfonyl Substituents: Design, Synthesis, Electronic Structure, and Mesomorphism of New Electron-Deficient Mesogens

Abstract: This paper describes the synthesis and physicochemical characterization of novel metal-free phthalocyanines Pc(SO2R)8, bearing eight peripheral alkylsulfonyl substituents. The key synthetic step is the efficient eightfold oxidation of sulfanyl (SR) into sulfonyl (SO2R) functions in the precursor Pc(SR)8. Quantum-chemical calculations show a considerable stabilization of the HOMO and LUMO levels of Pc(SO2R)8 as a result of the presence of the strongly electron-withdrawing groups, while the HOMO−LUMO gap remains nearly unaffected. The redox behavior and electronic spectra of Pc(SO2R)8 were investigated by cyclic voltammetry and electronic absorption spectroscopy, respectively, to confirm the theoretical predictions. Particularly noteworthy is the first reduction potential of −0.14 V vs the saturated calomel electrode (SCE), which falls within the empirically established air-stability window for n-type semiconductors. Supramolecular structures of mesophases of Pc(SO2R)8 and their synthetic precursors Pc(SR)8...

Enantioseparations of non-benzenoid and oligo-Tröger’s bases by HPLC on Whelk O1 column

Abstract: The separation of enantiomers of several ‘bis- and tris-Troger’s bases’ by HPLC on commercially available chiral stationary phase Whelk O1 is described for the first time. The observed structure–enantioselectivity relationships are in agreement with the previously established molecular recognition model. For all ‘bis- and tris-Troger’s bases’ studied, satisfactory to excellent enantioselectivities were observed.