A method for the preparation of uniaxially oriented thin films of terthiophene (20–50 μm thick) is introduced. It relies on the crystal growth with a Bridgman-type process that decouples nucleation and growth phenomena. An effective thermal gradient of 6–11.6 °C/mm has been used in which the sample (terthiophene powder deposited on either glass or fluorinated glass substrates) is displaced from a hot zone to a cold zone at a constant rate of 2.5–5 μm/s. The size and orientation of crystals have been investigated by polarized optical microscopy and X-ray diffraction measurements. A coexistence of two polymorphs of terthiophene has been observed, but optimal gradient conditions enabling the selective crystallization of only the room temperature stable polymorph have been found. Terthiophene films deposited on fluorinated glass substrates and crystallized using the thermal gradient technique show a stronger tendency to polymorphism and random orientation of crystallites for all gradient conditions tested. The monoclinic unit cell (a = 15.410 Å, b = 5.709 Å, c = 26.052 Å, β = 97.77°) of the room temperature phase orients its ab plane parallel to the substrate. Pole figures demonstrate the growth of uniaxially aligned crystals with the [100] and [−100] directions along the gradient axis. Finally, a tentative explanation for this peculiar in-plane orientation is given based on crystal morphology calculations.
This paper describes the synthesis and physicochemical characterization of novel metal-free phthalocyanines Pc(SO
2
R)
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(SO
2
R)
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(SO
2
R)
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(SO
2
R)
8
and their synthetic precursors Pc(SR)
8
were studied in detail with the aid of powder X-ray diffraction in combination with differential scanning calorimetry and polarized light optical microscopy. As it was demonstrated earlier for many different discotic mesogens, installation of either linear or swallow-tail branched peripheral alkyl substituents plays an important role in the formation of mesophases. However, an unusual behavior was found for the Pc(SO
2
R)
8
series: swallow-tail alkyl chains resulted in higher order in columnar mesophases compared to the linear analogues.
SummaryA 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.
Plasticity is an inherent feature of chromosomal DNA replication in eukaryotes. Potential origins of DNA replication are made in excess, but are used (fired) in a partly stochastic, partly programmed manner throughout the S phase of the cell cycle. Since most origins have a firing efficiency below 50%, population-based analysis methods yield a cumulative picture of origin activity (obtained by accretion) that does not accurately describe how chromosomes are replicated in single cells. DNA combing is a method that allows the alignment on silanized glass coverslips, at high density and with uniform stretching, of single DNA molecules in the Mb range. If this DNA is isolated from cells that have been labelled with halogenated nucleotides (BrdU, CldU, IdU), it is possible to determine the density and position of replication origins as well as the rate and symmetry of fork progression, quantitatively and on single DNA molecules. This chapter will successively describe (a) the preparation ofsilanized coverslips, (b) the incorporation of halogenated nucleotides in newly synthesized DNA in yeast and mammalian cell lines, (c) the preparation and combing of genomic DNA, and finally (d) the acquisition and analysis of single-molecule images to extract salient features of replication dynamics.
New alpha,omega-semifluorinated dithiols HS-(CH2)11-(CF2)n-(CH2)11-SH, called DTn, and corresponding dithioacetate molecules CH3COS-(CH2)11-(CF2)n-(CH2)11-SCOCH3, called DTAn ( n = 4, 6, 8), were synthesized and used to create self-assembled monolayers (SAMs) on both untreated copper surfaces and electrochemically reduced ones. The aim of this study is to assess the organization of the resulting SAMs, particularly the effect of the presence of two perhydrogenated segments surrounding the perfluorinated one, and the ability of these difunctional molecules to bind copper substrates by only one end per molecule. In each case, the organization of the SAM is rather poor and only DTA8 molecules seem to adopt an upright position on reduced copper. In addition, the layers have been investigated by cyclic voltammetry (CV) to assess their coverage. DT4 SAMs reveal a covering ratio higher than 99%.
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