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Light‐induced generation of charges into an electron acceptor–donor phase‐segregated blend is studied. The blend is made of highly ordered nanoscopic crystals of 3″‐methyl‐4″‐hexyl‐2,2′:5′,2″:5″,2‴:5‴,2″″‐quinquethiophene‐1″,1″‐dioxide embedded into a regioregular poly(3‐hexylthiophene) matrix, acting as acceptor and donor materials, respectively. Kelvin probe force microscopy investigations reveal a tendency for the acceptor nanocrystals to capture the generated electrons whereas the donor matrix becomes more positively charged. The presence of particular positively charged defects, i.e., nanocrystals, is also observed within the film. The charging and discharging of both materials is studied in real time, as well as the effect of different acceptor–donor ratios. Upon prolonged thermal annealing at high temperatures the chemical structure of the blend is altered, leading to the disappearance of charge separation upon light irradiation. The obtained results allow a better understanding of the correlation between the nanoscopic structure of the photoactive material and solar‐cell performance.

We demonstrate that highly stable fluorescent nanobeads can be obtained by emulsion copolymerization of oligothiophene methyl methacrylates and styrene and that deposition on a planar surface by microfluidic lithography induces the spontaneous nanobead self-assembling. The average nanobead diameter was controlled in the submicron scale by varying the amount of surfactant used in the polymerization reaction. Photoluminescence and pump−probe experiments proved that the nanobeads had retained the optical signature of the oligothiophenes, yet preventing their aggregation. Scanning electron microscopy images of the self-assembled nanobeads are reported.

The synthesis via the Stille coupling of a new family of oligomers derived from benzo[b]thiophene is reported. Owing to their branched molecular structure lacking any symmetry element, these compounds display a low tendency to crystallization and better film‐forming properties than their linear counterparts. Spin‐coated films show photoluminescence efficiencies up to 50 %. Light‐emitting diodes with spin‐coated films as the active layers display markedly improved performance with respect to similar devices based on linear oligothiophenes, with luminance values up to more than 10 000 cd m–2. Semiempirical PM3 and ZINDO/S calculations provide insight into the molecular geometries and electron distribution of the frontier orbitals of the new compounds. Cyclic voltammetry data indicates that the transformation of the thienyl sulfur of benzo[b]thiophene to the corresponding thienyl‐S,S‐dioxide leads an increase in electron affinity by 0.5–0.7 V, analogous to that of the corresponding linear oligomers.

The synthesis of polyvinyl polymers by radical polymerization of α-vinyl-ω-alkyl-terminated thiophene and bi-, ter-, and quaterthiophenes is reported. The photoluminescence properties of the polymers in solution and in thin film are described. In thin film, self-assembly-induced white photoluminescence was observed for poly(5-vinyl-5‘ ‘‘-hexylquaterthiophene). For this polymer, single crystals with rectangular shape and micrometer size were obtained by drop casting from CS2. MM3 calculations on model diads and triads indicate that, on increasing the size of the side groups, van der Waals interactions promote the stacking of the pendants on the same side of the polyvinyl chain.

The photoluminescence (PL) frequencies and quantum efficiencies of dithieno[3,2-b;2‘,3‘-d]thiophene-4,4-dioxide (1), its 3,5-dimethyl derivative (2), and the corresponding 4-oxide (3) are reported and discussed in relation to their single-crystal X-ray structures. The peculiar packing modalities of dioxides 1 and 2, based on dimeric units originated by short S···O contacts between molecules related by an inversion center, cause an unusually high bathocromic shift of PL frequencies from solution to solid state. This effect is accompanied by a marked decrease in solid-state PL efficiencies (12% and 16%) compared to those in solution (75% and 77%). In monoxide 3 the loss of local symmetry inherent to the change SO2 → SO deeply modifies the self-assembly and PL properties, and the PL efficiency in the solid state is close to that in solution. Ab initio calculations on the ground and excited states of compound 1 were performed and compared to those of a conformationally mobile counterpart. Oligomers containing dithienothiophene 2 as internal core were synthesized and found to be characterized by high PL efficiencies in the solid-state (up to 48%) as well as in solution (up to 85%). The current−voltage and luminance−voltage plots of an electroluminescent diode fabricated with one of these new rigid-core oligothiophene-S,S-dioxides are reported.

The results of X-ray crystallographic investigations of compounds containing a 2,2′-bithienyl fragment are summarized and analyzed. The structural characteristics of unsubstituted bithiophene, 5-monosubstituted, 5,5′-, 3,3′-, 4,4′-, and 3,4′-disubstituted, and more highly substituted bithiophenes and also the structure of α-conjugated oligothiophene derivatives are considered.

We report a number of investigations into a variety of surface and bulk phenomena which are particularly relevant to the design of polymer optoelectronic devices, and in particular to light-emitting diodes (LEDs). First, we consider the surface properties of the most common anode, a thin layer of indium tin oxide (ITO), as modified by chemical and physical treatments. We show how the treatments affect the electrode workfunction, surface energy, morphology, sheet resistance and therefore, the LEDs efficiency and lifetime. We will also consider the effect of a conducting polymer hole-transport layer, such as poly(styrene sulfonate) doped poly(3,4-ethylene dioxythiophene) (PEDOT), incorporated between the ITO and the active layer. Secondly, we turn our attention to the optimisation of the photoluminescence (PL) efficiency, and report examples of how the polymer microstructure and possibly the engineering of disorder in a class of poly(p-phenylene vinylene)s and poly- or oligo-thiophenes can determine a significant increase of the PL efficiencies in the solid state.

A new class of thiophene-based polymers characterized by the presence of one nonaromatic thienyl S,S-dioxide moiety (O) to every two, four, and six aromatic thienyl units (T) was prepared from the newly synthesized precursors TOT, TTOTT, and TTTOTTT, and electrochemically characterized. The polymers displayed remarkably greater electron affinities than that of polythiophene and could be reversibly n-doped at moderate potentials, while still maintaining the property of also being p-doped at moderate potential values. All polymers were characterized by good p-doping/undoping cyclability, while at least four aromatic units to every nonaromatic one were needed to ensure good n-doping/undoping cyclability. ZINDO/S//PM3 calculations on TOT, TTOTT, and TTTOTTT and on (TOT)3 and (TTOTT)3, as models for the corresponding polymers, showed that the presence of the nonaromatic units does not affect the π,π* character of the frontier orbitals but decreases their energy, in particular that of the LUMO. The calculations allow the cyclability properties of the polymers in the p- and n-doping domains to be rationalized in terms of delocalization of the electronic charge of p- and n-type charge carriers over the aromatic units.

Optical absorption and photoluminescence of both unsubstituted and alkyl-substituted oligohiophenes thin films, grown on various inorganic and organic substrates with the Molecular Beam Deposition technique, have been studied. Dramatic orientation effects, associated with large dichroism in the linear optical properties, are observed upon molecular deposition onto properly cleaved potassium acid phtalate substrates. X-ray diffraction data and optical anisotropy are consistent with a card pack supramolecular organization, in which the separation between the molecules and their orientation with respect to the substrate are strongly affected by the lateral substitutions.The polarization behavior of the optical excitations in films of both unsubstituted and laterally substituted oligothiophenes provides novel information on the electronic structure of these compounds

In this study an in vitro Magnetic Resonance Spectroscopic characterization of water soluble metabolites and the lipid fraction obtained from 31 tumors (14 glioblastomas, 3 anaplastic astrocitomas, 2 anaplastic oligodendrogliomas, 2 oligodendrogliomas and 10 meningiomas) is reported. The 1H MR spectrum of normal brain tissue is also shown, it is characterized by a low Cho/Cr signal intensity ratio and an intense NAA resonance. The regional metabolic heterogeneity of glioblastomas is documented. For these tumors, specific molecular composition by MRS cannot be defined. Oligodendrogliomas and anaplastic oligodendrogliomas showed typical Cho/Cr and Ala/Cr metabolite ratios. The degree of histological endothelial proliferation of the malignant astrocitomas and oligodendrogliomas was correlated to the presence of Cholesteryl esters in the 13C Magnetic Resonance spectrum of the lipid fraction obtained from these tumors. Meningiomas are mainly characterized by high Cho/Cr and Ala/Cr ratios.

The diagnosis of central nervous system (CNS) involvement appears to be a major problem in systemic lupus erythematosus (SLE), especially when the clinical signs are non-specific or neuroimaging is unremarkable. Two SLE patients with mild neuropsychiatric manifestations were studied with magnetic resonance imaging (MRI), single photon emission tomography (SPET) and localized proton magnetic resonance spectroscopy (H-1 MRS). MRI was normal in both patients. SPET revealed areas of hypoperfusion in both patients. H-1 MRS demonstrated metabolic abnormalities in the regions corresponding to the hypoperfused areas. A correlation between H-1 MRS and SPET was noted: patients with mild neuropsychiatric SLE may have disturbances evident on SPET and H-1 MRS in the presence of normal anatomy on MRI, suggesting that CNS involvement in SLE has very strong physiological and neurometabolic components in individual patients.

The trend of variation of sulfur and oxygen shieldings of X-SO2-Y and X-SO-Y substrates is rationalized in terms of the joint effects of n -> σ* conjugative interactions and ligands electronegativity. The relative weight of these effects is different in the two classes of compounds, the former being dominant in the series X-SO2-Y and the latter in the series X-SO-Y.

Abstract: We examined 14 vegetative brain-injured patients with proton magnetic resonance single-volume spectroscopy (1H MRS) at 1.5 T to establish whether there were changes in relative concentrations of N -acetyl aspartate (NAA), choline (Cho) and creatine (CR) metabolites from those found in healthy brains. Spectra were obtained from two different (2 × 2 × 2 cm) volumes of interest in the left and in the right frontal cortex, normal on MRI. All spectra revealed abnormalities compared with normal spectra obtained from age-matched control subjects. Values outside the normal range for at least one of the metabolite ratios were observed in all patients. Cho/Cr was markedly higher and NAA/Cho and NAA/Cr were markedly lower than in the control subjects. At different times six patients regained awareness and the ability to obey commands, and four were re-examined; changes in metabolite ratios were observed, which were different in individual patients. The NAA/Cho ratio reaches statistical significance in discriminating between the patients with a poor outcome (death or prolonged vegetative state) and those who regained awareness; the dividing line appears to be at a value of about 1.6.

A new class of processable, chemically stable, and easily synthesized and purified α,ω-bis(dimethyl-tert-butylsilyl) oligothiophenes is described. Information on the solid-state properties was obtained by single crystal X-ray diffraction and CPMAS NMR spectroscopy. Molecular packing was characterized by a sandwich-type organization, with the molecular planes between adjacent layers along the stacking direction being exactly parallel. Vacuum-evaporated thin films of the tetramer, pentamer, and hexamer displayed field effect transistor activity, with charge mobilities increasing with the substrate deposition temperatures in the range 28−80 °C. The best FET performance was achieved with the pentamer which was characterized by an on/off ratio > 10³, reproducibility, and a device stability in air of months.

It is shown by carbon-13 NMR that the only product of the imidazole ring-opening of 7-methyl-guanosine at physiological pH is 2-amino-6-hydroxy-5-N-methylformamido-4-(N-β-ribofurano-sylamino)pyrimidine and that, contrary to previous results, the hydrolysis of the glycosylic bond at pH=7.2 is a much slower process than the ring opening. The ring opened formamidopyrimidine derivative is a very mobile molecule existing under different conformations depending on the solvent, and in water it is capable of giving different kinds of aggregates. Possible biochemical implications of these results are discussed.

Mono- and binuclear oligothiophene rhodium complexes are obtained by single and double C−S bond cleavage of 2,2‘:5‘,2‘‘:5‘‘,2‘‘‘-quaterthiophene, respectively. S-Methylation of the C−S insertion products, followed by carbonylation of the resulting thioether complexes give the functionalized oligothiophenes 5-[1-(methylthio)-buta-1,3-diene]-2,2‘:5‘,2‘‘-terthiophene and 5,5‘-bis[1-(methylthio)-buta-1,3-diene]-2,2‘-bithiophene. The rhodium metal is recovered as a bis(carbonyl) complex.

New conjugated polymers containing variable amounts of thienyl and thienyl-S,S-dioxide units have been prepared by chemical or electrochemical polymerization of the appropriate substrates. The presence of the thienyl S,S-dioxide units leads to the decrease of the LUMO energies with respect to those of the ‘all thienyl’ counterparts. Electrochemical and spectro electrochemical data of n-doping of these materials are reported.

Regiospecifically methyl substituted α-conjugated thiophene oligomers have been synthesized and their structural and conformational properties investigated by 13C NMR, X-ray and force field MMP2 calculations. The use of these molecules as 'monomers' for electropolymerization affords poly(3-methylthiophenes) showing spectroelectrochemical properties which depend on the size and the substitution pattern of the starting oligorners.

A recent study1 of the reactivity (H-D base-catalyzed exchange) of diastereotopic α sulfonium protons, CαCα, S+-C(HaHb)-, has suggested an important geometrical factor contributing to the stability of the quasi-ylide transition state. This is the syn or anti alignment of the incipient lone pair orbital with one of the adjacent S+-Cα bonds. Thus, for example, of the ylides derived from A, a rigid sulfonium precursor, B (lone pair anti to Cα) appears to be more stable than C (lone pair gauche to both Cα and Cα). A MO study suggests the stabilizing factor in question is due to the [image omitted] orbital interaction between the lone pair group orbital and the σ* group orbital of the adjacent S+-Cα bond, the interaction being at a maximum when the orbitals involved are either syn or anti coplanar.

For Abstract see ChemInform Abstract in Full Text.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The emission properties of tetra and hexa methyl sulphanyl (SMe) substituted sexithiophenes have been studied in solution form using time-resolved up-conversion photoluminescence technique. The SMe substituents have an electron donating effect which compensates for the loss of π-electron conjugation caused by the twisted conformation of the molecular geometry. Enhanced conjugation however does not lead to long recombination time due to the heavy atom effect, which increases the nonradiative decay rate.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.