High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Interdependence of chemical structure, thin‐film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high‐mobility, solution‐processed polymers for large‐area and flexible electronics applications. There is a specific need to achieve >1 cm² V^?1 s^?1 field‐effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron‐transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene‐diimide based donor–acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field‐effect transistors show maximum μ of 2.4 cm² V^?1 s^?1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface‐segregated prevalently edge‐on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high‐electron‐mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure–property nexus in semiconducting polymer thin films.     

Optical reorientation in cholesteric nematic mixtures

Abstract

The optical Fréedericksz transition for linearly polarized light at normal incidence is studied in mixtures of nematic E7 and cholesteric C15 in cells coated for homeotropic alignment. The reorientation process is found to be dramatically different from the case of pure nematic samples showing the phenomenon of optical phase locking and large hysteresis. These effects are ascribed to the occurrence of self-induced stimulated light scattering, which does not occur in pure nematics.     

Determination of the dielectric function of porous silicon by high-order laser-harmonic radiation

Porous-silicon reflectance has been determined over a large energy range, from 1 eV to 16 eV, by combining a NIR/visible/UV spectrometer with a new VUV light source as laser-harmonic radiation. The porous-silicon dielectric function was deduced from reflectance measurements by Kramers–Kronig analysis. We point out that, for the first time, laser harmonics have been applied in the optical characterization of materials as a new and suitable alternative to synchrotron radiation. Received: 9 January 2001 / Accepted: 28 April 2001 / Published online: 20 June 2001     

A new photocyclization approach to the rare 1,3-thiazino[6,5-b]indol-4-one derivatives

The analogs of indole phytoalexin cyclobrassinon have been prepared in four steps from corresponding 1-substituted 2-chloroindole-3-carboxylic acids, employing a hitherto unknown photochemical cyclization of new indolyl thiocarbamates to 1,3-thiazino[6,5-b]indole-4-one derivatives as a key step.     

Zum Phosphornachweis

Ohne Zusammenfassung     

Mechanical Properties of 3-Glycidoxypropyltrimethoxysilane Based Hybrid Organic-Inorganic Materials

Hybrid organic-inorganic materials were synthesized from acid catalysed sols of tetraethyl orthosilicate, 3-glycidoxypropyltrimethoxysilane and titanium or zirconium alkoxides. The mechanical properties of these materials were measured in different conditions of preparation. The elastic modulus E was determined by a resonance method and by Knoop microindentation. After a thermal treatment at 125°C for 120 h, E was around 3–5 and 1–2 GPa for the samples synthesized with titanium butoxide or zirconium butoxide, respectively. An increase in E in the samples cured for longer times was observed. Knoop microhardness also increased with the heating time and was larger in samples synthesized from titanium alkoxides than zirconium alkoxides. The two methods gave results in good agreement when applied to samples treated for shorter times. In the other samples Knoop microindentation gave a larger value of E compared to the resonance vibration method. Hardness to elastic modulus ratio, H/E, was evaluated by Knoop microindentation. The elastic recovery at the longest heat treatment time was similar to that of soda-lime glasses. Fracture toughness was measured by three points flexural test, a _KIc in the range of 0.4–0.5 MPa m^1/2 was evaluated for samples treated during 168 h.     

Oligothiophenes Nano‐organized on a Cyclotetrasiloxane Scaffold as a Model of a Silica‐Bound Monolayer: Evidence for Intramolecular Excimer Formation

Excimer formation in a new class of terthiophene‐based fluorophores covalently bonded to a cyclotetrasiloxane scaffold has been demonstrated and the photophysical process ruling it has been investigated in detail and modeled theoretically. In contrast to the conventional systems in which long‐living fluorophores such as pyrene are linked in the same molecule, an excimer is formed only when two terthiophene‐based branches nano‐organized on the same cyclotetrasiloxane scaffold are close enough together when excitation takes place. In such a case, excimer formation is extremely efficient, and the new bound excited states are quite stable.     

New approaches in GMO detection

The steady rate of development and diffusion of genetically modified plants and their increasing diversification of characteristics, genes and genetic control elements poses a challenge in analysis of genetically modified organisms (GMOs). It is expected that in the near future the picture will be even more complex. Traditional approaches, mostly based on the sequential detection of one target at a time, or on a limited multiplexing, allowing only a few targets to be analysed at once, no longer meet the testing requirements. Along with new analytical technologies, new approaches for the detection of GMOs authorized for commercial purposes in various countries have been developed that rely on (1) a smart and accurate strategy for target selection, (2) the use of high-throughput systems or platforms for the detection of multiple targets and (3) algorithms that allow the conversion of analytical results into an indication of the presence of individual GMOs potentially present in an unknown sample. This paper reviews the latest progress made in GMO analysis, taking examples from the most recently developed strategies and tools, and addresses some of the critical aspects related to these approaches.