Solvent-Adaptive Behavior of Oligospirobifluorenes at the Surface of Quartz Crystal Microbalances-A Conformational Process.

Oligospirobifluorenes represent promising building blocks for the generation of microporous sensor materials based on their restricted flexibility. The contact with specific solvents leads to a change of the three-dimensional spirobifluorene structure. The single fluorene moieties unfold to an open structure with an increased volume due to intermolecular interactions with the solvent, detectable by NMR spectroscopy. The induced microporosity was further investigated by affinity comparisons of aromatic analytes with high fundamental frequency quartz crystal microbalances.

Solvent-Adaptive Behavior of Oligospirobifluorenes at the Surface of Quartz Crystal Microbalances- A Conformational Process.

Invited for this month's cover are the groups of Siegfried R. Waldvogel at the Johannes Gutenberg University Mainz and of Josef Salbeck at the University Kassel (both Germany). The image shows the swelling of a blowfish to represent the reversible conformational change of an oligospirobifluorene derivative upon solvation. Read the full text of the article at 10.1002/cplu.201600583.

Photoinduced sign change of the magnetoresistance in field-effect transistors based on a bipolar molecular glass.

The application of a novel bipolar molecular glass in field-effect transistors leads to devices with photoinduced magnetoresistance (MR) sign change. In darkness a low external magnetic field increases the resistance (positive MR up to +0.1%), while a magnetic-field induced resistance decrease (negative MR up to -6.5%) can be achieved under illumination.

Electronic properties of spiro compounds for organic electronics.

The electronic properties of p-type, n-type, and ambipolar spiro materials have been investigated using a combination of photoemission spectroscopy, electron energy-loss spectroscopy, and density functional based calculations. Our results provide insight into the occupied density of states as well as the electronic excitation spectra. Comparison of experimental and theoretical data allows the identification of the orbitals responsible for charge transport and optical properties.

Ultralong single organic semiconducting nano/microwires based on spiro-substituted perylenetetracarboxylic diimide.

An ultralong single organic semiconducting nano/microwire (NMW) is difficult to obtain. Here we show that this NMW can easily be prepared by using drying under solvent atmosphere method. This technique is not only unique, but also very compatible with our active material, spiro-substituted perylenetetracarboxylic diimide. A single NMW with a length of up to ∼5.5 mm and an aspect ratio of ∼9200 can be obtained. Finally, we succeeded to measure the electrical resistivity of a single NMW with values between 1 × 10(2) and 1 × 10(4) Ω m and the growth direction can be controlled as well by using a prestructured substrate.

Bipolar redox behaviour, field-effect mobility and transistor switching of the low-molecular azo glass AZOPD.

We present electrochemical and spectroelectrochemical data for the bipolar azo compound N,N'-diphenyl-N,N'-bis[4-(phenylazo)phenyl]-4,4'diaminobiphenyl (AZOPD) demonstrating reversible bipolar redox behaviour with a bandgap of 2.1 eV. The reduced species formed upon two-electron transfer can be described as bis(radical anion) as was confirmed by comparison with a reference compound with only one azo chromophore. Hole and electron transport behaviour in amorphous films was demonstrated by the fabrication of organic field-effect transistors using gold and magnesium contacts, respectively. The transistors are sensitive to light due to E-Z photoisomerization.

N,N'-dimethyl-2,3-dialkylpyrazinium salts as redox-switchable surfactants? Redox, spectral, EPR and surfactant properties.

N,N'-dimethyl-2,3-dialkylpyrazinium salts show reversible transitions between all redox stages and a monolayer formation at the air-water interface that suggests their use as redox-switchable surfactants.