Towards continuous junction (CJ) organic electronic devices: Fast and clean post-polymerization modification by oxidation using dimethyldioxirane (DMDO)

An advanced design concept for organic electronic devices relying on functional polymers is presented. The concept aims at realizing a gradual transition from an electron-donating to an electron-accepting material in a specific post-polymerization modification step. Hence, this approach facilitates a straight forward fabrication compared to conventional multi-layer architectures. The synthesis via microwave-assisted Cu(I)-catalyzed azide-alkyne cycloaddition of the reactive polymers based on sulfur, selenium and tellurium as active sites is presented; full characterization of model compounds and polymers is provided. Additionally, a reliable procedure for post-polymerization oxidation applying dimethyldioxirane is developed. Photophysical and electrochemical characteristics of the novel polymers reveal the feasibility but also the challenges of the continuous junction concept

Systematic investigations on 1,2,3-triazole-based compounds capable of second harmonic generation

1,2,3-Triazole-functionalized ene–yne compounds, synthesized by thiophene (selenophene) ring fragmentation followed by azide–alkyne cycloaddition, were investigated as a basis for nonlinear optical (NLO) materials capable of second harmonic generation (SHG). The structure–property relationship was mapped by systematic variation of the molecular scaffold, viz., elongation of the alkyl groups, isomerizations of both the double bond as well as the triazole moiety, sulfur oxidations, and a sulfur–selenium exchange. Nine novel molecular compounds were synthesized, of which eight are solids at room temperature. The latter were characterized by single-crystal X-ray diffraction (XRD). Five crystal structures lacked of inversion symmetry, a prerequisite for NLO activity. The corresponding materials were examined regarding SHG, UV–vis absorption, and powder XRD. By substituting S for Se, we were able to increase the SH intensity by a factor of 20. On the basis of the results, we propose a strategy to further improve the SHG efficiency of this class of materials

Stable organic field-effect-transistors with high mobilities unaffected by supporting dielectric based on phenylene-bridged thienobenzothiophene

We report on the electrical properties of organic field-effect transistors (OFET) based on a new class of organic semiconductors. The molecules consist of the same thieno[2,3-b][1] benzothiophene building blocks, connected by different pi-bridge spacers (ethylene, phenylene, and fluorophenylene). Molecular orbitals and highest occupied molecular orbital/lowest unoccupied molecular orbital energies were calculated and compared with results from cyclic voltammetric and UV-vis absorption measurements. In order to study the influence of the bridge groups on the molecular arrangement and surface interaction, the transistor performance on a wide range of dielectrics has been investigated in detail. These include as grown SiO2 and Al2O3 and also treated with octadecyltrichrolosilane and octadecylphosphonic acid, as well as Cytop and Parylene C. An extended study of the multitude of combinations of these materials revealed mobilities up to similar to 1 cm(2)/Vs, measured for devices made of the phenylene-bridged compound. Surprisingly, the mobility was quite independent of the supporting gate dielectric. Stability over time has been observed with no degradation after 5 months. By eliminating the hysteresis using Cytop, we were able to show that some of the molecules form films without long-term charge carrier trapping. These are interesting features for practical industrial processing of organic electronics. (C) 2014 AIP Publishing LLC

Charge-transfer states in triazole linked donor-acceptor materials: strong effects of chemical modification and solvation

A series of 1,2,3-triazole linked donor–acceptor chromophores are prepared by Click Chemistry from ene–yne starting materials. The effects of three distinct chemical variations are investigated: enhancing the acceptor strength through oxidation of the sulphur atom, alteration of the double bond configuration, and variation of the triazole substitution pattern. A detailed photophysical characterization shows that these alterations have a negligible effect on the absorption while dramatically altering the emission wavelengths. In addition, strong solvatochromism is found leading to significant red shifts in the case of polar solvents. The experimental findings are rationalized and related to the electronic structure properties of the chromophores by time-dependent density functional theory as well as the ab initio algebraic diagrammatic construction method for the polarization propagator in connection with a new formalism allowing to model the influence of solvation onto long-lived excited states and their emission energies. These calculations highlight the varying degree of intramolecular charge transfer character present for the different molecules and show that the amount of charge transfer is strongly modulated by the conducted chemical modifications, by the solvation of the chromophores, and by the structural relaxation in the excited state. It is, furthermore, shown that enhanced charge separation, as induced by chemical modification or solvation, reduces the singlet–triplet gaps and that two of the investigated molecules possess sufficiently low gaps to be considered as candidates for thermally activated delayed fluorescence

Synthesis of 1,1-Disubstituted Tetrahydroisoquinolines by Lithiation and Substitution, with in Situ IR Spectroscopy and Configurational Stability Studies.

Lithiation of N-Boc-1-phenyltetrahydroisoquinolines was optimized by in situ IR spectroscopy. The kinetics for rotation of the carbamate group and for the enantiomerization of the organolithium were determined. The organolithium is configurationally stable at low temperature, and the asymmetric synthesis of 1,1-disubstituted tetrahydroisoquinolines can be achieved with high yields and high enantiomer ratios. The chemistry was applied to the preparation of FR115427 and provides a way to recycle the undesired enantiomer in the synthesis of solifenacin