Topology Effects in Molecular Organic Electronic Materials: Pyrene and Azupyrene*.

Pyrene derivatives play a prominent role in organic electronic devices, including field effect transistors, light emitting diodes, and solar cells. The flexibility in the desired properties has previously been achieved by variation of substituents at the periphery of the pyrene backbone. In contrast, the influence of the topology of the central π-electron system on the relevant properties such as the band gap or the fluorescence behavior has not yet been addressed. In this work, pyrene is compared with its structural isomer azupyrene, which has a π-electron system with non-alternant topology. Using photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, and other methods, it is shown that the electronic band gap of azupyrene is by 0.72 eV smaller than that of pyrene. The difference of the optical band gaps is even larger with 1.09 eV, as determined by ultraviolet-visible absorption spectroscopy. The non-alternant nature of azupyrene is also associated with a more localized charge distribution. Further insight is provided by density functional theory (DFT) calculations of the molecular properties and ab initio coupled cluster calculations of the optical transitions. The concept of aromaticity is used to interpret the major topology-related differences.

Iodonium Cation-Pool Electrolysis for the Three-Component Synthesis of 1,3-Oxazoles.

The synthesis of 1,3-oxazoles from symmetrical and unsymmetrical alkynes was realized by an iodonium cation-pool electrolysis of I2 in acetonitrile with a well-defined water content. Mechanistic investigations suggest that the alkyne reacts with the acetonitrile-stabilized I+ ions, followed by a Ritter-type reaction of the solvent to a nitrilium ion, which is then attacked by water. The ring closure to the 1,3-oxazoles released molecular iodine, which was visible by the naked eye. Also, some unsymmetrical internal alkynes were tested and a regioselective formation of a single isomer was determined by two-dimensional NMR experiments.

Allylic Oxidation of Ester-Substituted 1,4-Dienes.

The cobalt-catalyzed hydrovinylation reaction and the Alder-ene reaction generate acyclic 1,4-dienes, which were investigated in the selenium dioxide oxidation to afford further functionalized dienes prone for follow-up reactions. The chemoselective allylic oxidation of ester-functionalized 1,4-dienes occurs at the most electron-rich double bond. The steric demand of the electron-rich, alkyl-substituted double bond determines the reaction pathway, whether the double bond transposition toward the conjugated 1,3-diene or the allylic oxidation is faster. As reaction products, 2,4-diene-6-ols or divinyl ketones were obtained.

Ambireactive (R3 P)2 BH2 Groups Facilitating Temperature-Switchable Bond Activation by an Iron Complex.

An iron pincer complex containing a hemi-labile (R3 P)2 BH2 group exhibits temperature-switchable reactivity patterns: a reversible B-H activation concomitant with a P-B bond cleavage is observed at room temperature. Below 4 °C, intra- and intermolecular C-H activation pathways are becoming faster and more dominant. Mechanistic investigations reveal that the lability of the (R3 P)2 BH2 group in combination with the exothermic formation of σ-bonded complexes are responsible for the switchable bond activation. Finally, a protocol for an iron-catalyzed H/D-exchange of organic solvents in the absence of oxidants has been developed.