A novel approach of electrolysis using alternating current was applied in the sulfur–sulfur bond metathesis of symmetrical disulfides towards unsymmetrical disulfides. As initially expected, a statistical distribution in disulfides was obtained. Furthermore, the influence of electrode polarisation by alternating current was investigated on a two‐disulfide matrix. The highly dynamic nature of this chemistry resulted in the creation of dynamic disulfide libraries by expansion of the matrices, consisting of up to six symmetrical disulfides. In addition, mixing of matrices and stepwise expanding of a matrix by using alternating current electrolysis were realised.
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 -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 -electron system with nonalternant 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 nonalternant nature of azupyrene is also associated with a more localized charge distribution, as can be seen in 1 H and 13 C nuclear magnetic resonance shifts, as well as the C1s core-level shifts. 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 DFT-based structures and for the theoretical assignment of the vibrational modes of the infrared spectra, where major topology-related differences are apparent.
Defects play a critical role for the functionality and
performance
of materials, but the understanding of the related effects is often
lacking, because the typically low concentrations of defects make
them difficult to study. A prominent case is the topological defects
in two-dimensional materials such as graphene. The performance of
graphene-based (opto-)electronic devices depends critically on the
properties of the graphene/metal interfaces at the contacting electrodes.
The question of how these interface properties depend on the ubiquitous
topological defects in graphene is of high practical relevance, but
could not be answered so far. Here, we focus on the prototypical Stone–Wales
(S–W) topological defect and combine theoretical analysis with
experimental investigations of molecular model systems. We show that
the embedded defects undergo enhanced bonding and electron transfer
with a copper surface, compared to regular graphene. These findings
are experimentally corroborated using molecular models, where azupyrene
mimics the S–W defect, while its isomer pyrene represents the
ideal graphene structure. Experimental interaction energies, electronic-structure
analysis, and adsorption distance differences confirm the defect-controlled
bonding quantitatively. Our study reveals the important role of defects
for the electronic coupling at graphene/metal interfaces and suggests
that topological defect engineering can be used for performance control.
The synthesis of 1,3‐oxazoles from symmetrical and unsymmetrical alkynes was realized by an iodonium cation‐pool electrolysis of I2in 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.
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