Search

Precise synthesis of graphene nanoribbons (GNRs) is of great interest to chemists and materials scientists because of their unique opto-electronic properties and potential applications in carbon-based nanoelectronics and spintronics. In addition to the tunable edge structure and width, introducing curvature in GNRs is a powerful structural feature for their chemi-physical property modification. Here, we report an efficient solution synthesis of the first pyrene-based GNR (PyGNR) with curved geometry via one-pot K-region oxidation and Scholl cyclization of its corresponding well-soluble tetrahydropyrene-based polyphenylene precursor. The efficient A 2 B 2 -type Suzuki polymerization and subsequent Scholl reaction furnishes up to ∼35 nm long curved GNRs bearing cove- and armchair-edges. The construction of model compound 1, as a cutout of PyGNR, from a tetrahydropyrene-based oligophenylene precursor proves the concept and efficiency of the one-pot K-region oxidation and Scholl cyclization, which is clearly revealed by single crystal X-ray diffraction analysis. The structure and optical properties of PyGNR are investigated by Raman, FT-IR, solid-state NMR, STM and UV-Vis analysis with the support of DFT calculations. PyGNR exhibits a narrow optical bandgap of ∼1.4 eV derived from a Tauc plot, qualifying as a low-bandgap GNR. Moreover, THz spectroscopy on PyGNR estimates its macroscopic charge mobility μ as ∼3.6 cm 2 V -1 s -1 , outperforming several other curved GNRs reported via conventional Scholl reaction., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Examples of isolated boron substituted nitroxide radicals are rare. The reaction of the reactive cyclic boraalkene 3 with nitrosobenzene yields a mixture of the [2 + 2] cycloaddition product 4a, the B -nitroxide radicals 5a and 6a and the azoxybenzene co-product 7a via a bora nitroso ene reaction pathway, the boron analogue of the nitroso ene reaction. The products were separated by flash chromatography, and the B -nitroxide radicals were characterized by X-ray diffraction and EPR spectroscopy. Radical 5a was shown to be a hydrogen atom abstractor. Both the B -nitroxide radicals are more easily oxidized compared to e.g. TEMPO, as shown by cyclic voltammetry., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Thermal treatment of the bicyclo[1.1.0]tetrasilatetraamide [Si 4 {N(SiMe 3 )Dipp} 4 ] 1 resulted in the formation of a highly unsaturated six-vertex silicon cluster [Si 6 {N(SiMe 3 )Dipp} 4 ] 2 with only four amine-substituents and two ligand-free silicon atoms. In solution, a major and a minor conformer of this cluster are in equilibrium according to multinuclear NMR spectroscopy, lineshape analysis, DFT calculations and molecular dynamics simulations. The bonding situation in the highly unsaturated cluster features lone pair type character at the ligand-free silicon atoms and partial single and double bond character in the upper butterfly-shaped ring of 2 . This allows to consider 2 as the silicon analogue of a butalene isomer., (This journal is © The Royal Society of Chemistry 2020.)

Interfaces that can change their chemistry on demand have huge potential for applications and are prerequisites for responsive or adaptive materials. We report on the performance of a newly designed n -butyl-arylazopyrazole butyl sulfonate (butyl-AAP-C 4 S) surfactant that can change its structure at the air-water interface by E / Z photo-isomerization in an unprecedented way. Large and reversible changes in surface tension (Δ γ = 27 mN m -1 ) and surface excess (Δ Γ > 2.9 μmol m -2 ) demonstrate superior performance of the butyl-AAP-C 4 S amphiphile to that of existing ionic surfactants. Neutron reflectometry and vibrational sum-frequency generation spectroscopy reveal that these large changes are caused by an unexpected monolayer-to-bilayer transition. This exceptional behavior is further shown to have dramatic consequences at larger length scales as highlighted by applications like the light-triggered collapse of aqueous foam which is tuned from high (>1 h) to low (<10 min) stabilities and light-actuated particle motion via Marangoni flows., (This journal is © The Royal Society of Chemistry 2020.)

In the presence of two molar equiv. of B(C 6 F 5 ) 3 p -benzoquinone reacts with persistent radicals TEMPO, trityl or decamethylferrocene by single electron transfer to give doubly O -borylated benzosemiquinone radical anions with TEMPO + , trityl or ferrocenium counter cations. All three [(C 6 F 5 ) 3 B] 2 -semiquinone radical anion salts were characterized by X-ray diffraction. The addition of donor reagent THF or DMSO induced rapid back electron transfer, in the case of the [(C 6 F 5 ) 3 B] 2 -semiquinone radical anion oxoammonium salt giving rise to the formation of the (C 6 F 5 ) 3 B-DMSO (or THF) Lewis adduct, p -benzoquinone and the TEMPO radical. The reaction of 9,10-anthraquinone or acenaphthenequinone with either the Gomberg dimer or in 1 : 1 stoichiometry in the presence of two molar equiv. of B(C 6 F 5 ) 3 gave the respective two-fold O-B(C 6 F 5 ) 3 containing 9,10-anthrasemiquinone or acenaphthene-semiquinone radical anion salts with either Ph 3 C + or counter cations. These products were also characterized by X-ray diffraction. The salts showed analogous back electron shuttling behavior upon treatment with DMSO. 9,10-Phenanthrenequinone reacted analogously with B(C 6 F 5 ) 3 and the electron rich ferrocene. The [(C 6 F 5 ) 3 B] 2 -9,10-phenanthrene-semiquinone salt was characterized by X-ray diffraction. The radical anions were characterized by ESR spectroscopy.

The trifunctional P/B/B frustrated Lewis pairs 11a-c featuring bulky aryl groups at phosphorus [Dmesp ( a ), Tipp ( b ), Mes* ( c )] react with H 2 by heterolytic hydrogen splitting followed by cleavage of HB(C 6 F 5 ) 2 to give the zwitterionic six-membered heterocyclic PH phosphonium/borate products 14a-c . Compounds 11a,b react with carbon monoxide by means of a Lewis acid induced CO insertion/rearrangement sequence that eventually results in the formation of the macrocyclic dimers 17a,b . The respective carbonylation reaction of the Mes*P/B/B FLP gives the macrocyclic trimer 18c . The new products were characterized spectroscopically and by X-ray diffraction and the reaction mechanism was analyzed by DFT calculations.