Carlos

Extra energy required: One of the most critical issues facing society today is energy – where do we get it from, how do we use it, how do we store it, how can we save it. Chemists play a decisive role in facing these challenges to secure a ready supply of energy for generations to come. To highlight the importance of this topic and the contributions that chemists around the world make, this special issue is dedicated to energy conversion and storage. Graphic designed by Freepik. http://www.freepik.com/free-vector/ batteries_800894.htm

Several carbazole-based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1-position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1, 2 a, and 3–6. The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X-ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1, 2 a, and 3–5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield (Φ_F) in the solid state, therefore boron complexes of the carbazole–benzothiazole hybrids 2 b–f, which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal-packing analyses, and the dyes exhibited color-tunable solid-state fluorescence.

Carbazole-based BODIPYs (see figure) were synthesized by using organometallic approaches. These compounds exhibited large Stokes shifts and fluoresced both in solution and in the solid state. The fluorescence properties correlated well with the results of crystal packing analyses, and these dyes exhibited color-tunable solid-state fluorescence.

The water stable UiO-66(Zr)-(CO₂H)₂ MOF exhibits a superprotonic conductivity of 2.3×10⁻³ S cm⁻¹ at 90 °C and 95 % relative humidity. Quasi-elastic neutron scattering measurements combined with aMS-EVB3 molecular dynamics simulations were able to probe individually the dynamics of both confined protons and water molecules and to further reveal that the proton transport is assisted by the formation of a hydrogen-bonded water network that spans from the tetrahedral to the octahedral cages of this MOF. This is the first joint experimental/modeling study that unambiguously elucidates the proton-conduction mechanism at the molecular level in a highly conductive MOF.

Proton conductivity: The superprotonic behavior of the water-stable UiO-66(Zr)-(CO₂H)₂ metal–organic framework (MOF) was examined at the molecular level by combining quasi-elastic neutron scattering measurements and aMS-EVB3 molecular dynamics simulations. The proton transport is shown to be assisted by the formation of a hydrogen-bonded network of water molecules that spans from the tetrahedral to the octahedral cages of this MOF.

Novel synthetic methodologies allow increasingly efficient access to known organic materials, as well as the preparation of otherwise inaccessible species. Pd-catalyzed coupling of aromatic dihalides to ortho-diaminoarenes furnishes embedded stable N,N′-dihydropyrazines expediently and in often excellent yields. The embedded N,N′-dihydropyrazines can then be oxidized by MnO₂ to give substituted azatetracenes, azapentacenes, azahexacenes, and azaheptacenes, which are soluble, processable, and stable. This powerful Pd-catalyzed methodology allows the preparation of azaacenes, including diaza-, tetraaza- and hexaazaacenes. In combination with a suitable Pd precursor, Buchwald-type biarylphosphines have been shown to give excellent results. Activated dihalides such as 2,3-dihaloquinoxalines are coupled easily under simplified conditions, whereas 2,3-dibromoacenes require more stringent conditions and advanced catalyst precursors. Pd catalysts effect the assembly of azaacenes with otherwise difficult to obtain substitution patterns. High yields and flexibility make this method most attractive.

Palladium catalysis is a new and powerful way to construct azaacene frameworks. It allows coupling of aromatic ortho-diamines to aromatic ortho-dihalides, resulting in embedded N,N′-dihydropyrazines. This reaction works well for N,N′-dihydropyrazines that are part of larger (≥4 ring), linearly annulated dihydroacene types. Oxidation of these N,N′-dihydropyrazines then gives azaacenes.

A new class of rigid twisted truxenone oligomers with an enlarged π backbone has been established by oxidative dimerization reactions. The resulting extended conjugated systems have large extinction coefficients and low-lying LUMO levels and show good solubility in common organic solvents, thus making them attractive compounds as new electron acceptors in organic electronics. Their suitability as electron acceptors has been demonstrated in bulk-heterojunction organic solar cells with poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) as the donor material.

Twisted: Rigid truxenone oligomers with an extended π backbone (see example structure) were synthesized by oxidative dimerization reactions. The resulting extended conjugated systems, which dissolve well in common organic solvents, have large extinction coefficients and low-lying LUMO levels. Their suitability as electron acceptors for organic electronics has been demonstrated in bulk-heterojunction organic solar cells.

Ultrapure blue-fluorescent molecules based on thermally activated delayed fluorescence are developed. Organic light-emitting diode (OLED) devices employing the new emitters exhibit a deep blue emission at 467 nm with a full-width at half-maximum of 28 nm, CIE coordinates of (0.12, 0.13), and an internal quantum efficiency of ≈100%, which represent record-setting performance for blue OLED devices.

A new, highly adaptable type of phosphinamide-based hydrogen bonding is representatively demonstrated in π-conjugated phosphole materials. The rotational flexibility of these intermolecular P=O−H−N hydrogen bonds is demonstrated by X-ray crystallography and variable-concentration NMR spectroscopy. In addition to crystalline compounds, phosphinamide hydrogen bonding was successfully introduced into the self-assembly of soft crystals, liquid crystals, and organogels, thus highlighting the high general value of this type of interaction for the formation of organic soft materials.

New HOPe: Dithienophosphole-based phosphinamides (see structure) display rotationally flexible hydrogen bonding that contrasts with that of their carboxamide cousins. Besides the novel hydrogen-bonding motif, these compounds also demonstrated unique photophysical and amphiphilic properties as a result of hydrogen-bond-directed self-assembly.

An efficient palladium-catalyzed asymmetric synthesis of axially chiral vinyl arenes from aryl bromides and hydrazones is reported. The products were easily oxidized to axially chiral biaryl compounds, and the phosphine oxides were readily reduced to phosphine ligands.

With a twist: An enantioselective palladium-catalyzed synthesis of atropisomeric vinyl arenes from aryl bromides and hydrazones is reported. The use of hydrazone precursors as coupling partners resulted in mild reaction conditions, and thus a broad functional-group tolerance. The products were isolated with ee values of up to 97 %. Ts=4-toluenesulfonyl.