Carlos

A novel class of multifused heteroacenes, developed and introduced by P. Bäuerle and co-workers on page 7217, combines the favorable structural and electronic elements of oligothiophenes and acenes. Their application in organic photovoltaics leads to encouraging power conversion efficiencies of 6.5%.

On page 6422, J.-H. Wu and G.-S. Liou demonstrate high-performance electrofluorochromic (EFC) devices using poly(4-cyanotriphenylamine) (CN-PTPA) with photoluminescent quantum yield of 21.9% as active layer. These reveal rapid response time less than 0.4 s, excellent EFC stability longer than 9000 s, and the highest fluorescence contrast ratio (Ioff/Ion) of 242 from neutral state to a non-fluorescent oxidized state to the best of our knowledge.

Monoamine 1, diamines 2–4, triamine 5, and tetraamine 6 have been synthesized by substituting dianisylamino groups at the 1-, 3-, 6-, and/or 8-positions of pyrene. Diamines 2–4 differ in the positions of the amine substituents. No pyrene–pyrene interactions are evident in the single-crystal packing of 3, 4, and 6. With increasing numbers of amine substituents, the first oxidation potential decreases progressively from the mono- to the tetraamine. These compounds show intense charge-transfer (CT) emission in CH₂Cl₂ at around 530 nm with quantum yields of 48–68 %. Upon stepwise oxidation by electrolysis or chemical oxidation, these compounds were transformed into radical cations 1^⋅+–6^⋅+ and dications 2²⁺–6²⁺, which feature strong visible and near-infrared absorptions. Time-dependent density functional theory studies suggested the presence of localized transitions from the pyrene radical cation and aminium radical cation, intervalence CT, and CT between the pyrene and amine moieties. Spectroscopic studies indicated that these radical cations and dications have good stability. Triamine 5 and tetraamine 6 formed efficient CT complexes with tetracyanoquinodimethane in solution. The results of EPR spectroscopy and density functional theory calculations suggested that the dications 2²⁺–4²⁺ have a triplet ground state, whereas 5²⁺ and 6²⁺ have a singlet ground state. The dication of 1,3-disubstituted diamine 4 exhibits a strong EPR signal.

Amine fine tuning: The radical cation and dication stability, spin distribution, spin state, and near-infrared absorptions of oligotriarylamines with a pyrene core (see figure) vary according to the number of amine substituents.

A series of ethynylated silanes, including tetraethynylsilane, was treated with tetraphenylcyclopentadienone at 300 °C under microwave irradiation to give the aromatized Diels–Alder adducts as sterically encumbered mini-dendrimers with up to 20 benzene rings. The sterically most congested adducts display red-shifted emission through intramolecular π–π interactions in the excited state.

Thermal enforcement: Naked tetraethynylsilane reacts with tetracyclone at 300 °C under microwave addition to give the sterically hindered fourfold cycloaddition product (see figure).

A ligand containing the thiazolo[5,4-d]thiazole (TzTz) core (acceptor) with terminal triarylamine moieties (donors), N,N′-(thiazolo[5,4-d]thiazole-2,5-diylbis(4,1-phenylene))bis(N-(pyridine-4-yl)pyridin-4-amine (1), was designed as a donor–acceptor system for incorporation into electronically active metal–organic frameworks (MOFs). The capacity for the ligand to undergo multiple sequential oxidation and reduction processes was examined using UV/Vis-near-infrared spectroelectrochemistry (UV/Vis-NIR SEC) in combination with DFT calculations. The delocalized nature of the highest occupied molecular orbital (HOMO) was found to inhibit charge-transfer interactions between the terminal triarylamine moieties upon oxidation, whereas radical species localized on the TzTz core were formed upon reduction. Conversion of 1 to diamagnetic 2+ and 4+ species resulted in marked changes in the emission spectra. Incorporation of this highly delocalized multi-electron donor–acceptor ligand into a new two-dimensional MOF, [Zn(NO₃)₂(1)] (2), resulted in an inhibition of the oxidation processes, but retention of the reduction capability of 1. Changes in the electrochemistry of 1 upon integration into 2 are broadly consistent with the geometric and electronic constraints enforced by ligation.

Give and take: A donor–acceptor–donor ligand, specifically designed to exhibit charge transfer, promotes conversion to diamagnetic cations during oxidation, each of which fluoresces at different wavelengths. Upon its incorporation into a metal–organic framework, the reducible nature of the thiazolo[5,4-d]thiazole core is carried forward, whereas oxidation processes cease altogether.

A 2e⁻/2H⁺ redox platform has been implemented in the ethenyl-bridged bisphosphol-3-ol 1 to afford the first phospholes that feature chemically reversible oxidations. Oxidation of the title compounds to the corresponding bisphosphol-3-one 2 leads to a change in conjugation topology and a concomitant hypsochromic shift of the lowest-energy absorption maximum by 100 nm. Electrochemical oxidation proceeds without any detectable intermediates, whereas the deprotonated form of 1 can be observed in an aprotic medium during the reduction of 2. This dianionic intermediate 3 is characterized by end absorptions that are bathochromically shifted by circa 200 nm compared to those of 2.

Teaching phospholes the switch: Unprecedented and reversible redox chemistry at the butadiene portion of phospholes is reported. Depending on the oxidation state of the implemented 2e⁻/2H⁺ redox platform in the ethenyl-bridged bisphospholes, the title compounds exhibit altered-conjugation topologies and thus optical properties. The reported chemistry enables future developments of new electrochromic switches that can be tuned over the entire visible spectrum.

Perovskite nanoparticle-based nanocomposite thin films composed of oleic acid-stabilized BaTiO₃ nanoparticles and poly(acrylic acid) are prepared by S.-W. Kim, J. Cho, and team on page 6262 using ligand exchange layer-by-layer assembly in organic media. The resultant nanocomposite films with high dielectric constant and low leakage current exhibit ferroelectric and piezoelectric properties that could be exactly controlled by the bilayer number, the type of inserted polymer, and the nanoparticle size.

Recent developments of plastic scintillators are reviewed, from 2000 to March 2014, distributed in two different chapters. First chapter deals with the chemical modifications of the polymer backbone, whereas modifications of the fluorescent probe are presented in the second chapter. All examples are provided with the scope of detection of various radiation particles. The main characteristics of these newly created scintillators and their detection properties are given.

Nous proposons dans cette revue les développements les plus récents sur la chimie des scintillateurs plastiques, plus précisément depuis 2000 jusqu′en mars 2014. La revue est divisée en deux sections : la première concerne les modifications chimiques de la matrice polymérique, alors que la deuxième section présente les modifications envisagées sur les molécules fluorescentes. Tous les exemples décrits sont fournis avec leurs propriétés caractéristiques de scintillation.

How have organic and polymer chemistry helped physicists to improve radiation detection? Various examples of chemically modified plastic scintillators (see figure) are given from 2000 to present.

The synthesis and characterization of a new type of chromophore, namely PePc consisting of a central phthalocyanine core and four fused perylene–bisimide (PBI) units is described for the first time. The entire architecture represents a highly extended conjugated heterocyclic π-system with C_4h symmetry. In order to guarantee pronounced solubility in organic solvents the corresponding PBI units were bay-functionalized with tert-butylphenoxy substituents. Next to the metal-free macrocycle, PePcH₂, also metallated macrocycles PePcM (M=Zn, Ni, Pb, Ru, Fe) were synthesized. The extensive fusion of the corresponding aromatic building blocks to the very large extended π-system leads to a very narrow HOMO–LUMO gap and as a consequence to transparency in the visible but light absorption in the NIR region. Significantly, the azomethine N-atoms N1N4 of PePcM and PePcH₂ are highly basic. The corresponding tetraprotonated systems can only be deprotonated with very strong non-nucleophilic bases such as phosphazene bases. In the protonated forms PePcMH₄⁴⁺ and PePcMH₆⁴⁺ the absorption maximum is shifted back to the visible region due to the loss of conjugation. The experimental findings were corroborated with quantum mechanical calculations.

Big wheel keep on turning: A new near infrared (NIR) chromophore, which is a hybrid of a central phthalocyanine core and four fused perylene moieties, is introduced. Complete characterization showed a surprisingly facile protonation of the azamethine groups of the phthalocyanine core and reversible switching of the NIR absorption in these very extended conjugated π-systems.

The development of a synthetic approach to a C_3v-symmetric tris-salicylaldehyde based on triptycene is presented. The tris-salicylaldehyde is a versatile precursor for porous molecular materials, as demonstrated in the [4+4] condensation reaction with a triptycene triamine to form a molecular shape-persistent porous cube. The amorphous material of the molecular porous cube shows a very high surface area of 1014 m² g⁻¹ (BET model) and a high uptake of CO₂ (18.2 wt % at 273 K and 1 bar). Furthermore, during the multistep synthesis of the tris-salicylaldehyde precursor, a relatively rare (twofold) addition of the aryne to the anthracene in the 1,4- and 1,4,5,8-positions have been found during a Diels–Alder reaction, as proven by X-ray structure analysis.

Get in shape! The synthesis of a shape-persistent porous molecular organic cube through a [4+4] condensation is presented. The amorphous material has a specific BET surface area of 1014 m² g⁻¹ and shows an uptake of 18.4 wt % of CO₂ (273 K, 1 bar) under ambient conditions with good Henry selectivities over N_2.

Corrosion is a global problem for any metallic structure or material. Herein we show how metals can easily be protected against acid corrosion using hydrophobic polyoxometalate-based ionic liquids (POM-ILs). Copper metal disks were coated with room-temperature POM-ILs composed of transition-metal functionalized Keggin anions [SiW₁₁O₃₉TM(H₂O)]ⁿ⁻ (TM=Cu^II, Fe^III) and quaternary alkylammonium cations (C_nH_2 n+1)₄N⁺ (n=7–8). The corrosion resistance against acetic acid vapors and simulated “acid rain” was significantly improved compared with commercial ionic liquids or solid polyoxometalate coatings. Mechanical damage to the POM-IL coating is self-repaired in less than one minute with full retention of the acid protection properties. The coating can easily be removed and recovered by rinsing with organic solvents.

This corrosion: Hydrophobic polyoxometalate-based ionic liquids (POM-ILs) are used as temporary acid-resistant coatings for copper metal. Complete protection against acid vapors and liquid acids is observed and the POM-IL coating can withstand mechanical damage by a self-repairing mechanism. The compounds are easily removed and recovered for subsequent usage.

Cold regions (the mountain chain in the illustration) and warm areas (the beach in the foreground) represent the temperature ramp applied to obtain extended molecular wires under illumination at the sub-monolayer level. The transhumance of amino-functionalized porphyrins along the close-packed atomic rows (the parallel roads) of the cold Ag(110) surface ends at the beach, where light induces their union (covalent bonding) as soon as they approach each other. For more details, see the Full Paper by A. Basagni et al. on page 14296 ff.

Extremely compliant sub-2-μm sensor films enable temperature mapping on complex 3D objects, like integrated circuits on printed circuit boards, food packages, and on human skin. In their stretchable form, these metal films withstand strains up to 275%. This imperceptible electronic foil technology platform offers new avenues for the design of complex, hybrid rigid-island stretchable-interconnect electronic devices such as RGB light-emitting diode (LED) strips that can be stretched and twisted without impairing their function.

We present a systematic study of metal–organic frameworks (MOFs) for the storage of oxygen. The study starts with grand canonical Monte Carlo simulations on a suite of 10 000 MOFs for the adsorption of oxygen. From these data, the MOFs were down selected to the prime candidates of HKUST-1 (Cu-BTC) and NU-125, both with coordinatively unsaturated Cu sites. Oxygen isotherms up to 30 bar were measured at multiple temperatures to determine the isosteric heat of adsorption for oxygen on each MOF by fitting to a Toth isotherm model. High pressure (up to 140 bar) oxygen isotherms were measured for HKUST-1 and NU-125 to determine the working capacity of each MOF. Compared to the zeolite NaX and Norit activated carbon, NU-125 has an increased excess capacity for oxygen of 237 % and 98 %, respectively. These materials could ultimately prove useful for oxygen storage in medical, military, and aerospace applications.

MOFs store oxygen too: Two metal–organic frameworks with open metal sites store oxygen at capacities far greater than that of an empty cylinder and are comparable to the state-of-the-art oxygen storage materials. Self-assembled materials allow for rational design of materials for adsorption of specific gases.