Toward Singlet–Triplet Bistable Nonalternant Kekulé Hydrocarbons: Azulene-to-Naphthalene Rearrangement

Recent developments of open-shell singlet diradicaloids motivated the search for stable singlet–triplet bistable nonalternant polycyclic hydrocarbons. During the synthesis of this type of molecule, such as the dibenzo-cyclohepta­[<i>def</i>]­fluorene <b>3</b>, an unexpected azulene-to-naphthalene rearrangement was observed at room temperature, which resulted in new nonalternant hydrocarbons <b>8a</b>/<b>8b</b> with a closed-shell singlet ground state. These studies provided insight into the unique chemistry of azulene and challenges for the synthesis of singlet–triplet bistable polycyclic hydrocarbons

7,14-Diaryl-Substituted Zethrene Diimides as Stable Far-Red Dyes with Tunable Photophysical Properties

Synthesis and physical characterizations of a series of 7,14-diaryl-substituted zethrene diimides (ZDIs) bearing different substituents (alkyl chain, oligoethyleneglycol ether chain, and aryl group) at the imide sites as well as at the bay regions are described in this study. The synthesis takes advantage of Pd-catalyzed cyclodimerization reaction that allows construction of zethrene core and substitution at the bay region in one single step. The partially cyclized ZDI is also separated as a minor product. The carboxylic acid group is introduced to the bay region for the purpose of further bioconjugation. The photophysical properties, electrochemical properties, and photostability of these ZDI dyes are investigated with UV/vis spectroscopic measurements, cyclic voltammetry measurements, and photoirradiation tests. These dyes exhibit tunable photophysical properties in the far-red spectral region with moderate fluorescent quantum yields and good stability. The enhanced stability as compared to the parent zethrene and the 7,14-substituted zethrenes can be attributed to the electron-withdrawing effect of the imide groups and the kinetic blocking of the most reactive sites at the bay region

Stable <i>meso</i>-Fluorenyl Smaragdyrin Monoradical

The facile synthesis and physical characterization of a <i>meso-</i>fluorenyl smaragdyrin monoradical <b>4</b>, which is stable due to efficient spin delocalization and kinetic blocking, is reported. It has a small energy gap and can be oxidized and reduced into the respective cation and anion, showing different charge distribution and electronic absorption properties

Elimination of Burn-in Open-Circuit Voltage Degradation by ZnO Surface Modification in Organic Solar Cells

Photodegradation of inverted organic solar cells based on ZnO as an electron transport layer (ETL) was studied over short time scales of 5 min and 8 h. Devices with ZnO as ETL reproducibly exhibited a steep loss of open-circuit voltage, <i>V</i>_OC, and shunt resistance, <i>R</i>_SH, in a matter of minutes upon illumination. Removing the UV-content of illumination minimized <i>V</i>_OC loss and impact on the device’s shunting behavior, indicating its role in the loss. Application of an ultrathin layer of Al on ZnO led to almost negligible photoinduced <i>V</i>_OC loss up to 8 h of exposure. By applying the fundamental Shockley diode equation, we approximated the <i>V</i>_OC loss to be caused by dramatic increases in reverse saturation current <i>I</i>₀. We attribute the increased rate of recombination to diminished carrier selectivity at the ZnO/organic interface. Devices with Al modified ZnO ETL demonstrated remarkable <i>R</i>_SH (1.4 kΩ cm² at 1 sun), rectification ratio (10⁶) and reverse saturation current density (2.1 × 10^–7 mA/cm²)

Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenyl­ethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

The straightforward synthesis of 3,5-di­(triphenyl­ethylenyl) BODIPYs <b>1</b>–<b>3</b> from the condensation of 2-(triphenyl­ethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of <b>1</b> resulted in a “1,2-migratory shift” of one triphenyl­ethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry

Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenyl­ethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

The straightforward synthesis of 3,5-di­(triphenyl­ethylenyl) BODIPYs <b>1</b>–<b>3</b> from the condensation of 2-(triphenyl­ethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of <b>1</b> resulted in a “1,2-migratory shift” of one triphenyl­ethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry

Two-Dimensional Molybdenum Disulfide as a Superb Adsorbent for Removing Hg²⁺ from Water

One feature of two-dimensional (2D) molybdenum disulfide nanosheets is the huge sulfur-rich surface area, which might lead to the strong adsorption of Hg²⁺ in water, because the sulfur on the surfaces could strongly bind to Hg²⁺. In this work, the adsorption of Hg²⁺ on 2D molybdenum disulfide sheets in water has been studied in order to develop a novel and efficient adsorbent for removing Hg²⁺ from water. The study was performed through the measurements of adsorption isotherm and kinetics, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The partially oxidized 2D molybdenum disulfide sheets with less than five S–Mo–S layers were prepared through the exfoliation of natural molybdenite. AFM observations illustrated a fast and multilayer Hg²⁺ adsorption on the surface of 2D molybdenum disulfide. The results of adsorption tests and SEM-EDS have indicated that 2D molybdenum disulfide was a superb adsorbent. The adsorption followed the Freundlich isotherm model and fitted well with pseudo-second-order kinetics model. The excellent Hg²⁺ capture property was mainly attributed to the complexation of Hg²⁺ with intrinsic S and oxidation-induced O atom exposed on 2D molybdenum disulfide surfaces, as well as the electrostatic interaction between negatively charged 2D molybdenum disulfide and cation Hg²⁺

Synthesis of [2]Catenanes by Template-Directed Clipping Approach

A series of [2]­catenanes were efficiently synthesized in high yields by a template-directed clipping approach with the formation of one macrocycle around another macrocycle containing a dialkylammonium recognition site. Their structures were identified by the NMR spectra and ESI mass spectrometry, and their geometries were investigated by the theoretical calculation

Kinetically Blocked Stable 5,6:12,13-Dibenzozethrene: A Laterally π‑Extended Zethrene with Enhanced Diradical Character

Although the ground-state and physical properties of zethrene and recently invented 1,2:8,9-dibenzozethrene have been well studied, the other dibenzozethrene isomer, i.e., 5,6:12,13-dibenzozethrene, remained unexplored. A short synthetic route to a kinetically blocked stable 5,6:12,13-dibenzozethrene derivative <b>5</b> is presented. The ground state is found to be open-shell singlet experimentally, and the theoretical <i>y</i>₀ was enhanced to 0.414, which corroborates nicely with the experimental and theoretical singlet–triplet energy gap

Improve the Operational Stability of the Inverted Organic Solar Cells Using Bilayer Metal Oxide Structure

Operational stability is a big obstacle for the application of inverted organic solar cells (OSCs), however, less talked about in the research reports. Due to photoinduced degradation of the metal oxide interlayer, which can cause shunts generation and degeneration in ZnO interlayer, a significant degradation of open circuit voltage (<i>V</i>_oc) and fill factor (FF) has been observed by in situ periodic measurements of the device current density–voltage (<i>J</i>–<i>V</i>) curves with light illumination. By combining TiO_<i>x</i> and ZnO to form bilayer structures on ITO, the photovoltaic performance is improved and the photoinduced degradation is reduced. It was found that the device based on ZnO/TiO_<i>x</i> bilayer structure achieved better operational stability as compared to that with ZnO or TiO_<i>x</i> interlayer