Water-soluble arylazoisoxazoles are introduced as an additional scaffold to the existing arylazoheteroarenes and open the door for tailor-made properties in molecular and materials chemistry. They were found to combine excellent photochromic behavior with long thermal life times. Supramolecular aggregates were formed by host–guest interaction and gelation.

Abstract

Azoheteroarenes are emerging as powerful alternatives to azobenzene molecular photoswitches. In this study, water-soluble arylazoisoxazole photoswitches are introduced. UV/vis and NMR spectroscopy revealed moderate to very good photostationary states and reversible photoisomerization between the E- and Z-isomers over multiple cycles with minimal photobleaching. Several arylazoisoxazoles form host–guest complexes with β- and γ-cyclodextrin with significant differences in binding constants for each photoisomer as shown by isothermal titration calorimetry and NMR experiments, indicating their potential for photoresponsive host–guest chemistry in water. One carboxylic acid functionalized arylazoisoxazole can act as a hydrogelator, allowing gel properties to be manipulated reversibly with light. The hydrogel was characterized by rheological experiments, atom force microscopy and transmission electron microscopy. These results demonstrate that arylazoisoxazoles can find applications as molecular photoswitches in aqueous media.

A copper molybdovanadate with mixed-valent vanadium (V⁴⁺/V⁵⁺=4/3) and molybdenum (Mo⁵⁺/Mo⁶⁺=8/2) cations exhibits improved catalytic activity (conv.: 96.8 %) compared with the complex (Cpyr)₅PV₂Mo₅W₅O₄₀ [conv.: 88.51 %, Cpyr=(C₁₆H₃₂C₅H₄N)⁺)] and could serve as a highly efficient heterogeneous catalyst in the selective oxidation of benzyl alcohols to benzaldehydes.

Abstract

A new organic-inorganic hybrid open-framework molybdovanadate with mixed-valences of vanadium (V⁴⁺/V⁵⁺=4/3) and molybdenum (Mo⁵⁺/Mo⁶⁺=8/2) cations has been synthesized. The complex possesses the unique V/Mo ratio (7/10), fascinating 8-C topological network and 1D 4-MR channels (7.793 Å×6.699 Å). Importantly, its catalytic activities for the selective oxidation of benzyl alcohol to benzaldehyde (oxidant: H₂O₂, 30 wt %) have been well evaluated. The results indicated that it exhibited improved catalytic activities (conv.: 96.8 %) compared with the catalyst (Cpyr)₅PV₂Mo₅W₅O₄₀ [conv.: 88.51 %, Cpyr=(C₁₆H₃₂C₅H₄N)⁺)], high recyclability and structural stability. Moreover, the conversions and selectivities (conv.: 82.4–92.5 %; sele.: 91.5–95.7 %) of the substrates containing electron donating groups (−OH, −CH₃, −OCH₃ and −Cl) were significantly higher than those of the substrate containing electron withdrawing group (−NO₂) (conv. 67.4 %; sele.: 80.8 %). This is due to the fact that the −NO₂ with a large Hammett substituent constant is not conducive to the generation of transition state products. The studies revealed the complex could act as a highly efficient heterogeneous catalyst in selective oxidation of benzyl alcohols.

Sulfone or carbonyl-based acceptor units were used to construct donor-acceptor conjugate organic fluorophores. Both TPA-SO and TPA-CO have solvent polarity-dependent photophysical properties for strong intramolecular charge transfer. As sulfone has weak intersystem crossing ability, TPA-SO has high fluorescence efficiency in solution and nanoparticles, and is a promising fluorescence dye.

Abstract

Electron-accepting units play vital roles in constructing donor-acceptor (D-A) conjugated organic optoelectronic materials; the electronic structures and functions of the acceptors need to be carefully unveiled to controllably tailor the optoelectronic properties. We have synthesized two D-A conjugated organic fluorophores, TPA-SO and TPA-CO, with similar molecular skeletons based on sulfone- or carbonyl-containing polycyclic aromatic acceptors. Both TPA-SO and TPA-CO display obvious solvent polarity-dependent photophysical properties and large Stokes shift of over 100 nm for strong intramolecular charge transfer processes. Experimental evidence indicates that the sulfone group in TPA-SO merely serves as a strong electron-withdrawing unit. TPA-SO shows yellowish-green emission with a peak at 542 nm and an absolute photoluminescence quantum yield (PLQY) of 98 % in solution, whereas the carbonyl group in TPA-CO can act as both an electron-withdrawing unit and spin transition convertor, so TPA-CO displays red emission with a low absolute PLQY of 0.32 % in solution. Impressively, upon going from solution to aggregate state, TPA-SO nanoparticles keep a high PLQY of 9.5 % and moderate biocompatibility, thus they are good nano-agents for cellular fluorescence imaging. The results reveal that the inherent acceptor characteristic acts as a crucial effect in the photophysical properties and applications of the organic fluorophores.

Controlled/living supramolecular polymerization has enabled the synthesis of well-defined nanostructures which are otherwise inaccessible under thermodynamically controlled, spontaneous self-assembly process. Yet, there is still room for improvement; here we show two-dimensional living supramolecular polymerization improved using an additive, which permits the synthesis of supramolecular nanosheets of better quality.

Abstract

Supramolecular polymers are formed through nucleation (i. e., initiation) and polymerization processes, and kinetic control over the nucleation process has recently led to the realization of living supramolecular polymerization. Changing the viewpoint, herein we focus on controlling the polymerization process, which we expect to pave the way to further developments in controlled supramolecular polymerization. In our previous study, two-dimensional living supramolecular polymerization was used to produce supramolecular nanosheets with a controlled area; however, these had rough edges. In this study, the growth of the nanosheets was controlled by using a ‘dummy’ monomer to produce supramolecular nanosheets with smoothed edges.

The chemistry at the germylene and dithiolene interface has rarely been explored. Here, we report a series of Lewis base-coordinated germanium(II) dithiolene complexes. Controlled hydrolysis of the carbene-coordinated germanium(II) dithiolene complex affords a dianionic bis-dithiolene-based germanium(II) species.

Abstract

The 1 : 2 reaction of the imidazole-based dithiolate (2) with GeCl₂ • dioxane in THF/TMEDA gives 3, a TMEDA-complexed dithiolene-based germylene. Compound 3 is converted to monothiolate-complexed (5) and N-heterocyclic carbene-complexed (7) germanium(II) dithiolene complexes via Lewis base ligand exchange. A bis-dithiolene-based germylene (8), involving a 3c–4e S-Ge-S bond, has also been synthesized through controlled hydrolysis of 7. The bonding nature of 3, 5, and 8 was investigated by both experimental and theoretical methods.

Changes in the assembly of Pt^II complexes on layered double hydroxide (LDH) nanoparticles. Under dry conditions, Pt^II complexes are attached to the LDH nanoparticles like starfish on the rocks, and exhibit a monomer-derived green emission. Under humid conditions, the mobility of Pt^II complexes increases due to the adsorption of water, like fish swimming among the rocks, resulting in an assembly-derived orange emission. More information can be found in the Research Article by M. Yoshida, M. Kato and co-workers (DOI: 10.1002/chem.202301993). Cover art by Hibiki Asahori.

The large-scale synthesis of cycloparaphenylene building blocks is illustrated. It represents the different syntheses in continuous flow and how the building blocks can be assembled. The final robotic arm allows aromatization to the macrocyclic CPP ring; the color change showing that all the phenyl units are now the same. More information can be found in the Research Article by H. A. Wegner and co-workers (DOI: 10.1002/chem.202302173).