Highly Efficient and Thermally Durable Luminescence of 1D Eu3+ Coordination Polymers with Arsenic Bridging Ligands.

In this work, bisarsine oxides were evaluated as novel bridging ligands, aiming to develop practical and efficient luminescent lanthanide coordination polymers. We have synthesized one-dimensional (1D) Eu3+ coordination polymers that incorporate bisarsine oxide bridging ligands and hexafluoroacetylacetonate anions. These polymers exhibited a denser packing of chains compared to analogous polymers bridged with bisphosphine oxides. The coordination polymers demonstrated exceptional thermal stability and substantial emission quantum yields. Additionally, the bisarsine oxides induced a pronounced polarization effect, facilitating a sensitive electric dipole transition that yields considerably narrow band red emission. Remarkably, the Eu3+ coordination polymers with bisarsine oxides maintained intense emission even at 550 K. A distinctive feature of these polymers is their heating-induced emission enhancement observed when the temperature was increased from 300 K to 400 K.

Phenyl-Substituted Cage Silsesquioxane-Based Star-Shaped Giant Molecular Clusters: Synthesis, Properties, and Surface Segregation Behavior.

The crystallinity, solubility, and physical properties of polyhedral oligomeric silsesquioxane (POSS) compounds are highly dependent on their organic substituents. We previously synthesized a series of isobutyl-substituted star-shaped POSS derivatives with aliphatic chain linkers of different length. In this study, we prepared C3- and C6-linked phenyl-substituted star-shaped POSS derivatives (3Ph-C3 and 3Ph-C6) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q8-silsesquioxane (Q8M8H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5iBu-C3 and 5iBu-C6). Although 3Ph-C6 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3Ph-C3 was soluble even in THF and toluene, suggesting that the shorter linkers of the derivative afford a wider range of solvents for dissolution. Differential scanning calorimetry analysis showed that 3Ph-C3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3Ph-C6. Thermogravimetric analysis showed that the shorter linker in the phenyl-substituted star-shaped POSS derivative significantly increased the decomposition temperature compared with the longer linker. The annealed cast film of 3Ph-C3 at 340 °C above its melting temperature formed a transparent film even after cooling to room temperature. However, an opaque whitish film was formed in the case of 3Ph-C6. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3Ph-C3 and 3Ph-C6 were prepared by casting their chloroform solutions onto glass substrates overnight at room temperature. The static water contact angle measurements and XPS analysis for the castings film containing 3Ph-C3 and 3Ph-C6 suggested that degree of the segregation amount of 3Ph-C3 was larger than that of 3Ph-C6. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3Ph-C3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.

Breathing Metal-Organic Frameworks Supported by an Arsenic-Bridged 4,4'-Bipyridine Ligand.

Bent ligands bridged by heteroatoms have drawn significant interest as supramolecular coordination architectures. Traditionally, divalent group 16 elements are preferred over trivalent group 15 elements because of the anticipated steric hindrance. In this study, we explore metal-organic frameworks (MOFs) based on dipyridinoarsoles (DPAs), 4,4'-bipyridines bridged with an arsenic atom. An MOF with methyl-substituted DPA collapsed upon solvent removal, whereas that with phenyl-substituted DPA demonstrated breathing behavior due to guest molecule adsorption/desorption. In contrast, MOFs using the phosphorus analogue dipyridinophosphole exhibit inferior adsorption and lack breathing behavior. This is the first study to investigate the interplay among substituents, bridging elements, and dynamic behavior in MOFs using bent group 15 ligands.

Pnictogen-Bridged Diphenyl Sulfones as Photoinduced Pnictogen Bond Forming Emission Motifs.

In this study, pnictogen (Pn)-bridged diphenyl sulfones were synthesized as motifs for photoinduced dynamic rearrangement. The newly synthesized sulfones exhibited dual fluorescence at 298 K. Density functional theory calculations revealed that the longer-wavelength fluorescence was derived from the geometries after structural relaxation through photo-driven pnictogen bond formation between the O atom lone pair of the sulfonyl moiety and the antibonding orbital of the Pn-C bond. This is the first report on emission dynamics driven by pnictogen bond formation upon photoexcitation.

1,2,5-Triarylcycloalka[c]arsoles: Structural Effects of Fused-cycloalkanes on Stability and Photophysical Properties.

Herein, we have synthesized a variety of cycloalkane-fused arsoles. Cyclopentane and cyclohexane were incorporated into the cycloalkane-fused arsoles. Surprisingly, cyclohexane-fused arsole 2 a gradually decomposed via oxidative ring-opening under ambient conditions, while cyclopentane-fused 1 a was stable. In addition, the Stokes shift of 2 a (7766 cm-1 ) is larger than that of 1 a (5120 cm-1 ). The effects of the fused cycloalkane on the stability and photophysical properties were attributed to the distortion of the cycloalkane. Computational calculations demonstrated that the cyclohexane moiety in 2 a was frustrated upon being incorporated into the rigid arsole ring, while the cyclopentane moiety in 1 a was much less distorted.

Synthetic Strategy for AB2-Type Arsines via Bidentate Dithiolate Leaving Groups.

Despite their potential for several transition-metal-catalyzed reactions, arsenic ligands are poorly diversified. In this work, we developed an efficient synthetic methodology for AB2-type ligands, which is a typical motif in phosphorus systems, for example, in Buchwald ligands. The introduction of 1,2-benzenedithiol to tribromoarsine reduces the reactivity of two of the three reaction sites. After the substitution reaction with the first nucleophile involving the elimination of bromide, the substitution reaction with the second nucleophile produced AB2-type arsines through the elimination of the dithiolate anion. Among the various types of obtained AB2-type arsines, the arsa-Buchwald ligands, which are arsenic analogues of Buchwald ligands, were applied to the Suzuki-Miyaura cross-coupling reaction. Some of the arsa-Buchwald ligands showed activity comparable to that of the well-known Buchwald ligand, SPhos. Furthermore, the arsenic analogue of SPhos showed higher activity and stability than SPhos under open-air conditions.

Emission Properties of Eu(III) Complexes Containing Arsine and Phosphine Ligands with Annulated Structures.

In this study, we synthesized Eu3+ complexes containing arsine and phosphine oxides with annulated structures as the antenna ligands. The type of bridging in the annulated structures controlled the energy level of the triplet excited state and the intersystem crossing efficiency, leading to different emission properties. Eu3+ complexes bearing the arsine oxides showed a higher intensity ratio of electric/magnetic dipole transitions and energy-transfer efficiency than the complexes with the corresponding phosphine oxides.

Systematic Study of Pnictogen-Fused Heterofluorenes.

Heteroatom-fused π-conjugated molecules have attracted considerable attention, and various elements for such fusion have been investigated. Herein, we focused on pnictogen-fused heterofluorenes. The structures, reactivity with O2 and I2, coordination ability to AuCl, and photophysical properties were systematically studied to better understand the effects of pnictogen atoms on the nature of π-conjugated molecules.

2,3-Diarylbenzo[b]arsole: Structural Modification and Polymerization for Tuning of Photophysical Properties.

2,3-Diarylbenzo[b]arsoles were synthesized from zirconacycles and diiodophenylarsine. The structural modification to the luminophore was attained through diarylacetylene precursors, Suzuki-Miyaura coupling, and oxidation of the arsenic atom. The emission properties were controlled according to these modifications. The 2,3-diarylbenzo[b]arsoles showed aggregation-induced emission enhancement; the stronger emission was observed in the solid states than in solutions. In addition, Suzuki-Miyaura polycondensation and olefin metathesis polymerization produced main- and side-chain polymers, respectively. The resultant polymers showed different emission behaviors such as aggregation caused quenching and aggregation induced emission enhancement.

Reversible pH Responsive Aggregation Behavior of Size-Controlled Calcium Carbonate Composite Nanoparticles by Phytic Acid in Aqueous Solution.

Composite colloidal nanoparticles were prepared by a carbonate controlled-addition method in the presence of phytic acid, in which an aqueous ammonium carbonate solution was added into an aqueous solution of phytic acid and CaCl2. The number-average particle size of the colloidal particles was 76 ± 18 nm formed by using the molar ratio [phytic acid]/[Ca2+] = 0.5 from the complexation time of 1 h. The composite nanoparticles were stable for more than 5 days in the suspension under the quiescent condition. After isolation of the nanoparticles by ultrafiltration, the dried samples could be redispersed in water. Effects of the complexation times of the aqueous solution of phytic acid and CaCl2 and the molar ratio ([phytic acid]/[Ca2+]) were studied. Increasing the concentration of the calcium reagents as well as increasing the complexation times increased the particle sizes. The minimum and maximum average particle sizes of 29 and 142 nm were obtained. The plot of the transmittance at 350 nm of the aqueous solution of the dispersion against pH values after addition of 0.05 M HCl for 6 h showed that, by gradually increasing turbidity with decreasing pH from 9.6 to 7.3, precipitates were recognized at below pH 7.5, and turbidity decreased with further decreasing pH beyond 7.2. Dynamic light scattering analysis showed that the particle diameters increased from 90 to 200 nm with decreasing pH from 9.6 to 7.2. When increasing the pH from 6.2, the precipitate was redispersed and the turbidity increased to a pH of 7.4. No precipitates were observed above a pH of 7.4. These results suggest that the present phytic acid stabilized nanoparticles exhibit pH-dependent reversible precipitation and redispersion without degradation under slightly acidic conditions.

Unsymmetric Dumbbell-Shaped Polyhedral Oligomeric Silsesquioxane (POSS) Compound as a Single-Component POSS Hybrid.

Dumbbell-shaped polyhedral oligomeric silsesquioxane (POSS) derivatives, in which two POSS units are linked through a bridge, have attracted attention in the last decade. Here, we prepared an unsymmetric dumbbell-shaped POSS derivative (3Ph-iBu) in which isobutyl- and phenyl-substituted POSS units are linked by a disiloxane unit and compared its thermal properties with those of the corresponding symmetric isobutyl- and phenyl-substituted dumbbell-shaped POSS derivatives (3iBu-iBu and 3Ph-Ph, respectively). The symmetric isobutyl- and phenyl-substituted dumbbell-shaped POSS derivatives, 3iBu-iBu and 3Ph-Ph, were almost completely phase-separated during a mixing process. This phase separation is due to the limited solubility of phenyl-substituted POSS compounds, which are only soluble in tetrahydrofuran (THF) and insoluble in hydrocarbons such as n-hexane and toluene, while the isobutyl-substituted POSS derivatives exhibit a wider spectrum of soluble solvents. The unsymmetric dumbbell-shaped POSS, 3Ph-iBu, showed hybrid properties of solubility in solvents and thermal behaviors. Differential scanning calorimetric (DSC) analysis showed that enthalpy of the phase transition of 3Ph-iBu was significantly lower than those of the mixture of 3iBu-iBu and 3Ph-Ph. No apparent melting behavior was observed above the phase transition. The thermal degradation of the weakest isobutyl substituents improves in the present single-component hybrid structure.

Drastic Enhancement of Photosensitized Energy Transfer Efficiency of a Eu(III) Complex Driven by Arsenic.

In this study, we focused on arsenic as a new potential motif for the ligand design of high-efficiency, luminous lanthanide complexes. A Eu3+ complex bearing triphenylarsine oxide had a photosensitized energy-transfer efficiency 7.9 times higher than that of a Eu3+ complex bearing triphenylphosphine oxide. This is mainly due to the heavy-atom effect of arsenic, which was supported by evaluating the photoluminescence spectra of their corresponding Gd3+ complexes.

Diarsine- vs diphosphine-protected Au13 clusters: Effect of subtle geometric differences on optical property and electronic structure.

In the design of ligand-protected metal clusters, the choice of protecting ligands is a critical factor because they can profoundly affect the nuclearity, geometry, and electronic structures to afford a diverse range of cluster compounds. Here, we report the synthesis of two novel diarsine-protected Au13 clusters ([Au13L5Cl2]3+, L = diarsine) and compare these clusters with diphosphine analogs in terms of the core geometry and optical properties. In the crystal structure, the cluster bearing C3-bridged diarsines {[Au13(dpap)5Cl2]3+, 3} had an apparently identical icosahedral Au13 core to [Au13(dppe)5Cl2]3+ (1) with C2-bridged diphosphines, but slight structural differences associated with the bridging unit of the ligands were found. Despite similar icosahedral Au13 cores 1 and 3, their absorption and photoluminescence profiles were evidently different. Theoretical calculations revealed that the subtle deformation of the Au13 icosahedron, rather than the coordinating atoms (As or P), notably influences the electronic structure to cause the difference in the absorption profiles.

Systematic Study on the Catalytic Arsa-Wittig Reaction.

Efficient catalytic arsa-Wittig reactions have been developed by using 1-phenylarsolane as a catalyst. A wide array of aldehydes was converted to the corresponding olefins in high yields with moderate to excellent E stereoselectivity in the presence of a catalytic amount of 1-phenylarsolane. Moreover, density functional theory calculations were carried out to afford insight into the E/Z selectivity.

Fundamental Study on Arsenic(III) Halides (AsX3; X = Br, I) toward the Construction of C3-Symmetrical Monodentate Arsenic Ligands.

Arsenic ligands have attracted considerable attention in coordination chemistry. Arsenic(III) halides are the most important starting materials in the preparation of monodentate arsenic ligands. In this work, we optimized the synthetic methodologies of arsenic(III) halides (AsX3; X = Br, I) and examined the difference of their physical properties such as solubility to organic solvent and reactivity to nucleophiles. In addition, a wide variety of monodentate arsenic ligands were prepared with the obtained AsX3. Finally, the obtained monodentate arsenic ligands were utilized for copper-free Sonogashira cross-coupling reaction in the reaction system with porphyrin. The results showed that monodentate arsenic ligands have higher catalytic activity compared with triphenylphosphine because of the difference of the electronic features of lone pairs between arsenic and phosphorus atoms.

The Dawn of Functional Organoarsenic Chemistry.

Organoarsenic chemistry was actively studied until the middle of 20th century. Although various properties of organoarsenic compounds have been computationally predicted, for example, frontier orbital levels, aromaticity, and inversion energies, serious concern to the danger of their synthetic processes has restricted experimental studies. Conventional synthetic routes require volatile and toxic arsenic precursors. Recently, nonvolatile intermediate transformation (NIT) methods have been developed to safely access functional organoarsenic compounds. Important intermediates in the NIT methods are cyclooligoarsines, which are prepared from nonvolatile inorganic precursors. In particular, the new approach has realized experimental studies on conjugated arsenic compounds: arsole derivatives. The elucidation of their intrinsic properties has triggered studies on functional organoarsenic chemistry. As a result, various kinds of arsenic-containing π-conjugated molecules and polymers have been reported for the last few years. In this minireview, progress of this recently invigorated field is overviewed.

Dibenzoarsepins: Planarization of 8π-Electron System in the Lowest Singlet Excited State.

Dibenzo[b,f]arsepins possessing severely distorted cores compared to those of other heteropins were synthesized. These derivatives exhibited dual photoluminescence in the green-to-red region (500-700 nm) and the near-ultraviolet region (<380 nm), which could be attributed to the planarization of the arsepin core in the lowest singlet excited (S1 ) state. The computational approach for the assessment of the aromatic indices revealed that the dibenzoarsepins studied show aromaticity (8π system) in the S1 states in line with Baird's rule. The lone pair electrons of the arsenic atoms play a crucial role in the aromaticity in the S1 states.

Peraryl Arsoles: Practical Synthesis, Electronic Structures, and Solid-State Emission Behaviors.

2,3,4,5-Tetraaryl-1-phenylarsoles were synthesized by utilizing safely generated diiodophenylarsine and zirconacyclopentadienes. The obtained peraryl arsoles showed aggregation-induced emission (AIE), where intense emission was observed in the solid states (quantum yields up to 0.61), whereas the corresponding solutions were very weakly emissive. The optical and electronic properties were examined by experimental and computational methods. It was elucidated that the aryl groups at the 2,5-positions affected the frontier orbitals and the aromaticity of the arsole core. On the other hand, those at the 1,3,5-positions were perpendicular to the luminophore and effective for a restriction of aggregation-caused quenching. Because the lone pair of the arsenic atom has a sufficient coordination ability due to the low aromaticity of the arsole moiety, a gold(I) chloride complex of 1,2,3,4,5-pentaphenylarsole was synthesized. The complex formation caused a blue shift of the emission from the bare ligand. Interestingly, the complex showed luminescent mechanochromism; grinding the crystals with a blue emission (λem =445 nm) gave amorphous samples with a greenish-blue emission (λem =496 nm).

Arsole-Containing π-Conjugated Polymer by the Post-Element-Transformation Technique.

A synthetic method to obtain an arsole-containing π-conjugated polymer by the post-transformation of the organotitanium polymer titanacyclopentadiene-2,5-diyl unit with an arsenic-containing building block is described. The UV/Vis absorption maximum and onset of the polymer were observed at 517 nm and 612 nm, respectively. The polymer exhibits orange photoluminescence with an emission maximum (Emax ) of 600 nm and the quantum yield (Φ) of 0.05. The polymer proved to exhibit a quasi-reversible redox behavior in its cyclic voltammetric (CV) analysis. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated to be -5.43 and -3.24 eV, respectively, from the onsets for oxidation and reduction signals in the CV analysis. Further chemical modification of the arsole unit in the π-conjugated polymer by complexation of gold(I) chloride occurred smoothly resulting in the bathochromic shift of the UV/Vis absorption and lowering of the LUMO energy level.

Color Tuning of the Aggregation-Induced Emission of Maleimide Dyes by Molecular Design and Morphology Control.

Aggregation-induced emission (AIE)-active maleimide dyes, namely, 2-p-toluidino-N-p-tolylmaleimide, 3-phenyl-2-toluidino-N-p-tolylmaleimide, 2-p-thiocresyl-3-p-toluidino-N-p-tolylmaleimide, and 2,3-dithiocresyl-N-arylmaleimides, were synthesized by facile synthetic procedures. The dyes show intense emission in the solid state, and emission colors were controlled from green (λmax =527 nm) to orange (λmax =609 nm) by varying the substituents at the 2- and 3-positions of the maleimide and the packing structures in the solid state. 2,3-Disubstituted maleimide dyes effectively underwent redshifts of their emission wavelength. Furthermore, some of the dyes exhibited mechanochromism and polymorphism, and their emission properties were dramatically dependent on the morphology of the solid samples. The mechanisms of the emission behaviors were investigated by X-ray diffraction. The substituent of the nitrogen atom of the maleimide ring affected the intermolecular interactions and short contacts, which were observed by single crystal X-ray crystallography, to result in completely different emission properties.