Zwitterionic Ladder Stilbenes with Phosphonium and Borate Bridges: Intramolecular Cascade Cyclization and Structure–Photophysical Properties Relationship

Synthesis of 1,2,4-diazaphospholes via base-promoted cyclization reaction of hydrazonoyl chlorides and [Bu4N][P(SiCl3)2]

Aromatic 1,2,4-diazaphospholes featuring distinct hybrid-mode nitrogen atoms (N(λ3σ2), N(λ3σ3)) and low-valent phosphorus atoms (λ3σ2) exhibited the characteristic of serving as unique hybrid ligands. This study presented a one-pot reaction involving the base-promoted stepwise cyclization of hydrazonoyl chlorides and [Bu4N][P(SiCl3)2] to yield 1,2,4-diazaphospholes, providing an effective method for synthesizing such compounds.

The Synthesis and Properties of Ladder-Type π-Conjugated Compounds with Pyrrole and Phosphole Rings

The phosphole ring is known as a useful building block for constructing π-conjugated organic materials. Here, we report ladder-type benzophospholo[3,2-b]indole (BPI) derivatives where the phosphole and the pyrrole rings are directly fused. Compounds 8a-8d with different aryl groups on the phosphorous center were successfully synthesized, and the solid-state structure of 8a was confirmed using X-ray crystallographic analysis. The BPIs exhibit relatively high fluorescence quantum yield (Φ 0.50-0.72) and demonstrate a larger Stokes shift compared with a series of benzophospholo[3,2-b]benzoheteroles. The benzophospholo[3,2-b]carbazole derivative 9, which possesses a benzene ring between the phosphole and the pyrrole rings of the BPI, was also synthesized, and its solid-state structure was confirmed using X-ray crystallographic analysis. Compound 9 was found to show a smaller Stokes shift compared with the BPI.

Cationic Organophosphorus Chromophores: A Diamond in the Rough among Ionic Dyes

Tunable electron-accepting properties of the cationic phosphorus center, its geometry and unique preparative chemistry that allows combining this unit with diversity of π-conjugated motifs, define the appealing photophysical and electrochemical characteristics of organophosphorus ionic chromophores. This Minireview summarizes the achievements in the synthesis of the π-extended molecules functionalized with P-cationic fragments, modulation of their properties by means of structural modification, and emphasizes the important effect of cation-anion interactions, which can drastically change physical behavior of these two-component systems.

Concise Synthesis of Phospholene and Its P-Stereogenic Derivatives

A simple method to build phospholene derivatives has been achieved in a one-pot reaction with readily available o-alkynylaryl bromides and alkylphosphine oxides. This method is also applicable to synthesize P-stereogenic phospholenes, and the resulting chiral phosphine was utilized as a ligand for coordination chemistry.

Structural Dynamics and Stereoselectivity of Chiral Benzylideneamine N,C-Chelate Borane Photo-Thermal Isomerization

New chiral N,C-chelate organoboron compounds based on benzylideneamines (bza) with the general formula of B(bza-R)Mes₂ (R=H or Me; Mes=mesityl) are reported. A chiral substituent group R- or S-CH(CH₃ )Ph (Ph=phenyl) was introduced to the imine center, which imposed a previously unobserved pseudo- or axial-chirality on the BMes₂ , creating distinct diastereomers. NMR spectroscopic studies established that the diastereomers undergo slow exchange in solution at ambient temperature. The chiral N,C-chelate B(bza-R)Mes₂ molecules undergo photoisomerization in the same manner as their non-chiral analogues, generating chiral BN-cyclooctatriene (BN-COT) derivatives. Most significantly, by tracking the photoisomerization with circular dichroism (CD) and ¹ H NMR spectra along with time-dependent density functional theory (TD-DFT) computational studies, the photoisomerization was established to proceed in a highly stereoselective manner, that is, one diastereomer converts exclusively to the corresponding diastereomer product in the photoreaction.

Electrooxidative CH/PH functionalization as a novel way to synthesize benzo[b]phosphole oxides mediated by catalytic amounts of silver acetate

Electrochemical oxidation synthesis of benzo[b]phosphole oxides has been performed at room temperature with catalytic amounts of AgOAc.

Synthesis and photophysical properties of novel benzophospholo[3,2-b]indole derivatives

The parent benzophospholo[3,2-b]indole was prepared by the reaction of dichlorophenylphosphine with a dilithium intermediate, which was prepared in two steps from 2-ethynyl-N,N-dimethylaniline. Using the obtained benzophosphole-fused indole as a common starting material, simple modifications were carried out at the phosphorus center of the phosphole, synthesizing various functionalized analogs. The X-ray structure analysis of trivalent phosphole and phosphine oxide showed that the fused tetracyclic moieties are planar. The benzophosphole-fused indoles, such as phosphine oxide, phospholium salt, and borane complex, exhibited strong photoluminescence in dichloromethane (Φ = 67–75%).

Effects of counter anions, P-substituents, and solvents on optical and photophysical properties of 2-phenylbenzo[b]phospholium salts

The effects of counter anions, P-substituents, and solvents on the optical and photophysical properties of 2-phenylbenzo[b]phospholium salts were studied.

Consecutive reduction, radical-cyclization, and oxidative-dehydrogenation reaction of ortho-substituted diboryl compounds

An elegant synthetic route to a ladder-type di-borate compound 2a was reported based on the reduction, radical-cyclization, and oxidative-dehydrogenation reaction of 1.

Phospha-fluorescein: a red-emissive fluorescein analogue with high photobleaching resistance

Phospha-fluorescein (POF), a phosphine oxide-containing analogue of fluorescein, was synthesized and its photophysical properties were examined. Compared with fluorescein and sila-fluorescein, POF displayed significantly red-shifted absorption and fluorescence as well as superior photobleaching resistance, while retaining the pH-responsive characteristics of fluorescein dyes.

A Macrocyclic Fluorophore Dimer with Flexible Linkers: Bright Excimer Emission with a Long Fluorescence Lifetime

Bright fluorescent molecules with long fluorescence lifetimes are important for the development of lifetime-based fluorescence imaging techniques. Herein, a molecular design is described for simultaneously attaining long fluorescence lifetime (τ) and high brightness (ΦF ×ɛ) in a system that features macrocyclic dimerization of fluorescent π-conjugated skeletons with flexible linkers. An alkylene-linked macrocyclic dimer of bis(thienylethynyl)anthracene was found to show excimer emission with a long fluorescence lifetime (τ≈19 ns) in solution, while maintaining high brightness. A comparison with various relevant derivatives revealed that the macrocyclic structure and the length of the alkylene chains play crucial roles in attaining these properties. In vitro time-gated imaging experiments were conducted as a proof-of-principle for the superiority of this macrocyclic fluorophore relative to the commercial fluorescent dye Alexa Fluor 488.

Ag-mediated cascade decarboxylative coupling and annulation: a convenient route to 2-phosphinobenzo[b]phosphole oxides

Structurally sophisticated 2-phosphinobenzo[b]phosphole oxide frameworks have been conveniently constructed by cascade decarboxylative coupling and annulation reactions.

Formation of a dihydroborole by catalytic isomerization of a divinylborane

Diphenylamino(divinyl)borane (1a) adds two molar equivalents of Piers' borane [HB(C6F5)2] to give the expected double hydroboration product. In contrast diisopropylamino(divinyl)borane (1b) reacts cleanly already with one molar equivalent of HB(C6F5)2 to give the α-borylated tetrahydroborole derivative 10 in good yield. Subsequent treatment of 10 with benzaldehyde proceeded by retro-hydroboration to give the hydroboration product of the aldehyde plus the dihydroborole 3b. We were able to achieve the divinylborane to dihydroborole isomerization (1b to 3b) catalytically: treatment of diisopropylamino(divinyl)borane (1b) with 15 mol% of Piers' borane at elevated temperature gave (diisopropylamino)dihydroborole 3b in good yield.

Computational studies of lewis acidity and basicity in frustrated lewis pairs

Computational studies that characterize the effects of Lewis acidity/basicity on FLP formation and reactivity are reviewed. Formation of the FLP encounter complex "cage" depends on Lewis acidities and basicities of substituent "external" atoms, and their abilities to interact intramolecularly. Computations indicate that these interactions are worth 9-18 kcal mol⁻¹ for partly fluorinated FLPs such as (F5C6)3B···P(t-Bu)3, and less for less fluorinated species such as (H5C6)3B···P(t-Bu)3. Reactivity within the cage depends on the "classical" Lewis acidities/basicities of the internal atoms. Energetics here fall into the range of 5-50 kcal mol⁻¹; the larger the value, the greater the ability of the FLP to capture or split a substrate. In several cases the computationally predicted reaction barriers differ little with internal Lewis acidity/basicity, indicating that the rate-determining step involves the substrate entering the cage rather than attack by the Lewis acid/base atoms. In others, barriers vary sizably with Lewis acidity/basicity, indicating the opposite. In one case it was shown that these effects cancel, such that the three component barriers are identical for a range of substituted Lewis acid FLP components.

Photochemical synthesis of a ladder diborole: a new boron-containing conjugate material

Climbing the ladder: Reductive cyclization of alkynyl haloboranes lead to the bis-benzocycloborabutylidene rather than the expected ladder diborole, despite the former being much less thermodynamically favored. Photochemical conversion to the ladder diborole was, however, quite facile upon irradiation at 254 nm.