Synthesis and optical properties of antimony(V) complexes of a trianionic N2O2-type tetradentate dipyrrin ligand.

LSbCl2, an air- and moisture-stable antimony(V)-dipyrrin complex at room temperature, was obtained by treating an excess amount (20 eq.) of SbCl3 with a trianionic N2O2-type tetradentate dipyrrin ligand (L) under visible-light irradiation and O2 atmosphere. The Cl ligands in LSbCl2 were replaced by OH ligands via hydrolysis, yielding LSb(OH)2. Further, the molecular structures and optical properties of the Sb(V)-dippyrin complexes were investigated. While LSbCl2 was non-fluorescent, LSb(OH)2 exhibited an intense red fluorescence with a photoluminescence quantum yield of 68%.

Boron complexes of π-extended nitroxide ligands exhibiting three-state redox processes and near-infrared-II (NIR-II) absorption properties.

Persistent radicals have attracted increasing attention owing to their fascinating properties, including multi-step redox and long-wavelength absorption characteristics. In this study, boron complexes with π-extended nitroxide ligands were synthesised via Buchwald-Hartwig amination reactions of the corresponding boron-nitroxide complex and diarylamines. These nitroxide complexes exhibited two-step and reversible one-electron oxidation processes, suggesting stable redox triads involving anionic aminoxide, neutral nitroxide-radical, and cationic oxoammonium ligands. Cationic boron complexes of the nitroxide radical ligands were obtained via chemical oxidation of the aminoxide complexes and structurally characterised. The cationic nitroxide-radical complexes exhibited strong absorptions at approximately 1100 nm, demonstrating their potential as near-infrared (NIR)-II-active functional dyes.

Design, Regioselective Synthesis, and Photophysical Properties of Perfluoronaphthalene-Based Donor-Acceptor-Donor Fluorescent Dyes.

A one-step route to a series of perfluoronaphthalene-based donor (D)-acceptor (A)-D fluorescent dyes with various electron-donating groups was developed. The perfluoronaphthalene moiety in the D-A-D dyes served as a good electron-accepting aromatic ring with excellent intramolecular charge transfer properties, as determined by density functional theory calculations and measurements of the fluorescence properties in solution, in poly(methyl methacrylate) (PMMA) films, and in crystal form. Notably, replacing the naphthalene ring with perfluoronaphthalene in the D-A-D dyes carrying the phenothiazine moiety not only stabilized the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels but also reduced the energy band gap to change the emission color from blue to yellow. Among the four synthesized perfluoronaphthalene D-A-D dyes, those bearing diphenylamino groups afforded the best fluorescence quantum yields in Et2O solution (0.60) and in PMMA film (0.65) because the propeller structure of the diphenylamino group that acts as a donor substituent effectively suppresses radiation-free deactivation. In contrast, in the crystalline state, the carbazoyl-bearing D-A-D dye provided the best fluorescence quantum yield (0.35) because the radiation-free inactivation was suppressed by π-πF stacking at the donor site, which was confirmed by single-crystal X-ray analysis.

Catalytic aerobic photooxidation of triarylphosphines using dibenzo-fused 1,4-azaborines.

Although dibenzo-fused 1,4-heteroaromatics are utilized as strongly reducing photocatalysts in organic synthesis and polymerization, they have rarely been employed in catalytic photooxidation. Moreover, to date, their boron-analogs, dibenzo-fused 1,4-azaborines (DBABs), have not been applied in photocatalysis despite their promising potential as photocatalysts. Accordingly, herein, aerobic photooxidation of triarylphosphines (Ar3P) was performed using DBABs as photocatalysts. The reaction smoothly proceeded in an aprotic solvent, and phosphine oxides were obtained in appropriate yields. Density functional theory calculations suggested that DBAB captured and activated phosphadioxirane intermediates, which were generated by the interaction of Ar3P with 1O2, at the Lewis acidic boron center.

Practical Synthesis of α-Trifluoromethylated Pyridines Based on Regioselective Cobalt-Catalyzed [2+2+2] Cycloaddition using Trifluoromethylated Diynes with Nitriles.

Regioselective cobalt-catalyzed [2+2+2] cycloaddition using fluorine-containing diynes with nitriles was described. Cycloaddition of fluorinated diynes with nitriles under the influence of CoCl2(phen), zinc bromide, and zinc dust in dichloroethane at 80°C for 3 h took place smoothly, exclusively affording the corresponding α-fluoroalkylated pyridines in excellent yields. In addition, dinitriles as substrate were also found to be suitable for this reaction, giving the corresponding fluoroalkylated bipyridine derivatives in excellent yields.

Fused-Nonacyclic Multi-Resonance Delayed Fluorescence Emitter Based on Ladder-Thiaborin Exhibiting Narrowband Sky-Blue Emission with Accelerated Reverse Intersystem Crossing.

Developing organic luminophores with unique capability of strong narrowband emission is both crucial and challenging for the further advancement of organic light-emitting diodes (OLEDs). Herein, a nanographitic fused-nonacyclic π-system (BSBS-N1), which was strategically embedded with multiple boron, nitrogen, and sulfur atoms, was developed as a new multi-resonance thermally activated delayed fluorescence (MR-TADF) emitter. Narrowband sky-blue emission with a peak at 478 nm, full width at half maximum of 24 nm, and photoluminescence quantum yield of 89 % was obtained with BSBS-N1. Additionally, the spin-orbit coupling was enhanced by incorporating two sulfur atoms, thereby facilitating the spin-flipping process between the excited triplet and singlet states. OLEDs based on BSBS-N1 as a sky-blue MR-TADF emitter achieved a high maximum external electroluminescence quantum efficiency of 21.0 %, with improved efficiency roll-off.

Cobalt-Catalyzed C-H Activation/Annulation of Benzamides with Fluorine-Containing Alkynes: A Route to 3- and 4-Fluoroalkylated Isoquinolinones.

The C-H activation/annulation reaction of various benzamides with fluoroalkylated alkynes in the presence of a Co(acac)2·2H2O catalyst proceeded very smoothly to give the corresponding 3- and 4-fluoroalkylated isoquinolinones in excellent yields with approximately 70% regioselectivities. These regioisomers could be successfully separated and obtained in pure form. Major or minor regioisomers were determined as 4- or 3-fluoroalkylated isoquinolinones, respectively, based on X-ray crystallographic analyses.

Syntheses of α-CF3-α-quaternary ketones via p-quinone methides and their derivatization to compounds with successively congested stereogenic centers.

New and successful results for the construction of new and structurally interesting compounds are reported via N-heterocyclic carbene (NHC)-catalyzed 1,6-conjugate additions of a variety of aldehydes to δ-CF3-δ-substituted p-quinone methides generated in situ, and the products are used for the 1,2-addition reactions of appropriate metal nucleophiles, enabling us to furnish highly diastereoselective products with a unique successive quaternary carbon-tertiary alcohol framework (up to dr = >99 : 1).

Clarification of the Reactivity of 1,3,3,3-Tetrafluoropropene Oxides.

Our computation has successfully clarified the reluctant behavior of trans- and cis-1,3,3,3-tetrafluoropropene oxides 1c toward nucleophiles and led to the expectation that these epoxides would react under the Brønsted acid activation conditions. Actually, this was the case, and these epoxides smoothly opened with CF3SO3H, whose elimination after the protection of the resultant OH group afforded the enol benzoates as the enolate precursors, which nicely allowed us to construct the corresponding aldol products by reactions with various aldehydes.

Construction of trifluoromethylated quaternary stereocenters via p-quinone methides.

Development of a new synthetic method for the construction of quaternary centers with a trifluoromethyl group was realized by way of 1,6-addition of various nucleophiles including active methylene compounds to highly reactive δ-trifluoromethylated p-quinone methides generated in situ from the corresponding tertiary carbonates with a catalytic amount of an appropriate base.

Synthesis and characterization of bent fluorine-containing donor-π-acceptor molecules as intense luminophores with large Stokes shifts.

Herein, we prepared novel bent fluorine-containing donor-π-acceptor (D-π-A) molecules from commercially available octafluorocyclopentene using a facile two-step procedure, revealing that the above molecules absorb UV-light and exhibit yellow photoluminescence (PL) with high PL efficiencies (ΦPL) in solution. The corresponding Stokes shifts exceeded 10 000 cm-1, and the maximum PL wavelength (λPL) strongly depended on solvent polarity or intermolecular interactions in the solid state. On the basis of a Lippert-Mataga plot, PL was confidently assigned to radiative relaxation from an intramolecular charge-transfer excited state. Moreover, the synthesized luminophores showed intense PL even in the crystalline state and exhibited alkoxy chain length-dependent PL behavior (e.g., high ΦPL, λPL = 486-540 nm).

Fluorine-Containing Dibenzoanthracene and Benzoperylene-Type Polycyclic Aromatic Hydrocarbons: Synthesis, Structure, and Basic Chemical Properties.

Intramolecular photocyclization of stilbene derivatives (Mallory reaction) is one of the efficient methods for building polycyclic aromatic hydrocarbon (PAH) frameworks, and is also expected to be applicable to synthesis of fluorine-containing PAHs (F-PAHs). In this study, dibenzoanthracene-type (4a) and benzoperylene-type (4b) F-PAHs were synthesized using the Mallory reaction of the 1,4-distyrylbenzene-type π-conjugated molecule (3a), which was prepared by addition-defluorination of available octafluorocyclopentene (OFCP) and aryllithium in three steps. The structure of 4a originating from π⁻π interaction was characterized by X-ray crystallographic analysis. The absorption maxima of UV-Vis spectra and emission maxima of photoluminescence spectra of the PAHs were positioned at a longer wavelength compared to those of the corresponding unsubstituted PAHs, presumably due to the electron-withdrawing nature of perfluorocyclopentene (PFCP) units. The effect of PFCP units in F-PAHs was also studied by time-dependent density functional theory (TD-DFT) calculation.

Stereoselective aldol reactions using pseudo C2 symmetric 1-benzyl-4-(trifluoromethyl)piperidine-2,6-dione.

Crossed aldol reactions of the CF3-containing pseudo C2 symmetric cyclic imide 3 were carried out by way of the corresponding boron bisenolate to stereoselectively furnish the desired products 4 and this procedure allowed the preferential construction of the diastereomers of the compounds previously obtained from the acyclic counterpart 1.

Thermoresponsive luminescence properties of polyfluorinated bistolane-type light-emitting liquid crystals.

We developed and characterized four polyfluorinated bistolane derivatives. These compounds, which possess either two alkoxy substituents or an alkoxy group and a bromine atom in their two molecular terminals, were synthesized from readily available 4-alkoxy-1-ethynylbenzene with a facile three-step procedure. Their thermodynamic and photophysical properties were evaluated in detail, and they were found to display both liquid-crystalline (LC) and photoluminescence properties. Remarkably, the photoluminescence behaviors dramatically changed during the thermal phase transition between the crystal and LC phases. Thus, these polyfluorinated bistolanes may be promising candidates for thermoresponsive luminous molecules.

Syntheses and Structures of d10 Coinage Metal Complexes of Electron-Accepting Phosphine Ligands Featuring a 3,3,4,4,5,5-Hexafluorocyclopentene Framework.

Cu(I), Ag(I), and Au(I) complexes of monophosphine or bisphosphine ligands based on the 3,3,4,4,5,5-hexafluorocyclopentene skeleton were synthesized and structurally characterized by X-ray crystallographic analysis. The electron-withdrawing nature of these polyfluorinated phosphines was experimentally revealed via UV/vis absorption studies and crystal structure analysis. Successful catalytic application of the Au(I) complex for alkyne hydration reactions was investigated.

Development of Novel Solid-State Light-Emitting Materials Based on Pentafluorinated Tolane Fluorophores.

We herein describe the synthesis of novel pentafluorinated tolane fluorophores, which possess an extended π-conjugated structure with a large molecular dipole moment along the longitudinal axis. We also report a detailed evaluation of both the photophysical and thermal behaviors of these fluorophores. All molecules displayed photoluminescence (PL) characteristics in both the crystalline state and in dilute solutions. The large longitudinal dipole moment induced solvatochromic PL behavior, which switched sensitively with changes in the solvent polarity. In addition, incorporation of the fluorinated tolane-based solid-state light-emitting moiety into the polymer side chain was found to be responsible for the PL characteristics observed in the solid state. It was also noteworthy that the polymerization protocol led to a significant enhancement in the thermal stability, with the thermal decomposition temperature increased by 90 °C. Accordingly, novel solid-state light-emitting materials with high thermal stabilities were successfully developed as promising candidates for use in light-emitting and optoelectronic applications.

Fluorine-containing bistolanes as light-emitting liquid crystalline molecules.

We synthesised a series of dissymmetric bistolane derivatives and evaluated their liquid-crystalline (LC) and photoluminescence properties in detail. In measuring LC behaviours, rational structural design based on the dissymmetric molecular structure and electron-density distribution facilitated the production of the LC phase with a wide temperature range (up to 97 °C). In addition, dissymmetric bistolane derivatives were shown to strongly emit blue-photoluminescence in dilute solution and in crystalline states. It was found that dissymmetric bistolanes possess emissive features in even the LC phase and photoluminescence behaviours such as emission intensity and colour were sensitively switched depending on the molecular aggregate structure caused by applying a thermal stimulus.

Stereochemically Defined Various Multisubstituted Alkenes Bearing a Tetrafluoroethylene (-CF2CF2-) Fragment.

Highly regio- and stereoselective transformation of commercially available 4-bromo-3,3,4,4-tetrafluoro-1-butene into multisubstituted alkenes having a tetrafluoroethylene fragment through Heck reactions and/or Suzuki-Miyaura cross-coupling reactions was established. Thus, the obtained alkenes underwent a smooth reductive coupling reaction with aldehydes under the influence of MeLi/LiBr-free, affording structurally unprecedented fluorinated materials.

Synthesis of a 1-Aryl-2,2-chlorosilyl(phospha)silene Coordinated by an N-Heterocyclic Carbene.

Phosphasilenes, P=Si doubly bonded compounds, have received considerable attention due to their unique physical and chemical properties. We report on the synthesis and structure of a chlorophosphasilene coordinated by an N-heterocyclic carbene (NHC), which has the potential of functionalization at the Si-Cl moiety. Treatment of a silylphosphine, ArPH-SiCl2RSi (Ar = bulky aryl group, RSi = Si(SiMe3)3) with two equivalents of Im-Me4 (1,3,4,5-tetramethylimidazol-2-ylidene) afforded the corresponding NHC-coordinated phosphasilene, ArP=SiClRSi(Im-Me4) as a stable compound. Bonding properties of the P=Si bond coordinated to an NHC will be discussed on the basis of theoretical calculations.

Activation of Dihydrogen by Masked Doubly Bonded Aluminum Species.

Activation of dihydrogen by masked dialumenes (Al=Al doubly bonded species) is reported. Reactions of barrelene-type dialumanes, which have the reactivity as masked equivalents of 1,2-diaryldialumenes ArAl=AlAr, with H2 afforded dihydroalumanes ArAlH2 at room temperature (Ar: bulky aryl groups). These dihydroalumanes form hydrogen-bridged dimers [ArHAl(µ-H)]2 in the crystalline state, while a monomer-dimer equilibrium was suggested in solution. The 1,2-diaryldialumenes generated from the barrelene-type dialumanes are the putative active species in the cleavage of H2 .