C-Halogenated 9,10-Diboraanthracenes: How the Halogen Load and Distribution Influences Key Optoelectronic Properties

Vicinal Vinylation of Boron-Doped Acenes via Heck Coupling

Silylated and halogenated benzenes 1,2-(Me3Si)2-4,5-X2-C6H2 [X = Br (3), I (4)] are versatile synthetic building blocks. 3 was prepared from known 1,2-(Me3Si)2-4,5-Cl2-C6H2 via C-Cl borylation/bromodeboronation; CuI-catalyzed Br/I exchange on 3 affords 4. 3 or 4 and BBr3 yield 9,10-dibromo-9,10-dihydro-9,10-diboraanthracenes (DBAs) 7 or 8. The B centers were protected with mesityl (Mes; 9, 10) or 2,4,6-tris(trifluoromethyl)phenyl (FMes; 11, 12) groups. Heck coupling of 9 and styrene/2,3,4,5,6-pentafluorostyrene furnishes the two tetravinyl-substituted green/blue emitters 13/14.

Brominated B1-Polycyclic Aromatic Hydrocarbons for the Synthesis of Deep-Red to Near-Infrared Delayed Fluorescence Emitters

Bromo-functionalized B1-polycyclic aromatic hydrocarbons (PAHs) with LUMOs of less than -3.0 eV were synthesized and used in cross-couplings to form donor-acceptor materials. These materials spanned a range of S1 energies, with a number showing thermally activated delayed fluorescence and significant emission in the near-infrared region of the spectrum. These B1-PAHs represent a useful family of acceptors that can be readily synthesized and functionalized.

Recent Advances in the Synthesis of Borinic Acid Derivatives

Borinic acids [R2B(OH)] and their chelate derivatives are a subclass of organoborane compounds used in cross-coupling reactions, catalysis, medicinal chemistry, polymer or optoelectronics materials. In this paper, we review the recent advances in the synthesis of diarylborinic acids and their four-coordinated analogs. The main strategies to build up borinic acids rely either on the addition of organometallic reagents to boranes (B(OR)3, BX3, aminoborane, arylboronic esters) or the reaction of triarylboranes with a ligand (diol, amino alcohol, etc.). After general practical considerations of borinic acids, an overview of the main synthetic methods, their scope and limitations is provided. We also discuss some mechanistic aspects.

Charge-Transfer Transitions Govern the Reactivity and Photophysics of Vicinally Diphosphanyl-Substituted Diborapentacenes

2,3-Difluoro-5,14-dihydro-5,14-diborapentacene (DBP) was endowed with two vicinal Ph₂ P groups by an S_N Ar reaction at both CF sites using Ph₂ PSiMe₃ . Computations reveal the ambipolar product P to undergo P-to-B charge transfer under ambient light irradiation. Consequently, P is prone to photooxidation by air, yielding the Ph₂ P(O) species PO. With S₈ or [Me₃ O][BF₄ ], P furnishes the Ph₂ P(S) or Ph₂ P(Me)⁺ derivatives PS or [PMe][BF₄ ]₂ . Along the series P, PO, PS, and [PMe][BF₄ ]₂ , the redox potentials shift anodically from E_1/2 =-1.89 V to -1.02 V (CH₂ Cl₂ ). Thus, derivatization of the Ph₂ P group allows late-stage modulation of the LUMO-energy level of the DBP. Derivatization also influences the emission properties of the compounds, as PO shows green (521 nm) and [PMe][BF₄ ]₂ red (622 nm) fluorescence in C₆ H₆ , while P and PS are dark. With CuBr and AgBr, P forms dimeric [M(μ-Br)]₂ complexes [PCu]₂ and [PAg]₂ , which show pronounced metal-to-ligand charge transfer (MLCT), making P a promising ligand for photocatalysts.

A Three‐Dimensional Inorganic Analogue of 9,10‐Diazido‐9,10‐Diboraanthracene: A Lewis Superacidic Azido Borane with Reactivity and Stability

Herein, we report the facile synthesis of a three‐dimensional (3D) inorganic analogue of 9,10‐diazido‐9,10‐dihydrodiboraantracene, which turned out to be a monomer in both the solid and solution state, and thermally stable up to 230 °C, representing a rare example of azido borane with boosted Lewis acidity and stability in one. Apart from the classical acid‐base and Staudinger reactions, E−H bond activation (E=B, Si, Ge) was investigated. While the reaction with B−H (9‐borabicyclo[3.3.1]nonane) led directly to the 1,1‐addition on N_α upon N₂ elimination, the Si−H (Et₃SiH, PhMe₂SiH) activation proceeded stepwise via 1,2‐addition, with the key intermediates 5_int and 6_int being isolated and characterized. In contrast, the cooperative Ge−H was reversible and stayed at the 1,2‐addition step.

Exploring Structure-Property Relations of B,S-Doped Polycyclic Aromatic Hydrocarbons through the Trinity of Synthesis, Spectroscopy, and Theory

Polycyclic aromatic hydrocarbons (PAHs) are prominent lead structures for organic optoelectronic materials. This work describes the synthesis of three B,S-doped PAHs with heptacene-type scaffolds via nucleophilic aromatic substitution reactions between fluorinated arylborane precursors and 1,2-(Me₃SiS)₂C₆H₄/1,8-diazabicyclo[5.4.0]undec-7-ene (72-92% yield). All compounds contain tricoordinate B atoms at their 7,16-positions, kinetically protected by mesityl (Mes) substituents. PAHs 1/2 feature two/four S atoms at their 5,18-/5,9,14,18-positions; PAH 3 is a 6,8,15,17-tetrafluoro derivative of 2. For comparison, we also prepared the skewed naphtho[2,3-c]pentaphene-type isomer 4. The simultaneous presence of electron-accepting B atoms and electron-donating S atoms results in a redox-ambiphilic behavior; the radical cations [1^•]⁺ and [2^•]⁺ were characterized by electron paramagnetic resonance spectroscopy. Several low-lying charge-transfer states exist, some of which (especially S-to-B and Mes-to-B transitions) compete on the excited-state potential-energy surface. Consistent with the calculated state characters and oscillator strengths, this competition results in a spread of fluorescence quantum yields (2-27%). The optoelectronic properties of 1 change drastically upon addition of Ag⁺ ions: while the color of 1 in CH₂Cl₂ changes bathochromically from yellow to red (λ_max from 463 to 486 nm; -0.13 eV), the emission band shifts hypsochromically from 606 to 545 nm (+0.23 eV), and the fluorescence quantum yield increases from 12 to 43%. According to titration experiments, higher order adducts [Ag_n1_m]ⁿ⁺ are formed. As a suitable system for modeling Ag⁺ complexation, our calculations predict a dimer structure (n = m = 2) with Ag₂S₄ core, approximately linear S-Ag-S fragments, and Ag-Ag interaction. The computed optoelectronic properties of [Ag₂1₂]²⁺ agree well with the experimentally observed ones.

Nucleophilic aromatic substitution approach to phosphanyl-substituted diboraanthracenes: biphilic compounds with tunable electron affinities

9,10-Dimesityl-9,10-dihydro-9,10-diboraanthracenes (Mes2DBAs) bearing one (1), two (2), or four (3) Ph2P-substituents were prepared from Ph2PSiMe3 and tetrafluorinated Mes2DBAs via a nucleophilic aromatic substitution protocol. Using compound 1 as the model...

Polyacrylamide-Based Binary Luminescent Copolymer Materials Exhibit Color-Tunable and Efficient Long-Lived Room Temperature Phosphorescence

Polymer-based pure organic room temperature phosphorescence (RTP) materials have garnered considerable interest, among which RTP systems with prolonged lifetimes and tunable emission colors are promising for applications in sensing, flexible electronics, bioassay, anti-counterfeiting, and data encryption. Herein, facile doping method is reported based on two types of copolymers with benzene/biphenyl-based light-emitting cores as their side chains, whereby the two copolymers are robustly crosslinked via noncovalent interactions including hydrogen bonding and halogen bonding that occur between the light-emitting cores and polyacrylamide backbones. Persistent RTP emission with prolonged lifetime up to 1.9 s and phosphorescence quantum yield as high as 40.1% are obtained in single copolymers, attributed to the conformation restriction of phosphorescent dyes originating from the rigid microenvironment. Furthermore, multicolor phosphorescence signals are observed in the doped binary luminescent copolymer systems that can be effectively regulated by the feed ratio of luminescent cores and irradiation wavelengths. Possible mechanisms for this efficient and long-lived color-tunable RTP system are discussed on the basis of the experimental data and theoretical calculations. In addition, it is also demonstrated that the color-tunable RTP emission of the doped copolymer systems under ambient conditions allows for further exploitation in the application of dynamic information encryption.

Doubly Boron-Doped TADF Emitters Decorated with ortho-Donor Groups for Highly Efficient Green to Red OLEDs

Doubly boron-doped thermally activated delayed fluorescence (TADF) emitters based on a 9,10-diboraanthracene (DBA) acceptor decorated with ortho-donor groups (Cz2oDBA, 2; BuCz2oDBA, 3; DMAC2oDBA, 4) are prepared to realize high-efficiency green-to-red organic light-emitting diodes (OLEDs). X-ray diffraction analyses of 2 and 4 reveal the symmetrical and highly twisted ortho-donor-acceptor-donor (D-A-D) structure of the emitters. The twisted conformation leads to a very small energy splitting (ΔE_ST <0.08 eV) between the excited singlet and triplet states that gives rise to strong TADF, as supported by theoretical studies. Depending on the strength of the donor moieties, the emission color is fine-tuned in the visible region from green (2) to yellow (3) to red (4). Carbazole-containing 2 and 3 exhibit high photoluminescence quantum yields (PLQYs) approaching 100 %, whereas DMAC-substituted 4 is moderately emissive (PLQY=44 %) in a doped host film. Highly efficient green-to-red TADF-OLEDs are realized with the proposed ortho-D-A-D compounds as emitters. The green and yellow OLEDs incorporating Cz2oDBA (2) and BuCz2oDBA (3) emitters exhibit high external quantum efficiencies (EQEs) of 26.6 % and 21.6 %, respectively. In particular, the green device shows an excellent power efficiency above 100 lm W^-1 . A red OLED fabricated with a DMAC2oDBA (4) emitter exhibits a maximum EQE of 10.1 % with an electroluminescence peak at 615 nm.

6,12-Dihydro-6,12-diboradibenzo[def,mno]chrysene: A Doubly Boron-Doped Polycyclic Aromatic Hydrocarbon for Organic Light Emitting Diodes by a One-Pot Synthesis

One-pot synthesis of a new doubly boron-doped polycyclic aromatic hydrocarbon of 6,12-dimesityl-6,12-dihydro-6,12-diboradibenzo[def,mno]chrysene (MDBDBC) was reported. MDBDBC features a rigid planar electron-deficient core structure and demonstrates good chemical and thermal stabilities. A low-lying LUMO of -3.53 eV, a low locally excited triplet energy of 1.92 eV, as well as green electroluminescence with maximum EQE of 4.9% were found for MDBDBC, suggesting its potential as an n-type unit for future organic light emitting diode applications.

Practical Synthesis of Ethynyl(phenyl)-λ3-Iodane Using Calcium Carbide as an Ethynyl Group Source

Stannylation of calcium carbide followed by Sn–hypervalent iodine(III) exchange reaction cleanly afforded the electrophilic ethynylating agent ethynyl(phenyl)-λ³-iodane in high yield. This two-step method uses very inexpensive materials and is readily operable without any special precautions.

CO2 reduction with protons and electrons at a boron-based reaction center

Borohydrides are widely used reducing agents in chemical synthesis and have emerging energy applications as hydrogen storage materials and reagents for the reduction of CO₂. Unfortunately, the high energy cost associated with the multistep preparation of borohydrides starting from alkali metals precludes large scale implementation of these latter uses. One potential solution to this issue is the direct synthesis of borohydrides from the protonation of reduced boron compounds. We herein report reactions of the redox series [Au(B₂P₂)] ⁿ (n = +1, 0, -1) (B₂P₂, 9,10-bis(2-(diisopropylphosphino)phenyl)-9,10-dihydroboranthrene) and their conversion into corresponding mono- and diborohydride complexes. Crucially, the monoborohydride can be accessed via protonation of [Au(B₂P₂)]^-, a masked borane dianion equivalent accessible at relatively mild potentials (-2.05 V vs. Fc/Fc⁺). This species reduces CO₂ to produce the corresponding formate complex. Cleavage of the formate complex can be achieved by reduction (ca. -1.7 V vs. Fc/Fc⁺) or by the addition of electrophiles including H⁺. Additionally, direct reaction of [Au(B₂P₂)]^- with CO₂ results in reductive disproportion to release CO and generate a carbonate complex. Together, these reactions constitute a synthetic cycle for CO₂ reduction at a boron-based reaction center that proceeds through a B-H unit generated via protonation of a reduced borane with weak organic acids.

Selective access to either a doubly boron-doped tetrabenzopentacene or an oxadiborepin from the same precursor

Depending on the solvent, a brominated arylborane gave the multiple helicene B₂-TBPA (pyridine) or the oxadiborepin ODBE (THF) after intramolecular Yamamoto coupling.

The well-known red emitter tetrabenzo[de,hi,op,st]pentacene (TBPA) has been transformed into a bright blue emitter (B₂-TBPA; λ_em = 472 nm; c-hexane) via substitutional doping with two boron atoms. In contrast to the electron-rich TBPA, which forms endo-peroxides with O₂ under daylight, the benchtop-stable B₂-TBPA is a good electron acceptor and undergoes reversible reduction at a moderate half-wave potential of E_1/2 = –1.73 V (vs. FcH/FcH⁺; THF). Although the size of B₂-TBPA falls within the nanoscale, the helically twisted compound readily dissolves in c-hexane and does not require solubilizing substituents. The synthesis of B₂-TBPA is based on the nickel-mediated Yamamoto-type dehalogenation of tetrabrominated 9,10-di(naphth-1-yl)-9,10-dihydro-9,10-diboraanthracene. This intramolecular C–C heterocoupling reaction shows a remarkable solvent dependence: B₂-TBPA forms only in pyridine (79% yield), whereas an oxadiborepin is obtained from THF solutions (ODBE, 81%; the reaction mixture is quenched with air in both cases). Insight into the corresponding reaction mechanism was gained from the isolation of intermediates and an investigation of their chemical properties. ODBE is an interesting blue emitter in its own right. Furthermore, it can be ring-opened with excess BBr₃ at the B–O–B moiety to afford a dimeric borabenzo[de]anthracene.

The effect of locking π-conjugation in organoboron moieties in the structures of luminescent tetracoordinate boron complexes

A series of 8 luminescent borafluorene complexes were extensively studied both experimentally and theoretically in order to elucidate the effect of organoboron moiety rigidification on the physicochemical properties of these compounds. Due to the spiro geometry of the boron atom, borafluorene and ligand units are perpendicularly aligned, which considerably affects the flexibility of the molecule as well as its solid-state structure. Through comparative analysis with close diphenyl analogues, we show how these structural features influence the thermal, photoluminescent and charge mobility behaviour of the studied compounds. Crystal structural analysis revealed that the molecules are connected mostly through C-HO and C-Hπ interactions formed between perpendicularly aligned borafluorene and ligand moieties from neighboured molecules, serving as a complementary donor and acceptor of electron density, respectively. This also efficiently prevents molecules from engaging in unfavoured π-stacking contact. Furthermore, structural analysis suggests that borafluorene complexes possess a considerable degree of flexibility due to OBN heterocycle distortions and mutual borafluorene-ligand plane movements. The magnitude of these effects strictly depends on the ligand structure and may lead either to enhancing or lowering the quantum yield value with respect to BPh₂ analogues, while the absorption and emission wavelength are slightly affected. The measured photophysical parameters for solid-state samples showed that the studied complexes are much better emitters in their crystalline states that in amorphous films. The TD-DFT and NTO calculations revealed a significant change in frontier molecular distribution, with the HOMO localized on the borafluorene moiety. However, as the HOMO-LUMO transition is geometrically not favoured, excitation occurred from HOMO-1 localized on the ligand. Finally, aggregation effects were discussed based on supramolecular arrangements in crystal structures and charge transfer rates obtained from theoretical calculations in the framework of the Marcus-Hush approximation. They suggest that borafluorene complexes are much better electron carriers with respect to non-annulated BPh₂ complexes.

Simultaneous expansion of 9,10 boron-doped anthracene in longitudinal and lateral directions

Doubly boron-doped anthracenes and pentacenes have been longitudinally and laterally expanded through annulation of thiophene or benzene rings. The obtained series of closely related compounds allowed an assessment of key structure-property relationships with a focus on optoelectronic characteristics. Most of the products are benchtop-stable blue emitters and capable of accepting two electrons in a reversible manner. The syntheses involved late-stage modifications through photocyclization or stepwise oxidative C-C coupling (DDQ/BF₃·Et₂O) as well as cyclocondensation of ortho-disilylated or -diborylated aryl building blocks.