BN Units Research Articles

Aromatic 1,4,2,3-Diazadiborole Featuring an Unsymmetrical B=B Entity: A Versatile Synthon for Unusual Boron Heterocycles.

The replacement of a CC unit with an isoelectronic BN unit in aromatic systems can give rise to molecules and materials with fascinating properties. We report here the synthesis, characterization, and reactivity of a 1,4,2,3-diazadiborole species, 2, featuring an unprecedented 6π-aromatic BN-heterocyclic moiety that is isoelectronic to cyclopentadienide (Cp-). Bearing an unsymmetrical B=B entity, 2 exhibits reactivity toward oxidants, protic reagents, electrophiles, and unsaturated substrates. This reactivity facilitates the synthesis of a variety of novel mono- and bicyclic organoboron derivatives through mechanisms including ring retention, cleavage/recombination, annulation, and expansion. These findings reveal innovative synthetic routes to BN-embedded aromatic compounds via desymmetrization, affording unique building blocks for synthetic chemistry.

Aromatic 1,4,2,3‐Diazadiborole Featuring an Unsymmetrical B=B Entity: A Versatile Synthon for Unusual Boron Heterocycles

AbstractThe replacement of a CC unit with an isoelectronic BN unit in aromatic systems can give rise to molecules and materials with fascinating properties. We report here the synthesis, characterization, and reactivity of a 1,4,2,3‐diazadiborole species, 2, featuring an unprecedented 6π‐aromatic BN‐heterocyclic moiety that is isoelectronic to cyclopentadienide (Cp−). Bearing an unsymmetrical B=B entity, 2 exhibits reactivity toward oxidants, protic reagents, electrophiles, and unsaturated substrates. This reactivity facilitates the synthesis of a variety of novel mono‐ and bicyclic organoboron derivatives through mechanisms including ring retention, cleavage/recombination, annulation, and expansion. These findings reveal innovative synthetic routes to BN‐embedded aromatic compounds via desymmetrization, affording unique building blocks for synthetic chemistry.

Computational study on reactivity, aromaticity, and absorption spectra of chrysene: effect of BN doping and substituents

Abstract Density functional study (DFT) is performed for understanding the reactivity, aromaticity, and UV-visible absorption spectra of chrysene-based materials. Effect of BN doping on the said parameters are analyzed along with the effect of –Me (methyl), –OH (hydroxyl), –CHO (formyl) –COOH (carboxyl) and –CN (cyano) substituents. Global reactivity parameters viz. energy of HOMO (E HOMO), global hardness (η), chemical potential (μ) and electrophilicity (ω) are computed. Nucleus independent chemical shifts (NICS) values are estimated to study the variation in aromaticity. Time dependent density functional theory (TD-DFT) is used to study the UV–Visible absorption spectra. Effects of BN doping and substituents on corresponding dipole moments and band gaps are also analyzed. Presence of BN unit and/or substituents induced considerable impact on global reactivity, dipole moment, band gap and aromaticity of the chosen systems, especially for BN doped chrysene at the edge. Absorption spectra which are red shifted in presence of BN and substituents are mostly found within the UV-region.

Assessing the Role of BN-Embedding Position in B2N2-Perylenes.

Incorporating heteroatoms can effectively modulate the molecular optoelectronic properties. However, the fundamental understanding of BN doping effects in BN-embedded polycyclic aromatic hydrocarbons (PAHs) is underexplored, lacking rational guidelines to modulate the electronic structures through BN units for advanced materials. Herein, a concise synthesis of novel B2N2-perylenes with BN doped at the bay area is achieved to systematically explore the doping effect of BN position on the photophysical properties of PAHs. The shift of BN position in B2N2-perylenes alters the π electron conjugation, aromaticity and molecular rigidness significantly, achieving substantially higher electron transition abilities than those with BN doped in the nodal plane. It is further clarified that BN position dominates the photophysical properties over BN orientation. The revealed guideline here may apply generally to novel BN-PAHs, and aid the advancement of BN-PAHs with highly-emissive performance.

Precise synthesis of BN embedded perylene diimide oligomers for fast-charging and long-life potassium-organic batteries.

Replacing the C[double bond, length as m-dash]C bond with an isoelectronic BN unit is an effective strategy to tune the optoelectronic properties of polycyclic aromatic hydrocarbons (PAHs). However, precise control of the BN orientations in large PAH systems is still a synthetic challenge. Herein, we demonstrate a facile approach for the synthesis of BN embedded perylene diimide (PDI) nanoribbons, and the polarization orientations of the BN unit were precisely regulated in the two PDI trimers. These BN doped PDI oligomers show great potential as organic cathodes for potassium-ion batteries (PIBs). In particular, trans-PTCDI3BN exhibits great improvement in voltage potential, reversible capacities (ca. 130 mA h g-1), superior rate performance (19 s to 69% of the maximum capacity) and ultralong cyclic stability (nearly no capacity decay over 30 000 cycles), which are among those of state-of-the-art organic-based cathodes. Our synthetic approach stands as an effective way to access large PAHs with precisely controlled BN orientations, and the BN doping strategy provides useful insight into the development of organic electrode materials for secondary batteries.

Avenue to novel o-carboranyl boron compounds - reactivity study of o-carborane-fused aminoborirane towards organic azides.

Herein we report the reactivity study of o-carborane-fused bis(trimethylsilyl)aminoborirane towards three different types of organic azides, i.e., aryl, alkyl, and silyl azides. The reaction with ArN3 (Ar = 2,6-iPr2C6H4, 2,6-C6H3Cl2, 2,4,6-C6H2Br3, C6F5) resulted in the cycloaddition of ArN3 to the borirane BN unit accompanied by silyl migration. Conversely, in the reaction with BnN3, only the BnN3 : borirane 1 : 2 ring expansion product was obtained. Finally, the reaction with Me3SiN3 resulted in a formal nitrene insertion product under thermal conditions. All of the newly obtained o-carborane-fused BN-containing heterocycles were fully characterized, and the mechanism of these substituent-dependent reactions was studied using DFT calculations.

Adsorption, Single‐Molecule Manipulation, and Self‐Assembly of Borazine on Ag(111)

AbstractThe interaction of borazine with metal supports and the concomitant surface chemistry play important roles in the synthesis of hexagonal boron nitride and the assembly of BN‐doped carbon nanostructures, thus making adsorbed borazine an intriguing model system. Herein, the first real space characterization of individual borazine molecules and highly ordered borazine self‐assemblies on solid supports, combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy, X‐ray photoelectron spectroscopy, and complementary density functional theory modeling is reported. Specifically, a weak, nondissociative adsorption of borazine with the ring aligned in parallel to the surface plane is observed on Ag(111) upon low temperature deposition. Borazine is found to favor hollow adsorption sites, which guide the assembly of intricate borazine assemblies including a porous, chiral honeycomb‐like network, and dense‐packed monolayer films. Additionally, a modification of the borazine adsorption configuration by STM‐based manipulation is demonstrated. Dehydrogenation of individual molecules by voltages pulses yields an upright standing borazine fragment bound via B to Ag. This study thus provides a comprehensive, single‐molecule level characterization of borazine adsorption and surface chemistry on a characteristic coinage metal support and may serve as a reference for advanced low‐dimensional materials based on functionalized borazines or including BN units as dopants.

Increasing Chemical Diversity of B2 N2 Anthracene Derivatives by Introducing Continuous Multiple Boron-Nitrogen Units.

Increasing the chemical diversity of organic semiconductors is essential to develop efficient electronic devices. In particular, the replacement of carbon-carbon (C-C) bonds with isoelectronic boron-nitrogen (B-N) bonds allows precise modulation of the electronic properties of semiconductors without significant structural changes. Although some researchers have reported the preparation of B2 N2 anthracene derivatives with two B-N bonds, no compounds with continuous multiple BN units have been prepared yet. Herein, we report the synthesis and characterization of a B2 N2 anthracene derivative with a BNBN unit formed by converting the BOBN unit at the zigzag edge. Compared to the all-carbon analogue 2-phenylanthracene, BNBN anthracene exhibits significant variations in the C-C bond length and a larger highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap. The experimentally determined bond lengths and electronic properties of BNBN anthracene are confirmed through theoretical calculations. The BOBN anthracene organic light-emitting diode, used as a blue host, exhibits a low driving voltage. The findings of this study may facilitate the development of larger acenes with multiple BN units and potential applications in organic electronics.

Increasing Chemical Diversity of B2N2 Anthracene Derivatives by Introducing Continuous Multiple Boron‐Nitrogen Units

AbstractIncreasing the chemical diversity of organic semiconductors is essential to develop efficient electronic devices. In particular, the replacement of carbon‐carbon (C−C) bonds with isoelectronic boron‐nitrogen (B−N) bonds allows precise modulation of the electronic properties of semiconductors without significant structural changes. Although some researchers have reported the preparation of B2N2 anthracene derivatives with two B−N bonds, no compounds with continuous multiple BN units have been prepared yet. Herein, we report the synthesis and characterization of a B2N2 anthracene derivative with a BNBN unit formed by converting the BOBN unit at the zigzag edge. Compared to the all‐carbon analogue 2‐phenylanthracene, BNBN anthracene exhibits significant variations in the C−C bond length and a larger highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap. The experimentally determined bond lengths and electronic properties of BNBN anthracene are confirmed through theoretical calculations. The BOBN anthracene organic light‐emitting diode, used as a blue host, exhibits a low driving voltage. The findings of this study may facilitate the development of larger acenes with multiple BN units and potential applications in organic electronics.

Poly(arylene iminoborane)s, Analogues of Poly(arylene vinylene) with a BN-Doped Backbone: A Comprehensive Study.

Despite the great success of the concept of doping organic compounds with BN units to access new materials with tailored prop-erties, its use in polymer chemistry has only been realized quite re-cently. Herein, we present a comprehensive study of oligo- and poly-(arylene iminoborane)s comprising a back-bone of phenylene or thio-phene moieties, as well as combinations thereof, linked via B=N units. The novel polymers can be regarded as BN analogues of poly-(p-phenylene vinylene) (PPV) or poly(thiophene vinylene) (PTV) or their copolymers, respectively. Our modular syn-thetic approach al-lowed us to prepare four polymers and twelve monodisperse oligo-mers with modulated electronic properties. Alter-nating electron-re-leasing di-aminoarylene and electron-accepting dibo-rylarylene building blocks give rise to a pronounced donor-acceptor character. Effective π-con-ju-ga-tion over the arylene iminoborane back-bone is evidenced by sys-tematic bathochromic shifts of the low-energy UV-vis absorp-tion max-imum with increasing chain length, which is furthermore sup-ported by crystallographic and compu-tational investigations. Further-more, all compounds investigated show emission of visible light in the solid state and aggregation-induced emission (AIE) behavior, due to the presence of partially flexible linear B=N linkages in the back-bone.

1,2,5‐Azadiborolane as a Building Block for Inorganic–Organic Hybrid Polymers

AbstractThe incorporation of BN units in organic scaffolds by isoelectronic/isosteric substitution of selected CC couples has emerged as an efficient tool to produce new materials with useful properties and functions. The knowledge about BN‐doped inorganic–organic hybrid polymers, however, is still rather scarce. This is especially true for linear or cyclolinear macromolecules that feature longer inorganic chains. Herein, we introduce 1,2,5‐azadiborolane as a polymer building block for the first time. An attempt to apply it for the synthesis of a cyclolinear poly(iminoborane) resulted after only two B−N coupling events in the formation of a molecular compound comprising a chain of three nitrogen and two boron atoms – as confirmed by single‐crystal X‐ray diffractometry. In combination with a p‐phenylene diamine‐based co‐monomer, we accomplished to incorporate the 1,2,5‐azadiborolane into a hybrid polymer of considerable molecular weight that features a B2N3 chain. We additionally synthesized a small molecular model compound for the polymer and characterized it crystallographically as well. Comparison of the UV‐vis spectra of the monomer, the oligomer, and the polymer revealed systematic red‐shifts of the longest‐wavelength absorption band with increasing number of BN units in the chain.

Reactions of 1,2-Azaborinine, a BN-Benzyne, with Organic π Systems.

Ortho-benzyne and 1,2-azaborinine are related by the formal exchange of the CC triple bond by the isoelectronic BN unit. The (2 + 2) and (2 + 4) cycloaddition reactions of 1,2-azaborinine with the different organic π systems (ethene, ethyne, 1,3-butadiene, 1,3-cyclopentadiene, furan, benzene) were examined computationally using density functional, second-order perturbation, and coupled-cluster methods. All reactions of 1,2-azaborinine with the studied substrates are highly exothermic and involve the formation of Lewis acid-base complexes of 1,2-azaborinine and respective π systems. The interaction between the π bond of the substrates and the empty p orbital of the boron atom in these complexes is remarkably strong, resulting in two-step mechanisms for the (2 + 2) and (2 + 4) cycloaddition reactions. Cycloaddition reactions have lower barriers than CH insertion reactions, and (2 + 4) reactions are favored over (2 + 2) cycloadditions.

Precise Molecular Design for Two Parent BN‐Pentacyclic Isomers Through Stitching Engineering Toward Extremely Sensitive Explosive Detection

AbstractThe incorporation of BN units into polycyclic aromatic hydrocarbons (PAHs) has been ascertained to be a promising strategy for creating novel materials with unique functions and properties. However, it poses a formidable challenge to achieve precise construction of BN‐PAHs with variable skeleton module, which conversely, enhances greater understanding of the structure‐property relationship. Herein, two BN‐pentacyclic isomers (P‐BN‐BT and I‐BN‐BT) with different stitching patterns are addressed comprehensively, in which the integrated analysis reveals that the geometric structure, aromaticity, and photophysical properties indeed vary with the variational stitching models. More interestingly, further investigations show that the I‐BN‐BT with twisted molecular configuration displays a low fluorescence quantum yield, while the P‐BN‐BT with fully planar conformation exhibits high quantum yield and exceptional mechanochromic luminescent (MCL) properties. More importantly, P‐BN‐BT shows extreme sensitivity toward 2,4,6‐trinitrophenol (TNP). Visual detection of TNP is handily performed by fabrication of the test strips, which reaches ppm level under daylight. This work provides systematic insight into the effects of BN doping and highlights the importance of accurate control of the stitching patterns in conjugated materials.

Synthetic Doping of Acenaphthylene through BN/CC Isosterism and a Direct Comparison with BN-Acenaphthene.

Boron/nitrogen-doped acenaphthylenes, a new class of BN-doped cyclopenta-fused polycyclic aromatic hydrocarbons, were synthesized via indole-directed C-H borylation. The reference molecule BN-acenaphthene was also synthesized in a similar manner. Both BN-acenaphthylene and BN-acenaphthene were unequivocally characterized by single-crystal X-ray analysis. The aromaticities of each ring in BN-acenaphthylenes were quantified by experimental and theoretical methods. Moreover, doping the BN unit into acenaphthylene can increase the LUMO level and decrease the HOMO level, resulting in wider HOMO-LUMO energy gaps. Furthermore, regioselective bromination of BN-acenaphthylene (B-Mes) afforded monobrominated BN-acenaphthylene in good yield. Subsequently, cross-coupling of brominated BN-acenaphthylene gave a series of BN-acenaphthylene derivatives. In addition, the photophysical properties of these BN-acenaphthylene derivatives can be fine-tuned by the substituents on the BN-acenaphthylene scaffold.

Synthesis, Characterization, and Properties of BN-Fluoranthenes.

Boron/nitrogen-doped fluoranthenes, a new class of BN-doped cyclopenta-fused polycyclic aromatic hydrocarbons, were synthesized via pyrrolic-type nitrogen directed C-H borylation. Regioselective bromination of BN-fluoranthene (3a) gave mono- and dibrominated BN-fluoranthenes. The halogenated BN-fluoranthene (3b) can undergo various of further cross-coupling reactions to deliver a series of BN-fluoranthenes. Moreover, incorporating BN unit in to fluoranthene resulted in a wider HOMO-LUMO energy gaps. The aromaticities of the BN-fluoranthene (3a) were quantified by experimental and computational studies.

1,6;2,3-Bis-BN Cyclohexane: Synthesis, Structure, and Hydrogen Release.

BN/CC isosterism has been widely investigated as a strategy to expand carbon-based compounds. The introduction of BN units in organic molecules always results in novel properties. In this work, we reported the first synthesis and characterization of 1,6;2,3-bis-BN cyclohexane, an isostere of cyclohexane with two adjacent BN pairs. Its ring flipping barrier is similar to that of cyclohexane. Protic hydrogens on N in 1,6;2,3-bis-BN cyclohexane show higher reactivity than its isomeric bis-BN cyclohexane. This compound exhibits an appealing hydrogen storage capability of >9.0 wt %, nearly twice as much as the 1,2;4,5-bis-BN cyclohexane.

"Spine Surgery" of Perylene Diimides with Covalent B-N Bonds toward Electron-Deficient BN-Embedded Polycyclic Aromatic Hydrocarbons.

BN-embedded polycyclic aromatic hydrocarbons (PAHs) with unique optoelectronic properties are underdeveloped relative to their carbonaceous counterparts due to the lack of suitable and facile synthetic methods. Moreover, the dearth of electron-deficient BN-embedded PAHs further hinders their application in organic electronics. Here we present the first facile synthesis of novel perylene diimide derivatives (B2N2-PDIs) featuring n-type B-N covalent bonds. The structures of these compounds are fully confirmed through the detailed characterizations with NMR, MS, and X-ray crystallography. Further investigation shows that the introduction of BN units significantly modifies the photophysical and electronic properties of these B2N2-PDIs and is further understood with the aid of theoretical calculations. Compared with the parent perylene diimides (PDIs), B2N2-PDIs exhibit deeper highest occupied molecular orbital energy levels, new absorption peaks in the high-energy region, hypsochromic shift of absorption and emission maxima, and decrement of photoluminescent quantum yields. Single-crystal field-effect transistors based on B2N2-PDIs showcase an electron mobility up to 0.35 cm2 V-1 s-1, demonstrating their potential application in optoelectronic materials.

Enhanced N-directed electrophilic C-H borylation generates BN-[5]- and [6]helicenes with improved photophysical properties.

Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest, e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C–H borylation methodology has been developed that provides access to azaborine containing helicenes (BN–helicenes). This borylation process proceeds via protonation of an aminoborane with bistriflimidic acid. DFT calculations reveal the borenium cation formed by protonation to be more electrophilic than the product derived from aminoborane activation with BBr3. The synthesised helicenes include BN-analogues of archetypal all carbon [5]- and [6]helicenes. The replacement of a CC with a BN unit (that has a longer bond) on the outer helix increases the strain in the BN congeners and the racemization half-life for a BN–[5]helicene relative to the all carbon [5]helicene. BN incorporation also increases the fluorescence efficiency of the helicenes, a direct effect of BN incorporation altering the distribution of the key frontier orbitals across the helical backbone relative to carbo-helicenes.

Prediction of three-dimensional stretchable boron nitride nanoribbons

In this paper, a series of fully sp2-hybrid three-dimensional boron nitride nanoribbons (3D-BNNRs) polymorphs entirely composed of hexagonal rings is described herein. The 3D-BNNRs can be considered as connected BNNRs with different widths. All the predicted structures are thermodynamically metastable with 0.111–0.281 eV per BN unit higher than hBN. The elastic constants and phonon dispersion calculations show the 3D-BNNRs are mechanically and dynamically stable. The 3D-BNNRs are semiconductors, which are independent of the width of BNNRs. Tensile strength calculations show the 3D-BNNRs are very strong in the BNNRs-like plane, comparable to graphene and BNNRs. Moreover, under uniaxial strains, the 3D-BNNRs are very stretchable, and can hold more deformation along the direction perpendicular to BNNRs motif than in other directions, although the ideal strengths are lower than those in-plane direction.

Parent B2 N2 -Perylenes with Different BN Orientations.

Introducing BN units into polycyclic aromatic hydrocarbons expands the chemical space of conjugated materials with novel properties. However, it is challenging to achieve accurate synthesis of BN-PAHs with specific BN positions and orientations. Here, three new parent B2 N2 -perylenes with different BN orientations are synthesized with BN-naphthalene as the building block, providing systematic insight into the effects of BN incorporation with different orientations on the structure, (anti)aromaticity, crystal packing and photophysical properties. The intermolecular dipole-dipole interaction shortens the π-π stacking distance. The crystal structure, (anti)aromaticity, and photophysical properties vary with the change of BN orientation. The revealed BN doping effects may provide a guideline for the synthesis of BN-PAHs with specific stacking structures, and the synthetic strategy employed here can be extended toward the synthesis of larger BN-embedded PAHs with adjustable BN patterns.