BN Units Research Articles

Parent B2N2‐Perylenes with Different BN Orientations

AbstractIntroducing 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 B2N2‐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.

Enhanced Activation of CO2 on h-BN Nanosheets via Forming a Donor–Acceptor Heterostructure with 2D M2X Electrenes

The activation of CO2 is the first crucial step in the CO2 reduction reaction (CO2RR), but it faces the challenge of the ultrahigh chemical stability of the CO2 molecule. Two-dimensional (2D) hexagonal boron nitride (h-BN) has been considered as a promising electrocatalytic interface material due to its high specific surface area, N- and B-active sites, and adjustable chemical reactivity through interactions with other materials. Here we report a donor–acceptor heterostructure (DAH) containing 2D h-BN and M2N (M = Ca, Sr, and Ba) or Y2C electrene, single-layer electride materials, toward the activation of the CO2 molecule on the basis of first-principles calculations. Our results demonstrate that a considerable number of electrons (0.1 e per BN unit) transfer from M2X electrene to the h-BN sheet due to the strong electrostatic interaction between the cation boron in the h-BN sheet and the anion electron gas in M2X electrides, which significantly enhances the CO2 activation activity of the h-BN monolayer. The adsorption of CO2 on h-BN is exothermic, with a negligible energy barrier down to 0.013 eV. Meanwhile, the overpotential of the hydrogenation of CO2 to HCOOH is as low as 0.17 V on the h-BN/Y2C DAH, implying superior performance for the CO2 reduction on the h-BN/M2X DAH. This work provides a strategy for activating CO2 on the h-BN monolayer by building a DAH with 2D electride materials.

Modulation of the Second Order Nonlinear Optical Properties of Helical Graphene Nanoribbons Through Introducing Azulene Defects or/and BN Units

Modulation of the Second Order Nonlinear Optical Properties of Helical Graphene Nanoribbons Through Introducing Azulene Defects or/and BN Units

BN/BO-Ullazines and Bis-BO-Ullazines: Effect of BO Doping on Aromaticity and Optoelectronic Properties.

We have achieved substitutional doping of ullazine with either two BO units or with one BO unit and one BN unit. The synthesis of these B-doped ullazines is straightforward, using demethylation and borylative cyclization as the key steps. Ullazine cores of both BN/BO-ullazines (2) and bis-BO-ullazines (3) are very close to being planar. Their electronic and photophysical properties were investigated by ultraviolet-visible, fluorescence spectroscopy, cyclic voltammetry, and density functional theory calculations.

Role of heteroatoms and substituents on the structure, reactivity, aromaticity, and absorption spectra of pyrene: a density functional theory study

Abstract Effect of heteroatoms viz. BN and substituents viz. –Me (methyl), –OH (hydroxyl), –NH2 (amine), –COOH (carboxyl), and –CN (cyano) on the structural parameters, global reactivity, aromaticity, and UV-visible spectra of pyrene are studied with the help of density functional theory (DFT). Global reactivity parameters such as global hardness (η) and electrophilicity (ω) are calculated using density functional reactivity theory (DFRT). Time dependent density functional theory (TD-DFT) is explored for interpreting the UV-visible absorption spectra. Aromaticity of the pyrene rings are predicted from the nucleus independent chemical shift (NICS) values. Presence of BN unit and substituent induces reasonable impact on the studied parameters. The observed absorption spectra lie predominantly within the UV-region (both blue and red shifts are observed in presence of BN and substituent). HOMO energy and absorption spectra are affected nominally in solvent phase.

B3N3-Substituted Nanographene Molecules: Influence of Planarity on the Electronic Structure and Molecular Orientation in Thin Films

BN-substituted nanographene molecules are currently the focus of interest because the substitution of C–C units by isoelectronic and isosteric BN units is a straightforward way of changing the elec...

Influence of BN-orientation pattern at spoke location of corannulene on electro-optical properties and aromaticity

One to five BN units have been embedded in corannulene at spoke location with two different orientation patterns. The effect of the number and orientation of BN units have been investigated employing the density functional theory (DFT). The BN-embedded corannulene structures show the significant changes in geometric structure, aromaticity and the first static hyperpolarizability (β0). The key role of BN orientation in bowl-shaped π-conjugated polyaromatic hydrocarbons with many BN units have been investigated for the first time. The aromaticity concept was evaluated employing NICS parameter. The bowl depth, dipole moment (μ) and β0 values have been obtained 0.0 Å, 0.0 Debye, 1.9 au for 5BN structure and 1.612 Å, 4.4 Debye, 963.6 au for 5NB structure. The HOMO-LUMO gap (HLG) value was reduced 11% for 5NB structure and increased 2% for 5BN structure. The average NICS(0) values increase in BN-orientation and decrease in NB-orientation structures. This work represents a new class of organic materials with appealing properties, which can indicate the importance of precise control of the BN substitution patterns in bowl-shaped π-conjugated polyaromatic hydrocarbons.

BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis, Aromaticity, and Reactivity

AbstractBN‐embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X‐ray crystallography, optical spectroscopy, and cyclic voltammetry. The B−N bonds show delocalized double‐bond characteristics and the conjugation can be extended through the trans‐orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN‐embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN‐embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge‐transfer interactions.

BN-Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis, Aromaticity, and Reactivity.

BN-embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X-ray crystallography, optical spectroscopy, and cyclic voltammetry. The B-N bonds show delocalized double-bond characteristics and the conjugation can be extended through the trans-orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN-embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN-embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge-transfer interactions.

Fluxional Bonds in Tubular Molecular Rotors B3-[Ta@B18] and B4-[Ta@B18]+ in 18-Electron Configurations

Boron and metal-doped boron nanoclusters possess unique fluxional behaviors in dynamics. Detailed bonding analyses performed in this work indicate that, similar to the experimentally observed B2-[Ta@B18]− (1), the theoretically predicted tubular molecular rotors B3-[Ta@B18] (2) and B4-[Ta@B18]+ (3) possess typical fluxional 4c–2e and 3c–2e σ-bonds atop the Ta-centered [Ta@B18] double-ring tube between the Bn unit (n = 3, 4) and upper B9 ring, unveiling the fluxional bonding nature of the Bn-[Ta@B18]q complex series (n = 2–4, q = n − 3) which follow the 18-electron rule in different charge states. Chiral conversions via pseudo-rotations are observed in the fluxional processes between the Bn unit (n = 3, 4) and Ta-centered [Ta@B18] double-ring tube.

BN‐Embedded Tetrabenzopentacene: A Pentacene Derivative with Improved Stability

AbstractConsiderable efforts have been devoted to achieving stable acene derivatives for electronic applications; however, the instability is still a major issue for such derivatives. To achieve higher stability with minimum structural change, CC units in the acenes were replaced with isoelectronic BN units to produce a novel BN‐embedded tetrabenzopentacene (BNTBP). BNTBP, with a planar structure, is highly stable to air, moisture, light, and heat. Compared with its carbon analogue tetrabenzopentacene (TBP), BN embedment lowered the highest occupied molecular orbital (HOMO) energy level of BNTBP, changed the orbital distribution, and decreased the HOMO orbital coefficients at the central carbon atoms, which stabilize BNTBP molecules upon exposure to oxygen and sunlight. The single‐crystal microribbons of BNTBP exhibited good performance in field‐effect transistors (FETs). The high stability and good mobility of BNTBP indicates that BN incorporation is an effective approach to afford stable large‐sized acenes with desired properties.

BN-Embedded Tetrabenzopentacene: A Pentacene Derivative with Improved Stability.

Considerable efforts have been devoted to achieving stable acene derivatives for electronic applications; however, the instability is still a major issue for such derivatives. To achieve higher stability with minimum structural change, CC units in the acenes were replaced with isoelectronic BN units to produce a novel BN-embedded tetrabenzopentacene (BNTBP). BNTBP, with a planar structure, is highly stable to air, moisture, light, and heat. Compared with its carbon analogue tetrabenzopentacene (TBP), BN embedment lowered the highest occupied molecular orbital (HOMO) energy level of BNTBP, changed the orbital distribution, and decreased the HOMO orbital coefficients at the central carbon atoms, which stabilize BNTBP molecules upon exposure to oxygen and sunlight. The single-crystal microribbons of BNTBP exhibited good performance in field-effect transistors (FETs). The high stability and good mobility of BNTBP indicates that BN incorporation is an effective approach to afford stable large-sized acenes with desired properties.

B2 N2 -Embedded Polycyclic Aromatic Hydrocarbons with Furan and Thiophene Derivatives Functionalized in Crossed Directions.

A series of polycyclic aromatic hydrocarbons (PAHs), consisting of two pairs of BN units, have been designed and their synthesis has been achieved by electrophilic C-H borylation. Two conjugation extension directions can be found in these B2 N2 -embedded PAHs. The B2 N2 -containing backbone with shorter effective conjugation length is isoelectronic with diaryl-fused anthracene, whereas the second derivative, with longer effective conjugation length, is isoelectronic with bis(trans-arylvinyl)benzene. By incorporating different aryl groups, i.e., furyl, thienyl, benzo[b]furyl, and benzo[b]thienyl groups, into the two crossed directions of the B2 N2 -embedded PAHs, their electronic and optical properties have been comparatively investigated by photophysical, electrochemical, and theoretical approaches. It is found that both the substituents and their conjugation extension directions have significant effects on the aromatic and photophysical properties of the B2 N2 -embedded PAHs. The conjugation extension in the shorter backbone is more pronounced on the effective conjugation length than the longer backbone. Moreover, all the B2 N2 -embedded PAHs behave as both Lewis acids and Lewis bases, and reversible photoluminescence switching can be observed by simply neutralizing the added Lewis acid or Lewis base.

High resolution photoelectron imaging of boron-bismuth binary clusters: Bi2Bn - (n = 2-4).

Bismuth boride is a heavy member of the III-V semiconductors. Although there have been some theoretical interests in this material, it has not been synthesized experimentally. Here, we report a high-resolution photoelectron imaging study on a series of boron-bismuth binary clusters, Bi2Bn - (n = 2-4), produced by laser vaporization of a B/Bi mixed target. Vibrationally resolved photoelectron spectra are obtained for all three clusters, and the measured vibrational and electronic information is used to compare with theoretical calculations to understand their structures and bonding. Bi2B2 - is found to be linear (D∞h, 2Πg) with a B2 unit and two terminal Bi atoms, while Bi2B3 - is found to be planar (C2v, 1A1), consisting of a B3 triangle with two bridging Bi atoms. Interestingly, the spectra of Bi2B4 - reveal two co-existing isomers; both are found to be planar and contain a rhombus B4 unit with two bridging Bi atoms in a trans (C2h, 2Au) and cis (C2v, 2B1) fashion separated only by 0.03 eV in energy. The interactions between the two Bi atoms and the Bn motifs are understood using chemical bonding analyses. This study shows that the Bi-B bonding is weak enough so that the Bn units maintain their structural integrity with the Bi atoms bonded to the cluster periphery only.

Formation of boron nitride islands in the graphene nanoflakes: A DFT study

Abstract We have applied density functional calculations to investigate the formation of boron nitride islands in the triangular and hexagonal graphene nanoflakes (GNFs). Based on the calculated reaction energies, BN doping of GNFs is found to be endothermic. The variation of reaction energies indicates that BN doping of the GNFs follow previously proposed ‘hexagon filling’’ rule. Based on the calculated NICS indexes, aromaticity inside these molecules can be explained within the framework of the Clar's Sextet Theory. In the case of BN-doped hexagonal and triangular GNFs, NICS(1) index shows aromaticity and nonaromaticity for the borazine like substructures, respectively. Moreover, the substitution of one BN unit in the 1,2 azaborine like rings leads to the increase of aromaticity and nonaromaticity in hexagonal and triangular GNFs, respectively. Based on our results, the BN doped hexagonal GNFs not only lose electrons somewhat more easily to form positive ions, but also obtain electrons more easily to form anions.

BN Embedded Polycyclic π-Conjugated Systems: Synthesis, Optoelectronic Properties, and Photovoltaic Applications.

In the periodic table of elements, boron (B, atomic number, 5) and nitrogen (N, atomic number, 7) are neighboring to the carbon (C, atomic number, 6). Thus, the total electronic number of two carbons (12) is equal to the electronic sum of one boron (5) and one nitrogen (7). Accordingly, replacing two carbons with one boron and one nitrogen in a π-conjugated structure gives an isoelectronic system, i.e., the BN perturbed π-conjugated system, comparing to their all-carbon analogs. The BN embedded π-conjugated systems have unique properties, e.g., optical absorption, emission, energy levels, bandgaps, and packing order in contrast to their all-carbon analogs and have been intensively studied in terms of novel synthesis, photophysical characterizations, and electronic applications in recent years. In this review, we try to summarize the synthesis methods, optoelectronic properties, and progress in organic photovoltaic (OPV) applications of the representative BN embedded polycyclic π-conjugated systems. Firstly, the narrative will be commenced with a general introduction to the BN units, i.e., B←N coordination bond, B-N covalent bond, and N-B←N group. Then, the representative synthesis strategies toward π-conjugated systems containing B←N coordination bond, B-N covalent bond, and N-B←N group will be summarized. Afterwards, the frontier orbital energy levels, optical absorption, packing order in solid state, charge transportation ability, and photovoltaic performances of typical BN embedded π-conjugated systems will be discussed. Finally, a prospect will be proposed on the OPV materials of BN doped π-conjugated systems, especially their potential applications to the small molecules organic solar cells.

Crystal Orbital Study on one-dimensional β-graphyne and its BN-substituted derivatives

In this study, one-dimensional (1D) β-graphyne (βGY) Nanoribbons (NRs) and its three types of BN-substituted derivatives are investigated by the self-consistent-field Crystal Orbital (SCF-CO) method. To the authors’ knowledge, little information about the structural, electronic and transport properties of the 1D βGY NRs and BN-substituted βGY derivatives has been reported before. The phonon analysis shows that these 1D NRs should be dynamically stable. The structures with more BN pairs are believed to be more stable. The BN substituted positions and the edge structures have great impact on the electronic properties of the studied NRs. These NRs can be conductors, semiconductors or insulators. It is found that the metallic NR with sp2 hybridized C atoms substituted by BN units has high superconducting transition temperature which is even higher than those of alkali-doped C60 complexes. The mobilities of charge carriers for these NRs are also calculated. The band structures and the mobilities of 1D NRs are compared with those of the corresponding two-dimensional (2D) slabs.

Cyclolinear Oligo- and Poly(iminoborane)s: The Missing Link in Inorganic Main-Group Macromolecular Chemistry.

The reaction of n-C8 H17 B[N(Me)SiMe3 ]2 (1) with n-C8 H17 BCl2 (2 a) yielded, instead of a linear poly(iminoborane), the aminoborane n-C8 H17 B(Cl)N(Me)SiMe3 (4) and after cyclotrimerization the borazine cyclo-(n-C8 H17 BNMe)3 (6). Side reactions that result in borazine formation were effectively suppressed if 1,3-bis(trimethylsilyl)-1,3,2-diazaborolidines 7 were employed as co-monomers in combination with dichloro- or dibromoboranes 2 or 8, respectively. Silicon/boron exchange polycondensation led to oligo(iminoborane)s 11 a,b,ac,d. Alternative synthetic routes to such species involve Sn/B exchange of 1,3-bis(trimethylstannyl)-2-n-octyl-1,3,2-diazaborolidine (16) and n-C8 H17 BBr2 (8 a), and the initiated polycondensation of the dormant monomer 14 in the presence of a Brønsted acid (HCl, HOTf, or HNTf2 ; Tf=trifluoromethylsulfonyl). Although an attempt to obtain an oligo-/poly(iminoborane) with phenyl side groups yielded only insoluble material, the incorporation of aryl groups was proven for a derivative with both phenyl and n-octyl boron substituents (11 ac), as well as for a derivative with 4-n-butylphenyl side groups (11 d). The highest-molecular-weight sample obtained was 11 ac. Featuring about 18 catenated BN units, on average, this is the closest approach to a poly(iminoborane) known.

Theoretical investigation on electronic properties and carrier mobilities of BN-substituted graphyne nanoribbons

This paper presents the self-consistent field crystal orbital studies of the BN-substituted graphyne nanoribbons (NRs) based on density functional theory. Two kinds of the substitution are considered: one is that the six-membered rings in the graphyne NRs are replaced by the corresponding BN hexagonal rings; another is the substitution of acetylenic linkages by BN units. The calculations show that all the optimized one-dimensional BN-substituted graphyne NRs still keep plane structures. These NRs are semiconductors with non-zero band gaps and their band gaps are wider than those of corresponding graphyne NRs but narrower than those of BNNRs. The substitution of hexagonal rings leads to wider band gap than the substitution of acetylenic linkages. The relationship of band gaps with the ribbon widths is different from different NR patterns. The stabilities of these BN-substituted graphyne NRs monotonically decrease as their widths increase and the molecular dynamics simulations show that these NRs would be stable when T<600K. Natural population analysis shows that BN bonds have stronger ionicity in the hexagonal rings than in the BN linkages. The dependence of the charge carrier mobilities on the ribbon widths is also quite different from different types of the BN-substituted graphyne NRs. It is found that both the substituting types and edge structures have important influence on the transport property of the BN-substituted NRs. Thus, BN substituting indeed plays an important role in tuning the electronic structure of graphyne.

BN Tetracene: Extending the Reach of BN/CC Isosterism in Acenes

The first synthesis of a tetracene BN isostere is reported. Comparison with its direct, all-carbon analogue reveals that the BN tetracene isostere exhibits a lower-lying HOMO and a slightly larger optical HOMO–LUMO gap. While all-carbon tetracenes are prone to photodecomposition, the BN tetracene scaffold is less light sensitive, owing in part to its much higher photoluminescence quantum yield. In the context of this larger BN tetracene family, we introduce simple guiding principles for predicting frontier orbital energies as a function of the position of the BN unit within the tetracene scaffold.