Renaissance of an Old Topic: From Borazines to BN-doped Nanographenes

Abstract

Graphene is one of the leading materials in today's science, but the lack of a band gap limits its application to replace semiconductors in optoelectronic devices. To overcome this limitation, the replacement of C=C bonds by isostructural and isoelectronic bonds is emerging as an effective strategy to open a band gap in monoatomic graphene layers. First prepared by Stock and Pohland in 1926, borazine is the isoelectronic and isostructural inorganic analogue of benzene, where the C=C bonds are replaced by B-N couples. The strong polarity of the BN bonds widens the molecular HOMO-LUMO gap, imparting strong UV-emission/absorption and electrical insulating properties. These properties make borazine a valuable molecular scaffold to be inserted as doping units in graphitic-based carbon materials to tailor a relevant band gap. It is with this objective that we became interested in the development of new synthetic organic methodologies to gain access to functionalized borazine derivatives. In particular, we have described the synthesis of borazine derivatives that, featuring aryl substituents at the B-centers bearing ortho-functionalities, are exceptionally stable against hydrolysis. Building on these structural motifs, we prepared hybrid BN-doped polyphenylene nanostructures featuring controlled doping patterns, both as dosage and orientation. Finally, exploiting the Friedel-Craft electrophilic aromatic substitution, we could develop the first rational synthesis of the first soluble hexa-peri-hexabenzoborazinocoronene and measured its optoelectronic properties, showing a widening of its gap compared to its full-carbon congener.

Polyaromatic Systems Combining Increasing Optical Gaps and Amplified Nonlinear Optical Properties. A Comprehensive Theoretical Study on B3N3 Doped Nanographenes

“…In the same context, a convincing bottom-to-up demonstration of how such borazine-doped nanographene monomers can be utilized as building blocks for the construction of graphene-like architectures, has been reported by Sánchez-Sánchez et al A next important step forward has been made by Bonifazi and co-workers who synthesized ,, complex polyphenylene dendritic chains bearing high concentrations of B 3 N 3 units of controlled orientations at preselected positions. Their results not only prove that multiple borazine units can coexist in the same carbon-based scaffold but also, as argued by Lorenzo-García and Bonifazi, might pave the way for the next long-awaited breakthrough in graphene chemistry which is the fabrication of two-dimensional multi-B 3 N 3 doped graphenes of tunable bandgaps.…”

“…Among other technological applications, the up-to-date research in BN-doped graphenes and/or polyaromatic motifs also suggests that such hybrids might find a prosper ground in the realm of nonlinear optical (NLO) materials. The latter statement is supported by recent experiments conducted by Biswas et al on heterostructures of hexagonal boron nitride-graphene oxide ( h BN-GO) and by earlier theoretical predictions − on hybrid nanographenes which provide solid proofs that h BN-graphene hybrids possess a strong NLO character that could be exploited in advanced NLO applications.…”

Boron–Nitrogen‐Doped Nanographenes: A Synthetic Tale from Borazine Precursors

“…[1][2][3][4] The substitution of C=Cb onds with isoelectronic and isostructural dipolar boron-nitrogen (BN) [5][6][7] andb oronoxygen (BO) [8][9][10][11] couples is an efficient method to gain control of the HOMO-LUMO bandgap withouts ignificant structural modifications of the molecular scaffold. [12,13] The use of polar BN and BO bonds typicallyw iden the HOMO-LUMO gap [14,15] and imparts dipole-driven self-assembly behaviors in the solid state [3,16] ando ns urfaces. [17][18][19] Noticeable examples include BN-doped pyrenes, [16] phenanthrenes, [20] anthracenes, [21] perylenes [22,23] and nanographenes.…”

On the adsorption affinity of graphene and white graphene sheets by dioxin‐like pollutants

“…This makes substrates based on white graphene be interesting not only as adsorbent agents but also as platforms integrated in sensors for laser‐based optical detection. Even more interesting are 2D hybrid materials based on boron, nitrogen and carbon, also called h‐BNCs [50–52], where the optical activity of the surface may be easily tuned. In these materials, graphene or white graphene nanoislands of different size may be “stamped,” whose optical response depends on the size and shape of the corresponding nanoisland [53–56].…”