Probing Peripheral H-Bonding Functionalities in BN-Doped Polycyclic Aromatic Hydrocarbons.

The replacement of carbon atoms at the zigzag periphery of a benzo[fg]tetracenyl derivative with an NBN atomic triad allows the formation of heteroatom-doped polycyclic aromatic hydrocarbon (PAH) isosteres, which expose BN mimics of the amidic NH functions. Their ability to form H-bonded complexes has never been touched so far. Herein, we report the first solution recognition studies of peripherally NBN-doped PAHs to form H-bonded DD·AA- and ADDA·DAAD-type complexes with suitable complementary H-bonding acceptor partners. The first determination of Ka in solution showed that the 1:1 association strength is around 27 ± 1 M-1 for the DD·AA complexes in C6D6, whereas it rises to 1820 ± 130 M-1 for the ADDA·DAAD array in CDCl3. Given the interest of BN-doped polyaromatic hydrocarbons in supramolecular and materials chemistry, it is expected that these findings will open new possibilities to design novel materials, where the H-bonding properties of peripheral NH hydrogens could serve as anchors to tailor the organizational properties of PAHs.

Synthesis and Optoelectronic Properties of Hexa-peri-hexabenzoborazinocoronene.

The first rational synthesis of a BN-doped coronene derivative in which the central benzene ring has been replaced by a borazine core is described. This includes six C-C ring-closure steps that, through intramolecular Friedel-Crafts-type reactions, allow the stepwise planarization of the hexaarylborazine precursor. UV/Vis absorption, emission, and electrochemical investigations show that the introduction of the central BN core induces a dramatic widening of the HOMO-LUMO gap and an enhancement of the blue-shifted emissive properties with respect to its all-carbon congener.

Selective and Sequential Aminolysis of Benzotrifuranone: Synergism of Electronic Effects and Ring Strain Gradient.

Benzotrifuranone (BTF), bearing three symmetry-equivalent lactone rings, is unique in its ability to undergo highly selective and sequential aminolysis reactions in one-pot to afford multifunctionalized molecules (>80% overall yield). New insight into this behavior is presented through kinetics measurements (by stopped-flow IR spectroscopy), X-ray crystal structure analysis, quantum chemical calculations, and comparison of BTF to other benzoate esters, including its ring expanded congener benzotripyranone (BTP). While the structure-property investigation confirms stepwise electronic/inductive lactone deactivation for both BTF and BTP, the unusually fast and selective aminolysis of BTF is only fully explained through synergistic ring strain effects. Experimental signatures of the significant ring strain of BTF (∼28 kcal mol-1 based on DFT calculations vs 17 kcal mol-1 for BTP) include its high lactone carbonyl stretching energy (1821 cm-1 in acetonitrile vs 1777 cm-1 for BTP) and bond length alternation within its benzenoid ring. While ring strain is relieved upon the sequential aminolysis of both BTF and BTP, it is only for the former that a ring strain gradient is established that contributes to the stepwise aminolysis rate differences and enhanced selectivity. The work shows how a combination of electronic effects and ring strain can underpin the design of small molecules capable of stepwise functionalization, of which there are notably few examples.

"Magic" surface clustering of borazines driven by repulsive intermolecular forces.

It's a kind of magic: Hydroxy pentaaryl borazine molecules self-assemble into small clusters (see structure) on Cu(111) surfaces, whereas with symmetric hexaaryl borazine molecules large islands are obtained. Simulations indicate that the observed "magic" cluster sizes result from long-range repulsive Coulomb forces arising from the deprotonation of the B-OH groups of the hydroxy pentaaryl borazine.

Boron-nitrogen doped carbon scaffolding: organic chemistry, self-assembly and materials applications of borazine and its derivatives.

Discovered by Stock and Pohland in 1926, borazine is the isoelectronic and isostructural inorganic analogue of benzene, where the C[double bond, length as m-dash]C bonds are substituted by B-N bonds. The strong polarity of such heteroatomic bonds widens the HOMO-LUMO gap of the molecule, imparting strong UV-emitting/absorption and electrical insulating properties. These properties make borazine and its derivatives valuable molecular scaffolds to be inserted as doping units in graphitic-based carbon materials to tailor their optoelectronic characteristics, and specifically their semiconducting properties. By guiding the reader through the most significant examples in the field, in this feature paper we describe the past and recent developments in the organic synthesis and functionalisation of borazine and its derivatives. These boosted the production of a large variety of tailored derivatives, broadening their use in optoelectronics, H2 storage and supramolecular functional architectures, to name a few.