Switchable (2 + 2) and (4 + 2) Cycloadditions on Boron Nitride Nanotubes under Oriented External Electric Fields: A Mechanistic Study.

The (2 + 2) and (4 + 2) cycloadditions are important approaches for the functional derivatizations of nanocarbon and hexagonal boron nitride (hBN) materials. However, as two competing reactions with similar reactivity, it is difficult to control the type of reactions and the corresponding adducts in practice. Here, we introduced a mechanistic study of the oriented external electric field (OEEF)-modulated cycloadditions of pristine and substituted benzynes on the zigzag boron nitride nanotubes. Owing to the distinct charge transfer directions between the competing (2 + 2) and (4 + 2) reactions and the resultant distinct responses of the barriers to the fields along the tube axis, we found that OEEF plays opposing catalytic roles in these two types of reactions and the effect of electric field as a catalyst or inhibitor can be easily reversed by flipping the field vector to achieve selective reactions and products at will.

Directional Diels-Alder cycloadditions of isoelectronic graphene and hexagonal boron nitride in oriented external electric fields: reaction axis rule vs. polarization axis rule.

The present study introduces the mechanisms for the oriented external electric field (OEEF)-participating cycloadditions of nanographene and the analogous hexagonal boron nitride (h-BN) nanoflakes. Despite the C-C and B-N pairs being isoelectronic, their different ionicities give rise to their distinct response to applied electric fields. For the nanographene models, the Diels-Alder addition obeyed the reaction axis rule and the activation barrier changed under an OEEF perpendicular to the carbon skeleton for enhanced/reduced intermolecular charge transfer, which provides a feasible strategy for the side-selective derivatization of graphene to obtain one-face-only adducts and Janus bifunctional products. By contrast, for the h-BN models, the variation of the activation barrier was pronounced when the electric field was aligned along the in-plane N-B bond rather than the well-accepted reaction axis. Electronic structure analyses indicated that, because of the opposite electron withdrawing/donating nature of the reacting sites of B/N, an OEEF along the N-B bond was capable of further enhancing the polarization via in-plane intramolecular charge transfer, resulting in a stabilized transition state and notable barrier reduction.

Curved Carbon Skeleton in Oriented External Electric Fields: Modulated Curvature, Directional Bowl Inversion, and Face-Selective Cycloadditions of Corannulene.

We introduced the oriented-external-electric-field-induced modification of bowl-shaped corannulene using density functional theory calculations. The results show that the electric field is capable of significantly modulating the polarization and electrostatic characteristics of the concave and convex surfaces of buckybowls. The structure-energy-reactivity relation can be precisely controlled, leading to a variety of unconventional properties for practical applications.

Newly-designed basket-shaped nanocarbon materials as strong and universal fullerene receptors.

We introduced the host-guest chemistry of newly-designed fullerene receptors consisting of buckybowl and alkyne subunits. DFT computations indicated that the huge π-π overlap results in significant binding energy that is larger than those of other known fullerene hosts. The flexibility of the carbon skeleton ensures that corannulenes can be easily twisted to capture different guests and thus are expected as universal hosts for fullerene encapsulation.