We investigate the structure of helicene monomers and stacked dimers on (111) facets of coinage metals. The effects of the coupling between intermolecular dispersive forces, intramolecular steric repulsion between end rings, and surface-molecule interactions are considered, as well as their implications to monolayer organization and surface commensuration.

A mediated electrosynthetic method has been developed for selective benzylic oxidation of methylarenes. Phthalimide-N-oxyl (PINO) radical generated by proton-coupled electrochemical oxidation of N-hydroxypthalimide serves as a hydrogen atom-transfer (HAT) mediator and as a radical trap for the benzylic radicals generated in situ. This mediated electrolysis method operates at much lower anode potentials relative to direct electrolysis methods for benzylic oxidation initiated by single-electron transfer (SET). A direct comparison of SET and mediated-HAT electrolysis methods with a common set of substrates shows that the HAT reaction exhibits a significantly improved substrate scope and functional group compatibility. The PINOylated products are readily converted into the corresponding benzylic alcohol or benzaldehyde derivative under photochemical conditions, and the synthetic utility of this method is highlighted by the late-stage functionalization of the non-steroidal anti-inflammatory drug celecoxib.

Crystal structure prediction (CSP), determining the experimentally observable structure of a molecular crystal from the molecular diagram, is an important challenge with technologically relevant applications in materials manufacturing and drug design. For the purpose of screening the randomly generated candidate crystal structures, CSP protocols require energy ranking methods that are fast and can accurately capture the small energy differences between molecular crystals. In addition, a good ranking method should also produce accurate equilibrium geometries, both intramolecular and intermolecular. In this article, we explore the combination of minimal-basis-set Hartree–Fock (HF) with atom-centered potentials (ACPs) as a method for modeling the structure and energetics of molecular crystals. The ACPs are developed for the H, C, N, and O atoms and fitted to a set of reference data at the B86bPBE-XDM level in order to mitigate basis-set incompleteness and missing correlation. In particular, ACPs are developed in combination with two methods: HF-D3/MINIs and HF-3c. The application of ACPs greatly improves the performance of HF-D3/MINIs for lattice energies, crystal energy differences, energy-volume and energy-strain relations, and crystal geometries. In the case of HF-3c, the improvement in the crystal energy differences is much smaller than in HF-D3/MINIs, but lattice energies and particularly crystal geometries are considerably better when ACPs are used. The resulting methods may be useful for CSP but also for quick calculation of molecular crystal lattice energies and geometries.

The adsorption of polyaromatic hydrocarbons (PAHs) on metallic substrates has been of interest in the field of optoelectronics due to the possibility of designing complex materials with tunable properties through surface functionalization with organic molecules. Much of the modelling research in this field has focused on perfectly symmetrical (idealized) substrates. Limited research has investigated the effect of substrate irregularities, such as adatoms, on the binding of PAHs onto substrates. Here, we examine how the presence of substrate-bound adatoms affects the binding of coronene and hexahelicene monomers and dimers onto Au(111) and Cu(111) substrates using a density functional theory approach. We found that helicene monomers were more effectively able to adapt to the presence of the adatoms than coronene by coiling around the adatoms. Whereas upon adsorption on an ideal (111) surface, coronene can establish significantly stronger dispersive interactions than helicenes, adatom defects reverse the trend. For helicenes, the degree of flattening near the surface and molecular coiling were strongly influenced by the extent of the adatom defect, as a result of the interplay between the molecule’s drive to maximize overlap with the underlying surface and the enhanced reactivity of lower-coordinated adatoms.