Molecular twisting, lifting and curling

The process of surface-assisted cyclodehydrogenation of polycyclic aromatic hydrocarbons has been recently adopted as one of the most effective, versatile, and flexible strategies for the bottom-up synthesis of fullerene, nanographene, and graphene nanoribbons. The large number of available precursors is the key to tailor the structural properties of carbon networks via polymerization reactions and to control their properties.
In this study we show that thermally assisted cyclodehydrogenation of coronene (C₂₄H₁₂) on Ir(111) takes place through sequential steps that include dramatic changes of the molecule's pristine configuration. For a comprehensive characterization of the reaction process we used several techniques, namely fast and high-energy resolution X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, ultraviolet photoelectron spectroscopy, angle resolved photoemission spectroscopy, temperature programmed desorption, and low energy electron diffraction. The experiments were paralleled by density functional theory calculations.
We have shown that coronene molecules adsorbed on Ir(111) undergo major conformational changes during dissociation. They firstly tilt upwards with respect to the surface, still keeping their planar

configuration, and subsequently experience a rotation, which changes the molecular axis orientation. Upon lifting, the internal C-C strain is initially relieved; as the dehydrogenation proceeds, the molecules experience a progressive increase in the average interatomic distance, and gradually settle to form dome shaped nano-graphene flakes. Our results provide important insight into the complex mechanism of molecular break-up, which could have implications in the synthesis of new carbon-based nanostructured materials. For example by exploiting this reaction mechanism, we envisage the possibility of creating new nanostructures with different functionalities by encapsulating single adatoms below the carbon dome, trough diffusion of the new species underneath the carbon disk.