Formation of difuran-diketopyrrolopyrrole adsorption layers on graphite probed in molecular simulations*

In this computational work, we investigate the adsorption layers of N-unsubstituted difuran-diketopyrrolopyrroles (DPP). Three conformational states differing in their dipole moments are distinguished. The adsorption layers are obtained during in-silico self-assembly on graphite surface through intermolecular hydrogen bonding in all-atom MD simulations. Two experimental processes are reproduced in the modelling: the vacuum deposition of the molecules one-by-one and the construction of the adlayers using the spin-coating technique. In all simulated systems, the formation of stable supramolecular polymers is observed which build the ordered carpets on the surface. However, the binding energetics, the strength and the type of the hydrogen bonding, and diffusion of the molecules on graphite are highly sensitive to the molecular conformation. We quantify each of these characteristics and provide a molecular picture of difuran-DPP adlayers relevant for organic field-effect transistor applications.