Perylene diimide cysteine derivatives self-assembled onto (111) gold surface: Evidence of ordered aggregation

Perylene diimide derivatives containing pendant cysteine residues are subjected to a strong self-assembly onto [1 1 11 Au films due to the presence of thiol functionality. The preparation of two different Au surfaces easies the understanding of both surface packing and morphology of the aggregated ordered films, by means of the combination of X-ray photoelectron spectroscopy, atomic force microscopy, and grazing incident wide X-ray scattering - synchrotron radiation - techniques. A proper correlation of the resulting data, together with conformational calculations - using a detailed molecular modelling - allow supplying a coherent scenario. In particular, isolated ordered pillars upstanding to the substrate plane are detected on native gold surface, while a pi-stacked aggregation "unregistered" normally to the film plane is observed when perylene derivatives are grafted onto thermally annealed gold surface. Such a surface organization is expected to be favourable to the charge mobility, therefore its use in organic field effect transistor is envisioned.