On-surface polymerisation and self-assembly of DPP-based molecular wires†

The incorporation of organic semiconducting materials within solid-state electronic devices provides a potential route to highly efficient photovoltaics, transistors, and light emitting diodes. Key to the realisation of such devices is efficient intramolecular charge transport within molecular species, as well as intermolecular/interdomain transport, which necessitates highly ordered supramolecular domains. The on-surface synthesis of polymeric organic materials (incorporating donor and/or acceptor moieties) is one pathway towards the production of highly ordered molecular domains. Here we study the formation of a polymer based upon a diketopyrrolopyrrole (DPP) monomer unit, possessing aryl-halide groups to facilitate on-surface covalent coupling and functionalised with alkyl chains which drive the self-assembly of both the monomer material prior to reaction and the domains of polymeric material following on-surface synthesis. The self-assembled structure of close-packed domains of the monomer units, and the ordered polymers, are investigated and characterised using scanning tunnelling microscopy and X-ray photoelectron spectroscopy.