On-surface synthesis and characterization of polyaniline oligomers

Abstract

Resumen del póster presentado a la Conferencia bienal Fuerzas y Túnel, celebrada en Jaca (España) del 27 al 29 de junio de 2018.Polyaniline (PANI) has been studied since 1835 because of its interest as inherently conducting polymer due to its wide range of potential applications that range from batteries to biosensors. The interest of PANI lies on its capability to express different properties depending on its nitrogen oxidation state: leucoemeraldine (the fully reduced form), emeraldine (the half-oxidized form), and pernigraniline (the fully oxidized form). There are two conventional synthesis methods, electrochemical processing and chemical oxidative polymerization of aniline in a wet environment. Although doped emeraldine structure present good conductivity, it has been shown that the size, the preparation method and the existence of a metal-polymer interface, influence the physical properties of the final PANI. Here, we present a new route to synthesize 1D oligomers of PANI based on a specific on-surface synthesis process. The synthesis was carried out using p-aminophenol (p-Ap) molecules as building blocks on a Pt(111) single-crystal in a UHV environment. At 200°C p-Ap molecules are activated inducing a shift base reaction resulting in oligomer chains with pernigraniline structure. The mechanism of the chemical reaction was followed by XPS, LT-STM/STS and nc-AFM and confronted with theoretical calculations. XPS show that oxygen is removed from the p-AP molecule resulting in a coupling of the precursors via the nitrogen. STM and nc-AFM reveals that oligomers are formed by ca. 10 molecular precursors. STS shows the presence of two broad unoccupied electronic states around 200 mV and 650 mV above the Fermi level that we are able to resolve spatially. Finally, DFT calculations show that the atomic structure is influenced by the substrate crystallography.Peer Reviewe