Synthesis and characterization of electroactive films based on benzo(a)pyrene

The polycyclic aromatic hydrocarbons (PAHs) are a group of compounds that might have practical applications due to their graphene-like properties. Derivatized PAHs can self-assemble in liquid crystal form. The chemical synthesis of large size PAHs can however be complicated and problematic. Electrochemical synthesis of PAHs molecules was studied in this work by cyclic voltammetry. Benzo(a)pyrene was used as the monomer. The resulting electroactive films consist of different PAHs in both size and symmetry. We call this mixture poly(benzopyrene) (PBP). The synthesis conditions of PBP were optimized to obtain thick and electrochemically stable films. The best film quality was achieved by potential scanning in propylene carbonate at low scan rate resulting in continues polymer growth during 10 scans giving approx. a 1 μm thick PBP film. During p- and n-doping studies the reduction and oxidation peaks were observed at 1.0 V and −1.6 V, respectively, with an electrochemical band gap of approx. 2.6 eV. The in situ UV–vis characterization of the PBP films was made by applying a constant potential with increasing steps. The optical band gap was approx. 2.5 eV and the absorption maximum was observed at ca. 420 nm. During p- and n-doping new induced bands were formed in the range 575–600 nm. UV–vis spectroscopy indicate that PBP mainly consist of units consisting of more than 40 carbon atoms and large number of π-electrons.