Polycyclic aromatic hydrocarbons (PAHs, example pictured) can be considered as small segments of graphene. They have useful optical and semiconducting properties. PAHs could have applications, e.g., in photovoltaics or light-emitting diodes, in particular, in the form of thin films. However, creating thin films from solution is hampered by the low solubility of PAHs and vacuum deposition only works for smaller PAHs. Thus, improved methods for the creation of PAH thin films would be useful.

Klaus Müllen, Max Planck Institute for Polymer Research, Mainz, Germany, Cheng Gu, Yuguang Ma, South China University of Technology, Guangzhou, and colleagues have developed a one-step electrochemical method to synthesize and deposit unsubstituted PAHs. The team used oligophenyl precursors, indium tin oxide (ITO) anodes, platinum or titanium cathodes, and Bu₄NPF₆ as the electrolyte.

Oxidation of the oligophenyl precursor compounds at the anode allowed for the synthesis and deposition of the corresponding PAHs in a single step. The precursors are oxidized to form a fully conjugated, “flat” π-system, which reduces the solubility and leads to the deposition of the products on the anode. Overall, the method produces high-quality PAH thin films with a controllable thickness.

• Electrochemical Synthesis, Deposition, and Doping of Polycyclic Aromatic Hydrocarbon Films,
  Cheng Zeng, Bohan Wang, Huanhuan Zhang, Mingxiao Sun, Liangbin Huang, Yanwei Gu, Zijie Qiu, Klaus Müllen, Cheng Gu, Yuguang Ma,
  J. Am. Chem. Soc. 2021.
  https://doi.org/10.1021/jacs.0c13298