Synthesis and Properties of Bis(naphthofuran)-Fused [7]Helicene Derivatives

Novel benzo[1,2-b:4,3-b′]dinaphthofuran (oxa[7]helicene) with various substituents in the central ring were designed and successfully synthesized based on the late stage central ring formation strategy from naphthofuranoneby using an efficient McMurry coupling or Friedel-Crafts acylation. The photochemical properties of helicenes were evaluated by UV-Visible absorption spectroscopy and fluorescence spectroscopy, while electrochemical behaviour including their energy profile were investigated by cyclic voltammetry and DFT calculations. According to the computational study, substituents on the central ring could influence both electron delocalization and MO distribution of oxa[7]helicenes resulting in the change in charge transporting ability. In comparison to the parent carbo[7]helicene, the furan unit in conjunction with substituents on helical system caused the bathochromic shift with different absorption pattern and exhibited higher fluorescence quantum yield (ϕ_f up to 0.63). These new materials showed promising characteristics in optoelectronic application.