Low-bandgap conjugated polymers have unique optical and electrochemical characteristics. They could have widespread applications in organic photoelectric devices. The designs of most low-bandgap polymers have focused on three factors: 1) the degree of bond length alternation, 2) the resonance energy of the aromatic unit, and 3) the substituents.

Weizhi Wang, Fudan University, Shanghai, China, and colleagues have prepared three low-bandgap polycyclic aromatic hydrocarbons with different spatial arrangements based on hexaphenylbenzene derivatives: a linear type (pictured), a V-shaped type, and a zigzag type. The team used a Yamamoto reaction with Ni(COD)₂ (COD= cyclooctadiene) as a catalyst for the synthesis. The resulting compounds differ in two factors: the mean deviation from planarity and the intermolecular and interchain coupling in the solid state, respectively.

UV/Vis absorption spectroscopy and measurements of the compounds’ emission spectra showed that a higher degree of planarity in the polymer chain led to a redshift. The trend of the bandgap agrees with the optical test results. The synthesized compounds were successfully used to assemble organic field-effect transistors (OFET devices) and could have potential for use in electronic devices.

• Synthesis and Characterization of Polycyclic Aromatic Hydrocarbons with Different Spatial Constructions Based on Hexaphenylbenzene Derivatives,
  Hua Chen, Haoyun Zhu, Yuli Huang, Junwei Yang, Weizhi Wang,
  Chem. Asian J. 2017.
  DOI: 10.1002/asia.201701061