On-surface stepwise dehalogenative homocoupling of 2,7-dibromotriphe-nylene on Au(111) surface

The dehalogenative homocoupling of DBTP molecules on Au(111) surface has been investigated at a single molecular level by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The length and morphology of the carbon-carbon coupling chain are adjusted by stepwise thermal excitation. Gradual annealing of the sample at 323 and 353 K promotes the dehalogenative homocoupling, resulting in the formation of oligomer and long straight chains that branch out or form combs. Such straight chains show an obvious zipper like double-chain structure when annealed at 373 K. Our results show that Br-H bonds between straight chains play a stabilizing role in the zipper structure. During further annealing to a maximum of 453 K, both dehalogenative homocoupling and cross-coupling occur between the chains. The number of monomers in the molecular chains formed at 453 K is 16-20, accounting for the largest proportion.