Atomic-scale construction and characterization of quantum dots array and poly-fluorene chains via 2,7-dibromofluorene on Au(1 1 1)

Abstract

The application of fluorene and its derivatives has been established in last decade, particularly showing the fabrication of blue polymer, organic light-emitting diode (OLED), organic solar cells (OSCs), etc. As low-cost but applied optoelectronic raw material, DBF [2,7-dibromofluorene] is expected to construct intriguing nanostructures on surface, while the related report has remained elusive so far. Here we demonstrate the construction of 2D nanoporous networks and 1D poly-fluorenes by utilizing DBF on Au(111) substrate. Their atomic structures and electronic properties were characterized by a combination of bond-resolved scanning tunneling microscopy (BR-STM), scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. Specifically, nanoporous double-wall networks exhibit confinement state and lower coupling between the neighboring pores, which is assigned to be a uniform quantum dots array. The dynamic synthesis of poly-fluorene was monitored timely during stepwise annealing. STS and DFT results reveal a bandgap of poly-fluorene around 2.25 eV. STS mapping and the simulations evidence the occupied state is mainly located at the armchair-edge. Our work opens an avenue for the extensive investigation of DBF on surface, building a platform for studying fluorene-like molecules and even their derivatives with prospects in functional optoelectronics and nanomaterials.