Engineering large nanoporous networks with size and shape selected by appropriate precursors

Abstract

Large domains of two-dimensional supramolecular porous nanostructures are interesting for various applications from electronics to biology. Here, we investigate the formation of Cu-coordinated networks on Cu(111) using scanning tunneling microscopy and density functional theory (DFT). We consider two molecules with three pyridyl end groups connected to a central benzene ring by either one or two phenyl groups, namely 1,3,5-tris[4-(pyridin)phenyl]benzene (TPyPB) and 1,3,5-tris[4-(pyridin)-[1,1’-biphenyl]benzene (TPyPPB), respectively. Upon deposition of TPyPB at room temperature, a honeycomb nanostructure forms, which is stabilized by Cu adatoms, as previously seen. Upon deposition at 400 K, the growth dynamics change, and molecules become trapped in the hexagonal pores. In contrast, deposition of TPyPPB at room temperature leads to vitreous structures, which rearrange at 400 K forming a low-defect and extended ordered honeycomb phase, which is also stabilized only in the presence of Cu adatoms. The DFT calculations for both honeycomb phases show an impressive agreement with the experimental results, considering the size of such structures. After annealing at 420 K, a complex flower-like structure composed of a mix of two- and three-fold coordinated Cu centers emerges. Further annealing to above 420 K leads to another new phase composed of a high molecular density motif, the so-called diamond phase.