Chiral surface networks of 3-HPLN — A molecular analog of rounded triangle assembly

The self-assembly of 3-hydroxyphenalenone (3-HPLN) on the Ag(111) surface has been studied with scanning tunneling microscopy and first-principles computations. The prochiral 3-HPLN molecule forms zipper-like chains when deposited on the Ag(111) surface, representing a 2D analog of their arrangement in bulk crystals. Upon annealing, local chiral trimer motifs form and serve as building blocks in extended 2D supramolecular networks not observed in 3D crystals. The extended network is porous and is held together via weak van der Waals interactions. The dispersion forces between trimers suggest that their handedness is overall racemic, but the asymmetric packing of 3-HPLN trimers around the pores leads to a chiral network. The offset alignment of neighboring 3-HPLN molecules in the unit cell resembles the offset between neighboring particles that are seen in the most efficient packings of rounded triangles. Computations illustrate that charge is transferred from the Ag(111) surface to the lowest unoccupied orbital of 3-HPLN, and a number of networks (including a honeycomb, as well as an alternative close-packed arrangement) are investigated.