Molecular trapping in two-dimensional chiral organic Kagomé nanoarchitectures composed of Baravelle spiral triangle enantiomers

The supramolecular self-assembly of a push-pull dye is investigated using scanning tunneling microscopy (STM) at the liquid–solid interface. The molecule has an indandione head, a bithiophene backbone and a triphenylamine–bithiophene moiety functionalized with two carboxylic acid groups as a tail. The STM images show that the molecules adopt an “L” shape on the surface and form chiral Baravelle spiral triangular trimers at low solution concentrations. The assembly of these triangular chiral trimers on the graphite surface results in the formation of two types of chiral Kagome nanoarchitectures. The Kagome-α structure is composed of only one trimer enantiomer, whereas the Kagome-β structure results from the arrangement of two trimer enantiomers in a 1:1 ratio. These Kagome lattices are stabilized by intermolecular O-H···O hydrogen bonds between carboxylic acid groups. These observations reveal that the complex structure of the push-pull dye molecule leads to the formation of sophisticated two-dimensional chiral Kagome nanoarchitectures. The subsequent deposition of coronene molecules leads to the disappearance of the Kagome-β structure, whereas the Kagome-α structure acts as the host template to trap the coronene molecules. A thin film that spontaneously forms into complex geometric patterns can undergo molecular recognition interactions helpful for sensing small molecules. A team led by Xinrui Miao from the South China University of Technology in Guangzhou and Fabien Silly at the Universite Paris-Saclay in Gif sur Yvette, France, used scanning tunneling microscopy to understand how photoactive dyes commonly used in organic solar cells self-organize into assemblies. The team first modified the dyes with carboxylic acids, giving them a spiral structure and enhanced hydrogen bonding capabilities. Atomic-scale imaging of the molecules on graphite revealed that at certain concentrations, groups of dyes could lock together into triangular tiles. In turn, the tiles connected into symmetric lattices containing nanoscale pores. Certain lattices could trap aromatic hydrocarbons within their hexagonal pores. Push-pull dye molecules self-assemble into two 2D Kagome nanoarchitectures composed of a single or two chiral Baravelle spiral triangular trimer enantiomers. Only one of the two nanoarchitectures is able to trap coronene molecules.