Porous honeycomb self-assembled monolayers: tripodal adsorption and hidden chirality of carboxylate anchored triptycenes on Ag

Saunak Das, Giulia Nascimbeni, Rodrigo Ortiz de la Morena, Fumitaka Ishiwari, Yoshiaki Shoji, Takanori Fukushima, Manfred Buck, Egbert Zojer, Michael Zharnikov

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)
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Abstract

Molecules with tripodal anchoring to substrates represent a versatile platform for the fabrication of robust self-assembled monolayers (SAMs), complementing the conventional monopodal approach. In this context, we studied the adsorption of 1,8,13-tricarboxytriptycene (Trip-CA) on Ag(111), mimicked by a bilayer of silver atoms underpotentially deposited on Au. While tripodal SAMs frequently suffer from poor structural quality and inhomogeneous bonding configurations, the triptycene scaffold featuring three carboxylic acid anchoring groups yields highly crystalline SAM structures. A pronounced polymorphism is observed, with the formation of distinctly different structures depending on preparation conditions. Besides hexagonal molecular arrangements, the occurrence of a honeycomb structure is particularly intriguing as such an open structure is unusual for SAMs consisting of upright-standing molecules. Advanced spectroscopic tools reveal an equivalent bonding of all carboxylic acid anchoring groups. Notably, density functional theory calculations predict a chiral arrangement of the molecules in the honeycomb network, which, surprisingly, is not apparent in experimental scanning tunneling microscopy (STM) images. This seeming discrepancy between theory and experiment can be resolved by considering the details of the actual electronic structure of the adsorbate layer. The presented results represent an exemplary showcase for the intricacy of interpreting STM images of complex molecular films. They are also further evidence for the potential of triptycenes as basic building blocks for generating well-defined layers with unusual structural motifs.
Original languageEnglish
Number of pages12
JournalACS Nano
VolumeArticles ASAP
Early online date14 Jun 2021
DOIs
Publication statusE-pub ahead of print - 14 Jun 2021

Keywords

  • Self-assembled monolayers
  • Triptycene
  • Polymorphism
  • Chirality
  • Scanning tunneling microscopy
  • Density functional theory calculations

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