Tailoring On-Surface Molecular Reactions and Assembly through Hydrogen-Modified Synthesis: From Triarylamine Monomer to 2D Covalent Organic Framework

Zachery Enderson, Harshavardhan Murali, Raghunath Dasari, Qingqing Dai, Hong Li, Timothy Parker, Jean-Luc Bredas, Seth Marder, Phillip First

Research output: Contribution to journalArticlepeer-review

3 Scopus Citations

Abstract

Relative to conventional wet-chemical synthesis techniques, on-surface synthesis of organic networks in ultrahigh vacuum has few control parameters. The molecular deposition rate and substrate temperature are typically the only synthesis variables to be adjusted dynamically. Here we demonstrate that reducing conditions in the vacuum environment can be created and controlled without dedicated sources-relying only on backfilled hydrogen gas and ion gauge filaments-and can dramatically influence the Ullmann-like on-surface reaction used for synthesizing two-dimensional covalent organic frameworks (2D COFs). Using tribromo dimethylmethylene-bridged triphenylamine ((Br3)DTPA) as monomer precursors, we find that atomic hydrogen (H) blocks aryl-aryl bond formation to such an extent that we suspect this reaction may be a factor in limiting the ultimate size of 2D COFs created through on-surface synthesis. Conversely, we show that control of the relative monomer and hydrogen fluxes can be used to produce large self-assembled islands of monomers, dimers, or macrocycle hexamers, which are of interest in their own right. On-surface synthesis of oligomers, from a single precursor, circumvents potential challenges with their protracted wet-chemical synthesis and with multiple deposition sources. Using scanning tunneling microscopy and spectroscopy (STM/STS), we show that changes in the electronic states through this oligomer sequence provide an insightful view of the 2D COF (synthesized in the absence of atomic hydrogen) as the end point in an evolution of electronic structures from the monomer.
Original languageAmerican English
Pages (from-to)7366-7376
Number of pages11
JournalACS Nano
Volume17
Issue number8
DOIs
StatePublished - 2023

NREL Publication Number

  • NREL/JA-5A00-87253

Keywords

  • covalent organic framework
  • DTPA
  • heterotriangulene
  • scanning tunneling microscopy
  • self-assembled monolayer
  • triangulene

Fingerprint

Dive into the research topics of 'Tailoring On-Surface Molecular Reactions and Assembly through Hydrogen-Modified Synthesis: From Triarylamine Monomer to 2D Covalent Organic Framework'. Together they form a unique fingerprint.

Cite this