Local Electronic Structure of Molecular Heterojunctions in a Single-Layer 2D Covalent Organic Framework

Trinity Joshi, Chen Chen, Huifang Li, Christian S. Diercks, Gaoqiang Wang, Peter J. Waller, Hong Li, Jean Luc Bredas, Omar M. Yaghi, Michael F. Crommie

Research output: Contribution to journalArticlepeer-review

73 Scopus citations


The synthesis of a single-layer covalent organic framework (COF) with spatially modulated internal potentials provides new opportunities for manipulating the electronic structure of molecularly defined materials. Here, the fabrication and electronic characterization of COF-420: a single-layer porphyrin-based square-lattice COF containing a periodic array of oriented, type II electronic heterojunctions is reported. In contrast to previous donor–acceptor COFs, COF-420 is constructed from building blocks that yield identical cores upon reticulation, but that are bridged by electrically asymmetric linkers supporting oriented electronic dipoles. Scanning tunneling spectroscopy reveals staggered gap (type II) band alignment between adjacent molecular cores in COF-420, in agreement with first-principles calculations. Hirshfeld charge analysis indicates that dipole fields from oriented imine linkages within COF-420 are the main cause of the staggered electronic structure in this square grid of atomically–precise heterojunctions.

Original languageEnglish (US)
Article number1805941
JournalAdvanced Materials
Issue number3
StatePublished - Jan 18 2019
Externally publishedYes


  • covalent organic frameworks
  • density functional theory
  • electronic structure
  • scanning tunneling microscopy and spectroscopy
  • type II heterojunctions

ASJC Scopus subject areas

  • General Materials Science
  • Mechanics of Materials
  • Mechanical Engineering


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