Direct Synthesis of Covalent Organic Framework Monolayer via Ullmann Coupling on Non-metallic Substrates
5 affiliations
- 1School of Integrated Circuits
- 2Shenzhen University
- 3Department of Physics and Materials
- 4Hong Kong Polytechnic University
- 5Research Centre for Nanoscience and Nanotechnology
Abstract
Two-dimensional covalent organic framework monolayers are promising porous materials for electronic and optoelectronic applications owing to their periodic nanoporous architectures and tunable electronic structures. However, on-surface Ullmann coupling used to construct such frameworks typically relies on catalytic single-crystal metal substrates, whose strong electronic coupling can obscure the intrinsic properties of the molecular layer and complicate device integration. Here, we demonstrate substrate-engineered Ullmann coupling of 1,3,5-tris(4iodophenyl)benzene toward monolayer two-dimensional covalent organic networks on nonmetallic substrates. On inert highly oriented pyrolytic graphite, externally deposited Fe species promote C–I bond activation and covalent coupling, whereas FeO thin films enable network formation without additional metal deposition through defect-derived Fe active centers. Density functional theory calculations reveal that the energetically favored pathways on HOPG, FeO, and Au(111) all involve transient metal-centered intermediates that facilitate dehalogenation and C–C bond formation, although the catalytic centers originate from different sources. Bias-dependent scanning tunneling microscopy further shows that substrate coupling governs the visibility of frontier electronic states: weakly interacting HOPG preserves orbital-like features that closely resemble calculated frontier states of the freestanding framework, whereas stronger interactions on FeO and Au(111) progressively perturb or screen these states. These results establish nonmetallic substrates as viable platforms for on-surface Ullmann coupling and highlight substrate engineering as a strategy for accessing intrinsic electronic properties of two-dimensional covalent organic materials.
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BibTeX
@misc{nie2026direct,
title = {{Direct Synthesis of Covalent Organic Framework Monolayer via Ullmann Coupling on Non-metallic Substrates}},
author = {Dong Nie and Jingyu He and Jinwei Fan and Siming Gu and Junqi He and Hafiza Saima Batoola and Ming Yang and Dingguan Wang},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008816/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008816/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Direct Synthesis of Covalent Organic Framework Monolayer via Ullmann Coupling on Non-metallic Substrates
AU - Dong Nie
AU - Jingyu He
AU - Jinwei Fan
AU - Siming Gu
AU - Junqi He
AU - Hafiza Saima Batoola
AU - Ming Yang
AU - Dingguan Wang
PY - 2026
DA - 2026/09/14
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008816/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008816/v1
AB - Two-dimensional covalent organic framework monolayers are promising porous materials for electronic and optoelectronic applications owing to their periodic nanoporous architectures and tunable electronic structures. However, on-surface Ullmann coupling used to construct such frameworks typically relies on catalytic single-crystal metal substrates, whose strong electronic coupling can obscure the intrinsic properties of the molecular layer and complicate device integration. Here, we demonstrate substrate-engineered Ullmann coupling of 1,3,5-tris(4iodophenyl)benzene toward monolayer two-dimensional covalent organic networks on nonmetallic substrates. On inert highly oriented pyrolytic graphite, externally deposited Fe species promote C–I bond activation and covalent coupling, whereas FeO thin films enable network formation without additional metal deposition through defect-derived Fe active centers. Density functional theory calculations reveal that the energetically favored pathways on HOPG, FeO, and Au(111) all involve transient metal-centered intermediates that facilitate dehalogenation and C–C bond formation, although the catalytic centers originate from different sources. Bias-dependent scanning tunneling microscopy further shows that substrate coupling governs the visibility of frontier electronic states: weakly interacting HOPG preserves orbital-like features that closely resemble calculated frontier states of the freestanding framework, whereas stronger interactions on FeO and Au(111) progressively perturb or screen these states. These results establish nonmetallic substrates as viable platforms for on-surface Ullmann coupling and highlight substrate engineering as a strategy for accessing intrinsic electronic properties of two-dimensional covalent organic materials.
ER -