2D covalent organic frameworks and 2D polymers

Light elements only (C, H, N, O, B), e.g. boronate-ester COF-5 or imine-linked frameworks

Also called COF-5, 2D polymers, 2DPA-1

nanosheet depends on form

Crystalline sheets built entirely from organic molecules joined by strong covalent bonds rather than metal nodes. Chemists can design pore size and chemistry before making them, which suits membranes, catalysts and light harvesting. A 2D polyaramid reported in 2022 formed films that were exceptionally stiff and strong for their weight and blocked gases – evidence that 2D polymers can be made in bulk from solution.

Data sheet

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Kind of sheet: nanosheet
Made by chemistry or cut from a solid, not peeled as a clean crystal layer
Behaves as: depends on form
Band gap: Typically semiconductors or insulators of ~1.5–3 eV, tunable through linker conjugation

In colour: this family, 1.5–3 eV. In grey: the other 39 families on the catalogue’s chart, each at the middle of its range.
Thickness: ~0.34–0.37 nm interlayer spacing in stacked COFs
Structure: Organic building blocks joined by covalent bonds into periodic, porous sheets that stack; 2D polymers are the single-layer or non-porous, molecularly thin counterparts
Stability: Boronate-ester COFs hydrolyse in moist air; imine-, β-ketoenamine- and sp²-carbon-linked frameworks are far more robust in water, acid and base.
First made: First crystalline COFs in 2005 (Côté, Yaghi and colleagues); ultrastrong solution-processable 2D polyaramid in 2022 (Zeng, Strano and colleagues)

Compare with other materials

Key properties

Designable, uniform pores from about 1 nm to several nm
The first COFs (2005) combined crystallinity with surface areas up to ~1,600 m²/g
Low density and light-element composition
Solution-processable 2D polyaramid (2DPA-1) films reported to be highly stiff, strong and impermeable to gases (2022)
Photoactive and redox-active frameworks demonstrated for hydrogen evolution and battery electrodes

How it is made

Solvothermal condensation with reversible bonds (boronate esters, imines) that let the network error-correct into crystals
On-surface synthesis on metal substrates in ultra-high vacuum – single-layer 2D polymers imaged by STM
Interfacial polymerisation at liquid/liquid or air/water interfaces – free-standing films
Irreversible polymerisation into self-assembling 2D polyaramid platelets

Uses, and how close they are

Separation membranes and water purificationlab
Photocatalysis and energy-storage electrodeslab
Lightweight barrier coatings from 2D polymerslab

Readiness runs lab → prototype → pilot → deployed.

Open problems

Can large-area single-crystalline COF films be grown, given that polycrystallinity and stacking faults limit transport and separation?
Reversible bonds give crystals but poor chemical stability – can irreversible linkages still yield long-range order?
Are 2D polymers such as 2DPA-1 truly two-dimensional throughout, and how do they compare with graphene as barrier materials at scale?

Going deeper

Short notes for specialists. Choose a lens in the header and yours comes first.

For theoreticians · your lens

Stacking offsets (eclipsed, inclined, serrated) change pore geometry, interlayer π coupling and band dispersion, so compare several stacking models against diffraction data. Classical force fields suit adsorption and diffusion; dispersion-corrected DFT is needed for stacking energies and band structures, and excitonic effects dominate optical spectra.

For experimentalists · your lens

Crystallinity is the headline issue: report PXRD with Pawley or Rietveld refinement against proposed stacking models, gas adsorption isotherms with BET surface area, and FTIR evidence of linkage formation. For films, use GIWAXS to determine orientation.

For engineers · your lens

Molecular precursors are expensive and syntheses slow, but the 2022 polyaramid result suggests solution-processed 2D polymer coatings could become practical barrier and structural materials.

Recent news

The newest items tagged 2D COFs, from the news feed updated 5 Oct 2026.

Journal 29 Sep 2026 ACS Applied Materials & Interfaces

Exfoliation of Molecular Crystals Enables Two-Dimensional Polymerization for Stable Photoelectric Response Devices

Two-dimensional polymers (2DPs) have emerged as a class of important materials with the unique advantages of an ultrathin, lightweight nature and a large accessible surface area, showing their promising potential in the area of optoelectronics, energy storage and conversion, and molecular separation. Currently, their…

Experiment2D COFs

All 1 item tagged 2D COFs in the news feed · RSS feed for 2D COFs

Key references

Porous, crystalline, covalent organic frameworksCôté et al. · Science 310, 1166 (2005)cited by 8,395doi:10.1126/science.1120411
Nano-architectures by covalent assembly of molecular building blocksGrill et al. · Nature Nanotechnology 2, 687 (2007)cited by 1,406doi:10.1038/nnano.2007.346
Wafer-sized multifunctional polyimine-based two-dimensional conjugated polymers with high mechanical stiffnessSahabudeen et al. · Nature Communications 7, 13461 (2016)cited by 378doi:10.1038/ncomms13461
Irreversible synthesis of an ultrastrong two-dimensional polymeric materialZeng et al. · Nature 602, 91 (2022)cited by 131doi:10.1038/s41586-021-04296-3