Radial growth of twist-stacked covalent organic framework nanofibers

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Summary:
The authors from CAS Institute of Chemistry & University of Parma developed twist-stacked covalent organic framework nanofibers (t-COFs) with intrinsic structural chirality, achieving |gabs| = 0.05 and |glum| = 0.04 for high-performance chiroptical applications.

Background:
1. Traditional 2D COFs stack in eclipsed/staggered modes; introducing continuous twist to break inversion symmetry remains elusive, and most chiral COFs rely on pre-installed chiral centers with moderate optical dissymmetry.
2. This work proposes a modulator-assisted radial-growth strategy: achiral Tp and diamines first assemble into twisted hexagonal-macrocycle nanotubes, which then serve as seeds for radially enlarging t-COF fibers while preserving a fixed twist of 0.16–0.30° per layer.

Research Content:
1. Synthesis
   – Tp + Azo/BD/Pa, 120 °C, 1,4-dioxane/6 M HAc, R/S-AMB or i-BA (1–3 eq) as modulator; 3 d solvothermal gives t-TpAzo-R-AMB (42 %), t-TpBD-R-AMB (32 %), t-TpPa-R-AMB (30 %).

2. Characterizations
   1) BET: t-TpAzo-R-AMB 1862 m² g⁻¹ (vs 1158 m² g⁻¹ for control), pore 2–4 nm.
   2) SEM/TEM: fiber diameter 30–120 nm, length µm; HRTEM shows (100) 2.80 nm & (110) 1.63 nm fringes spirally intermittent.
   3) Chiroptical: ECD 500–600 nm, |gabs|max 0.05; CPL 620 nm, |glum|max 0.04; both values scale positively with fiber diameter.

3. Application
   – Demonstrated as circular-polarized light emitters and enantio-biased adsorbents; left- or right-handed fibers obtained on demand by choosing R-/S-AMB.

4. Mechanism
   – Slow amine exchange kinetically decouples in-plane growth from out-of-plane stacking; modulator-capped macrocycles π–π assemble into twisted nanotube seeds, followed by radial layer-by-layer addition that conserves the initial twist angle, yielding aperiodic yet ordered chiral channels.

Outlook:
t-COFs provide a general, scalable route to high-g-factor chiral porous polymers from cheap achiral monomers, opening new avenues for asymmetric catalysis, CPL lasers and spin-selective devices.

Radial growth of twist-stacked covalent organic framework nanofibers
Authors: Xiao-Rui Ren, Baichuan Kou, Qing Hao, Francesco Bertocchi, Ying Xu, Lu Wang, Zhen-Lian Zhao, Ting Chen, Li-Jun Wan, Dong Wang
DOI: 10.1038/s41467-025-66586-y
Link: https://www.nature.com/articles/s41467-025-66586-y

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