Jul 2026· Journal of the American Chemical Society· Vol 148, pp. 29186-29194· 1 citation· 58 references
Medicine
Abstract
Precisely tailoring the macroscopic morphology of covalent organic frameworks (COFs) fundamentally drives their physicochemical properties. However, the robust and highly directional nature of covalent bonds makes such control at the single-crystal level a formidable challenge. Resolving this bottleneck, we establish a synergistic Brønsted and Lewis dual-acid catalytic strategy to dictate the controlled axial growth and morphological evolution of large (≥50 μm) three-dimensional(3D) COFs single crystals (the XNU-375-X; X = 1-6, a, p, EtOH) featuring a dia topology. Modulating the concentration of dysprosium trifluoromethanesulfonate (Dy(OTf)3), acting as the Lewis acid, drastically suppresses the twinning rate. Consequently, this targeted regulation drives a continuous morphological transition from octahedral to tetragonal bipyramidal geometries. Single-crystal X-ray diffraction (SCXRD) explicitly confirms the microscopic structural consistency throughout this macroscopic evolution. Crucially, during guest solvent removal and exchange, these crystallographic analyses directly capture a rare structural flexibility and dynamic "breathing" effect, evidenced by a massive 46% volume variation. Density functional theory (DFT) calculations elucidate the underlying growth kinetics. Conditional on the specific exposed facets ({100} versus {001}), Dy3+ exhibits differential adsorption behaviors that effectively passivate lateral free amine sites. To the extent that these sites govern horizontal proliferation, this selective binding simultaneously promotes ordered c-axis stacking and intrinsic self-correction. Ultimately, this work bridges the gap in the precision morphological tailoring of 3D COFs single crystals, providing a robust platform for the anisotropic growth and targeted synthesis of complex porous architectures.
Understanding the structural and dynamic factors that govern the formation of covalent and non-covalent organic 2D crystalline materials is key to controlling their quality, including defect density and lateral dimensions. Gaining such insight enables the rational tuning of their physicochemical properties.
In this contribution, we showcase how scanning probe microscopy—particularly scanning tunneling microscopy (STM) and atomic force microscopy (AFM)—can be leveraged to investigate the structure and evolution of substrate-supported metal–organic frameworks (sMOFs) and covalent organic frameworks (sCOFs) at the liquid–solid interface.
We outline approaches for tracking and steering the growth of sMOFs and sCOFs across diverse scenarios: from achiral to chiral, from single layers to multilayer architectures, and from monocomponent to multicomponent systems. Beyond offering high-resolution visualization, scanning probe microscopy can also play an active role in directing on-surface growth processes, with very high spatial resolution.
Steven De Feyter· ECS Meeting Abstracts· 0 citations
Three-dimensional covalent organic frameworks (3D COFs) are promising crystalline porous materials, but the elucidation of their structure remains challenging, particularly for those featuring spiroborate linkages. Herein, we report the synthesis of a 3D crystalline COF with nbo topology, constructed from a rigid square-planar monomer, tetracyclopentatetraphenylene (TCTP), and spiroborate linkages. Theoretical calculations revealed that the TCTP core has higher rigidity than phthalocyanine, effectively suppressing structural fluctuations during framework formation. The structure of the resulting TCTP-COF was successfully determined using microcrystal electron diffraction (MicroED), revealing a noninterpenetrated cubic framework. TCTP-COF exhibits high crystallinity, thermal stability up to 320°C, and permanent porosity with a Brunauer-Emmett-Teller surface area of 1360 square meters per gram. This work represents the structural determination of a spiroborate-linked 3D crystalline COF using MicroED methods, providing a design strategy for expanding the chemical space of highly ordered 3D COF architectures.
The on-surface synthesis of atomically precise carbon nanomaterials has emerged as a powerful strategy to overcome the limitations of solution-based chemistry, enabling the fabrication of low-dimensional polymers and networks with unprecedented structural control. In particular, the development of single-layer two-dimensional (2D) covalent organic frameworks (COFs) remains a central challenge due to their promising applications in a variety of fields, as sensing, catalysis, and (opto)electronics. [1,2]
Here, we report a stepwise on-surface synthetic approach that exploits steric hindrance and sequential thermal activation to engineer and transform two COFs with atomic precision by scanning probe techniques. An ex-professo designed molecular precursor, functionalized with gem-dibromoalkene groups and a phenanthroline moiety, is employed to guide controlled coupling reactions under ultra-high vacuum conditions. Initial debromination leads to the formation of sterically controlled one-dimensional covalent chains, which self-assemble into a two-dimensional supramolecular network. Subsequent annealing yields a 2D organometallic network. Further thermal activation drives carbon–carbon coupling reactions between wires to form a 2D-COF composed of linear chains connected through ethynylene bridges. Remarkably, continued annealing triggers an unprecedented COF-to-COF transformation, in which the ethynylene linkages convert into antiaromatic pentalene moieties, demonstrating in situ chemical transformations of 2D-COFs in a stepwise manner.
This work establishes a general strategy for the bottom-up synthesis and thermal transformation of 2D-COFs at interfaces, validating the combination of steric control and sequential reactions as a viable alternative to symmetric precursor design, and opens new avenues for tailoring the structure and electronic properties of atomically precise 2D-COFs by thermal stimuli.
[1] R.-R. Liang et al. "Two-Dimensional Covalent Organic Frameworks With Hierarchical Porosity" Chem. Soc. Rev. 2020, 49, 3920
[2] C. Wang et al. " 2D Covalent Organic Frameworks: From Synthetic Strategies to Advanced Optical-Electrical-Magnetic Functionalities" Adv. Mater. 2022, 34, 2102290
Ana Barragán, Elena Pérez Elvira, Diego J. Vicent et al.· ECS Meeting Abstracts· 0 citations
The development of fast proton-conducting materials that operate above 150°C with high chemical stability is both challenging and critically important for advancing proton-exchange membrane fuel cells (PEMFCs). In this study, we constructed two three-dimensional COFs with covalent phosphonate modification using a solvent-free, melt-phase post-synthetic modification (PSM) strategy. This approach simultaneously reduces imine to amine linkages and constructs C─P bonds, covalently anchoring phosphonate groups without disrupting crystal integrity. Single-crystal x-ray diffraction (SCXRD) analysis reveals precise geometric changes in the framework and the formation of an extended N─H···O═P hydrogen-bond network. The functionalized single-crystal COFs exhibit excellent anhydrous proton conduction along the crystallographic c-axis at exceptionally high temperatures, achieving 8.91 × 10-3 S cm-1 at 210°C for COF-300-DMP and 5.65 × 10-3 S cm-1 at 230°C for COF-300-DEP. The remarkably low activation energies (0.196‒0.229 eV) indicate a Grotthuss-type hopping mechanism. This work not only establishes a generalizable route for COF functionalization but also provides a definitive blueprint for designing advanced proton conductors for extreme environments.
Aiping Yao, Linlin Huo, Chunyi Sun et al.· Angewandte Chemie· 0 citations
Hybrid organic-inorganic perovskites present a diverse structural landscape in which dimensionality governs optoelectronic properties. Although chemical modification of organic spacers is commonly employed to tailor connectivity, the influence of crystallization kinetics on dimensional topology selection remains largely unexplored. This study demonstrates that the cooling rate during solution growth serves as a decisive control parameter, directing the self-assembly of nonanediaminium lead iodide perovskite (H3NC9H18NH3)PbI4 into either a thermodynamically stable two-dimensional (2D) layered phase or a kinetically trapped zero-dimensional (0D) cluster-based polymorph. Slow evaporation at elevated temperature produces the 2D layered structure, whereas rapid cooling to 50 °C or quenching in liquid nitrogen selectively yields the 0D phase, which consists of isolated face-sharing [Pb3I12]6- trimers. Single-crystal and powder X-ray diffraction confirm the structural purity of both polymorphs. Optical absorption measurements indicate a dimensionality-driven bandgap shift from 2.47 eV (2D) to 2.78 eV (0D). Low-temperature photoluminescence spectroscopy reveals fundamentally distinct emission mechanisms: the 2D polymorph exhibits narrow free-exciton emission, while the 0D polymorph displays intense broadband luminescence attributed to radiative recombination at anion-related defects, as evidenced by its correlation with lattice disorder. These results establish thermal history as an independent synthetic dimension, orthogonal to chemical design, enabling on-demand switching between excitonic and defect-mediated emission within a single composition. This approach provides a scalable pathway for engineering low-dimensional hybrid materials for tunable solid-state lighting, scintillators, and quantum-light sources.
Mikhail I. Balanov, A. V. Shtareva, Viktor G. Bardakov et al.· Journal of Physical Chemistr...· 0 citations
This study demonstrates the template-free preparation of uniform macroscopic helical flower-like structures from a solution of a single axially chiral compound via simple annealing. To achieve a balance between structural flexibility and rigidity while introducing hydrogen-bonding sites, the molecular design connects the binaphthalene-azobenzene core to the terminal benzoic acid groups via flexible alkyl chains. The synthesized microflower displays a highly ordered, "windmill-like" spiral architecture, exhibiting unambiguous handedness. This structure achieves a clear macroscopic manifestation of chirality. Morphological analysis traces the macroscopic chirality to screw dislocation formation and progressive twist accumulation within the lamellae. Crystallographic and spectroscopic evidence reveals that these defects originate from solvent-hydrogen-bond-directed interlayer slip and precise axial chirality transfer through helical molecular chain formation. This work provides a straightforward route to macroscopically chiral structures with elegant and intricate morphologies, providing a new paradigm for the expression and amplification of molecular axial chirality at the macroscopic scale.
Yanyi He, Xin Dong, Jingsong Feng et al.· ACS Applied Materials and In...· 0 citations