Unlocking MOF-based nanoparticle impellers through dimensional engineering to achieve optically controlled cargo delivery

Professor Ying-Wei Yang's research group at Jilin University successfully constructed an azobenzene-modified metal-organic framework (MOF)-based nano-impeller platform using a dimensional engineering strategy. They synthesized two-dimensional layered Zn-Azo-MOF-1 and three-dimensional network Zn-Azo-MOF-2 with the same composition but different dimensions. They found that the photoisomerization efficiency of the two-dimensional framework (cis isomer content 33%) was an order of magnitude higher than that of the three-dimensional framework (3%). Mechanical grinding triggered interlayer slip in the two-dimensional structure, breaking the spatial confinement and activating efficient photoisomerization. Analysis of rotational energy barriers and framework-ligand interactions revealed the mechanism by which dimensionality and mechanical activation synergistically regulate the photo-switching dynamics. The constructed two-dimensional Zn-Azo-MOF-1 achieved 99% cargo release within 50 minutes under alternating UV-Vis irradiation, successfully extending the nano-impeller function from an amorphous platform to a crystalline platform, providing a dimensional engineering design principle for the programmable switching behavior of stimulus-responsive materials. The article was published as an open access Research Article in CCS Chemistry, the flagship journal of the Chinese Chemical Society.

Background information:

Molecular machines, as dynamic systems at the nanoscale, can convert external energy into directed mechanical motion, showing great potential in smart materials and drug delivery. The 2016 Nobel Prize in Chemistry was awarded for the design and synthesis of molecular machines, while the 2025 Nobel Prize in Chemistry will recognize the pioneering work on metal-organic frameworks (MOFs). How to organically combine these two fields to achieve efficient molecular machine functions in crystalline frameworks has always been a major challenge in supramolecular chemistry (Figure 1). Introducing dynamic molecular switches into crystalline materials faces fundamental challenges: the conflict between the spatial confinement effect of rigid lattices and the conformational freedom of molecules severely restricts photoresponse performance. Although azobenzene, as a classic photochromic molecule, exhibits excellent trans- cis isomerization properties in solution, in the solid state, especially in framework structures, restricted molecular motion, aggregation effects, and environmental sensitivity significantly reduce its photo-switching efficiency.

Highlights of this article:

1.  Break through traditional design thinking and establish a dimensional engineering strategy. Using a solvent-controlled coordination assembly strategy, two types of zinc-based MOFs with the same molecular composition but different dimensions, namely two-dimensional layered Zn-Azo-MOF-1 and three-dimensional network Zn-Azo-MOF-2, were precisely synthesized with organic ligands containing azobenzene side groups as building blocks. The system revealed the decisive influence of framework dimension on photoisomerization efficiency (Figure 2).

2.  Synergistic mechanism of mechanical activation and dimensional regulation. The study found that mechanical polishing can break the spatial confinement of two-dimensional MOFs by inducing interlayer slip and exfoliation. Atomic force microscopy analysis confirmed that partial exfoliation phenomenon with coexistence of single-layer (1.4 nm), double-layer (2.6 nm), and triple-layer (3.9 nm) structures after polishing was observed, providing a structural basis for activating efficient photoisomerization (Figure 3).

3.  Quantitatively revealing the regulatory laws of spatial confinement on optical switching dynamics. Density functional theory calculations show that the isomerization barrier of the three-dimensional framework structure (336.44 eV) is 12.9 times higher than that of the two-dimensional monolayer structure (25.01 eV) . Analysis using the Independent Gradient Model (IGMH) based on Hirshfeld partitioning further reveals that stronger π-π stacking and hydrogen bonding interactions within the three-dimensional framework significantly restrict the conformational transitions of azobenzene.

4.  First achievement of efficient cargo delivery using crystalline MOF-based nano-impellers. A large-scale bidirectional isomerization of azobenzene side groups was achieved using an alternating UV-Vis irradiation strategy. Time-resolved release curves established a quantitative relationship between isomer composition and release behavior, confirming that the periodic arrangement of azobenzene units in the MOF lattice can generate a synergistic mechanical perturbation effect, achieving 99% cargo release within 50 minutes, successfully extending the nano-impeller function from an amorphous platform to a crystalline platform (Figure 4).

Summary and Outlook:

This study successfully extended the functionality of nano-impellers from amorphous to crystalline MOF platforms through a dimensional engineering strategy. The two-dimensional layered framework combined with mechanical activation broke spatial confinement, enabling efficient photoisomerization and on-demand cargo delivery. This dimensional regulation strategy provides a universal principle for designing stimulus-responsive crystalline materials, and is expected to be applied in catalysis, sensing, drug delivery, and other fields, achieving programmable functional regulation of materials through architectural design rather than complex molecular modification.

The relevant research results were published as an open access Research Article in CCS Chemistry, the flagship journal of the Chinese Chemical Society. Xin Li, a doctoral student at the College of Chemistry, Jilin University, is the first author, and Professor Ying-Wei Yang is the corresponding author. This research was supported by the National Natural Science Foundation of China (Project No.: 22571119) and the "Medicine + X" Interdisciplinary Innovation Team Project of the Bethune Medical School of Jilin University (Project No.: 2022JBGS04).

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About the journal: CCS Chemistry is the Chinese Chemical Society’s flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem.

About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman’s Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/.