Extreme Confinement Effects on the Incorporated Dyes in Metal–Organic Frameworks

Abstract

Confinement of fluorescent dyes is known to enhance fluorescence properties by reducing aggregation and restricting molecular motion, but few studies have attempted to modulate the extent of confinement. In this work, we explored extreme confinement by exploiting the rigid structure of metal–organic frameworks (MOFs). Other than the commonly known restriction of peripheral substituents in fluorescent molecules for aggregation-induced emission (AIE)-like effects, the more powerful confinement surprisingly led to buckling of the chromophore core, leading to reduced fluorescence lifetime. We name these effects buckling-induced quenching (BIQ). By studying 14 dyes in zeolitic-imidazolate framework 8 (ZIF8), we systematically analyzed their confined behaviors, establishing strong correlations: The reduction of chromophore planarity always leads to a decrease of fluorescence lifetimes, whereas reduction in the longest dimension of the confined molecule, while maintaining chromophore planarity, always leads to an increased lifetime. Confinement in the larger cavities of ZIF71 leads to signs of alleviation, in good agreement with our hypotheses. The BIQ effects provide an important complement for the well-known confinement effects, and the extreme confinement serves also as an important reference for more subtle effects in various applications.

Keywords

buckling-induced quenching (BIQ) effect / extreme confinement / metal−organic framework / molecular conformation / uniform pore structure

References

[1] a) K. Liu, X. Qiao, C. Huang, X. Li, Z. Xue, and T. Wang, “Spatial Confinement Tunes Cleavage and Re-Formation of C=N Bonds in Fluorescent Molecules,” Angewandte Chemie International Edition 60 (2021): 14365-14369. b) J. C. Yu, Y. J. Cui, H. Xu, et al., “Confinement of Pyridinium Hemicyanine Dye Within an Anionic Metal-Organic Framework for Two-Photon-Pumped Lasing,” Nature Communications 4 (2013): 2719. c) Z. D. Gu, M. K. Li, C. Chen, et al., “Water-Assisted Hydrogen Spillover in Pt Nanoparticle-Based Metal–Organic Framework Composites,” Nature Communications 14 (2023): 5836.

[2] F. Liu, Y. Yang, X. Wan, et al., “Space-Confinment-Enhanced Fluorescence Detection of DNA on Hydrogel Particles Array,” ACS Nano 16 (2022): 6266-6273.

[3] B. Hua, W. Zhou, Z. Yang, et al., “Supramolecular Solid-State Microlaser Constructed From Pillar[5]Arene-Based Host-Guest Complex Microcrystals,” Journal of the American Chemical Society 140 (2018): 15651-15654.

[4] a) Y. Zhao, H. Zeng, X. W. Zhu, W. Lu, and D. Li, “Metal-Organic Frameworks as Photoluminescent Biosensing Platforms: Mechanisms and Applications,” Chemical Society Reviews 50 (2021): 4484-4513. b) W. Q. Zhou, J. W. Ye, W. J. Zhang, M. J. Huang, L. Chen, and X. M. Chen, “Fluorescent Probes With Variable Intramolecular Charge Transfer: Constructing Closed-Circle Plots for Distinguishing D₂O From H₂O,” Analytical Chemistry 95 (2023): 8239-8249. c) X. F. Zhong, G. J. Luo, W. B. Li, et al., “A Series of Naphthalenediimide-Based Metal–Organic Frameworks: Synthesis, Photochromism and Inkless and Erasable Printing,” Dalton Transactions 51 (2022): 14852-14857.

[5] L. Zhang, A. Song, Q. C. Yang, et al., “Integration of AIEgens Into Covalent Organic Frameworks for Pyroptosis and Ferroptosis Primed Cancer Immunotherapy,” Nature Communications 14 (2023): 5355.

[6] B. Fang, P. Li, J. Jiang, et al., “Confinement Fluorescence Effect (CFE): Lighting up Life by Enhancing the Absorbed Photon Energy Utilization Efficiency of Fluorophores,” Coordination Chemistry Reviews 440 (2021): 213979.

[7] J. Liu, N. Wang, Y. Yu, et al., “Carbon Dots in Zeolites: A New Class of ThermallyActivated Delayed Fluorescence Materialswith Ultralong Fifetimes,” Science Advances 3 (2017): e1603171.

[8] a) L. Zhu, B. Zhu, J. Luo, and B. Liu, “Design and Property Modulation of Metal-Organic Frameworks With Aggregation-Induced Emission,” ACS Materials Letters 3 (2021): 77-89. b) S. J. Chen, H. Wang, Y. N. Hong, and B. Z. Tang, “Fabrication of Fluorescent Nanoparticles Based on AIE Luminogens (AIE Dots) and Their Applications in Bioimaging,” Materials Horizons 3 (2016): 283-293. c) P. P. Dong, Y. Y. Liu, Q. C. Peng, et al., “Luminescent MOFs Constructed by Using Butterfly-Like AIE Ligands,” Dalton Transactions 52 (2023): 1913-1918. d) N. Feng, X. L. Huang, Y. K. Zhao, et al., “Intelligent Point-of-Care Microchip Based on Ternary Hybrids: Incorporating AIEgens and Nanozymes Into Metal–Organic Frameworks,” Advanced Functional Materials 35 (2025): 2410900.

[9] B. Shen, L. Liu, Y. Huang, et al., “Installing Hydrogen Bonds as a General Strategy to Control Viscosity Sensitivity of Molecular Rotor Fluorophores,” Aggregate 5 (2024): e421.

[10] J. Wu, Y. Wang, P. Jiang, X. Wang, X. Jia, and F. Zhou, “Multiple Hydrogen-Bonding Induced Nonconventional Red Fluorescence Emission in Hydrogels,” Nature Communications 15 (2024): 3482.

[11] H. Kurz, C. Hils, J. Timm, et al., “Self-Assembled Fluorescent Block Copolymer Micelles With Responsive Emission,” Angewandte Chemie International Edition 61 (2022): e202117570.

[12] S. Ye, H. Zhang, J. Fei, C. H. Wolstenholme, and X. Zhang, “A General Strategy to Control Viscosity Sensitivity of Molecular Rotor-Based Fluorophores,” Angewandte Chemie International Edition 60 (2021): 1339-1346.

[13] a) X. Cheng, J. Huang, R. Wang, et al., “Inorganic-Organic Coprecipitation: Spontaneous Formation of Enclosed and Porous Silica Compartments With Enriched Biopolymers,” Nanoscale 15 (2023): 2394-2401. b) X. J. Cheng, Y. M. Pu, S. T. Ye, X. Xiao, X. Zhang, and H. Y. Chen, “Measuring Solvent Exchange In Silica Nanoparticles With Rotor-Based Fluorophore,” Advanced Materials 36 (2024): 2305779.

[14] M. Tu, H. Reinsch, S. Rodríguez-Hermida, et al., “Reversible Optical Writing and Data Storage in an Anthracene-Loaded Metal-Organic Framework,” Angewandte Chemie International Edition 58 (2019): 2423-2427.

[15] J. V. Morabito, L. Y. Chou, Z. Li, et al., “Molecular Encapsulation Beyond the Aperture Size Limit Through Dissociative Linker Exchange in Metal-Organic Framework Crystals,” Journal of the American Chemical Society 136 (2014): 12540-12543.

[16] A. F. Möslein, M. Gutiérrez, B. Cohen, and J. C. Tan, “Near-Field Infrared Nanospectroscopy Reveals Guest Confinement in Metal-Organic Framework Single Crystals,” Nano Letters 20 (2020): 7446-7454.

[17] a) M. Gutiérrez, Y. Zhang, and J. C. Tan, “Confinement of Luminescent Guests in Metal-Organic Frameworks: Understanding Pathways From Synthesis and Multimodal Characterization to Potential Applications of LG@MOF Systems,” Chemical Reviews 122 (2022): 10438-10483. b) W. L. Xue, G. Q. Li, H. Chen, et al., “Melt-Quenched Glass Formation of a Family of Metal-Carboxylate Frameworks,” Nature Communications 15 (2024): 2040.

[18] a) O. M. Yaghi, “The Reticular Chemist,” Nano Letters 20 (2020): 8432-8434. b) B. E. R. Snyder, A. B. Turkiewicz, H. Furukawa, et al., “ALigand Insertion Mechanism for Cooperative NH3 Capture in Metal–Organic Frameworks,” Nature 613 (2023): 287-291. c) H. H. Liu, W. P. Ye, Y. Mu, et al., “Highly Efficient Blue Phosphorescence From Pillar-Layer MOFs by Ligand Functionalization,” Advanced Materials 34 (2022): 2107612. d) J. J. Zhu, H. Q. Chen, L. Wang, et al., “High-Efficient Dynamic Kinetic Resolution of Amines With a Core-Shell Hollow Mesoporous MIL-101@Pd@ZIF-8 Nanocatalyst and Lipase,” Microporous and Mesoporous Materials 329 (2022): 111490. e) S. Yuan, L. Huang, Z. H. Huang, et al., “Continuous Variation of Lattice Dimensions and Pore Sizes in Metal– Organic Frameworks,” Journal of the American Chemical Society 142 (2020): 4732-4738.

[19] a) X. C. Huang, Y. Y. Lin, J. P. Zhang, and X. M. Chen, “Ligand-Directed Strategy for Zeolite-Type Metal-Organic Frameworks: Zinc(II) Imidazolates With Unusual Zeolitic Topologies,” Angewandte Chemie International Edition 45 (2006): 1557-1559. b) L. Y. Chen, Y. Peng, H. Wang, Z. Z. Gu, and C. Y. Duan, “Synthesis of Au@ZIF-8 Single- orMulti-Core– Shell Structures for Photocatalysis,” Chemical Communications 50 (2014): 8651-8654.

[20] X. Xiao, G. Y. He, J. B. Ma, X. J. Cheng, R. X. Wang, and H. Y. Chen, “The Throttle Effect in Metal-Organic Frameworks for Distinguishing Water Isotopes,” Nano Letters 24 (2024): 15283-15290.

[21] R. Ma, Q. Li, J. Yan, et al., “Thermodynamically Controllable Synthesis of ZIF-8 Exposing Different Facets and Their Applications in Single Atom Catalytic Oxygen Reduction Reactions,” Nano Research 16 (2023): 9618-9624.

[22] G. Lu, S. Li, Z. Guo, et al., “Imparting Functionality to a Metal-Organic Framework Material by Controlled Nanoparticle Encapsulation,” Nature Chemistry 4 (2012): 310-316.

[23] A. Lyons, V. Zickus, R. Álvarez-Mendoza, et al., “Fluorescence Lifetime Hong-Ou-Mandel Sensing,” Nature Communications 14 (2023): 8005.

[24] C. Wang, A. Fukazawa, M. Taki, Y. Sato, T. Higashiyama, and S. Yamaguchi, “A Phosphole Oxide Based Fluorescent Dye With Exceptional Resistance to Photobleaching: A Practical Tool for Continuous Imaging in STED Microscopy,” Angewandte Chemie International Edition 54 (2015): 15213-15217.

[25] K. J. Wang, H. Si, X. C. Du, et al., “Reversible Emission Color, Brightness, and Shape Changes of AIEgen-Containing Bulk Polymers,” Advanced Functional Materials 35 (2025): 2412856.

[26] F. L. Ma, Q. Jia, Z. W. Deng, et al., “Boosting Luminescence Efficiency of Near-Infrared-II Aggregation-Induced Emission Luminogens via a Mash-Up Strategy of π-Extension and Deuteration for Dual-Model Image-Guided Surgery,” ACS Nano 18 (2024): 9431-9442.

[27] J. Y. Hao, W. J. Zhang, Y. Y. Li, et al., “Precision Nanoconfined Self-Assembly of ACQ Carbon Dots for Enhanced Solid-State Fluorescence,” Advanced Science (2025): 2503317.

[28] a) T. Lu and F. Chen, “Multiwfn: A Multifunctional Wavefunction Analyzer,” Journal of Computational Chemistry 33 (2012): 580-592. b) T. Lu, Sobtop, Version 1.0 (dev3.1), accessed July 1, 2023, http://sobereva.com/soft/Sobtop.

[29] Z. Hu, L. Zhang, and J. Jiang, “Development of a Force Field for Zeolitic Imidazolate Framework-8 With Structural Flexibility,” Journal of Chemical Physics 136 (2012): 244703.

[30] T. Liu, “Simple, Reliable, and Universal Metrics of Molecular Planarity,” Journal of Molecular Modeling 27 (2021): 263.

[31] S. Toliautas, J. Dodonova, A. Žvirblis, et al., “Enhancing the Viscosity-Sensitive Range of a BODIPY Molecular Rotor by Two Orders of Magnitude,” Chemistry - A European Journal 25 (2019): 10342-10349.

[32] Z. X. Liu, W. Chi, Q. Qiao, et al., “Molecular Mechanism of Viscosity Sensitivity in BODIPY Rotors and Application to Motion-Based Fluorescent Sensors,” ACS Sensors 5 (2020): 731-739.

[33] a) D. A. Reed, B. K. Keitz, J. Oktawiec, et al., “A Spin Transition Mechanism for Cooperative Adsorption in Metal-Organic Frameworks,” Nature 550 (2017): 96-100. b) M. Zhang, G. X. Feng, Z. G. Son, et al., “Two-Dimensional Metal–Organic Framework With Wide Channels and Responsive Turn-On Fluorescence for the Chemical Sensing of Volatile Organic Compounds,” Journal of the American Chemical Society 136 (2014): 7241-7244.

[34] a) S. Matsika, “Electronic Structure Methods for the Description of Nonadiabatic Effects and Conical Intersections,” Chemical Society Reviews 121 (2021): 9407-9449. b) S. Suzuki, S. Sasaki, A. S. Sairi, R. Iwai, B. Z. Tang, and G. I. Konishi, “Principles of Aggregation-Induced Emission: Design of Deactivation Pathways for Advanced AIEgens and Applications,” Angewandte Chemie International Edition 59 (2020): 9856-9867. c) H. W. Yong, J. R. Rouxel, D. Keefer, and S. Mukamel, “Direct Monitoring of Conical Intersection Passage via Electronic Coherences in Twisted X-Ray Diffraction,” Physical Review Letters 129 (2022): 103001.

[35] a) X. J. Ma, K. R. Meihaus, Y. J. Yang, et al., “Photocatalytic Extraction of Uranium From Seawater Using Covalent Organic Framework Nanowires,” Journal of the American Chemical Society 146 (2024): 23566-23573. b) C. Z. Wang, J. Chen, Q. H. Li, et al., “Pore Size Modulation in Flexible Metal-Organic Framework Enabling High Performance Gas Sensing,” Angewandte Chemie International Edition 62 (2023): e202302996.

[36] Y. Zhang, M. Gutiérrez, A. K. Chaudhari, and J. C. Tan, “Dye-Encapsulated Zeolitic Imidazolate Framework (ZIF-71) for Fluorochromic Sensing of Pressure, Temperature, and Volatile Solvents,” ACS Applied Materials & Interfaces 12 (2020): 37477-37488.

[37] C. Wang, W. Li, K. Liao, Z. Wang, Y. Wang, and K. Gong, AuToFF Program; Vesrion 1.0 (Hzwtech, 2023).

RIGHTS & PERMISSIONS

2025 The Author(s). Aggregate published by SCUT, AIEI and John Wiley & Sons Australia, Ltd.