The rise of "soft" crystal sponges: a new frontier in smart materials toward applications

Soft porous crystals (SPCs), with soft metal-organic frameworks (MOFs) as prominent examples, have attracted significant attention as a new generation of functional materials due to their remarkable porosity, adjustable structures, and structural adaptivity. Their distinctive dynamic behavior—enabling reversible structural deformations or conformational changes in response to external stimuli such as temperature, pressure, guest molecules, electric, magnetic, and optical fields—endows them with significant potential for applications in gas adsorption and separation, sensing, drug delivery, smart devices, etc.

Yet, despite their promising potential, most applications remain at the proof-of-concept level, and many envisioned uses have not yet been fully explored in SPCs. Practical deployment is still hindered by persistent challenges, including limited long-term stability, poor intrinsic electrical conductivity, and the complexities associated with large-scale synthesis. Fortunately, rational design strategies, such as hybridization, doping, and functionalization, show considerable potential in tackling these problems. A team of scientists has recently summarized key advancements in SPCs across dosage-related applications, including moderate and high-dose scenarios as well as trace or low-dose ones. They emphasized the significance of "dose-sensitive" applications for “scaling softness” in industrialization. Their work is published in Industrial Chemistry & Materials on July 16, 2025.

“The 21st century is the ‘age of gas’. The development of new adsorbents and separation materials with high energy efficiency, excellent selectivity, and high capture capacity is crucial for the effective utilization of gaseous resources. As a new class of adaptive materials, soft porous crystals (SPCs) hold promises for achieving efficient resource utilization,” said Susumu Kitagawa, a distinguished professor in MOF chemistry at Kyoto University, “In this review, we focus on soft metal–organic frameworks (MOFs). MOF is a representative example of SPC, and it would not be an overstatement to say that the future of new porous materials lies in SPC. We propose a conceptual framework for exploring their research landscape based on dosage levels, in the context of ‘scaling softness.’ We reveal their promising applications in fields such as gas storage and separation, catalysis, nuclear industry, and devices, providing valuable guidance for future material design and process development. We also provided an outlook on the remaining challenges to this field under real-world conditions.”

“The understanding of SPCs’ flexibility is not static; it evolves as research progresses. For example, the first second-generation MOF to be demonstrated, [Co₂(4,4'-bpy)₃(NO₃)₄], was also the first soft porous crystal with local dynamics. Calgary Framework 20 (CALF-20), with high CO₂ adsorption capacity, was shown to be flexible in a recent study.” 

“Characterizations and theoretical calculations explain the factors influencing the dynamic behavior of SPCs, which is crucial for finely tuning their switching behavior to meet targeted application demands,” said Ken-ichi Otake, an Associate Professor at Kyoto University, “Building upon conventional characterization techniques, advanced in situ and operando methods have been developed, enabling real-time observation of dynamic structural changes and phase transformations of SPCs. These approaches provide deep mechanistic insights into material behavior under working conditions.”

“Throughout a material’s evolution from fundamental to applied research, a common challenge emerges: researchers often prioritize exploring new frontiers over advancing industrialization, as evidenced by the development of MOFs and SPCs. To fully unlock their potential, the pursuit of novel applications and the drive toward industrialization must progress in parallel,” said Ming-Shui Yao, a Professor at the Institute of Process Engineering, CAS, “Several SPCs have already achieved large-scale production on a ton or kilogram scale. Key factors such as long-term stability, volume instability during cyclic operation, crystal size control, and shaping should be considered for industrial-scale production.”

The researchers emphasize that the dosage of materials directly affects their economic viability and practical feasibility, a characteristic known as “dose sensitivity”. In trace or low-dose applications, high performance and batch consistency are essential. While for moderate and high-dose applications, cost-effectiveness becomes more crucial. The “dose sensitivity” of SPCs is a consensus achieved at the roundtable forum of the Seminar and Academic Training on Soft Porous Coordination Chemistry 2023 (SPCC 2023) hosted by the authors, held at the end of August in Beijing (distinguished roundtable guests: Professors Qiang Xu and Sihai Yang).

“SPCs have achieved continuous progress in recent years. Some other types of SPCs, including soft COFs, HOFs, and zeolites, have also been developed and reported,” said Susumu Kitagawa, “For years, we have been dedicated to understanding the design, synthesis, and functional properties of MOFs, with a particular focus on their dynamic behaviors and guest-responsive characteristics. We also continuously strive to bridge the gap between fundamental science and practical applications. We believe that the development of SPCs holds immense promise for the future.”

“In this review, our main goal is to provide readers with a comprehensive understanding of SPCs’ promising applications across d based on dosage usage to bring these materials from the lab to the marketplace,” Yao said.

The research team includes Jiahui Guo, Sai Chu, Fangli Yuan, and Ming-Shui Yao from the Institute of Process Engineering, Chinese Academy of Sciences; and Ken-ichi Otake and Susumu Kitagawa from Kyoto University.

This work is funded by the CAS President’s International Fellowship for Visiting Scientists and for Distinguished Scientists, the National Natural Science Foundation of China, the research fund of State Key Laboratory of Mesoscience and Engineering, and the JSPS KAKENHI Grant-in-Aid for Scientific Research (S).

Industrial Chemistry & Materials is a peer-reviewed interdisciplinary academic journal published by Royal Society of Chemistry (RSC) with APCs currently waived. ICM publishes significant innovative research and major technological breakthroughs in all aspects of industrial chemistry and materials, especially the important innovation of the low-carbon chemical industry, energy, and functional materials. Check out the latest ICM news on the blog.