Molecular systems specifically designed to convert dynamic functions at the molecular scale into a response visible to the naked eye in multifunctional smart materials: is it still science fiction?
For years, research in the field of Materials Science has been focusing on the study of molecular systems sensitive to external stimuli, housed within porous materials with the aim of exploiting their dynamic functions (for example movement), integrating them into multifunctional intelligent materials. However, the construction of highly porous structures with responsiveness to external stimuli, for example through light excitation, is still in its infancy. In this field, one of the most fascinating challenges is the creation of real molecular switches activated by light stimuli, capable of inducing an active modification in the nanoporous material and leading to the execution of macroscopic work (Porous Switchable Framework, PSF).
Thanks to the constant research on this hot topic by a group of researchers from the Department of Materials Science of the University of Milan-Bicocca composed by Prof. Angiolina Comotti, Prof. Silvia Bracco, Prof. Piero Sozzani, Dr. Jacopo Perego and Dr. Charl Bezuidenhout, in collaboration with Nobel Prize winner Ben Feringa of the University of Groningen in the Netherlands, a project considered science fiction until recently is becoming reality.
The nanosponge that absorbs and expels CO2 on command
Through the incorporation of molecular switches into porous materials it is now possible to achieve remote control of gas absorption and release properties. The results of the research “Construction of a three-state responsive framework from a bistable photoswitch” (DOI: 10.1016/j.chempr.2023.08.004) were published in the international journal Chem (Impact Factor 23.5, Journal Citation Report 2022 Clarivate Analytics , 2023). The nanoporous structure switchable by a two-state molecular switch was fabricated using 3D polymerization of a photo-active monomer to produce light-driven expandable or contractile porous architectures that absorb or expel CO2, just as a sponge can absorb and expel water. The interplay of porosity, flexibility and reversible photo-isomerization between “two isomers” generates “three distinct porosity states” that can be accessed sequentially. This flexible and responsive porous structure represents a step forward towards light-sensitive materials capable of amplifying movement on a molecular scale and converting it into a response visible to the naked eye.
Molecular hooks for the fabrication of multifunctional nanoporous switchable architectures
An innovative chemical synthesis approach has enabled the fabrication of multifunctional highly porous switchable structures by modular and high-precision anchoring with molecular hooks. The results of the research “Construction of Multi-Stimuli Responsive Highly Porous Switchable Frameworks by In-Situ Solid-State Generation of Spiropyran Switches” (DOI: 10.1002/adma.202305783) were published in the prestigious journal Advanced Materials (Impact Factor 29.4, Journal Citation Report 2022 Clarivate Analytics, 2023).
The innovative in situ solid-state grafting approach led to the generation of three porous structures grafted with “spiropyran” groups bearing distinct functional groups that exhibit various stimuli-responsiveness from an indole-based parent material. This method was extremely efficient and allowed for the first time to obtain multi-stimulating, structurally robust spiropyran materials with high pore capacity, essential for reversible and quantitative isomerization in the bulk. These dynamic architectures have shown potential for active pH control, absorption and release of reactive gases, contaminant removal, and water harvesting.