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How dimensionally distinct supramolecular structures arise under different light intensities. Credit: Assistant Professor Kenta Tamaki from Chiba University.<\/p>\nIn the future, there could be materials that can reconfigure themselves on demand, adapting their structure and properties like living organisms.\u00a0<\/p>\n
A team of Japanese scientists have created a supramolecular polymer system that transforms into 1D, 2D, or 3D structures by adjusting light intensity.<\/p>\n
The Chiba University researchers say this development could lead to a new generation of highly adaptable \u201csmart\u201d materials. The current materials are generally static once their form is established.<\/p>\n
This work demonstrates a non-biological system that changes its structure or state depending on the amount of energy it receives, much like living organisms.\u00a0<\/p>\n
How dimensionally distinct supramolecular structures arise under different light intensities. Credit: Assistant Professor Kenta Tamaki from Chiba University.<\/p>\n
Changes in light intensity <\/p>\n
The study addresses a core challenge in materials<\/a> science: creating out-of-equilibrium molecular assemblies \u2014 structures that exist outside their stable thermodynamic state.<\/p>\n While previous studies have achieved such states using external energy, few systems could adaptively respond to how much energy was input.<\/p>\n \u201cOur group has long been pursuing unique research aimed at controlling the nano- to mesoscale morphologies of molecular assemblies using light,\u201d said Professor Shiki Yagai.<\/p>\n \u201cHowever, we had not yet realized an out-of-equilibrium system that, much like living organisms, changes its structure or state depending on the amount of energy it receives,\u201d Yagai added.\u00a0<\/p>\n The innovation lies in a specially designed molecule that combines a light-responsive \u201cazobenzene\u201d unit with a \u201cbarbituric acid-based merocyanine\u201d core.\u00a0<\/p>\n This unique combination allows the material to exhibit supramolecular polymorphism \u2013 the ability to form different assembly structures \u2013 triggered and controlled by light.<\/p>\n Initially, the synthesized molecules self-assemble into 1D coiled nanofibers. When left undisturbed under ambient light, these naturally transition into more thermodynamically stable 2D nanosheets. This is where the light-intensity magic begins.<\/p>\n Adaptive materials<\/p>\n When the 2D nanosheets were exposed to strong ultraviolet (UV) light, researchers observed a dramatic reversal.<\/p>\n The material transformed back into 1D linear nanofibers.\u00a0<\/p>\n High-speed atomic force microscopy (HS-AFM) revealed that this change was due to the azobenzene unit\u2019s photoisomerization, which disrupted the hydrogen bonds holding the 2D sheets together.<\/p>\n Interestingly, this transformation occurred specifically along certain facets of the nanocrystals that were more exposed to light.<\/a><\/p>\n Even more remarkably, when exposed to weak UV light, the system took a completely different path.\u00a0<\/p>\n Transmission electron microscopy (TEM) and AFM observations showed that smaller nanosheets disassembled, while larger ones began to grow vertically, forming intricate 3D nanocrystals.\u00a0<\/p>\n This process, known as Ostwald ripening, involves smaller structures dissolving and redepositing onto larger ones. HS-AFM beautifully captured these localized growth events, including secondary nucleation and epitaxial growth.<\/p>\n \u201cThis out-of-equilibrium supramolecular system paves the way for developing highly functional materials that can alter their states in response to external stimuli, much like living systems,\u201d concluded <\/a>Yagai. <\/p>\n \u201cLooking ahead, by incorporating photoactive, electroactive, or even catalytic functions directly into the molecular design, it may be possible to create systems whose functional performance spontaneously adapts to environmental changes.\u201d<\/p>\n