| Jun 17, 2026 |
Darkness helps light-responsive nanomaterials evolve into stable nanotubes
Light-dark cycles help photoresponsive molecules reorganize into stable nanotubes, revealing a route to adaptive nanomaterials and smart devices.
(Nanowerk News) Life on Earth has evolved under an uninterrupted rhythm of day and night. While light provides the energy that powers countless molecular processes, periods of darkness often allow biological systems to reorganize, recover and transform that energy into functional outcomes.
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Inspired by this natural balance, an international team led by Javier Montenegro at the Centre for Research in Biological Chemistry and Molecular Materials (CiQUS) of the Universidade de Santiago de Compostela has demonstrated that the same principle can govern the behavior of simple synthetic molecular systems.
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The study (Angewandte Chemie International Edition, "Light and Dark Cycles Control the Structural Evolution of Photoresponsive Supramolecular Systems") shows that alternating light and dark phases does more than merely switch molecular activity on and off. Instead, darkness acts as a crucial stage in which molecular assemblies reorganize and evolve towards more stable and sophisticated structures.
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The research was led experimentally by Dr. Alejandro Méndez-Ardoy from the Institute of Chemical Research (IIQ, CSIC–University of Seville), with contributions from Patricia Fulías Guzmán and Adrián Sánchez Fernández at CiQUS, as well as collaborators from the Stratingh Institute for Chemistry at the University of Groningen.
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The team investigated small photoresponsive peptides capable of changing their chemical state when exposed to light. These molecules contain a photoswitch that toggles between two forms with distinct properties: one that is more water-soluble in the dark and another that becomes more hydrophobic under illumination. This reversible transformation alters intermolecular interactions and triggers supramolecular self-assembly.
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When exposed to visible light, the molecules spontaneously organize into nanoscale helical ribbons. Once the light is removed, however, these structures begin to relax, partially collapse and gradually disassemble.
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The researchers discovered that if illumination is applied in repeated cycles—returning before the assemblies completely break down—these partially relaxed structures become stepping stones towards a new and more advanced architecture: highly uniform and stable supramolecular nanotubes.
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“Our work shows that dark periods open alternative pathways for structural evolution that are faster and more effective than keeping the light on continuously,” explains Javier Montenegro, an Oportunius researcher at CiQUS.
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“Even in very simple photoresponsive molecular systems, while light provides the energy needed to build complex self-assembled structures, it is the resting phases that allow the system to reorganize and access the most stable architectures.”
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According to the researchers, this behavior echoes fundamental biological processes and may even offer clues about how early light-driven systems on Earth gained structural complexity.
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“Light–dark cycles generate a form of structural learning,” Montenegro says. “The system continuously explores different organizational routes and progressively selects the most robust configurations during periods when energy input is absent.”
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The study further demonstrates that periodic light–dark cycles are more effective than constant illumination at driving this structural transition. During the dark phases, thermal relaxation and molecular reorganization reduce defects and promote a more ordered packing of molecules.
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As a result, the system evolves towards nanotubes with greater stability and a higher degree of molecular organization.
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Beyond its fundamental significance, the work opens new avenues for the design of adaptive materials that respond dynamically to external stimuli. Understanding how fluctuating energy inputs influence the evolution of supramolecular systems could help guide the development of smart materials, nanoscale devices and biomimetic systems whose properties can be programmed through controlled energy cycles.
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“This study offers a new perspective on how interruptions in energy supply can shape the complexity of molecular systems,” Montenegro concludes. “What matters is not only when energy is present, but also when it disappears.”
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