Nanotechnology discovery unlocks unique molecular interactions using light
by Erica Marchand
Paris, France (SPX) Dec 28, 2024

Researchers at the University of Bologna, led by Prof. Alberto Credi, have developed an innovative method to manipulate molecular assembly using light energy. This approach allows for the creation of a molecular configuration that defies the natural thermodynamic equilibrium, a feat previously considered unattainable.

"We have shown that by administering light energy to an aqueous solution, a molecular self-assembly reaction can be prevented from reaching a thermodynamic minimum, resulting in a product distribution that does not correspond to that observed at equilibrium," says Alberto Credi.

"Such a behavior, which is at the root of many functions in living organisms, is poorly explored in artificial molecules because it is very difficult to plan and observe. The simplicity and versatility of our approach, together with the fact that visible light - i.e., sunlight - is a clean and sustainable energy source, allow us to foresee developments in various areas of technology and medicine."

A New Frontier in Nanotechnology

Nanotechnology relies heavily on the self-assembly of molecular components to form nanometer-scale systems and materials. Typically, these processes strive for a state of thermodynamic equilibrium, or minimum energy. However, living organisms rely on chemical processes that occur outside equilibrium, sustained by external energy. Reproducing these complex mechanisms in artificial systems could open doors to revolutionary applications such as smart drugs and responsive materials.

How It Works: Molecular Fitting

The study focuses on cyclodextrins - hollow, cone-shaped, water-soluble molecules - and azobenzene derivatives, which change shape under light exposure. In water, these molecules self-assemble into supramolecular complexes, with azobenzene fitting into the cyclodextrin cavity.

The azobenzene molecule's two ends and the cyclodextrin's distinct rims create two possible complexes: A and B. Complex A is more stable, while complex B forms more rapidly. Normally, only the more stable complex, A, is present at equilibrium.

When visible light irradiates the solution, the azobenzene molecule changes shape, disrupting the assembly. However, continued illumination drives the system to favor the formation of the less stable complex, B. Once the light is turned off, the molecules slowly return to their equilibrium state, with complex A dominating.

This innovative mechanism demonstrates how light energy can direct molecular assembly away from equilibrium, enabling the creation of dynamic materials and devices that mimic biological processes. Applications could include nanomotors and other non-equilibrium molecular systems.

Research Report:Light-driven ratcheted formation of diastereomeric host-guest systems

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