Light-driven methods enable molecular adaptations not possible with other methods.

A team led by Professor Alberto Credi from the University of Bologna used a clever combination of photochemical (or light-induced) reactions and self-assembly processes to insert thread-like molecules into the cavities of ring-like molecules. It follows a high-energy geometry that is not possible in thermodynamic equilibrium. In other words, light makes it possible to create molecular “fits” that are otherwise inaccessible.

“By applying light energy to the aqueous solution, we prevent the molecular self-assembly reaction from reaching a thermodynamic minimum, resulting in a product distribution that is inconsistent with that observed at equilibrium. ” said Alberto Credi.

“Such behavior, which lies at the root of many functions in living organisms, is very difficult to plan and observe, and is therefore largely unstudied in artificial molecules. The simplicity and versatility of our approach makes it possible to use visible light, In other words, sunlight is a clean and sustainable energy source that can be used for many areas of technology and medicine.”

The study was published in the journal Chem.

The self-assembly of molecular components to obtain systems and materials with nanometer-scale structures is one of the fundamental processes of nanotechnology. This takes advantage of the tendency of molecules to evolve to reach a state of thermodynamic equilibrium, or minimum energy state.

However, living organisms function through chemical changes that occur away from thermodynamic equilibrium and can only occur by providing external energy.

Replicating such mechanisms in artificial systems is a complex and ambitious challenge, which, if achieved, would enable the creation of new materials that can respond to stimuli and interact with their environments, which would For example, it could be used to develop smart drugs and active agents. material.

molecular fit

The interlocking components are cyclodextrin, a truncated cone-shaped hollow water-soluble molecule, and an azobenzene derivative, a molecule whose shape changes under the influence of light. In water, interactions between these components lead to the formation of supramolecular complexes in which filamentous azobenzene species are inserted into the cyclodextrin cavities.

In this study, the filamentous compound has two different ends. The two edges of the cyclodextrin are also different, so inserting the former into the latter produces two different complexes with different relative orientations of the two components.

Complex A is more stable than complex B, but the latter forms more rapidly than the former. In the absence of light, only the thermodynamically favored complex, namely A, is observed at equilibrium.

When the solution is irradiated with visible light, azobenzene changes from an elongated shape similar to cyclodextrin to a bent shape that does not fit with the cavity. As a result, the complex dissociates. However, the same light can bend azobenzene back from its bent form to its extended form, potentially causing the dissociated components to reassemble.

Complex B forms much faster than A, so under continuous illumination a steady state is reached where complex B is the major product. When the light disappears, the azobenzene slowly reverts to the extended form, and after a while only the A complex is observed.

This self-assembly mechanism, combined with photochemical reactions, makes it possible to harness the energy of light to accumulate unstable products, opening new methodologies for chemical synthesis, as well as for dynamic molecular materials and working devices ( This opens the way to the development of nano-motors, etc. under non-equilibrium conditions similar to those of living organisms.

This research is the result of a joint research between the Department of Industrial Chemistry “Toso Montanari”, the Department of Chemistry “Tiamisian”, the Department of Agricultural and Food Science and Technology of my alma mater, the University of Coruña in Spain, and the Isof-Cnr Institute in Bologna.