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Designing Light-Powered Molecular Switches

Combining multiple light-responsive switches into a single molecule is considered a promising strategy for building advanced molecular systems — including molecular machines, energy-storage materials, and systems capable of performing complex logic operations. The problem is that such multi-switch systems typically perform poorly: the close proximity of individual photoswitching units causes them to interfere with one another nad disspate energy, often resulting in a complete loss of photochemical activity. Until now, an effective strategy to overcome this limitation had been lacking.

A research team including Arturo Llamosí, Marek P. Szymański, Magdalena Zimnicka and Agnieszka Szumna — presents a solution to this problem in a new study published in Angewandte Chemie International Edition. The researchers designed a tetra‑photoswitchable molecule in which all four photoswitching units switch simultaneously and efficiently, without the loss of performance typical of similar systems, because the switching process follows a thermodynamically favorable pathway and because the switchable untits communicate by a network of intramolecular hydrogen bonds.

An equally important challenge was reversing this process — which intaillay was not achievable under typical solution conditions. The team showed that the key lies in inverting the relative stability of the isomers through deprotonation carried out under mechanochemical conditions.

DFT calculations and gas-phase ion mobility mass spectrometry confirmed the mechanism behind these transformations.

The strategy opens a new, general route to designing efficient, multi-responsive molecular switches — solving a problem that has long limited the practical use of such systems.

A. Llamosí, M. P. Szymański, M. Zimnicka, A. Szumna, „Thermodynamically Driven Multi-Site Photoswitching in Tetraoxindole Cavitands Controlled by Hydrogen Bonding and Mechanochemistry”, Angew. Chem. Int. Ed.