A dive into deep-sea fish-inspired supramolecular light-driven machinery

An international team of chemists, including members from the Weizmann Institute, Tampere University, and researchers from Poland and the UK, have developed a bioinspired supramolecular approach. This method transforms photoswitchable molecules from their stable state to a metastable one using low-energy red light. The innovation enables rapid, highly selective, and efficient switching. This has potential applications in energy storage, light-activated drug activation, and sensing technologies.

Nature’s vision system as inspiration

The vision system, which has evolved over millions of years, is intricately complex. Nature uses a supramolecular chemistry approach to make vision sensitive across the visible light spectrum. The visual pigment, cis-retinal, changes shape upon photon capture. This shift leads to alterations in the surrounding proteins' supramolecular organisation, triggering a cascade of chemical signals that result in visual perception in the brain.

Deep-sea fish and synthetic systems

Prof. Rafal Klajn, the lead author, explains, “Some deep-sea fish have evolved antenna-like molecules capable of absorbing photons in the red wavelength range, whose abundance at great depths is close to zero. After absorbing a photon, this antenna molecule transfers its energy to the nearby retinal molecule, thus inducing its conformational change from the cis to trans-retinal. In synthetic systems, such process would enable using low-energy light for applications in for instance energy storage or controlled drug release.”

Superior supramolecular machine

The researchers have created a supramolecular machine, inspired by this natural phenomenon. It efficiently converts azobenzenes, commonly used synthetic photoswitchable molecules, from stable to metastable states using almost any visible light wavelength. This involves a metal–organic cage that encloses an azobenzene molecule and a light-absorbing antenna molecule, the sensitiser. In the cage's confined space, chemical reactions otherwise impossible become feasible.

Overcoming azobenzenes’ limitations

Dr. Nikita Durandin from Tampere University discusses overcoming azobenzenes' limitations, “A common problem of azobenzenes is that they cannot efficiently undergo photoswitching from the stable trans form to the metastable cis form upon low-energy red and near-infrared light, but the process has to be driven by UV light. This substantially limits their applications in fields such as photocatalysis or photopharmacology. Now, using the supramolecular caging approach we can reach almost quantitative trans-to-cis isomerisation with any color of visible range.”

Ultrafast photochemical processes

Dr. Tero-Petri Ruoko, an expert in ultrafast spectroscopy, adds, “Time-resolved spectroscopic studies done at Tampere University revealed that the photochemical processes triggering the isomerisation happen superfast, in the nanosecond range. In other words, almost one billion times faster than the blink of your eyes.”

Future applications in soft robotics and drug delivery

Prof. Arri Priimägi, leading the Smart Photonics Materials group, sees potential future applications in soft robotics and light-activated drug delivery systems. The group is already progressing towards the next generation of light-driven supramolecular machines, leveraging the developed methodologies.
The research article titled “Disequilibrating azobenzenes by visible-light sensitisation under confinement” has been published in Science.