Two light switches combined in one molecule

University of Groningen scientists led by Professor of Organic Chemistry Ben Feringa have developed a molecule containing two separate light switches. Feringa has thus created another tool for building light-controllable functional materials. An article on the double switch was published in the journal Nature Communications on 12 July.

Feringa is a pioneer in catalysis, molecular motors and molecular switches. An inspiring example of the possible applications of his work is an antibiotic containing a light-controlled ‘on/off-switch’ . But so far, the control has only been binary. A double switch would offer more flexibility, but the problem is to find two switches that don’t interfere with each other.

Several classes of light-controlled molecular switches are available, but it is hard to find two that respond to non-overlapping wavelengths. Only then is it possible to control them individually. In the Nature Communications article, the University of Groningen scientists describe how they found two such switches and brought them together in one molecule.

The two switches are a ‘Donor-Acceptor Stenhouse Adduct’ (DASA) and an azobenzene. Feringa and colleagues describe how they first managed to control the two switches separately in a solution containing both molecules. They then produced a single molecule containing both switches and discovered that the two switches did not affect each other’s operation, once they had taken some precautionary measures.

The DASA switch can change the solubility of the molecule: first it is soluble in water but after switching it is more at home in toluene. In a test tube containing separate layers of toluene and water, the molecule will migrate once white light triggers the switch.

The azobenzene switch can make the molecule bind to a circular organic compound known as cyclodextrin . A molecule containing both switches can thus be made to pick up a cyclodextrin ring and transport it from water to toluene. The binding properties and the location can be managed, using ultraviolet and white light respectively.

As Feringa explains, this opens the door to smart materials with properties that can be controlled in a non-invasive and reversible manner. ‘It is still early days, but if you can switch two properties independently, you might for example use this to transport molecules through a cell membrane. And you could also design a double-action light-controlled catalyst.’ But, he adds, ‘to realize this will take a lot of hard work!’

Reference: Michael M. Lerch, Mickel J. Hansen, Willem A. Velema, Wiktor Szymanski & Ben L. Feringa: Orthogonal photoswitching in a multifunctional molecular system . Nature Communications 12 July 2016, doi:10.1038/ncomms12054

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