Near-IR Light Powers Molecular Motor with Low-energy Photons Via Antenna

Chemists at the University of Groningen have designed a near-infrared light-powered rotary motor, the type that can be used to deliver autonomous motion to a system, or to ensure that a system responds to a prompt on command. The chemists administered near-infrared light to their molecular motor through an antenna.

Many biological applications require low-energy, low-intensity light to power a molecular motor and effectively penetrate tissue. UV light, effective at making molecular motors operational, can be harmful to sensitive surrounding materials. University of Groningen professor of organic chemistry Ben Feringa designed and introduced a light-driven, unidirectional rotary molecular motor in 1999, and, 17 years later, he received the Nobel Prize in chemistry for his conceptualization and production of molecular machines.

The new generation of the molecular motor under infrared light. Courtesy of Nong Hoang, University of Groningen.

Until now, though, variations of these machines have been unable to entice a system’s motor molecule to directly accept two low-energy photons, rather than a single high-energy photon. The new approach uses a covalent bond to combine the motor molecule with an antenna, allowing the excited antenna to absorb and then transport the near-infrared photons to the molecule.

The motor system necessitates closely tuning the energy levels of both the antenna and motor as individual components. Led by Lukas Pfeifer, then a postdoctoral researcher in the Feringa lab and now based at the École Polytechnique Fédérale de Lausanne in Switzerland, the scientists designed a distinct molecular motor that requires identical amounts of energy as the antenna is able to provide to generate movement. The team also used a component to link the antenna without interfering with the rotation of the motor.

Maxim Pshenichnikov, professor of ultrafast spectroscopy at the University of Groningen and an author of the paper introducing the rotary motor design, described the direct transfer of excitation as similar to how a pair of guitar strings resonate when only one is struck.

The times of the sequences of events that set the motor in motion ranged from picoseconds to minutes. Using ultrafast spectroscopy, as well as nuclear magnetic resonance, team members determined that after the antenna captured the two near-infrared photons, a complete transfer of energy takes place and drives the motor into motion.

According to Feringa, prospects and applications of the work will span responsive materials and biomolecular systems. By simplifying the structure of the complex, the scientists can incorporate additional functionalities. The motor molecule, for example, could serve to trigger the release of a vesicle’s contents in a biological system.

The research was published in Science Advances (www.doi.org/10.1126/sciadv.abb6165).