Fluorescence was achieved in light-driven molecular actuators

Two photoluminescence functions, photoluminescence (PL) and unidirectional spin, are combined by hybridization of a PL dye and a molecular motor. The molecular design provides optical regulation of these functions as well as additional synergistic effects. Credit: Ryojun Toyoda

Rotating molecular motors were first created in 1999, in the laboratory of Ben Feringa, Professor of Organic Chemistry at the University of Groningen. These motors are driven by light. For many reasons, it would be nice to be able to make these kinetic particles visible. The best way to do this is to make them glow. However, combining two light-mediated functions into a single molecule presents a major challenge. Feringa’s lab has now managed to do just that, in two different ways. These two types of light-driven fluorescent rotor actuators are described in Nature Communications (September 30) and science progress (4 November).

“Following the successful design of molecular actuators in the past decades, the next important goal was to control various functions and properties using such actuators,” explains Feringa, who shared the 2016 Nobel Prize in Chemistry. In rotating engines, it is particularly difficult to design a system that has another function that is controlled by light energy, in addition to rotational motion.”

Feringa and his team were particularly interested in fluorescence because this is a key technology widely used for detection, for example in biomedical imaging. Normally, two of these photochemical events are incompatible in the same molecule; Either the light-powered motor runs and there is no fluorescence or there is fluorescence and the motor does not run. Feringa says, “We have now demonstrated that both functions can exist in parallel in the same molecular system, which is rather unique.”

Ryojun Toyoda, a postdoctoral researcher in the Feringa group who is now a professor at Tohoku University in Japan, added a fluorescent dye to the classic Feringa rotor. “The trick was to prevent these two functions from hindering each other,” Toyoda says. Enables to quench direct interactions between dye and motor. This was done by placing the dye perpendicular to the top of the motor to which it was attached. “This limits interaction,” Toyoda explains.

different colors

In this way, the fluorescence and rotational function of the motor can coexist. Moreover, it turns out that changing the solvent allows him to fine-tune the system: “By changing the polarity of the solvent, the balance between both functions can be changed.” This means that the engine has become sensitive to its environment, which could point the way for future applications.

Co-author Sherine Faraji, professor of theoretical chemistry at the University of Groningen, helped explain how this happens. Kiana Moghadam, a postdoctoral researcher in her group, performed extensive quantum mechanical calculations and demonstrated how the key energies that govern the dynamics of exciting images strongly depend on the polarity of the solvent.

Another useful property of this fluorescent kinetic molecule is that different dyes can be attached to it as long as they have a similar structure. “Therefore, it is relatively easy to make glowing engines of different colors,” Toyoda says.

Light-powered molecular engines light up

The bifunctional actuator was prepared by chemically attaching an antenna to a molecular motor. Rotation and photoluminescence (PL) can be controlled using light of different wavelengths. Credit: Lucas Pfeiffer


Lukas Pfeifer built a second fluorescent engine, while also working as a postdoctoral researcher in the Feringa group. He has since joined the Polytechnique Fédérale in Lausanne, Switzerland: “The solution I’m using was based on a motor molecule I had already made, which is driven by two low-energy near-infrared photons.” Actuators powered by near-infrared light are useful in biological systems, as this light penetrates deeper into tissues than visible light and is less harmful to tissues than UV light.

“I added an antenna to the kinetic molecule that collects the energy of two infrared photons and transmits it to the actuator. While working on this, we discovered that with some modification, the antenna can also cause fluorescence,” Pfeiffer says. It turns out that a molecule can have two different excited states: in one state, energy is transferred to the motor part and drives rotation, while the other state causes the molecule to shine.


“In the case of this second motor, the whole molecule fluoresces,” explains Professor Maxim Bechenichnikov, who performed spectroscopy for both types of fluorescent motors and is a co-author of both papers. “This actuator is a chemical entity in which the wave function is not determined, and depending on the energy level, it can have two different effects. By changing the wavelength of light, and therefore the energy received by the molecule, you can get either rotation or fluorescence.” “Our synergistic approach in principle and practice highlights the interaction between theoretical and empirical studies, and demonstrates the strength of these joint efforts,” Faraji adds.

Now that the team has combined both movement and fluorescence in the same molecule, the next step will be to demonstrate movement and simultaneously detect the molecule’s location by fluorescence tracking. Feringa says, “This is very powerful and we may apply it to show how these actuators can cross the cell membrane or move inside the cell, as fluorescence is a widely used technique to show where molecules are in cells. We can also use it to track the movement caused by a powered actuator. Photovoltaics, for example at the nanoscale trajectory or perhaps tracking motor-induced transport at the nanoscale. This is all part of the follow-up research.”

more information:
Ryojun Toyoda et al, Synergistic interaction between photoisomerization and photoluminescence in a light-driven rotary molecular motor, Nature Communications (2022). DOI: 10.1038 / s41467-022-33177-0

Lukas Pfeifer et al, spin- and photoluminescence dual-function synthetic molecular motors, science progress (2022). DOI: 10.1126/sciadv.add0410. www.science.org/doi/10.1126/sciadv.add0410

Presented by the University of Groningen

the quote: Fluorescence in Light-Driven Molecular Motors (2022, Nov 4) Obtained Nov 6, 2022 from https://phys.org/news/2022-11-fluorescence-light-driven-molecular-motors.html

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