Fluorescence achieved in light-driven molecular motors
Rotating molecular motors were first created in 1999, in the laboratory of Ben Feringa, professor of organic chemistry at the University of Groningen. These engines are powered by light. For many reasons it would be good to be able to visualize these motor molecules. The best way to do this is to make them fluoresce. However, combining two light-mediated functions in a single molecule is quite challenging. The Feringa laboratory has now succeeded in doing so, in two different ways. These two types of fluorescent light-driven rotary motors were described in: nature communication (September 30) and scientific progress (the 4th of November).
“After the successful design of molecular motors over the past decades, an important next goal was to control various functions and properties using such motors,” explains Feringa, who took part in the 2016 Nobel Prize in Chemistry. “Because these are light-powered rotary motors, it is particularly challenging to design a system that would have a different function controlled by: light energynext to the rotary motion.”
Feringa and his team were particularly interested in fluorescence as this is an excellent technique widely used for detection, for example in biomedical imaging. Usually two such photochemical events are incompatible in the same molecule; whether the light-driven motor is working and there is no fluorescence or there is fluorescence and the motor is not working. Feringa says, “We’ve now shown that both functions can coexist in the same molecular system, which is quite unique.”
Ryojun Toyoda, a postdoctoral researcher in the Feringa group, who now holds a professorship position at Tohoku University in Japan, added a fluorescent dye to a classic Feringa rotary engine. “The trick was to keep these two functionalities from blocking each other,” Toyoda says. He managed to extinguish the direct interactions between the dye and the motor. This was done by placing the dye perpendicular to the top part of the engine to which it was attached. “This limits the interaction,” Toyoda explains.
In this way, the fluorescence and the rotational function of the motor can coexist. Furthermore, it was found that changing the solvent allows him to tune the system: “By varying the solvent polarity, the balance between both functions can be changed.” This means that the engine has become sensitive to its environment, which could lead the way for future applications.
Co-author Shirin Faraji, professor of Theoretical Chemistry at the University of Groningen, helped explain why this is. Kiana Moghaddam, a postdoc in her group, performed extensive quantum mechanical calculations and demonstrated how the main energetic factors determining photo-excited dynamics strongly depend on the polarity of the solvent.
Another useful property of this fluorescent motor molecule is that different dyes can be attached to it, as long as they have a similar structure. “So it’s relatively easy to make engines that glow in different colors,” Toyoda says.
A second fluorescent engine was built by Lukas Pfeifer, also a postdoctoral researcher in the Feringa group. Since then, he has joined the École Polytechnique Fédérale in Lausanne, Switzerland: “My solution was based on a motor molecule that I already madewhich is powered by two energy-efficient near-infrared photons.” Motors powered by near-infrared light are useful in biological systems because this light penetrates deeper into tissue than visible light and is less damaging to tissue than UV light.
“I added an antenna to the motor molecule that collects the energy from two infrared photons and passes it on to the motor. While we were working on this, we found that with some adjustments, the antenna can also cause fluorescence,” says Pfeifer. It turned out that the molecule can have two different excited states: in one state the energy is transferred to the motor part and causes rotation, while the other state causes the molecule to fluoresce.
“In the case of this second motor, the whole molecule fluoresces,” explains Professor Maxim Pshenichnikov, who has performed spectroscopic analysis of both types of fluorescent motors and who is a co-author of both papers. “This motor is a chemical entity on which the wave function is not located and, depending on the energy level, it can have two different effects. By changing the wavelength of the light, and thus the energy the molecule receives, you get either rotation or fluorescence .” Faraji adds, “Our synergistic approach in principle and in practice emphasizes the interplay between theoretical and experimental studies, and it illustrates the power of such combined efforts.”
Now that the team has combined both movement and fluorescence in the same molecule, the next step would be to demonstrate mobility while simultaneously detecting the molecule’s location by tracing the fluorescence. Feringa says: “This is very powerful and we could apply it to show how these motors can traverse a cell membrane or move inside a cell, as fluorescence is a common technique to show where molecules are in cells. We could also use it to trace the motion caused by the light-driven motor, for example on a nanoscale trajectory or perhaps motor-induced transport at the nanoscale. This is all part of follow-up research.”
Ryojun Toyoda et al, Synergistic interplay between photoisomerization and photoluminescence in a light-driven rotating molecular motor, nature communication (2022). DOI: 10.1038/s41467-022-33177-0
Lukas Pfeifer et al, Artificial Dual Function Molecular Motors Performing Rotation and Photoluminescence, Scientific progress (2022). DOI: 10.1126/sciadv.add0410. www.science.org/doi/10.1126/sciadv.add0410
University of Groningen
Quote: Fluorescence Achieved in Light-Driven Molecular Motors (2022, Nov. 4), retrieved Nov. 6, 2022 from https://phys.org/news/2022-11-fluorescence-light-driven-molecular-motors.html
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