The vibrational power antenna provides “a complete new manner of doing a response” analysis
“This is a completely new way of triggering a reaction that no one has thought of before,” says Alec Wodtke from the Max Planck Institute for Biophysical Chemistry in Germany about his team’s unique system that extracts vibration energy from infrared light and uses it to perform isomerization. “We can bring energy into a system in ways that go beyond what is possible with simple thermal energy,” adds Wodtke. One day this could allow chemists to perform reactions that traditional synthesis cannot.
In photosynthetic plants and bacteria, light harvesting proteins concentrate visible light energy and transmit it to a reaction center. This means that organisms can capture more light than the reaction center alone. However, infrared light lacks the energy to generate these excited electronic states – it can only form vibrational states with lower energy – and is therefore of no use to plants. “What we have set up is analogous to light collection systems, but for infrared, which is actually bizarre because you normally need excited electronic states for light collection,” explains Wodtke. His team discovered that excited vibrational states can also be bundled and the energy transported to a reaction center.
In the structure of the team, the reaction center is a monolayer of “heavy” carbon monoxide containing carbon-13 and oxygen-18 that sits on a sodium chloride surface. The infrared harvesting part of the experiment is a thick top layer – up to 100 monolayers – of regular carbon monoxide. The entire experiment is kept at an extremely low temperature in order to immobilize the gaseous components.
‘When we pumped all of the vibrational energy into the isotope of light [using an infrared laser]This would efficiently transfer all of the energy to the heavy isotope, and we could actually use it to trigger a reaction, ”says Wodtke. Compared to the direct excitation of the heavy isotope layer, its vibrational energy density was 30 times higher when using the infrared harvesting layer.
The reaction in this case is simple: the carbon monoxide molecules, which are initially bound to the surface via the carbon atom, turn upside down. However, Wodtke and his colleagues hope to use vibrational energy pooling to drive other processes such as Diels-Alder reactions or even the activation of carbon dioxide.
‘[This is] A very selective method to control a reaction under conditions that are far removed from thermal equilibrium – very high vibration energy at very low temperature, ”says Rainer Beck, who carries out quantum state-resolved reactivity measurements at the Swiss Federal Institute of Technology in Lausanne. He emphasizes that the study also shows the importance of sensor technology, as it was only made possible by a new, highly sensitive detector that can localize individual infrared photons.
Robert Field from the Massachusetts Institute of Technology in the United States, where he studies the structural and dynamic properties of molecules, is impressed. “This experiment is intended for textbooks on elementary statistical mechanics.”
At first glance, the structure resembles Maxwell’s demon, a thought experiment on how the second law of thermodynamics could be violated by reducing the entropy of a system. “Normally you don’t think about being able to control how a molecule binds to a surface. Thermodynamics determines the relative amounts of one isomer compared to another,” explains Field. To be able to influence this is like removing surface defects and reducing the entropy of the surface.
“This is of tremendous practical importance,” concludes Field. Since energy can be conducted to near-surface defects in solids, an infrared antenna could be used to temporarily remove contaminants. “I think the Wodtke Group will likely apply for patents to use them in applications where surfaces are modified in a constructive way.”