Fast light pulse triggers the charge transfer into the water

The study was only made possible by the new laser laboratories in the ZEMOS research building, in which all external interference signals are minimized.
Photo Credit: © RUB, Marquard

With new technology, researchers were able to observe live what happens in the first picosecond when a proton detaches from a dye after light.

In certain molecules, the so-called photoc acids, a proton can be released locally by excitation with light. The solution suddenly changes the pH - a kind of fast switch that is important for many chemical and biological processes. So far, however, it is still unclear what actually happened at the moment of proton release. This is exactly what researchers in the Ruhr Explores Solvation Cluster of Excellence could do RESOLV the Ruhr University Bochum is now experimentally observing using new technology. They saw a tiny quake that only lasted three to five picoseconds before the proton came loose. They report on this in the journal Chemical Sciences.

Claudius Hoberg and Martina Havenith (right) carried out the investigations in the ZEMOS research building.
Photo Credit: © RUB, Marquard

So far, the focus has been on dye or base

One of the most studied so-called photoc acids is pyranin, the fluorescent dye that is used, for example, in yellow highlighter. "Despite a wealth of experimental studies, the process that started with the detachment of the proton was still controversial," reports Prof. Dr. Martina Havenith, spokeswoman for RESOLV. However, the entire replacement process also takes place on a time scale of only 90 picoseconds. A picosecond corresponds to one millionth of a millionth of a second.

While previous studies focused primarily on changing the dye after the lighting, the team was able to observe the change in the solvent, in this case the water, for the first time during this process. This was achieved with the help of a newly developed technology, the "Optical Pump THz Probe Spectroscopy".

Ultra-fast energy transmission

"We were able to follow how an oscillation occurs at the beginning, which then subsides as a result," describes Martina Havenith. “On the border between photoc acid and water, an earthquake is triggered immediately after the lighting is excited, which lasts about three to five picoscillations before the proton dissolves. "The original ultra-fast energy transfer within less than one picosecond leads to a restructuring of the water molecules in the immediate vicinity and opens the way for the subsequent proton migration.

The detection was made possible by the new laser laboratories in the ZEMOS research building. There, all external interference signals, such as electromagnetic radiation, temperature and humidity fluctuations, are minimized. This is the only way to detect even the tiniest quakes in a water jet with the dye.

Funding: The work was funded by the German Research Foundation (DFG) as part of the Ruhr Explores Solvation Cluster of Excellence, EXC 2033-390677874-Resolv funding, as well as by the European Research Council as part of the ERC Advanced Grant 695437 (THz Calorimetry) and the Mercator Research Center Ruhrall as part of a professorship by the.

Published in journal: Chemical Science

Additional information: Authors are; Claudius Hoberg, Justin J Talbot, James Shee, Thorsten Ockelmann, Debasish Das Mahanta, Fabio Novelli, Martin Head-Gordon, Martina Havenith

The accompanying simulations were carried out at the University of California at Berkeley in the Martin Head-Gordon working group. It belongs to CALSOLV, the sister institute of RESOLV.

Source/Credit: Ruhr University Bochum

Reference Number: chm033123_01

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