Nav: Home

Seeing energized light-active molecules proves quick work for Argonne scientists

September 08, 2016

For people who enjoy amusement parks, one of the most thrilling sensations comes at the top of a roller coaster, in the split second between the end of the climb and the rush of the descent. Trying to take a picture at exactly the moment that the roller coaster reaches its zenith can be difficult because the drop happens so suddenly.

For chemists trying to take pictures of energized molecules, the dilemma is precisely the same, if not trickier. When certain molecules are excited -- like a roller coaster poised at the very top of its run - they often stay in their new state for only an instant before "falling" into a lower energy state.

To understand how molecules undergo light-driven chemical transformations, scientists need to be able to follow the atoms and electrons within the energized molecule as it rides on the energy "roller coaster."

In a recent study, a team of researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory, Northwestern University and the Technical University of Denmark used the ultrafast high-intensity pulsed X-rays produced by the Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility at SLAC National Accelerator Laboratory, to take molecular snapshots of these molecules.

By using the LCLS, the researchers were able to capture atomic and electronic arrangements within the molecule that had lifetimes as short as 50 femtoseconds -- which is about the amount of time it takes light to travel the width of a human hair.

"We can see changes in these energized molecules which happen incredibly quickly," said Lin Chen, an Argonne senior chemist and professor of chemistry at Northwestern University who led the research.

Chen and her team looked the structure of a metalloporphyrin, a molecule similar to important building blocks for natural and artificial photosynthesis. Metalloporphyrins are of interest to scientists who seek to convert solar energy into fuel by splitting water to generate hydrogen or converting carbon dioxide into sugars or other types of fuels.

Specifically, the research team examined how the metalloporphyrin changes after it is excited with a laser. They discovered an extremely short-lived "transient state" that lasted only a few hundred femtoseconds before the molecule relaxed into a lower energy state.

"Although we had previously captured the molecular structure of a longer-lived state, the structure of this transient state eluded our detection because its lifetime was too short," Chen said.

When the laser pulse hits the molecule, an electron from the outer ring moves into the nickel metal center. This creates a charge imbalance, which in turn creates an instability within the whole molecule. In short order, another electron from the nickel migrates back to the outer ring, and the excited electron falls back into the lower open orbital to take its place.

"This first state appears and disappears so quickly, but it's imperative for the development of things like solar fuels," Chen said. "Ideally, we want to find ways to make this state last longer to enable the subsequent chemical processes that may lead to catalysis, but just being able to see that it is there in the first place is important."

The challenge, Chen said, is to prolong the lifetime of the excited state through the design of the metalloporphyrin molecule. "From this study, we gained knowledge of which molecular structural element, such as bond length and planarity of the ring, can influence the excited state property," Chen said. "With these results we might be able to design a system to allow us to harvest much of the energy in the excited state."

A paper based on the research, "Ultrafast excited state relaxation of a metalloporphyrin revealed by femtosecond X-ray absorption spectroscopy," was published in the June 10 online edition of the Journal of the American Chemical Society.
-end-
The research was funded by the DOE's Office of Science and by the National Institute of Health.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

The U.S. Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website.

DOE/Argonne National Laboratory

Related Molecules Articles:

Discovery of periodic tables for molecules
Scientists at Tokyo Institute of Technology (Tokyo Tech) develop tables similar to the periodic table of elements but for molecules.
New method for imaging biological molecules
Researchers at Karolinska Institutet in Sweden have, together with colleagues from Aalto University in Finland, developed a new method for creating images of molecules in cells or tissue samples.
How two water molecules dance together
Researchers have gained new insights into how water molecules interact.
Hand-knitted molecules
Molecules are usually formed in reaction vessels or laboratory flasks.
How molecules teeter in a laser field
When molecules interact with the oscillating field of a laser, an instantaneous, time-dependent dipole is induced.
Data storage using individual molecules
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled.
Small molecules come into focus
Many biologically important small molecules, like hormones and amino acids, are too small to be measured by conventional detection methods.
We now know how RNA molecules are organized in cells
With their new finding, Canadian scientists urge revision of decades-old dogma on protein synthesis
A new way to create molecules for drug development
Chemists at The Ohio State University have developed a new and improved way to generate molecules that can enable the design of new types of synthetic drugs.
How ions gather water molecules around them
Charged particles in aqueous solutions are always surrounded by a shell of water molecules.
More Molecules News and Molecules Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab