A team of Berkeley Lab and UC Berkeley researchers, led by Lab Deputy Director and physical bioscientist Graham Fleming, was able to follow the flow of excitation energy in both time and space in a molecular complex using a new technique called two-dimensional electronic spectroscopy. The technique respresents an important step towards learning more about how nature efficiently transfers energy from one molecule to another.

The Fleming group developed the new technique in what's known as the Fenna-Matthews-Olsen (FMO) photosynthetic light-harvesting protein, a molecular complex in green sulphur bacteria that absorbs photons and directs the excitation energy to a reaction center, where it can be converted to chemical energy. In doing so, the researchers made a surprise finding.

Fleming and his colleagues expected to find that the excitation energy from harvested photons in the light-capturing pigment molecules was transported to the FMO reaction center molecules step-by-step down the energy ladder. Instead, they discovered distinct energy pathways, based on the spatial arrangements of the molecules, whereby some of the intermediate steps in the energy ladder are skipped.

“I think our technique will prove to be a revolutionary method for studying energy flow in complex systems where multiple molecules interact strongly,” said Fleming, an internationally-acclaimed leader in spectroscopic studies of the photosynthetic process. “Using two-dimensional electronic spectroscopy, we can map the flow of excitation energy through space with nanometer spatial resolution and femtosecond temporal resolution.”

More on this story is available in the April 1 issue of The View and in the full paper on Nature's website