Quantum-Mechanical Secret Revealed in Photosynthesis: Future of Solar Energy

First Posted: Jun 21, 2013 08:58 AM EDT

Converting sunlight into energy could mean a new way to power our homes, vehicles and electronic devices. Yet doing so in an efficient manner has plagued solar energy for years. Now, though, scientists have looked at veritable powerhouses when it comes to converting sun into energy: plants. And they've found that the high efficient energy transport in these biological organisms is connected to a quantum-mechanical phenomenon that they've now examined.

Until now, this quantum-mechanical phenomenon has never been directly observed at work at room temperature. Yet researchers have now been able to show for the first time at ambient conditions that the quantum mechanisms of energy transfer make photosynthesis more robust in the face of environmental influences. Known as coherence, this quantum phenomenon is manifested in so-called photosynthetic antenna proteins that are responsible for the absorption of sunlight and energy transport to the photochemical reaction centers of photosynthesis.

Actually observing this phenomenon, though, was no easy task. Energy transport during photosynthesis is extremely fast and takes place on a molecular scale. Because of this, the scientists had to push ultrafast spectroscopy techniques to the single-molecule limit. They sent ultrafast femtosecond light flashes to capture a high-speed series of "pictures" of the states of individual antenna proteins after light absorption. To put it into perspective, a femtosecond is when light travels only one hundredth of the diameter of a human hair. These "images" allowed the researchers to understand how solar energy is transported through single proteins.

"We have been able to observe how energy flows through sunlight absorbing photosynthetic systems with unprecedented spatial and temporal resolution," said Richard Hildner, first author of the new study, in a news release. "This allowed us to observe the fundamental role of quantum effects in photosynthesis at ambient conditions."

So what did they find from these snapshots? The researchers evaluated the energy transport pathways of separate individual but chemically identical antenna proteins. They found that each protein uses a distinct pathway and that the transport pathways within single proteins can vary over time due to changes in environmental conditions.

"These results show that coherence, a genuine quantum effect of superposition of states, is responsible for maintaining high levels of transport efficiency in biological systems, even when they adapt their energy transport pathways due to environmental influences," said Niek van Hulst, one of the researchers, in a news release.

The findings reveal a little bit more about photosynthesis, which could eventual lead to new research aimed at developing a new generation of solar cells. It could allow scientists to create more efficient means to convert sunlight into energy which could mean cleaner solar energy.

The findings are published in the journal Science.

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