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More efficient solar and sensory technologies

Findings by a team from UNIFI, INO-CNR, MIT published on Nature Materials
Solar and sensory technologies will be more efficient thanks to a combination of quantum physics and biochemistry. This is the result of the study 'Enhanced energy transport in genetically modified excitonic networks' published on Nature Materials.

The work has been carried out by an international team of researchers from the Department of Physics and Astronomy and the European Laboratory for Nonlinear Spectroscopy (LENS) at the University of Florence; the Quantum Science and Technology in Arcetri, Florence (QSTAR), the Department of Chemistry of the University of Perugia, the National Institute of Optics, the National Research Council (INO-CNR), the Massachusetts Institute of Technology (MIT) and the ENI Donegani Research Centre in Novara. The project is part of the framework agreement ENI-CNR and the partnership ENI-MIT signed in 2008.

Photosynthesis is what makes life of Earth possible and it is activated thanks to a process in which light is captured by a "receiving protein antenna" and then retransmitted by a chain of pigments linked to it called chromophores, to a "power plant", the centre of reaction, where it is converted in biologically usable energy.

To reach optimal transport efficiencies, imitating natural systems, the research team utilized artificial photosynthetic antennas developed at MIT labs. These antenna systems were obtained genetically modifying the protein structure of a harmless virus and anchoring to specific points in its structure two kinds of chromophores: donors (light-absorbing) and receivers (light-emitting).

The genetic modification of the virus allows to control the distance between the chromophores' anchoring points and consequently the interaction intensity, which, in turn, is responsible for the transport efficiency of excitation energy.

While the photosynthetic process has overall efficiencies below 1%, the transportation of energy in the form of electronic excitation has an efficiency of almost 100%, even at room temperature, which is much greater that the best solar cells. Experimental results, backed up by theoretical models, have proved in recent years that, at the root of this extraordinary efficiency, there are effects that can only be explained by quantum physics, by which the "energy unit" (exciton) is created on a number of chromophores simultaneously and takes parallel tracks in order to optimise the path toward the centre of reaction. In such conditions the active molecular movements at room temperature, instead of being an obstacle as one would expect, they speed up the processes.

"To analyse the energy transport in antenna systems - reports Paolo De Natale, director of INO-CNR - we have made an experiment in which these light-harvesting systems are stimulated with high-speed laser impulses that are first absorbed by the donor molecules and then re-emitted by the receivers, thus allowing the measurement of transport efficiency. For genetically engineered systems we have measured a propagation of the exciton twice as fast as the same antennas based on non modified viruses. the consequence are propagation distances 67% longer."

"The study - explains Filippo Caruso, from the Department of Physics and Astronomy, LENS and QSTAR - is the experimental verification of the theoretical discoveries on the importance of external noise and quantum effects in order to explain energy transport on complex photosynthetic systems of bacteria that are probably the forefathers of life on Earth. The study hence represents a fundamental step forward towards new quantum technologies for solar and sensor power, inspired by what Nature has been doing in an excellent manner and with great success for billions of years."

25 January 2016