Artificially replicating the biological process of photosynthesis is a goal being sought on many fronts, and it promises to one day improve light-to-energy efficiencies of solar collection well beyond what's possible with photovoltaic cells. One of the first steps on the road to achieving this objective is to imitate the mechanisms at work in the transfer of energy from reception through to output.

To this end, Scientists have recently experimented with a combination of biological and photonic quantum mechanical states to form new half-light half-matter particle, called the “polariton.” It could help realize fully synthetic systems by mimicking the energy transport systems of biological photosynthesis.

Studying energy transfer mechanisms in photosynthesis, researchers from the University of Southampton, in collaboration with the Universities of Sheffield and Crete, identified that the major shortcoming in attempting to replicate biological energy movement – the Forster Resonance Energy Transfer (FRET) – was the infinitesimally small distances over which the process worked.

In essence, FRET relies on donor molecules to initially absorb energy from sunlight and then pass that energy on to an acceptor molecule (a “chromophore”) in a radiationless process. However, this function also depends on an exceptionally close proximity from each molecule to the next (typically 1 to 10 nanometers) and largely precludes efficient energy transport in more practical synthetic systems with greater transfer distance requirements.

To attempt to overcome these limiting factors, the researchers designed an alternate intermolecular energy transfer system that uses light interacting with two different organic molecules in an optical cavity. The device consists of an optical cavity made by two metallic mirrors which trap the photons in a confined environment in which two different organic molecules reside. By adjusting the spacing between the mirrors based on the inherent optical makeup of the organic materials, and then bombarding the cavity with high-energy photons, a new quantum state results that is an amalgamation of the trapped photons and the excited states of the molecules.

In effect, the photon essentially "glues" together these quantum mechanical states, forming a new half-light, half-matter particle – the polariton – which is then responsible for the efficient transfer of energy from one material to the other over a distance that is significantly longer than those observed in usual FRET-type processes.

"The possibility to transfer energy over distances comparable to the wavelength of light has the potential to be of both fundamental and applied interest" said Dr. Niccolo Somaschi, from the University of Southampton's Hybrid Photonics group. "At the fundamental level, the present work suggests that the coherent coupling of molecules may be directly involved in the energy transfer process which occurs in the photosynthesis.”

As one element in replicating the energy transfer process of photosynthesis, this work should both advance our knowledge of the principles at work in biological light-to-energy energy transformation, and offer new possibilities in designing artificial systems that improve the efficiencies inherent in natural systems.

Details of the research were published in the journal Nature Materials