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
Source: University of Southampton
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