Optimizing Molecular Photoswitches for Solar Energy Harvesting
Molecular photoswitches that can both convert and store energy could
be used to make solar energy harvesting more efficient. A team of
researchers has used a quantum computing method to find a particularly
efficient molecular structure for this purpose. As the team describe in
the journal Angewandte Chemie, their procedure was based on a
dataset of more than 400,000 molecules, which they screened to find the
optimum molecular structure for solar energy storage materials.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
At present, solar energy is either used directly to generate
electricity, or indirectly via the energy stored in heat reservoirs. A
third route could involve first storing the energy from the sun in
light-sensitive materials and then releasing it as needed. The EU-backed
project MOST (“Molecular Solar Thermal Energy Storage”) is exploring
molecules such as photoswitches that can absorb and store solar energy
at room temperature to create entirely emission-free utilization of
solar energy a reality.
The research teams of Kurt V. Mikkelsen at the University of
Copenhagen, (Denmark) and Kasper Moth–Poulsen at the Technical
University of Catalonia, Barcelona (Spain), have taken a closer look at
the photoswitches best suited for this task. They studied molecules
known as bicyclic dienes, which switch to a high-energy state when
illuminated. The most prominent example of this bicyclic diene system is
known as norbornadiene quadricyclane, but a vast number of similar
candidates exist. The researchers explain: “The resulting chemical space
consists of approximately 466,000 bicyclic dienes that we have screened
for their potential applicability in MOST technology.”
Screening a database of this size is typically done by machine
learning, but this requires large amounts of training data based on
real-world experiments, which the team did not have. Using a previously
developed algorithm and a novel evaluation score, “eta”, the screening
and evaluation of the database molecules yielded a clear result: all six
of the top scoring molecules differed from the original norbornadiene
quadricyclane system at a crucial point in the structure. The
researchers concluded that this structural change, an expansion of the
molecular bridge between the two carbon rings in the bicyclic part,
allowed the new molecules to store more energy than the original
norbornadiene.
The researchers’ work demonstrates the potential for optimizing solar
energy storage molecules. However, the new molecules must first be
synthesized and tested under real conditions. “Even though the systems
can be synthetically prepared, there is no guarantee that they are
soluble in relevant solvents and that they will actually photoswitch in
high yield or at all, as we have assumed in eta,” the authors caution.
Despite this, the team have developed a new, large set of training
data for machine learning algorithms and have thus shortened the arduous
research step prior to synthesis for chemists tackling such systems in
the future. The authors envision this much larger repository of bicyclic
dienes coming into its own for research into photoswitches for a
variety of applications, potentially making it easier for molecules to
be tailored to specific requirements.
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About the Author
Kurt Valentin
Mikkelsen is a Professor at the Department of Chemistry, University of
Copenhagen, Denmark. Using scientific computing methods, the Mikkelsen
Group investigates the dynamics and thermodynamics of reactions related
to the exploitation of solar energy, linear and nonlinear molecular
properties, as well as scattering properties of atmospheric molecular
clusters.
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