Following light absorption in the near-UV and VIS spectral region,
molecular properties are profoundly affected. Such changes, attributable to
the formation of electronic excited states, are transient. Within a few
fractions of a second, molecules tend to return to their initial
equilibrium state by emitting the excess of energy as heat or light. The
latter process is termed photoluminescence and can be extremely useful for
a variety of purposes. For instance it is possible to design luminescent
probes for biomedical analysis (fluoroimmunology) by which one can measure
the concentration of viruses or bacteria in a biological matrix. The light emitted by such
probes enable quantitative determination of antigens [Fig. 1]. The detection of the light
signal is easy and the method is very practical, therefore this analytical
technique is a viable alternative relative to radioimmunology, which
implies the use of radioactive compounds. In our labs we have investigated
several synthetic lanthanide complexes with unique photophysical
properties, that can be used as luminescent probes in fluoroimmunology.
°°°°
The assembly of several molecular subunits in a more complex structure may
give rise to a supramolecular structure. In a system of this type it is
possible to address light excitation to a specific component, creating a
localized excited state. This can result in sizeable interactions with the
nearby subunits, such as energy or electron transfer. These fundamental
processes are of paramount importance in some natural phenomena. In natural
photosynthesis, for instance, light triggers a cascade of chemical reaction
which eventually produces molecules with high energy content, such as
carbohydrates. In brief, the electromagnetic energy input (sunlight) is
transformed into chemical energy (vegetables, the basis of food chain).
It is possible to take advantage of energy and electron transfer
processes in much simpler synthetic systems, in order to convert sunlight into
electricity rather than chemical energy. In collaboration a CNRS French
team in Strasbourg (Dr. J.F. Nierengarten) we have designed and
investigated supramolecular systems made of two subunits, i.e. a fullerene electron acceptor and an
external aromatic part acting as light harvesting and electron donor at the
same time [Fig. 2]. Systems of this type, deposited on a solid substrate and inserted in
photovoltaic devices, has originated photocurrent following light
irradiation. This is an example of "plastic" solar cell, based on organic
materials. From the development of these systems a new generation of
photovoltaic devices is expected which, in perspective, can produce
electricity at competitive costs and limit the use of non-renewable and
polluting fossil fuels.
Dr. Nicola Armaroli, member of the staff of the photochemistry laboratory
at the Institute for Organic Synthesis and Photoreactivity has been awarded
the Grammaticakis-Neumann International Prize in Photochemistry. This prize
is presented once a year by Swiss Society for Photochemistry & Photophysics
to a young research scientist for an outstanding contribution to the
science of photochemistry (http://www.sgpp.ch/grammaticakis.html)
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