Much in the way that the chlorophyll in plants collects sunlight, synthetic
molecules have been designed to harvest incoming light. Light harvesting
has been demonstrated with conjugated polymers, in which multilayered
systems can exhibit an increase in surface fluorescence. These systems have
been limited to thin films of up to 16 layers, because beyond this,
internal energy losses reduce the light-collecting abilities.

Now Kim et al. have overcome this problem by maximizing the one-dimensional
energy transfer by using a series of photoluminescent polymers. The systems
are designed to have a large spectral overlap, so that the emission spectra
maxima of the lower layers are similar to the absorbance spectra maxima of
the higher layers. Energy is transferred through the thickness of the
sample, because any photons traveling back toward the substrate are not
absorbed by the lower layers. The interfaces between the different
materials create energy traps and thus a decrease in the photoluminesence.
Nevertheless, the preferential transfer of the energy toward the surface is
increased. These materials can be used as very sensitive sensors for light-
trapping materials, such as the explosive TNT. -- MSL

J. Am. Chem. Soc., ASAP paper