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Artificial photonic antenna systems have been realised by incorporating organic dyes in a nanoporous material.
We have been using zeolite L in most of our experiments as it has proven to be a very versatile host. Its crystals
are cylindrically shaped porous aluminosilicates featuring hexagonal symmetry. The size and aspect ratio of the
crystallites can be tuned over a wide range. A nanometre sized crystal consists of many thousand one-dimensional
channels oriented parallel to the cylinder axis. These can be filled with suitable organic guests.
Geometrical constrains of the host structure lead to supramolecular organisation of the guests in the channels.
Thus very high concentrations of non- or only very weakly interacting dye molecules can be realised. A special
twist is added to these systems by plugging the channel openings with a second type of fluorescent dye, which
we call stopcock molecule. The two types of molecules are precisely tuned to each other; the stopcocks are able
to accept excitation energy from the dyes inside the channel, but cannot pass it back. The supramolecular
organisation of dyes inside the zeolite channels is what we call the first stage of organization. It allows light
harvesting within the volume of a dye-loaded zeolite L crystal and also radiationless energy transport to either
the cylinder ends or centre. The second stage of organisation represents the coupling to an external acceptor or
donor stopcock fluorophore at the ends of the zeolite L channels, which can then trap or inject electronic
excitation energy. The third stage of organization is realised by interfacing the material to an external device via
a stopcock intermediate. We observed that electronic excitation energy transfer in dye-zeolite L materials occurs
mainly along the channel axis. This important finding means that macroscopically organised uni-directional
materials can be prepared. In order to achieve this, we prepared oriented zeolite L monolayers, filled them with
luminescent dyes, and finally added a stopcock. The new materials offer unique possibilities as building blocks
for optical, electro-optical and sensing devices.
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