Abstract

Host–guest composites with photonic antenna properties are described. The material consists of cylindrical zeolite L crystals the channels of which are filled with chains of joined but electronically non-interacting dye molecules. Light shining on a crystal is first absorbed and the energy is then transported by the dye molecules inside the tubes to the desired part. Data on crystals in the size range of 30 nm up to 3000 nm are reported. The synthesis principle we are using is based on the fact that molecules can diffuse into individual channels. This means that given the appropriate conditions, they can also leave the zeolite by the same way. In some cases, however, it is desirable to block their way out, for stability reasons. This is done by adding a closure molecule. The general approach to connect the antenna function to its surroundings is to add “stopcock” molecules which generally consist of a head, a spacer and a label. They can either trap excitation energy on the external surface or inject excitation energy into the dye-loaded crystal. The stopcock molecules act as bridges between the dye molecules inside the channels and the outside world. Functionalisation of the closure and the stopcock molecules is an option for tuning e.g. wettability, refractive index, and chemical reactivity.

The wide-ranging tunability of the dye–zeolite L composites makes them useful for many applications. We discuss demonstration experiments which show the process of energy transfer and energy migration as educational tools, applications as high quality and non-toxic pigments, use as strongly luminescent pigments applicable as colour-changing media for LEDs, options for realising nanoscaled laser materials, and finally the challenge for realising solid state solar cells based on sensitisation of a thin semiconductor layer by energy transfer, the reversal of which can also lead to a new generation of LEDs.