Photonic antenna

Methanofullerene 20 with phenylacetylene dendrimer addends has also been reported [45] (Fig. 10). The UV absorption of fullerodendrimer 20 is particularly strong and is mainly attributed to transitions located on the two dendritic branches of the molecule. The photophysical investigations revealed that the large poly(aryl)acetylene branches act as photon antennae [46]. 

Plants are masters of efficiently transforming sunlight into chemical energy. In this process, every plant leaf acts as a photonic antenna in which photonic... 

We reported the preparation of sophisticated bipolar three-dye photonic antenna materials for light harvesting and transport [22]. The principle is illustrated in Figure 1.12. Zeolite L microcrystals of cylinder morphology are used as host for organizing several thousand dyes as monomers into well-defined zones. 

Figure 1.12. Principle of a bipolar three-dye photonic antenna. A crystal is loaded with a blue, a green, and a red emitting dye. After selective excitation of the blue dye in the middle, energy transfer takes place to both ends of the crystal where the red dye fluoresces. (See insert for color representation.)...

This chapter shows that zeolite L is a very suitable host for the arrangement of a wide variety of chromophores. The structure of zeolite L is such that the formation of non-fluorescent dimers inside the channels can be prohibited and chromophores can be aligned in a certain direction. We have shown that this host-guest system can be used to make very efficient nanoscale two-directional photonic antenna systems. A broad spectral absorption range can be achieved by using several different cationic and neutral dyes. 

The two cationic dyes, Py+ as a donor and Ox" as an acceptor, were found to be very versatile for demonstrating photonic antenna functionalities for light harvesting, transport, and capturing, as illustrated in Fig. 7. They can be incorporated into zeolite L by means of ion exchange, where they are present as monomers because of the restricted space. In this form they have a high fluorescence quantum yield and favourable spectral properties. The insertion of the dyes can be visualised by means of fluorescence microscopy. The fluorescence anisotropy of Ox -loaded zeolite L has recently been investigated in detail by conventional and by confocal microscopy techniques [15],... 

Figure 7 Simplified view of a bidirectional photonic antenna. The middle part shown in tight gray contains donor molecules D. After excitation of D to D, the excitation energy migrates with equal probability to the left and to the right until it reaches an acceptor A (dark gray) which captures the excitation energy and emits it as red-shifted light.

After this overview of photonic antenna properties, we now turn to some intriguing optical properties we have recently observed in different dye-zeolite guest-host composites. 

The dye-zeolite composites reported so far show fascinating photonic antenna properties which are perhaps comparable to some extent to those of natural systems. Tuning their chemical and photochemical behavior, organizing information exchange between their inside and the external world, but also organizing individual crystals on a surface in order to realize, for example, monodirectional functionalities remain a challenge which we address in this section. 

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