Photonics guest/host systems

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. 

To realize the above system, it is required to design a polymer which reversibly changes the molecular properties, such as hydrophilicity, by the external stimulation. Many molecules are known to be reversibly transformed to other isomers by external stimulation, such as photons, electrons or chemicals. Table 1 lists a few examples. Azobenzene shows the property change by photoirradiation. It isomerizes from the trans to the cis form by ultraviolet irradiation, and the dipole moment increases from 0.5 to 3.1 deb ye. The polar cis form returns to the less polar tram form by visible irradiation. Electrochemical oxidation of ferrocene changes the hydrophilicity. When it is oxidized from Fe(II) to Fe(III), the hydrophilicity increases. The Feflll) state returns to the Fe(II) state by either electrochemical or chemical reduction. Host molecules also change the properties in the presence of suitable guest ions. Benzo[18]crown-6, for example, captures potassium ions in the cavity, and increases the hydrophilicity. 

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