Basic Ideas for Future Developments

A large number of sensitive fluorescent probes are now available for the measurement of pH and of the concentration of ions. 

Each indicator has to be designed according to the ion probed in its particular environment and the technique used, so that the possibility of preparation of a universal molecular system is unlikely. The indicators have to fulfill some minimum requirements. Obviously, the binding properties of the ionophore have to be matched with the target ion to be monitored in its environment. But also the electronic interaction of the ionophore with the fluorophore in the ground or the excited states has to be significantly altered by the presence of the ion. 

Some of the research directions under current consideration contain the following ideas  

For this type of integrated fluoroionophores, the photochemical processes can be accelerated and can lead to very fast and reversible photochemical ion release or ion takeup. One example has been described recently 140 where Ca2+ or Li+ is ejected in some picoseconds. By this way, the application of biologically useful chelators, which have their binding constant altered by an irreversible photoreaction taking at best some milliseconds, 141 can be extended to ultrashort time scales. 

As shown above with the example of Rhodamine dyes, TICT channels can be introduced into most other dye systems giving a large flexibility in choosing absorption and emission wavelengths to adapt to given conditions of the material to be investigated. 

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