Crown-containing PET sensors

Various examples of PET sensors will be now presented these are classified according to the chemical structure of the recognition moiety. 

In PET-4, the crown does not contain nitrogen atoms but four sulfur atoms and is known for its strong affinity towards Cu11. This sensor is also based on the PET 

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Fig. 10.TI. Crown-containing PET sensors (PET-1 de Silva A. P. and de Silva S. A. (1986) J. Chem. Soc., Chem. Commun. 1709.

Examples of PET sensors containing various kinds of crowns are given in Figure 10.11. PET-1 is the first and simplest coronand PET sensor. Its fluorescence quantum yield increases from 0.003 to 0.14 upon binding of K+ in methanol. 

Chemically modified crowned spirobenzopyran 112, containing a pyrenyl fluorophore attached at the nitrogen atom, can function as a fluorescence emission switch <2004T6029>. This sensor displayed a quenching of the PET fluorescence emission of the fluorophore in the absence of metal ions (the merocyanine form was not produced). When, however, the spiro form of 112 was converted into the merocyanine form by metal ion complexation of the crown ether portion of the molecule, a fluorescence resonance energy transfer (FRET) from the pyrene to the merocyanine moiety took place, producing fluorescence emission. 

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