Spacer—Receptor Systems Normal Logic

LUMOPHORE-SPACER-RECEPTOR SYSTEMS (NORMAL LOGIC) 

The switching efficiency of lumophore-spacer-receptor systems can be improved by using multiple receptor modules. The PET rate is increased in the device when free of guest ions since more than one site can provide the transiting electron. The simplest cases, such as 4, are those where the receptor units are well separated to prevent interdependent ion binding with an interposed lumophore to minimize the lumophore-receptor spacing for maximum PET rates. Besides this statistical effect, receptors may also cooperatively participate in PET. This may be the case in 5 and 6.  

Lumophores other than hydrocarbons have been incorporated into the aminoalkyl aromatic family of ionically switchable luminescent devices. For instance, metal-loporphyrin systems such as have been used to good advantage. These cases absorb and emit at wavelengths as long as 596 and 650 nm, respectively. Such red-shifted systems are particularly attractive for monitoring ion movements in 

The PET systems of the aminoalkyl aromatic type discussed so far display a very simple behavior in that luminescence intensity (or quantum yield) is the only variable. Such systems are very user-friendly as a result and tolerate a wide variety of communication wavelengths. However these simple systems could be adapted to include an additional absorptiometric sensing channel which can confirm the results of ion density (pH say) obtained via luminescence. Of course, such increased user-confidence is only attained with a proportionate reduction in simplicity. Now excitation needs to be done at the isosbestic wavelength. These systems, e.g. 11 and 12, use a push-pull fluorophore with electron donor and acceptor substituents which give rise to internal charge transfer (ICT) excited states. In contrast, the simple PET systems employed aromatic hydrocarbon fluorophores with essentially pure nn excited states. The charge separation in ICT states can cause electrostatic 

This is the first demonstration of self-regulated PET, i.e. the PET process is controlled by the characteristics of the lumophore within the working device. Self-regulation is an important aspect of self-organized molecular proc- 

---