Lumophore-spacer-receptor systems

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. ... 

Lumophore-spacer-receptor systems are not by any means limited to the ami-noalkyl aromatic family even if we focus on the receptor unit. Still, the latter family is likely to remain a major provider of ionically switchable luminescent devices. Aminoalkyl aromatics also serve as the platform for the development of luminescent PET sensors for a whole class of nonionic saccharides. While aliphatic amines, either singly or in arrays, can serve as receptors for a variety of cationic... 

LUMOPHORE-SPACER-RECEPTOR SYSTEMS WITH REDOX ACTIVE GUESTS... 

Cu(II) is one of the best examples of a redox active guest, but apparently not when it is imprisoned in a cryptand such as 53. In this case, the Cu(II) is silent over a wide potential range during cyclic voltammetry. System 53 is designed as a lumophore-spacer-receptor system such as 28-30 and 33-34 in Section 1 with multiple lumophores. It also shows similar luminescence off-on switching with and even with Cu(II). The possibility of Cu(II) induced production of from moisture appears to have been ruled out. The absence of EET is a mystery which can only be dispelled by further studies on this interesting system. 

An early report [57] from Michael Schuster and his team at the Technical University of Munich, Germany highlighted the lumophore-spacer-receptor system 13 which showed strong fluorescence recovery with intrinsic quenchers... 

But the bulk of results have emerged from Shinkai s laboratories [178] in Fukuoka and Kurume, Japan. His prototypical example, 24, is essentially a classical aminomethylaromatic lumophore-spacer-receptor system with a twist that the weak B-N bond allows rather rapid PET from the amine unit to the anthracene resulting in weak fluorescence [176], The binding of glucose to produce the boronate ester leads to a much stronger B-N bond that arrests the PET process and produces a large fluorescence enhancement. 

Ionically switchable lumophore-spacer-receptor systems can also be outfitted with an additional PET inactive receptor to enhance guest binding, especially when larger organic structures are involved. For instance, GABA is one of the most important neurotransmitters with the GABA receptor being one of the most studied... 

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