Lumophore

The key features of the EHI system are the monochromators and PUT assembly, since the former allow for minor variations In excitation or emission wavelength that may be necessary to differentiate lumophores of closely related structure, and the latter provides a means of quantitating luminescent species under study. Each monochromator has a resolution capability of 1 nm, and we anticipate that by careful selection of excitation and... 

From a different perspective, the lumophore appended receptor represents a molecular-scale light switch, which is triggered by a chemical species (whether or not it is of biological or technological consequence). Thus, photonic signals can be chemically generated with spatial, temporal, colour... 

A similarly wide choice of lumophores can be found within photophysics and photochemistry.191 The excitation (or absorption) and emission bands of luminescence come in a variety of wavelength positions, intensities and shapes. Another parameter, which is gaining in popularity among designers, is the luminescence lifetime. Time-resolved observation is a neat way of dissecting out the response of the luminescent device from the emissive noise of real-life matrices. Photostability of lumophores is a parameter which perhaps deserves more attention as more and more demanding applications are being tackled. 

Now that receptors and lumophores have been sourced, we can focus on how they can be joined to create the devices we are seeking. This objective can be achieved in two fundamentally different ways directly or via a connector (Figure l).1101 The former... 

On examining structure 1, we notice the steric crowding at the link between the tetracarboxylate receptor and the linearly fused tricyclic system. Thus, orthogonalization occurs at this link, making it a virtual spacer. The spatial isolation of the two ji-electron systems allows us to describe the tricyclic unit as the lumophore. The tetracarboxylate receptor also coexists as a clearly distinguishable module. 

The mechanistic basis of 3 and 4 is a double application of the argument used for the YES operation with 1. Each receptor in 3 is capable of launching a PET process if the lumophore is powered up by ultraviolet excitation. In other words, the fluorescence of the 9-cyanoanthracene unit is efficiently quenched by either the amine or the 1,2-dioxybenzene group within the benzo-15-crown-5 ether unit. These quenching processes are predictable from thermodynamic calculations or from related bimolecular quenching experiments in the literature. The small separation of the amine from the lumophore ensures rapid PET kinetics. On the other hand, the presence of four bonds between the benzo-15-crown-5 ether and the lumophore is probably responsible for the incomplete quenching seen between this pair. No information is yet available regarding possible folded conformations of 3. 

However, there is an important subtlety in 4. While amine receptor-anthracene lumophore pairs produce excellent PET based quenching, a benzo-15-crown-5 ether receptor is demonstrably incapable of transferring an electron to an excited anthracene lumophore unless the latter carries an electron withdrawing substituent. Then, what is the secret of 4 s success First, only one rapid PET process is... 

Connecting lumophores and receptors with spacers permits the build-up of modular systems of increasing logical complexity. Even the simplest of these systems can be powerful molecular sensors. 

Metal-to-hgand charge transfer (MLCT) systems are mostly based upon complexes of ruthenium and rhenium. The simplest and best known example of a MLCT lumophore is tris(2,2 -bipyridyl)ruthenium(ii) where photon absorption leads to an excited state composed of a centre and a radical anion on one of the bipyridyl units. 

Such systems can undergo ion recognition when made up of a ruthenium or rhenium polypyridyl lumophore and a crown ether receptor for metal ions, similar to the ICT examples given above. There are many examples in the hterature, but one will have to sufhce in this context. Compound (3.85) is interesting because it shows significant luminescence enhancement with Pb. ... 

Upon photoexcitation, lumophores, especially those with groups held outside but close to the Jt-electron system of the lumophore, show an increased susceptibility to redox reactions. Knowledge of the redox potentials of these reactions can be used... 

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... 

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-... 

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... 

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