Quench luminescence

Figure 3.40 Example of the Perrin plot of static quenching. Luminescence of a metal complex [Ru (bpy)32+] in rigid glycerol in the presence of increasing concentrations of methylviologen (quenching by electron transfer)...

A PET reporter site tethered to the rim of the bucket allows the chemosensing strategy of Scheme 12 to be developed. In this construct, the bucket simply acts as a scaffold for the PET reporter site. The receptor is not required for analyte recognition and large changes in conformation are not required for signal transduction. Rather, electron transfer from a lone pair to the frontier orbitals of the excited reporter quenches luminescence, which is recovered by the interaction of the analyte with the lone pair (see Fig. 6). 

Figure 19 Signal amplification produced from chemosensors wired in series. The method has been most thoroughly elaborated for signal transduction derived from a quenching process, (a) Luminescence quenching from individual monomer subunits upon molecular recognition, (b) Signal response from receptors wired in series. Only fractional occupancy is required to quench luminescence from polymer backbone. (Adapted from Ref. 6.)...

Measuring the variations of the intensity ratio /inp/Zyb under pressure, Takarabe (1996) was able to determine the energy difference bt and found a pressure-induced shift of 70 meV/GPa which is close to the shift of the band-edge related luminescence due to the bound e-h pairs. Furthermore, under pressure it was possible to completely recover the thermally quenched luminescence of the Yb3+ ion at temperatures of 220 K and 260 K (Takarabe et al., 1994) as well as at room temperature (Takarabe, 1996). The minimum pressure at which the luminescence could be observed again was shown to increase with increasing temperature. All these facts fitted well to the proposed back-transfer model, which was thus strongly supported by the pressure experiments. 

Protons are relatively simple targets for sensor molecules and do not require engineered receptors, however, achievement of selective interactions with other chemical species requires much more elaborate receptors. In the most cases cations are bound via electrostatic or coordinative interactions within the receptors alkali metal cations, which are rather poor central ions and form only very weak coordination bonds, are usually bound within crown ethers, azacrown macrocycles, cryptands, podands, and related types of receptor moieties with oxygen and nitrogen donor atoms [8], Most of the common cation sensors are based on the photoinduced electron transfer (PET) mechanism, so the receptor moiety must have its redox potential (HOMO energy) adjusted to quench luminescence of the fluorophore (Figure 16.3). 

Weak interchain electronic coupling. Interchain excited state complexes (e.g. excimers and exciplexes), which may quench luminescence. Dephasing of inter-molecular wavefunctions. 9... 

The addition of trace l-AA caused significant quenching luminescence 6.7x10-3 No data <5.3 Human serum 2010 132... 

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