PET sensor

The scientists from Hong Kong reported83 on a sol-gel derived molecular imprinted polymers (MIPs) based luminescent sensing material that made use of a photoinduced electron transfer (PET) mechanism for a sensing of a non-fluorescent herbicide - 2,4-dichlorophenoxyacetic acid. A new organosilane, 3 - [N,V-bis(9-anthrylmethyl)amino]propyltriethoxysilane, was synthesized and use as the PET sensor monomer. The sensing MIPs material was fabricated by a conventional sol-gel process. 

Fluorescent lamp coatings, ethylene oxide polymers in, 10 688-689 Fluorescent lamps, mercury in, 16 41 Fluorescent lighting phosphors, cerium application, 5 688-689 Fluorescent photo-induced electron transfer (PET) sensor, 24 54 Fluorescent pigments, for inks, 14 318 Fluorescent probes, 11 150 16 388 modified-base oligonucleotides as, 17 633-634... 

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.

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

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. 

Figure 10.14 shows examples of chelating PET sensors. PET-12 to PET-14 are selective for calcium. In PET sensors, the changes in fluorescence quantum yield are accompanied by proportional changes in excited-state lifetime. Therefore, compounds PET-12 to PET-14 were found to be suitable for fluorescence lifetime imaging of calcium. 

A distinct advantage of PET sensors is the very large change in fluorescence intensity usually observed upon cation binding, so that the expressions off-on and on-off fluorescent sensors are often used. Another characteristic is the absence of shift of the fluorescence or excitation spectra, which precludes the possibility of intensity-ratio measurements at two wavelengths. Furthermore, PET often arises from a tertiary amine whose pH sensitivity may affect the response to cations. 

This type of probe, often called fluorescent photoinduced electron transfer (PET) sensors, has been extensively studied (for reviews, see Refs. 22 and 23). Figure 2.2 illustrates how a cation can control the photoinduced charge transfer in a fluoroiono-phore in which the cation receptor is an electron donor (e.g., amino group) and the fluorophore (e.g., anthracene) plays the role of an acceptor. On excitation of the fluorophore, an electron of the highest occupied molecular orbital (HOMO) is promoted to the lowest unoccupied molecular orbital (LUMO), which enables photoinduced electron transfer from the HOMO of the donor (belonging to the free cation receptor) to that of the fluorophore, causing fluorescence quenching of the latter. On... 

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... 

System 22 is an earlier example which incorporates Tsien s selective calcium receptor 23. ° System 23 has also been employed for the construction of ratiometric fluorescent sensors involving wavelength shifts. System 22 and other related PET sensors provide some of the most visually dramatic fluorescence off-on switching induced by biologically relevant levels of calcium ions in addition to their consistent predictability of most sensor parameters. 

The predictive power of the luminescent PET sensor principle is again apparent here. Further, the benzocrown ether and the amine receptors would selectively bind Na" and H, respectively. A remarkable feature here is that no molecular wiring is needed to allow the human operation of this two-input molecular device. The device self-selects its own ion inputs into the appropriate signal channels by means of the chemoselective receptor modules. Since the output signal is fluorescence, even a single molecule can interface with detectors in the human domain, including the dark-adapted eye. Tanaka s 45 is another example where fluorescence quenching is achieved only when Ba and SCN are present. This was mentioned in Section 6. Similarly, several sensor systems—1,17, and 21—could be employed... 

Fig. 8.14 PET sensor (schematic according sponding energy levels of the uncomplexed...

Balzani, Vogde et al. demonstrated for dendritic cyclam compounds that signalling units are dendritically amplified by increasing the number of peripheral fluorophores. Opportunities for these PET sensor systems exist in the combination of selective coordination sites with the dendritic architecture. The mechanism resembles that described above, but can be influenced by the introduction of dendritic units of different generations into the sensor system. The distance between the terminal naphthalene groups of the dendron and the receptor (ion as guest in the cyclam core) is of crucial importance for electron transfer (ET) (Fig. 8.15) [53],... 

The structural mutation of our 29 by variation of the macrocycle (via its heteroatoms and carbon bridges), the lumophore, and the spacer is obviously a rich vein to mine for luminescent PET sensors. Kubo s laboratory (formerly at Kyushu University, now at Kanagawa University, Japan) has systematically explored this line [81-84], 33 has a straight swap of 1-pyrenyl for 9-anthryl [81]. 34 to 36 [81-83] use two nitrogens in the crown ether instead of the one in 29,... 

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