Photoinduced Electron Transfer PET

PET corresponds to the primary photochemical process of the excited-state species, R — I, where R can be an electron donor or electron acceptor when reacting with another molecule, M. 

Photoinduced electron transfer (PET) has been widely used as the preferred tool in fluorescent sensor design for atomic and molecular species [53-56]. PET sensors generally consist of a fluorophore and a receptor linked by a short spacer. Changes in 

Two Other systems are worthy of special mention since they differ from that outlined above The simple monoboronic acid 15 used by James and co-workers, which can selectively signal the fiiranose form of saccharides [61], and the on-ofP PET system 16 of Kijima, where steric crowding on saccharide binding breaks the B-N bond found in the free receptor [62]. 

Liimane et al. have attempted to use the calixarene framework 21 as a core on which to develop novel saccharide selective systems [70]. Observed pp for 21 were 115 for D-fructose and 24 for D-glucose in 33.3 wt% methanol-water at pH 7.77 (phos- 

Diboronic acid 22 with a small spacing of the boronic add groups has been synthesized by James and co-workers and shown to be selective for D-sorbitol [72]. The for 22 were 350 M for D-sorbitol and 330 for D-fructose in 300 1 (v/v) water-methanol at pH 8.0. Conversely, diboronic add 23 prepared by Linnane et al. with a larger spacing between the boronic add groups loses selectivity and sensitivity [73]. 

An allosteric diboronic add 25 has been prepared by James with this system formation of a 1 2 metal/crown sandwich causes the release of bound saccharide due to a metal induced conformational change [75]. 

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Saeva, F. D. Photoinduced Electron Transfer (PET) Bond Cleavage Reactions. 156, 59-92... 

James TD (2007) Saccharide-Selective Boronic Acid Based Photoinduced Electron Transfer (PET) Fluorescent Sensors. 277 107-152... 

The second group of intermolecular reactions (2) includes [1, 2, 9, 10, 13, 14] electron transfer, exciplex and excimer formations, and proton transfer processes (Table 1). Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. PET is involved in many photochemical reactions and plays... 

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. 

Radical cations can also be produced in solution by photoinduced electron transfer (PET) in polar solvents. Although this method is widely used to study the processes involved in the formation and decay of ion pairs224, free radical cations appear only as transients in such experiments. 

Tetrahydropyrrolo[l,4]oxazine 74, obtained by photoinduced electron-transfer (PET) oxidative activation of substituted prolinol, undergoes nucleophilic substitution of the OH at position C-3 with allyltrimethylsilane in the presence of TiCU (Scheme 8). The reaction was highly stereoselective and produced, after hydrolysis of the resultant amide 75, optically active a-hydroxy acid 76 together with the auxiliary (.S )-prolinol that can be effectively recycled <1998TL7153>. 

Parkesh R, Lee TC, Gunnlaugsson T (2007) Highly selective 4-amino-1,8-naphthalimide based fluorescent photoinduced electron transfer (PET) chemosensors for Zn(II) under physiological pH conditions. Org Biomol Chem 5 310-317... 

Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. This process is involved in many organic photochemical reactions. It plays a major role in photosynthesis and in artificial systems for the conversion of solar energy based on photoinduced charge separation. Fluorescence quenching experiments provide a useful insight into the electron transfer processes occurring in these systems. 

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... 

Electronic excitation of molecules lead to a drastic change of their reactivities. One effect of the excitation is the powerfiil change of the redox properties, a phenomenon which may lead to photoinduced electron transfer (PET) [1-4] The electron-donating as well as the electron-accepting behavior of the excited species are approximately enhanced by excitation energy. This can be explained by means of a simple orbital scheme. By excitation of either the electron donor (D) or the acceptor (A) of a given pair of molecules, the former thermodynamically unfavorable electron transfer process becomes exergonic (A et) (Scheme 1). 

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