Photo-induced electron transfer sensors

Gunnlaugsson and co-workers have studied several receptors containing a thiourea group attached to an anthracene moiety [33]. These compounds were designed to behave as fluorescent PET (photo-induced electron transfer) sensors for the detection of anionic species. Proton NMR titration experiments, conducted in DMSO-de, confirmed that the anions bind to the... 

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... 

Most fluorescent PET molecular sensors, including pH indicators of this type, consist of a fluorophore linked to an amine moiety via a methylene spacer. Photo-induced electron transfer (see Chapter 4, Section 4.3), which takes place from amino groups to aromatic hydrocarbons, causes fluorescence quenching of the latter. When the amino group is protonated (or strongly interacts with a cation), electron transfer is hindered and a very large enhancement of fluorescence is observed. 

The mechanism of the change of fluorescence intensity of xanthene-based fluorescent sensors was also studied, and it was hypothesized that photo-induced electron transfer between the xanthene and 9-aromatic moiety might be important. Nagano and Urano et al. systematically synthesized xanthene derivatives bearing various substituted phenyl groups at the 9-position, and confirmed that electron transfer has a significant role in their fluorescence properties they also showed that the determinants of electron transfer efficiency are physical parameters of the xanthene or... 

Fluorescence characteristics of the products were studied in relationship to complexing activity, and the 2- and the 6-derivatives can be used as fluorescence sensors. Treatment of p-cyclodextrin with the disulfonyl chloride 24 gave capped derivatives linked through 0-6 of the AD rings or AC rings in the ratio 76 24. Yields were low, but the products are potential hosts for photo-induced electron transfer reactions. In related work cycloinulohexaose was capped by use of diphenyl-4,4 -disulfonyl chloride through 0-6 of the A-C related units. This allowed displacement reactions and, for example, phenylthio-derivatives could be made in the AC relationship. ... 

These ICT sensors have one drawback for potential real-world sensor development, which is pH sensitivity. In the case of fluorescent photo-induced electron transfer (PET) sensors, the interaction between o-methylphenylboronic acids (Lewis acids) and proximal tertiary amines (Lewis bases) has been exploited, while the precise nature of the amino base-boronic acid (N- B) interaction is deba-jgjj 8,9,27,29 jjjg interaction between a boronic acid and proximal amine lowers the p Ta of the boronic and allows pH-insensitive binding over a wide range. 

The mechanism by which the addition of sugar enhances fluorescence response is shown in Figure 13.4. In this fluorescent sensor, the pyrene fluorophore serves as an electron donor and the phenylboronic acid moiety serves as an electron acceptor. In other words, photo-induced electron transfer (PET) from the donor (pyrene) to the acceptor (acidic or neutral form of phenylboronic acid) causes quenching in the absence of sugar. 

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