Guests chemosensors

Several pyridyl-substituted indolizines are fluorescent and their photophysics have been studied <1999MI155, 2002MI279>. This property has found application in the synthesis of indolizine-substituted /3-cyclodextrins <2005T3939> used as fluorescent chemosensors for organic guest molecules <2005CAR1706, 2005JFC385>. 

The combination of dyes with microporous materials opens-up a way to develop selective chemosensors microporous zeolites with an anchored squaraine 27 (Fig. 13) and some other types of dyes can be used as chemosensors for the chromogenic discrimination of amines [75], These dye-zeolite hosts are expected to be promising sensor materials allowing the visible discrimination of selected target guests by size and/or polarity within families or closely related molecules. It was found that the response of the solid to amines was basically governed by the three-dimensional architecture of the solid material. 

Ueno et al. also prepared the b i s (2 - n ap h t h y I s u I fe n y 1) - y - CD series in which the naphthyl moieties are very limited in their movement because the linker between naphthalene and CD is only sulfur [37], All isomers of 12(AB), 13(AC), 14(AD), and 15(AE) exhibit only monomer fluorescence due to the rigid linker. It means that the two naphthalene moieties cannot take face-to-face orientation because of the limited flexibility. Although the excimer cannot be used for sensing molecules, Ueno et al. found that the monomer fluorescence intensity increases with increasing guest concentration. Thus, this modified CD series can be used as chemosensors of a different type. 

Calixarenes modified with a reporter site are equally competent chemosen-sors for the detection of a variety of analytes according to Scheme 6, especially when the analyte is cationic. The tt-cavity of a tetraanionic resorcin[4]arene readily binds cationic guests, a feature that Inouye et al. have exploited in the development of an acetylcholine chemosensor [358], The fluorescence from a pyrene-modified N-alkylpyridinium is strongly quenched upon its association with the tetraphenolate form of resorcin[4]arene (24). This quenching is consis-... 

As far as chemical sensors are concerned, colorimetric chemosensors for anions based on calix[4]pyrrole (16-18, 22-31) showed strong binding to the fluoride anion. Receptors (29-31) are the first naked-eye detectable chemosensors that are able to discriminate between different anionic substrates as a result of detectable colour changes. On the other hand, the fluorescence of the receptors (16-18, 22-28) is quenched significantly in the presence of anionic guests. 

Park JS et al (2010) Positive homotropic allosteric receptors for neutral guests annulated tetrathiafulvalene-calix[4]pyrroles as colorimetric chemosensors for nitroaromatic explosives. Chemistry 16 848-854... 

Cyclodextrins have been used for enhancing the phosphorescence of guests by encapsulation [12]. de Silva et al. employed cyclodextrins as transparent shields to protect the phosphor molecule sterically from contact with its environment (especially O2) while allowing access to photons. Sensing remains viable because the proton receptor module is not enveloped (Figure 9) [13]. The authors used this system as a phosphorescent PET (photoinduced electron transfer) chemosensor for... 

Binding a Molecular Entity with Selectivity. While much of organic chemistry focusses on the selective creation of covalent bonds, such irreversible associations of potential analytes yield chemodosimeters (designed for cumulative assay) in contrast to chemosensors (designed for real-time assay). Thus, sensing applications require the existence of receptors (hosts) that associate with analytes (guests) selectively and reversibly. 

Other applications of photochemistry include the development of sensitive fluorescent chemosensors for analysis of dilute solutions of inorganic cations and anions and the study of the diffusion of individual molecules in solution at room temperature. Fluorescent compoimds have been used as replacements for radioisotopes in the analysis of biological compoimds and the study of biologically active compounds and living systems. Photochemical reactions also offer alternative probes for the characterization of the microenvironments in diverse solid and liquid media, including crystals, zeolites, alumina, silica and clay surfaces, semiconductor surfaces, liquid crystals and host-guest inclusion complexes, polymer films, monolayers and supported multilayers of surfactant molecules, mi-celles, and dendrimers. ... 

By linking two L-tryptophan units at the lower rim of calix[4]arenes through amide bonds. He et al. synthesized three chiral receptors (92a-c) that, together with other similar hosts reported by the same authors and discussed in recent review articles, can be used as fluorescent chemosensors for the enantioselective recognition of amino acid anions and other chiral guest species. Host 92b formed the most stable 1 1 complexes in DMSO-[Pg.860]

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