Sensors luminescent molecular

The low quantum yield of the 3MLCT emission for [Pt(ClANAN)L]C104 36 (L=Ph2PCH2NHPh) is attributable to photoinduced electron transfer (PET) quenching by the amine component [38]. However, the emission intensity varies over a wide pH range in aqueous and micellar solutions presumably due to the extent of PET suppression through protonation at the amine moiety. As the amine receptor becomes protonated at low pH, quenching of the excited state is precluded. Hence the emission intensity is noticeably en- 

Compound M M distance /A UV-vis absorption3 Amax/nm Solid-state emission Amax/nm 298 K 77 K Fluid emission0 2max/nm 298 Ka 77 Kd 

The luminescent cyclometalated complex [Pt(C4ANAN)py]+ 39 immobilized in Nafion film has been observed to exhibit a solvatochromic shift in emission maximum from 530 to 650 nm upon immersion in ethanol but no effect was detected with aprotic organic solvents (Fig. 19) [41]. On the contrary, the emission of the [Pt(C4ANAN)]+ luminophore anchored on silica materials (MCM-41/-48 and silica gel) showed a blue shift from Tmax 665 to 550 nm upon exposure to pentane vapor but no shift was observed for ethanol vapor (Fig. 20). 

The distinctive shift in emission energy arising from reversible switching between 3MMLCT and 3MLCT excited states, which can be induced by intru- 

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Rogers CW, Wolf MO. Luminescent molecular sensors based on analyte coordination to transition-metal complexes. Coord Chem Rev 2002 233-234 341-50. 

Figure 16.4 Principle of the PCT (photoinduced charge transfer), chemically driven, luminescent molecular sensor based on the donor-spacer-acceptor architecture, (a) Binding of analyte trigger to the donor (green) moiety results in hypsochromic shift of absorption (emission) band (b) binding of the same analyte to the acceptor moiety (red) results in bathochro-mic shift of corresponding transition...

Abstract Silver clusters, composed of only a few silver atoms, have remarkable optical properties based on electronic transitions between quantized energy levels. They have large absorption coefficients and fluorescence quantum yields, in common with conventional fluorescent markers. But importantly, silver clusters have an attractive set of features, including subnanometer size, nontoxicity and photostability, which makes them competitive as fluorescent markers compared with organic dye molecules and semiconductor quantum dots. In this chapter, we review the synthesis and properties of fluorescent silver clusters, and their application as bio-labels and molecular sensors. Silver clusters may have a bright future as luminescent probes for labeling and sensing applications. 

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... 

Figure 16.1 Main classes of fluorescent molecular sensors of ions and molecules based on (a) quenching of luminescence by collisions with analyte (b) quenching or (c) increase of fluorescence of the complexing fluorophore (d,e) the same processes in fluorophore-receptor assemblies [1]...

Luminescence quenching in functionalized macrocycles forms the basis of a class of efficient molecular sensors for transition metals. A recent example is given by system 15b, in which an anthracene fragment has been appended to the carbon... 

The interplay between nanopartides and biological systems is of spedal relevance for semiconductor nanopartides, known simply also as quantum dots (QDs). In recent years, these have emerged as ideal systems for molecular sensors and biosensors, based largely on their sizewide variety of chemical functionalities with which QDs can be equipped that makes them ideal partners for different biosystems. In contrast to former passive optical labds, specifically functionalized QDs can operate as optical labds so as to observe the dynamics of biocatalytic transformations and conformational transitions of proteins. This development will surely open a wide variety of doors in modem nanobiotechnology. 

Accordingly, this review is focused on actual sensors, and does not cover the multitude of molecular probes or indicators that have been designed for applications in solution. A notable number of research articles and also reviews on LLCs have been published that term responsive luminescent complexes misleadingly as (molecular) sensor . These cannot be considered in the main part of this overview. Nevertheless, since several of these molecular probes can be incorporated into optical sensors as the receptor part, the next section will summarize a selection of LLC structures that respond to different types of analytes and discuss the basic processes involved. 

The second application of luminescence spectroscopy in polymer science has been as a tool to study polymer systems themselves. Here a fluorescent or phosphorescent dye is introduced into a polymer environment as a molecular sensor of the environment. One chooses the dye with a knowledge of its spectroscopy in the hopes that changes in its emission spectrum, or, in a pulsed experiment, its emission decay profile, will convey detailed molecular level information about the polymer system itself. These are the experiments which mimic applications of luminescent sensor techniques in biology, where these dyes provide information about hydrophobicity in proteins, local polarity at water-membrane interfaces, distances in antibody-antigen interactions, and a wide variety of other issues concerning system morphology and dynamics. 

Orellana G., Moreno-Bondi M.C., From Molecular Engineering of Luminescent Indicators to Environmental Analytical Chemistry in the Field with Fiber-Optic (Bio)sensors, in 15th Optical Fiber Sensors Conference Technical Digest (OFS-2002), IEEE, Piscataway, NJ, 2002 pp. 115-118 (ISBN 0-7803-7289-1). 

Optical sensors for oxygen are among the few sensors, which have found practical application for process-monitoring and clinical diagnostics. They are generally based on compounds such as platinum porphyrins or ruthenium phenanthroline derivatives (Table 17) which show a decrease in luminescence upon exposure to molecular oxygen15. 

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. 

Keywords Luminescence m Fluorescence m Phosphorescence a Sensors a Switches a Logic Gates a Supramolecular Systems a Truth Tables a Photoinduced Electron Transfer a Molecular-Level Devices... 

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