Singlet molecular probes

Fluorescence of Excited Singlet-State Acids in Certain Organized Media Applications as Molecular Probes... 

Chemical methods can also be employed to assess the competition between the formation of 02 and O2. A specific chemical probe may react either with 02 or O2 and 5ueld a fluorescent product. For example, nonfluorescent 3 -(p-aminophenyl)fluorescein reacts with hydroxyl radicals, formed subsequently to the formation of O2, to give fluorescein as oxidation product (83), whereas Singlet Oxygen Sensor Green (Molecular Probes) specifically reacts with 02 to give another fluorescent product (84). Admittedly, this again is not a direct comparison between 02 and O2, and the conversion... 

Case 4 Only the quencher migrates. This is the most common situation with excited singlet state probes. The quenching efficiency will be determined by the rate of access of the quencher to the supramolecular strucmre ( g+[H]) and the efficiency of quenching within the supramolecular system The association to the supramolecular complex is a bimolecular process, whereas the quenching efficiency within the supramolecular structure is viewed as a uni-molecular process. This picture is concepmally analogous to the formation of an encounter complex in solution before reaction, where the volume of the encounter complex is defined by the supramolecular structure. Thus, an overall effective quenching rate constant [ q(eff)] can be defined which takes into account the association process and the intrinsic reactivity ... 

In this chapter, we concentrate on luminescence approaches that are most suitable for stilbenes to be molecular probes and are based on specific and nonspecific labeling, competition, solvatochromism, experimental molecular dynamics, and singlet-singlet and triplet-triplet energy transfer. A general survey is made of the physical principles and application of the fluorescence probe methods stressing on latest developments in this area. 

The molecular probe pyrene is commonly employed to elucidate solute-solvent interactions in normal liquids (18,35). Because of the high molecular symmetry, the transition between the ground and the lowest excited singlet state is only weakly allowed, subject to strong solvation effects (36-39). As a result, in the fluorescence spectrum of pyrene the relative intensities of the first (/i) and third I2) vibronic bands vary with changes in solvent polarity and polarizability. The ratio h/h serves as a convenient solvation scale, often referred to as the Py solvent polarity scale. Py values for an extensive list of common liquid solvents have been tabulated (15,16). 

Mishra, A.K., Fluorescence of excited singlet state acids in certain organized media Applications as molecular probes, in Understanding and Manipulating Excited State Processes, Molecular and Supramolecular Photochemistry Series, V. Ramamurthy and K.S. Schanz lids., Marcel Dekker, New York, 2001, vol. 8, chap. 10. 

By fluorescence analyses just upon laser ablation and of ablated surface, Molecular aspects of ablation echanisa were elucidated and a characterization of ablated Materials was perforaed. Laser fluence dependence of poly(N-vinylcarbazole) fluorescence indicates the iaportance of Mutual interactions between excited singlet states. As the fluence was increased, a plasna-like eaission was also observed, and then fluorescence due to diatonic radicals was superinposed. While the polyner fluorescence disappeared Mostly during the pulse width, the radicals attained the naxinun intensity at 100 ns after irradiation. Fluorescence spectra and their rise as well as decay curves of ablated surface and its nearby area were affected to a great extent by ablation. This phenonenon was clarified by probing fluorescence under a Microscope. 

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