Photophysical probes

Figure 13.12 Functional moieties used as photophysical probes...

Another spectroscopic method that has been used to study the multiphasic structure of Nafion uses photophysical probes. This is well explained in a paper by Kalyanasundaram and Thomas, and references therein. These authors studied the perturbations of the five predominant vibronic band intensi-... 

Photophysical Probes of DNA Sequence-Directed Structure and Dynamics... 

Ionic liquids are a class of solvents and they are the subject of keen research interest in chemistry (Freemantle, 1998). Hydrophobic ionic liquids with low melting points (from -30°C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also of interest. NMR and elemental analysis have characterized the molten salts. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1,2, 3, and 4(5)-positions on the imidazolium cation on these properties has been scrutinized. Viscosities as low as 35 cP (for l-ethyl-3-methylimi-dazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of l-ethyl-3-methyl-imidazolium bis((trifluoromethyl)sulfonyl)amide. The hydrophobic molten salts are promising solvents for electrochemical, photovoltaic, and synthetic applications (Bon-hote et al., 1996). 

Use of Photophysical Probes to Study Dynamic Processes in Supramolecular Structures... 

Photophysical Probes for Organized Assemblies Kankan Bhattacharyya... 

The data concerning [Rn(phen)2(dppz)] + nicely illustrate the concept of molecnlar light switch (dppz for 28). When the complex is bonnd to DNA, the excited-state lifetime is approximately 200 ns, whereas withont bonnding, it is only 200 ps. This light-switch effect provides the basis for a valuable photophysical probe of nucleic acids. Luminescent characteristics of the complexes bonnd to DNA can also be used to illustrate the chiral discrimination associated with binding to the right-handed hehx. Direct oxidation of... 

Photophysical processes can be used to probe the local structure of organized systems that are difficult to characterize by conventional analytical protocols. Photophysical probes provide valuable structural information for monolayers assembled on metal supports and for polymeric composites. In the latter case, it has been possible to determine the level of thermal residual strain and to monitor architectural deformations. Fluorescence from single molecules continues to attract great attention while the dynamics of photodissociative processes have been reviewed, with emphasis given to experimental techniques. ... 

Pyrene has been used widely as a photophysical probe because of its long fluorescence lifetime and great tendency for excimer formation. Emission characteristics of pyrene molecules depend on the nature of the solvent. The ratio of relative intensities of the 1st (373 nm) and lllrd (383 nm) peaks, Ijjj/Ij, in a pyrene emission spectrum decreases as the polarity of the solvent increases. This... 

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