• Journal of Photoscience
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• v.6 no.4
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• pp.159-163
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• 1999

The fluorescence quenching of 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) and 1,4-di-[2-(5-phenyloxazolyl)]-benzene (POPOP) by aniline has been carried out in different solvent mixtures of dioxane and acetonitrile at room temperature. The quenching is found to be appreciable and a positive deviation from linearity was observed in the Stern-Volmer plot in all the solvent mixtures. Various rate constants for the quenching processes have been determined using a modified Stern-Volmer equation. From the positive deviations of linear Stern-Volmer plots and the dependence of rate constants on the polarity of the solvents, it has been concluded that both static and dynamic quenching processes are responsible for the observed positive deviation in the Stern-Volmer plot.

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1031-1034
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• 2009

Fluorescence of quinolones including norfloxacin, ciprofloxacin and S- and R-ofloxacin is quenched upon association with single and double-stranded DNA (ss- and ds-DNA). The ratios of fluorescence intensity in the presence of DNA to its absent were plotted with respect to the DNA concentration to construct the Stern-Volmer plot. The slope of the Stern-Volmer plot become larger as the temperature is lowered, ensuring that the fluorescence quenching is static process, i.e., the fluorescence is quenched by formation of the non-fluorescent complex between quinolone and DNA. In the static quenching mechanism, the quenching constant which is equivalent to the slope of the Stern-Volmer plot, is considered as the equilibrium constant for the association of quinolones and DNA. From the temperature-dependent equilibrium constant, ${\Delta}H^0\;and\;{\Delta}S^0$ was obtained using the van’t Hoff relation. In general, association of the quinolone with ds- as well as ss-DNA is energetically favorable (an exothermic) process while the entropy change was unfavorable. Due to the steric effect of the substituents, the effect of the quinolone ring is smaller on the ss-DNA compared to ds-DNA.

• Bulletin of the Korean Chemical Society
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• v.24 no.1
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• pp.119-122
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• 2003

• Journal of Photoscience
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• v.10 no.3
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• pp.225-229
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• 2003

The fluorescence quenching of 5-methyl-3-phenyl-2-[s-oxadiazol-2'-thionen5'-yl] indole by carbon tetrachloride ($CCl_4$) and aniline in different solvents viz., dioxane, benzene, toluene, methanol, propanol has been carried out at room temperature to understand the role of quenching mechanisms. The Stern-Volmer plots have been found to be linear. As probability of quenching per encounter 'p' is less than unity, and the activation energy for quenching 'E$_{a}$' is greater than the activation energy of diffusion 'E$_{d}$', it is inferred that the fluorescence of quenching mechanism is not due to material diffusion alone.e.e.

• Bulletin of the Korean Chemical Society
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• v.28 no.9
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• pp.1573-1578
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• 2007

Fluorescence quenching of norfloxacin (NOR) by Cu2+, Ni2+, Co2+ and Mn2+ was studied in water. The change in the fluorescence intensity and lifetime was measured as a function of quencher concentration at various temperatures. According to the Stern-Volmer plots, the NOR was quenched both by collisions and complex formation with the same quencher. However, the static quenching had a more important effect on the emission. Large static and dynamic quenching constants support significant ion-dipole and orbital-orbital interactions between NOR and cations. The both quenching constants by Cu2+ were the largest among quenchers. Also, quenching mechanism of Cu2+ was somewhat different. The change in the absorption spectra due to the quencher provided information on static quenching. The fluorescence of NOR was relatively insensitive to both the dynamic and static quenching compared with other quinolone antibiotics. This property can be explained by the twisted intramolecular charge transfer.

• Journal of Photoscience
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• v.11 no.1
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• pp.11-17
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• 2004

Fluorescence quenching of l,4-bis [2-(2-methylphenyl) ethenyl]-benzene (Bis-MSB) by carbon tetrachloride in five different solvents namely hexane, cyclohexane, toluene, benzene and dioxane has been carried out at room temperature with a view to understand the quenching mechanisms. The Stern-Volmer plot has been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the Ground state complex and Sphere of action static quenching models. Using these models various rate parameters have been determined. The magnitudes of these parameters imply that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation in the Stem-Volmer plots is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximation model, it was possible to check whether these bimolecular reactions as diffusion limited and to estimate independently distance parameter R' and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R'and D with the values of the encounter distance R and the mutual diffusion coefficient D determined using the Edwardis empirical relation and Stokes-Einstein relation.

• Textile Coloration and Finishing
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• v.13 no.6
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• pp.33-33
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• 2001

The physical properties and the dyeability of the easily dyeable polyester yarn(EDY) were investigated and compared with those of regular polyester (REG-PET). The EDY, copolymerized with small amount of polyethylene glycol(PEG), showed higher intensity of aliphatic CH peak in IR spectrum, lower density and lower compactness than those of the REG-PET from the analysis of IR, density gradient column and XRD respectively. In the physical properties, the EDY has lowers $T_g,\;T_m$, specific stress and initial modulus, and also has higher strain than that of the REG-PET. The EDY can be dyed under atmospheric pressure and its dyeing rate was faster than REG-PET due to low $T_d$, and this seems to be caused by the increased flexibility of Polymer chain in amorphous region of the EDY due to the copolymerization of PEG.ns being within the experimental error, the average values of lifetim.
$\tau$(t) are taken for further calculations. Rate constants such as Stern-Volmer quenching constants K$_{sv}$, quenching rate parameters k$_q$ and k''$_q$, static quenching constant V and kinetic distance r are determined using the modified Stern-Volmer eq.
tion and sphere of action static quenching model. In order to see whether the reactions are diffusion limited, equations k$_q$ = e$^{-Eq/RT}$ and k''$_q$ = e$^{-Eq/RT}$ are used to determine the values of E$_q$ and E''$_q$, the activati.
energies for collisional quenching and the values of E$_q$ are 14.53, 17.28 and 16.20 kJ mole$^{-1}$ for MPNO1, MPNO2 and 2-PI respectively and the values of E''$_q$ are 14.62 and 17.73 for MPNO1 and MPNO2 respectively. From the magnitudes of various quantities it has.
een concluded that the reactions are diffusion limited and the observed positive deviations in the S-V plot are due to static and dynamic quenching.

• Bulletin of the Korean Chemical Society
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• v.27 no.12
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• pp.2002-2010
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• 2006

This study examined the quenching of ofloxacin (OFL) and flumequine (FLU) fluorescence by $Cuj^{2+}$, $Ni^{2+}$, $Co^{2+}$ and $Mn^{2+}$ in an aqueous solution. The change in the fluorescence intensity and lifetime was measured at various temperatures as a function of the quencher concentration. According to the Stern-Volmer plots, the fluorescence emission was quenched by both collisions (dynamic quenching) and complex formation (static quenching) with the same quencher but the effect of static quenching was larger than that of dynamic quenching. Large static and dynamic quenching constants for both OFL and FLU support significant ion-dipole and orbital-orbital interactions between fluorophore and quencher. For both molecules, the static and dynamic quenching constants by $Cu^{2+}$ were the largest among all the metal quenchers examined in this study. In addition, both the static and dynamic quenching mechanisms by $Cu^{2+}$ were somewhat different from the quenching caused by other metals. Between $Ni^{2+}$ and FLU, a different form of chemical interaction was observed compared with the interaction by other metals. The change in the absorption spectra as a result of the addition of a quencher provided information on static quenching. With all these metals, the static quenching constant of FLU was larger than those of OFL. The fluorescence of OFL was quite insensitive to both the dynamic and static quenching compared with FLU. This property of OFL can be explained by the twisted intramolecular charge transfer in the excited state.

• Bulletin of the Korean Chemical Society
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• v.20 no.7
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• pp.796-800
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• 1999

Three anthrylazacrown ethers in which the anthracene fluorophore π system is separated from the electron donor atoms by one methylene group were synthesized, and their photophysical study was accomplished. These fluorescent compounds showed a maximum fluorescence intensity at pH=5 in aqueous solutions and a decrease in fluorescence intensity upon binding of paramagnetic metal cations (Mn 2+ (d 5 ), Co 2+ (d 7 ), Cu 2+ (d 9 )). The decrease in fluorescence intensity may be attributed to the paramagnetic effect of metal cations to deactivate the excited state by the nonradiative quenching process. The benzylic nitrogen was found to play an important role in changing fluorescence intensity. From the observed linear Stern-Volmer plot and the fluorescence lifetime independence of the presence of metal ions, it was inferred that the chelation enhanced fluorescence quenching (CHEQ) mechanism in the system is a ground state static quenching process. Enhanced fluorescence was also observed when an excess Na + ion was added to the quenched aqueous solution, and it was attributed to cation displacement of a complexed fluorescence quencher.

• Bulletin of the Korean Chemical Society
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• v.17 no.4
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• pp.358-362
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• 1996

The ionic strength dependent binding mode of 9-aminoacridine (9AA), a well-known DNA intercalator, to DNA is studied by flow linear dichroism, circular dichroism, fluorescence techniques and equilibrium dialysis. The DNA-bound 9AA exhibits spectral properties corresponding to the intercalative binding mode disregarding the salt concentrations; the angle between the long-axis transition moment of the 9AA molecule and DNA helix axis is calculated to be about 65°, indicating a significant deviation from the classical intercalation. At low salt concentrations, however, upwards bending curve in Stern-Volmer plot is observed (where 9AA is a fluorophore and DNA a quencher), indicating the coexistence of both static and dynamic quenching mechanisms or the existence of an additional binding site.