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ZnII and CdII complexes of 2,2'-bipyridyl-3,3'-diol: discrimination with time-resolved fluorometry
(1996)
Steady-state and time-resolved fluorometry of fluorescent pollutants and heavy metal complexes
(1997)
Time-resolved laser-induced fluorescence spectroscopy is one of the most sensitive optical methods which is well suited for on-line in situ analysis. Here, three examples for the steady- state and time-resolved fluorescence analysis of environmentally important analytes, the fluorescent monoaromatic hydrocarbons benzene, toluene, and xylene as well as non fluorescent heavy metal ions forming a fluorescent complex with a cation coordinating fluorescence probe, are presented and the potential of both methods is discussed. For BTX, various mixtures of the spectrally similar compounds B, T, and X showing different fluorescence lifetimes were studied with both methods. As an example for fluorometric metal ion analysis, the fluorescence probe BP(OH)2 (2,2'-bipyridyl- 3,3'-diol) was employed for the determination of d10 metal ions in water and the newly developed fluorescence probe APTA for the detection of Cu(II). Cation complexation of BP(OH2 yields spectrally very similar complexes which differ in their fluorescence lifetimes. Complexation of APTA to Cu(II) leads to small spectral changes and a strong increase in fluorescence quantum yield and lifetime. For the analytes studied, a comparison of the detection limits, standard deviations, and linear dynamic range of both methods clearly demonstrates the analytical potential of time-resolved fluorometry.
Im Rahmen dieses Projekts wurden Fluoreszenzfarbstoffe und neue intrinsische und konjugierte Fluoreszenzmarker mit Sauerstoff, Schwefel, Stickstoff-Heteromakrozyklen als kationenspezifische Rezeptoren für analytische Applikationen der zeitaufgelösten Fluorometrie von der Kiewer Gruppe synthetisiert. Die in Berlin an diesen Verbindungen durchgeführten fluorometrischen Charakterisierungen und spektroskopischen Untersuchungen zum Kationenkomplexierungsverfahren ermöglichten die Aufstellung von ersten Designprinzipien für Fluoreszenzmarker für Übergangs- und Schwermetallionen.
The photophysical behavior of a newly synthesized aza crown-substituted boron-dipyrromethene (BDP) dye and its dimethylamino analogue were investigated with steady-state and time-resolved fluorometry and compared to a reference compound. In solvents more polar than hexane, excitation of the dyes leads to a fast charge transfer from the locally excited (LE) state to a weakly emissive charge-transfer (CT) state. The donor-substituted compounds show dual emission from the LE and CT state, both fluorescence quantum yields being low. The rate constant of excited-state charge separation, calculated from the global analysis of time-resolved emission data, was determined to 1.6 × 1011 s-1 in 1,4-dioxane. The crowned compound forms 1:1-complexes with various alkali and alkaline-earth metal ions, which exist as two conformers in solution. In these complexes, coordination of the cation to the nitrogen donor atom of the crown inhibits the charge-transfer process, leading to a cation-dependent enhancement of the LE emission and the fluorescence lifetimes by factors >103. This efficient "switching on" of the fluorescence renders the crowned BDP dye an extremely sensitive fluorescent probe for metal ions.
The simultaneous analytical discrimination of spectrally very similar components with time- and wavelength-resolved fluorescence spectroscopy is demonstrated for the fluorescent probe BP(OH)2 and its complexes with the d10 metal ions CdII and ZnII in water. Whereas the absorption and emission spectra of the three components largely overlap the fluorescence lifetimes differ significantly. As a consequence, analyzing steady-state emission spectra of samples containing unknown amounts of both metal ions yields poor results for the analytical validity but the recording of fluorescence decay curves at different emission wavelengths improves the quality of the results drastically. The two techniques are compared in terms of goodness and analytical accuracy of the fit as well as analytical applicability.