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- Fluorescence (2)
- Fluoreszenz (2)
- Ionophor (2)
- 2,2´-Bipyridyl-3,3´-diol (1)
- Bifunctional (1)
- Biphenyl (1)
- Calcium (1)
- CdII (1)
- Cyaninfarbstoffe (1)
- Fluorescent probe (1)
The acceptor strength of the boron-dipyrromethene chromophore in directly linked donoracceptor compounds can be tuned by substituents in such a way that a fast excited state charge transfer takes place even for the comparatively weak benzo crown electron donor. This leads to strong fluorescence quenching. Upon binding of cations (Na+ and K+) to the benzo crown receptor, the donor properties of the latter are further reduced, partly suppressing charge transfer. Large fluorescence enhancement factors and cation-selective fluorescence decay times result which are the basis for improved analytical application of these dyes as highly sensitive fluorescent probes.
Syntheses and photophysical properties of a series of cation-sensitive polymethine and styryl dyes
(2000)
The syntheses and photophysical properties of 20 cation-sensitive fluoroionophores carrying the tetraoxa monoaza 15-crown-5 receptor are described and discussed. Whereas complexation induces only weak effects for the positively charged hemicyanine probes, the closely related styryl dyes show stronger changes in their photophysical properties upon cation binding in the analytically advantageous near-infrared (NIR) region. The strongest effects in both cation-induced spectral effects and complex stability constants are observed for the uncharged probes of styryl base-type, but these probes usually absorb and emit at shorter wavelengths in the UV/VIS region. For both styryl dyes and styryl bases, in some cases cation-induced fluorescence enhancement or quenching is found.
Several series of crown fluoro-chromo-ionophores covering a broad spectral range are investigated experimentally and compared to their theoretically studied dimethylamino (DMA) analogues. It is shown that the logarithm of the complex stability constants log KS for NaI and CaII ions do not correlate with the observed complexation-induced shift. Likewise, an unsatisfactory correlation is found between the local charge density on the amino nitrogen of the DMA dyes and log KS. However, using the charge of the whole dimethylamino group instead strongly improves this correlation. This can be understood by considering pyramidalization and hyperconjugation effects on the amino nitrogen. The observed correlation allows a novel approach to the design of fluoroionophores with optimized properties.
From the fluorescence properties of chalcones as a function of solvent polarity, and by the comparison to derivatives with donors and acceptors and with various selectively bridged bonds, it can be concluded that two emissive and two nonemissive states are needed to describe the fluorescence behavior. Three of these states are connected with bond twisting and lead to species with high or low dipole moment, two of them situated in the proximity of a conical intersection.
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.