Fluorescence studies and semiempirical calculations on alkali ion indicators |
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Authors: | F Kastenholz E Grell J W Bats G Quinkert K Brand H Lanig F W Schneider |
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Institution: | (1) Max-Planck-Institute of Biophysics, Kennedy-Allee 70, D-60596 Frankfurt/M., Germany;(2) Institute of Organic Chemistry, University of Frankfurt, D-60439 Frankfurt/M., Germany;(3) Institute of Physical Chemistry, University of Wuerzburg, D-97070 Wuerzburg, Germany |
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Abstract: | Two newly synthesized cryptands act as sensitive Na+- and K+-selective indicators for cation concentrations above 20 M. The fluorescence properties change markedly upon cation binding. In addition, the free ligands exhibit a pronounced sensitivity to pH, which is considerably lower for the cation complexes. Time resolved fluorescence is characterized by a decay time of about 5 ns that is attributed to the diprotonated protolytic state of the uncomplexed ligands. Semiempirical calculations show the systematic influence of the nitrogen lone pairs or the N–H bond on the stability of the system. The cause of the strong fluorescence intensity increase observed upon protonation of the fluorescent cryptands may be attributed to an increase in the S1–T
x
energy gap as a consequence of bridgehead nitrogen protonation.This is a peer-reviewed conference proceeding article from the Third Conference on Methods and Applications of Fluorescence Spectroscopy, Prague, Czech Republic, October 18–21, 1993. |
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Keywords: | Cryptands alkali ion indicators pH sensitivity semiempirical calculations AM1 |
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