Crown-5 Stilbenes Forming Emissive TICT States

Monoaza-15-Crown-5 Stilbenes Forming Emissive TICT States 

When protonation of a probe leads to dramatic effects on the electronic absorption and emission as described above, one can expect that cations other than protons might be capable of inducing similar effects if these ions can be made to bind to the basic atom of the probe molecule. A simple but effective method to do so exists in the formal replacement of the amino substituents ofchromophores by aza crowns. In the resulting chromoionophores the amine nitrogens possess simultaneously an electron-donor 

Fluorescent Calcium Indicators in Current Use in Molecular Biology 

and ( — ) CH2CI1. Above Presumed excited state equilibration between a metal ligand complex where the amino group is engaged in complexation (LM ) or where a solvent molecule takes over the complexing function (IVS/M T), 

Structurally these compounds combine a eight-coordinate tetracarboxylate chelating site with stilbene chromophores. Of the six dyes proposed in Ref. 121 only Indo-1 leads to a short-wavelength fluorescence shift when bound to Ca2+. It is also the probe with the smallest D-A interactions as revealed by the shortest wavelength of fluorescence of the free ligand. As a consequence, the decrease of the electron density of the nitrogen binding site is not sufficient to break completely the interaction with Ca2+ in the excited state and the spectrum is considerably blueshifted. 

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