Supramolecular interactions of hexacyanocobaltate(III) with polyamine receptors containing a terminal anthracene sensor

The fluorescence emission properties of a series of chemosensors containing a polyamine receptor bearing an anthracene signaling unit were studied. The fluorescence emission intensity is dependent on the protonation degree of the receptor, the fully protonated form exhibiting the highest emission intensity. By removing protons from the nitrogens a quenching effect can be observed, due to an electron-transfer from the amine to the excited fluorophore. The rate constant of the quenching process is exponentially dependent on the distance of the nitrogen from which the electron is transferred (β=0.6 Å−1). The ability of the chemosensors for signaling anions was tested through the model anion hexacyanocobaltate(III). The temperature dependence of the association constants shows that at least for this compound, the change in solvation entropy is probably the controlling parameter to account for the binding.