MULTI-PROTONATION OF A [3]-CATENAND AND A MONO-COPPER [3]-CATENATE - ABSORPTION-SPECTRA AND LUMINESCENCE PROPERTIES

The absorption and luminescence spectra and the excited state lifetime s and quantum yields of a [3]-catenand and its mono-copper catenate in CH2Cl2 solution at room temperature undergo profound, fully reversibl e changes upon addition of CF3COOH. The [3]-catenand contains four 2,9 -dianisyl-1,10-phenanthroline (dap) chelating ligands. In its mono-cop per complex, two of the four ligands are engaged in the coordination o f a Cu(I) ion. Protonation of the free catenand takes place through fo ur distinct families of isobestic points exhibited by the absorption s pectrum on increasing acid concentration. The presence of four success ive protonation steps is also indicated by changes in the luminescence spectra. Comparison of the absorption and luminescence spectral chang es observed upon the protonation of isolated dap units and of a previo usly investigated [2]-catenand shows that protonation of the [3]-caten and does not involve independent ligand units, but implies a cooperati ve action of pairs of ligands which organize themselves around one or two protons to form ''proton catenates''. For the mono-copper complex, the spectral changes indicate the presence of two distinct protonated species which again implies a cooperative action of the two dap units not involved in metal coordination. In the partially protonated forms of the [3]-catenand, the protonated moiety quenches the fluorescence of the non-protonated one, while in the protonated mono-copper catenat e the fluorescence of the protonated moiety is quenched by the metal c ontaining one.