N. Armaroli et al., MULTI-PROTONATION OF A [3]-CATENAND AND A MONO-COPPER [3]-CATENATE - ABSORPTION-SPECTRA AND LUMINESCENCE PROPERTIES, New journal of chemistry, 18(7), 1994, pp. 775-782
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.