The steady-state fluorescence emission spectra of the azacyclophanes 2,5,8,11-tetraaza paracyclophane (L1), 2,6,9,13-tetraazaparacyclophane (L2), 14,15,17,18-tetramethyl-2,5,8,11-tetraazaparacyclophane (L3) and 16,17,19,20-tetramethyl-2,6,9,13-tetraazaparacyclophane (L4) as a function of pH have been measured. The fully protonated species of each cyclophane gives the highest fluorescence-emission quantum yield. The shapes of the titration curves have been explained by the existence of an electron-transfer quenching effect from a non-protonated amine to the benzene chromophore. This effect is greater for macrocycles in which the first deprotonated amine group is closer to the benzene. The association constants for the interaction of the four fully protonated macrocycles with K3[Co(CN)6] have been measured either by potentiometry or from fluorescence-emission measurements, and increase in the order L3 ≈ L4 < L1 ≈ L2. The photoaquation quantum yields of K3[Co(CN)6] have been measured in the presence of the macrocycles L1 and L2, and indicate that three of the CN nitrogens of the complex are involved in adduct formation with the fully protonated macrocycles, as supported by molecular modelling.
|Number of pages||5|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - 1 Dec 1995|