Synthesis, complexation and photophysics in protic solvents of lanthanide complexes of novel calix[4]arene polycarboxylic-2,2'-bipyridine mixed ligands

Two novel cone calix[4]arene ligands 11a and 11b bearing two iminodiacetic chelating units and two C-6 or C substituted 2,2'-bipyridine chromophores in diametral position at the lower rim were synthesized. These ligands form complexes with lanthanide ions in methanol solution whose stability (4.5 < log K-ass < 6.2) depends on the substitution pattern (C-6 or C-5) of the 2,2'-bipyridine units. Contrary to that observed with other neutral calixarene ligands, the luminescence properties of the Eu3+ and Tb3+ complexes are not very much affected by the type of the 2,2'-bipyridine chromophore. Luminescence lifetimes (0.31 ms < tau < 1.1 ms) and quantum yields (0.017 < phi < 0.130) are higher for Terbium compared with the corresponding Europium complexes.