Non-covalent binding of sensitizers for lanthanide(III) luminescence in an EDTA-bis(b-cyclodextrin) ligand

EDTA-linked ß-cyclodextrin dimer 3 was synthesized from EDTA bis(anhydride) 1 and mono(propylamino)-appended -cyclodextrin 2. p-tert-Butylbenzoate 5, bound by the ß-cyclodextrin cavities of 3 with an association constant of 104 M-1 in water, acts as a sensitizer for the EuIII and TbIII complexes of 3. Luminescence spectroscopy, microcalorimetry, and GdIII-induced NMR relaxation rate measurements prove that 3 forms a 1:2 complex with 5 and that one of the -cyclodextrin-bound sensitizers coordinates to the EDTA-encapsulated LnIII ion. The EuIII complex of 3 forms strong 1:1 complexes (K = 107 M-1) with bis(propylamido adamantyl)-functionalized biphenyl sensitizers 7 and 8 in water. Both ß-cyclodextrins of 3 are involved in the binding of these guests. The amide functionality adjacent to the biphenyl unit in 7 and 8 coordinates to the EDTA-encapsulated LnIII ion. For these biphenyl-based antennae both binding to ß-cyclodextrin and coordination to the LnIII center are crucial for efficient sensitization