Time-resolved luminescence of terbium complexes with poly(2-and 4-vinylpyridine N-oxide)s in aqueous solution

Terbium complexes with polymer ligands of poly(2- and 4-vinylpyridine N-oxide)s (P2VPNO, P4VPNO) in aqueous solution were prepared and characterized. Multi-exponential decays of the D-5(4) --> F-7(5) terbium transition at 545 nm of [P2VPNO-Tb3+] and [P4VPNO-Tb3+] complexes were measured. The non-linearity of semi-logarithmic plots of time-resolved luminescence was more pronounced in [P4VPNO-Tb3+] than in [P2VPNO-Tb3+], being reduced by addition of salts such as sodium formate or acetate. We assume that multi-exponential decays of Tb3+ in the complexes are caused by a back metal-to-ligand energy transfer via triplet state of N-oxide polymer ligand. By carrying out separate experiments in water and deuterium oxide, the number of coordinated water molecules in the [P4VPNO-Tb3+] complex was estimated as 4-5, assuming that the Tb3+ aqua complex contains nine water molecules.