Intensely luminescent materials obtained by combining lanthanide ions, 2,2′-bipyridine, and poly(ethylene glycol) in various fluid or solid environments

Steady-state luminescence spectroscopy and luminescence decay analysis have been employed to study the association of two rare earth ions (i.e., EU(3+)and Tb3+) with poly(ethylene glycol) in the absence and in the presence of 2,2'-bipyridine, which acted as an antenna of near-UV radiation. Three different systems have been studied at various polymer concentrations, i.e., aqueous solutions, transparent composite organic/inorganic sol-gel matrixes made by hydrolysis of tetramethoxysilane, and polymer matrixes. The photophysical behavior of the luminescent species has been studied in conjunction with the poly(ethylene glycol) content. In both aqueous solutions and silica matrixes, luminescence intensity and decay time were found to increase by increasing polymer concentration. Addition of 2,2'-bipyridine resulted in complex formation between the ligand and the lanthanide ions. This complex was stabilized by association with the polymer chains. Excitation at the ligand absorption wavelength (337 nm) resulted in ligand-to-metal energy transfer and strong luminescence emission, characterized by the narrow-band emission of the metal. The complex between lanthanide ions and 2,2'-bipyridine possessed its own particular photophysical characteristics and emitted a bright broad blue luminescence with an excitation maximum around 380 nm. Freeze-drying of aqueous solutions of medium size poly(ethylene glycol) containing lanthanide ions and 2,2'-bipyridine produced an intensely luminescent solid material emitting the characteristic luminescence of the metal when excited at the ligand absorption band (337 nm) or the characteristic luminescence of the complex when excited at 380 nm.