ELECTROCHEMICAL SWITCHING OF FLUORESCENCE FROM EUROPIUM IONS DISSOLVED IN POLY(ETHYLENE OXIDE) OLIGOMERS

Europium salts were dissolved in poly(ethylene oxide) (PEG) oligomers. The europium ions were revealed to be electrochemically redox-active in PEO oligomers. Trivalent europium ions (EU(3+)) showed red fluoresc ence (lambda(em) = 614 nm) in PEO oligomers, and a new intensive blue fluorescence (lambda(em) = 450 nm) was obtained after reducing the Eu3 + into Eu2+ by giving negative potential (-0.7 V versus Ag). Reversibl e fluorescence switching was also carried out by changing the given po tential alternately. Sufficient color change required about 20 min bec ause of slow electrode reaction. The fluorescence intensity from europ ium ions was affected by the molecular weight of matrix PEG. The amoun t of terminal hydroxyl groups and local viscosity were revealed to aff ect the fluorescence as the vibrational quenching and diffusion coeffi cient, respectively. The PEO oligomer with average molecular weight of 600 gave the most intensive fluorescence.