Time resolved luminescence and vibrational spectroscopic studies on complexes of poly(ethylene oxide) oligomers and EuTFSI 3 salt

Abstract

AC impedance, FT-Raman/IR, DSC, continuous and time resolved luminescence measurements have been conducted on solutions of poly(ethylene glycol) (PEG), MW 400, and poly(ethylene glycol)-dimethyl ether (DME), MW 425, complexed with Eu[N(CF 3SO 2) 2] 3 salt, EuTFSI 3. Ion-polymer interactions are manifested as changes in characteristic vibrational modes of the polymer, including CH 2 and –OH stretching motions at ∼2700–3700 cm −1, and also in cation-induced polymer modes at ∼865–910 cm −1. Comparing the vibrational features of the TFSI anion (i.e., both Raman and IR), we find no modes that are substantially changing with increasing salt concentration, or upon change of cation (i.e., M=Li +, Na + or Eu 3+). This observation suggests that TFSI-salts are highly dissociated in PEO oligomer solvents even up to relatively high salt concentrations (i.e., O:M=26: 1). Clear evidence of –OH end-group coordination in the PEG systems emerges from IR spectra and the strong dependence of T g upon salt concentration, and also from the pronounced temperature dependence of the ionic conductivity. Despite of this, however, few distinct differences could be observed in the luminescence spectra between the PEG and the DME host materials. Luminescence spectra of Eu 3+ show a relatively small distribution of energies (30 cm −1 FWHM in 5D 0– 7F 0) in a low-symmetry site throughout the entire concentration range investigated for both PEG and DME solvents. The population decays of the 5D 0 excited state, measured by exciting to the degenerate state 5D 1 with a pulsed dye laser, are also very similar for the PEG and DME hosts (lifetimes=0.35 ms).