Light emission of a polyfluorene derivative containing complexed europium ions

Abstract

The photophysical properties of a new alternating copolymer containing fluorene, terpyridine, and complexed sites with trivalent europium (Eu3+) ions (laPPS66Eu) were investigated, using the non-complexed backbone (laPPS66) and a low molecular weight compound of similar chemical structure of the ligand/Eu3+ site (laPPS66M) as a model compound. The analogous gadolinium complex (laPPS66Gd) was aka synthesized to determine the triplet state of the complex. H-1 and C-13 nuclear magnetic resonance (NMR) analysis, Fourier transform infrared (FT-IR) spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), elemental analyses, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) characterized the chemical structure and thermal properties of the synthesized materials. A level of Eu3+ insertion of 37% (molar basis) in the polymer backbone was achieved. The photoluminescence studies were performed in the solid state showing the occurrence of polymer-to-Eu3+ energy transfer brought about by the spectral overlap between the absorption spectra of the Eu3+ complex and the emission of the polymer backbone. A detailed theoretical photoluminescence study performed using time-dependent DET (TD-DFT) calculations and the recenty developed LUMPAC luminescence package is aka presented. The high accuracy of the theoretical calculations was achieved on comparison with the experimental values. Aiming at a deeper leveE of understanding of the photoluminescence process, the ligand-to-Eu3+ intramolecular energy transfer and back-transfer rates were predicted. The complexed materials showed a dominant pathway involving the energy transfer between the triplet of the dbm (dibenzoyErnethane) ligand and the D-5(1) and D-5(0) Eu3+ levels.