Synthesis and lanthanide-sensing behaviour of polyfluorene/1,10-phenanthroline copolymers

Copolymers containing alternating fluorene and 1,10-phenanthroline units, prepared by Suzuki coupling, were found to be capable of binding with Eu3+ and Tb3+ ions in the presence of dibenzoylmethane (dbm) or acetylacetonate (acac) ligands. Photoluminescence studies of the Eu-containing polymer showed a measurable additional longer wavelength emission on complexation compared to the uncomplexed polymer. Narrow linewidth red emission from the metal-centred Eu f states (5D0 → 7F2) was only observed on raising the concentration of the solution or in the solid state. The lack of intra-chain energy transfer to the Eu atomic levels at low concentration is proposed to be due to the low-spectral overlap between fluorene emission and ligand absorption. The Tb-containing polymer emission evolves into a broad, polymer backbone-based green emission at higher concentrations and in the solid state. Here, the stabilization of phen triplet levels due to conjugation with respect to the Tb atomic levels prevents energy transfer to the Tb metal states. Solution time-resolved emission studies on both polymers showed that after complexation, in addition to the emission from the unmodified polymer, a new long wavelength singlet emission emerges with slightly longer lifetime (0.7–2 ns).