Photoluminescence and electroluminescence of near-infrared emitting lanthanide complexes in conjugated polymer hosts.

摘要

The photoluminescent and electroluminescent properties of near-infrared emitting lanthanide monoporphyrinate complexes blended into conjugated polymers were investigated. The lanthanide monoporphyrinate complexes, Ln(TPP)L consisted of a lanthanide (Ln = Er3+, Nd3+, Pr 3+, Tm3+, Yb3+) coordinated to 5,10, 15, 20-tetraphenylporphyrin (TPP) and a capping ligand, L. The capping ligand was either an acetylacetonate (acac), tris-pyrazoylborate (TP), or (cyclopentadienyl) tris(diethoxyphosphito-P)cobaltate) (L(OEt) ₃) anion. The optical absorption properties of these complexes resembled “regular” metalloporphyrin absorption which was not significantly influenced with different coordinated lanthanide ions or capping ligands. The photoluminescent properties showed quenching of the porphyrin emission and sensitized near-infrared emission from Yb3+ (2F _5/2 → 2F_7/2, [977 nm]); Nd3+ (4F_3/2 → 4I_11/2, [880 nm]), 4F_3/2 → 4I_13/2 [1060 nm], 4F_3/2 → 4I _15/2 [1330 nm]); and Er3+ (4I_13/2 → 4I_15/2, [1520 nm]) was observed in CH₂Cl₂. The photoluminescent quantum yields of the Yb(TPP)TP and Yb(TPP)(LOEt)₃ were 3.2% and 2.4%, respectively.; Photoluminescent studies of Ln(TPP)L blended into a bis-alkoxy poly( p-phenylene) (PPP-OR11) host show that energy transfer from the host to the lanthanide complex does occur resulting in sensitized near-infrared emission. Electroluminescence (EL) was observed from films containing Ln(TPP)L in PPP-OR11. In all devices, the visible emission from the host was strongly suppressed. For devices where Ln(TPP)L was Yb3+, Nd 3+, or Er3+, near-infrared emission was observed. For electroluminescent devices made with Yb(TPP)TP in PPP-OR11, the external quantum efficiencies were typically 10−4. Substituting PPP-OR11 with polystyrene improved the external quantum efficiencies to 10−3 suggesting that charge hopping between Ln(TPP)TP may be more important than Förster energy transfer from polymer host to Ln(TPP).