Near-Infrared Photo- and Electroluminescence of Alkoxy-Substituted Poly(p-phenylene) and Nonconjugated Polymer/Lanthanide Tetraphenylporphyrin Blends

The photoluminescent and electroluminescent properties of near-infrared (near-IR) emitting lanthanide monoporphyrinate complexes, Ln(TPP)L (L = hydridotris(1-pyrazolyl)-borate (Tp) or (cyclopentadienyl)tris(diethylphosphinito)cobaltate(I) L(OEt)) blended into conjugated and nonconjugated polymer hosts were characterized. A blue-emitting alkoxy-substituted poly(p-phenylene) (PPP-OR11) was used as the conjugated polymer host and nonconjugated hosts included polystyrene, poly(methyl methacrylate), poly(n-butyl methacrylate), and poly(bisphenol A-carbonate). Complete quenching of the PPP-OR11 host fluorescence (i.e., > 95%) is observed at 5 mol % of Ln(TPP)Tp, and host quenching is accompanied by sensitization of near-IR emission from the lanthanide complex. The photoluminescence results suggest that energy transfer occurs from PPP-OR11 to Ln(TPP)L, presumably via the Forster mechanism. Near-IR light emitting diodes (PLEDs) consisting of Yb(TPP)Tp blended into PPP-OR11 and the nonconjugated polymer hosts were characterized. PLEDs fabricated with PPP-OR11 exhibited turn-on voltages of approximately 4 V, whereas nonconjugated polymer devices had higher turn-on voltages (ca. 8 V), independent of the polymer used. Comparable external electroluminescence (EL) efficiencies on the order of 10 -4 were observed from both the conjugated and nonconjugated polymer host devices. Taken together, the available evidence suggests that the dominant mechanism operating in the EL devices involves the Ln(TPP)L complex as the charge-transport material, the center for electron-hole recombination, and the emitter.