Synthesis and Characterization of Red Electrophosphorescent Polymers Containing Pendant Iridium(III) Complex Moieties

Abstract

A series of fluorene-carbazole copolymers containing the pendant phosphor chromophore Ir(absn) 2 (acac) (absn: 2-(1-naphthyl)benzothiazole; acac: acetylacetone) were designed and synthesized via Yamamoto coupling. In the film state, these copolymers exhibited absorption and emission peaks at approximately 389 and 426 nm, respectively, which originated from the fluorene backbone. However, in electroluminescent (EL) devices, a significantly red-shifted emission at approximately 611 nm was observed, which was attributed to the pendant iridium(III) complex. Using these copolymers as a single emission layer, polymer light-emitting devices with ITO/PEDOT:PSS/polymer:DNTPD/TmPyPb/LiF/Al configurations exhibited a saturated red emission at 611 nm. The attached iridium(III) complex had a significant effect on the EL performance. A maximum luminous efficiency of 0.85 cd/A, maximum external quantum efficiency of 0.77, maximum power efficiency of 0.48 lm/W, and maximum luminance of 883 cd/m 2 were achieved from a device fabricated with the copolymer containing the iridium(III) complex in a 2% molar ratio.

High Triplet Energy Level Achieved by Tuning the Arrangement of Building Blocks in Phosphorescent Polymer Backbones for Furnishing High Electroluminescent Performances in Both Blue and White Organic Light-Emitting Devices

“…Clearly, these nonelectroactive alkyl chains will definitely hamper the charge-carrier injection/transporting processes of the emission layer (EML) deposited by these polymeric emitters. On the basis of the working mechanism of OLEDs, − charge-carrier injection/transporting processes are very crucial for the EL performance of OLEDs. − Hence, conjugated backbones are typically adopted in phosphorescent polymers to elevate their ability for charge-carrier injection/transporting. − Unfortunately, conjugated backbones in phosphorescent polymers typically possess low-energy nonemissive triplet states, which greatly enhance the opportunity for undesired back energy-transfer processes from the emissive triplet states of the phosphorescent sites to the nonemissive triplet states for the conjugated polymer backbones. − Hence, this situation will lead to a significant reduction in device performance. Clearly, the back energy-transfer issue should be paid more attention in blue- and white-emitting polymers containing blue phosphorescent chromophores that possess a relatively high triplet energy level ( E T ) to raise the possibility of back energy-transfer processes.…”