Enhancement of Phosphorescence of Ir Complexes Bound to Conjugated Polymers:  Increasing the Triplet Level of the Main Chain

Abstract

Conjugated fluorene-alt-pyridine and fluorene-alt-thiophene polymers containing phosphorescent iridium complexes have been synthesized. Exchanging the 2,5-linked pyridine group with the 3,4-linked thiophene group resulted in a blue shift in the absorption and emission spectra of the conjugated polymers. Upon incorporation of the thienyl unit, phosphorescent quantum yields of films increased from 0.05 to 0.20 and electrophosphorescent external quantum efficiencies increased from 0.32 to 0.84%. These results are attributed to raising the triplet energy of the main chain polymer, with respect to the Ir phosphor, thereby reducing quenching of the phosphor by the main chain.

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…[87][88][89][90][118][119][120][121][122][123][124][125] One of the earliest examples of an iridium(III)-complex-containing polymer was obtained by Kim and coworkers in a one-pot, two-step complexation reaction; after treating Ir(acac) 3 with 2-phenylpyridine, the ligand-equipped polymer [poly((2-(4-vinylphenyl)pyridine)co-vinylcarbazole)] was added to achieve the formation of polymer-bound tris-cyclometallated Ir III complexes under rather harsh conditions (170 8C for 12 h). [118] Photoluminescence (PL) investigations in solutions pointed to an intermolecular energy transfer between host and guest rather than an intramolecular one.…”

“…Applying this copolymer as the emissive layer (EML) in multilayer devices, a maximum quantum efficiency (QE) of 4.4% and a power efficiency of 5.0 lm W À1 could be achieved. Also, Holdcroft and co-workers [119] as well as Langecker and Rehahn [120] performed inter alia complexation reactions on conjugated copolymers in order to obtain systems equipped with tris-cyclometallated fac-iridium(III) complexes. Altering the reaction sequence applied by Kim's group, Holdcroft and co-workers treated first the polymer, poly(9,9-dihexylfluorenealt-pyridine), with Ir(acac) 3 at 250 8C for 12 h, which is supposed to lead to the formation of mono-cyclometallated Ir III intermediates.…”

“…By adapting the iridium(III)-and the ligand-feed, the extent of complexation at the polymer could be varied. [119] Langecker and Rehahn [120] applied a different synthetic procedure. The treatment of poly(2,7-fluorene-co-5,4 0 -(2-phenylpyridine)) with a fourfold excess of [Ir(ppy) 2 -m-Cl] 2 and silver triflate at about 100 8C for 4 days resulted in the coordination of roughly 50% of the polymer-bound ligand sites (2-phenylpyridine).…”

Synthesis and Characterization of Iridium-Containing Green Phosphorescent Polymers for PLEDs

“…In previous reports, phosphorescent metal complexes were incorporated as a portion of the polymer main chain or grafted as a pendant by a long alkyl side chain. [4][5][6] Many orange or red phosphorescent polymers with high efficiencies have been reported. [7][8][9] Fewer green and blue phosphorescent polymers with high efficiencies, however, have been reported thus far.…”

New poly(4,4′-dicyano-4″-vinyl-triphenylamine) host material for single-layer Ir complex phosphorescent light-emitting devices

“…21 Phosphorescent polymers consisting of host materials and heavy-metal complexes were reported. [22][23][24][25] However, the difficult synthesis procedures of phosphorescent polymers limit their commercial applications. Compared with complicated phosphorescent polymers, blending is a simple way to manipulate and optimize the composition ratio of host materials and guest organometallic complexes.…”