Greenish‐yellow‐, yellow‐, and orange‐light‐emitting iridium(III) polypyridyl complexes with poly(ε‐caprolactone)–bipyridine macroligands

Abstract

A set of novel greenish-yellow-, yellow-, and orange-light-emitting polymeric iridium(III) complexes were synthesized with the bridge-splitting method. The respective dimeric precursor complexes, [Ir(ppy) 2 --Cl] 2 (ppy ϭ 2-phenylpyridine) and [Ir(ppy-CHO) 2 --Cl] 2 [ppy-CHO ϭ 4-(2-pyridyl)benzaldehyde], were coordinated to 2,2Ј-bipyridine carrying poly(⑀-caprolactone) tails. The resulting emissive polymers were characterized with one-dimensional ( 1 H) and two-dimensional ( 1 H-1 H correlation spectroscopy) nuclear magnetic resonance and infrared spectroscopy, gel permeation chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and the successful coordination of the iridium(III) centers to the 2,2Јbipyridine macroligand was revealed. The thermal behavior was studied with differential scanning calorimetry and correlated with atomic force microscopy. Furthermore, the quantitative coordination was verified by both the photophysical and electrochemical properties of the mononuclear iridium(III) compounds. The photoluminescence spectra showed strong emissions at 535 and 570 nm. The color shifts depended on the substituents of the cyclometallating ligands. Cyclic voltammetry gave oxidation potentials of 1.23 V and 1.46 V. Upon the excitation of the films at 365 nm, yellow light was observed, and this could allow potential applications in light-emitting devices.

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

“…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). Schubert and co-workers reported a number of charged, polymer-equipped bis-cyclometallated Ir III complexes obtained by reacting dimeric chloro-bridged iridium(III) precursor complexes with poly(e-caprolactone)-functionalized bipyridine [87,88] or poly(ethylene glycol) [89,121] and PS-functionalized terpyridines (here acting as a bidentate ligand only). [121] Detailed investigations by means of size exclusion chromatography (SEC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry showed the formation of well-defined materials.…”

“…To suppress crystallization or aggregation occurring in blended films [86,87] and to enhance the processability (e.g., via inkjetprinting or spin-coating, by inducing film-forming abilities [88] ), cationic Ir III complexes have successfully been introduced into polymeric materials, both non-conjugated [89][90][91] and conjugated ones. [92][93][94][95] In addition to the complexes bearing three bidentate ligands, the analogous compounds containing two tridentate ligands [96] (e.g., 2,2 0 :6 0 ,2 00 -terpyridine, 2,6-diaryl-pyridine, and their derivatives) have recently gained more attention as potential candidates for applications in areas such as luminescent sensors or materials for directional energy and electron transfer.…”

“…While the formation of tris-cyclometallated [118][119][120] and bis-terpyridine iridium(III) complexes [122] are usually rather demanding with respect to temperature and conversion, other types of complexes, e.g., charged bis-cyclometallated complexes bearing bipyridine, can often be obtained in high yields at rather mild conditions. [89,90] Steric demands (e.g., in the case of coordination sites in a conjugated backbone, [119,120] polymer blocks, [121] or crosslinked systems [125] ) is an aspect, which might need to be considered as well. Complex-free polymers are usually easier to investigate by techniques such as SEC, and influences of incorporated complexes are easily revealed by comparing final and precursor polymers.…”

Molecular organization of a water-insoluble iridium(III) complex in mixed monolayers

“…Specifically, organometallic triplet emitters, such as Ir(III) and Pt(II) complexes, are of particular interest because of their promising use as photosensitizers in catalytic photoinduced hydrogen production [3], oxygen-sensing materials [4], and in electroluminescent devices, OLEDs [5][6][7][8] and LECs [9][10][11][12], as well. In these last devices, when using phosphorescent dyes, the triplet exciton contributes to light emission and the efficiency is greatly improved compared with that of conventional fluorescent devices, which use the emission from only the single exciton.…”

Luminescent sensitization and blue shift emission of Ir(ppy)2(VPHD) by copolymerization with MMA

“…Furthermore, covalent polymers with well-defined chemical structure are easy to be synthesized without the possibility of phase separation or dopant aggregation. Recently, a few covalent polymers functionalized with iridium (III) complexes chelated by bis-cyclometalated ligands and an ancillary ligand such as acetylacetonate, bipyridine, pyrazole and their structural analogs [18][19][20] were reported.…”