Phosphorescence Color Tuning by Ligand, and Substituent Effects of Multifunctional Iridium(III) Cyclometalates with 9‐Arylcarbazole Moieties

Abstract

The synthesis, isomeric studies, and photophysical characterization of a series of multifunctional cyclometalated iridium(III) complexes containing a fluoro- or methyl-substituted 2-[3-(N-phenylcarbazolyl)]pyridine molecular framework are presented. All of the complexes are thermally stable solids and highly efficient electrophosphors. The optical, electrochemical, photo-, and electrophosphorescence traits of these iridium phosphors have been studied in terms of the electronic nature and coordinating site of the aryl or pyridyl ring substituents. The correlation between the functional properties of these phosphors and the results of density functional theory calculations was made. Arising from the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such a moiety can increase the highest-occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent phosphor with 2-phenylpyridine ligands. Remarkably, the excited-state properties can be manipulated through ligand and substituent effects that allow the tuning of phosphorescence energies from bluish green to deep red. Electrophosphorescent organic light-emitting diodes (OLEDs) with outstanding device performance can be fabricated based on these materials, which show a maximum current efficiency of approximately 43.4 cd A(-1), corresponding to an external quantum efficiency of approximately 12.9 % ph/el (photons per electron) and a power efficiency of approximately 33.4 Lm W(-1) for the best device. The present work provides a new avenue for the rational design of multifunctional iridium-carbazolyl electrophosphors, by synthetically tailoring the carbazolyl pyridine ring that can reveal a superior device performance coupled with good color-tuning versatility, suitable for multicolor-display technology.

Organic Optoelectronic Materials

“…Novel nitrogen-containing heptacyclic bisindoloquinoline 166 was synthesized via an intramolecular cyclization of anthrazoline derivatives. Its single crystal FETs had carrier mobility as high as 1.0 cm 2 V −1 s −1 with on/off current ratios greater than 10 4 [197]. Tetraazapentacene derivatives, 167 and 168 exhibited mobilities of 0.02 and 0.01 cm 2 V −1 s −1 in air, respectively [198].…”

“…Qin and coworkers [207] fabricated a (ppy) 2 Ir(acac)-based OLED on p-silicon anode using (continued) [196], Ir(FCzppy) 3 [197], Ir(CCzppy) 3 [197], Ir (CzppyF) 3 [197], Ir(CzppyC) 3 [197], Ir(CzppyF) 2 Ir(acac) [197], and Ir(CzppyC) 2 Ir (acac) [197]. Because of the hole transporting nature of the carbazole moiety, one of the most commonly used structures for the host material, HOMO energy level has been raised less than 5.0 eV.…”

New Design Tactics in OLEDs Using Functionalized 2‐Phenylpyridine‐Type Cyclometalates of Iridium(III) and Platinum(II)

“…Recently, a triphenylamine group has been introduced to the ligands of Ir III complexes to afford bifunctional triplet emitters (see 1-16 in Figure 1). [12,13] Emitter 1, developed by Wong and co-workers, exhibits the HOMO level of approximately 4.95 eV which is higher than that of its mother complex [IrA C H T U N G T R E N N U N G (ppy) 3 ] (5.08 eV). It indicates that an aromatic amine moiety can effectively facilitate the HI process.…”

“…Besides 1, there are also some highly efficient green phosphors derived from carbazole showing HI/HT features ( Figure 1). [13] For example, emitter 4 can give peak EL parameters at L max of 14 730 cd m À2 , h ext of 11.6 %, h L of 38.0 cd A À1 , and h P of 24.0 Lm W À 1 . Emitter 6 even shows a better EL behavior with L max of 28 400 cd m À2 at 9.2 V, h ext of 12.9 %, h L of 43.4 cd A À1 , and h P of 33.4 Lm W À1 .…”

Organic Semiconductor Electroluminescent Materials

“…Based on Ir(ppy) 3 and (ppy) 2 Ir(acac), more green phosphorescent Ir complexes have been developed by directly grafting carbazole moiety onto ppy cyclometalation ligand, such as Ir(Czppy) 3 [196], Ir(FCzppy) 3 [197], Ir(CCzppy) 3 [197], Ir (CzppyF) 3 [197], Ir(CzppyC) 3 [197], Ir(CzppyF) 2 Ir(acac) [197], and Ir(CzppyC) 2 Ir (acac) [197]. Because of the hole transporting nature of the carbazole moiety, one of the most commonly used structures for the host material, HOMO energy level has been raised less than 5.0 eV.…”