Study of Ion-Paired Iridium Complexes (Soft Salts) and Their Application in Organic Light Emitting Diodes

Abstract

Three Ir-based materials were synthesized through metathesis reaction between halide and alkali metal salts of two cationic and three anionic Ir complexes, respectively. The resulting "soft salt" complexes are composed of an organometallic cation and an organometallic anion. The electrochemical and photophysical characterization of these compounds is reported. The redox potentials of the soft salts are shown to be determined by the lowest energy potentials of the two ions. Energy transfer between the ions in solution is observed, and found to take place at diffusion controlled rates. Organic LEDs were prepared with each of the three soft salts, using the simple structure of anode/PVK/soft salt/BCP/cathode. The soft salts yielded maximal external quantum efficiencies (EQE) ranging from 0.2% to 4.7%. The study suggests that the internal energy alignment between two ions in the soft salts is responsible for the widely disparate results. To achieve a high EQE, it is critical to have the HOMO and LUMO values of one of the ions fall between those of the other ion, that is, one ion has both the lowest oxidation potential and the least negative reduction potential.

Label-free luminescent detection of LMP1 gene deletion using an intermolecular G-quadruplex-based switch-on probe

“…Complex 2: (Reported) (Leung et al, 2013b). Complex 3: (Reported) (Wu et al, 2010). Complex 4: (Reported) .…”

Solution-processed blue phosphorescent OLEDs with carbazole-based polymeric host materials

“…Among all triplet emitters under investigations, iridium complexes have been identified as the most promising candidates as these organometallic complexes have high photoluminescence quantum yields at room temperature, relatively short excited state lifetimes and excellent color tunability [9]. So far, neutral [10][11][12][13][14], cationic [15][16][17][18], anionic [19][20] and even soft salts [21][22][23] where both the anionic and the cationic complex can contribute to light emission were successfully used as triplet emitters for electroluminescent devices.…”

Photophysical Properties of Highly Efficient Blue-Green Emitting Cationic Iridium (III) Complexes Containing Two 2-Phenylbenzothiazole Ligands and One Diphosphine Ligand

“…24 The room temperature quantum yields (QY) of the Ir1 and Ir2 complexes were 52 and 45%, respectively. Wu C. et al 25 reported the photophysical properties of cationic Ir(III) complexes with soft anions and found QY values were sensitive to ligand size and counter ion nature, and found that greater steric hindrances increased QYs by increasing distance between iridium complexes. Moreover, soft salts, such as PF 6 −1 salts, have higher QYs than halide salts because larger anion sizes increase intermolecular distances.…”