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Yellowish-orange and red emitting quinoline-based iridium(III) complexes: Synthesis, thermal, optical and electrochemical properties and OLED application

2020; Elsevier BV; Volume: 268; Linguagem: Inglês

10.1016/j.synthmet.2020.116504

1879-3290

Nuray Altınölçek, Ahmet Battal, Mustafa Tavaslı, Joseph Cameron, William J. Peveler, Holly A. Yu, Peter J. Skabara,

Organic Electronics and Photovoltaics

Two novel heteroleptic iridium(III) acetylacetonate (acac) complexes K3a and K3b were synthesised from cyclometallating ligands of 2-(4′-formylphenyl)quinoline 11a and 2-(5′-formylphenyl)quinoline 11b. Complexes K3a and K3b were fully characterised by NMR spectroscopy, mass spectrometry and FT-IR. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) indicate that both complexes were amorphous solids, stable up to 303 °C and 313 °C, respectively. Complexes K3a and K3b showed strong, high-energy absorption bands (<400 nm) due to ligand-centred (1LC) transitions and weaker, low-energy absorption bands (400−600 nm) arising from a mixture of metal-to-ligand charge transfer (1MLCT/3MLCT) and ligand-centred (3LC) transitions. In degassed dichloromethane solutions, complexes K3a and K3b gave yellowish-orange and red phosphorescent emissions at 579 nm and 630 nm, with quantum efficiencies of 99.3 % and 79.3 %, respectively. At positive potential, complexes K3a and K3b exhibited a one-electron reversible oxidation (Eox1/2) peak at 0.69 V and a quasi-reversible oxidation (Eox1/2) peak at 0.60 V, respectively, which were assigned to the Ir(III)/Ir(IV) couple. At negative potentials, complexes K3a and K3b exhibited a one-electron irreversible reduction peak at -1.79 V and -1.94 V, respectively. Phosphorescent organic light-emitting diodes (PhOLEDs) were fabricated with a device configuration of ITO/PEDOT:PSS/EML/TPBi/LiF/Al, in which K3a and K3b gave yellowish-orange and red electroluminescence (EL) at 572 nm and 628 nm, respectively. Complex K3a gave the highest luminance of 2773 cd/m2, current efficiency of 3.3 cd/A, external quantum efficiency of 1.2 % and maximum power efficiency of 1.05 lm/W with a turn-on voltage of 5.0 V (Device A).