Aryl-substituted acridanes as hosts for TADF-based OLEDs

Abstract

Four aryl-substituted acridan derivatives were designed, synthesized and characterized as electroactive materials for organic light emitting diodes based on emitters exhibiting thermally activated delayed fluorescence. These compounds possessed relatively high thermal stability with glass-transition temperatures being in the range of 79–97 °C. The compounds showed oxidation bands arising from acridanyl groups in the range of 0.31–038 V. Ionization potentials of the solid films ranged from 5.39 to 5.62 eV. The developed materials were characterized by triplet energies higher than 2.5 eV. The layer of 10-ethyl-9,9-dimethyl-2,7-di(naphthalen-1-yl)-9,10-dihydroacridine demonstrated hole mobilities reaching10−3 cm2/V·s at electric fields higher then ca. 2.5 × 105 V/cm. The selected compounds were used as hosts in electroluminescent devices which demonstrated maximum external quantum efficiencies up to 3.2%.

Improving the chemical stability of blue heteroleptic iridium emitter FIrpic in the lowest triplet state through ancillary ligand modification: a theoretical perspective

“…Similarly, the lower SOMO is mainly located on the bis-dfppys moieties (52%) and central Ir atom (40%), while the higher SOMO + 1 is mainly located on bis-dfppys (89%), as indicated in Table S2 (ESI †). This means that the phosphorescence of FIrpic derives from the 3 MLCT state. Considering that the photophysical characters of the transition metal complexes are mainly dominated by the lowest excited state, 50 one of the major challenges for getting blue phosphorescence with sufficiently large 3 MLCT transition energies should be the selection of suitable surrounding ligands.…”

“…This means that the phosphorescence of FIrpic derives from the 3 MLCT state. Considering that the photophysical characters of the transition metal complexes are mainly dominated by the lowest excited state, 50 one of the major challenges for getting blue phosphorescence with sufficiently large 3 MLCT transition energies should be the selection of suitable surrounding ligands. However, in addition to the 3 MLCT excited state mentioned above, there is another energetically accessible metal centered (MC) excited state (one electron is excited to the metal e g orbital).…”

“…Moreover, these excited states have quite different electronic character because of their different orbital parentage. Thereby, the 3 MLCT state will be raised to a close or higher region of the 3 MC state by such an approach for achieving large emission energy, which limits the phosphorescence of the complex as d-d transition is prohibited in the metal centered (MC) excited state and since the 3 MC state is a non-emissive deactivation channel. [51][52][53] As reported, there are three possible relaxation pathways through the 3 MC state: (1) a photodissociation that gives reaction products; (2) a direct nonradiative decay to the ground state; (3) a photodissociation and successive recombination.…”

“…In addition, the density at the Ir center of T 1 0 is much larger compared with the original octahedral structure. Considering that this opening process from the T 1 to T 1 0 state has a low energy barrier, it can be predicted that the non-emissive 3 MC state should be easily accessed from the emissive 3 MLCT state for the FIrpic excited states. After that, through MECP between the PEC of S 0 , the 3 MC can return to the 3 MLCT or relax to the ground state.…”

“…Organic Light Emitting Diodes (OLEDs) have attracted significant attention over the past few years because of their promising application in next-generation display technologies and generation light sources with a lighter, thinner and more flexible design. [1][2][3][4] Since the pioneering works of Forrest, Thompson and Baldo reporting electro phosphorescent OLEDs (PhOLEDs) with a theoretical 100% internal quantum efficiency, 5 the OLED efficiency has been advanced as a result of the development and application of highly efficient phosphorescent guest molecules including transition metals, such as Ir(III) or Pt(II) complexes, which can harvest both triplet and singlet excitons for emission. [6][7][8][9][10][11] Now, devices based on highly efficient PhOLEDs have successfully penetrated into the market of large-area solidstate lighting and full-color display applications.…”