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Four-coordinate boron compounds derived from 2-(2-pyridyl)phenol ligand as novel hole-blocking materials for phosphorescent OLEDs

Authors
Journal
Journal of Organometallic Chemistry
0022-328X
Publisher
Elsevier
Publication Date
Volume
694
Issue
12
Identifiers
DOI: 10.1016/j.jorganchem.2009.01.035
Keywords
  • Four-Coordinate Boron
  • 2-(2-Pyridyl)Phenol
  • Hole-Blocking Material
  • Organic Light-Emitting Diode
  • Phosphorescence
Disciplines
  • Mathematics
  • Physics

Abstract

Abstract Four-coordinate boron compounds of Ph 2B · 1 ( 2) and (C 6F 5) 3B( 1 · H) ( 3) were prepared from the reaction of 2-(2-pyridyl)phenol ( 1 · H) ligand with triarylborane starting materials, BPh 3 and B(C 6F 5) 3, respectively, and tested as hole-blocking layer (HBL) materials in phosphorescent OLEDs. While the crystal structure of 2 reveals the pseudo-tetrahedral geometry around the boron center with bidentate [ N, O] chelation by 1, 3 is characterized as the zwitterionic four-coordinate system where the ligand 1 · H acts as monodentate [ O] chelator with N-protonation. UV–Vis absorption and PL spectra of 2 and 3 are consistent with the ligand-centered, HOMO–LUMO electronic transitions with charge transfer from a phenoxide ring to a pyridine, which was further supported by time dependent DFT calculation for 2. Both compounds are found to possess the HOMO–LUMO energy gap of 3.1 eV appropriate for hole-blocking materials for phosphorescent OLEDs. The devices incorporating 2 and 3 as HBL materials displayed stable green phosphorescence of Ir(ppy) 3 (ppy = 2-phenylpyridine) with low turn-on voltage of 3.2 and 3.4 V, respectively, indicating that 2 and 3 function as HBL materials. Although both devices show the short lifetime (<1 h) probably owing to the low thermal stability, the device based on 2 displays better performances in terms of luminance, power and luminance efficiency, and external quantum efficiency in a wide range of current densities (0.1–100 mA/cm 2) than the reference device incorporating BAlq as HBL materials.

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