n-Type ternary zinc complexes: Synthesis, physicochemical properties and organic light emitting diodes application

We report synthesis, characterization and use of ternary zinc complexes as emissive and electron transport material in organic light emitting devices (OLED). 5,7-Dimethyl-8-hydroxyquinoline or 2-carbonitrile-8-hydroxyquinoline have been used with 2-(2-hydroxyphenyl)benzoxazole to synthesize (2-(2-hydroxyphenyl)benzoxazolato) (5,7-dimethyl-8-hydroxyquinolinato)zinc(II) [Zn(HPB)(Me2q)] and (2-(2-hydroxyphenyl) benzoxazolato)(2-carbonitrile-8-hydroxyquinolinato)zinc(II) [Zn(HPB)(CNq)] complexes. These complexes possessed high thermal stability and having good film forming property. Optical properties of the synthesized complexes have been studied by UV–visible absorption, photo-luminescence and time resolved photo-luminescence spectroscopy. Density functional theoretical calculations have been performed to demonstrate the three-dimensional geometries and the frontier molecular orbital energy levels of these compounds. Synthesized materials show quite good efficiency in multilayered device structure ITO/α-NPD/Zinc complex/BCP/Alq3/LiF/Al with maximum brightness of 7017 cd/m2 and 6925 cd/m2 having electroluminescence spectral peak emission centered at 567 nm and 569 nm, respectively. Electron mobility of these molecules were found to be 1.5 × 10−6–1.2 × 10−5 cm2/V s for electric field range 1000–1200 (V/cm)1/2 and hence showed very high efficiency as electron transport layer in device structure ITO/α-NPD/5% Ir(ppy)3 doped CBP/BCP/Zn(HPB)(Me2q) or Zn(HPB)(CNq)/LiF/Al.