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

• n-Type ternary zinc complexes have been synthesized and characterized.
• These complexes possessed short excited state lifetime leads to better fluorescence efficiency.
• The Zn complexes have EL spectrum centered at 567 nm and 569 nm.
• They possessed high electron mobility (∼10−5 cm2/V s).

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.

Three dimensional structure of the synthesized zinc complexes with minimal energy, schematic diagram of the fabricated OLED device based on synthesized complexes as emissive material and the atomic force microscopic images of the deposited thin films using zinc complexes with representative picture of the working OLED showing bright orange light emission.Figure optionsDownload as PowerPoint slide