Ternary zinc complexes as electron transport and electroluminescent materials

• Ternary zinc complexes have been synthesized and characterized.
• These complexes possessed high glass transition temperature (180 and 128 °C).
• The Zn complexes have EL spectrum centered at 549 and 554 nm.
• They possessed high electron mobility (4 × 10−6 and 4.57 × 10−6 cm2 V−1 s−1).

Ternary zinc complexes: [2-(2-hydroxyphenyl)benzoxazolato]5-chloro-8-hydroxy quinolinatozinc(II) [Zn(HPB)(Clq)] and [2-(2-hydroxyphenyl)benzoxazolato]5,7-dichloro-8-hydroxyquinolinatozinc(II) [Zn(HPB)(Cl2q)]) were synthesized and characterized as electroluminescent materials. These complexes possessed high thermal stability (>300 °C) and high glass transition temperature (>150 °C). The excited state lifetime of these complexes measured by transient photo-luminescence spectroscopy showed 4.19, 11.02 ns and 2.67, 10.7 ns for Zn(HPB)(Clq) and Zn(HPB)(Cl2q), respectively. The electroluminescence spectra showed peak emission centered at 549 and 554 nm, respectively, for these materials. Both the molecules were found to be quite efficient in a multilayered device structure ITO/α-NPD/Zinc complex/BCP/Alq3/LiF/Al with yellow emission having Internationale d'Eclairage (CIE) coordinates x = 0.37 and y = 0.57 for Zn(HPB)(Clq); and x = 0.40 and y = 0.56 for the Zn(HPB)(Cl2q) complex. Electron mobilities of these molecules were found to be 3 × 10−6–7 × 10−6 s for electric field range 1000–1200 (V/cm)1/2. These molecules showed very high efficiency as electron transport layer with device structure ITO/α-NPD/5% Ir(ppy)3 doped CBP/BCP/Zn(HPB)(Clq) or Zn(HPB)(Cl2q)/LiF/Al and therefore are better electron transporters as compared to Alq3 in a device structure of ITO/α-NPD/5% Ir(ppy)3 doped CBP/BCP/Alq3/LiF/Al.

Schematic energy level diagrams of the devices having synthesized zinc complexes as emissive materials. Comparative current density-voltage-luminescence, current and power efficiencies of the devices having zinc complex as emissive materials show that the synthesized zinc complexes are good candidature for organic light emitting devices as emissive layer materials.Figure optionsDownload as PowerPoint slide