Ternary zinc complexes as electron transport and electroluminescent materials

Abstract

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.