Synthesis, characterization, and electroluminescent performance of a novel copolyfluorene containing pendant crown ether groups

Abstract

AbstractCopolyfluorene PFC containing pendant crown ether moieties was prepared by the palladium‐catalyzed Suzuki coupling reaction. The photo‐physical and electrochemical properties were investigated by absorption, photoluminescence (PL) spectroscopy, and cyclic voltammetry to elucidate the influence of the crown ether groups. In film state, its PL spectra (peaked at 430 and 452 nm) show noticeable red‐shift relative to 423 and 448 nm of poly(9,9‐dihexylfluorene) (PF). Thermal annealing leads to appearance of new emission at about 520 nm which has been attributed to formation of excimer. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of PFC were estimated to be −5.68 and −2.65 eV which contributed to balanced charges injection. Double‐layer electroluminescent device using PFC as emitting layer (ITO/PEDOT:PSS/PFC/Ca/Al) revealed maximum luminance (7910 cd/m2) and maximum luminance efficiency (2.3 cd/A) superior to those of PF device (860 cd/m2, 0.29 cd/A). Moreover, inserting a PFC layer between the PF emitting layer and calcium cathode led to reduced turn‐on voltage (4.1 V), much lower than 7.1 and 6.6 V of the double‐layer PFC and PF devices, respectively, and enhanced device performance (2800 cd/m2 and 0.53 cd/A). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2985–2995, 2009