Highly efficient white electroluminescence from dual-core star-shaped single polymer: performance improved by changing the non-emissive core

Abstract

Two series of dual-core star-shaped polyfluorenes (DC-TPAs and DC-SBFs) based on a small quantity of green-emitting phenylmaleimide cores and a good deal of non-emissive cores were prepared by a one-pot Suzuki reaction. Triphenylamine (TPA) and 9,9-spirobifluorene (SBF) are employed as the non-emissive cores to construct DC-SBFs and DC-TPAs, respectively. Due to the π-conjugation extended by the fluorene units, the phenylmaleimide core displays a yellow emission which contributes to the white emission with the blue-emitting polyfluorene arms. DC-SBFs with four arms exhibit a better protection for emissive cores and a higher energy transfer efficiency than DC-TPAs with three arms. Consequently, the quantum yield of white emission of the polymers in the film was improved by changing TPA into SBF as the non-emissive core, reaching 0.80 for DC-SBF03. Additionally, the electrons and holes can be transported smoothly in DC-SBFs. A very high electroluminescent efficiency was obtained for DC-SBF03 with a maximum luminous efficiency of 17.4 cd A⁻¹, power efficiency of 10.9 lm W⁻¹ and external quantum efficiency of 6.2% when applied in the solution-processing white polymeric light-emitting devices (WPLEDs) with a LiF/Al cathode. The results denote that the non-emissive core plays a key role in the performance of the star-shaped single white polymers. It provides another way to improve the efficiencies of WPLEDs by designing simple non-emissive cores of the dual-core polymers, and avoiding the complicated synthesis of fluorophores.