Polyfluorene-based white light conjugated polymers incorporating orange iridium(iii) complexes: the effect of steric configuration on their photophysical and electroluminescent properties

Abstract

Different kinds of polyfluorene-based white light conjugated polymers with phosphorescent iridium(III) complexes as orange emission groups and polyfluorene as blue emission groups were designed and synthesized. On the basis of adjusting substituent positions on iridium(III) complexes, the conjugated polymers exhibited different steric configurations, i.e. hyperbranched and linear structures, and the PL emission peaks of iridium(III) complexes had a significant change. Compared to linear conjugated polymers, hyperbranched white light conjugated polymers showed the best thermal stability and film forming properties. The white light single-emissive-layer devices with simplified configuration were also prepared in a wet process. All these devices realized good electroluminescence, especially the hyperbranched conjugated polymers in which the roll off phenomenon at high current density was effectively suppressed. Furthermore, EL spectra of hyperbranched polymers exhibited good stability at different driving voltages. A maximum luminance of 2469 cd m⁻², a maximum current efficiency of 1.73 cd A⁻¹ and the commission internationale de l'Eclairage (CIE) coordinates of (0.25, 0.23) showed white light was achieved from the HPF-Ir10 devices.