Red light-emitting hyperbranched fluorene-alt-carbazole copolymers with an iridium complex as the core

Red light-emitting hyperbranched copolymers with an iridium complex as the core and fluorene-alt-carbazole as the branches were synthesized by one-pot Suzuki polycondensation. Efficient energy transfer from the poly(3,6-carbazole-alt-2,7-fluorene) segment to the iridium complex occurs when the Ir complex content is as low as 1 mol% in the copolymer. A maximal external quantum efficiency of 6.1% ph/el and a luminous efficiency of 4.7 cd A(-1) were obtained with a CIE coordinate of (0.63, 0.32) for the device made from PFCzPh20NapyIr2 copolymer. The efficiency loss upon the increase of current density is significantly reduced since the highly branched structure could suppress the interchain interaction of polymers and the self quenching of the Ir complex. The integration of a phosphorescent complex into hyperbranched polymers can provide a successful molecular design route for solution-processable polymers for PLED applications.