Improvement of color purity in blue-emitting polyfluorene by copolymerization with dibenzothiophene

Abstract

High molecular weight, readily soluble copolymers of 9,9-dioctylfluorene and dibenzothiophene (DBTh) comonomer (less than or equal to 50 mol%) are synthesized by Suzuki polycondensation. PL efficiencies and EL external quantum efficiencies of random copolymers decrease with increasing DBTh content. For the alternating copolymer, a PL efficiency of 62% and an EL external quantum efficiency of 0.42% are obtained. Excimer emission is effectively depressed when the DBTh content is greater than 20 mol%. It is indicated that the meta-linkages of 2,8-substitution of DBTh are effective in enhancing blue emission of polyfluorene.