Polarized white emission from fluorene-based polymer blends

Three alternating co-polyfluorenes emitting primary red, green and blue (ROB) colors have been synthesized via a palladium-catalyzed Suzuki coupling reaction. All copolymers reveal good thermal stability and nematic liquid crystalline behavior. The polymers were fabricated to form a polarized electroluminescent device using poly(ethylene dioxythiophene)-poly(styrene sulfonicacid) (PEDOT-PSS) as an alignment layer. For the case of primary colors, a host-guest approach that utilized a blue light emission PI as a host with a green light P2 or a red light P3 as a guest led to approximately two- to fourfold enhancement in luminescence in comparison with that of a neat film in polymer light emitting diodes (PLEDs), 1039 versus 2205 cd/m2 and 284 versus 1146cd/m2. In the case of white light, as a consequence of blending, polarized emission peak ratio of up to 4.4 and a pure white luminance brightness of up to 1895 cd/m2 have been attained. © 2005 The Japan Society of Applied Physics.