The fabrication and characterization of single-component polymeric white-light-emitting diodes

By using Ni⁰-mediated polymerization, we have systematically synthesized a series of fluorene-based copolymers composed of blue-, green-, and red-light-emitting comonomers with a view to producing polymers with white-light emission. 2,7-Dibromo-9,9-dihexylfluorene, {4-(2-[2,5-dibromo-4-{2- (4-diphenylamino-phenyl)-vinyl}-phenyl]-vinyl)-phenyl}-diphenylamine (DTPA), and 2-{2-(2-[4-{bis(4-bromo-phenyl)amino}-phenyl]-vinyl)-6-tert-butyl-pyran-4- ylidene}-malononitrile (TPDCM) were used as the blue-, green-, and red-light-emitting comonomers, respectively. It was found that the emission spectra of the resulting copolymers could easily be tuned by varying their DTPA and TPDCM content. Thus with the appropriate red/green/blue (RGB) unit ratio, we were able to obtain white-light emission from these copolymers. A white-light-emitting diode using the polyfluorene copolymer containing 3 % green-emitting DTPA and 2 % red-emitting TPDCM (PG3R2) with a structure of indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid)/PG3R2/Ca/Al was found to exhibit a maximum brightness of 820 cd m ^-2 at 11 V with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33,0.35), which are close to the standard CIE coordinates for white-light emission (0.33,0.33).