White electroluminescence from a single polyfluorene containing bis-DCM units

A series of fluorene-based copolymers composed of blue- and orange-light-emitting comonomers were synthesized through palladium-catalyzed Suzuki coupling reactions. 9,9-Dihexylfluorene and 2-(2,6-bis-{2-[1-(9,9- dihexyl-9H-fluoren-2-yl)-1,2,3,4-tetrahydroquinolin-6-yl]-vinyl} -pyran-4-ylidene)-malononitrile (DCMF) were used as the blue- and orange-light-emitting chromophores, respectively. The resulting single polymers exhibited simultaneous blue (423/450 nm) and orange (580-600 nm) emissions from these two chromophores. By adjusting the fluorene and DCMF contents, white light emission could be obtained from a single polymer; a device with an ITO/ PEDOT:PSS/polymer/Ca/Al configuration was found to exhibit pure white electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.31), a maximum brightness of 1180 cd/m², and a current efficiency of 0.60 cd/A. Furthermore, the white light emission of this device was found to be very stable with respect to variation of the driving voltage. The CIE coordinates of the device were (0.32, 0.29), (0.32, 0.29), and (0.33, 0.31) for driving voltages of 7, 8, and 10 V, respectively.