White electroluminescence from a single polymer: A blue-emitting polyfluorene incorporating orange-emitting benzoselenadiazole segments on its main chain

We have developed efficient white-light-emitting polymers through the incorporation of low-bandgap orange-light-emitting benzoselenadiazole (BSeD) moieties into the backbone of a blue-light-emitting bipolar polyfluorene (PF) copolymer, which contains hole-transporting triphenylamine and electron-transporting oxadiazole pendent groups. By carefully controlling the concentrations of the low-energy-emitting species in the resulting copolymers, partial energy transfer from the blue-fluorescent PF backbone to the orange-fluorescent segments led to a single polymer emitting white light and exhibiting two balanced blue and orange emissions simultaneously. Efficient polymer light-emitting devices prepared using this copolymer exhibited luminance efficiencies as high as 4.1 cd/A with color coordinates (0.30, 0.36) located in the white-light region. Moreover, the color coordinates remained almost unchanged over a range of operating potentials. A mechanistic study revealed that energy transfer from the PF backbone to the low-bandgap segments, rather than charge trapping, was the main operating process involved in the electroluminescence process. (c) 2007 Wiley Periodicals, Inc. Inc.