Synthesis and Electroluminescence of New Polyfluorene Copolymers with Phenothiazine Derivative. Their Application in White-Light-Emitting Diodes

Abstract

New alternating polymers based on 2,7-dibromo-9,9-bis(4-octyloxy-phenyl) fluorene (BOPF), poly{9,9-bis-(4-octyloxy-phenyl)-fluorene-2,7-diyl- co -3,7-bis(1-cyanovinyl-3-phenothienyl)-1-(2′-ethylhexyloxy)-4-methoxybenzene-3′,7′-diyl} (PFPCVBs), have been designed, synthesized, and characterized. The PFPCVBs were synthesized through palladium-catalyzed Suzuki coupling reactions. BOPF and 3′,7-bis[3-(7′-bromo-phenothienyl)-1-cyanovinyl]-1-(2′-ethyl-hexyloxy)-4-methoxy-benzene (BPCVB) were used as the blue- and orange-light-emitting chromophores, respectively. These polymers were found to be thermally stable and readily soluble in common organic solvents. The photoluminescence (PL) spectra of the synthesized polymers contain both blue and orange emissions from these two chromophores. Moreover, by adjusting the BOPF and BPCVB contents, white-light emission can be obtained from a single PFPCVB polymer. EL devices with ITO/PEDOT:PSS/polymer/Balq/LiF/Al configurations using these polymers were found to produce blue and orange emissions. The EL emissions of PFPCVB 025 and PCPCVB 050 were found to result in white electroluminescence with Commission Internationale de L’Eclairage (CIE) coordinates of (0.30, 0.36) and (0.33, 0.39), respectively. The EL emissions of PFPCVB 025 are stable with respect to variation in the voltage, and were found to have the coordinates (0.30, 0.36), (0.29, 0.35), and (0.28, 0.34) at various device driving voltages. The device using PFPCVB 050 exhibits a maximum brightness of 1740 cd/m 2, a maximum current efficiency of 1.95 cd/A, and a maximum external quantum efficiency of 0.9%.