Synthesis and electroluminescence properties of poly(9,9-di-n-octylfluorenyl-2,7-vinylene) derivatives for light-emitting display

Abstract

9,9-Dialkylfluorenevinylene-based electroluminescence (EL) polymers, poly(9,9-di-n-octylfluorenyl-2,7-vinylene) poly(FV) and poly [(9,9-di-n-octylfluorenyl-2,7-vinylene)-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene}] poly(FV-co-MEHPV), have been synthesized by the Gilch polymerization method. The structure and properties of those polymers were characterized using H-1, C-13 NMR, UV-vis spectroscopy, elemental analysis, GPC, DSC, TGA, photoluminescence (PL), and EL spectroscopy. The 9,9-dialkylfluorenevinylene-based EL polymers were soluble in common organic solvents and easily spin-coated onto the indium-tin oxide (ITO)-coated glass substrates. The weight-average molecular weight (M-w) and polydispersity of poly(FV) and poly(FV-co-MEHPV) were in the range (22.2-43.2) x 10(4) and 1.9-3.0, respectively. Double-layer light-emitting displays (LEDs) with an ITO/PEDOT/polymer/Al configuration were fabricated, and the devices using poly(FV-co-MEHPV) showed better EL properties than those using pure poly(FV) or MEH-PPV. The emission maxima of poly(FV) and poly(FV-co-MEHPV), with various feed ratios of MEH-PPV contents, were observed at 507 and 585 mn, respectively, regardless of copolymer compositions. This phenomenon can be explained by energy transfer from poly(FV) segments with wide band gap to MEH-PPV blocks with smaller band gap in these copolymer systems. The turn-on voltages of poly(FV) and its copolymers dramatically decreased to 2.5 V as compared with those for poly(9,9-dialkylfluorene)s (PF)s. Maximum brightness and luminescence efficiencies were increased up to 1350 cd/m(2) and 0.51 cd/A, respectively.