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7 March 2005 Light-emitting diodes of non-fully conjugated coil-like copolymers for tunable emission and carbon nanotube effect
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Non-fully conjugated 6F-PBO graft copolymers of poly(Am-co-B(1-m)) with poly[2,2-(m-2-hydroxyl-phenylene)- 4-4’-hexafluoroisopropane-bibenzoxazoles] (Am) and poly[2,2-(1,4-didecylhydroxyl-phenylene)-4-4’-hexafluoroisopro-pane-bibenzoxazoles] (B(1-m)) were synthesized with molar fraction m from 0, 0.25, 0.5, 0.75 to 1. The 6F-PBO random copolymers had identical benzoxazole with trifluoromethyl-ethyl as the backbone and pendants of mono-hydroxl (6F-PBO-OH, Am) and/or di-decyloxyl (6F-PBO-di(OC10H21), B(1-m)) on their phenylene rings. The copolymers were investigated by ultraviolet-visible (UV-Vis) light absorption covering 185 nm to 800 nm and photoluminescence (PL) emission excited at 363 nm. The PL exhibited a chromatic tuning range from green to white emission as m decreased. Light emitting devices (LEDs) of Al/copolymer/indium-tin-oxide were fabricated. A threshold voltage of 6 V was achieved for all 6F-PBO copolymer LEDs. The photometric coordinates of their electroluminescence (EL) emission were from (0.25, 0.53) to (0.24, 0.31) covering a visible range including white light emission. Another non-fully conjugated coil-like copolymer of poly(Am-co-C(1-m)) with 6F-PBO-OH (Am) and poly[2,2’-(2-hydroxy-o-phenylene)- 5,5’-bibenzimidazole] (Pbi-OH, C(1-m)) were synthesized and fabricated into LEDs. UV-Vis showed superposition of individual absorption from the 6F-PBO-OH and the Pbi-OH components. The PL and the EL had a red shift with increasing Pbi-OH content seemed to suggest that Pbi-OH was more charge delocalized than 6F-PBO-OH. PL and EL showed a green emission which was not tunable according to m. The threshold voltages were about at 2 ~ 3 V. Composites of poly(Am-co-C(1-m)) and multi-wall carbon nanotube (MWNT) were in situ synthesized for dispersion of the nanotubes. Few MWNT aggregations were observed via scanning electron microscope. The threshold voltages were 2 ~ 5 V. There was a red shift with MWNT addition in the PL and the EL but remained a green emission. Thus, up to 2 wt.% of MWNT was inconsequential on the PL and the EL emissions of the copolymer poly(Am-co-C(1-m)).
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Shih Jung Bai, Chien-Chang Wu, and Yi-Long Hsu "Light-emitting diodes of non-fully conjugated coil-like copolymers for tunable emission and carbon nanotube effect", Proc. SPIE 5739, Light-Emitting Diodes: Research, Manufacturing, and Applications IX, (7 March 2005);

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