Light-emitting diodes of non-fully conjugated coil-like copolymers for tunable emission and carbon nanotube effect

Non-fully conjugated 6F-PBO graft co polymers of poly(A m - co -B (1- m ) ) with poly[2,2-( m -2-hydroxyl-phenylene)- 4-4’- hexa fluoroisopropane- bi benzoxazoles] (A m ) and poly[2,2-(1,4- di decylhydroxyl-phenylene)-4-4’- hexa fluoroisopro-pane- bi benzoxazoles] (B (1- m ) ) were synthesized with molar fraction m from 0, 0.25, 0.5, 0.75 to 1. The 6F-PBO random co polymers had identical benzoxazole with tri fluoromethyl-ethyl as the backbone and pendants of mono -hydroxl (6F-PBO-OH, A m ) and/or di -decyloxyl (6F-PBO- di (OC 10 H 21 ), B (1- m ) ) on their phenylene rings. The co polymers 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/ co polymer/indium-tin-oxide were fabricated. A threshold voltage of 6 V was achieved for all 6F-PBO co polymer 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 co polymer of poly(A m - co -C (1- m ) ) with 6F-PBO-OH (A m ) and poly[2,2’-(2-hydroxy- o -phenylene)- 5,5’- bi benzimidazole] (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 de localized 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(A m - co -C (1- m ) ) and multi -wall carbon nanotube ( M WNT) were in situ synthesized for dispersion of the nanotubes. Few M WNT aggregations were observed via scanning electron microscope. The threshold voltages were 2 ~ 5 V. There was a red shift with M WNT addition in the PL and the EL but remained a green emission. Thus, up to 2 wt.% of M WNT was inconsequential on the PL and the EL emissions of the co polymer poly(A m - co -C (1- m ) ).