Extremely color-stable blue light-emitting polymers based on alternating 2,7-fluorene-co-3,9-carbazole copolymer

摘要

Novel alternating 2,7-fluorene-co-3,9-carbazole copolymer(3,9-PFCz) was synthesized by Suzuki polycondensation between 3-bromo-9-(2-iodo-9,9-dioctyl-9H- fluoren-7-yl)-9H-carbazole and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2- yl)-9,9-dioctylfluorene. Cyclic voltammetry studies showed a higher HOMO level (-5.23 eV) than the polyfluorene homopolymer(PFO). The glass transition temperature of the copolymer (110°C) was much higher than that of the PFO (67°C). After the copolymer had been annealed at 200°C for 2 h, the PL spectra showed almost no change and no aggregation- or oxidation-related undesirable long-wavelength emission has been observed. The light-emitting diode in configuration of ITO/PEDOT/EML/CsF/Al showed a maximum external quantum efficiency of 1.54% with a luminance of 435 cd·m-2and the maximum brightness of 2 630 cd · m-2with CIE coordinate (0.17, 0.14) was achieved at 8.4 V. The device prepared in configuration of ITO/PEDOT/PVK/polymer/Ba/Al exhibits an efficient, stable blue emission;it has a turn-on voltage of 6 V and maximum external quantum efficiency of 1.1%. The EL emission remains stable at high current density and after thermal treatment at 150°C for 30 min. Extremely color-stable blue emission from alternating poly[(2,7-fluorene)-co-(3,9-carbazole)] copolymer makes it a promising candidate for flat-panel display applications.

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