Search

Abstract: The morphology of fluorescent polyfluorene (PF) derivatives has strong effects on their electroluminescent (EL) performance. Herein, the influence of processing solvents on the morphology of PF-based white emissive polymer and its correlation to the EL behavior is studied. It is found that the PF copolymer films prepared from chlorobenzene:toluene (CB:TOL) solvent mixtures show stronger tendency to form crystalline α phase PF upon thermal annealing than those prepared from pure TOL or CB solvents. The evaporation rate difference in solvent mixtures can assist in the formation of crystal nucleus and enhance the crystallinity of PF backbone after thermal annealing. The results also reveal that the solvent mixture-processed fluorescent PF-based white emissive polymer not only shows more efficient blue emission, but also more balanced electron and hole transport. Accordingly, both the white emission purity and the light-emitting efficiency of the light-emitting diodes based on PF-based white emissive polymer are greatly enhanced. [Copyright &y& Elsevier]

Abstract: A series of copolymers (CNPFs) containing low-band-gap 1,8-naphthalimide moieties as color tuner was prepared by a Yamamoto coupling reaction of 2,7-dibromo-9,9-dioctylfluorene (DBF) and different amount of 4-(3,6-dibromocarbazol-9-yl)-N-(4′-tert-butyl-phenyl)-1,8-naphthalimide (Br–CN) (0.05–1mol% feed ratio). The light emitting properties of the resulting copolymers showed a heavy dependence on the feed ratio. In photoluminescence (PL) studies, an efficient color tuning through the Förster energy transfer mechanism was revealed from blue to green as the increase of Br–CN content, while in electroluminescence (EL) studies, the color tuning was found to go through a charge trapping mechanism. It was found that by introduction of a very small amount of Br–CN (0.1–0.5mol%) into polyfluorene, the emission color can be tuned from blue to pure green with Commission International de l''Echairage (CIE) coordinates being (0.21, 0.42) and (0.21, 0.48). A green emitting EL single-layer device based on CNPF containing 0.1mol% of Br–CN showed good performances with a low turn-on voltage of 4.2V, a brightness of 9104cd/m2, the maximum luminous efficiency of 2.74cd/A and the maximum power efficiency of 1.51lm/W. To further improve the EL performances through balancing the charge trapping process, a copolymer (BCNPF05) derived from 0.5mol% of a triarylamine-containing 4-{3,6-bis-[4″-(4‴-bromophenyl-p-tolyl-amino)-phenyl]-carbazol-9-yl}-N-(4′-tert-butyl-phenyl)-1,8-naphthalimide (Br–BCN) and 99.5mol% of 2,7-dibromo-9,9-dioctylfluorene was also prepared. As expected, a single layer EL device based on BCNPF05 exhibited better performances with a brightness of 14228cd/m2, the maximum luminous efficiency of 4.53cd/A and the maximum power efficiency of 1.57lm/W. [Copyright &y& Elsevier]