A novel bright blue electroluminescent polymer: poly[4,4′‐biphenylene‐α‐(9″,9″‐dihexyl‐3‐fluorenyl) vinylene]

Poly4,4′‐biphenylene‐α‐(9”,9”‐dihexyl‐2‐fluorenyl)vinylene] (PBPHFV) was synthesized by nickel catalyzed coupling reaction of 1,2‐bis(bromophenyl)‐1‐(9”,9”‐dihexyl‐2‐fluorenyl)ethene and characterized by spectroscopic methods and elemental analysis. PBPHFV is soluble in common organic solvents. The weight average molecular weight (Mw) of PBPHFV is about 15000. PBPHFV showed good thermal stability as weight loss was less than 5 % on heating to 420 C under nitrogen atmosphere. The polymer film showed maximum absorption and emission at 370 nm and 485 nm, respectively. A bright blue electroluminescence (λ_max = 465nm, maximum intensity = 4116 cd/m²) was obtained when the device was fabricated with the structure of ITO/PEDOT/PBPHFV/LiF/Al. The turn on voltage of the device was 4.3 V and the maximum efficiency was 0.22 lm/W. When the blend with PVK (PBPHFV : PVK = 1:5) was used as an emitting layer, the maximum brightness and efficiency of the device were 9342 cd/m² and 1.66 lm/W, respectively.