Synthesis and properties of novel electrophosphorescent conjugated polyfluorenes based on aminoalkyl-fluorene and bipyridine with rhenium(I) complexes

Novel bipyridine-based aminoalkyl-polyfluorene and their corresponding rhenium complex-contained copolymers with different rhenium complex contents in polymer backbone were synthesized by Suzuki polymerization and post-polymerization, respectively. The aminoalkyl-polyfluorenes have good solubility in organic solvents and also are able to dissolve in methanol by adding a few drops of acetic acid. The solubility in polar solvents such as alcohol provides a great advantage in fabrication of multi-layer PLEDs. However, the rhenium complex-based copolymers become insoluble in common organic solvents; instead have a good solubility in polar solvents, such as methanol and DMF. The optoelectronic and electroluminescent properties of these copolymers (bipyridine- and rhenium-based copolymers) were investigated. The electroluminescent properties of these copolymers were found to have similar device performances by using high work function metal (Al) and low work function metal (Ba) as cathodes. We also found that these rhenium copolymers can be used as the electron transport layer in PLED. After inserting a thin rhenium copolymer layer between emission layer (P-PPV or PFO-DBT15) and cathode, a great improvement in EL performance could be achieved.