New oligomers containing pendant 4-aryl-7-phenylfluorene units as efficient charge transporting materials for OLEDs

Abstract Monomers and oligomers containing electronically isolated 4-aryl-7-phenylfluorene fragments have been synthesized by the multi-step synthetic route. The materials were characterized by thermo-gravimetric analysis, differential scanning calorimetry and electron photoemission technique. The oligomers represent materials of very high thermal stability having initial thermal degradation temperatures in the range of 402–412 °C. The glass transition temperatures of the amorphous oligomers were in the rage of 97–129 °C. The electron photoemission spectra of thin layers of the oligomeric materials showed ionization potentials in the range of 5.7–6.1 eV. Hole injecting/transporting properties of the electroactive oligomers were tested in the structures of organic light emitting diodes with tris(quinolin-8-olato)aluminium as a green emitter. The device containing hole-transporting material with 4-biphenyl-7-phenylfluorene electrophores exhibited the best overall performance with low turn on voltage of 4.4 V, high current efficiency exceeding 3.6 cd/A and maximum brightness exceeding 3200 cd/m 2 .