Very low amplified spontaneous emission threshold and electroluminescence characteristics of 1,1′-diphenyl substituted fluorene derivatives

A blue amplified spontaneous emission with a very low threshold was observed in novel fluorene derivatives doped into a 4,4′-bis-(N-carbazole)-biphenyl (CBP) host. With 6 wt%-2,7-bis[4′-(N,N-diphenylamino)-1,1′-biphenyl-4-yl]-9,9-bis(1,1′-biphenyl-4-yl)-9H-fluorene (BDF2) or 2,7-bis[1,1′-biphenyl-4-yl]-9,9-bis(1,1′-biphenyl-4-yl)-9-H-fluorene (BBF) as a dopant, high photoluminescence quantum efficiencies of 90% ± 1% and 78% ± 2% with extremely low amplified spontaneous emission thresholds of 0.15 ± 0.05 μJ/cm² (300 W/cm²) and 0.17 ± 0.04 μJ/cm² (340 W/cm²) were obtained. We also observed a high gain coefficient (38 cm^-1) and a low loss coefficient (6 cm^-1) in a 6 wt%-BDF2:CBP thin film optical-waveguide. Furthermore, an organic light emitting diode with BDF2 as an emitter demonstrated a high external quantum efficiency (η_ext) of 4.5% ± 0.1%. In addition, electroluminescence from an organic field-effect transistor with BDF2 as an active material was also observed with a maximum η_ext of 0.02%.