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 6wt%-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 mu J/cm(2) (300 W/cm(2)) and 0.17 +/- 0.04 mu J/cm(2) (340 W/cm(2)) 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 (eta(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 eta(ext) of 0.02%. (c) 2007 Elsevier B.V. All rights reserved.