Novel EDOT and fluorene-based electroluminescent “bricks” as materials for OLEDs

Abstract

Luminescent materials based on 3,4-ethylenedioxythiophene (EDOT) and dihexylfluorene were designed. EDOT–fluorene– EDOT molecule, C3, was synthesized in high yields by a Stille cross-coupling reaction. The formylation of EDOT units yielded C4 molecule and a subsequent coupling reaction of C4 with a Wittig reagent produced C5. Electrochemical and optical experiments allowed us to accurately determine the energy level diagram corresponding to these three new molecules. Finally, in order to compare the electroluminescent behaviour of the bricks C3, C4 and C5, a simple monolayer OLED structure [ITO/PEDOT-PSS(50 nm)/Cx(50 nm)/Ca(100 nm)/Al(100 nm)] was designed. In the case of C5, energetic barriers at both interfaces were significantly reduced. For these reasons, devices based on C5 exhibit very high luminance values of approximately 1000 Cd/m2 at low applied voltage (below 10 V) with a turn-on voltage of 4.5 V. Maximum quantum and luminous efficiencies of 0.3 Cd/A and 0.1 lm/W are reported. According to the basic single layer structure, such values are very promising if C5 is used as emissive material in a multilayer-device.