Synthesis and characterization of arylamino end-capped silafluorenes for blue to deep-blue organic light-emitting diodes (OLEDs)

Diphenylamino- or cabazolyl-endcapped silafluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been designed, synthesized, and characterized. Double layer electroluminescent devices of these silafluorene derivatives exhibited efficient blue emission. The non-doped double layer OLEDs containing TDMS, TDPS, CDMS, or CDPS exhibited better electroluminescence efficiencies than those of the devices using the reference emitter DPFL-NPB, among which the best device was with TDPS, which showed a maximum current efficiency of 1.62 cd A−1 and an external quantum efficiency (EQE) of 1.36%. The solution processed device using TDPS as dopant exhibited a high performance with an EQE of 2.48% and an obviously low turn-on voltage of 4 V, when compared to the results of the reference device. The replacement of the carbon atom of the fluorene unit with a silicon atom could lower the energy gap effectively and improve the thermal stability as well as optical performances. The results indicate that the end-capped arylamino groups affect the organic light-emitting diode (OLED) performances greatly and aryl or alkyl substitution on the 9-position of a silafluorene unit is also crucial to the OLED performances of this kind of silafluorene.

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