Two
derivatives of tetrafluorophenylcarbazole and tri/tetraphenylethylene
displaying aggregation-induced emission enhancement were synthesized
and investigated by theoretical and experimental tools. The synthesized
compounds exhibit efficient emission in solid state with fluorescence
intensity maxima at 511 and 502 nm and photoluminescence quantum yields
of 57 and 27%. They exhibit high thermal stability with 5% weight
loss temperatures of 362 and 314 °C and glass-forming properties
with glass-transition temperatures of 112 and 80 °C. Ionization
potentials measured by photoelectron emission spectrometry were found
to be comparable (5.83 and 5.87 eV). The layers of the compounds showed
bipolar charge-transporting properties with balanced electron and
hole mobilities reaching 10–3 cm2/V s
at high electric fields. Exciplex-host-based OLEDs containing one
or two emitting layers of tetraphenylethenyl-containing emitter were
fabricated and showed more than 50% higher external quantum efficiency
as compared to that of the corresponding nondoped device. The best
nondoped OLED containing the synthesized emitter showed turn-on voltage
of 9.1 V, maximum brightness of 11 800 cd/m2, maximum
current efficiency of 4.5 cd/A, and external quantum efficiency of
ca. 1.7%. The best modified device, with exciplex-based host layer
showed turn-on voltage of 9.1 V, maximum brightness of 16 300
cd/m2, maximum current efficiency of 7.3 cd/A, and external
quantum efficiency of ca. 2.6%.
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