Three
primary color-emissive oligocarbazole end-capped molecules
(namely, CSBF, CPhC, and CNTD) were designed and synthesized by end-capping different aromatic
fluorophores of naphtho[2,3-c][1,2,5]thiadiazole,
phenanthrocarbazole (PhC), and spiro[benzo[c]fluorene-7,9′-fluorene]
with a structurally hindered electron-donating oligocarbazole unit. CSBF, CPhC, and CNTD exhibited strong
pure blue, green, and red fluorescence emission colors in solid films,
respectively, with hole-transporting property, high thermal and electrochemical
stability, and excellent film-forming property by a solution casting
process. The ternary blend thin film of CSBF/CPhC/CNTD (97.3:1.7:1.0) showed a high-quality mixed and
compatible thin film with a high photoluminescence quantum yield of
84%, pure white color emission, and a good hole mobility of 9.75 ×
10–8 cm2 V–1 s–1. The solution-processed organic light-emitting diodes
(OLEDs) using these materials as a non-doped emissive layer produced
deep blue, green, saturated red, and white emission colors with CIE
coordinates of (0.15, 0.09), (0.31, 0.58), (0.67, 0.33), and (0.33,
0.32), which are about the points for standard pure deep blue, green,
red, and white colors. These OLEDs delivered low turn-on voltages
(V
on) of 3.0–4.6 V, high luminance
efficiencies (LEs) of 1.25–6.67 cd A–1, and
high maximum external quantum efficiencies (EQEs) of 1.74–4.10%.
In particular, the white OLED showed a remarkable device performance
with a V
on of 3.0 V, an EQE of 4.02%,
an LE of 6.67 cd A–1, and great white color purity
and stability. Our results prove that the oligocarbazole unit is a
multipurpose component for constructing solution-processable light-emitting
molecules with different emission colors. It not only helps to maintain
the high emissive property of the fluorophores but also enhances their
hole-transporting property, allowing a simple device architecture
to be fabricated with high electroluminescent efficiency.