the vacuum deposition method, with the following configuration:
ITO (150 nm)/a-NPD (40 nm)/4 (30 nm)/TPBI (30 nm)/LiF
(1 nm)/Al (200 nm) (a-NPD: 4,4¢-bis((1-naphthyl)phenylamino)-
1,1¢-diphenyl). 4a exhibited a nearly pure blue EL spectrum with
CIE coordinates of x = 0.150 and y = 0.104, which are close to
the standard blue values of the National Television Standards
Committee (NTSC) (x = 0.14, y = 0.08). The device using 4a
demonstrated good performance, with a maximum luminance
of 4,116 cd m-2 and a current efficiency of 0.88 cd A-1. Its
external quantum efficiency was 1.12% at 0.4 mA. However, the
EL spectrum of 4e exhibited an unintentional color change when
the applied voltage was increased (Fig. S2†).
In summary, diimidazo[1,2-a:2¢,1¢-c]quinoxaline derivatives
were synthesized, and their optical properties were investi-
gated. The new methods to construct a diimidazo[1,2-a:2¢,1¢-
c]quinoxaline skeleton were achieved by the reaction of an-
ionic 1,2-di(imidazolyl)benzene with iodine or a Pd-catalyst with
good yields. Enhancement of the fluorescent quantum yield was
achieved by changing the pyrrole moieties of 1 to imidazole moi-
eties. Blue fluorescence with a high quantum yield was obtained
from4 bearing aryl groups at the 3 and 10 positions of 3. We also
showed that 4 have the potential to be used as efficient emitting
materials in OLEDs. Our investigations to further improve the EL
properties and on the use of diimidazoquinoxalines as fluorescence
sources are under way.
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