Table 1 Device configuration and efficiency of OLED device using
3,6,9,12-tetrakis(4-tert-butylphenyl)chrysene (7)
Peak
Efficiency/ Radiance/ wavelength/
Device configuration
cd Aꢀ1
cd mꢀ2
nm
MPMP(300 A)/emitter(400 A)/ 1.5
DPA(100 A)/AlQ(300 A)/
LiF(10 A)/Al(500 A)
500
450
(40 nm), DPA/AlQ (40 nm) as the electron transport material,
and LiF/Al as the cathode. Molecular structures of MPMP,
DPA and AlQ are shown in Scheme 3.
The (x,y) color coordinates of 7 are based on the 1931
convention, and are found at 0.23 and 0.35. The compound
was deposited as a neat film. The electroluminescent spectrum
shows a peak at 450 nm, but with a long tail, presumably due
to aggregation in the neat film. This long tail could be
eliminated if compound 7 were used as dopant in a host
matrix.10 Table 1 summarizes the device configuration and
the efficiency of the OLED device made from 7.
Fig. 1 ORTEP drawing of 3,6,9,12-tetrakis(4-tert-butylphenyl)chry-
sene (7). Thermal ellipsoids drawn to the 50% probability level. The
phenyl ring connected at C3 is rotationally disordered and nicely
resolved to a 0.67 : 0.32 ratio. Only the major conformation is shown.
In conclusion, we present here the first example of a tetra-
substituted chrysene, in which four aromatic substituents are
located in the 3, 6, 9 and 12 positions. The initial OLED device
was assembled incorporating chrysene 7. Further studies to
optimize the device architecture will be required to evaluate
the potential of tetra-substituted chrysenes in OLEDs.
chrysene 7. The tert-butylphenyl groups in positions 3 and 9
are perpendicular relative to the central ring, while the tert-
butylphenyl groups in positions 6 and 12 fluctuate around the
central chrysene ring, even in the solid state. There are no
aromatic–aromatic interactions of the chrysene core of 7,
indicating that the introduction of four tert-butylphenyl
groups broke the p-stacking. In general, p-stacking has been
found to be detrimental to OLEDs. Simple PAH molecules
like pyrene and chrysene have a tendency to form excimers
that decrease the fluorescence efficiency in condensed media.9
The bulky substituents of the substituted PAH are believed
to prevent the excimer formation that causes the concentration
quenching of fluorescence in the solid state.
Notes and references
z Synthesis of compounds: 3,6,9,12-tetrabromochrysene (2): bromine
(85 g, 0.53 mol) in trimethyl phosphate (100 ml) was added dropwise
to a stirred solution of chrysene (20.0 g, 0.0876 mol) dissolved in
trimethyl phosphate (300 ml) at 60 1C. The reaction temperature was
slowly increased to 100 1C and kept for 3 days at that temperature.
The resultant precipitate was filtered, washed with methanol (2 ꢂ 100
ml) and dried in vacuum. Yield of 3,6,9,12-tetrabromochrysene (2) was
39.14 g (82.14%) with no mp below 300 1C (decomposition above
300 1C). Direct probe GC-MS: exact mass found for C18H8Br4 is
543.73 g molꢀ1. Calculated mass found for C18H8Br4 is 543.73 g molꢀ1
for most abundant isotope combination.
3,6,9,12-Tetrakis(4-tert-butylphenyl)chrysene (7): 3,6,9,12-tetrabro-
mochrysene (2) (5.0 g, 0.00919 mol), 4-tert-butylphenylboronic acid
(3) (9.82 g, 0.0552 mol), tris(dibenzylideneacetone) dipalladium(0) (4)
(1.26 g, 0.00138 mol), di-tert-butyl(trimethylsilylmethyl)phosphane (5)
(0.62 g, 0.02670 mol), caesium carbonate (6) (17.97 g, 0.0552 mol) and
1,4-dioxane (100 ml) were refluxed for 48 h. The resultant mixture was
poured into 200 ml of water and extracted twice by 200 ml of
methylene chloride. The organic phase was dried over magnesium
sulfate overnight and filtered. The solvent was removed on a rotary
evaporator and the residue was purified by chromatography on silica
gel with petroleum ether–diethyl ether (10 : 0.5) as eluant. Yield of
3,6,9,12-tetrakis(4-tert-butylphenyl)chrysene (7) was 2.05 g (30%) as a
white solid with mp 376.48 1C. The melting point was measured by
DSC method. Additionally the purity was evaluated by LC-MS
method. It was found to be 99.17% based on retention area. 1H
NMR (CD2Cl2) 1.30 (s, 9H, t-Bu), 1.35 (s, 9H, t-Bu), 1.50 (s, 18H, t-
Bu), 7.60–9.20 (m, 24H, arom.-H). GC-MS (direct probe): exact mass
found for C58H60 is 756.47 g molꢀ1. Calculated mass found for C58H60
is 756.47 g molꢀ1. The pattern of the substitution of the chrysene ring
was confirmed from X-ray analysis.
Compound 7 shows blue photoluminescence. An OLED
device was fabricated from 7 by a thermal evaporation tech-
nique. The device configuration consists of ITO as the anode,
MPMP (30 nm) as the hole transport material, emitters
3,6,9,12-Tetrakis(4-tert-butylphenyl)chrysene (7) shows blue photolu-
minescence in toluene solution with a PL peak at 430 nm. The solution
quantum yield in toluene is measured to be 0.49 with 350 nm excitation
wavelength and quinine sulfate as the standard. For comparison
purpose, the solution PL quantum yield of unsubstituted chrysene is
0.12–0.17.13
Scheme 3
ꢁc
This journal is The Royal Society of Chemistry 2008
2320 | Chem. Commun., 2008, 2319–2321
Ionkin, Alex S.
