Pyrene-based Y-shaped solid-state blue emitters: Synthesis, characterization, and photoluminescence

Article abstract of DOI:10.1002/asia.201200530

A series of pyrene-based Y-shaped blue emitters, namely, 7-tert-butyl-1,3-diarylpyrenes 4 were synthesized by the Suzuki cross-coupling reaction of 7-tert-butyl-1,3-dibromopyrene with a variety of p-substituted phenylboronic acids in good to excellent yields. These compounds were fully characterized by X-ray crystallography, UV/Vis absorption and fluorescence spectroscopy, DFT calculations, thermogravimetric analysis, and differential scanning calorimetry. Single-crystal X-ray analysis revealed that the Y-shaped arylpyrenes exhibited a low degree of π stacking owing to the steric effect of the bulky tert-butyl group in the pyrene ring at the 7-position, and thus, the intermolecular π-π interactions were effectively suppressed in the solid state. Despite the significantly twisted nonplanar structures, these molecules still displayed efficient intramolecular charge-transfer emissions with clear solvatochromic shifts on increasing solvent polarity. An intriguing fact is that all of these molecules show highly blue emissions with excellent quantum yields in the solid state. Additionally, the two compounds containing the strongest electron-accepting groups, CN (4 d) and CHO (4 f), possess high thermal stability, which, together with their excellent solid-state fluorescence efficiency, makes them promising potential blue emitters in organic light-emitting device applications. Shades of blue: Pyrene-based Y-shaped blue solid-state emitters, 7-tert-butyl-1,3-diarylpyrenes 1, were synthesized by Suzuki cross-coupling reactions in good to excellent yields. Studies on single-crystal X-ray structures and the photophysical properties of these compounds strongly suggest that they are promising blue emitters in organic light-emitting device applications. Copyright

Full text of DOI:10.1002/asia.201200530

DOI: 10.1002/asia.201200530
Pyrene-Based Y-shaped Solid-State Blue Emitters: Synthesis,
Characterization, and Photoluminescence
Xing Feng,[a] Jian-Yong Hu,*[a, b] Liu Yi,[a] Nobuyuki Seto,[a] Zhu Tao,[c] Carl Redshaw,[d, e]
Mark R. J. Elsegood,[f] and Takehiko Yamato*[a]
Abstract: A series of pyrene-based Y-
shaped blue emitters, namely, 7-tert-
butyl-1,3-diarylpyrenes 4 were synthe-
sized by the Suzuki cross-coupling re-
action of 7-tert-butyl-1,3-dibromopyr-
ene with a variety of p-substituted phe-
nylboronic acids in good to excellent
yields. These compounds were fully
characterized by X-ray crystallography,
UV/Vis absorption and fluorescence
spectroscopy, DFT calculations, ther-
mogravimetric analysis, and differential
scanning calorimetry. Single-crystal X-
ray analysis revealed that the Y-shaped
arylpyrenes exhibited a low degree of
p stacking owing to the steric effect of
the bulky tert-butyl group in the pyrene
ring at the 7-position, and thus, the in-
termolecular p–p interactions were ef-
fectively suppressed in the solid state.
Despite the significantly twisted non-
planar structures, these molecules still
solvatochromic shifts on increasing sol-
vent polarity. An intriguing fact is that
all of these molecules show highly blue
emissions with excellent quantum
yields in the solid state. Additionally,
the two compounds containing the
strongest electron-accepting groups,
CN (4d) and CHO (4 f), possess high
thermal stability, which, together with
their excellent solid-state fluorescence
efficiency, makes them promising po-
tential blue emitters in organic light-
emitting device applications.
displayed
efficient
intramolecular
charge-transfer emissions with clear
Keywords: luminescence · organic
light-emitting devices · pyrenes ·
structure elucidation
activity relationships
· structure–
Introduction
[a] X. Feng, Dr. J.-Y. Hu, L. Yi, N. Seto, Prof. T. Yamato
Department of Applied Chemistry
Since pioneering works on small-molecule organic light-
emitting devices (OLEDs) were reported by Tang et al.,[1]
OLEDs have attracted increasing industrial and academic
interest owing to their high technological potential for next-
generation full-color flat panel displays and solid-state light-
ing.[1–4] Despite investigations into various organic com-
pounds (such as small molecules, conjugated polymers, and
carbon nanotubes) for OLED applications, the design and
synthesis of blue light-emitting compounds with satisfactory
multifunctional properties for high-performance OLEDs re-
mains a challenge. Moreover, understanding of the underly-
ing structure–property relationships in such systems is
a topic of ongoing interest.
Faculty of Science and Engineering, Saga University
1 Honjo-machi, Saga 840-8502 (Japan)
Fax : (+81)952-28-8679
E-mail: yamatot@cc.saga-u.ac.jp
[b] Dr. J.-Y. Hu
Department of Organic Device Engineering
Yamagata University, Yonezawa
Yamagata 992-8510 (Japan)
E-mail: hujianyong@yz.yamagata-u.ac.jp
[c] Prof. Z. Tao
Department Key Laboratory of Macrocyclic
and Supramolecular Chemistry of Guizhou Province
Guizhou University, Guiyang
Guizhou, 550025 (P.R. China)
[d] Dr. C. Redshaw
Pyrene is one of the classical polycyclic aromatic hydro-
carbons (PAHs), with a high fluorescence (FL) quantum
yield in solution and efficient excimer emission.[5–8] The ten-
dency of pyrene and its derivatives to form excimers has
been widely used in supramolecular design and for probing
the structural properties of macromolecular systems. The ex-
cimer FL of pyrene and its derivatives has also been em-
ployed to detect guest molecules[9] and sense environmental
parameters.[10] However, because the formation of p aggre-
gates/excimers leads to an additional emission band at
a longer wavelength and quenching of FL with low FL
quantum yields at high concentration or in the solid state,
the use of pyrene and its derivatives as red–green–blue
School of Chemistry, University of East Anglia
Norwich, NR4 7 JT (UK).
[e] Dr. C. Redshaw
Present address:
Department of Chemistry, University of Hull
Hull, HU6 7RX (UK)
[f] Dr. M. R. J. Elsegood
Chemistry Department, Loughborough University
Loughborough, LE11 3TU (UK)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201200530. It contains additional
characterization data (1H and 13C NMR spectra of compounds 4 and
5), crystal packing, and UV/Vis and fluorescence spectra of all com-
pounds as well as quantum chemistry calculation results.
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(RGB) emitters in OLED applications is still rather limited.
To suppress the formation of pyrene dimers, many types of
butterfly- and star-shaped molecules based on pyrene have
been designed and synthesized for organic optoelectronic
applications. Since the first example of a p-type organic
field-effect transistor (OFET) based on butterfly-shaped
pyrene-type molecules was reported by Zhu and co-work-
ers,[11] pyrene-based, star-shaped, organic semiconductors
have been prepared for optoelectronic devices, such as
OLED applications. For instance, Sonar and co-workers[12]
prepared 1,3,6,8-tetraaryl-functionalized pyrenes for applica-
tions in solution-processed organic electronic devices and
the 1,3,6,8-tetrakis(4-butoxyphenyl)pyrene derivative as the
active emitter showed high efficiencies with deep-blue emis-
sion, low turn-on voltages, and a maximum brightness.
Thomas and co-workers developed new blue- to yellow-
emitting materials by incorporating fluorene-based chromo-
phores on the pyrene core with an acetylene linkage and
using multifold palladium-catalyzed cross-coupling reac-
tions.[13] Both mono- and tetra-substituted alkynylpyrenes
were tested as emitting dopants with the host material, 4,4-
bis(9H-carbazol-9-yl)biphenyl (CBP), in multilayered
OLEDs and exhibited bright blue or yellow electrolumines-
cence. Chow and co-workers also developed a series of steri-
cally inhibited, p-stacked 1,3,6,8-tetraarylpyrenes, which
were explored as blue-emitting materials in OLEDs.[14] Kim
with co-workers investigated the two-photon absorption
properties and charge-transfer (CT) dynamics of a series of
covalently linked N,N-dimethylaniline (DMA) and pyrenyl
derivatives.[15,16] Kang and co-workers explored a series of
deep-blue dopants through a Buchwald–Hartwig coupling
reaction with N-phenyl-p-(R)-phenylamines and 1,6-dibro-
mopyrene;[17] here the emission colors can be controlled by
introducing electron-donating or -withdrawing R groups.
Sankararaman and Venkataramana reported a pyrene oc-
taaldehyde derivative that showed aggregation through
played a key role in inhibiting p-stacking interactions be-
tween neighboring pyrene units. Moreover, the multiple
conjugation pathways could also be pivotal in creating inter-
esting optoelectronic properties. Herein, we report the syn-
thesis, characterization, and photophysical properties of
a series of Y-shaped aryl-functionalized pyrenes. The aim of
our study was two-fold as follows: 1) to investigate the rela-
tionship between molecular structure and photophysical
properties; and 2) to explore how the substituted donating
or accepting groups at the para position of the benzene ring
opposite to the tBu group affect both the crystal packing
and the photophysical properties.
Results and Discussion
According to previous reports, 7-tert-butyl-1,3-dibromopyr-
ene (3)[20,21] can be synthesized from 2-tert-butylpyrene (2)
with Br2 at temperatures below ꢀ788C. However, the reac-
tion conditions are hard to control and complex by-products
are formed. Although the tBu groups can be preferably used
to obtain the 1,3-dibromopyrene selectively, electrophilic
substitution of pyrene can occur at other positions, such as
the 5- or 5,9-positions, by formylation and acetylation.[25]
Furthermore, the use of two tBu groups (i.e., at the 2- and
7-positions) allows substitution at the 4-, 5-, 9-, and 10-posi-
tions of the pyrene molecule to occur.[26,27] Herein, we
report new, milder conditions for the bromination of 2 and
the synthetic route is shown in Scheme 1. Pyrene was first
ꢀ
strong p···p and C H···p interactions in solution and in the
solid state.[18] Spectroscopic evidence suggested that the sum
ꢀ
of the multiple p···p and C H···p interactions could become
significant and might have influenced the optical properties
of materials. Gopidas and Suneesh examined the photoin-
duced electron-transfer processes in a 1,6-bis(phenylethy-
nyl)pyrene–phenothaiazine dyad (BPEP–PT) by using vari-
ous techniques.[19] In addition to these star-shaped 1,3,6,8-
tetra-substituted pyrenes, Mꢁllenꢂs group recently reported
a remarkable poly-7-tert-butyl-1,3-pyrene[20,21] as an effective
blue emitter for OLEDs applications, in which the tBu
group played an important role for suppressing undesirable
p-stacking interactions in the solid state. On the other hand,
similar Y-shaped pyrene derivatives were synthesized for in-
vestigations into intramolecular excimer formation and de-
layed FL in triplet–triplet annihilation.[22] Recently, to inhib-
it undesirable face-to-face p stacking in solution and in the
solid state, our group reported two types of cruciform- and
hand-shaped alkynyl-functionalized p-conjugated pyr-
enes.[23,24] Single-crystal X-ray analysis indicated that the
bulky tBu group in the pyrene rings at the 2,7- or 7-positions
Scheme 1. Synthesis of pyrene derivatives 4a–4 f. BTMABr3 =benzyltri-
methylammonium tribromide.
mono-tert-butylated to afford the 2-tert-butylpyrene (2),
which was then treated with BTMABr3 (3.5 equiv) in dry
CH2Cl2 at room temperature to give the desired 1,3-dibro-
mopyrene 3 in good yield (76%). The 7-tert-butyl-1,3-bisar-
ylpyrenes 4 were synthesized from dibromide 3 with the cor-
responding arylboronic acid by the Suzuki cross-coupling re-
action in good to excellent yields.
The chemical structures of the compounds 4 were con-
firmed by X-ray diffraction, 1H/13C NMR spectroscopy,
FTIR spectroscopy, MS, and elemental analysis (EA).
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Pyrene-Based Solid-State Blue Emitters
Table 1. Photophysical and electrochemical properties of Y-shaped molecules 4a–4 f and 5.
[e]
[f]
Y-shaped
molecule
lmax abs [nm]
Soln[a] Film[b]
lmax PL [nm][c]
loge
[mꢀ1 cmꢀ1
Stokes shift [nm]
Ff[d]
Tm
Td
Soln[a]
Film[b]
G
]
Soln[a]
Film[b]
Soln/thin film
[8C]
[8C]
4a
4b
4c
4d
4e
4 f
5
360
363
362
365
360
372
363
368
369
372
375
370
382
–
396 (291)
400 (292)
402 (292)
421 (291)
403 (291)
484 (291)
400 (292)
452 (290)
451 (290)
450 (285)
474 (288)
456 (289)
482 (293)
–
4.54
4.54
4.51
4.49
4.52
4.46
4.53
36
37
40
56
43
112
37
84
82
78
99
86
100
–
0.38/0.42
0.50/0.64
0.56/0.58
0.78/0.68
0.67/0.69
0.76/0.48
–
186
263
167
282
215
178
214
322
330
173
371
287
372
–
[a] Maximum absorption wavelength measured in dichloromethane at room temperature. [b] Measured in thin neat films. [c] The values in the parenthe-
ses are excitation wavelengths. PL=photoluminescence. [d] Measured in dichloromethane and neat thin films, respectively. [e] Melting temperature (Tm)
obtained from DSC measurements. [f] Decomposition temperature (Td) obtained from TGA.
Table 2. Summary of crystal data of Y-shaped molecules of 4a, 4c, 4d, 4 f, and 5.
The crystal structures of 4a,
4c, 4d, and 4 f (Figure 1) are
characterized by 2D layered
Complex
4a
4c
4d
4 f
5
formula
Mr
crystal system
space group
a [ꢃ]
b [ꢃ]
c [ꢃ]
a [8]
b [8]
C32H26
410.53
triclinic
C34H30O2
470.61
monoclinic
P21/c
18.815(14)
15.629(11)
8.851(6)
90.00
103.255(9)
90.00
2533(3)
4
C34H24N2
460.58
monoclinic
P21/c
9.933(8)
14.177(11)
17.386(13)
90.00
100.539(12)
90.00
2407(3)
4
C34H26O2
466.55
monoclinic
P21/c
16.8067(13)
15.1341(12)
9.7272(8)
90.00
102.9103(13)
90.00
2411.6(3)
4
1.285
150(2)
6805
5331
328
C42H38O8
670.72
orthorhombic
Pnma
13.298(5)
31.064(12)
8.702(3)
90.00
90.00
90.00
3595(2)
4
1.239
ꢀ
structures involving C H···p
ꢀ
bonds, p–p interactions, and hy-
drogen bonds. Although the ter-
minal moieties are different,
the architectures are almost
identical to each other. Howev-
er, some differences were found
between 4 f and the others.
Thus, we will describe the crys-
tal structures in detail and at-
tempt to interpret the effect of
the molecular structure on the
optical properties.
P1
9.937(9)
12.976(11)
19.018(17)
100.097(10)
93.575(10)
105.895(10)
2306(4)
4
1.183
293(2)
7951
4110
g [8]
V [ꢃ3]
Z
1calcd [mgmꢀ3
T [K]
]
1.234
123
5722
4734
1.271
123
5427
4856
100(2)
4204
2585
unique reflns
obsd reflns
parameters
578
330
328
252
R
(int)
0.0415
0.0683
0.2085
1.009
0.0640
0.1034
0.3036
1.186
0.0526
0.0897
0.2204
1.227
0.0287
0.0453
0.1325
1.043
0.0932
0.0975
0.3173
1.068
Compound 4a crystallizes in
the triclinic crystal system with
ꢀ
space group P1, whereas com-
2
[a] Conventional R on Fhkl: Sj jFo jꢀjFc j j/sjFo j. [b] Weighted R on jFhkl j : S[w(F2oꢀFc2)2]/S[w(Fo2)2]1/2
.
pounds 4c, 4d, and 4 f crystal-
lize in the monoclinic crystal
system (space group P21/c for
4c, 4d, and 4 f). In the crystals,
All results were consistent with the formation of the ex-
pected Y-shaped arylpyrenes 4. All compounds are very
soluble in common organic solvents, such as CH2Cl2, CHCl3,
tetrahydrofuran (THF), and toluene. The thermal properties
of 4 were investigated by thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) measurements.
The decomposition temperatures (Td) of pyrenes 4a–f were
in the range of 173–3728C, corresponding to a 5% weight
loss. Key thermal data for these pyrene derivatives are sum-
marized in Table 1.
the terminal moieties adopt a reasonably twisted conforma-
tion, with a dihedral angle (torsion angle) relative to the
pyrene core falling in the range 44.2–79.08 for 4a, 46.7–56.68
for 4c, 52.9–54.78 for 4d, and 38.8–43.68 for 4 f. The torsion
angles between the central pyrene ring and the terminal aryl
groups in the present structures are less than that in the
crystal structure of 1,3,6,8-tetrakis(2,4,6-trimethylphenyl)-
pyrene (86.2–88.28),[10] which suggests that the terminal aryl
groups do not contribute effectively toward suppressing in-
termolecular interactions in the solid state.
Our previous reports have shown that bulky tBu groups
substituted at the 2,7- or 7-positions of the pyrene ring can
play a crucial role in pyrene systems.[24,25] On one hand, the
sterically bulky tBu groups were used to suppress undesira-
ble face-to-face p stacking in solution and in the solid state.
On the other hand, the electron-donating tBu group can
also be beneficial for making the wavelength of absorption
and FL emission less bathochromically shifted. Moreover,
these twist angles with steric hindrance between the pyrene
core and the terminal chromophore groups can effectively
X-ray Crystallography
Attempts to prepare crystals of 4b and 4e suitable for X-ray
crystallography were unsuccessful; however, crystals of 4a,
4c, 4d, and 4 f were obtained by slow evaporation of a mix-
ture of dichloromethane/hexane at room temperature. Key
crystallographic data are listed in Table 2; crystal structures
of each molecule are shown in Figure 1.
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the phenyl ring with the adja-
ꢀ
cent
pyrene
core
(C61
H61···C18=2.96 ꢃ
and
a
aC61-H61-C18=157.28),
the terminal phenyl moieties
are almost perpendicular to
each other with an angle of
79.08 between the phenyl ring
and the pyrene core.
Figure 3 shows the crystal
packing for compound 4 f. Each
molecule is arranged in a regu-
ꢀ
lar off-set geometry with C
ꢀ
H···p (C25 H25···C1=2.88 ꢃ,
ꢀ
C34 H34···C9=2.85 ꢃ
and
and
ꢀ
ꢀ
C21 H21···C28=2.68 ꢃ)
hydrogen
bond
(C22
H22···O1=2.86 ꢃ) noncovalent
interactions along the c axis.
The distance between pyrene
centroids in neighboring mole-
cules is 5.79 ꢃ, which means
that the stacking interactions
between the pyrene moieties
are rather weak. In comparison
with 4a, 4c, and 4d, possessing
electron-withdrawing aldehyde
Figure 1. X-ray structures of compounds 4a, 4c, 4d, and 4 f. Hydrogen
atoms are omitted for clarity.
hinder tight intermolecular packing in the solid state. In
compound 4a, the molecules pack in a herringbone motif, as
shown in Figure 2. Two neighboring pyrene moieties are
present with displaced face-to-face patterns possessing
a centroid to centroid distance of 5.52 ꢃ and a slip angle of
28.18, which is indicative of the existence of p–p interac-
ꢀ
tions. Furthermore, there are three kinds of short C H···p
ꢀ
ꢀ
(C61 H61···C18=2.96 ꢃ,
C55 H55···C21=3.34 ꢃ,
and
ꢀ
C54 H54···C24=3.21 ꢃ) noncovalent interactions present in
the stacking structures. Arising from strong interactions of
Figure 3. Crystal packing diagram of 4 f viewed parallel to the c axis.
groups, the molecular structure of compound 4 f is more
planar with a smaller torsion angle between the phenyl
group and the pyrene core; this increases p conjugation and
delocalization of the electron density, which can be ex-
plained in terms of the noncovalent interaction between the
pyrene rings that could lead to strong cooperative effects.[28]
Photophysical Properties
The photophysical properties of the compounds 4 were ex-
amined both in dichloromethane and as films. All spectral
data are summarized in Table 1. The UV/Vis absorption
Figure 2. Crystal packing diagram of 4a viewed down the a axis.
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Pyrene-Based Solid-State Blue Emitters
tion bands of 4 are significantly red-shifted by about 48–
56 nm relative to those in solution (e.g., lem =452 nm for 4a,
451 nm for 4b, 450 nm for 4c, 474 nm for 4d, and 456 nm
for 4e; Figure 5).
Figure 4. Normalized UV/Vis a) absorption and b) emission spectra of
compounds 4a–f recorded in dichloromethane at about 10ꢀ5–10ꢀ6 m at
258C.
spectra for 4, recorded in dichloromethane, are shown in
Figure 4a.
Figure 5. Normalized UV/Vis a) absorption and b) emission spectra of
Compounds 4a–f exhibit similar absorption behavior and
two prominent absorption bands were observed in the re-
gions l=280–295 and 360–375 nm. The short wavelength ab-
sorption located at l=280–295 nm revealed a vibronic fea-
ture for the unsubstituted parent pyrene and the higher
energy absorption was associated with the intramolecular p–
p* transition. This absorption behavior is related to that ob-
served for similar molecular structures with pyrene as the
core. More interestingly, the absorption bands for compound
4 f were broader and larger red-shifts were observed at
a lmax of 293 and 372 nm. This was thought to be due to ex-
tended delocalization of the p electrons over a large area of
the molecule, which was expected to broaden the absorption
band and increase optical density.[29] The intensities of the
absorption bands exhibited the following order: CHO>
CN>CF3 >OMe>tBu>H.
To further investigate the photophysical properties, the
FL emission spectra for compounds 4 (Figure 4b) revealed
that all pyrene derivatives emitted deep-blue emissions in
the region of 370–450 nm, without observing any extra tail-
ing absorption up to 550 nm; the exception was 4 f. All of
the Y-shaped compounds exhibit bright-blue FL emissions,
even at concentrations as low as 10ꢀ6 m. Compounds 4a, 4b,
4c, 4d, and 4e exhibited a similar emission model, with
band maxima located at 396, 400, 402, 421, and 403 nm in
CH2Cl2, respectively. In the thin films, the emission absorp-
4a–4 f in neat thin films.
This was consistent with the phenomena observed in the
absorption spectra and ascribed to the effect of the substitu-
ents and intramolecular conformations of the similar Y-
shaped pyrene derivatives. Additionally, the terminal aryl-
phenyl substituents at the 6,8-position should barely hinder
intermolecular interactions in the solid state owing to the
small twist angle between the phenyl moieties and the
pyrene core. However, the emission spectrum of 4 f exhibits
a permanent broad absorption band with maximum emis-
sion peaks at 421 and 484 nm, which suggests that there are
strong intermolecular interactions occurring in solution.
Clearly, the bathochromic shift of the 4 f FL lmax was larger
than those for the compounds 4a, 4b, and 4c. This can be
ascribed to the terminal aldehyde groups, which can enlarge
the p-conjugation length of the pyrene derivatives. Further-
more, the effects of concentration on the FL emissions of 4
were examined in CH2Cl2. Upon increasing the concentra-
tion from 3.0ꢄ10ꢀ8 to 5.0ꢄ10ꢀ4 m, the intensities of the emis-
sion band gradually increased and only the maximum ab-
sorption peaks for the monomer were observed without
extra excimer emissions (see Figure S6 in the Supporting In-
formation). This evidence suggested that the attachment of
the single bulky tert-butyl group at the 7-position could pre-
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vent two Y-shaped molecules from getting close enough to
result in excimer emission at high concentration and in the
solid state. The quantum yield values, Ff, of 4 (Table 1)
were recorded in solution (from 0.38 to 0.78) and in the thin
film (from 0.42 to 0.69). In contrast, the PL spectrum of 4 f
is about 2 nm blue-shifted in the solid state (ꢁ482 nm) rela-
tive to that of the FL emission observed in solution
of the singlet excited states as a function of increasing polar-
ity of the solvents.[32]
More importantly, the FL emission colors in solution
strongly depended on the polarity of the solvents; for exam-
ple, in cyclohexane, the FL of solution is deep blue, whereas
in CH2Cl2, DMF, or CH3CN it is sky blue. We have also
used a Lippert–Mataga plot to determine the line relation-
ship of Stokes shift (Dnst) against the solvent parameter Df-
A
similar regions to those observed in dichloromethane and
tetrahydrofuran. This phenomenon suggests that the dielec-
tric constant of compound 4 f in the solid film lies close to
that in tetrahydrofuran and is less than that in dichlorome-
thane.[30,31]
ACHTUNGTRENNUNG
groups in the pyrene ring on the geometric arrangements
and the photophysical properties, we further prepared com-
pound 5 from 4 f. This was achieved by an addition reaction
with ammonium acetate (yield: 19%), in which two acetate
groups were introduced at the para position of the benzene
rings in the Y-shaped architecture to extend the terminal
substitution group chains (Scheme 2).
The effects of solvent were investigated by using cyclo-
hexane, THF, CH2Cl2, CH3CN, and N,N-dimethylformamide
(DMF). The emission maxima of 4a–4c, with electron-do-
nating groups, were slightly shifted by up to 5 nm, depend-
ing on the solvent polarity. However, for compounds 4d–4 f,
with electron-withdrawing groups, the solvent dependence
in the emission spectra is remarkable, with large bathochro-
mic shifts of 25 nm for 4d, 10 nm for 4e, and 75 nm for 4 f,
(see Figure S7 in the Supporting Information). Figure 6
shows the normalized UV/Vis absorption and FL spectra for
compound 4 f in various solvents. Because of the presence
of CHO moieties, the absorption spectra of compound 4 f
does not show any clear change, whereas the emission spec-
trum exhibits a more significant redshift in polar solvents
than in nonpolar solvents from cyclohexane to DMF. This
solvatochromism can be attributed to the decrease in energy
Scheme 2. Synthetic route to compound 5.
The chemical structure of 5 was initially determined on
1
the basis of EA and spectral data. The H NMR spectrum of
5 in CDCl3 shows a singlet at d=2.20 ppm for the methyl
protons, a singlet at d=7.71 ppm for the aromatic protons,
and a singlet at d=7.82 ppm for the methine protons. These
data strongly support the proposed structure of 5. A suitable
crystal of 5 was obtained from a solution in a mixture of di-
chloromethane and acetone (1:1) by slow evaporation at
room temperature. Low-temperature X-ray diffraction anal-
ysis revealed that compound 5 crystallized in the orthorhom-
bic space group Pnma (Figure 7).
The asymmetric unit consists of half of the molecule,
which lies on a mirror plane, with the terminal acetate units
adopting a branched shape at the para position of each C6H4
aromatic ring. The torsion angle between the pyrene and
C6H4 ring is 65.138. The molecules of 5 adopt a 1D, slipped,
face-to-face motif with off-set head-to-tail stacked columns,
which contrasts with the herringbone structures observed
ꢀ
for 4a, 4c, 4d, and 4 f. The tBu group is involved in a C
ꢀ
H···p (C18 H18···C10) interaction with an intermolecular
distance of 2.71 ꢃ. There is some two-fold tBu group disor-
der with an occupancy ratio 0.5:0.5 for C18, C19, and C20.
However, there is no p stacking in this structure (see the
Supporting Information) and this crystal structure demon-
strates how the presence of the bulky tBu group and an ace-
tate group at the para position of the C6H4 rings can pre-
clude the herringbone and stacking motifs found in most
PAH structures.[34]
Figure 6. Normalized UV/Vis a) absorption and b) emission spectra of 4 f
in cyclohexane, THF, CH2Cl2, CH3CN, and DMF at 258C.
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Pyrene-Based Solid-State Blue Emitters
carbon to an sp3 carbon center, which cut the LUMO-stabi-
lizing donor–acceptor conjugation of 4 f. Similarly, the FL
emission bands of 5 were also hypsochromically shifted by
about 76 nm in comparison to that of 4 f. The results demon-
strated that the presence of the tBu group and extending the
substituent chain efficiently suppressed p stacking in the
structure and effectively influenced the photophysical prop-
erties.
Quantum Chemistry Computations
To obtain insight into the electronic structure of these aryl-
functionalized pyrenes, DFT calculations (B3LYP/6-31G*
basis set) were performed on 4a–4 f with the Gaussian 03W
software package.[35] The energies of the HOMO and
LUMO levels for these compounds are collected in Table 3.
The frontier orbital energies remain similar for all of the
compounds; this indicates that the frontier orbitals are de-
rived from the pyrene moieties in all compounds. The im-
portance of the donor group on the pyrene ring is also at-
tributed to the low-energy band, which allows a charge
transfer (CT) transition between pyrene and phenyl seg-
ments. The HOMO–LUMO (H–L) energy gaps (DE) for all
of the compounds were calculated to be in the range 3.32–
3.54 eV (Figure 9), which was consistent with the first
energy transition (350–375 nm).
Figure 7. X-ray single-crystal structure of compound 5. Hydrogen atoms
are omitted for clarity.
The photophysical properties of compound 5 were investi-
gated in dichloromethane. The UV/Vis absorption spectra of
5 have a sharp p–p* transition centered at about 363 nm
(Figure 8). The longest wavelength p–p* band of 5 was hyp-
sochromically shifted by about 9 nm in comparison to 4 f.
This shift was due to the extended terminal acetate units re-
placing the carbaldehyde group of 4 f, thus saturating the sp2
Calculation of the theoretical maximum absorption values
was consistent with the experimental values (360–372 nm).
Similarly, the H–L energy gaps for these compounds sug-
gests that the HOMO and LUMO are mainly comprised of
the same pyrene core segment. The twist angle between the
pyrene and phenyl group was also affected by the para sub-
stituents and followed the order CHO<CN<tBu<OMe<
CF3 <H (based on optimized structural data, see the Sup-
porting Information). The compounds are more planar with
a smaller torsional angle, leading to extended delocalization
of the p electrons over a large area of the molecule. The in-
terplanar distance between the pyrene cores is longer, so
that the p–p interactions are weakened by the substituents;
thus broadening the absorption band and increasing the op-
tical density, leading to stronger solid-state FL emission.
In addition, when investigating the effect of solvent polar-
ity in cyclohexane, THF, CH2Cl2, CH3CN, and DMF, only
Figure 8. Normalized UV/Vis absorption (dashed lines) and emission
(solid lines) spectra of 4 f and 5 in dichloromethane at about 10ꢀ5–10ꢀ6
at 258C.
m
Table 3. Computed frontier orbital energies for Y-shaped compounds 4a–4 f.
[e]
Compound LUMO+1 LUMO
HOMO
[eV]
HOMOꢀ1 HOMO–LUMO
HOMO[a] LUMO[b] Energy gap[c] Measured[d]
Calcd lmax
[nm]
[eV]
[eV]
[eV]
DE [eV]
[eV]
[eV]
[eV]
lmax [nm]
4a
4b
4c
4d
4e
4 f
5
ꢀ0.63
ꢀ0.57
ꢀ0.49
ꢀ1.63
ꢀ1.09
ꢀ1.85
ꢀ0.82
ꢀ1.55
ꢀ1.47
ꢀ1.41
ꢀ2.20
ꢀ1.90
ꢀ2.15
ꢀ1.69
ꢀ5.09
ꢀ5.01
ꢀ4.93
ꢀ5.61
ꢀ5.44
ꢀ5.47
ꢀ5.22
ꢀ5.99
ꢀ5.90
ꢀ5.71
ꢀ6.48
ꢀ6.31
ꢀ6.34
ꢀ6.09
3.54
3.54
3.32
3.40
3.51
3.54
3.53
ꢀ5.44
ꢀ5.48
ꢀ5.44
ꢀ5.69
ꢀ5.67
ꢀ5.67
ꢀ2.20
ꢀ2.28
ꢀ2.27
ꢀ2.62
ꢀ2.51
ꢀ2.69
3.24
3.20
3.17
3.07
3.16
2.98
360
363
362
365
360
372
363
350.8
350.8
374.1
365.3
353.8
350.8
351.8
[a] Calculated from the empirical formula HOMO=ꢀ(Eox +4.8). [b] LUMO=HOMO+Eg. [c] Eg estimated from UV/Vis absorption spectra. [d] Maxi-
mum absorption wavelength measured in dichloromethane at room temperature. [e] DFT (B3LYP/6-31G*) calculations were carried out with the use of
structures optimized at the B3LYP/6-31G* level of theory.
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Jian-Yong Hu, Takehiko Yamato et al.
FULL PAPER
angle. In compounds 4d and 4 f, the electron-accepting
groups, namely, cyano and aldehyde groups, enlarged the p-
conjugation length and led to delocalization of electron den-
sity, and given that the phenyl moieties twisted with small
angles, the trend was to form cofacial p–p stacking between
adjacent pyrene cores. Compound 5, with longer and flexible
terminal moieties, effectively suppressed p–p stacking and
led to an emission band in the deep-blue region. Com-
pounds 4 and 5 have high blue FL emissions with high quan-
tum efficiencies, good solubilities in common organic sol-
vents, and high stabilities. Thus, on the basis of their excel-
lent photophysical properties, these compounds are poten-
tially useful as blue emitters for OLED applications.
Figure 9. Schematic representations of HOMOꢀ1, HOMO, LUMO, and
LUMO+1 of 4 and 5.
Experimental Section
General
compounds 4d and 4 f exhibit reasonable solvatochromism
in the excited state. This suggests that peripheral electron-
withdrawing groups, such as CHO (4 f) and CN (4d), are
necessary to impart CT character on the molecule. Their re-
sults are in good agreement with the DFT calculations. Fur-
thermore, we also investigated the electrochemical charac-
teristics of the pyrene derivatives 4 by cyclic voltammetry.
The pyrenes were scanned positively and negatively, sepa-
rately, in 0.10m tetrabutylammonium perchlorate in anhy-
drous dichloromethane and THF with a scan rate of
100 mVsꢀ1 at room temperature. All compounds 4 showed
quasi-reversible or reversible processes (see the Supporting
Information). In particular, compound 4c in CH2Cl2 showed
a quasi-reversible oxidation wave with half-wave potentials
(Eoxi1/2) at 1.43 V and an irreversible oxidation wave at
a high oxidation potential 1.83 V (vs. the ferrocene couple
Fc/Fc+; see Table S3 in the Supporting Information). The
HOMO and LUMO energy levels were evaluated by using
All melting points (Yanagimoto MP-S1) are uncorrected. 1H NMR spec-
tra (300 MHz) were recorded on a Nippon Denshi JEOL FT-300 NMR
spectrometer with SiMe4 as an internal reference: J values are given in
Hz. IR spectra were measured as KBr pellets in a Nippon Denshi JIR-
AQ2OM spectrophotometer. UV/Vis spectra were recorded on a Perkin–
Elmer Lambda 19 UV/VIS/NIR spectrometer. Mass spectra were ob-
tained on a Nippon Denshi JMS-01SA-2 spectrometer at 75 eV by using
a direct-inlet system. EA was performed by using a Yanaco MT-5 instru-
ment. Gas–liquid chromatography (GLC) analyses were performed by
using a Shimadzu gas chromatograph, GC-14A; silicone OV-1, 2m; pro-
grammed temperature rise, 128Cminꢀ1; carrier gas nitrogen, 25 mLminꢀ1
.
Materials
According to a reported method, compound 3[20] was synthesized from 2-
tert-butylpyrene[36] with Br2 at a low temperature. The reaction conditions
were hard to control to avoid the formation of complex by-products, so
new milder conditions were explored and are shown in Scheme 1.
Synthesis of 2-tert-Butylpyrene (2)
A mixture of pyrene 1 (5 g, 24.2 mmol) and 2-chloro-2-methylpropane
(2.62 g, 3.23 mL) was added to CH2Cl2 (40 mL) at 08C and stirred for
15 min. Powdered anhydrous AlCl3 (3.62 g, 27.2 mmol) was slowly added.
The reaction mixture was continuously stirred for 3 h at room tempera-
ture and the reaction process was tracked by GC, then the solution was
poured into a large excess of ice/water. The reaction mixture was extract-
ed with dichloromethane (2ꢄ50 mL). The combined organic extracts
were washed with water and brine, dried with anhydrous MgSO4, and the
solvent was evaporated. The residue was recrystallized from hexane to
afford pure 2-tert-butylpyrene (4.56 g, 71%) as a gray powder. Further
recrystallization from hexane gave 2 as colorless prisms. M.p. 111.5–
113.28C (lit.[36] M.p. 110–1128C). The 1H NMR spectrum was in agree-
ment with the reported values. 1H NMR (300 MHz, CDCl3): d=1.59 (s,
9H; tBu), 8.18 (d, J=9.2 Hz, 2H; pyrene-H), 8.30 (s, 2H; pyrene-H),
8.37 (d, J=9.2 Hz, 2H; pyrene-H), 8.47 ppm (s, 1H; pyrene-H).
the empirical formula HOMO=ꢀ
ACHTUGNTRENN(NUG Eox+4.8) from the on-set
of the first oxidation. LUMO=HOMOꢀEg, and the optical
energy gap was derived from the lowest energy absorption
onset in the absorption spectra. Values are listed in Table 3
and show that experimental data corresponds well with the-
oretical calculations.
Conclusion
We have synthesized a series of Y-shaped, pyrene-based,
solid-state blue emitters by a Suzuki cross-coupling reaction
using 3 in good to excellent yields. For the five crystal struc-
tures studied herein, the results revealed the effects of the
substituent groups on the structures. Substitution at the p-
positions of the benzene rings of the Y-shaped molecules
can change the crystal structure and crystal-packing array.
Depending on the electron-donating or -accepting groups
and the length of the group, the Y-shaped arylpyrenes ex-
hibit stable, soluble, and remarkable blue photophysical
properties. Compounds 4a and 4c, with electron-donating
groups, exhibited shifted face-to-face patterns with a slippage
Synthesis of 7-tert-Butyl-1,3-dibromopyrene (3)
A solution of BTMABr3 (4.41 g, 3.5 mmol) in CH2Cl2 (20 mL) was added
dropwise to a mixture of 2 (2.58 g, 1 mmol) and CaCO3 (2 g, 20 mmol) in
CH2Cl2 (30 mL) at 08C for 1 h under argon atmosphere. The resulting
mixture was allowed to slowly warm to room temperature and was
stirred overnight. The reaction mixture was poured into ice water
(60 mL) and neutralized with a 10% aqueous solution of Na2S2O3. The
mixture solution was extracted with dichloromethane (2ꢄ50 mL). The or-
ganic layer was washed with water (2ꢄ20 mL) and brine (20 mL), and
then the solution was dried (MgSO4) and condensed under reduced pres-
sure. The crude compound was washed with hot hexane to afford 3
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Pyrene-Based Solid-State Blue Emitters
(3.02 g, 76%) as a colorless solid. Recrystallization from hexane gave 3
as a gray solid. M.p. 199.5–201.28C.
Ar-H), 8.04 (d, J=9.2 Hz, 2H; pyrene-H4,10), 8.11 (d, J=9.2 Hz, 2H;
pyrene-H5,9), 8.28 ppm (s, 2H; pyrene-H6,8); 13C NMR (75 MHz, CDCl3):
d=150.0, 145.6, 134.9, 132.3, 131.3, 131.0, 129.1, 128.2, 128.0, 125.3, 124.0,
123.3, 123.1, 118.8, 111.3, 35.3, 31.9 ppm; IR (KBr): n˜max =2960, 2729,
1604, 1495, 1462, 1400, 1362, 1228, 1153, 877, 841, 816, 729, 661, 607,
Synthesis of 1,3-Bisaryl-7-tert-butylpyrenes (4)
Compounds 4a–4 f were synthesized from 3 with the corresponding aryl-
boronic acid by a Suzuki coupling reaction in high yield.
559 cmꢀ1
;
MS: m/z: 460.2 [M]+; elemental analysis calcd (%) for
C34H24N2 (460.5): C 88.67, H 5.25, N 6.08; found: C 88.59, H, 5.32, N
5.81.
A mixture of 3 (200 mg, 0.5 mmol), 4-formylphenylboronic acid (300 mg,
2.0 mmol) in toluene (12 mL), and ethanol (4 mL) at room temperature
was stirred under argon, and a 2m aqueous solution of K2CO3 (20 mL)
7-tert-Butyl-1,3-bis(4-trifluoromethylphenyl)pyrene (4e) was obtained as
colorless prisms (recrystallized from CH2Cl2/n-hexane, 1:1; 230 mg,
67%). M.p. 2158C; 1H NMR (300 MHz, CDCl3): d=1.60 (s, 9H; tBu),
7.78 (d, J=8.4 Hz, 4H; Ar-H), 7.83 (d, J=8.4 Hz, 4H; Ar-H), 7.88 (s,
1H; pyrene-H2), 8.07 (d, J=9.6 Hz, 2H; pyrene-H4,10), 8.10 (d, J=9.6 Hz,
2H; pyrene-H5,9), 8.26 ppm (s, 2H; pyrene-H6,8); 13C NMR (75 MHz,
CDCl3): d=149.8, 144.6, 135.5, 131.0, 130.9, 129.8, 129.4, 128.6, 128.4,
128.2, 126.1, 125.5, 125.4, 125.3, 124.4, 123.2, 122.9, 122.5, 35.3, 31.9 ppm;
IR (KBr): n˜max =2958, 1616, 1326, 1167, 1122, 1062, 1015, 845, 724, 614,
508, 472 cmꢀ1; MS: m/z: 546.2 [M]+; elemental analysis calcd (%) for
C34H24F6 (546.2): C 74.72, H 4.43; found: C 74.61, H 4.05.
and [PdACHTUNGTRENNUNG(PPh3)4] (70 mg, 0.06 mmol) were added. After the mixture was
stirred for 30 min at room temperature under argon, the mixture was
heated to 908C for 24 h with stirring. After cooling to room temperature,
the mixture was quenched with water, extracted with CH2Cl2 (3ꢄ
100 mL), and washed with water and brine. The organic extracts were
dried with MgSO4 and the solvent was evaporated. The residue was puri-
fied by column chromatography eluting with (CH2Cl2/n-hexane, 1:1) to
give 4 f as a white solid. Recrystallization from CH2Cl2/n-hexane (1:1)
gave 4 f (166 mg, 71%) as a light-green powder. M.p. 1788C; 1H NMR
(300 MHz, CDCl3): d=1.60 (s, 9H; tBu), 7.85 (d, J=7.9 Hz, 4H; Ar-H),
7.92 (s, 1H; pyrene-H2), 8.09 (d, J=6.9 Hz; 4H; Ar-H), 8.11–8.14 (m,
4H; pyrene-H4,5,9,10), 8.27 (s, 2H; pyrene-H6,8), 10.16 ppm (s, 2H; CHO);
13C NMR (75 MHz, CDCl3): d=191.9, 149.8, 147.3, 135.6, 135.3, 131.3,
131.0, 129.8, 128.8, 128.2, 125.3, 124.3, 123.1, 123.0, 35.3, 31.9 ppm; IR
(KBr): n˜max =2960, 1699, 1602, 1564, 1462, 1388, 1360, 1306, 1207, 1167,
877, 843, 841, 822, 729, 602, 517 cmꢀ1; MS: m/z: 466.2 [M]+; elemental
analysis calcd (%) for C34H26O2 (466.0): C 87.52, H 5.62; found: C 87.21,
H 5.56.
Synthesis of 7-tert-Butylpyrene-1,3-biscarbaldehyde tetraacetate (5)
A mixture of 4 f (46.7 mg, 0.1 mmol), ammonium acetate (308.4 mg,
4 mmol), and glacial acetic acid (10 mL) was heated at reflux for 5 h and
then cooled to room temperature. The mixture was quenched with
a 10% aqueous solution of NaHCO3, which was then extracted with di-
chloromethane (2ꢄ50 mL). The organic layer was washed with water (2ꢄ
20 mL) and brine (20 mL), the solution was dried (MgSO4), and con-
densed under reduced pressure. The crude compound was purified by
column chromatography eluting with (CH2Cl2/acetone, 3:1) to give 5 as
a yellow solid (13 mg, 19%). M.p. 2148C; 1H NMR (300 MHz, CDCl3):
d=1.59 (s, 9H; tBu), 2.20 (s, 12H; Me), 7.71 (s, 8H; Ar-H), 7.82 (s, 2H;
CH), 7.89 (s, 1H; pyrene-H2), 8.03 (d, J=9.2 Hz, 2H; pyrene-H4,10), 8.14
(d, J=9.2 Hz, 2H; pyrene-H5,9), 8.22 ppm (s, 2H; pyrene-H6,8); 13C NMR
(75 MHz, CDCl3): d=168.9, 142.6, 136.2, 134.5, 131.1, 130.9, 127.9, 126.8,
125.3, 122.6, 125.3, 122.6, 122.5, 89.8, 89.7, 35.2, 31.9, 31.8, 21.0, 20.9 ppm;
IR (KBr): n˜max =3465, 2974, 1756, 1630, 1371, 1249, 1218, 1072, 1009, 974,
943, 836, 730, 607, 568, 524, 466 cmꢀ1; MS: m/z: 670.11 [M]+; elemental
analysis calcd (%) for C34H24F6 (670.75): C 75.21, H 5.71; found: C 75.02,
H 5.83.
A similar procedure with phenyl boronic acid, 4-tert-butylphenylboronic
acid, 4-methoxyphenylboronic acid, 4-cyanophenylboronic acid, and 4-tri-
fluoromethylphenylboronic acid was followed for the synthesis of 4a–4e.
7-tert-Butyl-1,3-diphenylpyrene (4a) was obtained as white prisms (re-
crystallized from CH2Cl2/n-hexane, 1:2; 124 mg, 63%). M.p. 1868C;
1H NMR (300 MHz, CDCl3): d=1.59 (s, 9H; tBu), 7.44–7.69 (m, 10H;
Ar-H), 7.94 (s, 1H; pyrene-H2), 8.01 (d, J=9.2 Hz, 2H; pyrene-H4,10),
8.18 (d, J=9.2 Hz, 2H; pyrene-H5,9), 8.20 ppm (s, 2H; pyrene-H6,8);
13C NMR (75 MHz, CDCl3): d=149.2, 141.1, 137.1, 131.2, 130.6, 129.0,
128.3, 127.8, 127.6, 127.2, 125.3, 125.1, 123.4, 122.2, 35.2, 31.9 ppm; IR
(KBr): n˜max =2958, 2900, 2866, 1766, 1597, 1484, 1462, 1442, 1396, 1360,
1227, 1151, 875, 837, 810, 764, 702, 613, 503, 457 cmꢀ1; MS: m/z: 410.2
[M]+; elemental analysis calcd (%) for C32H26 (410.2): C 93.62, H 6.38;
found: C 93.81, H 6.19.
Crystal Data and Refinement Details for 4a, 4c, 4d, 4 f, and 5
Crystallographic data for compounds 4a, 4c, 4d, 4 f, and 5 (see Table 2)
were collected on SMART ApexII CCD[37,38] or Rigaku Saturn 724 dif-
fractometers with MoKa radiation (l=0.71073 ꢃ). Structure solution and
refinement were routine, except for 5, in which the tBu group was mod-
eled with 50/50 disorder of the three methyl groups. Data (excluding
structure factors) on the structures reported here have been deposited
with the Cambridge Crystallographic Data Centre with deposition num-
bers CCDC 879770 (4a), 879771 (4c), 879772 (4d), 884805 (4 f), and
879773 (5). These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
7-tert-Butyl-1,3-bis(4-tert-butylphenyl)pyrene (4b) was obtained as
a white powder (recrystallized from CH2Cl2/n-hexane, 1:3; 177 mg, 70%).
M.p. 2638C; 1H NMR (300 MHz, CDCl3): d=1.44 (s, 18H; Ar-tBu), 1.59
(s, 9H; pyrene-tBu), 7.56 (d, J=8.6 Hz, 4H; Ar-H), 7.61 (d, J=8.4 Hz,
4H; Ar-H), 7.97 (s, 1H; pyrene-H2), 8.00 (d, J=9.2 Hz, 2H; pyrene-
H4,10), 8.19 (s, 2H; pyrene-H6,8), 8.23 ppm (d, J=9.2 Hz, 2H; pyrene-
H5,9); 13C NMR (75 MHz, CDCl3): d C =150.1, 149.1, 138.2, 137.1, 131.1,
130.3, 129.2, 127.6, 127.4, 125.4, 125.34, 123.5, 122.1, 35.2, 34.7, 31.9,
31.5 ppm; IR (KBr): n˜max =2960, 1914, 1772, 1592, 1496, 1458, 1394, 1363,
1268, 1227, 1200, 1147, 1112, 1024, 877, 843, 810, 723, 665, 613, 567,
422 cmꢀ1; MS: m/z: 522.3 [M]+; elemental analysis calcd (%) for C40H42
(522.3): C 91.90, H 8.10; found: C 91.81, H 7.99
7-tert-Butyl-1,3-bis(4-methoxyphenyl)pyrene (4c) was obtained as yellow
prisms (recrystallized from CH2Cl2/n-hexane, 1:1; 113 mg, 69%). M.p.
1678C; 1H NMR (300 MHz, CDCl3): d=1.58 (s, 9H; pyrene-tBu), 7.10
(d, J=8.8 Hz, 4H; Ar-H), 7.60 (d, J=8.6 Hz, 4H; Ar-H), 7.91 (s, 1H;
pyrene-H2), 8.00 (d, J=9.4 Hz, 2H; pyrene-H4,10), 8.18 (d, J=9.4 Hz, 2H;
pyrene-H5,9), 8.19 ppm (s, 2H; pyrene-H6,8); 13C NMR (75 MHz, CDCl3):
d=159.0, 149.1, 136.8, 133.5, 131.7, 131.2, 129.1, 127.6, 127.4, 125.4, 125.2,
123.5, 122.0, 113.8, 55.4, 35.2, 31.9 ppm; IR (KBr): n˜max =2958, 1610,
1512, 1498, 1456, 1396, 1363, 1286, 1246, 1174, 1039, 877, 835, 727, 660,
607, 580, 553, 418 cmꢀ1; MS: m/z: 470.2 [M]+; elemental analysis calcd
(%) for C34H30O2 (470.2): C 86.77, H 6.43; found: C 86.53, H 6.41.
Acknowledgements
This work was performed under the Cooperative Research Program of
“Network Joint Research Center for Materials and Devices (Institute for
Materials Chemistry and Engineering, Kyushu University)”. We would
like to thank the OTEC at Saga University and the International Collab-
orative Project Fund of Guizhou province at Guizhou University for fi-
nancial support. We also would like to thank the EPSRC (overseas travel
grant to C.R.) and The Royal Society for financial support.
7-tert-Butyl-1,3-bis(4-cyanophenyl)pyrene (4d) was obtained as light-
yellow prisms (recrystallized from CH2Cl2/n-hexane, 2:1; 120 mg, 54%).
M.p. 2828C; 1H NMR (300 MHz, CDCl3): d=1.60, (s, 9H; tBu), 7.77 (d,
J=8.4 Hz, 4H; Ar-H), 7.83 (s, 1H; pyrene-H2), 7.86 (d, J=8.6 Hz, 4H;
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Received: June 13, 2012
Revised: July 25, 2012
Published online: && &&, 0000
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ÝÝ These are not the final page numbers!

FULL PAPER
Shades of blue: Pyrene-based Y-
shaped blue solid-state emitters, 7-tert-
butyl-1,3-diarylpyrenes 1, were synthe-
sized by Suzuki cross-coupling reac-
tions in good to excellent yields. Stud-
ies on single-crystal X-ray structures
and the photophysical properties of
these compounds strongly suggest that
they are promising blue emitters in
organic light-emitting device applica-
tions.
Luminescent Compounds
Xing Feng, Jian-Yong Hu,* Liu Yi,
Nobuyuki Seto, Zhu Tao,
Carl Redshaw, Mark R. J. Elsegood,
Takehiko Yamato*
&&&& — &&&&
Pyrene-Based Y-shaped Solid-State
Blue Emitters: Synthesis, Characteri-
zation, and Photoluminescence
Chem. Asian J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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