A new series of short axially symmetrically and asymmetrically 1,3,6,8-tetrasubstituted pyrenes with two types of substituents: Syntheses, structures, photophysical properties and electroluminescence

Article abstract of DOI:10.1016/j.molstruc.2016.07.105

A new series of short axially symmetrically (4a and 4b) and asymmetrically (4c and 4d) 1,3,6,8-tetrasubstituted pyrene-based compounds with two phenyl moieties and two diphenylamine units on the pyrene core were designed and synthesized based on stepwise synthetic strategy. These compounds were structurally characterized and their photoelectric properties were investigated by spectroscopy, electrochemical and theoretical studies. The structures of 4a and 4b were determined by single-crystal X-ray diffraction analysis, indicating that the compounds are twisted by the peripheral substituents and the intermolecular π-π interactions have been efficiently interrupted. The four compounds exhibit high absolute fluorescence quantum yields (Ф_F) in dichloromethane (83.31–88.45%) and moderate Ф_Fs in film states (20.78–38.68%). In addition, compounds 4a and 4b display relatively higher absolute Ф_Fs than those of 4c and 4d in film states. All the compounds exhibit high thermal stability with decomposition temperatures above 358?°C and the values of 4c and 4d are higher than 4a and 4b. Compounds 4a and 4b can form morphologically stable amorphous thin films with T_g values of 146?°C and 149?°C, respectively. However, there are no obvious T_g observed in compounds 4c and 4d. Electroluminescent devices using 4a and 4b as doped emission layer show promising device performance with low turn-on voltage (3.0?V), maximum brightness around 15100?cd/m² and 16100?cd/m², maximum luminance efficiency of 12.4?cd/A and 13.6?cd/A and maximum external quantum efficiency of 5.34% and 5.63%, respectively.

Full text of DOI:10.1016/j.molstruc.2016.07.105

Journal of Molecular Structure 1127 (2017) 237e246
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
A new series of short axially symmetrically and asymmetrically
1,3,6,8-tetrasubstituted pyrenes with two types of substituents:
Syntheses, structures, photophysical properties and
electroluminescence
Ran Zhang, Tengfei Zhang, Lu Xu, Fangfang Han, Yun Zhao, Zhonghai Ni*
School of Chemical Engineering and Technology, China University of Mining and Technology, Xuzhou 221116, People's Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of short axially symmetrically (4a and 4b) and asymmetrically (4c and 4d) 1,3,6,8-
tetrasubstituted pyrene-based compounds with two phenyl moieties and two diphenylamine units on
the pyrene core were designed and synthesized based on stepwise synthetic strategy. These compounds
were structurally characterized and their photoelectric properties were investigated by spectroscopy,
electrochemical and theoretical studies. The structures of 4a and 4b were determined by single-crystal X-
ray diffraction analysis, indicating that the compounds are twisted by the peripheral substituents and the
Received 22 February 2016
Received in revised form
9 July 2016
Accepted 25 July 2016
Available online 28 July 2016
intermolecular
absolute fluorescence quantum yields (
states (20.78e38.68%). In addition, compounds 4a and 4b display relatively higher absolute
p
-
p
interactions have been efficiently interrupted. The four compounds exhibit high
F) in dichloromethane (83.31e88.45%) and moderate Fs in film
Fs than
Keywords:
Ф
Ф
Ф
Pyrene-based compounds
Molecular configurations
Photoluminescence
Electroluminescence
those of 4c and 4d in film states. All the compounds exhibit high thermal stability with decomposition
temperatures above 358 ꢀC and the values of 4c and 4d are higher than 4a and 4b. Compounds 4a and 4b
can form morphologically stable amorphous thin films with Tg values of 146 ꢀC and 149 ꢀC, respectively.
However, there are no obvious Tg observed in compounds 4c and 4d. Electroluminescent devices using 4a
and 4b as doped emission layer show promising device performance with low turn-on voltage (3.0 V),
maximum brightness around 15100 cd/m2 and 16100 cd/m2, maximum luminance efficiency of 12.4 cd/A
and 13.6 cd/A and maximum external quantum efficiency of 5.34% and 5.63%, respectively.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
introducing different peripheral attachments into the suitable po-
sitions of pyrene core [10,12,13]. Indeed, a larger number of pyrene-
Pyrene as one of the most known polyaromatic hydrocarbons
(PAHs) has been paid everlasting attention in the development of
organic fluorescent materials [1e5]. In recent years, numerous in-
vestigations have been carried out on the design and synthesis of
pyrene-based compounds and their applications in organic light-
emitting diodes (OLEDs), organic field-effect transistors (OFETs),
and organic photovoltaic devices (OPVs) because of their excellent
fluorescence property, outstanding thermal stability, high charge
carrier mobility and hole-injection ability [6e11]. To develop more
excellent pyrene-based materials, the effective strategy is to tune
the molecular structures and the photoelectric properties by
based compounds with various peripheral groups and interesting
photoelectric properties have been synthesized and exploited as
efficient emitting and transporting materials for high performance
photoelectric devices [10,14e17]. Furthermore, some pyrene-based
materials have been exploited as emitters for conventional
solution-processed organic electronic devices, since they have
sufficient solubility and good film-forming abilities [18e20].
Among the many different modification methods on the pyrene
core for novel pyrene-based photoelectric materials, the 1,3,6,8-
terasubstituted pyrene-base compounds have the special advan-
tages which facilitates not only the controlling on the intermolec-
ular interactions but also the intramolecular electronic distribution
[3,21e23]. For example, the incorporation of phenyl moieties,
ethynyl groups and trimethylsilyl units at the 1,3,6,8-positions in
pyrene can twist the structure and prevent excimer formation,
* Corresponding author.
E-mail address: nizhonghai@cumt.edu.cn (Z. Ni).
http://dx.doi.org/10.1016/j.molstruc.2016.07.105
0022-2860/© 2016 Elsevier B.V. All rights reserved.

238
R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
resulting in dramatic improvement in the photoluminescence
properties, especially in the fluorescence quantum yield [24e28].
However, to the best of our knowledge, most of the reported
1,3,6,8-tetrasubstituted pyrene compounds are modified using the
same substituents. There are very few examples of symmetrically
and asymmetrical 1,3,6,8-tetrasubstituted pyrenes with different
peripheral segments on the pyrene ring due to the difficulty in
synthesis and separation [16,23].
Based on the above considerations, we designed and synthe-
sized a series of short axially symmetrically and asymmetrically
1,3,6,8-tetrasubstituted pyrenes with two phenyl moieties and two
diphenylamine units on the pyrene core through the stepwise
derivatization and functional transformation strategy using pyrene
as the precursor (Scheme 1). The intermolecular interactions be-
tween the planar pyrene rings can be prevented by the peripheral
phenyl segments and diphenylamine groups and the incorporation
of arylamine units can improve the hole-injection and hole-
transporting capability of the materials. Moreover, such architec-
tures with two different substituents can more efficiently optimize
the intramolecular electron distribution than those of 1,3,6,8-
tetrasubstituted pyrenes with the same peripheral groups
[16,29,30]. Herein, we report the design, synthesis, photoelectrical
and electroluminescence properties of short axially symmetrically
and asymmetrically 1,3,6,8-tetrasubstituted pyrenes with two
types of substituents.
carbon working electrode, a platinum auxiliary electrode and a
calomel reference electrode. The solvent in all experiments was dry
dichloromethane and the supporting electrolyte was 0.1 M tetra-
butylammonium hexafluorophosphate. The glass-transition tem-
peratures (Tg) of the compounds were determined with differential
scanning calorimetry (DSC) under a nitrogen atmosphere by using a
DSC6000 ꢁ(P1erkinElmer). Samples were heated to 400 ꢀC at a rate of
10 ꢀC min and cooled at 10 ꢀC minꢁ1 then heated again under the
same heating conditions as used in the initial heating process, the
values of Tg were determined from the second heating scan.
Decomposition temperatures (Td) were determined with ther-
mogravimetric analysis (TGA) under a nitrogen atmosphere by
using a DTG-60AH (Shimadzu). Samples were heated to 700 ꢀC at a
rate of 10 ꢀC minꢁ1. Crystals data of compounds were selected on a
Bruker APEX II CCDC diffractometer with graphite-monochromated
Mo-K
a
radiation (
l
¼ 0.71073 Å) at 293 K using the
u-scan tech-
nique. The structures were solved by direct methods with the
SHELXS-97 computer program, and refined by full-matrix least-
squares methods (SHELXL-97) on F2 [31]. The ground state geom-
etries of all molecules were fully optimized using density functional
theory (DFT) at the B3LYP/6-31G (d,p) level, as implemented in
Gaussian 09 W software package [32]. The electronic transitions
were calculated using the time-dependent DFT (B3LYP) theory and
the 6-31G (d, p) basis set.
2.2. OLED fabrication and performance evaluation
2. Experimental section
ITO-coated glasses with a sheet resistance of 30
U per square
were used as substrates. Before the devices were fabricated, the
substrates were first cleaned with acetone, ethanol, and deionized
water. Then, they were oven-dried at 120 ꢀC and treated with UV-
ozone under ambient conditions for 5 min. Finally, the cleaned
glasses were transferred to a vacuum deposition system at
approximately 4 ꢂ 10ꢁ4 Torr. Thermally evaporated organic layers
were sequentially grown onto the ITO substrates at a rate of
1ꢁ2Å sꢁ1. The cathode was completed via the thermal deposition of
Cs2CO3 at a rate of 0.1 Å sꢁ1 and then covered with Al metal
deposited at a rate of 10 Å sꢁ1. EL luminances and spectra were
obtained using an AvaSpec-ULS2048L fiber spectrometer, and the
currentꢁvoltage characteristics were determined with a computer-
controlled Keithley 4200 SCS in ambient atmosphere. EQE was
calculated from the current density, luminance, and EL spectrum,
assuming a Lambertian distribution.
2.1. General
Dichloromethane was distilled from calcium hydride. All other
chemicals were purchased from commercial sources and used
without further purification. 1H and 13C NMR spectra were collected
on a Bruker-400 MHz or Bruker-600 MHz spectrometer in CDCl3
solution with TMS as an internal standard. Mass spectra were ob-
tained on a Bruker Ultraflextreme MALDI TOF/TOF mass spec-
trometer. Elemental analysis (C, H, N) of the dried solid samples
were carried out using an Elementary Vario El analyzer. UVeVis
spectra were recorded on Shimadzu UV-3600 with a UV-VIS-NIR
spectrophotometer. Emission spectra were performed by a HITA-
CHI fluorescence spectrometer (F-4600). The absolute fluorescence
quantum yields (
F F) were determined by FM-4P-TCSPC Transient
State Fluorescence Spectrometer using an integrating sphere for
dilute dichloromethane and thin films which obtained by drop-
casting on quartz plate. Cyclic voltammetry experiments were
performed with a CHI660A electrochemical work station. All
measurements were carried out at room temperature with a con-
ventional three-electrode configuration consisting of a glassy
2.3. Synthesis
2.3.1. Synthesis of 1,8-diphenylpyrene (2a)
Under the atmosphere of nitrogen, the mixture of 1,8-
Scheme 1. The strategy for new 1, 3, 6, 8-tetrasubsituted pyrene-based photoelectric materials (4ae4d).

R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
239
dibromopyrene (85%) and 1,6-dibromopyrene (15%) (1.80 g,
2.4. General procedure for the synthesis of compounds 3ae3d
5 mmol) [33], phenylboronic acid (1.46 g, 12 mmol), Pd(PPh3)4
(0.12 g, 0.1 mmol) and 2 M potassium carbonate solution (12 mL)
were dissolved in toluene (80 mL) and refluxed for 24 h. After the
reaction was finished, the mixture was poured into water and
extracted with dichloromethane. The organic layer was dried over
MgSO4 and the solvent was removed under vacuum. Then, the
crude products were purified by silica gel column chromatography
Br2 (6.3 mmol) in 15 mL DMF was added dropwise into the
solution of 2 (3 mmol) in 15 mL DMF. After stirring for 10 h at room
temperature, water was added. The precipitated solid was collected
and then recrystallized from toluene and ethanol solutions.
3,6-dibromo-1,8-diphenylpyrene (3a) was obtained as a faint
yellow solid after recrystallization from toluene and ethanol (3:1)
mixture. Yield: 1.47 g, 96%. MALDI TOF-MS: m/z 512.2 [M]þ.
3,6-dibromo-1,8-bis-(4-methylphenyl)pyrene (3b) was ob-
tained as a faint yellow solid after recrystallization from toluene
and ethanol (2:1) mixture. Yield: 1.59 g, 98%. MALDI TOF-MS: m/z
540.0 [M]þ.
3,8-dibromo-1,6-diphenylpyrene (3c) was obtained as a faint
yellow solid after recrystallization from toluene. Yield: 1.49 g, 97%.
MALDI TOF-MS: m/z 512.3 [M]þ.
3,8-dibromo-1,6-bis-(4-methylphenyl)pyrene (3d) was ob-
tained as a faint yellow solid after recrystallization from toluene.
Yield: 1.59 g, 98%. MALDI TOF-MS: m/z 539.9 [M]þ.
using hexane/dichloromethane mixture as eluent afforded
a
mixture of 2a and 2c. Finally, the mixture was recrystallized from
dichloromethane/ethanol (2:3) solution and the pure compound 2a
was obtained as white solid. Yield: 1.15 g, 65%. 1H NMR (600 MHz,
CDCl3)
d
8.23 (d, J ¼ 7.8 Hz, 2H), 8.12 (d, J ¼ 11.1 Hz, 4H), 7.99 (d,
J ¼ 7.8 Hz, 2H), 7.63e7.60 (m, 4H), 7.53 (t, J ¼ 7.6 Hz, 4H), 7.45 (t,
J ¼ 7.4 Hz, 2H). 13C NMR (151 MHz, CDCl3)
d 141.15 (s), 137.62 (s),
130.94 (s), 130.62 (s), 128.37 (s), 127.85e126.96 (m), 125.41 (s),
125.25 (s), 124.83 (s). MALDI TOF-MS: m/z 354.171 [M]þ. Elemental
analysis: anal. Calcd for C28H18: C, 94.88; H, 5.12; Found: C, 94.93; H,
5.08.
2.3.2. Synthesis of 1,8-bis(4-methylphenyl)pyrene (2b)
2.5. General procedure for the synthesis of the compounds 4ae4d
The compound was synthesized with the same method as for
compound 2a by using 4-methylphenylboronic acid (1.63 g,
12 mmol). Accordingly, the pure compound 2b was obtained by
recrystallizing from dichloromethane/ethanol (1:2) mixture as
Under the atmosphere of nitrogen, a mixture of 3 (2.5 mmol),
diphenylamine (1.02 g, 6 mmol), bis(dibenzylideneacetone)palla-
dium (Pd (dba)2) (48 mg, 0.05 mmol), P (t-Bu)3 (0.1 g/mL in toluene,
0.15 ml, 0.075 mmol), sodium tert-butoxide (0.58 g, 6 mmol) and
toluene (50 mL) were heated at 80 ꢀC for 4e5 h. After it cooled,
water and dichloromethane were added and the organic layer was
separated. Then, the organic layer was dried over MgSO4 and the
solvent was removed under vacuum. The crude products were
purified by silica gel column chromatography using hexane/
dichloromethane mixture as eluent.
white solid. Yield: 1.21 g, 65%. 1H NMR (400 MHz, CDCl3)
d 8.25 (d,
J ¼ 8.0 Hz, 2H), 8.15 (d, J ¼ 16.8 Hz, 4H), 8.01 (d, J ¼ 8.0 Hz, 2H), 7.55
(d, J ¼ 8.0 Hz, 4H), 7.38 (d, J ¼ 8.0 Hz, 4H), 2.51 (s, 6H). 13C NMR
(101 MHz, CDCl3) d 150.10 (s),138.13 (s),137.50 (s),130.79 (s),130.27
(s), 128.44 (s), 127.66 (s), 127.34 (s), 125.63e124.99 (m), 124.71 (s),
34.66 (s), 31.48 (s). MALDI TOF-MS: m/z 382.215 [M]þ. Elemental
analysis: anal. calcd for C30H22: C, 94.20; H, 5.80; Found: C, 94.31; H,
5.72.
3,6-bis(N,N-diphenyl)-1,8-diphenylpyrene (4a) was obtained as
a yellow powder solid. (silica gel column chromatography from
hexane: dichloromethane ¼ 60:1). Yield: 1.46 g, 85%. 1H NMR
2.3.3. Synthesis of 1,6-diphenylpyrene (2c)
A mixture of 1,6-dibromopyrene (1.80 g, 5 mmol), phenyl-
boronic acid (1.46 g,12 mmol), Pd(PPh3)4 (0.12 g, 0.1 mmol) and 2 M
potassium carbonate solution (12 mL) in toluene (80 mL) was
heated to reflux for 24 h under nitrogen. After the reaction was
finished, the mixture was poured into water and extracted with
dichloromethane. The organic layer was dried over MgSO4 and the
solvent was removed under vacuum. Then, the crude products
were purified by silica gel column chromatography using hexane/
dichloromethane mixture as eluent afforded 2c as white plate
(400 MHz, CDCl3)
d
8.13 (d, J ¼ 5.5 Hz, 4H), 7.85 (s, 2H), 7.60e7.50
(m, 10H), 7.23e7.21 (m, 8H), 7.19e7.09 (m, 8H), 6.95 (t, J ¼ 7.3 Hz,
4H). 13C NMR (101 MHz, CDCl3)
d
148.50 (s), 140.50 (d, J ¼ 10.9 Hz),
138.99 (s), 130.53 (s), 129.70 (s), 129.17 (s), 128.36 (s), 128.08 (s),
127.49e126.91 (m), 124.95 (s), 123.76 (s), 122.07 (s), 121.79 (s).
MALDI TOF-MS: m/z 688.3 [M]þ. Elemental analysis: anal. calcd for
C
52H36N2: C, 90.67; H, 5.27; N, 4.07; Found: C, 90.58; H, 5.31; N,
4.09.
3,6-bis(N,N-diphenyl)-1,8-bis-(4-methylphenyl)pyrene
(4b)
crystals. Yield: 1.6 g, 90%. 1H NMR (400 MHz, CDCl3)
d
8.23 (dd,
was obtained as a yellow powder solid (silica gel column chroma-
J ¼ 8.5, 5.8 Hz, 4H), 8.05 (dd, J ¼ 20.9, 8.5 Hz, 4H), 7.71e7.65 (m, 4H),
tography from hexane: dichloromethane ¼ 20:1). Yield: 1.56 g, 87%.
7.60 (t, J ¼ 7.4 Hz, 4H), 7.52 (t, J ¼ 7.3 Hz, 2H). 13C NMR (101 MHz,
1H NMR (400 MHz, CDCl3)
d
8.12 (d, J ¼ 18.8 Hz, 4H), 7.83 (s, 2H),
CDCl3)
d
141.29 (s), 137.85 (s), 130.62 (s), 130.41 (s), 128.84 (s),
7.49 (d, J ¼ 8.0 Hz, 4H), 7.33 (d, J ¼ 7.6 Hz, 4H), 7.22e7.18 (m, 8H),
128.38 (s), 127.78 (s), 127.47 (s), 127.25 (s), 125.30 (s), 125.20 (s),
124.49 (s), 29.72 (s). MALDI TOF-MS: m/z 354.154 [M]þ. Elemental
analysis: anal. calcd for C28H18: C, 94.88; H, 5.12; Found: C, 94.94; H,
5.07.
7.13e7.08 (m, 8H), 6.95 (t, J ¼ 7.4 Hz, 4H), 2.48 (s, 6H). 13C NMR
(101 MHz, CDCl3) d 148.52 (s),140.47 (s),138.92 (s),137.56 (s),137.19
(s), 130.41 (s), 129.73 (s), 129.11 (d, J ¼ 7.4 Hz), 127.95 (s), 127.31 (s),
127.15 (s), 124.93 (s), 123.66 (s), 122.05 (s), 121.74 (s), 21.27 (s).
MALDI TOF-MS: m/z 716.3 [M]þ. Elemental analysis: anal. calcd for
2.3.4. Synthesis of 1,6-bis(4-methylphenyl)pyrene (2d)
C
54H40N2: C, 90.47; H, 5.62; N, 3.91; Found: C, 90.35; H, 5.73; N,
3.81.
3,8-bis(N,N-diphenyl)-1,6-diphenylpyrene (4c) was obtained as
The compound was synthesized with the same method as for
compound 2c by using 4-methylphenylboronic acid (1.63 g,
12 mmol). Accordingly, the pure compound 2d was obtained as
white powder solid. Yield: 1.62 g, 92%. 1H NMR (400 MHz, CDCl3)
a yellow powder solid (silica gel column chromatography from
hexane: dichloromethane ¼ 15:1). Yield: 1.34 g, 78%. 1H NMR
d
8.22 (dd, J ¼ 8.4, 6.3 Hz, 4H), 8.03 (dd, J ¼ 21.3, 8.5 Hz, 4H), 7.57 (d,
(400 MHz, CDCl3)
d
8.15 (d, J ¼ 9.6 Hz, 2H), 8.07 (d, J ¼ 9.2 Hz, 2H),
J ¼ 7.9 Hz, 4H), 7.41 (d, J ¼ 7.8 Hz, 4H), 2.54 (s, 6H). 13C NMR
7.85 (s, 2H), 7.57e7.43 (m, 10H), 7.22 (t, J ¼ 8.4 Hz, 8H), 7.11 (d,
(101 MHz, CDCl3)
d 138.37 (s), 137.79 (s), 136.95 (s), 130.50 (s),
J ¼ 8.0 Hz, 8H), 6.96 (t, J ¼ 7.6 Hz, 4H). 13C NMR (101 MHz, CDCl3)
130.30 (s), 129.10 (s), 128.89 (s), 127.77 (s), 127.35 (s), 125.29 (s),
125.25 (s), 124.41 (s), 29.72 (s), 21.31 (s). MALDI TOF-MS: m/z
382.212 [M]þ. Elemental analysis: anal. calcd for C30H22: C, 94.20;
H, 5.80; Found: C, 94.28; H, 5.74.
d 148.55 (s), 140.41 (s), 139.16 (s), 130.52 (s), 129.60 (s), 129.21 (s),
128.33 (s), 127.76 (s), 127.41e127.31 (m), 125.63 (s), 123.08 (s),
122.06 (s), 121.79 (s). MALDI TOF-MS: m/z 688.3 [M]þ. Elemental
analysis: anal. calcd for C52H36N2: C, 90.67; H, 5.27; N, 4.07; Found:

240
R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
C, 90.72; H, 5.24; N, 4.04.
dibromopyrene was obtained, but regrettably, the relatively more
soluble 1,8-dibromopyrene fraction still contained a small amounts
of 1,6-dibromopyrene (15%). The continuous separation of 1,6- and
1,8-dibromopyrenes are tedious and difficult due to the slight dif-
ference in solubility of the dibromopyrenes. Therefore, we start the
experiments using the impure 1,8-dibromopyrene because it is
possible to obtain the final pure 1,8-disubstituted pyrene-based
compounds in the flowing steps. Secondly, the pure 1,6-
dibromopyrene was changed to 2c and 2d easily by Suzuki
coupling reaction with high yields. Accordingly to the same
method, the mixture of 85% 1,8-dibromopyrene and 15% 1,6-
dibromopyrene were transformed to the key intermediates 2a
and 2b respectively containing slight 2c and 2d. There are signifi-
cant differences of solubility between 2a and 2c, 2b and 2d, and
therefore the pure key intermediates 2a and 2b were relatively
readily obtained from recrystallization. Thirdly, compounds 2ae2d
were brominated with liquid bromine, yielding another key in-
termediates 3ae3d in very high yields above 95%. The presence of
two bromide substituents drastically reduced the solubility of the
compounds, which fails to obtain the detailed characterizations of
3ae3d. Finally, the target products 4ae4d were prepared by
BuchwaldeHartwig coupling reaction between the compound 3
and diphenylamine with yields of 80e90%. Compounds 4a and 4b
show excellent solubility in common organic solvents, but the
3,8-bis(N,N-diphenyl)-1,6-bis(4-methylphenyl)pyrene (4d) was
obtained as a yellow powder solid (silica gel column chromatog-
raphy from hexane: dichloromethane ¼ 20:1). Yield: 1.34 g, 75%. 1H
NMR (400 MHz, CDCl3)
d
8.09 (dd, J ¼ 8.0 Hz, 9.6 Hz, 4H), 7.81 (s,
2H), 7.44 (d, J ¼ 8.0 Hz, 4H), 7.30 (s, 4H), 7.23e7.18 (m, 8H), 7.10 (d,
J ¼ 7.6 Hz, 8H), 6.94 (t, J ¼ 7.8 Hz, 4H), 2.44 (s, 6H). 13C NMR
(101 MHz, CDCl3)
d 148.51 (s), 140.47 (s), 138.92 (s), 137.37 (d,
J ¼ 36.4 Hz), 130.41 (s), 129.73 (s), 129.11 (d, J ¼ 7.3 Hz), 127.95 (s),
127.23 (d, J ¼ 15.9 Hz), 124.93 (s), 123.66 (s), 122.05 (s), 121.74 (s),
21.27 (s). MALDI TOF-MS: m/z 716.4 [M]þ. Elemental analysis: anal.
calcd for C54H40N2: C, 90.47; H, 5.62; N, 3.91; Found: C, 90.27; H,
5.57; N, 3.89.
3. Results and discussion
3.1. Synthesis
The synthetic routes of the intermediates and target compounds
are shown in Scheme 2 using pyrene as the starting material. Firstly,
bromination of pyrene afforded a mixture of 1,8-dibromopyrene
(1a) and 1,6-dibromopyrene (1c) as reported in the literature
[33]. The mixture isolated by fractional recrystallization from
toluene into two components and the less soluble pure 1,6-
Scheme 2. Procedures for the syntheses of compounds 4ae4d.

R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
241
Fig. 1. Absorption (A) and normalized emission spectra (B, excitation wavelength: 410 nm) of the compounds 4ae4d recorded in dichloromethane at 1 ꢂ 10ꢁ5 M concentration.
solubilities of 4c and 4d are very poor, which indicates that the
symmetrical configuration of pyrene can significantly increase the
solubility. The solubilities of compounds 4ae4d in various solvents
(mg/ml) are listed in Table S1. The poor solubility limits the syn-
thesis and purification of more new asymmetrically 1,3,6,8-
tetrasubstituted pyrene-based photoelectric materials. Further-
more, the X-ray diffraction patterns (Fig. S1) for drop-casting film
samples of compounds 4a and 4b show representative broad
diffuse band, indicating that 4a and 4b can form amorphous thin
films. However, the diffraction patterns for film samples of 4c and
4d exhibit sharp peaks, demonstrating that the films of 4c and 4d
are crystalline state.
4b display blue-shift relative to those of asymmetrical compounds
4c and 4d, indicating that the symmetrical configuration can
reduce the
p-conjugation of the compounds to some extent.
Compound 4b exhibits slightly red-shift compared with that of 4a,
which demonstrates that the incorporation of methyl groups in-
creases the
p-conjugation of the molecules, similarly, compound
4d also shows minor red-shift than that of 4c. Compounds 4ae4d
show small Stokes shifts (1927e2203 cmꢁ1 in dichloromethane),
indicating less energy loss during the relaxation process and
thereby ensuring efficient fluorescence. As shown in Fig. 2, the
emission spectra of these compounds in thin films exhibit obvious
bathochromic shift relative to those in dichloromethane solution
with the values of 55 nm, 24 nm, 32 nm and 19 nm for 4a, 4b, 4c
and 4d, respectively, suggesting that there exists intermolecular
3.2. Photophysical properties
pep interactions in film state. Compounds 4b and 4d are blue-shift
than those 4a and 4c, respectively, stating that the introduction of
methyl groups can increase the molecular twist and weaken the
The UVevis absorption and photoluminescence (PL) spectra of
compounds 4ae4d in dilute dichloromethane are shown in Fig. 1.
The detailed photophysical data are presented in Table 1. The ab-
sorptions of compounds 4a and 4b have some differences with 4c
and 4d. Compounds 4c and 4d exhibit small red-shift compared
with those of 4a and 4b and the absorption fine structures of 4c and
4d are more obvious than those of 4a and 4b, which indicates that
the different molecular configurations have some effects on the
absorptions of the compounds. The compounds 4ae4d feature the
longest wavelength absorptions at ca. 436e439 nm maybe attrib-
uted to the charge transfer from pyreneylamine to pyrene. The
absorptions for compounds 4ae4d at ca. 332e334 nm probably
ascribed to the charge transfer from diphenylamine units to pyrene.
However, the absorptions of 4a and 4b are very weaker than those
of 4c and 4d. It is probably caused by the different charge distri-
bution which is attribute to the different molecule configuration.
The higher energy bands appearing at ca. 297e299 nm are may be
intermolecular
pep interactions. The red-shifts of 4a and 4b are
larger than 4c and 4d, respectively, which may be indicate that the
asymmetrical structure is more beneficial to interrupt the inter-
molecular pep interactions. The PL spectra of the four compounds
have no obvious trailing at long wavelengths, indicating that the
formation of an excimer or exciplex can be effectively suppressed,
other than some pyrene-based materials [36e39]. It is probably
because that the peripheral substituents twist the molecular
backbone and suppress the intermolecular interactions
[16,17,29,30]. The absolute fluorescence quantum yields FFs of
compounds 4ae4d in dichloromethane and in film state were
determined using an integrating sphere. These compounds show
high FFs in dichloromethane with the range from 83.31 to 88.45%.
The FFs of compounds 4ae4d in film states (20.78e38.68%) show a
decreasing tendency compared to those in dichloromethane due to
the intermolecular interactions in film states. Compounds 4b and
4d exhibit higher FFs than those of 4a and 4c, indicating that the
introduction of methyl groups to peripheral phenyl ring can more
effectively prevent the intermolecular interactions. Moreover, the
FFs of 4a and 4b are higher than 4c and 4d, demonstrating that the
assigned to pyrene and phenyl localized pep* transitions [34]. The
intense bands of 4ae4d appearing at ca. 256 nm probably stem
from phenyl ring present in the molecule [35].
The PL spectra of compounds 4ae4d in dichloromethane display
emission peak in green region. The symmetrical compounds 4a and
Table 1
Physical parameters of the compounds 4ae4d.
Stokes shift (cmꢁ1
)
a
a
c
Com.
labs (nm)
lem (nm)/(FF (%))
lemb (nm)/(FFc (%))
4a
4b
4c
4d
257, 299, 340, 436
257, 299, 340, 436
256, 297, 333, 439
258, 298, 332, 437
479 (88.45)
476 (85.31)
486 (83.31)
483 (84.35)
534 (31.57)
500 (38.68)
518 (20.78)
502 (27.45)
2059
1927
2203
2179
a
Measured in dichloromethane.
Measured as drop-coated film.
Absolute quantum yield measured using integrating sphere.
b
c

242
R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
profiles for compound 4ae4d with different solvent polarities are
illustrated in Figs. S2eS5. The absorption spectra show the four
compounds are insensitive to the solvent polarity with the shift
below 8 nm. In the emission spectra, compounds 4ae4d display a
remarkable and positive solvatochromism, which indicates that the
excited state is more stable in polar solvent probably due to the
separation of charges in the higher energy state [12,40]. The Stokes
shifts of compounds 4ae4d in different solvents were calculated to
know the structural reorganization occurring during electronic
excitation. Stokes shift values in different solvents for the com-
pounds follow the order 4a < 4b < 4c < 4d. Larger Stokes shift
observed for 4d indicates appreciable structural reorganization due
to photo-excitation from ground state to excited state [34].
Furthermore, the relationships of Stokes shift against the solvent
parameter ET (30) of the compounds 4ae4d were investigated as
shown in Fig. S6. The slopes of the correlation plots are in the order
of 4c (84.53) < 4b (93.10) < 4d (93.89) < 4a (103.04), which in-
dicates that more pronounced intramolecular charge transfer is
occurred in compound 4a [34].
Fig. 2. Normalized emission spectra of the compounds 4ae4d recorded as thin films
(excitation wavelength: 390 nm).
symmetrical structure is more beneficial to improve the PL
properties.
To better understand the effect of environments on the elec-
tronic spectroscopies of the compounds, we study the absorption
and emission spectra of compounds 4ae4d in different polar sol-
vents such as toluene (TOL), dichloromethane (DCM), tetrahydro-
furan (THF), methanol (MeOH), N,N-dimethylformamide (DMF)
and acetonitrile (MeCN). The pertinent data are summarized in
Table S2 and Table S3. The changes in absorption and emission
3.3. Crystal structure and theoretical calculation
Suitable single crystals of compounds 4a and 4b for X-ray
crystallography were obtained by the slow evaporation of a mixture
of dichloromethane/hexane at room temperature. However, efforts
to obtain the suitable single crystals of 4c and 4d were failed due to
their limited solubility in common solvent. The detailed
Fig. 3. X-ray structure diagram of the compounds 4a (left) and 4b (right).
Fig. 4. Crystal packing diagram of 4a (left) and 4b (right).

R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
243
Fig. 5. Electronic distributions observed for the frontier orbitals for the compounds 4ae4d.
information about the crystal data for compounds 4a and 4b is
summarized in Table 3. Compounds 4a and 4b crystallize in the
triclinic crystal system with space group Pꢁ1. The crystal structure
diagrams of the two compounds are shown in Fig. 3.
X-ray diffraction analysis shows that the center pyrene cores of
4a and 4b are linked by two phenyl moieties at the 1, 8-positions
and two diphenylamine attachments at the 3, 6-positions of the
pyrene core. The bond lengths of CeN in the compounds are in a
narrow range of 1.417(4)e1.428(4) Å for 4a and 1.403(4)e1.448(4)
Å for 4b. The bond angles of CeNeC in the compounds 4a and 4b
range from 116.82 (3) to 123.08 (3)ꢀ. In the two crystal structures,
the phenyl units attached on the 3, 6-positions of pyrene ring are
completely not coplanar with the pyrene plane, which are evi-
denced by the dihedral angles are 57.76 (3)ꢀ and 54.14 (3)ꢀ for 4a
and 4b, respectively. Of course, the pyrene cores are also twisted by
diphenylamine units with the dihedral angle between pyrene and
phenyl moieties in the range of 68.51(3)e87.42(3)ꢀ for 4a and
78.67(3)e88.14(3)ꢀ for 4b. The four atoms including the nitrogen
atom and the three carbons bonded by nitrogen atom are almost
coplanar with the maximal deviations of 0.022 (4) Å (N1) and 0.103
(4) Å (N2) for 4a, 0.027 (4) Å (N1) and 0.067 (3) Å (N2) for 4b.
The crystal packing diagrams of 4a and 4b are shown in Fig. 4. As
Table 2
Electrochemical and thermal properties of the compounds.
a
d
Com.
Eox
,
mV
Egb/Eg cal.c (eV)
HOMO/LUMO (eV)
HOMO/LUMO c (eV)
Td/Tg (ꢀC)
4a
4b
4c
4d
0.385
0.335
0.285
0.265
2.64/2.99
2.61/2.99
2.58/2.87
2.57/2.86
ꢁ5.17/ꢁ2.53
ꢁ5.17/ꢁ2.56
ꢁ5.29/ꢁ2.71
ꢁ5.27/ꢁ2.70
ꢁ4.73/ꢁ1.74
ꢁ4.68/ꢁ1.69
ꢁ4.82/ꢁ1.95
ꢁ4.80/ꢁ1.94
358/146
365/149
399/ND
408/ND
a
Measured in dry dichloromethane. All Eox data are reported relative to ferrocene.
b
c
Calculated from the absorption edge, Eg ¼ 1240/lonset
.
Obtained from the quantum chemical calculation.
d
HOMO values were deduced from the relation: HOMO ¼ Eox þ 4.8. LUMO values were calculated from the relation: band gap ¼ HOMO ꢁ LUMO.

244
R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
Table 3
and phenyl moieties on the pyrene core. For 4a and 4b, two inde-
pendent units are mainly linked by CeH$$$ interactions, forming
Summary of the crystal data of 4a and 4b.
p
two-dimensional layer-like supramolecular structures. It is note
Parameter
4a
4b
worthy that the intermolecular interactions of compound 4b seem
Empirical formula
C53H38Cl2N2
773.75
293
0.71073
triclinic
Pꢁ1
C54H40N2
716.88
293
0.71073
triclinic
Pꢁ1
Mr (g molꢁ1
T/K
)
more weak than those of compound 4a because the CeH$$$
p
intermolecular interactions of 4b originate from methyl group
hydrogen atoms other than aromatic ring hydrogen atoms of 4a.
Thus, the newly prepared compounds 4a and 4b with less inter-
molecular interactions suggests that they might be advantageous as
promising emitters in solid state.
Wavelength (Å)
Crystal system
Space group
a/Å
b/Å
c/Å
11.347 (2)
12.125 (2)
14.684 (3)
99.99 (3)
97.84 (3)
98.09 (3)
1942.9 (7)
2
1.323
808.0
0.209
6861
5589
514
0.0235
0.0646
0.2377
0.979
10.885 (2)
12.055 (2)
15.992 (3)
83.34 (3)
87.20 (3)
70.47 (3)
1964.3 (7)
2
1.212
756.0
0.070
9105
5969
499
0.1036
0.0713
0.1503
0.977
To deeply investigate the electronic structures, orbital energies,
electron densities of the highest occupied molecular orbital
(HOMO) and lowest occupied molecular orbital (LUMO) states of
the compounds 4ae4d, as well as to understand the absorption
characteristics, density functional theory (DFT) calculations (B3LYP/
6-31G (d, p) basis set) were performed on the three compounds
with the Gaussian 09 W software package. Three-dimensional
optimized geometries and electronic distributions in the frontier
molecular orbitals of compounds 4ae4d are shown in Fig. 5 and the
HOMOeLUMO energy gaps (Eg cal.) were calculated and are pre-
sented in Table 2. The prominent wavelength vertical transitions
and their assignments are summarized in Table 4. The calculated
structures of compounds 4ae4d reveal that all molecules adopt
non-coplanar conformations. The electronic distributions of com-
pounds 4a and 4b are symmetrical, which is different from 4c and
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
V (Å3)
Z
Dcalc (g cmꢁ3
F (000)
)
m
(mmꢁ1
)
Unique reflections
Observed reflections
Parameters
R (int)
R [I > 2s (I)]
wR2 (all data)
GOF on F2
4d whose p-electrons are asymmetrical. The measured wavelength
known to all, the efficient
p-stacking in emitting materials could
absorption peaks and energy gaps of these compounds are smaller
than the theoretically forecast values but the changing tendencies
are similar. The longest wavelength transitions are mainly due to
the electronic excitation from the HOMO to LUMO, while the sec-
ond absorptions largely result from the HOMO e 1 to LUMO
lead to extensive excimer formation in thin film with low quantum
yields of fluorescence, which makes a big obstacle for the solid state
applications in photoelectric devices. From Fig. 4, no intermolecular
p-p interactions were observed in the two crystals due to the big
sterically hindrance arising from the bulky diphenylamine groups
Table 4
Predicted (TDDFT B3LYP/6-31G (d,p)) vertical transitions and their assignments.
Com.
labs (nm)
f
Assignment
4a
478.48
433.41
377.27
476.44
431.02
376.92
474.72
431.52
381.28
473.37
429.00
382.24
0.4359
0.0584
0.0664
0.4611
0.0606
0.0672
0.5056
2.8732
3.2518
0.5272
2.8901
3.2436
HOMO / LUMO (95.1%), HOMO e 2 / LUMO (3.5%)
HOMO e 1 / LUMO (96.6%)
HOMO / LUMO þ 1 (84.6%), HOMO e 3 / LUMO (12.0%)
HOMO / LUMO (95.0%), HOMO e 2 / LUMO (3.5%)
HOMO e 1 / LUMO (97.7%)
HOMO / LUMO þ 1 (84.9%), HOMO e 3 / LUMO (11.5%)
HOMO / LUMO (95.1%), HOMO e 2 / LUMO (3.2%)
HOMO e 1 / LUMO (99.0%)
HOMO / LUMO þ 1 (74.2%), HOMO e 2 / LUMO (15.5%)
HOMO / LUMO (95.1%), HOMO e 2 / LUMO (3.2%)
HOMO e 1 / LUMO (99.0%)
4b
4c
4d
HOMO / LUMO þ 1 (70.3%), HOMO e 2 / LUMO (19.8%)
Fig. 6. The current densityevoltageeluminance curves with varying thickness of the compounds 4a and 4b (A); Luminance efficiency of the compounds 4a and 4b (B).

R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
245
Table 5
EL performance: ITO/HAT-CN (5 nm)/NPB (30 nm)/CBP: 10 wt% 4a or 4b (25 nm)/Bphen (40 nm)/Cs2CO3 (2 nm)/Al (150 nm).
Lmaxc at voltage (cd mꢁ2/V)
hmax (cd/A)
EQEe (%)
a
b
d
Devices
Emitters
Von (V)
ELmax (nm)
I
II
4a
4b
3.0
3.0
534
501
15100/12
16100/13
12.4
13.6
5.34
5.63
a
Turn-on voltage (V) at a luminance of 1 cd mꢁ2
Emission maximum.
.
b
c
Maximum luminance (cd mꢁ2) at the applied voltage (V).
Luminance efficiency (cd Aꢁ1).
d
e
External quantum efficiency (%).
electronic excitation. For compounds 4ae4d, the HOMO orbitals are
contributed by the diphenylamine and pyrene core, while the
LUMO orbitals are mainly distributed over the electron-rich pyrenyl
segments, which indicates that the longest absorption bands real-
ized for 4ae4d can be assigned to a charge transfer from pyr-
current densityꢁvoltageꢁluminance (JꢁVꢁL) characteristics and
the current densityꢁefficiency curves of the fabricated OLEDs are
shown in Fig. 6. The essential performance electric parameters are
demonstrated in Table 5. The turn-on voltages of the 4a- (device I)
and 4b-based (device II) devices are very low with the values all of
3.0 V, which indicates that the performance of the devices is decent.
The device II using 4b as dopant shows the best device perfor-
mance with a maximum brightness (Lmax) of 16100 cd/m2, a
maximum luminance efficiency (hmax) of 13.6 cd/A, a maximum
external quantum efficiency of 5.63%. The 4a-based device exhibits
a relatively lower device performance with an Lmax of 15100 cd/m2,
eneylamine to pyrene. The
p-electrons in the HOMO e 1
compounds 4a and 4b are mainly distributed on the diphenylamine
unit and a little on the pyrene core, which indicates that the second
transitions mainly stem from the charge transfer from the diphe-
nylamine moieties to the pyrene core.
a
hmax of 12.4 cd/A, a maximum external quantum efficiency of
3.4. Electrochemical and thermal studies
5.34%. The devices I and II emit strong green emission with lEL
peaked at 534 nm and 501 nm, respectively. Furthermore, the
electroluminescence (EL) spectra of the devices match with their
corresponding PL spectra, indicating that the EL purely originate
from the emitting layers.
The electrochemical properties of compounds 4ae4d were
studied by cyclic voltammetry (CV) measurements and the oxida-
tion potentials of these compounds were calculated by calibrating
with the internal ferrocene standard (Fig. S7). The relevant pa-
rameters are collected in Table 2. Compounds 4ae4d display two
quasi-reversible oxidation waves arising from the oxidation of the
amine. The HOMO values of compounds 4a, 4b, 4c and 4d esti-
mated from the onset potentials of oxidation peak
are ꢁ5.17 eV, ꢁ5.17 eV, ꢁ5.29 eV and ꢁ5.27 eV, respectively. The
LUMO values of these compounds calculated by HOMO and Eg are
in the range from ꢁ2.53 to ꢁ2.71 eV. The HOMO values of com-
pounds 4a and 4b with symmetrical structure are larger than 4c
and 4d and more close to the barrier of ITO (ꢁ4.8 eV), which in-
dicates that the hole-transporting abilities of 4a and 4b are better
than those of compounds 4c and 4d.
4. Conclusions
In conclusion, a new series of short axially symmetrically and
asymmetrically 1,3,6,8-tetrasubstituted pyrene-based derivatives
with different substituents on the pyrene core have been elabo-
rately designed and successfully synthesized. The crystal structures
of 4a and 4b indicate that the molecule is twisted by the peripheral
substituents and the intermolecular
p-p interactions have been
efficiently interrupted. Compounds 4a and 4b exhibit higher ab-
solute fluorescence quantum yields than those of 4c and 4d in
dichloromethane and as drop-coating films, which reveals the
symmetrical structure can benefit to improve the PL properties of
the compounds. Compounds 4ae4d exhibit high thermal stability
and the values of 4c and 4d are higher than 4a and 4b, indicating
that the asymmetrical configuration can slightly increase thermal
stability of the compounds. The compounds 4a and 4b can form
morphologically stable amorphous thin films with Tg values of
146 ꢀC and 149 ꢀC, respectively. However, there are no obvious Tg
observed in compounds 4c and 4d. Organic light-emitting diodes
featuring compounds 4a and 4b as doped emission layer show
promising device performance with low turn-on voltage (3.0 V),
maximum brightness around 15100 cd/m2 and 16100 cd/m2,
maximum luminance efficiency of 12.4 cd/A and 13.6 cd/A and
maximum external quantum efficiency of 5.34% and 5.63%,
respectively.
The thermal properties of the compounds 4ae4d were investi-
gated by thermogravimetric analysis (TGA) and differential scan-
ning calorimetry (DSC) under a nitrogen atmosphere, the relevant
data are shown in Table 2 and Figs. S8 and S9. These compounds
show high thermal stability and the decomposition temperatures
(Td) corresponding to 5% weight loss are 358, 365, 399 and 408 ꢀC
for compounds 4a, 4b, 4c and 4d, respectively. DSC thermograms of
the compounds 4a and 4b display high glass transition temperature
(Tg) values at 146 and 149 ꢀC, respectively, and no crystallization
and melting peaks being observed at higher temperatures, indi-
cating an excellent amorphous glass state stability [41]. However,
compound 4c and 4d do not show obvious Tg most likely due to
their crystallinity and small heat capacity.
3.5. Electroluminescence
Two representative compounds 4a and 4b were employed as the
doped emitting layers in OLEDs with the following configuration:
ITO/HAT-CN (5 nm)/NPB (30 nm)/CBP: 10 wt% 4a or 4b (25 nm)/
Bphen (40 nm)/Cs2CO3 (2 nm)/Al (150 nm). Here, 1,4,5,8,9,11-
hexaazatriphenylene hexacarbonitrile (HAT-CN) acts as the hole
injection layer, NPB as the hole-transporting layer (HTL), the 4a or
4b: 4,40-bis(N-carbazolyl)-1,10-biphenyl (CBP) guestehost systems
were chosen as emitting-material layer, 1,10-Bathophenanthroline
(Bphen) was conducted as electron-transporting layer (ETL). The
Acknowledgements
This work was supported by the Fundamental Research Funds
for the Central Universities (2015XKZD08) and the Priority Aca-
demic Program Development of Jiangsu Higher Education
Institutions.

246
R. Zhang et al. / Journal of Molecular Structure 1127 (2017) 237e246
[20] Y.J. Pu, M. Higashidate, K.i. Nakayama, J. Kido, Solution-processable organic
Appendix A. Supplementary data
fluorescent dyes for multicolor emission in organic light emitting diodes,
J. Mater. Chem. 18 (2008) 4183e4188.
[21] T.M. Figueira-Duarte, S.C. Simon, M. Wagner, S.I. Druzhinin, K.A. Zachariasse,
K. Müllen, Polypyrene dendrimers, Angew. Chem. Int. Ed. 47 (2008)
10175e10178.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.07.105.
[22] J.Y. Hu, X. Feng, H. Tomiyasu, N. Seto, U. Rayhan, M.R.J. Elsegood, C. Redshaw,
T. Yamato, Synthesis and fluorescence emission properties of 1,3,6,8-
tetraarylpyrenes, J. Mol. Struct. 1047 (2013) 194e203.
[23] X. Feng, H. Tomiyasu, J.Y. Hu, X.F. Wei, C. Redshaw, M.R.J. Elsegood,
L. Horsburgh, S.J. Teat, T. Yamato, Regioselective substitution at the 1,3- and
6,8-Positions of pyrene for the construction of small dipolar molecules, J. Org.
Chem. 80 (2015) 10973e10978.
References
[1] K.C. Stylianou, R.H. Samantha, Y. Chong, J. Bacsa, J.T.A. Jones, Y.Z. Khimyak,
D. Bradshaw, M.J. Rosseinsky, A guest-responsive fluorescent 3D microporous
metal-organic framework derived from a long-lifetime pyrene core, J. Am.
Chem. Soc. 132 (2010) 4119e4130.
[2] J.C. Wu, Y. Zou, C.Y. Li, W. Sicking, I. Piantanida, T. Yi, C. Schmuck, A molecular
peptide beacon for the ratiometric sensing of nucleic acids, J. Am. Chem. Soc.
134 (2012) 1958e1961.
[3] K.R.J. Thomas, N. Kapoor, M.N.K. Prasad Bolisetty, J.H. Jou, Y.L. Chen, Y.C. Jou,
Pyrene-fluorene hybrids containing acetylene linkage as color-tunable emit-
ting materials for organic light-emitting diodes, J. Org. Chem. 77 (2012)
3921e3932.
[4] B. Kim, Y. Park, J. Lee, D. Yokoyama, J.H. Lee, J. Kido, J. Park, Synthesis and
electroluminescence properties of highly efficient blue fluorescence emitters
using dual core chromophores, J. Mater. Chem. C 1 (2013) 432e440.
[5] I.V. Astakhova, V.A. Korshun, J. Wengel, Highly fluorescent conjugated pyrenes
in nucleic acid probes: (phenylethynyl)pyrenecarbonyl-functionalized locked
nucleic acids, Chem. Eur. J. 14 (2008) 11010e11026.
[6] B.R. Kaafarani, L.A. Lucas, B. Wex, G.E. Jabbour, Synthesis of novel pyrene
discotics for potential electronic applications, Tetrahedron Lett. 48 (2007)
5995e5998.
[24] Z.J. Zhao, S.M. Chen, J.W.Y. Lam, P. Lu, Y.C. Zhong, K.S. Wong, H.S. Kwok,
B.Z. Tang, Creation of highly efficient solid emitter by decorating pyrene core
with AIE-active tetraphenylethene peripheries, Chem. Commun. 46 (2010)
2221e2223.
[25] M. Sase, S. Yamaguchi, Y. Sagara, I. Yoshikawa, T. Mutai, K. Araki, Piezochromic
luminescence of amide and ester derivatives of tetraphenylpyrene-role of
amide hydrogen bonds in sensitive piezochromic response, J. Mater. Chem. 21
(2011) 8347e8354.
[26] H. Maeda, T. Maeda, K. Mizuno, K. Fujimoto, H. Shimizu, M. Inouye, Alky-
nylpyrenes as improved pyrene-based biomolecular probes with the advan-
tages of high fluorescence quantum yields and long absorption/emission
wavelengths, Chem. Eur. J. 12 (2006) 824e831.
€
ꢀ
[27] A. Hayer, V. Halleux, A. Ko1hler, A. El-Garoughy, E.W. Meijer, J. Barbera, J. Tant,
ꢀ ^
J. Levin, M. Lehmann, J. Gierschner, Jerome Cornil, Y.H. Geerts, Highly fluo-
rescent crystalline and liquid crystalline columnar phases of pyrene-based
structures, J. Phys. Chem. B 110 (2006) 7653e7659.
[7] H. Lee, B. Kim, S. Kim, J. Kim, J. Lee, H. Shin, J.H. Lee, J. Park, Synthesis and
electroluminescence properties of highly efficient dual core chromophores
with side groups for blue emission, J. Mater. Chem. C 2 (2014) 4737e4747.
[8] R. Zhang, Y. Zhao, G.L. Li, D.S. Yang, Z.H. Ni, A new series of pyrenyl-based
triarylamines: syntheses, structures, optical properties, electrochemistry and
electroluminescence, RSC Adv. 6 (2016) 9037e9048.
[28] K. Fujimoto, H. Shimizu, M. Furusyo, S. Akiyama, M. Ishida, U. Furukawa,
T. Yokoo, M. Inouye, Photophysical properties of 1,3,6,8-tetrakis(arylethynyl)
pyrenes with donor or acceptor substituents: their fluorescence sol-
vatochromism and lightfastness, Tetrahedron 65 (2009) 9357e9361.
[29] R. Zhang, Y. Zhao, T.F. Zhang, L. Xu, Z.H. Ni, A series of short axially sym-
metrically 1,3,6,8-tetrasubstituted pyrene-based green and blue emitters with
4-tert-butylphenyl and arylamine attachments, Dyes Pigments 130 (2016)
106e115.
[9] Z.M. Zhang, Y. Zhao, R. Zhang, L.F. Zhang, W.Q. Cheng, Z.H. Ni, Design and
synthesis of
a new series of tetra(polycyclic aryl)ethenes: achieving
€
aggregation-induced emission and efficient solid-state photoluminescence,
Dyes Pigments 118 (2015) 95e101.
[30] V.L. Malinovskii, R. Haner, Synthesis of polysubstituted pyrenes with tuned
spectroscopic properties for two-point attachment, Eur. J. Org. Chem. 16
(2006) 3550e3553.
[31] G.M. Sheldrick, A short history of SHELX, Acta Crystallogr. Sect. A Found.
Crystallogr. A64 (2008) 112e122.
[32] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, Gaussian 09, Revision A.02, Gaussian, Inc., Wallingford, CT,
2009.
[10] T.M. Figueira-Duarte, K. Müllen, Pyrene-based materials for organic elec-
tronics, Chem. Rev. 111 (2011) 7260e7314.
[11] K.R.J. Thomas, J.T. Lin, Y.T. Tao, C.W. Ko, Novel green light-emitting carbazole
derivatives: potential electroluminescent materials, Adv. Mater. 12 (2000)
1949e1951.
[12] R. Zhang, L.H. Xu, H. Chen, Z.H. Qin, Y. Zhao, Z.H. Ni, Convenient synthesis of 1-
thiohydroxypyrene by Newman-Kwart rearrangement, Chem. Res. Chin. Univ.
31 (2015) 224e227.
[33] J. Grimshaw, J. Trocha-Grimshaw, Characterisation of 1.6- and
1 .8-
dibromopyrenes, J. Chem. Soc. Perkin Trans. 1 (1972) 1622e1623.
[13] A.G. Crawford, Z.Q. Liu, I.A.I. Mkhalid, M.H. Thibault, N. Schwarz, G. Alcaraz,
A. Steffen, J.C. Collings, A.S. Batsanov, J.A. Howard, T.B. Marder, Synthesis of 2-
and 2,7-functionalized pyrene derivatives: an application of selective C-H
borylation, Chem. Eur. J. 18 (2012) 5022e5035.
[14] Y.L. Liu, T. Shan, L. Yao, Q. Bai, Y.C. Guo, J.Y. Li, X. Han, W.J. Li, Z.M. Wang,
B. Yang, P. Lu, Y.G. Ma, Isomers of pyrene-imidazole compounds: synthesis
and configuration effect on optical properties, Org. Lett. 17 (2015)
6138e6141.
[15] X. Feng, J.Y. Hu, X.F. Wei, C. Redshaw, T. Yamato, Influence of substituent
position on thermal properties, photoluminescence and morphology of pyr-
eneefluorene derivatives, J. Mol. Struct. 1086 (2015) 216e222.
[16] Z.M. Zhang, F.F. Han, R. Zhang, N. Li, Z.H. Ni, Design, syntheses and
aggregation-induced emission properties of two new enlarged
tetraarylethene-based luminogens, Tetrahedron Lett. 57 (2016) 1917e1920.
[17] Y. Niko, S. Kawauchi, S. Otsu, K. Tokumaru, G.i. Konishi, Fluorescence
[34] D. Karthik, K.R.J. Thomas, J.H. Jou, S. Kumar, Y.L. Chen, Y.C. Jou, Deep-blue
emitting pyrene-benzimidazole conjugates for solution processed organic
light emitting diodes, RSC Adv. 5 (2015) 8727e8738.
[35] K.R. Justin Thomas, M. Velusamy, J.T. Lin, C.H. Chuen, Y.T. Tao, Hex-
aphenylphenylene dendronised pyrenylamines for efficient organic light-
emitting diodes, J. Mater. Chem. 15 (2005) 4453e4459.
[36] H.Y. Oha, C. Lee, S. Lee, Efficient blue organic light-emitting diodes using
newly-developed pyrene-based electron transport materials, Org. Electron 10
(2009) 163e169.
[37] H.C. Liu, Q. Bai, L. Yao, H.Y. Zhang, H. Xu, S.T. Zhang, W.J. Li, Y. Gao, J.Y. Li, P. Lu,
H.Y. Wang, B. Yang, Y.G. Ma, Highly efficient near ultraviolet organic light-
emitting diode based on a meta-linked donoreacceptor molecule, Chem. Sci.
6 (2015) 3797e3804.
[38] T. Oyamada, S. Akiyama, M. Yahiro, M. Saigou, M. Shiro, H. Sasabe, C. Adachi,
Unusual photoluminescence characteristics of tetraphenylpyrene (TPPy) in
various aggregated morphologies, Chem. Phys. Lett. 421 (2006) 295e299.
[39] F.M. Winnik, Photophysics of preassociated pyrenes in aqueous polymer so-
lutions and in other organized media, Chem. Rev. 93 (1993) 587e614.
[40] N. Kapoor, K.R.J. Thomas, Fluoranthene-based triarylamines as hole-
transporting and emitting materials for efficient electroluminescent devices,
New J. Chem. 34 (2010) 2739e2748.
[41] A. Thangthong, N. Prachumrak, R. Tarsang, T. Keawin, S. Jungsuttiwong,
T. Sudyoadsuk, V. Promarak, Blue light-emitting and hole-transporting ma-
terials based on 9,9-bis(4-diphenylaminophenyl)fluorenes for efficient elec-
troluminescent devices, J. Mater. Chem. 22 (2012) 6869e6877.
enhancement of pyrene chromophores induced by alkyl groups through sep
conjugation: systematic synthesis of primary, secondary, and tertiary alky-
lated pyrenes at the 1, 3, 6, and 8 positions and their photophysical properties,
J. Org. Chem. 78 (2013) 3196e3207.
[18] T. Keawin, N. Prachumrak, S. Namuangruk, S. Pansay, N. Kungwan, S. Maensiri,
S. Jungsuttiwong, T. Sudyoadsuk, V. Promarak, Efficient bifunctional materials
based on pyrene- and triphenylamine-functionalized dendrimers for elec-
troluminescent devices, RSC Adv. 5 (2015) 73481e73489.
[19] F. Liu, C. Tang, Q.Q. Chen, S.Z. Li, H.B. Wu, L.H. Xie, B. Peng, W. Wei, Y. Cao,
W. Huang, Pyrene functioned diarylfluorenes as efficient solution processable
light emitting molecular glass, Org. Electron 10 (2009) 256e265.