Short axially asymmetrically 1,3-disubstituted pyrene-based color-tunable emitters: Synthesis, characterization and optical properties

Article abstract of DOI:10.1016/j.tet.2020.131828

In contrast to conventional pyrene-based emitters which feature D-π-A type structures, a new class of emitters possessing a short axis are gaining interest owing to both their academic importance and promising applications in organic optoelectronic materi

Full text of DOI:10.1016/j.tet.2020.131828

Tetrahedron 78 (2021) 131828
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Short axially asymmetrically 1,3-disubstituted pyrene-based color-
tunable emitters: Synthesis, characterization and optical properties
,
Chuan-Zeng Wang a b, Zi-Jin Pang a, Ze-Dong Yu a, Zhao-Xuan Zeng a, Wen-Xuan Zhao a,
,
, *
Zi-Yan Zhou a **, Carl Redshaw c, Takehiko Yamato b
a School of Chemical Engineering, Shandong University of Technology, Zibo, 255049, PR China
b Department of Applied Chemistry, Faculty of Science and Engineering, Saga University, Onjo-machi 1, Saga, 840-8502, Japan
c Department of Chemistry, The University of Hull, Cottingham Road, Hull, Yorkshire, HU6 7RX, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
In contrast to conventional pyrene-based emitters which feature D-p-A type structures, a new class of
Received 16 October 2020
Received in revised form
25 November 2020
Accepted 28 November 2020
Available online 3 December 2020
emitters possessing a short axis are gaining interest owing to both their academic importance and
promising applications in organic optoelectronic materials. Herein, donor and acceptor substituents were
introduced at 1-, 3-positions by employing a two step bromination reaction. Two 1-donor-3-acceptor
pyrenes were systematically investigated by 1H/13C NMR spectroscopy, optical spectroscopy, and theo-
retical calculations. The preliminary research of the substituent positions and substitutions pattern on
the properties of the materials as well as on the frontier orbitals is reported. The experimental results
indicated the strong impact on the photophysical properties endowed with the possibility of precise
color-control of pyrene derivatives through substituent variation.
Keywords:
Pyrene chemistry
Asymmetric synthesis
Color-tunable emitters
Photo-physical properties
Density functional theory
© 2020 Elsevier Ltd. All rights reserved.
1. Introduction
numerous isomers that are very difficult to separate [11].
Interestingly, 2,7-disubstituted pyrene derivatives exhibit
In recent years, the functionalization of pyrene has inspired
numerous researchers due to its unique properties in the material
arena [1e3]. The synthesis of asymmetric derivatives is one of the
most popular topics and typically involves the design of donor-
acceptor (D-A) type molecules. Such species shows great adjust-
ability for optoelectronic properties because of their large co-
efficients excited-state intramolecular charge transfer (ICT) [4e6].
It is known that long axial asymmetrically pyrene-based de-
rivatives functionalized at the 1-, 3-, 6-, 8-positions can be accessed
by an electrophilic substitution reaction due to the HOMOs have
largest coefficients, and such species possess outstanding proper-
ties [7e10]. Moreover, 1,6- or 1,8-disubstituted and 1,3,6,8-
tetrasubstituted asymmetric pyrene-based materials appending
two or two pairs of different groups have been reported with
excellent photoelectric properties [1,2]. However, high chemical
activity has led to many challenges such as the formation of
distinct difference in their optical behaviour, such as single mo-
lecular white emitters [12], adjustable redox potentials and frontier
orbitals [13e15]. Recently, a controllable regioselective approach at
alternative positions was established by Yamato and co-workers
[16], which achieved the stepwise functionalization at the K-re-
gion (5-, 9-positions) and the active sites (1-, 3-positions). The
strategy expands the scope of pyrene-based photoelectric mate-
rials. Meanwhile, there has been some significant work based on
functionalization along the short axis. Müllen and co-workers
opened up new methods to functionalize pyrene at the K-region
via bromination and presented a few examples possessing long
wave emission (>600 nm) [17,18]. There are also a number of re-
ports concerning D-p-A type pyrenes, such as those obtained by
combining 2,7- or 1,8-acceptor moieties with 4,5- donor moieties
which led to strongly red-shifted absorptions with high molar ab-
sorptivities [19e21], and a series of green and blue emitters pre-
pared by introducing donor and acceptor groups at the 1,8-
positions and 3,6-positions, respectively [22,23]. On the basis of
these studies, the possibility of position-dependent photoelectric
* Corresponding author.
** Corresponding author.
E-mail addresses: zyzhou@sdut.edu.cn (Z.-Y. Zhou), yamatot@cc.saga-u.ac.jp
(T. Yamato).
properties inspired our interest to construct D-
systems in less explored positional regions.
p-A type pyrene
https://doi.org/10.1016/j.tet.2020.131828
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C.-Z. Wang, Z.-J. Pang, Z.-D. Yu et al.
Tetrahedron 78 (2021) 131828
In our previous report, we presented a facile and predictive
strategy to tune the emission color by constructing D-p-D pyrenes
pyrene is presented, and the key step of this novel strategy is the
bromination reaction at the 1- and 3-positions by employing ben-
zyltrimethylammonium tribromide (BTMABr3) and NBS under
moderate conditions. All products and intermediates were fully
characterized by high-resolution mass spectrometry and NMR
spectroscopy (see Figs. S2e10 in the Supporting information). The
thermal stabilities of 6 were researched byꢀ1thermogravimetric
analysis (TGA) at a heating rate of 10 ꢁC min under a nitrogen
atmosphere (Fig. S11). The results showed that emitters 6 exhibited
high thermal stabilities (Td > 400 ꢁC), which also suggest great
potential application in organic electronics materials.
at the 1-, 3-positions [24]. Taking account of the above consider-
ations, two 1-donor-3-acceptor pyrenes with tuneable highest
occupied molecular orbital (HOMO) and lowest unoccupied mo-
lecular orbital (LUMO) levels are presented (Scheme 1). New pyrene
chemistry has therefore been developed for the stepwise func-
tionalization at the 1-, 3-positions starting from 7-tert-butylpyrene.
2. Results and discussion
2.1. Synthesis and characterization
2.2. Photophysical properties
In general, the electrophilic substitution reaction shows high
activity at the 1-, 3-, 6-, and 8-positions of pyrene. Thus, various
pyrene derivatives [1] can be easily accessed depending on the
experimental conditions. However, it is quite difficult to introduce
different substituents selectively at the 1- and 3-positions of pyrene
by direct electrophilic aromatic substitution reactions due to the
formation of 1,6- and 1,8-substituted products. According to pre-
vious reports, 7-tert-butyl-1,3-dibromopyrene 3 [25,26] can be
synthesized from 2-tert-butylpyrene 1 with Br2 at temperatures
below ꢀ78 ꢁC based on a positional protective strategy by
employing a tert-butyl group. However, the sensitivity to experi-
mental conditions leads to the formation of complex by-products,
which also limits the synthesis of this kind of compound to some
extent. Previously, we reported that treatment of 2-tert-butylpyr-
ene 1 with benzyltrimethylammonium tribromide (BTMABr3) (3.5
equiv.) in dry CH2Cl2 at room temperature afforded the desired 1,3-
dibromo-7-tert-butylpyrene 3 in good yield (76%). Moreover a
mixture of 1 and BTMABr3 (1.1 equiv.) in CH2Cl2 at room temper-
ature for 12 h afforded the desired product 2 in 84% yield along with
recovery of the starting compound 1 and 1,3-dibromo-7-tert-
butylpyrene 3 [27,28]. On the other hand, bromination of 1 was
performed with N-bromosuccinimide (NBS) (1.1 equiv.) in THF at
room temperature for 12 h, which exclusively afforded 2 in 94%
yield. The 7-tert-butyl-1-arylpyrenes 4 were synthesized from
bromide 2 with the corresponding arylboronic acid by the Suzuki-
Miyaura cross-coupling reaction in good yields. Bromination of 4a
and 4b with BTMABr3 (1.5 equiv.) in CH2Cl2eMeOH at room tem-
perature for 6 h occurred selectively at the 3-position to afford the
desired 1-aryl-3-bromopyrene 5a and 5b in 88 and 98% yields,
respectively. The target 1,3-asymmetrically substituted pyrenes 6
were synthesize from 5 by Sonogashira coupling reactions with the
corresponding arylacetylenes as shown in Scheme 2. In particular, a
new method to introduce the functional groups at the terminal of
Detailed studies of their photophysical properties were per-
formed by comparing with the reference compound 1,3-diphenyl-
7-tert-butylpyrene 7 [26]. As shown in Fig. 1 left and Table 1, the
absorption spectra of 6 in CH2Cl2 (DCM) solution exhibit a set of
obvious absorption bands at around 270e340 nm with a shoulder
band observed at around 400 nm. By comparing the spectrum of
reference compound 7 given in Table 1, the absorption bands at
short wavelengths benefit from the bathochromic shift of the ab-
sorption of the phenyl and pyrene core, which can be ascribed to
the intramolecular pep* transition of the extended p-conjugation
of alkynyl and phenyl groups, while the low-energy shoulder ab-
sorption with high molar absorption coefficients indicates that
their excited states possess significant charge transfer absorption
associated with the intramolecular charge transfer from the ary-
lethynyl units to the aryl group via the pyrene core. Meanwhile, a
slight difference of the shoulder at 400 nm and an obvious differ-
ence at around 350 nm indicated that the strength and region of
charge transfer play a significant role on the absorption properties.
This indicates that a more efficient excited-state intramolecular
charge transfer has occurred in this type of pyrene derivatives.
On the other hand, the emission spectra of emitters 6 present a
simple and clear emission band. More specifically, the emission
maxima are in the range 502e525 nm in dilute DCM solution with
an obvious red-shift (more than 100 nm) compared with com-
pound 7 (396 nm) (Fig. 1 right). Compounds 6a and 6b exhibit
green emission with peaks at 502 nm and 525 nm, respectively. The
photoluminescence quantum yields of emitters 6 were also recor-
ded, and two compounds exhibit reasonable quantum yields (ФF),
especially for 6a, the ФF in DCM solution up to 88%, showing a
substantial enhancement compared to 7 (ФF ¼ 38%), which benefit
from expanded
p conjugated system. On the other hand, the ФF
value of 6b shows an increasing trend due to the influence of the
distinct intramolecular charge transfer. As expected, based on our
novel design strategy of short axially asymmetrically 1-donor-3-
acceptor pyrenes, the two compounds exhibit efficient color-
tunable properties.
In order to investigate the emission mechanism of these two
short axially D-p-A type pyrene emitters, solvatochromism was
carried out in solvents of different polarities (dimethylformamide
(DMF), tetrahydrofuran (THF), dichloromethane (DCM), 1,4-
dioxane, and cyclohexane). Pertinent data for the absorption and
emission spectra are shown in Fig. 2 and Figs. S12e17). The ab-
sorption spectra of compounds of type 6 all present zero or mini-
mum solvent dependence. In sharp contrast, significant
solvatochromism was observed for the emission spectra of both
emitters. Both compounds 6aeb exhibited a significant bath-
ochromic shift for their emission spectra in different solution, as
large as 116 nm, and 95 nm for 6a, and 6b, respectively. Based on
the case study of 6a, as depicted in Fig. 2b, which exhibited sig-
nificant color change from sky-blue to yellow from cyclohexane
solution to DMF solution. The results further indicate that emitters
Scheme 1. Illustration of the pyrene-based D-p-A emitters.
2

C.-Z. Wang, Z.-J. Pang, Z.-D. Yu et al.
Tetrahedron 78 (2021) 131828
Scheme 2. Synthetic route to emitters 6.
the dipolar moment of the intramolecular excited state is larger
than the ground state because of the substantial charge redistri-
bution. The value of the slope for 6a (12802), and 6b (10529) is far
larger than that for 7 (ꢀ200). Moreover, compared with the other
D-p-A systems, the slope of the fitting lines for this project are
larger than most reported results [6,31], which is mainly due to
their dissimilar intramolecular charge transfer effectiveness and
pathways of the 1-donor-3-acceptor pyrene system. The other
crucial factor, the twisted intramolecular charge transfer (TICT),
might also play an important role in the solution state due to the 4-
N,N-dimethylaminophenyl moiety [32]. As a control, comparing
with other reported asymmetrically pyrene derivatives with phenyl
groups and aryne groups [16,33], high tunability and more distinct
charge separations were observed by employing this efficient
strategy.
Fig. 1. UVeVis absorption spectra (left arrow) and fluorescence spectra (right arrow) of
6a, 6b and 7 in DCM solutions at ~ 10ꢀ5 e 10ꢀ7 M at room temperature.
2.3. Quantum chemistry calculations
6 are tuneable and favorable luminescent materials. Meanwhile,
this result of solvatochromism was further elucidated by the rela-
tionship between the Lippert equation and the Stokes shifts in
various solvents [29,30]. The Lippert-Mataga plots present a linear
correlation together with a high slope value, which indicate that
To investigate the orbital energies, electron densities, electronic
structures of the highest occupied molecular orbital (HOMO) and
lowest unoccupied molecular orbital (LUMO) states of the com-
pounds 6 and 7, as well as to elucidate the photophysical charac-
teristics, density functional theory (DFT) calculations were carried
Table 1
Optical absorption and emission spectroscopic data of compounds 6a, 6b and 7.a
lmaxabs [nm]b
lmaxPL [nm]c
Stokes-shift [nm]
HOMO (eV)
LUMO (eV)
D
Ed (eV)
FF
e
Compounds
6a
6b
7
396
398
360
502
525
396
106
137
36
ꢀ4.56
ꢀ4.76
ꢀ5.09
ꢀ1.60
ꢀ1.90
ꢀ1.55
3.05
2.86
3.54
0.88
0.07
0.38
a
All measurements were performed under degassed conditions.
b
c
~ ꢂ 10ꢀ5 M in CH2Cl2, labs is the absorption band appearing at the longest wavelength.
~ ꢂ 10ꢀ7 M in CH2Cl2, lex is the fluorescence band appearing at the shortest wavelength.
DFT/B3LYP/6-31G* using Gaussian.
d
e
Absolute quantum yield ( 0.01e0.03) in dichloromethane.
3

C.-Z. Wang, Z.-J. Pang, Z.-D. Yu et al.
Tetrahedron 78 (2021) 131828
Fig. 2. (a) Emission spectra of 6a in cyclohexane, 1,4-dioxane, THF, DCM, and DMF at room temperature; (b) LippertꢀMataga plots for compound 6a.
out on the two compounds at the B3LYP/6-31G* level. In general,
acceptor groups have an effect on the LUMOs because they are
prone to accept electrons, donor groups on the other hand can
provide a significant contribution to the HOMOs because they are
exhibited an obvious adjustability of color and other properties.
Two compounds exhibit high thermal stability and good solubility.
The present work opens up new avenues to explore a novel func-
tionalization strategy and to broaden the scope for constructing
efficient pyrene-based optoelectronic materials. Ongoing works are
focusing on this type of emitter and will be published soon.
prone to donate electrons [34]. For this kind of donor-
p-acceptor
(D- -A) structures, the energy gaps of these new emitters can be
p
significantly tuned compared with the naked components. As
depicted in Fig. 3, the significant difference of distribution of
LUMOs and HOMOs of emitters 6 result from the presence of the
strong electron-donating nature of the N,N-dimethylaminophenyl
group [33], and especially for compound 6b, the efficient electron-
withdrawing nature of the formyl group provided energetically
enhanced LUMOs, which are mainly distributed over the pyrene
core and 4-formylphenyl substituents. The results of these theo-
4. Experimental section
All melting points are uncorrected. All reactions were per-
formed under a dry N2 atmosphere. Solvents were Guaranteed
reagent (GR) for dimethylformamide (DMF), tetrahydrofuran (THF),
dichloromethane (DCM), 1,4-dioxane, and cyclohexane, and stored
over molecular sieves. Other reagents were obtained commercially
and used without further purification. Reactions were monitored
using thin layer chromatography (TLC). Commercial TLC plates
(Merck Co.) were developed and the spots were identified under UV
light at 254 and 365 nm. Column chromatography was performed
on silica gel 60 (0.063e0.200 mm). All synthesized compounds
were characterized using 1H/13C NMR spectroscopy, and by HRMS
(FAB) mass analysis. Fluorescence spectroscopic studies were per-
formed in various organic solvents in a semimicro fluorescence cell
retical calculations indicate that the emitters
6 can exhibit
enhanced ICT character compared with 7, the fluorescent behaviour
is sensitive to structural change, which impacts on the distribution
of the LUMOs and HOMOs, particularly polarity [35], which is
consistent with the experimental results, such as emission spectra,
solvatochromism.
3. Conclusion
(Hellma®, 104F-QS, 10 ꢂ 4 mm, 1400
mL) with a Varian Cary Eclipse
spectrophotometer. Fluorescence quantum yields were measured
using absolute methods.
In summary, two novel D-p-A emitters were prepared by a
stepwise bromination reaction, a Suzuki-Miyaura cross-coupling
reaction, and a Sonogashira coupling reaction in reasonable yield.
Depending on the electron-withdrawing/donating groups along
the short axis, the theoretical and experimental results of 6
4.1. General procedure for the synthesis of 2
N-Bromosucccinimide (NBS) (195.8 mg, 1.1 mmol) was slowly
added to a solution of 2-tert-butylpyrene 1 (258 mg, 1 mmol) in dry
tetrahydrofuran (10 mL) at 0 ꢁC under a nitrogen atmosphere. The
resulting mixture was allowed to slowly warm up to room tem-
perature and stirred overnight. The reaction mixture was quenched
with Na2S2O3 and extracted with CH2Cl2 (2 ꢂ 20 mL). The combined
organic extracts were dried with anhydrous MgSO4 and evapo-
rated. The residue was crystallized from hexane to give pure 1-
bromo-7-tert-butylpyrene 2 as white crystals (318 mg, 94%). The
1H NMR spectrum agreed with the reported values [27].
4.2. The SuzukieMiyaura coupling reaction towards the synthesis
of 4aeb
A mixture of 1-bromo-7-tert-butylpyrene 2 (675 mg, 2.0 mmol),
ethanol (10 mL) and arylboronic acid (4.0 mmol) in toluene (40 mL)
at room temperature was stirred under argon, and Pd(PPh3)4
(35 mg, 1.5 mol%) and a 2 M aqueous solution of Na2CO3 (40 mL)
were added. After the mixture was stirred for 30 min under argon
at room temperature, the mixture was heated to 90 ꢁC with stirring
Fig. 3. HOMO/LUMO energy levels and frontier molecular orbitals obtained from DFT
calculations on 6a, 6b and 7 with optimized geometries.
DE is an energy bandgap of
these three compounds estimated from difference between the HOMO and LUMO
values.
4

C.-Z. Wang, Z.-J. Pang, Z.-D. Yu et al.
Tetrahedron 78 (2021) 131828
for 24 h. The mixture was cooled to room temperature, and the
mixture was quenched with water, extracted with CH2Cl2
(2 ꢂ 100 mL), and washed with water and brine. The organic ex-
tracts were dried with MgSO4 powder and the solvent was
evaporated.
(100 MHz, CDCl3)
d
(ppm) ¼ 192.13, 150.26, 146.45, 136.65, 135.57,
131.36, 131.25, 130.98, 130.82, 130.03, 129.82, 129.55, 128.65, 127.84,
126.25, 125.89, 124.42, 123.54, 123.40, 122.56, 119.62, 35.43, 32.00.
FAB-MS: m/z calcd for C27H21BrO 440.0776 [Mþ]; found 440.0775
[Mþ].
4.3. Synthesis of 7-tert-butyl-1-phenylpyrene (4a)
4.7. Synthesis of 7-tert-butyl-1-phenyl-3-(4-N,N-
dimethylaminophenylethynyl)pyrene (6a)
A
similar procedure with phenylboronic acid (488 mg,
4.0 mmol), was followed for the synthesis of 4a [36]. 4a was ob-
tained as white solid (recrystallized from hexaneeCHCl3 (9:1);
A mixture of 7-tert-butyl-1-phenyl-3-bromopyrene 5a (150 mg,
0.36 mmol), N,N-dimetylaminophenyl acetylene (105 mg,
0.73 mmol), PPh3 (9 mg, 0.036 mmol), CuI (7 mg, 0.36 mmol),
PdCl2(PPh3)3 (13 mg, 0.036 mmol) were added to a degassed so-
lution of DMF (8 mL) and Et3N (8 mL). The resulting mixture was
stirred at 100 ꢁC for 24 h. After it was cooled to room temperature,
the reaction was quenched with water. The mixture was extracted
with CH2Cl2 (2 ꢂ 50 mL), the organic layer was washed with water
(2 ꢂ 30 mL) and brine (30 mL), and then the solution was dried
(MgSO4), and evaporated. The residue was purified by column
chromatography eluting with a hexaneeCHCl3 (3:2) mixture to give
6a as a yellow crystalline powder (86.1 mg, 50%). M.p. 206e208 ꢁC;
510 mg, 76%). 1H NMR (400 MHz, CDCl3)
d
(ppm) ¼ 1.58 (s, 9H, tBu),
7.48 (m, 1H, Ar-H), 7.56 (t, J ¼ 7.4, 2H, Ar-H), 7.64 (d, J ¼ 7.7 Hz, 2H,
Ar-H), 7.94 (d, J ¼ 7.8 Hz, 1H, pyrene-H), 8.00 (d, J ¼ 9.3 Hz, 1H,
pyrene-H), 8.07 (d, J ¼ 1.5 Hz, 2H, pyrene-H), 8.14 (d, J ¼ 9.3 Hz, 1H,
pyrene-H), 8.18 (d, J ¼ 8.0 Hz, 1H, pyrene-H), 8.21 (d, J ¼ 9.3 Hz, 1H,
pyrene-H), 8.22 (d, J ¼ 9.3 Hz, 1H, pyrene-H).
4.4. Synthesis of 7-tert-butyl-1-(4-formylphenyl)pyrene (4b)
A similar procedure with 4-formylphenylboronic acid (600 mg,
4.0 mmol), was followed for the synthesis of 4b. 4b was obtained as
yellow solid (recrystallized from hexaneeCHCl3 (6:1); 379 mg,
1H NMR (400 MHz, CDCl3)
d
(ppm) ¼ 1.59 (s, 9H, tBu), 3.03 (s, 6H,
NMe2), 6.74 (d, J ¼ 7.2 Hz, 2H, Ar-H), 7.49 (d, J ¼ 7.0 Hz, 1H, Ar-H),
7.54e7.62 (m, 4H, Ar-H), 7.65 (d, J ¼ 7.1 Hz, 2H, Ar-H), 7.99 (d,
J ¼ 9.0 Hz, 1H, pyrene-H), 8.10 (d, J ¼ 8.8 Hz, 1H, pyrene-H), 8.17 (m,
3H, pyrene-H), 8.25 (s, 1H, pyrene-H), 8.68 (d, J ¼ 8.9 Hz, 1H, pyr-
53%). M.p.134e136 ꢁC; 1H NMR (400 MHz, CDCl3)
d
(ppm) ¼ 1.59 (s,
9H, tBu), 7.83 (d, J ¼ 8.0 Hz, 2H, Ar-H), 7.94 (d, J ¼ 7.8 Hz, 2H, Ar-H),
8.04 (d, J ¼ 9.3 Hz, 1H, Ar-H), 8.06e8.12 (m, 5H, pyrene-H),
8.19e8.25 (m, 2H, pyrene-H), 10.16 (s, 1H, CHO), FAB-MS: m/z calcd
for C27H22O 362.1671 [Mþ]; found 362.1670 [Mþ].
ene-H). 13C NMR (100 MHz, CDCl3)
d
(ppm) ¼ 149.50,140.86, 137.33,
133.00, 131.50, 131.15, 130.81, 130.67, 128.49, 128.27, 128.06, 127.45,
125.83, 125.22, 122.91, 122.59, 118.49, 112.05, 96.57, 87.72, 40.44,
35.36, 32.04. FAB-MS: m/z calcd for C36H31N 477.2457 [Mþ]; found
477.2454 [Mþ].
4.5. Synthesis of 7-tert-butyl-1-phenyl-3-bromopyrene (5a)
Compound 7-tert-butyl-1-phenylpyrene 4a (334 mg, 1.0 mmol)
was added to CH2Cl2 (9 mL) and MeOH (25 mL), and the mixture
was stirred under argon atmosphere at 0 ꢁC. After 30 min, BTMABr3
(585 mg, 1.5 mmol) was added. The resulting mixture was stirred
for 6 h at room temperature under argon. The mixture was
extracted with CH2Cl2 (2 ꢂ 50 mL), and the combined extracts were
washed with water and brine, dried with MgSO4 powder and
concentrated. The residue was chromatographed over silica gel
(Wako C-300, 200 g) with hexaneeCHCl3 (9:1) as eluent to give a
white solid (366 mg, 88%). M.p. 110e112 ꢁC; 1H NMR (400 MHz,
4.8. Synthesis of 7-tert-butyl-1-(4-formylphenyl)-3-(4-N,N-
dimethylaminophenylethynyl)pyrene (6b)
A mixture of 7-tert-butyl-1-(4-formylphenyl)-3-bromopyrene
5b (120 mg, 0.27 mmol), N,N-dimetylaminophenyl acetylene
(78 mg, 0.54 mmol), PPh3 (6.7 mg, 0.027 mmol), CuI (5 mg,
0.27 mmol), PdCl2(PPh3)3 (10 mg, 0.027 mmol) were added to a
degassed solution of DMF (6 mL) and Et3N (6 mL). The resulting
mixture was stirred at 100 ꢁC for 24 h. After it was cooled to room
temperature, the reaction was quenched with water. The mixture
was extracted with CH2Cl2 (2 ꢂ 40 mL), the organic layer was
washed with water (2 ꢂ 30 mL) and brine (30 mL), and then the
solution was dried (MgSO4), and evaporated. The residue was pu-
rified by column chromatography eluting with a hexaneeCHCl3
(1:1) mixture to give 6b as an orange crystalline powder (53.5 mg,
CDCl3)
d
(ppm) ¼ 1.59 (s, 9H, tBu), 7.47e7.62 (m, 5H, Ar-H), 7.94 (d,
J ¼ 8.0 Hz, 1H, pyrene-H), 8.01 (d, J ¼ 9.2 Hz, 1H, pyrene-H), 8.08 (d,
J ¼ 9.3 Hz, 1H, pyrene-H), 8.17 (d, J ¼ 9.2 Hz, 1H, pyrene-H),
8.20e8.24 (m, 2H, pyrene-H), 8.27 (s, 1H, pyrene-H), 8.43 (d, J ¼ 9.2,
1H, pyrene-H). FAB-MS: m/z calcd for C26H21Br 412.0827 [Mþ];
found 412.0827 [Mþ].
39%). M.p. 255e257 ꢁC; 1H NMR (400 MHz, CDCl3)
d
(ppm) ¼ 1.60
4.6. Synthesis of 7-tert-butyl-1-(4-formylphenyl)-3-bromopyrene
(5b)
(s, 9H, tBu), 3.04 (s, 6H, NMe2), 6.74 (d, J ¼ 7.5 Hz, 2H, Ar-H), 7.60 (d,
J ¼ 8.9 Hz, 2H, Ar-H), 7.83 (d, J ¼ 7.8 Hz, 2H, Ar-H), 8.03 (s, 2H,
pyrene-H), 8.07 (d, J ¼ 7.8 Hz, 2H, Ar-H), 8.09 (s, 1H, pyrene-H), 8.18
(d, J ¼ 10.2 Hz, 1H, pyrene-H), 8.22 (s, 1H, pyrene-H), 8.29 (s, 1H,
Compound 7-tert-butyl-1-(4-formylphenyl)pyrene 4b (200 mg,
0.56 mmol) was added to CH2Cl2 (5 mL), MeOH (15 mL), and the
mixture was stirred under argon atmosphere at 0 ꢁC. After 30 min,
BTMABr3 (328 mg, 0.84 mmol) was added. The resulting mixture
was stirred for 6 h at room temperature under argon. The mixture
was extracted with CH2Cl2 (2 ꢂ 30 mL), and the combined extracts
were washed with water and brine, dried with MgSO4 powder and
concentrated. The residue was chromatographed over silica gel
(Wako C-300, 150 g) with hexaneeCHCl3 (7:1) as eluent to give a
pale-yellow solid (240 mg, 98%). M.p. 122e124 ꢁC; 1H NMR
pyrene-H), 8.69 (d, J ¼ 10.0 Hz, 1H, pyrene-H), 10.16 (s, 1H, CHO). 13
C
NMR (100 MHz, CDCl3)
d
(ppm) ¼ 192.23, 150.41, 149.78, 147.40,
135.65, 135.39, 133.03, 131.48, 131.39, 131.34, 130.90, 131.07, 130.28,
129.95,128.77, 128.62, 127.84,125.79,125.07, 124.52, 123.32, 122.99,
122.92, 118.75, 112.04, 110.14, 97.06, 86.58, 40.38, 35.40, 32.02. FAB-
MS: m/z calcd for C37H31NO 505.2406 [Mþ]; found 505.2357 [Mþ].
Declaration of competing interest
(400 MHz, CDCl3)
d
(ppm) ¼ 1.52 (s, 9H, tBu), 7.73 (d, J ¼ 7.7 Hz, 2H,
Ar-H), 7.97 (d, J ¼ 7.7 Hz, 2H, Ar-H), 8.02 (d, J ¼ 7.9 Hz, 2H, pyrene-
H), 8.15 (d, J ¼ 7.9 Hz, 2H, pyrene-H), 8.19 (s, 1H, pyrene-H), 8.24 (s,
1H), 8.38 (d, J ¼ 9.3 Hz, 1H, pyrene-H), 10.10 (s, 1H, CHO). 13C NMR
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
5

C.-Z. Wang, Z.-J. Pang, Z.-D. Yu et al.
Tetrahedron 78 (2021) 131828
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Acknowledgments
This work was performed under the Cooperative Research
Program of “Network Joint Research Center for Materials and De-
vices (Institute for Materials Chemistry and Engineering, Kyushu
University)”. We would like to thank the Natural Science Founda-
tion of Shandong Province (Grant No. ZR2019BB067) The EPSRC is
thanked for an overseas travel grant to C.R. (EP/R023816/1).
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Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2020.131828.
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