[4 + 2]cycloaddition reaction to approach diazatwistpentacenes: Synthesis, structures, physical properties, and self-assembly

Article abstract of DOI:10.1021/jo500400d

Three novel diazatwistpentacenes (1,4,6,13-tetraphenyl-7:8,11:12-bisbenzo- 2,3-diazatwistpentacene (1, IUPAC name: 9,11,14,16-tetraphenyl-1,6- dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine); 1,4-di(pyridin-2-yl)-6,13- diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (2, IUPAC name: 9,16-diphenyl-11,14-di(pyridin-2-yl)-1,6-dihydrobenzo[8,9]triphenyleno[2,3-g] phthalazine); and 1,4-di(thien-2-yl)-6,13-diphenyl-7:8,11:12-bisbenzo-2,3- diazatwistpentacene (3, IUPAC name: 9,16-diphenyl-11,14-di(thien-2-yl)-1,6- dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine)) have been successfully synthesized through [4 + 2] cycloaddition reaction involving in situ arynes as dienophiles and substituted 1,2,4,5-tetrazines as dienes. Their structures have been determined by single-crystal X-ray diffraction, confirming that all compounds have twisted configurations with torsion angles between the pyrene unit and the 2,3-diazaanthrance part as high as 21.52° (for 1), 24.74° (for 2), and 21.14° (for 3). The optical bandgaps for all compounds corroborate the values derived from CV. The calculation done by DFT shows that the HOMO-LUMO bandgaps are in good agreement with experimental data. Interestingly, the substituted groups (phenyl, pyridyl, thienyl) in the 1,4-positions did affect their self-assembly and the optical properties of as-resulted nanostructures. Under the same conditions, compounds 1-3 could self-assemble into different morphologies such as microrods (for 1), nanoprisms (for 2), and nanobelts (for 3). Moreover, the UV-vis absorption and emission spectra of as-prepared nanostructures were largely red-shifted, indicating J-type aggregation for all materials. Surprisingly, both 1 and 2 showed aggregation-induced emission (AIE) effect, while compound 3 showed aggregation-caused quenching (ACQ) effect. Our method to approach novel twisted azaacenes through [4 + 2] reaction could offer a new tool to develop unusual twisted conjugated materials for future optoelectronic applications.

Full text of DOI:10.1021/jo500400d

Article
pubs.acs.org/joc
[4 + 2] Cycloaddition Reaction To Approach Diazatwistpentacenes:
Synthesis, Structures, Physical Properties, and Self-assembly
Junbo Li,†,‡ Peizhou Li,§ Jiansheng Wu,† Junkuo Gao,∥ Wei-Wei Xiong,† Guodong Zhang,† Yanli Zhao,§
and Qichun Zhang*,†
†School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
‡School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430074, China
§Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University,
Singapore 637459, Singapore
∥College of Materials and Textile, Zhejiang Sci-Tech University, Hangzhou 310018, China
S
* Supporting Information
ABSTRACT: Three novel diazatwistpentacenes (1,4,6,13-tetraphenyl-7:8,11:12-
bisbenzo-2,3-diazatwistpentacene (1, IUPAC name: 9,11,14,16-tetraphenyl-1,6-
dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine); 1,4-di(pyridin-2-yl)-6,13-diphen-
yl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (2, IUPAC name: 9,16-diphenyl-
11,14-di(pyridin-2-yl)-1,6-dihydrobenzo[8,9]triphenyleno[2,3-g]phthalazine); and
1,4-di(thien-2-yl)-6,13-diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (3,
IUPAC name: 9,16-diphenyl-11,14-di(thien-2-yl)-1,6-dihydrobenzo[8,9]triphenyleno-
[2,3-g]phthalazine)) have been successfully synthesized through [4 + 2] cycloaddition
reaction involving in situ arynes as dienophiles and substituted 1,2,4,5-tetrazines as
dienes. Their structures have been determined by single-crystal X-ray diffraction,
confirming that all compounds have twisted configurations with torsion angles
between the pyrene unit and the 2,3-diazaanthrance part as high as 21.52° (for 1),
24.74° (for 2), and 21.14° (for 3). The optical bandgaps for all compounds
corroborate the values derived from CV. The calculation done by DFT shows that the
HOMO−LUMO bandgaps are in good agreement with experimental data. Interestingly, the substituted groups (phenyl, pyridyl,
thienyl) in the 1,4-positions did affect their self-assembly and the optical properties of as-resulted nanostructures. Under the same
conditions, compounds 1−3 could self-assemble into different morphologies such as microrods (for 1), nanoprisms (for 2), and
nanobelts (for 3). Moreover, the UV−vis absorption and emission spectra of as-prepared nanostructures were largely red-shifted,
indicating J-type aggregation for all materials. Surprisingly, both 1 and 2 showed aggregation-induced emission (AIE) effect, while
compound 3 showed aggregation-caused quenching (ACQ) effect. Our method to approach novel twisted azaacenes through [4
+ 2] reaction could offer a new tool to develop unusual twisted conjugated materials for future optoelectronic applications.
Since oligoacenes can be conveniently prepared through [4 +
2] reactions involving arynes as dienophiles,5,6 this type of
reaction should be a promising method to construct larger
azaacenes. In this report, we demonstrate that larger
diazatwistpentacenes can be prepared through [4 + 2] reaction
between 3,6-disubstituted 1,2,4,5-tetrazines as dienes and in situ
arynes as dienophiles (from 1,4′-diphenyl-naphtho-(2.3:1.2)-
pyrene-6-amino-7′-carboxylate acid).6 In addition, we also
investigate how different substitution groups (e.g., phenyl,
pyridyl, thienyl) in 1-/4-positions on the backbones of 6,13-
diphenyl-7:8,11:12-bisbenzo-2,3-diazatwistpentacene (IUPAC
name: 9,11,14,16-tetraphenyl-1,6-dihydrobenzo[8,9]-
triphenyleno[2,3-g]phthalazine) affect their assembly and the
morphologies/properties of the resulting nanoparticles since
the self-assembly of organic semiconductor molecules into
INTRODUCTION
■
Integrating pyrene species into the backbones of oligoacenes1−3
would make the resulting frameworks twisted, and this type of
materials (namely twistacenes)4−6 has great potential applica-
tions in organic semiconductor devices. If some CH groups in
the backbone of oligotwistacenes are replaced by N atoms,
these compounds will become oilgotwistazaacenes.7−12 In fact,
some oligoazaacenes have been demonstrated as promising
materials for ion sensing, OLED, FET, memory devices,
phototransistors, and solar cells.7−12
Although azaacenes could be prepared through several
methods7c,8a (e.g., SN2 reaction between diamines and
dihydroxy (or dihalo) compounds following by oxidation, or
condensation between diamine (or tetraamine) and diketone
(or tretraketone)), new methods are still required to approach
larger azaacenes (n > 6) because all current methods involve
byproduct water,7−10 which could react with targeted azaacenes
and switch the configuration of N atoms from sp2 to sp3.13
Received: February 19, 2014
Published: April 17, 2014
© 2014 American Chemical Society
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micro/nanostructures is very important to tune their optical
properties as well as for device performance.14 Our results
clearly show that the different substituent groups at 1-/4-
positions have a big effect on optical properties and the shape/
size of the resulting particles.
to the reported method,6a and the target compounds 1−3 were
prepared through a [4 + 2] cycloaddition reaction involving in
situ arynes as dienophiles (from precursor 4 reacting with
isoamyl nitrite) and 3,6-diphenyl-1,2,4,5-tetrazine, 3,6-di-
(pyridin-2-yl)-1,2,4,5-tetrazine, or 3,6-di(thien-2-yl)-1,2,4,5-tet-
razine as dienes (Scheme 1), respectively. All new compounds
1
were fully characterized by H NMR, 13C NMR, and HR-MS.
RESULTS AND DISCUSSION
■
Synthesis, Characterization, and Crystal Structures.
The general synthetic approach to compounds 1−3 is shown in
Scheme 1. Compound 4 was synthesized in five steps according
Moreover, the structures of compounds 1−3 were furthermore
confirmed by single crystal structure analysis. The as-prepared
compounds 1−3 could be dissolved in common organic
solvents such as methylene chloride, chloroform, tetrahydrofur-
an (THF), o-dichlorobenzene (ODCB), and N,N-dimethylfor-
mide.
Scheme 1. Synthetic Routes of Compounds 1−3
To investigate the effects of substitution groups on the
molecular packing arrangement in the solid state, the single
crystals of compounds 1−3 were grown by slow evaporation of
dichloromethane/methanol (1:1) mixed solutions in room
temperature. As shown in Figure 1, all compounds display
significantly twisted structures. Compound 1 possesses a
triclinic space group P-1. Its unit cell data are as follows: a =
10.9885(4) Å, b = 11.6518(4) Å, c = 15.3264(6) Å, α =
85.39(0)°, β = 89.27(0)°, γ = 73.76(0)°. The torsion angle
between pyrene unit and 2,3-diazaanthrance part is about
21.52° (C13−C26−C12−C25), which is smaller than the reported
Figure 1. (a) Crystal structure of compound 1 (hydrogen atoms and the solvent CH2Cl2 are omitted) and the crystal packing arrangement. (b)
Crystal structure of compound 2 (hydrogen atoms are omitted) and the crystal packing arrangement. (c) Crystal structure of compound 3
(hydrogen atoms are omitted) and the crystal packing arrangement.
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twistpentacene.6b Moreover, the lengths of the C17−C7 and
C26−C12 bonds are 1.49 and 1.48 Å, which are longer than the
rest of the C−C bonds. Additionally, the individual molecules
are stacked in head-to-tail mode. There are weak π−π stacking
interactions between the pyrene unit and the 2,3-diazaan-
thrance part, and the distance between them is nearly 4.02 Å
(Supplementary Figure S1). When the substituted groups at 1-/
4-positions were changed into pyridyl groups, a large unit cell
(monoclinic) with space group of C2/c for compound 2 was
obtained. Its unit cell data are as follows: a = 26.9975(6) Å, b =
14.9487(3) Å, c = 16.8201(4) Å, β = 99.47(0)°. The torsion
angle is about 24.74°, which is larger than that of compound 1.
The individual molecules stacking in the crystal of compound 2
also adopt head-to-tail mode. Interestingly, there is no stacking
between the pyrene unit and the 2,3-diazaanthrance part;
instead, there are weak π−π stacking interactions between 2,3-
diazaanthrance units. The distance between two neighboring
2,3-diazaanthrance units is nearly 4.02 Å (Supplementary
Figure S2), which could explain the larger unit cell for
compound 2. When the substituted groups in 1-/4-positions
are replaced by 2-thienyl, compound 3 is obtained and has a
triclinic space group P-1. Its unit cell data are as follows: a =
10.3831(6) Å, b = 13.0198(5) Å, c = 13.2997(6) Å, α =
81.76(0)°, β = 78.2(0)°, γ = 70.81(0)°. The torsion angle is
about 21.14°, which is similar to that of compound 1 but
smaller than that of compound 2. There are two major
intermolecular interactions stabilizing the crystal packing in
compound 3. The first one is the weak π−π stacking
interactions between the pyrene piece and the 2,3-diazaan-
thrance unit, and the other is the weak π−π stacking
interactions between two 2,3-diazaanthrance units (Figure
1c). The distance between them is nearly 3.88 Å (Supple-
mentary Figure S3). Such arrangement might come from the
smaller space hindrance of thienyl groups.
obvious changes, but all peaks are red-shifted. Four absorption
peaks for compound 2 appear at 341, 358, 378, and 464 nm,
while compound 3 has more red-shifted absorption peaks at
342, 359, 381, and 471 nm, respectively. Such red-shifts may be
a result of the enhancement of an intramolecular charge
transfer (ICT) process with the replacement of electron-
withdrawing groups (pyridyl group) or electron-donating
groups (thienyl groups) at 1-/4-positions. Meanwhile, the
color of the solutions change from yellow to dark yellow
(Figure 2, inset). Unlike the parent twistpentacene, which
shows high fluorescence (Φf = 0.69 in CH2Cl2),6b all as-
prepared diazatwistpentacenes show very weak fluorescence
(Figure 3), which indicates that the substitution of N atoms in
Figure 3. Fluorescence spectra of compounds 1−3 (1 × 10−5 M) in
THF. The inset shows the fluorescence color of compounds 1−3 (1 ×
10−3 M) in THF. Excitation wavelength is 350 nm.
2-/3-positions will strongly quench the fluorescence. Actually,
the weak fluorescence behavior is common for 1,2-diazine-
containing molecules, which is possibly caused by the
intersystem crossing effect.15 The fluorescence quantum yield
of compound 1 in THF is 0.0028, using quinine sulfate
dehydrate as the standard (Φf = 0.58 in 0.1 M H2SO4),16 while
pyridyl groups in 1-/4-positions induce a red-shift fluorescence
with a lower intensity (Φf = 0.0020). Interestingly, thienyl
groups (3) can slightly enhance the fluorescence intensity (Φf =
0.0063) compared to phenyl (1) and pyridyl groups (2). The
possible reason is that thienyl group is a stronger electron-
donating group than phenyl and pyridyl groups, which can
increase electron density of the conjugated system and induce a
stronger fluorescence.15a The fluorescence differences are also
confirmed by simulated fluorescence spectra (Supplementary
Figure S6). These results clearly suggest that different
substituent groups at 1-/4-positions did affect the optical
properties of diazatwistpentacenes.
Different Optical and Electrochemical Properties. The
UV−vis absorption spectra of compounds 1−3 were recorded
in THF at room temperature. As shown in Figure 2, in the low
The electrochemical properties of compounds 1−3 were
studied in a three-electrode electrochemical cell with
tetrabutylammonium hexafluorophosphate (Bu4NPF6, TBAF)
(0.1 M) as an electrolyte and Ag/AgCl as a reference electrode
(Figure 4 and Table 1). All compounds show two reversible
reduction peaks and two irreversible oxidation peaks. The onset
oxidative potentials for compounds 1−3 were measured as
1.34, 1.23, and 1.30 V, respectively. On the basis of the
Figure 2. UV−vis spectra of compounds 1−3 (1 × 10−5 M) in THF.
The inset shows the color of compounds 1−3 (1 × 10−3 M) in THF.
energy region, the absorption peak of compound 1 is at 441 nm
with a shoulder at 465 nm. In the high energy region, there are
onset
three peaks at 338, 356, and 376 nm, respectively. The λmax
equation HOMO = −Eonset − 4.4 eV,10a the HOMO energy
ox
is nearly 500 nm (Supplementary Figure S4), which is similar to
the parent twistpentacene.6b When the substituted groups at
1-/4-positions were changed from phenyl to pyridyl (2) or
thienyl (3), the number and shape of absorption peaks have no
levels for 1−3 were calculated as −5.74, −5.63, and −5.70 eV,
respectively. Meanwhile, the LUMO energy levels for
compounds 1−3 were calculated to be −3.23, −3.30, and
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Figure 5. Wave functions for the HOMO and LUMO of compounds
1−3.
Figure 4. Cyclic voltammetry curves of 1−3 in CH2Cl2 solution
containing 0.1 M TBAP electrolyte. Scanning rate: 100 mV/s.
−3.38 eV, respectively. It is worth noting that the change of the
substituent groups from phenyl to pyridyl and thienyl groups
induces an increase of HOMO energy level but causes a
decrease of LUMO energy level, which results in the smaller
bandgaps of compounds 2 and 3 compared with that of
compound 1.
the reprecipitation with the help of surfactants might be one of
the most convient methods. In our research, the self-assembly
of compounds 1−3 was realized through the addition of a THF
solution of compounds 1−3 (10−3 M, 1 mL) into an aqueous
solutions containing P123 block polymers (1 mg/mL, 5 mL) as
the surfactant. Interestingly, the change of the substituted
groups at 1-/4-positions has large effect on the self-assembled
structures. Compounds 1−3 readily form different nano/
microstructures as microrods, nanoprisms, and nanobelts,
respectively (Figure 6). As shown in Figure 6a, compound 1
forms microrods with diameters in the range of 550 nm to 1.2
μm and lengths of 3−10 μm. The XRD patterns (Figure 6b)
further confirmed that the as-prepared microrods are single
crystals and the preferential orientation is the (001) lattice
plane. However, when phenyl groups in 1-/4-positions are
replaced by pyridyl groups, the self-assembled structure
dramatically changed from microrods to nanoprisms. As
shown in Figure 6c, the as-prepared nanoprisms have widths
between 250 and 550 nm and lengths between 200 and 390
nm. Meanwhile, the powder XRD spectrum shows that the as-
obtained nanostructures have the same pattern as the simulated
one, which indicated that the self-assembled nanoprisms are
crystalline and show phase purity. Moreover, when the 1-/4-
positions are changed with thienyl groups, larger areas of
nanobelts with diameters of 120−190 nm and lengths of 1−2
μm were formed. Actually, the self-assembly of compounds 1−
3 without P123 was also investigated. As shown in
Supplementary Figure S7, compounds 1 and 2 cannot form
uniform nanostructure in aqueous solution, while compound 3
can form large-scale quadrangles with diameters between 300
and 400 nm and lengths of 1−2.3 μm. These results suggest
that the soft-template P123 is a key for the control of the shape
and size during self-assembly. The possible self-assembly
The molecular geometries of compound 1−3 were optimized
using density functional theory (DFT) at the B3LYP/6-31G*
level.17 The ground state frontier molecular orbitals of the
optimized molecules were also calculated at the same level. As
shown in Figure 5, both the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO)
of compound 1 are mainly localized on the pyrene units and
2,3-diazaanthrance parts. When phenyl groups at 1-/4-positions
were replaced by pyridyl groups, the HOMO orbital still mainly
localized on the pyrene units and 2,3-diazaanthrance parts, but
the LUMO orbital localized on pyrene, 2,3-diazaanthrance, and
pyridyl groups, respectively. For compound 3, except for the
localization on pyrene units and 2,3-diazaanthrance parts, the
HOMO orbital also localized on thienyl groups, while the
LUMO orbital mainly localized on the pyrene units and 2,3-
diazaanthrance parts. The calculated HOMO and LUMO
orbital energy levels were summarized in Table 1.
Self-Assembly and Optical Changes. Since self-assembly
is a very interesting phenomenon, which can be investigated to
understand the behaviors and properteis of as-prepared
materials in micro/nanoscale,14 it is highly desirable for us to
do some research in this direction. Currently, organic
nanostructures can be obtained through hard/soft templates,18
reprecipitation,19 chemical reaction,20 laser ablation,21 electro-
chemical methods,22 and seed-induced growth23 through weak
interactions such as hydrogen bonding, π−π stacking, electro-
static interaction, and hydrophobic interaction. Among them,
Table 1. Optical and Electrochemical Data of Compounds 1−3
red
a
ox
a
Eonset
Eonset
E
LUMO
c
HOMO
d
Egap/λ
LUMO
HOMO
E
εmax/λmax
λ
em g
gapb
onseet
f
f
gapf
compd
(V)
(V)
(eV)
(eV)
(eV)
(eV/nm)
(eV)
(eV)
(eV)
(103 M−1 cm−1/nm) (nm)
Φf
1
2
3
−1.17
−1.10
−1.02
1.34
1.23
1.30
2.51
2.33
2.32
−3.23
−3.30
−3.38
−5.74
−5.63
−5.70
2.51/494
2.41/515
2.37/523
−2.34
−2.35
−2.41
−5.31
−5.16
−5.24
2.97
2.81
2.83
9.3/441
8.3/464
9.1/471
450
472
466
0.0028
0.0020
0.0063
a
b
c
Obtained from cyclic voltammograms in CH2Cl2. Reference electrode was Ag/AgCl. Egap = Eonsetox − Eonsetred. Calculated according to the formula
d
e
f
ELUMO = EHOMO + Egap
. Calculated from cyclic voltammograms. Optical band gap, Egap = 1240/λonset. Obtained from theoretical calculations.
g
Excitation wavelength was 350 nm.
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Figure 6. (a) SEM image of compound 1 with micrororods. (b) XRD patterns of microrods. (c) SEM image of compound 2 with nanoprisms. (d)
XRD patterns of nanoprisms. (e) SEM image of compound 3 with nanobelts. (e) XRD patterns of nanobelts.
processes are proposed as follows: THF is a good solvent and
water is a poor solvent for compounds 1−3. When THF
solutions are injected into the aqueous solution containing
P123, compounds 1−3 tend to aggregate to form crystalline
micro/nanostructures due to intermolecular π−π stacking and
the hydrophobic effect.24 Meanwhile, the different packing in
single crystal structures of compounds 1−3 could explain the
formation of different nano/microstructures during self-
assembly under the same conditions.
The UV−vis spectra of compounds 1−3 in THF solution
and the related microrods, nanoprisms, and nanobelts in
aqueous solution are shown in Figure 7a. The UV−vis
absorption of all nanostructures become broad and drastically
red-shifted compared to those of 1−3 in THF solution. The
microrods (formed from 1) and nanobelts (formed from 3)
have three similar absorption peaks at 393, 467, 499 nm
(microrods) and 395, 480, 505 nm (nanobelts), respectively.
However, nanoprisms (formed from 2) show broader peaks
and a larger red-shift with one absorption peak at 545 nm. The
red-shifts of absorption peaks for all particles suggest J-type
aggregations.25 More interestingly, in THF solution, com-
pounds 1−3 show very weak fluorescence with fluorescence
quantum yields of 0.0028, 0.0020 and 0.0063, respectively.
After self-assembly, the emission wavelengths were all red-
shifted but the emission strength changes were different.
Compounds 1 and 2 showed obvious aggregation-induced
emission (AIE) effects,26 and the fluorescence quantum yields
were increased to 0.0140 and 0.0059 with nanostructures
dispersed in aqueous solutions. It should be noted that the
fluorescence quantum yield of microrods is 4.1 times higher
than that of compound 1 in THF. However, compound 3
shows aggregation-caused quenching (ACQ)27 effect, and the
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Figure 7. (a) UV−vis spectra: compound 1 in THF solution (a), microrods (formed by 1) dispersed in aqueous solution (b), compound 2 in THF
solution (c), nanoprisms (formed by 2) dispersed in aqueous solution (d), compound 3 in THF solution (e), and nanobelts (formed by 3) dispersed
in aqueous solution (f). Fluoroescence spectra: (b) compound 1 in THF and the microrods in aqueous solution; (c) compound 2 in THF and the
nanoprisms in aqueous solution; and (d) compound 3 in THF and the nanobelts in aqueous solution. Excitation wavelength is 350 nm.
Preparation of SEM Samples. One drop of the solution (20 μL)
was put on a silica wafer and dried over 12 h. The as-prepared samples
were then coated with gold in an ion coater for 40 s.
fluorescence quantum yields was decreased to be 0.0034. The
AIE effects in self-assembled particles for compounds 1 and 2
might have some potential applications as biosensors.
Synthesis. Compound 1. Under an atmosphere of dry argon, 3,6-
diphenyl-1,2,4,5-tetrazine (182 mg, 0.78 mmol) and an excess of
isoamyl nitrite (1 mL) were added into 30 mL of 1,2-dichloroethane.
The mixture was heated to reflux, and then the corresponding acid 4
(400 mg, 0.78 mmol) dispersed in 20 mL of 1,2-dichloroethane was
added to the mixture dropwise. After addition, the mixture was kept
refluxing overnight. Then, the mixture was cooled to room
temperature, and the solvent was removed under reduced pressure.
The resultant residue was purified by silica gel column chromatog-
raphy using CH2Cl2/CH3OH (80/1, v/v) as eluent to afford
CONCLUSIONS
■
In summary, we have successfully synthesized three novel
diazatwistpentacene derivatives through [4 + 2] cycloaddition
reactions, and the as-prepared compounds have been fully
characterized. Our results showed that different substitution
groups at the 1-/4-positions have large effects on the optical
properties, single crystal packing, and corresponding self-
assembly. The self-assembly of compounds 1−3 showed
completely different nano/microstructures, which have differ-
ent optical properties in aqueous solutions. Our synthetic
method as well as the obtained information from the effect of
different substitution groups at the 1-/4-positions on the
properties of diazatwistpentacene derivatives could offer a
guideline to prepare novel larger azaacenes.
1
compound 1 as a yellow solid (154 mg, 30%). Mp: >300 °C. H
NMR (CDCl3, 300 MHz) δ: 7.34 (t, 2H, J = 7.8 Hz), 7.49−7.53 (m,
16H), 7.80−7.90 (m, 10H), 8.80 (s, 2H). 13C NMR (CDCl3, 75 MHz)
δ: 122.2, 125.0, 126.8, 126.9, 127.0, 128.0, 128.3, 129.2, 129.3, 129.4,
129.7, 130.1, 130.9, 131.2, 132.1, 133.6, 136.4, 137.1, 141.2, 159.4.
HRMS (ESI-TOF) m/z: [M + H]+ calcd for C50H31N2 659.2487,
found 659.2489. Anal. Calcd for C50H30N2: C, 91.16; H, 4.59; N, 4.25.
Found: C, 91.04; H, 4.70; N, 4.16.
Compound 2. Under an atmosphere of dry argon, 3,6-di(pyridin-2-
yl)-1,2,4,5-tetrazine (184 mg, 0.78 mmol) and an excess of isoamyl
nitrite (1 mL) were added into 30 mL of 1,2-dichloroethane. The
mixture was heated to reflux, and then the corresponding acid 4 (400
mg, 0.78 mmol) dispersed in 20 mL of 1,2-dichloroethane was added
to the mixture dropwise. After addition, the mixture was kept refluxing
overnight. Then, the mixture was cooled to room temperature, and the
solvent was removed under reduced pressure. The resultant residue
was purified by silica gel column chromatography using CH2Cl2/
CH3OH (60/1, v/v) as eluent to afford compound 2 as a brown solid
EXPERIMENTAL SECTION
■
General Procedures. All chemicals were used directly without
further purification. Ultrapure water was obtained from the Millipore
S. A. 67120 apparatus with a resistivity of 18.2 MΩ cm.
Optical Study. A 1.0-cm quartz cuvette in a volume of 3.0 mL was
used for all spectra collection. Unless otherwise noted, for all
measurements the excitation wavelength was at 350 nm. The slit
width of excitation was 5.0 nm, and the slit width of emission was 5.0
nm.
Self-Assembly. One milliliter of THF solution (1 mM 1) was
injected into 5 mL of water containing P123 with strong stirring. After
continuously stirring for 15 min, the obtained solution was aged
overnight to give microrods. The similar method is used for self-
assembling compounds 2 and 3.
1
(113 mg, 22%). Mp: >300 °C. H NMR (CDCl3, 300 MHz) δ: 7.32
(t, 2H, J = 7.8 Hz), 7.38−7.42 (m, 2H), 7.54−7.64 (m, 10H), 7.87−
7.93 (m, 8H), 8.31 (d, 2H, J = 9 Hz), 8.65 (d, 2H, J = 9 Hz), 9.73 (s,
2H). 13C NMR (CDCl3, 75 MHz) δ: 122.0, 123.8, 125.0, 125.4, 126.3,
126.8, 126.9, 127.7, 127.8, 129.1, 129.6, 129.9, 130.8, 131.2, 132.6,
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133.7, 136.9, 137.5, 141.5, 148.4, 156.2, 156.8. HRMS (ESI-TOF) m/
z: [M + H]+ calcd for C48H29N4 661.2392, found 661.2391. Anal.
Calcd for C48H28N4: C, 87.25; H, 4.27; N, 8.48. Found: C, 87.40; H,
4.35; N, 8.38.
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Compound 3. Under an atmosphere of dry argon, 3,6-di(thiophen-
2-yl)-1,2,4,5-tetrazine (192 mg, 0.78 mmol) and an excess of isoamyl
nitrite (1 mL) were added into 30 mL of 1,2-dichloroethane. The
mixture was heated to reflux, and then the corresponding acid 4 (400
mg, 0.78 mmol) dispersed in 20 mL of 1,2-dichloroethane was added
to the mixture dropwise. After addition, the mixture kept refluxing
overnight. Then, the mixture was cooled to room temperature, and the
solvent was removed under reduced pressure. The resultant residue
was purified by silica gel column chromatography using CH2Cl2/
CH3OH (100/1, v/v) as eluent to afford compound 3 as a brown solid
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1
(167 mg, 32%). Mp: >300 °C. H NMR (CDCl3, 300 MHz) δ: 7.12
(dd, 2H, J1 = 6.0 Hz, J2 = 3.0 Hz), 7.37 (t, 2H, J = 9.0 Hz), 7.53−7.56
(m, 4H), 7.59−7.63 (m, 10H), 7.90−7.97(m, 6H), 9.24 (s, 2H). 13C
NMR (CDCl3, 75 MHz) δ: 121.2, 126.1, 126.0, 126.3, 127.0, 127.2,
127.5, 128.2, 129.1, 129.5, 129.6, 129.7, 130.9, 131.6, 132.2, 133.9,
137.2, 139.8, 141.5, 152.3. HRMS (ESI-TOF) m/z: [M + H]+ calcd
for C46H27N2S2:671.1616, found 671.1608. Anal. Calcd for
C46H26N2S2: C, 82.36; H, 3.91; N, 4.18. Found: C, 82.28; H, 4.13;
N, 4.23.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
CIF files of compounds 1−3, related figures, and original H
NMR, 13C NMR, and HR-MS spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: qczhang@ntu.edu.sg.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Q.Z. acknowledges financial support from AcRF Tier 1 (RG
16/12) and Tier 2 (ARC 20/12 and ARC 2/13) from MOE
and the CREATE program (Nanomaterials for Energy and
Water Management) from NRF.
(13) Gao, J.; Zhang, Q. Israel J. Chem. 2014, DOI: 10.1002/
ijch.201400003.
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