Synthesis, Characterization, and Properties of Diazapyrenes via Bischler-Napieralski Reaction

Article abstract of DOI:10.1021/acs.joc.8b03096

Via Bischler-Napieralski cyclization of amide precursors as the key step, a series of diazapyrene derivatives were designed and successfully synthesized. Their crystal structures, optoelectronic properties, and acid-responsive feature were investigated, which demonstrated that the doping of nitrogen atoms to the pyrene framework remarkably modulates their physical and chemical properties.

Full text of DOI:10.1021/acs.joc.8b03096

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Article
Synthesis, Characterization and Properties of
Diazapyrenes Via Bischler-Napieralski Reaction
Yi Han, Zhenzhu Hu, Meifang Liu, Mengwei Li, Tingting Wang, and Yulan Chen
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 26 Feb 2019
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Synthesis, Characterization and Properties of Diazapyrenes
Via Bischler-Napieralski Reaction
†§
†§
‡
*†
†
Yi Han, Zhenzhu Hu, Meifang Liu, Mengwei Li, Tingting Wang and Yulan
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Chen*†
†
Tianjin Key Laboratory of Molecular Optoelectronic Science, Department of
Chemistry, Tianjin University, Tianjin, 300350, P. R. China.
‡
Department of Chemistry, Weifang University, Weifang, 261061, P. R. China.
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Abstract
Via Bischler-Napieralski cyclization of amide precursors as the key step, a series of
diazapyrene derivatives were designed and successfully synthesized. Their crystal
structures, optoelectronic properties and acid-responsive feature were investigated,
which demonstrated that the doping of nitrogen atoms to the pyrene framework
remarkably modulates their physical and chemical properties.
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Keywords: diazapyrenes, Bischler-Napieralski cyclization, acid-responsive feature
1
. Introduction
Polycyclic aromatic hydrocarbons (PAHs) are of considerable academic and industrial
1
importance due to their excellent charge-transfer abilities, and broad functionality
2
with tunable optophysical properties. Pyrene, as the simplest peri-fused PAH, is a
typical fluorogenic motif and ideal building block for constructing large conjugated
3
systems. Pyrene chemists have greatly extended the variety of available protocols to
4
synthesize various functionalized pyrenes for diverse applications. Among these
protocols, doping heteroatoms to the lattice of aromatics is an effective strategy to
5
modulate their intrinsic physicochemical properties. Concerning the potential
dopants, electronegative nitrogen has a smaller atomic radius and one more electron
6
than carbon. Thus, chemical doping of nitrogen into pyrene is of interest for novel
photophysical, electrochemical and responsive properties.7
4
,10- and 4,9-azapyrenes are the nitrogen isosteres of pyrene with two nitrogen
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atoms at different sites of pyrene skeleton (Scheme 1), which can be served as
promising candidates for biomolecular probes, chemosensors and optoelectronic
devices. However, literature precedents on 4,10-, 4,9-azapyrenes and their derivatives
are limited, mainly because the synthetic procedures require multi-steps and harsh
reaction conditions. As a result, systematic investigations of the optophysical
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properties of these aza-analogues have rarely been reported. Moreover, to make
diazapyrene-containing macromolecules or other functional materials, their
corresponding dihalogenated derivatives should be synthesized first. Unfortunately,
attempted halogenation of diazapyrene failed based on previously reported protocols.9
Therefore, the development of efficient synthetic methods to achieve regioselective
incorporation of nitrogen atoms into pyrene, for instance, to afford 4,10-,
4
,9-azapyrenes and their dibromo-substituted derivatives, is highly desirable yet
challenging.
We recently reported the application of Bischler-Napieralski cyclization as the key
step to prepare phenanthridine, 1,10-phenanthroline derivatives and S, N-heteroarenes.
Considering the electron rich feature of thiophene group, this reaction works well
with S, N-heteroarenes.10 In this article, we extend this reaction to pyrene based
materials. Herein, a series of diazapyrene derivatives (4,10-NPy-1, 4,10-NPy-2,
4,9-NPy-1, 4,9-NPy-Br, Fig. 1) were designed and synthesized through
Bischler-Napieralski cyclization of the corresponding amide precursors. We
demonstrated that if the precursors were delicately designed with amide groups
located at the “2-, 6-” or “2-, 7-” positions of biphenyl, two-folded
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Bischler-Napieralski cyclization would facilely lead to the formation of diazapyrene
cores with the N-doping at specific positions of the pyrene ring. We not only
developed an efficient synthetic strategy to enrich the chemical diversity of
diazapyrene compounds, but also studied the intriguing photophysical properties and
acid-responsive behaviors of these compounds. Since pyrene chemistry is strongly
position-dependent, our current efforts regarding various diazapyrene isomers greatly
contribute to the understanding of fundamental structure-property relationship of
diazapyrenes.
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Fig. 1 Chemical structures of diazapyrene derivatives in this work.
2
. Results and discussion
The structures and synthetic routes of the target compounds including substituted
diazapyrenes with nitrogens at different sites (4,10-NPy-1, 4,10-NPy-2, 4,9-NPy-1),
dibrominated diazapyrene (4,9-NPy-Br) and diazapyrene-based π-conjugated
oligomer
(Fl-NPy)
are
outlined
in
Scheme
1.
First,
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-tert-butyl-2,6-dinitrobromobenzene (N ) was prepared by nitration of commercially
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available 4-tert-butylbromobenzene in a yield of 53%. Then, Suzuki-Miyaura
cross-coupling reaction between N and p-tert-butyl benzyl boric acid was readily
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carried out by using Pd(PPh3)4 as the catalyst precursor, affording
2,6-dinitro-4,4’-di-tert-butylbiphenyl (C1) in
a
yield of 77%. Next,
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2,6-diamino-4,4-di-tert-butylbiphenyl (R ) was prepared from C with Fe powder as
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reductant, and A -1 (or A -2) was obtained by the followed amidation with pivaloyl
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chloride (or acetyl chloride) in a total yield of 59% (or 60%) with the two steps.
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Finally, Bischler-Napieralski cyclization of these amides, using POCl as the solvent
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and P O as the catalyst under refluxing was accomplished successfully, with the
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target compounds (4,10-NPy-1 and 4,10-NPy-2) prepared in moderate yield (41% and
3%).
We also found that the Bischler-Napieralski cyclization herein was very sensitive to
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the substitution of the amides. For instance, 4,9-NPy-1 can be obtained under a
synthetic route similar to 4,10-NPy-1, but modified cyclization conditions are
required, using ionic liquid of molten aluminum chloride–sodium chloride as the
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catalyst. Moreover, as shown in Scheme 1, under similar reaction conditions, the
intermediate A -2 cannot be converted to the target compound 4,9-NPy-2. This
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outcome is reasonable since the transformation of amide to 4,9-diazapyrene
presumably involves two successive ring closures: carbonium-ion formation being
followed by intramolecular electrophilic attack, which is greatly influenced by steric
effect.8,11 According to the optimal configuration of the amides (Fig. S1, Supporting
Information), tert-butyl group existed in A -2 has a larger steric hindrance than methyl
2
in A -1, which may be not conducive to the electrophilic cyclization. In addition, to
2
obtain functionable or polymerisable diazapyrene monomer, the dibrominated
compound 4,9-NPy-Br was successfully synthesized from the dibrominated amide
precursor, which was not available by other reported approaches. As expected,
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4,9-NPy-Br was demonstrated as a new building block for constructing new
conjugated materials, for instance, by Suzuki coupling with 9,9-dioctyl-2-boronic
ester-fluorene to afford Fl-NPy with a yield of 74%. Tert-butyl group existed in A -2
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has a larger steric hindrance than methyl in A -1.
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Scheme 1. Synthetic routes to 4,10-NPy-1, 4,10-NPy-2, 4,9-NPy-1, 4,9-NPy-Br and
Fl-NPy.
All target molecules can be dissolved in common organic solvents, such as
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dichloromethane, chloroform, and tetrahydrofuran, and were characterized by H
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NMR and C{1H} NMR spectroscopy as well as high-resolution mass spectrometry.
The thermal properties of 4,10-NPy-1, 4,10-NPy-2 and 4,9-NPy-1 were measured by
the thermogravimetric analysis (TGA) under a nitrogen atmosphere. As shown in Fig.
S5 (Supporting Information), they all exhibit good thermal stability with a weight loss
o
of 5% at approximately 240 C, indicating their high potential to be robust organic
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materials.
Single crystals of 4,9-NPy-Br suitable for X-ray measurements were obtained by
slow evaporation of chloroform solutions in isopropyl alcohol atmosphere. The
structure of 4,9-NPy-Br was solved and refined in a triclinic P-1 space group. As
depicted in Fig. 2, the main scaffold of 4,9-NPy-Br showed small dihedral angles of
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less than 2 , consisting with the highly planar conformation of pyrene. 4,9-NPy-Br is
arranged parallel to the dislocation packing motif driven by multiple intermolecular
interactions, such as C-H···N and C-H···π interactions, with distances in the range of
2.59-2.89 Å. The shortest distance between the rigid planes consisted of the parallel
neighboring molecules is 3.39 Å, manifesting the significant π-π interactions mainly
stemmed from its large conjugation. Unfortunately, other crystals suitable for
single-crystal X-ray diffraction were unavailable.
Fig. 2 (a) Single crystal structure and (b) packing diagram of 4,9-NPy-Br.
Detailed photophysical properties of these diazapyrene molecules were investigated
by UV-vis absorption and fluorescence spectroscopies. 2,7-Di-tert-butylpyrene
(Py-tBu) was chosen as the reference compound to study the effect of nitrogen
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doping of pyrene on their optical properties. It was found that in CH Cl solution, all
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nm, which was attributed to the -* transition (Fig 3a). The distinct vibrational
structures according to their absorption spectra, together with small Stokes shift of ca.
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5 nm, revealed the rigidity of the skeleton. Compared to Py-tBu, the incorporation of
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nitrogen-atoms in 4,10-NPy-1, 4,10-NPy-2 and 4,9-NPy-1 led to the additional n-π*
transition with the appearance of absorption peaks at lower energy region at 360 and
380 nm.13 Accordingly, narrower optical gaps of 4,10-NPy-1, 4,10-NPy-2 and
4
,9-NPy-1 were estimated from the onset of UV-vis absorption spectra as 3.19, 3.20
and 3.21 eV, respectively (E = 3.51 eV for Py-tBu), suggesting that the incorporation
g
of nitrogen-atoms could reduce the energy gap of diazapyrenes.
Fig. 3 (a) UV-vis absorption and (b) fluorescence spectra of Py-tBu, 4,10-NPy-1,
-5
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,10-NPy-2 and 4,9-NPy-1 ( = 340 nm) in CH Cl (3.0 x 10 M).
ex
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All the four compounds showed blue emission in diluted solutions with emission
peaks at about 380-400 nm (Fig. 3b). There was a large difference concerning their
fluorescence quantum yields (Φ) (Table S3, Supporting Information). In detail, the
fluorescence quantum yields of 4,10-NPy-1 and 4,9-NPy-1 in dilute CH Cl solution
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were 25% and 26%, which were higher than that of Py-tBu (9%). As for 4,10-NPy-2,
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the value of Φ decreased remarkably (Φ = 2%), most probably because the stretching
vibration of tert-butyl groups at the 5- and 9- positions promoted non-radiative
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dissipation of excited state. Additionally, from solution to film, then solid state, the
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absorption for the three molecules exhibited red-shifting due to the increased
aggregation effect (Fig. S7-9, Supporting Information).
Since the incorporation of heteroatoms into PAHs usually alters their electronic
properties considerably, the electrochemical properties of these diazapyrenes and
Py-tBu were then compared by using cyclic voltammetry (CV). Fig. 4 depicted a
reversible oxidation wave for Py-tBu while irreversible and anodically shifted
oxidation peaks for diazapyrenes in CH Cl . Accordingly, the HOMO energy levels
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of Py-tBu, 4,10-NPy-1, 4,10-NPy-2 and 4,9-NPy-1 were estimated to be -5.59, -5.80,
-5.89 and -5.81 eV, respectively, from the onset reduction potential with reference to
+
Fc /Fc. The LUMO energy levels were calculated based on the absorption edges,
which were -2.08, -2.61, -2.69 and -2.60 eV, respectively. The low-lying HOMO and
LUMO energy levels of diazapyrenes manifested their potential application as p-type
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semiconductors. All the photophysical and electronic data are summarized in Table
S2.
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Fig. 4 Cyclic voltammograms of Py-tBu, 4,10-NPy-1, 4,10-NPy-2 and 4,9-NPy-1
-1
measured in CH Cl with 0.1 M TBAPF as electrolyte (scan rate = 100 mVs ).
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To gain further insight into their electronic structures, the electronic distribution of
HOMO and LUMO energy levels of these diazapyrenes were calculated by using

Gaussian 09 software at the level of B3LYP/6-31G . As shown in Fig. 5, their
optimized structures displayed fully planar skeletons with electron density of the
HOMO and LUMO delocalized over the whole molecules, indicating that there was
no obvious intramolecular charge transfer (ICT) effect. With high electronegative
nitrogen atoms in the pyrene framework,7,16 all the molecules owned lower HOMO
and LUMO levels compared to those of Py-tBu, which was also in good agreement
with the experimental results.
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Fig. 5 Molecular-orbital amplitude plots and energy levels of the HOMOs and
LUMOs for Py-tBu, 4,10-NPy-1, 4,10-NPy-2 and 4,9-NPy-1 in the gas phase, as
calculated at the level of B3LYP/6-31G*.
Furthermore, nitrogen-doped PAHs usually achieve their application as
acid-responsive materials owing to the protonated ability of the nitrogen atom.7,10a In
order to investigate the potential of these diazapyrenes to serve as acid-responsive
materials, their protonation experiments in CH Cl were carried out (Fig. 6, S10-12,
2
2
Supporting Information). Taking 4,10-NPy-2 for example, with the addition of TFA
from 0 to 50 eq, the absorption peaks at higher energy region from 306 to 365 nm
decreased, accompanied by the appearance of long wavelength absorption band at 400
nm. The new absorption band implied the appearance of protonated species and could
be attributed to the enhanced charge transfer transition.17 Under 365 nm UV
irradiation, the corresponding fluorescence spectra showed pronounced variation: the
fluorescence intensity of 4,10-NPy-2 at 386 and 407 nm (purple-blue emission band)
decreased dramatically, while a new bright blue-green emission peaked at 470 nm
appeared and its intensity increased with the increase of TFA. The purple-blue
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fluorescence of 4,10-NPy-2 can be recovered after treated with TEA, making it
+
suitable for a turn-on sensor of H (Fig. S11b, Supporting Information).
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Fig. 6 (a) Fluorescence spectra of 4,10-NPy-2 in CH Cl with different concentrations
2
2
of TFA. (b) Switching the maximum emission wavelength of 4,10-NPy-2 sensor as a
function of the fuming-air cycle numbers (ex = 340 nm). (c) Photographs of
4
,10-NPy-2 deposited on a piece of filter paper under daylight, before and after fumed
with TFA vapor under UV light (The letter “T” was written with Py-tBu solution, and
“
J” and “U” were written with 4,10-NPy-2 solution).
Considering the unique acid responsive feature of these diazapyrenes in solution,
their applications in solid-state fluorescent sensing devices were explored.
Interestingly, it was found that all these materials can be utilized as security ink in a
solid-state sensory system. One example is illustrated in Fig. 6c. Three letters (TJU)
were written with Py-tBu (for the letter “T”) and 4,10-NPy-2 (for the letters “J” and
“
“
U”) solutions on the filter paper. At first, it was difficult to detect the presence of
TJU” by the naked eyes under daylight and when the filter paper was excited under a
365 nm UV lamp, the pattern presented as purple-blue “TJU”. After being fumed with
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TFA vapor, the letters “J” and “U” turned to light blue-green emission under UV
irradiation while the letter written by Py-tBu was not responsive. Furthermore, this
process is reversible and the blue pattern made from these diazapyrenes could be
recovered when the paper was fumed with TEA vapor (Fig. S13-15, Supporting
Information). This reversible process at room temperature makes diazapyrene a
promising candidate for double security protection material.
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. Conclusions
Bischler-Napieralski cyclization of delicately designed amide precursors was
demonstrated as a facile approach to synthesize a series of diazapyrene derivatives,
which were found as smart materials with the ability to respond to acid both in
solution and solid states. Using this strategy, not only the position of nitrogen atoms
can be controlled, but also different substituted groups can be attached onto the
pyrene ring, greatly facilitating the modulation of their optoelectronic properties and
molecular geometries at the molecular level. Notably, the dibrominated diazapyrene
synthesized by this method is a promising compound to develop various
diazapyrene-based π-conjugated polymers or other macromolecular systems for
diverse applications, and further investigations are in progress.
4
. Experimental Section
General. Unless otherwise noted, the commercially available reagents were
purchased from commercial suppliers and used without further purification.
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Dichloromethane (CH Cl ) was distilled over CaH . Tetrahydrofuran (THF) was
2
2
2
purified by distillation from benzophenone and sodium. All reactions were monitored
by TLC with silica gel 60 F254. Column chromatography was carried out on silica gel
(200-300 mesh). The catalyst precursor Pd(PPh ) was prepared according to the
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literature , and stored in a Schlenk tube under nitrogen atmosphere.
1
13
Measurements. H NMR (400 MHz) and C{1H} NMR (100 MHz) spectra were
recorded in deuterated solvents on a 400 MHz Bruker AV400 spectrometer. The high
resolution electrospray mass spectra (ESI-TOF) of products were recorded on a
micrOTOF-Q II 10204 mass spectrometer. FT-IR spectra of samples were recorded
on a Bruker Model Alpha. Melting points were measured with SGW X-4A apparatus.
Elemental analyses were recorded on Flash EA 1112. The UV-vis absorption spectra
were obtained on PerkinElmer Lambda 750 spectrophotometer. Fluorescence spectra
were recorded on
a
Hitachi F-7000 fluorescence spectrophotometer.
Thermogravimetric analyses (TGA) were carried out using a TA Instruments Q-50
with a heating rate of 10 °C/min. Cyclic voltammetric experiments were carried out
using a CHI 150E electrochemical workstation (CH Instruments, ChenHua, Shanghai,
China). All voltammograms were acquired at room temperature. A standard three
electrode electrochemical cell arrangement was employed using Pt carbon as working
electrode, a Pt wire as counter electrode, and saturated calomel as reference electrode
in 0.1 M tetrahydrofuran containing tetrabutylammonium hexafluorophosphate
-1
(TBAPF ) as the supporting electrolyte with a sweep rate of 100 mVs . The potentials
6
+
are reported vs the Fc /Fc redox couple as a standard.
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Synthesis
4
-Tert-butyl-2,6-dinitrobromobenzene (N1).19 4-tert-butylbromobenzene (20.00 g,
o
9
4.33 mmol) was added dropwise to stirred fuming nitric acid (50 mL) at 0 C in an
1
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ice water bath. The mixture was stirred at 25 C for 2h and then poured into
vigorously stirring ice–water (200 mL). The yellow-green precipitate was collected by
filtration and washed with water and saturated aqueous NaHCO solution, affording
3
1
the product as pale yellow-green needles (15.20 g, 53%). H NMR (400 MHz, CDCl ):
3
13
1
δ 7.88 (s, 2H), 1.39 (s, 9H); C H NMR (100 MHz, CDCl ): δ 154.5, 151.7, 124.8,
3
103.9, 35.6, 30.7.
2
,6-Dinitro-4,4’-di-tert-butylbiphenyl (C ). A mixture of N (3.00 g, 9.93 mmol),
1 1
(tert-butyl) phenyl) boronic acid (2.60 g, 14.60 mmol), Na CO (2.40 g, 22.64 mmol),
2
3
TBAB (0.30 g, 0.93 mmol), toluene (50 mL) and H O (11 mL) was carefully
2
degassed before and after Pd(PPh ) (0.30 g, 0.26 mmol) was added. The mixture was
3
4
heated to reflux and stirred under nitrogen overnight. The reaction mixture was
extracted with CH Cl and washed with saturated brine. The combined organic layers
2
2
were dried over anhydrous MgSO and concentrated under reduced pressure. The
4
residue was purified by chromatography on silica gel column eluting with petroleum
1
ether/CH Cl (v/v, 4/1) to afford C as an ivory solid (2.80 g, 77%). H NMR (CDCl ,
2
2
1
3
400 MHz): δ 7.93 (s, 2H), 7.41 (d, J = 7.7 Hz, 2H), 7.16 (d, J = 7.6 Hz, 2H), 1.43 (s,
1
3
1
9
H),1.33 (s, 9H). C H NMR (CDCl , 100 MHz): δ 153.8, 152.3, 150.9, 127.8,
3
127.4, 127.1, 125.7, 123.5, 35.5, 34.7, 31.2, 30.8.
2
,6-Diamino-4,4'-di-tert-butylbiphenyl (R ). The mixture of glacial acetic acid (120
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mL), C (5.00 g, 13.58 mmol) and iron powder (11.00 g, 196.43 mmol) was heated at
1
8
0 °C for an hour. After cooling to room temperature, the iron powder was removed
by filtration. After a large amount of water was added to the filtrate, solid appeared in
the solution. The crude product was collected by filtration and used directly in the
next step without further purification. The amidation yield is the total yield of two
steps.
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N,N'-(4,4'-Di-tert-butyl-[1,1'-biphenyl]-2,6-diyl)diacetamide
(A -1).
Acetyl
1
chloride (5.00 g, 63.69 mmol) was added dropwise to the mixture solution of R (3.80
1
o
g, 12.83 mmol), triethylamine (5 mL) and anhydrous CH Cl (120 mL) at 0 C. After
2
2
stirring at room temperature overnight, the reaction was quenched with water and
extracted with CH Cl . The combined organic extracts were dried over anhydrous
2
2
MgSO and concentrated under reduced pressure. The residue was purified by
4
chromatography on silica gel column eluting with CH Cl /EA (v/v, 5/1) to afford
2
2
-1
A -1 as a white solid (2.90 g, 59%). FT-IR (powder, cm ): 3318, 3198, 2957, 1664,
1
o
1
1
515, 1420, 1358, 1267, 870, 833. mp 221222 C. H NMR (CDCl , 400 MHz): δ
3
8.13 (s, 2H), 7.57 (d, J = 7.7 Hz, 2H), 7.21 (d, J = 7.3 Hz, 2H), 6.70 (s, 2H), 1.93 (s,
1
3
1
6
1
H), 1.38 (d, J = 8.0 Hz, 18H). C H NMR (CDCl , 100 MHz): δ 168.1, 152.2,
3
35.3, 130.1, 129.9, 126.9, 119.8, 114.9, 35.2, 34.9, 31.3, 31.2, 24.7. HRMS
+
(ESI-TOF) m/z: [M  Na] Calcd for C H N NaO 403.2356; Found 403.2355. Anal.
2
4
32
2
2
Calcd for C H N O : C, 75.75; H, 8.48; N, 7.36. Found: C, 75.81; H, 8.45; N, 7.52.
2
4
32
2
2
2,7-Di-tert-butyl-5,9-dimethylpyrido[5,4,3,2-lmn]phenanthridine (4,10-NPy-1). A
solution of A -1 (0.30 g, 0.78 mmol), P O (0.51 g, 3.59 mmol) and POCl (8 mL)
1
2
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was stirred at reflux for 24 h under N . After cooling to room temperature, water was
2
added carefully to the solution. The aqueous phase was adjusted to pH = 9 with
NaOH solution and extracted with dichloromethane, then dried over anhydrous
1
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MgSO and evaporated to dryness. The product was purified by chromatography on
4
alkaline Al O column eluting with CH Cl and the residue was recrystallized in
2
3
2
2
-1
methanol to afford 4,10-NPy-1 as a white solid (0.11 g, 41%). FT-IR (powder, cm ):
o
1
2
4
953, 1591, 1476, 1365, 1269, 868, 728, 649, 559. mp 209210 C. H NMR (CDCl ,
3
00 MHz): δ 8.66 (s, 2H), 8.43 (s, 2H), 3.22 (s, 6H), 1.63 (s, 9H), 1.59 (s, 9H).
1
3
1
C H NMR (CDCl , 100 MHz): δ 159.4, 153.2, 150.0, 141.5, 125.6, 124.3, 124.1,
3
+
1
22.3, 110.6, 35.9, 35.8, 32.0, 31.9, 23.2. HRMS (ESI-TOF) m/z: [M  H] Calcd for
C H N 345.2325; Found 345.2316. Anal. Calcd for C H N : C, 83.68; H, 8.19; N,
2
4
29
2
24 28
2
8
.13. Found: C, 83.25; H, 8.45; N, 7.82.
N,N'-(4,4'-Di-tert-butyl-[1,1'-biphenyl]-2,6-diyl)bis(2,2-dimethylpropanamide)
(A -2). A -2 was synthesized following the procedure for A -1, with R (3.60 g, 12.15
1
1
1
1
mmol), Et N (5 mL), pivaloyl chloride (7.20 g, 59.71 mmol) in DCM (50 mL) as
3
reagents. The desired product A -2 was obtained as a white solid (3.80 g, 60%).
1
-1
FT-IR (powder, cm ): 3402, 3292, 2961, 1687, 1645, 1497, 1416, 1166, 1000, 863,
o
1
8
48, 665, 562. mp  300 C. H NMR (CDCl , 400 MHz): δ 8.23 (s, 2H), 7.61 (d, J =
3
7.8 Hz, 2H), 7.23 (d, J = 8.0 Hz, 2H), 7.07 (s, 2H), 1.38 (s, 18H), 0.99 (s, 18H).
1
3
1
C H NMR (CDCl , 100 MHz): δ 176.1, 152.8, 135.6, 130.2, 130.1, 127.0, 119.2,
3
+
1
13.3, 39.7, 35.3, 34.9, 31.3, 27.2. HRMS (ESI-TOF) m/z: [M  Na] Calcd for
C H N NaO 487.3295; Found 487.3294. Anal. Calcd for C H N O : C, 77.54; H,
3
0
44
2
2
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9.54; N, 6.03. Found: C, 77.52; H, 9.71; N, 6.27.
2
4
,5,7,9-Tetra-tert-butylpyrido[5,4,3,2-lmn]phenanthridine
(4,10-NPy-2).
,10-NPy-2 was synthesized following the procedure for 4,10-NPy-1, with A -2 (0.50
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
8
9
0
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0
g, 1.08 mmol), P O (3.20 g, 22.54 mmol), and POCl (15 mL) as reagents.
2
5
3
-1
4
,10-NPy-2 was obtained as a white solid (0.20 g, 43%). FT-IR (powder, cm ): 2972,
o
1
1
619, 1557, 1467, 1364, 1196, 1158, 880. mp  300 C. H NMR (CDCl , 400 MHz):
3
1
3
1
δ 9.06 (s, 2H), 8.40 (s, 2H), 1.84 (s, 18H), 1.63-1.60 (d, J = 10.8 Hz, 18H). C H
NMR (CDCl , 100 MHz): δ 167.7, 152.7, 146.8, 140.8, 128.8, 125.7, 122.9, 110.1,
3
+
40.6, 35.8, 32.0, 31.2. HRMS (ESI-TOF) m/z: [M  H] Calcd for C H N 429.3264;
3
0
41
2
Found 429.3262. Anal. Calcd for C H N : C, 84.06; H, 9.41; N, 6.54. Found: C,
3
0
40
2
83.88; H, 9.35; N, 6.76.
-Bromo-4-tert-butyl-2-nitrobenzene (N2).20 The compound of 4-tert-
1
butylbromobenzene (18.70 g, 88.20 mmol) was carefully added to the mixture
solution of concentrated sulfuric acid (10.00 mL) and nitric acid (9.00 mL). The
o
mixture was stirred for 20 h at 30 C. After poured into ice water, the mixture was
extracted with Et O and washed with saturated brine. The combined organic phases
2
were dried over MgSO and concentrated. The residue was recrystallized in
4
isopropanol to give N (20.10 g, 89%).
2
4,4'-Di-tert-butyl-2,2'-dinitro-1,1'-biphenyl (C ). To a solution of N (20.00 g,
2
2
7
7.82 mmol) in DMF (240 mL), copper powder (10.80 g, 169.94 mmol) was added.
The mixture was stirred under reflux in nitrogen atmosphere for 3 h. After the mixture
was cooled to room temperature, the precipitate was filtered and DMF was evaporated
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under reduced pressure. The residue was dissolved in DCM and washed with
saturated brine. The combined organic phase was dried over anhydrous MgSO and
4
concentrated. After the residue was recrystallized in ethanol, the product was obtained
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
8
9
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1
2
3
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6
7
8
9
0
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3
4
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9
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1
as a yellow solid (12.30 g, 89%). H NMR (400 MHz, CDCl ): δ 8.18 (d, J = 1.6 Hz,
3
1
3
1
2
H), 7.67 (dd, J = 8.0, 1.7 Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H), 1.41 (s, 18H). C H
NMR (100 MHz, CDCl ): δ 152.9, 147.3, 131.2, 130.8, 130.5, 121.7, 35.1, 31.1.
3
4
,4'-Di-tert-butyl-[1,1'-biphenyl]-2,2'-diamine (R ). According to the procedure for
2
R , the reaction mixture of glacial acetic acid (100 mL), C (5.00 g, 14.04 mmol) and
1
2
iron powder (11.00 g 196.43 mmol) was heated at 80 °C for an hour. After cooling to
room temperature, the iron powder was removed by filtration. After a large amount of
water was added to the filtrate, solid appeared in the solution. The crude product was
collected by filtration and used directly in the next step without further purification.
The amidation yield is the total yield of the two steps.
N,N'-(4,4'-Di-tert-butyl-[1,1'-biphenyl]-2,2'-diyl)diacetamide
(A -1).
Acetyl
2
chloride (5.00 g, 63.69 mmol) was added dropwise to the mixture solution of R (3.80
2
o
g, 12.83 mmol), triethylamine (5 mL) and anhydrous CH Cl (120 mL) at 0 C. After
2
2
stirring at room temperature overnight, the reaction solution was extracted with
CH Cl and water. The combined organic extracts were dried over anhydrous MgSO
4
2
2
and evaporated to dryness. The residue was purified by chromatography on silica gel
column eluting with CH Cl /EA (v/v, 5/1) to afford A -1 as a white solid (2.90 g,
2
2
2
-1
60%). FT-IR (powder, cm ): 3403, 3306, 2950, 1667, 1557, 1524, 1460, 1412, 1366,
o
1
1
273, 822, 642, 556, 510. mp 171172 C. H NMR (400 MHz, CDCl ): δ 8.20 (s,
3
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2
2
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2
2
2
2
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2H), 7.24 (d, J = 1.8 Hz, 2H), 7.12 (d, J = 8.0 Hz, 2H), 6.93 (s, 2H), 1.99 (s, 6H), 1.38
1
3
1
(
s, 18H). C H NMR (100 MHz, CDCl ): δ 169.2, 152.3, 135.3, 130.2, 126.5,
3
+
1
22.3, 120.7, 34.9, 31.3, 24.2. HRMS (ESI-TOF) m/z: [M  Na] Calcd for
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
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4
5
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7
8
9
0
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2
3
4
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7
8
9
0
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2
3
4
5
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7
8
9
0
C H N NaO 403.2356; Found 403.2362. Anal. Calcd for C H N O : C, 75.75; H,
2
4
32
2
2
24 32
2
2
8
.48; N, 7.36. Found: C, 75.49; H, 8.67; N, 7.59.
2,7-Di-tert-butyl-5,10-dimethylpyrido[2,3,4,5-lmn] phenanthridine (4,9-NPy-1).
A -1 (0.20 g, 0.53 mmol) was carefully added to the melt of aluminium chloride (0.70
2
o
g, 5.25 mmol) and sodium chloride (0.40 g, 6.84 mmol) at 100 C in nitrogen
o
atmosphere. After the mixture was heated to 250 C for 8 h, ice water was added
carefully. The aqueous layer was basified with sodium hydroxide, then the
precipitated powder was filtered and purified by chromatography on silica gel column
eluting with CH Cl to afford 4,9-NPy-1 (0.06 g, 33%) as a light yellow solid. FT-IR
2
2
-1
o
1
(
powder, cm ): 2952, 1559, 1355, 1244, 875, 653, 556. mp 294296 C. H NMR
1
3
1
(400 MHz, CDCl ): δ 8.63 (s, 2H), 8.45 (s, 2H), 3.22 (s, 6H), 1.61 (s, 18H). C H
3
NMR (100 MHz, CDCl ): δ 160.7, 151.7, 141.1, 126.3, 124.3, 119.3, 118.0, 35.5,
3
+
31.4, 23.3. HRMS (ESI-TOF) m/z: [M + H] Calcd for C H N 345.2325; Found
2
4
29
2
3
8
45.2328. Anal. Calcd for C H N : C, 83.68; H, 8.19; N, 8.13. Found: C, 83.36; H,
24 28 2
.23; N, 7.77.
2
0
4,4’-Dibromo-2,2’-dinitrobenzene (C ). 2,5-Dibromonitrobenzene (5.00 g, 17.93
3
mmol) and copper powder (2.50 g, 39.34 mmol) were added to DMF (70 mL). The
mixture was stirred at 125 °C for 3.5 h. After cooling, the precipitate was filtered and
DMF was evaporated under reduced pressure. The residue was dissolved in DCM and
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washed with saturated brine. The combined organic phase was dried over anhydrous
MgSO4 and concentrated. After the residue was recrystallized in ethanol,
1
4
,4’-dibromo-2,2’-dinitrobenzene was obtained as a yellow solid (2.63 g, 73%). H
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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5
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0
1
2
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4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
NMR (400 MHz, CDCl ): δ 8.39 (s, 2H), 7.83 (d, J = 8.2 Hz, 2H), 7.16 (d, J = 8.2 Hz,
3
1
3
1
2
H). C H NMR (100 MHz, CDCl ): δ 147.5, 136.9, 132.2, 132.2, 128.2, 123.1.
3
4,4'-Dibromo-[1,1'-biphenyl]-2,2'-diamine (R ). R was synthesized following the
3
3
procedure for R , with C (1.00 g, 2.48 mmol), iron powder (1.66 g 29.64 mmol) in
2
3
glacial acetic acid (70 mL) as reagents. The crude product was collected by filtration
and used directly in the next step without further purification. The amidation yield is
the total yield of the two steps.
N,N'-(4,4'-Dibromo-[1,1'-biphenyl]-2,2'-diyl)diacetamide (A ). A was synthesized
3
3
following the procedure for A -1, with R (1.00 g), Et N (1.00 mL), acetyl chloride
2
3
3
(
1.14 g, 14.52 mmol) in CH Cl (60 mL) as reagents. The desired product A was
2
2
3
-1
obtained as an off-white solid (0.61 g, 57%). FT-IR (powder, cm ): 3405, 3281, 1675,
o
1
1
504, 1402, 1270, 1006, 869, 811, 588. mp 145146 C. H NMR (400 MHz, CDCl ):
3
δ 8.33 (s, 2H), 7.39 (d, J = 8.1 Hz, 2H), 7.04 (d, J = 8.1 Hz, 2H), 6.84 (s, 2H), 2.00 (s,
1
3
1
6
1
H). C H NMR (100 MHz, CDCl ): δ 169.1, 136.5, 131.6, 128.5, 126.9, 126.5,
3
+
23.4, 24.2. HRMS (ESI-TOF) m/z: [M  Na] Calcd for C H Br N NaO 448.9295;
1
6
14
2
2
2
Found 448.9296. Anal. Calcd for C H Br N O : C, 45.10; H, 3.31; N, 6.57; O, 7.51.
1
6
14
2
2
2
Found: C, 45.08; H, 3.56; N, 6.44; O, 7.66.
2,7-Dibromo-5,10-dimethylpyrido[2,3,4,5-lmn]phenanthridine
,9-NPy-Br was synthesized following the procedure for 4,9-NPy-1, with A (0.5 g,
(4,9-NPy-Br).
4
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1.18 mmol), aluminium chloride (1.40 g, 10.50 mmol) and sodium chloride (0.90 g,
1
5.40 mmol) as reagents. The desired product 4,9-NPy-Br was obtained as a light
-1
yellow solid (0.18 g, 39%). FT-IR (powder, cm ): 1554, 1426, 1326, 1023, 865, 815,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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5
6
7
8
9
0
1
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4
5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
1
673, 558. mp  300 C. H NMR (400 MHz, CDCl ): δ 8.69 (s, 2H), 8.56 (s, 2H), 3.18
3
1
3
1
(
s, 6H). This compound is too insoluble to record a C H NMR spectrum. HRMS
+
(
ESI-TOF) m/z: [M  H] Calcd for C H Br N 390.9264; Found 390.9258. Anal.
1
6
11
2
2
Calcd for C H Br N : C, 49.27; H, 2.58; N, 7.18. Found: C, 49.17; H, 2.48; N, 7.21.
1
6
10
2
2
2
,7-Di-tert-butylpyrene (Py-tBu).12 Py-tBu was synthesized according to the
1
reported procedure. H NMR (400 MHz, CDCl ): δ 8.18 (s, 2H), 8.02 (s, 2H), 1.56 (s,
3
1
8H).
2,7-Bis(9,9-dioctyl-9H-fluoren-2-yl)-5,10-dimethylpyrido[2,3,4,5-lmn]phenanthri
dine (Fl-NPy). A mixture of 4,9-NPy-Br (300 mg, 0.8 mmol), 9,9-dioctyl-2-boronic
ester-fluorene (1.00 g, 1.94 mmol), NaHCO (1.30 g, 15.47 mmol), THF (50 mL) and
3
H O (20 mL) was degassed before and after Pd(PPh ) (18 mg, 0.015 mmol) was
2
3 4
added. The mixture was heated to reflux and stirred under nitrogen for 24 h. The
reaction mixture was extracted with CH Cl (3 × 100 mL), and the combined organic
2
2
layers were dried over anhydrous MgSO and concentrated under reduced pressure.
4
The residue was purified by chromatography on silica gel column eluting with
petroleum ether/CH Cl (v:v, 2:3) to afford Fl-NPy as an ivory solid (0.57 g, 74%).
2
2
-1
o
1
FT-IR (powder, cm ): 2920, 2843, 1441, 1361, 868, 829, 736. mp  300 C. H NMR
(400 MHz, CDCl ) δ 8.90 (s, 2H), 8.74 (s, 2H), 7.91 (s, 4H), 7.89 (s, 2H), 7.80 (d, J =
3
7
.0 Hz, 2H), 7.37 (dd, J = 15.0, 7.8 Hz, 6H), 3.34 (s, 6H), 2.12–2.01 (m, 8H), 1.55 (s,
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0H), 1.20–1.00 (m, 38H), 0.78 (t, J = 6.9 Hz, 12H). C H NMR (100 MHz,
CDCl ) δ 161.3, 152.0, 151.1, 142.3, 141.2, 140.5, 127.9, 127.4, 126.9, 126.9, 126.1,
3
1
25.2, 123.0, 122.6, 122.2, 121.3, 120.4, 120.0, 119.3, 55.4, 40.5, 31.8, 29.3, 29.2,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
+
23.9, 23.5, 22.6, 14.0. HRMS (ESI-TOF) m/z: [M + H] Calcd for C H N
7
4
93
2
1
009.7333; Found 1009.7339. Anal. Calcd for C H N : C, 88.04; H, 9.19; N, 2.77.
74 92 2
Found: C, 87.06; H, 8.87; N, 2.63.
Acknowledgements
This work was supported by the National Key Research and Development Program of
China (Grants 2017YFA0204503 and 2017YFA0207800), the National Natural
Science Foundation of China (Grants 21522405, 51503142 and 21734006) is
gratefully acknowledged. We thank Dr. X. W. Lou (Eindhoven University of
Technology) for helpful discussions about the manuscript.
Supporting Information
1
13
1
H NMR and C H NMR spectra and HRMS (ESI-TOF) spectra, single crystal
data, UV-vis absorption spectra, fluorescence spectra, photographs, TGA data,
computational data. The Supporting Information is available free of charge on the
ACS Publications website at DOI: xxx
Author Information
Corresponding Author
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*E-mail:yulan.chen@tju.edu.cn; lmw@tju.edu.cn
Author Contributions
§Yi Han and Zhenzhu Hu contributed equally to this work.
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Notes and References
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Edges. Chem. Commun. 2017, 53, 8474. (d) Murai, M.; Iba, S.; Ota, H.; Takai, K.
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