Photoactive amorphous molecular materials based on quinoline amines and their synthesis by Friedl?nder condensation reaction

Article abstract of DOI:10.1016/j.tet.2010.09.108

A new class of conjugated quinoline amines was prepared by Friedl?nder condensation reaction. They showed stable amorphous state below glass transition temperatures as examined by differential scanning calorimetry and X-ray diffraction studies. Additional

Full text of DOI:10.1016/j.tet.2010.09.108

Tetrahedron 66 (2010) 9319e9326
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Tetrahedron
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Photoactive amorphous molecular materials based on quinoline amines
€
and their synthesis by Friedlander condensation reaction
*
Alexi K. Nedeltchev, Haesook Han, Pradip K. Bhowmik
Department of Chemistry, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4003, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
€
A new class of conjugated quinoline amines was prepared by Friedlander condensation reaction. They
showed stable amorphous state below glass transition temperatures as examined by differential scan-
ning calorimetry and X-ray diffraction studies. Additionally, they exhibited fluorescence properties in the
blue to green region of visible spectrum in both solution and solid state. Their fluorescence quantum
efficiencies in chloroform were in a broad range of 3e45%. Interestingly, they formed stable fibers with
micrometer thickness drawn from melt, which were characterized by polarizing optical microscopy and
scanning electron microscopy studies.
Received 1 September 2010
Received in revised form 30 September 2010
Accepted 30 September 2010
Available online 8 October 2010
Keywords:
Amorphous materials
Photoluminescence
Quantum yields
Ó 2010 Elsevier Ltd. All rights reserved.
Friedlander condensation reaction
Quinoline amines
1. Introduction
this design is met with some success, in many cases, rapid cooling
processes from their melts are required to prevent molecules from
Since the discovery of fluorescent compounds, they have found
applications as fluorophores, used for the detection of cell mem-
branes, proteins and DNA,1 sensors for heavy metals,2 and most
recently as light-emitting layers in organic semiconductors.3 To
make fluorescent compounds appropriate for these diverse appli-
cations different requirements must be met. Above all, their high-
quantum yields are one of the most desirable properties. The
amorphous molecular materials have attracted unabated attention
as materials for optoelectronic devices as hole transporting/block-
ing, electron transporting/blocking and ambipolar layers. Amor-
phous state is advantageous over crystalline, polycrystalline or
liquid-crystalline states since it is easier to produce a film, it is
transparent, and it has homogeneous properties. Amorphous
polymers are also well-known, but they are polydispersed, in many
cases, difficult to purify, characterize, and process. It is a challenging
task to synthesize amorphous molecular materials that are capable
of forming into stable glasses below their glass transition temper-
atures (Tg), since small molecules have a natural tendency to
crystallize; therefore, they have to possess certain structural ir-
regularities in their chemical architectures. The general factor
necessary to prevent crystallization is to use large rigid structures
with bulky substituents, which cause non-planarity. Even though
producing high-ordered crystalline states. While forced to attain
glassy states via cooling processes, such films often tend to crys-
tallize over time, which could severely limit their potential.4 Ad-
ditionally, the method is known as vapor deposition that can be
applied to organic compounds to produce amorphous phase with
extraordinary thermodynamic and kinetic stability, and high den-
sity. Its stability is optimized when deposition occurs on a substrate
at a temperature of 50 K below its Tg.5
To overcome these disadvantages we designed a novel class of
quinoline amines as amorphous molecular materials. They are
completely conjugated and each of their molecular structures are
asymmetric that evidently contributes to its sustaining amorphous
state, which is known to favor the amorphous state.4 Amino groups
were added in different positions of the 2-phenyl group: the phenyl
group attached at the 2-position of the quinoline moiety. The var-
iation of chemical structures would enable one to study the effect of
molecular structures on their thermal transitions as well as tuning
of fluorescence properties and optimization of quantum yields.
2. Results and discussion
€
The Friedlander condensation reaction is a facile synthetic
method for preparing quinolines, oligoquinolines, polyquinolines,
and polyanthrazolines.6,7 It has numerous applications as a key step
in the total synthesis of many natural products like streptonirin,8a
camptothecin,8b irinotecan,8c and nothapodytine B.8d To prepare
* Corresponding
(P.K. Bhowmik).
author.
E-mail
address:
pradip.bhowmik@unlv.edu
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.09.108

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A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
a class of quinoline amines 1be7b, we used an acid-catalyzed
crystallization exotherms, demonstrating its stability in the amor-
phous state. Overall, it has both the highest Tg and Tm among the
compounds examined, since it possesses the most symmetrical
€
Friedlander condensation reaction followed by hydrogenation with
hydrazine monohydrate in presence of Pd/C as shown in Scheme 1.
Scheme 1. Synthesis of quinoline amines 1be7b in two steps.
The thermal properties of quinoline amines 1be7b are compiled
in Table 1. In the first heating cycle, they exhibited notable melting
transitions (Tm) of the solvent-induced crystals, ranging from 89 to
194 ꢀC. In the second heating cycles, all of them showed only the Tg.
Their amorphous states were presumably related to the presence of
asymmetric structural moieties. Both Tg and Tm temperatures were
found to be affected by the different substituents. Compounds 1b
and 2b showed identical Tm and Tg where 3b had a little lower Tm of
140 ꢀC, and consequently lower Tg of 40 ꢀC since the amino group is
in the low-symmetry meta position. The three compounds 4be6b
are disubstituted amines as well as isomers of one another. The first
substituent is an amino group at position Z and the second sub-
stituent is another amino group at positions R6, R5, and R4, re-
spectively. Their thermal transitions were significantly increased;
Tm values ranged from 132 to 194 ꢀC, and Tg values ranged from 61
to 90 ꢀC.
chemical structure. These thermal properties demonstrated that
compounds/glasses 1be7b are excellent candidates for amorphous
molecular materials4b for electronic devices and their thermal
transitions are tunable with the modifications of their chemical
structures. In addition, given their relatively low Tg and Tm tem-
peratures, they are attractive candidates for future studies of mo-
lecular dynamics of glassy materials.9
The X-ray powder diffraction (XRD) patterns of the compounds
in this study further confirm that they can form completely amor-
phous materials. In Fig. 2 the representative XRD patterns are dis-
played for comparison of the crystalline and amorphous states of
amino quinoline 1b and diamino quinoline 4b. The multiple sharp
peaks of strong intensities present in Fig. 2a,b are indicative of the
highly crystalline nature of these compounds. On the other hand,
Fig. 2c,d show broad diffraction peaks with relatively low in-
tensities at both small and wide angles, which are the characteristic
Table 1
Thermal properties of quinoline derivatives 1ae7a and 1be7b
Compound
1a
2a
3a
4a
5a
6a
7a
First heating
Second heating
210 ꢀC (Tm
210 ꢀC (Tm
)
)
167 ꢀC (Tm
166 ꢀC (Tm
)
)
159 ꢀC (Tm
158 ꢀC (Tm
)
)
282 ꢀC (Tm
282 ꢀC (Tm
)
)
246 ꢀC (Tm
246 ꢀC (Tm
)
)
229 ꢀC (Tm
60 ꢀC (Tg)
)
133 ꢀC (Tm
133 ꢀC (Tm
)
)
Compound
1b
2b
3b
4b
5b
6b
7b
First heating
150 ꢀC (Tm
52 ꢀC (Tg)
0.77
)
150 ꢀC (Tm
52 ꢀC (Tg)
0.77
)
140 ꢀC (Tm
40 ꢀC (Tg)
0.76
)
194 ꢀC (Tm
90 ꢀC (Tg)
0.78
)
192 ꢀC (Tm
76 ꢀC (Tg)
0.85
)
132 ꢀC (Tm
61 ꢀC (Tg)
0.82
)
89 ꢀC (Tm
)
Second heating
15 ꢀC (Tg)
a
Tg/Tm
0.80
a
Ratio of absolute temperatures (K).9
Compound 7b is also a disubstituted amine but has an amino
group at position Z and a hexyl group at position R6. It showed the
lowest Tm of 89 ꢀC and the lowest Tg at 15 ꢀC. The representative
DSC thermograms of compound 4b are shown in Fig. 1. In the first
heating cycle, it exhibited a sharp Tm at 194 ꢀC. After the first
heating cycle, it was cooled slowly at a rate 10 ꢀC/min and showed
a Tg at 90 ꢀC in the first cooling cycle. Interestingly, its Tg retained in
the subsequent cycles without any cold-crystallization: crystalli-
zation above the glass transition temperature on heating and
features of glassy phases of compounds. These peaks can be
assigned to the intermolecular short-range interactions that are
parallel and perpendicular to the long axes of the molecules. The
d-spacing values of 1b and 4b obtained from the diffuse peak
maxima at small angles by using Bragg’s equation are 0.98 and
0.91 nm, respectively, comparable to the molecular lengths ca.
1.1 nm obtained from the MM2 calculation. Meanwhile, the broad
wide-angle diffraction peaks indicate an average intermolecular
separation of 0.46 and 0.47 nm, respectively, and they are the result

A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
9321
quite interesting, since it could be a very useful tool for the con-
struction of compounds that are capable of forming fibers from
their nano-sized objects in the burgeoning field of nano-
technology.11a To our knowledge, these amines are the first exam-
ples of organic compounds that are capable of forming fibers from
their melts. This property may be related to the amorphous nature
of these compounds that remains to be explored. Note here that in
the literature there is one example of a peptidomimetic molecule
that undergoes self-assembly forming micro- and nano-fiber in the
melt on cooling.11b Most fibers, usually produced from the orga-
nogels prepared in various solvents including water, reported in the
literature can only been seen by POM and scanning electron mi-
crocopy (SEM) studies. In some cases, one could be able to pull fi-
bers from the organogel with a pair of tweezers. There are many
intermolecular interactions in the formation of organogels some of
which include hydrogen bond, hydrophobic and electrostatic as-
sociation, and van der Waals interactions.11bed Additionally, fibers
usually form from the melts and solutions of polymers because of
their macromolecular sizes.12 In this regard, the formation of fibers
from organic amines in the melts constitutes a new and promising
area of research in nanotechnology. Fig. 3a,b shows photomicro-
graphs of POM and Fig. 6c,d shows SEM images of hand-drawn fi-
bers of 1b and 4b from their melts. The morphologies of these fibers
were found to be isotropic in nature with very smooth surfaces as
examined with both POM and SEM studies. In Fig. 3c the SEM
revealed some roughness to the surface of the fiber of compound
1b, while the cross-section showed its uniform nature. On the other
hand, compound 4b, exhibited much smoother surface than 1b
(Fig. 3d). The cross-section of the compound 4b demonstrated
Fig. 1. DSC thermograms of compound 4b obtained at heating and cooling rates of
10 ꢀC/min in nitrogen.
of
pep
stacking of these heterocyclic amine molecules.10 On
melting these compounds between two cover glasses, we were able
to form thin amorphous films, which we then examined with po-
larizing optical microscopy (POM) studies to understand their film
morphologies. In all cases, the samples produced uniformly iso-
tropic thin films, which are very similar to many amorphous mo-
lecular materials.4 Remarkably, we successfully drew fibers by
pulling their melts with a pair of tweezers with thickness of
60e120
mm, which are visible to the naked eye. The formation of
fibers from the melts of heterocyclic amines by self-assembly is
Fig. 2. XRD plots of compounds 1b and 4b (a,b) in their crystalline states obtained from solvents recrystallization and (c,d) in their amorphous states prepared from their melts,
respectively.

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A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
Fig. 3. (a,b) photomicrographs with POM (magnification 400x) and (c,d) images of SEM of hand-drawn fibers from the melts of compounds 1b and 4b, respectively.
a similar uniformity as for 1b. At the present time, it is difficult to
speculate the molecular interactions that are involved in the for-
mation of fibers from these compounds in these series.
On one hand, quinine is a naturally occurring compound that
exhibits strong fluorescence and, therefore, is usually used as
a fluorescent standard.1 On the other hand, quinoline does not
fluoresce at all even though it is structurally similar to quinine,
which has two additional substituents. These results convey the
concept that substituents have a key effect on the properties of
fluorophores. Recently, phase-tunable fluorophores based on ben-
zobis(imidazolium) salts have also been reported in the literature.13
In our studies we utilized a different type of quinoline moiety and
attached substituents in different positions in order to examine
how they affect their light emission properties as well as their
quantum yields. Optical properties of both UVevis absorption and
photoluminescence including quantum yields14 of 1be7b are
summarized in Table 2. Since they had excellent solubilities in
various organic solvents, their photoluminescence properties were
Table 2
Optical properties of quinoline amines 1be7b
Compound
1b
2b
3b
4b
5b
6b
7b
UV abs CHCl3 (nm)
PL lem Toluene (nm)
PL lem CHCl3 (nm)
PL lem THF (nm)
PL lem CH3OH (nm)
PL lem CH3CN (nm)
PL lem film (nm)a
FF (%)c CHCl3
280, 300sh
419
290, 420
408
345
412
417
475
491
510
404
2d
290, 440
426
300, 420
419
325, 435, 480
310, 415
418
426
426
445
460
448
db
3
485
446
463
443
482
452
491
478
436
448
467
443
430
31
434
444
461
448
430
23
483
446
462
444
418, 529
45
402, 508
9
421, 514
32
a
Film was prepared in a polystyrene matrix cast from CHCl3.
Too weak to measure the light emission.
b
c
Quantum yield was determined against diphenylanthracene as standard (FF¼0.9) in solution.10
d
Quantum yield was measured in THF.

A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
9323
examined in various solvents having a wide range of polarities.
Their photoluminescence spectra in chloroform are displayed in
Fig. 4. The wavelengths of light emission range from blue (417 nm)
to green (485 nm). Compounds 1b, 2b, and 7b showed distinctive
green emission with lem values at 485, 482, and 483 nm, when
excited at 290, 410, and 300 nm, respectively. On the other hand,
structurally similar compound 3b showed a hypsochromically
shifted lmax of 417 nm when excited at 300 nm. This large differ-
ence was due to the fact that the amino group is meta relative to the
quinoline moiety. Disubstituted compounds 4be6b had lem at 436,
434, and 426 nm when excited at 300, 265, and 350 nm, re-
spectively, showing a slight hypsochromic shift when changing the
position of the second amino group from para- to meta- to ortho-.
When comparing the optical properties of these compounds, it was
found that changing the substituents and their positions had a key
effect on their fluorescence behavior. Moreover, their fluorescence
properties in various organic solvents also suggested a strong evi-
dence of solvatochromic effect.1 Taking compound 3b for instance
showed a large bathochromic shift with increasing solvent polarity
(Fig. 5a). When examined in low polarity solvent toluene (
showed a major lem peak at 412 nm when excited at 300 nm
whereas in high polarity acetonitrile (
e¼2.4), it
e
¼37.5) a major lem was ob-
served at 512 nm when excited at 300 nm. The difference between
their lmax values was 98 nm, which was due to the more polar
excited state than the ground state, which is a positive sol-
vatochromism.1 On the other hand, examining the optical proper-
ties of compound 1b revealed a more complex behavior (Fig. 5b). A
slight change in solvent polarity from toluene (
¼5.5), caused a large bathochromic shift of 67 nm, which had lem
values of 419 and 485 nm. Additionally, it showed a hypsochromic
shift in THF (
¼7.58) since its lem decreased to 446 nm. In changing
to methanol (
¼32.6) a slight bathochromic shift was observed at
lem¼463 nm. In acetonitrile ( ¼37.5) again a hypsochromic shift
e¼2.4) to CHCl3
(e
e
e
e
was detected (lem¼443 nm). Our attempts to measure the light
emission in their neat solid states were unsuccessful presumably
due to self-quenching phenomenon. However, we measured their
light emissions in a polystyrene matrix (Fig. 6), which eliminated
the self-quenching,15 and the results of their optical properties are
compiled in Table 2.
Fig. 5. Photoluminescence spectra of compounds (a) 3b and (b) 1b measured in var-
ious organic solvents.
Quantum yields are important factors for light-emitting com-
pounds1 and therefore, understanding how to correlate them with
isomeric compounds is of significant interest in the field of mate-
rials chemistry. Considering the monosubstituted amines 1be3b,
their quantum yields vary dramatically as shown in Table 2. Com-
pound 1b, which contained an amino group at the Z position that
was directly connected to the quinoline moiety of the molecule,
showed a high quantum yield of 45%. Compounds 2b and 3b, which
contained amino groups attached on to the phenyl ring para-(R6)
and meta-(R5) with respect of the quinoline moiety, had very low
quantum yields of 9% and 2%, respectively. These results conveyed
Fig. 6. Photoluminescence spectra of compounds 1be5b and 7b measured in poly-
styrene matrix film cast from CHCl3.
Fig. 4. Photoluminescence spectra of compounds 1be7b measured in CHCl3.

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A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
the concept that having an amino group at the Z position is crucial
for obtaining a high quantum yield for these compounds. This
phenomenon is usually observed in aromatic amines, which are
dipolar both in the ground state S0, and in the excited state S1. This
behavior is in consistent with our results. The common light-
emitting aromatic amines include aniline, N,N-dimethylaniline,
4-aminodiphenyl ether, and aminofluorene.16 The excellent quan-
tum yields of 4be7b with the exception of compound 6b further
confirmed these optical properties. The reason for the low quantum
yield of 6b was presumably related to the second amino group
ortho to the quinoline moiety. This amino group was hydrogen
bonded to the nitrogen of the quinoline moiety that was de-
termined from the analysis of its 1H NMR spectrum. The chemical
shift of hydrogen bonded aromatic amine protons with quinoline
appears further downfield with respect to that of aromatic amine
protons signal. This non-covalent interaction results in de-
stabilization of the excited state of the chromophore, which in
return lowers the quantum efficiency.
to ca. 0.05 at 350 nmwavelength, the output was measured using the
luminescence spectrophotometer at the same wavelength and
compared it to known9,10-diphenylanthracene standard using Eq.1:
ꢀ
ꢁꢀ
ꢁꢀ
ꢁ
2
Iunk
Istd
Astd
Aunk
hunk
hstd
funk
¼
fstd
(1)
F
is the fluorescence quantum yield, I is the absorption of the exci-
tation wavelength, A is the area under the emission curve, and is
h
the refractive index of the solvents used. Subscript std denotes the
standard and subscript unk denotes the unknown.19 The X-ray dif-
fraction studies were performed on finely powdered samples at rt
with X-ray diffraction spectrometer using Cu Ka radiation as an
X-ray source at 45 kV and 40 mA. The images of hand-drawn fibers
with a pair of tweezers from the melts were taken with a polarized
optical microscope (POM) equipped with crossed polarizers and
a red quarter plate, and a scanning electron microscope (SEM). The
calculation of molecular length along the long axis of molecule was
obtained using the program of ChemDraw combining energy min-
imized MM2 calculations.
3. Conclusions
In conclusion, we successfully synthesized several quinoline
4.2. Synthetic procedures
€
amine compounds by Friedlander condensation reactions and also
€
examined extensively their thermal and optical properties. All
compounds formed stable amorphous phases after the first melting
transitions of solvent-recrystallized samples as determined with
DSC and XRD techniques. Thus, we were able to simplify the pro-
cedures to form stable glasses from organic amines, which did not
require the utilization of any special techniques including vapor
deposition.5 They emitted blue to green light as well as exhibited
solvatochromism phenomenon. Their quantum yields were also
suitable for a variety of applications. Additionally, we successfully
were able to draw thin smooth fibers from the melts of these
quinoline amines and to examine their morphologies with POM
and SEM. The understanding for the mechanism of self-assembly of
these diamines could lead to the development of new materials in
the field of nanotechnology. Overall, their properties were tunable
implying their versatility as amorphous molecular materials for
various electronic and optoelectronic devices. Moreover, quinoline
diamine compounds 4be6b could be used as asymmetric mono-
mers for the preparation of high performance polymers. Addi-
tionally, polymers such as polyamides and polyimides are suitable
as charge-transporting layers in optoelectronic devices.17 We are
currently investigating their potential as suitable monomers in the
development of poly(pyridinium salt)s,18 the results of which will
be reported elsewhere in due course.
Compounds 1a, 4e7a were successfully prepared by Friedlander
condensation reaction as described in the literature.20a Synthesis of
compound 4a was reported with a yield of 55% and mp of
276e277 ꢀC.20a In another report, 4a was also synthesized by using
diphenyl phosphate, but neither yield nor melting point was
repoted.20b In our hands, we were able to prepare it with a yield as
high as 87% and mp of 281 ꢀC as examined with the DSC mea-
surement. Furthermore, the structure of 4a was not confirmed in
the literature by any means.20a,b We determined its structure by
elemental analysis and 1H and 13C NMR spectroscopy. Compounds
2a and 3a were prepared by employing different procedure since
2-aminobenzophenone was unreactive in the identical synthetic
reaction conditions.20b,c All amino compounds 1be7b were suc-
cessfully prepared via hygrogenation with hydrazine monohydrate
over Pd/C catalyst in ethanolic solutions in good yields. Compound
4b has been reported in literature in poor yield of 57% and mp of
191e192 ꢀC.20b We were able to make it in 81% yield and mp 194 ꢀC.
Note here that compound 2b was prepared in one-step synthesis
via microwave chemistry in good yield of 80%.20d
4.2.1. 6-Nitro-2,4-diphenyl-quinoline (1a). A total of 7.50 g (31.0
mmol) 2-amino-5-nitrobenzophenone and 3.75 g (31.0 mmol)
acetophenone was added to 60.0 mL of acetic acid. Sulfuric acid
(6 mL) was added to the reaction mixture, which was heated to
reflux for 4 h. After completion, the reaction was cooled down to rt.
It was poured slowly into ammonium hydroxide/ice mixture (150/
120 by volume in mL). The precipitate was collected and washed
with hot water and ethanol sequentially. The crude compound was
recrystallized from DMF to afford 9.40 g (28.8 mmol, yield 93%) of
4. Experimental section
4.1. Chemicals and characterization
1
The H and 13C NMR spectra were recorded with an NMR spec-
trometer equipped with three RF channels operating and 400 MHz
and 100 MHz, respectively. Solutions were prepared by dissolving ca.
25 mg of compounds per mL of DMSO-d6 or CDCl3 with TMS as in-
ternal standard. The phase transitions of these compounds were
measured using differential scanning calorimetry (DSC) under a ni-
trogen flow at heating and cooling rates of 10 ꢀC/min. The tempera-
ture axis of the DSC thermogram was calibrated with reference
standards of high purity indium and tin before use. Compounds of
8e10 mg were used for these analyses. The UVevis absorption
spectra of compounds in various organic solvents were recorded
using a UVevisible spectrophotometer in quartz cuvette. Their
photoluminescence properties, in both solution and film states, were
analyzed using a luminescence spectrophotometer. Quantum yields
were analyzed by adjusting the solution absorption using the UVevis
a spongy white compound. 1H NMR (400 MHz, DMSO-d6)
d ppm
8.68 (d, J¼2.53 Hz, 1H), 8.50 (dd, J¼9.2, 2.58 Hz, 1H), 8.40 (m, 2H),
8.33 (d, J¼9.2 Hz, 1H), 8.27 (s, 1H), 7.73 (m, 2H), 7.71e7.64 (m, 3H),
7.62e7.56 (m, 3H). 13C NMR (100 MHz, DMSO-d6)
d ppm 159.0,150.6,
150.2, 144.8, 137.5, 136.2, 131.4, 130.58, 129.6, 129.2, 128.9, 128.9,
127.8, 124.0, 123.1, 122.3, 120.3. [Found: C, 77.19; H, 4.40; N, 8.79.
requires C21H14N2O2 (326.36): C, 77.29; H, 4.32; N, 8.58%].
4.2.2. 6-Nitro-2(4-nitrophenyl)-4-phenylquinoline (4a). Yield¼87%,
recrystallized from DMF. 1H NMR (400 MHz, DMSO-d6)
d ppm 8.68
(d, J¼2.10 Hz, 1H), 8.60 (d, J¼8.8 Hz, 2H), 8.48 (dd, J¼9.2, 2.32 Hz,
1H), 8.35 (t, J¼7.3 Hz, 3H), 8.29 (s, 1H), 7.65 (m, 5H). 13C NMR
(100 MHz, DMSO-d6) d ppm 157.7, 152.0, 150.9, 149.6, 146.0, 144.36,
136.9, 132.6, 130.6, 130.1, 129.9, 129.4, 125.4, 124.4, 123.8, 123.1,

A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
9325
121.6, 121.4. [Found: C, 67.80; H, 3.60; N, 11.42. requires C21H13N3O4
(371.36): C, 67.92; H, 3.53; N, 11.32%].
suspension. The reaction mixture became clear as the reaction
proceeded. It was kept at reflux for another 12 h. Upon completion
of the reaction, the mixture was filtered over Celite twice to remove
the Pd/C catalyst. The ethanol was removed under reduced pres-
sure. The crude product was recrystallized from isopropanol to
afford 6.20 g (20.9 mmol, yield 91%). Note the crystals grew slowly.
4.2.3. 6-Nitro-2(3-nitrophenyl)-4-phenylquinoline (5a). Yield¼88%,
recrystallized from DMF. 1H NMR (400 MHz, DMSO-d6)
d ppm 9.12
(t, J¼1.98 Hz, 1H), 8.77 (d, J¼8.0 Hz, 1H), 8.68 (d, J¼2.5 Hz, 1H), 8.48
(dd, J¼9.2, 2.54 Hz, 1H), 8.33 (m, 3H), 7.84 (t, J¼8.0 Hz, 1H),
1H NMR (400 MHz, DMSO-d6)
d
ppm 8.20 (m, 2H), 7.85 (d, J¼9.0 Hz,
7.75e7.57 (m, 5H). 13C NMR (100 MHz, DMSO-d6)
d
ppm 151.8,
1H), 7.74 (s, 1H), 7.61e7.54 (m, 4H), 7.53e7.43 (m, 3H), 7.43e7.35
(m, 1H), 7.20 (dd, J¼9.0, 2.5 Hz, 1H), 6.82 (d, J¼2.4 Hz, 1H), 5.67 (s,
149.6, 148.0, 145.7, 142.8, 140.4, 139.5, 131.1, 129.9, 129.8, 129.3,
128.7, 127.7, 122.3, 119.2, 115.0,112.7, 103.1. [Found: C, 67.76; H, 3.63;
N, 11.47. requires C21H13N3O4 (371.36): C, 67.92; H, 3.53; N, 11.32%].
2H). 13C NMR (100 MHz, DMSO-d6)
d ppm 151.0, 148.3, 146.0, 142.9,
139.9, 139.4, 131.3, 130.0, 129.6, 129.5, 129.4, 129.0, 128.7, 127.8,
127.2, 122.5, 119.2, 103.1. [Found: C, 85.01; H, 5.54; N, 9.50. requires
C21H16N2 (296.37): C, 85.11; H, 5.44; N, 9.45%].
4.2.4. 6-Nitro-2(2-nitrophenyl)-4-phenylquinoline (6a). Yield¼56%,
recrystallized from DMF. 1H NMR (400 MHz, DMSO-d6)
d ppm 8.92
(d, J¼2.5 Hz, 1H), 8.51 (dd, J¼9.2, 2.53 Hz, 1H), 8.28 (d, J¼9.2 Hz,1H),
4.2.9. 2(4-Aminophenyl)-4-phenylquinoline (2b). Yield¼48%, the
compound was eluted in chloroform through a column chroma-
tography on silica gel, it was vacuum dried and it was recrystallized
8.06 (dd, J¼8.1, 1.01 Hz, 1H), 7.86e7.73 (m, 2H), 7.61 (m, 7H). 13C
NMR (100 MHz, DMSO-d6)
d ppm 159.0, 151.7, 150.7, 146.2, 136.4,
135.2, 133.2, 132.1, 131.8, 130.4, 129.8, 129.8, 129.4, 125.2, 125.1,
123.6, 123.2, 122.7. [Found: C, 67.75; H, 3.58; N, 11.43. requires
C21H13N3O4 (371.36): C, 67, 92; H, 3.53; N, 11.32%].
from isopropanol. 1H NMR (400 MHz, DMSO-d6)
d ppm 8.06 (dd,
J¼11.2, 8.5 Hz, 3H), 7.86 (s, 1H), 7.74 (m, 2H), 7.65e7.51 (m, 5H), 7.46
(dd, J¼11.2, 4.0 Hz, 1H), 6.70 (d, J¼8.6 Hz, 2H), 5.58 (s, 2H). 13C NMR
(100 MHz, DMSO-d6)
d ppm 156.0, 150.5, 148.1, 147.8, 137.8, 129.4,
4.2.5. 6-Nitro-2(4-hexylphenyl)-4-phenylquinoline (7a). Yield¼92%,
129.1, 128.5, 128.3, 125.5, 125.4, 125.0, 124.3, 117.6, 113.6. [Found: C,
84.90; H, 5.53; N, 9.64. requires C21H16N2 (296.37): C, 85.11; H, 5.44;
N, 9.45%].
recrystallized from methanol. 1H NMR (400 MHz, DMSO-d6)
d ppm
8.60 (d, J¼2.5 Hz, 1H), 8.41 (dd, J¼9.2, 2.57 Hz, 1H), 8.23 (dd, J¼8.7,
6.28 Hz, 3H), 8.15 (s, 1H), 7.76e7.57 (m, 5H), 7.32 (d, J¼8.2 Hz, 2H),
2.61 (t, J¼7.6 Hz, 2H), 1.57 (m, 2H), 1.27 (d, J¼16.3 Hz, 6H), 0.83 (dd,
4.2.10. 2(3-Aminophenyl)-4-phenylquinoline (3b). Yield¼82%, recry-
J¼9.1, 4.77 Hz, 3H). 13C NMR (100 MHz, DMSO-d6)
d
ppm 159.8,
stallized from isopropanol. 1H NMR (400 MHz, CDCl3)
d ppm 8.23
151.2, 151.0, 146.1, 146.1, 137.0, 135.8, 132.1, 130.4, 130.0, 129.8, 129.7,
128.5, 124.7, 123.8, 123.7, 123.0, 121.0, 35.7, 31.8, 31.4, 29.0, 22.8,
14.6. [Found: C, 78.88; H, 6.35; N, 6.99. requires C27H26N2O2
(410.52): C, 79.00; H, 6.38; N, 6.82%].
(d, J¼8.4 Hz, 1H), 7.78 (s, 1H), 7.75e7.67 (m, 1H), 7.61e7.57 (m, 1H),
6.78 (dd, J¼7.8, 1.7 Hz, 1H), 7.29 (t, J¼7.8 Hz, 1H), 7.57e7.48 (m, 6H),
7.46 (m, 1H), 7.89 (d, J¼7.8 Hz, 1H), 3.79 (d, J¼0.9 Hz, 2H). 13C NMR
(100 MHz, CDCl3) d ppm 157.0, 149.0, 148.7, 147.0, 140.7, 138.4, 130.0,
129.7, 129.5, 128.6, 128.3, 126.2, 125.8, 125.6, 119.5,117.9, 116.2, 114.1.
[Found: C, 85.07; H, 5.38; N, 9.30. requires C21H16N2 (296.37): C,
85.11; H, 5.44; N, 9.45%].
4.2.6. 2(4-Nitrophenyl)-4-phenylquinoline (2a). A total of 4.00 g
(20.3 mmol) 2-aminobenzophenone, 3.35 g (20.3 mmol) 40-nitro-
acetophenone, and 20.3 g (81.1 mmol) of diphenyl phosphate was
heated to 140 ꢀC for 6 h under nitrogen flow. Upon completion of
the reaction, the mixture was cooled down to rt and was pre-
cipitated in 10% triethylamine/methanol. The crude product was
collected and washed with excess methanol. The compound was
eluted in chloroform through a column chromatography on silica
4. 2.11. 6-Amino-2(4-aminophenyl)-4-phenylquinoline
(4b). Yield¼81%, recrystallized from isopropanol. 1H NMR
(400 MHz, DMSO-d6)
d
ppm 7.92 (d, J¼8.6 Hz, 2H), 7.75 (d, J¼8.9 Hz,
1H), 7.63e7.57 (m, 1H), 7.57e7.52 (m, 4H), 7.52e7.45 (m, 1H), 7.13
(dd, J¼8.9, 2.4 Hz, 1H), 6.77 (d, J¼2.4 Hz, 1H), 6.66 (d, J¼8.7 Hz, 2H),
gel. It was recrystallized from acetonitrile to afford 7.00
(21.5 mmol, yield 85%) of pale yellow crystals. 1H NMR (400 MHz,
TFA-d1)
ppm 8.66 (d, J¼7.35 Hz, 2H), 8.47 (dd, J¼8.44, 5.22 Hz, 2H),
8.35 (d, J¼7.36 Hz, 2H), 8.33e8.24 (m, 2H), 8.06 (t, J¼7.75 Hz, 1H),
7.77 (m, 5H). 13C NMR (100 MHz, TFA-d1)
ppm 162.9, 162.3, 161.9,
g
5.37 (s, 2H), 5.48 (s, 2H). 13C NMR (100 MHz, DMSO-d6)
d ppm 151.9,
150.2, 147.3, 145.7, 142.9, 139.7, 130.7, 129.9, 129.3, 128.6, 128.2,
127.4, 127.0, 122.1, 118.3, 114.4, 103.6. [Found: C, 80.86; H, 5.31; N,
13.71. requires C21H17N3 (311.39): C, 81.00; H, 5.50; N, 13.49%].
d
d
161.5, 161.0, 151.3, 150.2, 138.8, 136.6, 136.3, 134.2, 131.3, 130.8,
129.6, 129.1, 128.9, 127.8, 126.9, 124.8, 121.0, 120.1, 118.5, 115.6, 112.8,
110.0. [Found: C, 77.55; H, 4.71; 8.95. requires C21H14N2O2 (326.36):
C, 77.29; H, 4.32; N, 8.58%].
4.2.12. 6-Amino-2(3-aminophenyl)-4-phenylquinoline
(5b). Yield¼88%, recrystallized from ethanol. 1H NMR (400 MHz,
DMSO-d6)
d
ppm 7.81 (d, J¼8.9 Hz, 1H), 7.67e7.44 (m, 7H), 7.31 (d,
J¼7.8 Hz, 1H), 7.25e7.09 (m, 2H), 6.80 (d, J¼2.4 Hz, 1H), 6.62 (dd,
J¼7.8, 2.2 Hz, 1H), 5.65 (s, 2H), 5.19 (s, 2H). 13C NMR (100 MHz,
4.2.7. 2(3-Nitrophenyl)-4-phenylquinoline (3a). Yield¼89%, after
precipitation in 10% triethylamine/methanol to afford the crude
product. It was washed with excess methanol recrystallized from
acetonitrile to give light purple crystals. 1H NMR (400 MHz, CDCl3)
DMSO-d6) d ppm 151.8, 149.6, 148.0, 145.7, 142.8, 140.4, 139.5, 131.1,
129.9, 129.8, 129.3, 128.7, 127.7, 122.3, 119.2, 115.0, 112.7, 103.1.
[Found: C, 80.92; H, 5.61; N, 13.77. requires C21H17N3 (311.39): C,
81.00; H, 5.50; N, 13.49%].
d
ppm 9.07 (t, J¼1.9 Hz, 1H), 8.58 (d, J¼7.8 Hz, 1H), 8.34e8.28 (m,
1H), 8.26 (d, J¼8.4 Hz, 1H), 7.93 (d, J¼7.8 Hz, 1H), 7.86 (s, 1H), 7.77
(ddd, J¼8.3, 6.9, 1.3 Hz, 1H), 7.69 (dd, J¼9.9, 6.02 Hz, 1H), 7.55 (m,
4.2.13. 6-Amino-2(2-aminophenyl)-4-phenylquinoline
(6b). Yield¼62%, the compound was eluted in chloroform in a silica
gel column chromatography for purification. It was then recrystal-
lized from isopropanol/ether (98/2 by volume in mL). Note that it is
difficult to get the correct ratio of this solvent-pair mixture because
of the volatility of ether. Crystals grew very slowly (2e3 days). 1H
6H). 13C NMR (100 MHz, CDCl3)
d ppm 153.9, 150.0, 148.8, 141.3,
137.9, 133.3, 130.2, 130.0, 129.9, 129.8, 129.5, 128.7, 127.1, 126.1,
125.8, 123.9, 122.4, 118.6. [Found: C, 77.23; H, 4.43; N, 8.50. requires
C21H14N2O2 (326.36): C, 77.29; H, 4.32; N, 8.58%].
NMR (400 MHz, DMSO-d6)
d
ppm 7.78 (d, J¼8.9 Hz, 1H), 7.73e7.65
4.2.8. 6-Amino-2,4-diphenyl-quinoline (1b). An ethanol suspension
(50.0 mL) of the 7.50 g (23.0 mmol) 6-amino-2,4-diphenyl-quino-
line was heated to 50.0 ꢀC in presence of 0.10 g of Pd/C and 5.00 mL
of hydrazine monohydrate were added over 30 min to this
(m, 1H), 7.59 (s, 1H), 7.52 (m, 5H), 7.17 (dd, J¼8.9, 2.4 Hz, 1H),
7.13e7.03 (m,1H), 6.92 (s, 2H), 6.66e6.56 (m,1H), 5.61 (s, 2H), 6.80 (t,
J¼5.4 Hz, 2H). 13C NMR (100 MHz, DMSO-d6)
d ppm 153.9, 148.7,
148.1,146.0,141.2,139.4,130.4,129.9,129.7,129.3,128.7,126.7,122.2,

9326
A.K. Nedeltchev et al. / Tetrahedron 66 (2010) 9319e9326
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120.9, 120.7, 117.1, 116.4, 103.4. [Found: C, 80.99; H, 5.62; N, 13.53.
requires C21H17N3 (311.39): C, 81.00; H, 5.50; N, 13.49%].
3. (a) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.;
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(7b). Yield¼76%, recrystallized from isopropanol/water. 1H NMR
(400 MHz, DMSO-d6)
d
ppm 8.09 (d, J¼8.3 Hz, 2H), 7.81 (d, J¼8.9 Hz,
1H), 7.70 (s, 1H), 7.62e7.52 (m, 4H), 7.52e7.47 (m, 1H), 7.27 (d,
J¼8.3 Hz, 2H), 7.17 (dd, J¼8.9, 2.46 Hz, 1H), 6.79 (d, J¼2.4 Hz, 1H),
5.61 (d, J¼7.0 Hz, 2H), 2.48 (td, J¼3.7, 1.8 Hz, 2H), 1.57 (dd, J¼14.0,
7.0 Hz, 2H), 1.36e1.15 (m, 6H), 0.84 (t, J¼14.0 Hz, 3H). 13C NMR
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(100 MHz, DMSO-d6)
d ppm 151.1, 148.1, 145.9, 143.5, 142.9, 139.4,
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137.4, 131.1, 130.0, 129.3, 128.7, 127.7, 127.1, 122.4, 119.0, 103.7, 35.6,
31.8, 31.5, 29.0, 22.8. [Found: C, 85.30; H, 7.55; N, 7.56, requires
C27H28N2 (380.54): C, 85.22; H, 7.42; N, 7.36%].
Acknowledgements
P.K.B. acknowledges the University of Nevada Las Vegas (UNLV)
for an Applied Research Initiative (ARI) grant, the donors of the
Petroleum Research Fund and Research Corporation for an award
(CCSA# CC5589) for the support of this research. A.K.N. acknowl-
edges the Graduate College (UNLV) for providing him a Nevada
Stars Graduate Assistantship for the period of 2006e2008. The
work is in part supported by the NSF under Grant No. 0447416 (NSF
EPSCoR RING-TRUE III), NSF-Small Business Innovation Research
(SBIR) Award (Grant OII-0610753), NSF-STTR Phase I Grant No. IIP-
0740289, and NASA GRC Contract No. NNX10CD25P.
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Supplementary data
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Structures and designations, and 1H and 13C NMR spectra of all
compounds are provided. Supplementary data related to this article
can be found online at doi:10.1016/j.tet.2010.09.108. These data
include MOL files and InChIKeys of the most important compounds
described in this article.
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References and notes
1. Lakowicz, J. R. Principles in Fluorescence Spectroscopy, 3rd ed.; Springer: New
York, NY, 2006, Chapter 3, p 63.