Synthesis, characterization and electronic effects investigations of new 5,7-disubstituted tris(8-quinolinolate)Al(III) complexes

Article abstract of DOI:10.1016/j.dyepig.2013.12.007

Eight 5,7-diaryl-8-hydroxyquinoline ligands were synthesized and characterized by ¹H, ¹³C NMR spectroscopy and mass spectrometry. The electron-donating and electron-withdrawing aryl groups were attached to the 5- and 7-positions of the quinolinolate ring via Suzuki coupling reaction. The aluminum complexes of these ligands exhibited successful tuning in the emission color, covering a large segment of the visible spectrum.

Full text of DOI:10.1016/j.dyepig.2013.12.007

Dyes and Pigments 103 (2014) 138e144
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, characterization and electronic effects investigations
of new 5,7-disubstituted tris(8-quinolinolate)Al(III) complexes
Saleh N. Al-Busafi*, FakhrEldin O. Suliman, Zaid R. Al-Alawi
Department of Chemistry, College of Science, Sultan Qaboos University, Box 36, Al-Khodh 123, Oman
a r t i c l e i n f o
a b s t r a c t
Eight 5,7-diaryl-8-hydroxyquinoline ligands were synthesized and characterized by 1H, 13C NMR spec-
troscopy and mass spectrometry. The electron-donating and electron-withdrawing aryl groups were
attached to the 5- and 7-positions of the quinolinolate ring via Suzuki coupling reaction. The aluminum
complexes of these ligands exhibited successful tuning in the emission color, covering a large segment of
the visible spectrum.
Article history:
Received 23 June 2013
Received in revised form
11 October 2013
Accepted 7 December 2013
Available online 18 December 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Suzuki coupling reaction
8-Hydroxyquinoline
Fluorescence sensors
Photophysical properties
Aluminum ion
OLEDs
1. Introduction
in the C-5 or C-7 positions of the quinoline skeleton cause a red-
shift of the complex emission, while a blue-shift is expected
8-Hydroxyquinoline (8-HQ), one of the most popular and ver-
satile organic reagents, and its derivatives have found a great va-
riety of applications ranging from pharmacological and
pharmaceutical agents [1] to electron carriers in organic light-
emitting diodes (OLEDs) [2] and fluorescent chemosensors for
metal ions [3]. 8-hydroxyquinoline has bactericidal activity of
comparable potency against non-replicating and replicating
Mycobacterium tuberculosis (Mtb) [4], and Staphylococcus aureus [5].
Moreover, many substituted 8-HQ exhibit greater activity against
bacterial strains and fungal strains than do the parent compounds,
but moderate activity compared with standard drugs [6,7].
It has been almost more than two decades since tris(8-
hydroxyquinoline)aluminum (III) [AlQ3] was introduced as an
electron-transporting material in organic light-emitting diodes
(OLEDs) [8]. Nowadays, OLEDs are gradually replacing liquid crystal
displays (LCD) as the most important full-color flat panel display
technology. In order to improve the efficiency of MQ3 (M ¼ metal
ion) complexes, researchers have centered their efforts on two
major aspects: changing the chelated metal ion and modifying the
structure of the chelating ligands [9e12]. Concerning the chelating
ligands, it has been predicted that electron-donating substituents
when electron-withdrawing groups are attached in the same po-
sitions. In this regard, blue-shifted absorbance/luminescence bands
were recorded for 8-hydroxy-5-piperidinylquinolinesulfonamide
complexes of aluminum [9]. A successful tuning in the emission
color of AlQ3 was achieved by attachment of electron-donating
(EDG) or electron-withdrawing (EWG) aryl groups to the 5-
position of the quinolinolate ligand [13].
Sensing metal ions by fluorescent chemosensors is highly
applicable to a wide range of technologies and has currently been
studied intensively [14]. A chemosensor having a bipodal thio-
carbamate scaffold attached to histidine moieties senses Hg2þ with
a remarkable selectivity [15]. Azathia crown ethers carrying pyrene
pendant as receptor molecules showed promising results as metal
sensor systems for Cu2þ, Zn2þ, and Cd2þ [16]. Aluminum (III) ion
exists widely in the environment due to acid rain and human ac-
tivities. Its toxicity to the environment and to humans is well
documented [17]. Therefore, detection of Al3þ is crucial to control
its concentration levels in the biosphere, hence its impact on hu-
man health. In this regard, 2-hydroxy-1-naphthaldehyde was used
as a highly sensitive and selective fluorescent sensor for Al3þ in
EtOHeH2O solution [18]. The fluorescent reagent sodium 4-(2,5-
diphenyl-1H-pyrrol-1-yl)benzoate (TriPP-COONa) showed good
detection limit (27
m
g Lꢀ1) for detecting aluminum ion in water
* Corresponding author. Tel.: þ968 24142305; fax: þ968 24141469.
E-mail address: saleh1@squ.edu.om (S.N. Al-Busafi).
samples [19]. An efficient fluorescent Al3þ receptor, 1-[[(2-
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.12.007

S.N. Al-Busafi et al. / Dyes and Pigments 103 (2014) 138e144
139
electron-poor Ar substituents
NO2
Cl
Ar
N
5
1
N
Ar
Ar
8
O
O
N
a
b
c
Al
Ar
N
O
electron-rich Ar substituents
OMe
N
Ar
Complex 1
Ar
d
e
f
g
h
Fig. 1. Structure of AlQ3 complexes 1aeh with electron-rich and electron-poor aromatic moieties.
furanylmethyl)imino]methyl]-2-naphthol exhibited high selec-
tivity and affinity towards Al3þ [20]. Owing to their chelating ability
toward a great number of metal ions, 8-HQ and its derivatives have
found many applications in the chemosensing field [21]. 8-
Hydroxyquinoline was used to detect Al3þ in soil extracts with
fluorometric detection limit of w1 ꢁ 10ꢀ8 M (0.3 ppb) Al [22].
Moderate selectivity for Al3þ over other metal ions with detection
limit reaching <10ꢀ7 M under weak acidic conditions was reported
for 8-hydroxyquinoline-carbaldehyde Schiff-base [23].
Nevertheless, there is a need for more research to achieve
higher selectivity and sensitivity to detect Al3þ over other metal
ions. Our approach concentrates on increasing the chelating
properties of 8-HQ derivative ligands to enhance the fluorescent
output of the produced AlQ3 complexes and consequently increase
the quantum yield and shifting the color to red regions by intro-
ducing electron-withdrawing and electron-donating phenyl moi-
eties at the C5 and C7 positions of 8-HQ [24]. In this paper, we
report the synthesis, spectroscopic identification, and photo-
physical behavior of eight AlQ3 complexes 1aeh in which the
phenyl groups at C5 and C7 of the ligands are substituted either
with electron-withdrawing groups aec or with electron-donating
groups deh (Fig. 1).
2. Results and discussion
2.1. Synthesis
The eight ligands were prepared starting from 8-hydroxy
quinoline following previously published method [25]. Dibromi-
nation of 8-HQ at C-5 and C-7 was performed satisfactorily using
the published method with some modifications in which the
concentrated sulfuric acid was replaced with acetic acid and the
reaction was performed at room temperature to give compound 2
in 75.4% yield. The hydroxyl group in 2 was protected smoothly by
the stable benzyl (Bn) group prior to the Pd-catalyzed coupling
reactions to yield intermediate 3 in 54.0%. Compounds 4aeh were
prepared by coupling intermediate 3 with a suitable arylboronic
acid using Suzuki cross-coupling reaction. Hence, the electron-rich
EDG arenes and electron-poor EWG arenes were, respectively,
attached to 8-benzyloxy-5,7-dibromoquinoline
3 in 50e89%
yield. Deprotection of the benzyl group was achieved by catalytic
transfer hydrogenation (CTH) using cyclohexa-1,4-diene and Pd/C
catalyst in absolute ethanol to give ligands 5aeh in 50e90% yield
(Scheme 1). The final AlQ3 complexes 1aeh were prepared by
reacting the ligands 5aeh with AlCl3$6H2O in methanol. All the
Ar EWG
Ar EWG
d)
EWG-Ar-B(OH)2
c)
EWG Ar
N
EWG Ar
N
OH
O
Ph
Br
4a-c
5a-c
Br
b)
a)
Br
N
Br
Ph
N
N
OH
O
OH
Ar EDG
Ar EDG
2
3
EDG-Ar-B(OH)2
c)
d)
EDG Ar
N
EDG Ar
N
Ph
OH
O
4d-h
5d-h
Scheme 1. Synthesis of compounds 5aeh; reaction conditions: a) Br2, AcOH, RT, 20 min; b) Bn-Cl, K2CO3, KI, acetone, reflux, 16 h; c) [Pd(pph3)4] (6%), Na2CO3, benzene, H2O, EtOH,
reflux, 24 h; d) 1,4-cyclohexadiene, PdeC (10%), EtOH, reflux, 5 h.

140
S.N. Al-Busafi et al. / Dyes and Pigments 103 (2014) 138e144
Fig. 2. 1H NMR of 5f.
synthesized complexes are new except 1d which was prepared
before by Hay et al. [25].
hydroxyquinoline complex. As expected, the introduction of two
aryl groups at C-5 and C-7 to the 8-HQ system results in a higher
The prepared ligands 5aeh exhibit a distinctive 1H NMR
coupling pattern for the protons 2, 3, 4, and 6 while protons that
belong to the substituted phenyl groups at C-5 and C-7 varies from
one ligand to another. In this regard, proton 2 appears as doublet of
doublet, shifted down field by N-atom of the pyridine ring. The J
values range from 1.0 to 1.4 Hz due to meta-coupling with H-4 and
4.0 to 4.5 Hz due to ortho-coupling with H-3. Proton 4 appears as
doublet of doublet with J values varies from 1.0 to 1.4 Hz due to
meta-coupling with H-2 and 8.0 to 8.4 Hz due to ortho-coupling
with H-3. Proton 3 appears up-field as doublet of doublet and
proton 6 as singlet (Fig. 2).
degree of conjugation and hence lowers the pe
p* transition en-
ergies for the complexes. Such result also supported by high
oscillating strength for the extended chromophores in complexes
1aeh (
complex AlQ3
3
¼ 2.6 ꢁ 104e8.9 ꢁ 104 Mꢀ1 cmꢀ1) relative to the parent
(
3
¼ 7.6 ꢁ 103
M
ꢀ1 cmꢀ1).
Examination of the data in Table 1 and fluorescence spectra in
Fig. 3 reveals successful emission color tuning in complexes 1aeh
arbitrated by the aryl electronic spacers at C-5 and C-7 of the qui-
nolinolate ring system. Almost direct correlation can be observed
between the photophysical properties and the electronic nature of
the attached aryl substituents. It is clear from Fig. 3 that the
emission shifts systematically from blue to green, yellow, and red
depending on the electronic nature of the modulator group. We
believe that aluminum complex in which the quinolinolate chro-
mophore is attached to two electronic effectors at C-5 and C-7
would exhibit amplified emission tuning compared to the C-5
substituted quinolinolate chromophores. The emission maxima of
complexes 1aeh span over 63 nm between 503 and 567 nm,
covering a significant portion of the visible light spectrum. The
2.2. Spectroscopic properties
The complexes 1aeh were studied by using UVevisible and
fluorescence spectroscopies and the resulting photophysical data
are summarized in Table 1. For the series, the
pe
p* absorption
maxima of the complexes shifted to lower energies relative to the
transition of the parent AlQ3 (lmax ¼ 388 nm), most likely due to the
extension in the conjugation of the quinoline chromophore. The
fluorescence maximum of 5,7-diphenyl-8-hydroxyquinoline 1d
exhibited a red shift of 15 nm compared to the parent 8-
Table 1
Photophysical propertiesa recorded for AlQ3 and complexes 1aeh in methanol at
23 ꢂC.
abs
max
b
c
Complex
l
(
3 )
lF [nm]
fF
sF[ns]
AlQ3
1a
1b
1c
1d
1e
1f
388 (7.6 ꢁ 103)
390 (8.9 ꢁ 104)
398 (5.5 ꢁ 104)
400 (5.7 ꢁ 104)
401 (5.7 ꢁ 104)
394 (2.6 ꢁ 104)
408 (4.6 ꢁ 104)
398 (6.0 ꢁ 104)
410 (4.5 ꢁ 104)
520
503
527
531
535
540
542
543
567
0.171
0.960
0.950
0.950
0.930
0.910
0.440
0.260
0.189
15.38
8.17
7.90
7.60
7.45
5.39
5.07
2.86
1.23
1g
1h
abs
max
a
l
¼ absorption maximum, lF ¼ fluorescence maximum, fF ¼ fluorescence
quantum yield, sF ¼ fluorescence lifetime.
b
Unite are [nm](Mꢀ1 cmꢀ1).
Determined by using quinine sulfate (in 0.05 M H2SO4) as a standard.
c
Fig. 3. Emission spectra of complexes 1aeh.

S.N. Al-Busafi et al. / Dyes and Pigments 103 (2014) 138e144
141
Fig. 4. a) Emission spectra of complexes formed between 5c and Al3þ, Naþ, Liþ, Mg2þ, Ca2þ, Fe3þ, Co2þ, Mn2þ, Zn2þand Cd2þ ions; b) Bar graph showing the change of emission
intensity of 5c at 531 nm when treated with various metal ions (max: 400 nm).
fluorescence of aluminum complex of 5,7-diphenyl-8-hydroxy
quinoline 1d (aryl substituent) is the reference of the series with
lF ¼ 535 nm since all the other ligands have either EW aryl groups
1aec or ED aryl groups 1eeh. Hence, substitution of EW aryl groups
at positions 5 and 7 of the quinoline ring shifted the fluorescence
maximum wavelength from 4 to 32 nm towards blue (hyp-
sochromic shift) relative to 5,7-diphenyl-8-hydroxyquinoline 1d as
in compounds 1aec. On the other hand, substitution of ED aryl
groups at positions 5 and 7 of the quinoline ring shifted the fluo-
rescence maximum wavelength from 5 to 32 nm towards red
(bathochromic shift) compared to 5,7-diphenyl-8-hydroxyquino
line 1d as in compounds 1eeh.
connecting the quinolinolate ligands with selected substituted aryl
moieties at C-5 and C-7. Ligand 5c shows high sensitivity towards
Al3þ in the presence of interference ions.
4. Experimental
4.1. General
Melting points were determined using Gallen-Kamp melting
point apparatus. NMR analysis (1H and 13C) were performed on a
Varian400 (VNMRS-400 MHz) spectrometer using CDCl3 solution
(referenced internally to Me4Si): J values are given in Hertz. IR
spectra were obtained with a Nicolet model Magna 560 spec-
trometer; absorption bands are recorded in wave number (cmꢀ1).
TLC was performed on dry silica gel plates and developed by using
hexane/ethyl acetate mixture as the eluent. Mass spectra were
obtained using Quattro Ultima Pt tandem quadruple mass spec-
trometer (Waters Corp. MA, USA) instrument. UVeVis spectra were
performed on Varian CARY 50 spectrophotometer. Fluorescence
spectra were recorded on a Perkin Elmer LS55 Luminescence
spectrophotometer.
Furthermore, close inspection of the data in Table 1 reveals that
the fluorescence quantum yield (fF) and lifetime (sF) of complexes
1aeh depend on the electronic properties of the substituted aryl
moieties connected to C-5 and C-7 of 8-HQ. For instance, the
fluorescence quantum yield of the eight complexes has increased
significantly relative to the parent 8-HQ from 11% in the case of 1h
to 462% for 1a. In addition, the fluorescence quantum yield and
lifetime decrease when the aryl groups are substituted with
electron-donating groups for complexes 1eeh, whereas electron-
withdrawing entities as in complexes 1aec lead to an increase in
both the fluorescence quantum yield and lifetime when compared
with non-substituted aryl group (complex 1d).
All reagents and solvents were purchased from SigmaeAldrich
and were used without further purification.
To examine the detection selectivity of the prepared ligands
4.2. Synthesis of 5,7-dibromo-8-hydroxyquinoline (2)
towards Al3þ, the response of ions such as Naþ, Liþ, Mg2þ, Ca2þ
,
Fe3þ, Co2þ, Mn2þ, Zn2þand Cd2þ was investigated for compound 5c.
The results are shown in Fig. 4. 5c itself exhibits weak fluorescence
A solution of bromine (8.79 g, 55.2 mmol) in acetic acid (25 mL)
was added over
5 min with stirring to a solution of 8-
in methanol. However, treatment with Al3þ (10
mM) resulted in a
hydroxyquinoline (4.00 g, 27.6 mmol) in acetic acid (25 mL). After
stirring at room temperature for further 15 min, 300 mL of cold
water was added to the mixture followed by 2 g of sodium meta-
bisulfite. The crude product was filtered and recrystallized from
ethanol to give the title compound as white solid (6.30 g, 75.4%),
significant increase in fluorescence intensify at 531 nm upon
excitation at 400 nm. No such effect was observed when other ions
(100 mM) were used. Therefore, 5c and possibly the other ligands
exhibit selectivity for Al3þ over other metal ions. In addition, using
5c, we obtained a detection limit for Al3þ of 0.11 ppb.
Mp: 198.2e199.4 ꢂC. IR (KBr) nmax in cmꢀ1: 3325, 3080, 1581 cmꢀ1
.
1H NMR (400 MHz, CDCl3):
J ¼ 8.6 Hz, 1H), 7.92 (s, 1H), 8.46 (dd, J ¼ 1.4, J ¼ 8.6 Hz,1H), 8.81 (dd,
(ppm) 105.60,
d
(ppm) 7.26 (s, 1H), 7.58 (dd, J ¼ 4.3,
3. Conclusion
J ¼ 1.4, J ¼ 4.3 Hz, 1H). dC (100.4 MHz, CDCl3):
d
110.54,123.42,127.70, 134.23, 136.52, 139.04,149.62,150.09. ESI-MS
In summary, starting from 8-hydroxyquinoline, we have syn-
(M)þ calcd for C9H5Br2NO:302.95, found:302.74.
thesized
a
series of 5,7-disubstituted tris(8-quinolinolate)
aluminum (III) complexes containing EW/ED groups connected via
aryl spacer groups. We have demonstrated that the emission color
and fluorescence quantum yield of the produced complexes influ-
enced by the electronic environment of the aryl substituents. The
spectroscopic measurements of the new AlQ3 complexes demon-
strate clearly the possibility of tuning their emission color by
4.3. Synthesis of 8-benzyloxy-5,7-dibromoquinoline (3)
A mixture of 5,7-dibromo-8-hydroxyquinoline (2) (5.00 g,
16.5 mmol), benzyl chloride (2.50 g, 19.8 mmol), potassium car-
bonate (3.70 g, 26.7 mmol) and potassium iodide (0.13 g,

142
S.N. Al-Busafi et al. / Dyes and Pigments 103 (2014) 138e144
0.78 mmol) in acetone (60 mL) was refluxed under N2 for 10 h. The
reaction mixture was poured into ice water, filtered and washed
with water. The crude product was recrystallized from ethanol/
water and dried under vacuum to yield white to green solid (3.5 g,
54.0%), Mp.: 114.5e116.5 ꢂC. IR (KBr) nmax in cmꢀ1: 3100, 1574, 1366.
134.18, 134.78, 136.40, 137.13, 137.47, 143.53, 149.92, 151.31. ESI-MS
(M þ H)þ calcd for C28H19Cl2NO: 456.36, found: 456.29.
4.4.4. Synthesis of 5,7-diphenyl-8-benzyloxyquinoline (4d)
The specific amount of chemical used is: Phenylboronic acid
(2.47 g, 16.8 mmol). The crude product was extracted with benzene,
recrystallized from ethanol, and dried under vacuum to give 4d
(2.37 g, 80.1%) as a brown solid. Mp.: 122.5e122.8 ꢂC. IR (KBr) nmax
1H NMR (400 MHz, CDCl3):
d
(ppm) 8.98 (dd, J ¼ 1.2, J ¼ 4.1 Hz, 1H),
8.47 (dd, J ¼ 1.2, J ¼ 8.5 Hz, 1H), 7.61 (d, J ¼ 8.4 Hz, 1H), 7.5 (dd,
J ¼ 4.1, J ¼ 8.5 Hz, 1H), 6.96 (d, J ¼ 8.4 Hz, 1H), 7.25e7.36 (m, 5H),
in cmꢀ1: 3019, 1353, 1210, 1073. 1H NMR (400 MHz, CDCl3):
d (ppm)
5.43 (s, 2H). dC (100.4 MHz, CDCl3):
d (ppm) 151.06, 122.3, 136.40,
128.75, 122.90, 134, 117.20, 152.73, 137.41, 116.70, 144.31, 128.47
(2C), 129.08, 128.60 (2C). ESI-MS (M)þ calcd for C16H11Br2NO:
393.10, found: 393.12.
5.18 (s, 2H), 7.40 (dd, J ¼ 4.0, J ¼ 8.0 Hz, 1H), 7.43e7.45 (m, 5H), 7.50
(m, 6H), 7.55 (s, 1H), 7.68 (m, 4H), 8.27 (dd, J ¼ 2.0, J ¼ 8.0 Hz, 1H),
9.02 (dd, J ¼ 4.0, J ¼ 2.0 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm)
76.34, 121.09, 127.29, 127.39, 127.61, 128.00 (2C), 128.14 (2C), 128.50
(4C), 129.70, 129.72, 129.97 (2C), 130.13 (2C), 133.92, 134.48, 135.95,
137.45, 138.14, 139.22, 143.60, 149.75, 151.11. ESI-MS (M þ H)þ calcd
for C28H21NO: 387.47, found: 388.04.
4.4. General procedure for the synthesis of compounds 4aeh
A mixture of 8-benzyloxy-5,7-dibromoquinoline (3) (3.00 g,
7.63 mmol), substituted phenylboronic acid (2.2 equiv), benzene
(30 mL), ethanol (12 mL), water (22 mL) and sodium carbonate
(3.70 g, 30.3 mmol) was degassed under nitrogen for 30 min. To the
mixture was added Pd(PPh3)4 (0.53 g, 0.46 mmol) and the reaction
was refluxed under nitrogen for 24 h.
4.4.5. Synthesis of 5,7-dinaphthyl-8-benzyloxyquinoline (4e)
The specific amount of chemical used is: 1-naphthalene boronic
acid (2.89 g, 16.8 mmol). The crude product was extracted with
benzene, recrystallized from ethanol, and dried under vacuum to
give 4e (2.49 g, 67.0%) as brown solid. Mp.: 179.1e182.2 ꢂC. IR (KBr)
nmax in cmꢀ1: 3010, 2870, 1590, 1219, 1095, 776. 1H NMR (400 MHz,
4.4.1. Synthesis of 5,7-bis(pyridin-4-yl)-8-benzyloxyquinoline (4a)
The specific amount of chemical used is: 4-Pyridinylboronic acid
(2.06 g,16.8 mmol). The crude product was extracted with benzene,
recrystallized from ethanol, and dried under vacuum to give 4a
(1.70 g, 55.6%) as a yellow powder. Mp.: 204.0e205.8 ꢂC. IR (KBr)
nmax in cmꢀ1: 3009, 2950, 1594, 1352, 745. 1H NMR (400 MHz,
CDCl3):
7.64 (s, 1H), 7.31 (m, 1H), 7.94 (dd, J ¼ 1.8, J ¼ 8.0 Hz 1H), 9.07 (dd,
(ppm) 76.76, 121.91,
d (ppm) 5.24 (s, 2H), 6.87e7.14 (m, 5H), 7.38e7.88 (m, 14H),
J ¼ 1.8, J ¼ 4.1 Hz, 1H). dC (100.4 MHz, CDCl3):
d
125.77, 125.26e128.19, 126.48, 128.89, 127.37, 127.81e128.38 (6C),
135.08, 135.08, 137.53, 143.36, 149.88. ESI-MS (M þ H)þ calcd for
CDCl3):
d
(ppm) 5.53 (s, 2H), 7.07 (m, 2H), 7.19 (m, 2H), 7.35e7.42
C36H25NO: 487.59, found: 488.37.
(m, 5H), 7.52 (m, 1H), 7.65 (s, 1H), 7.67 (m, 2H), 8.11 (dd, J ¼ 1.2,
J ¼ 8.3 Hz, 1H), 8.74 (m, 2H), 8.98 (dd, J ¼ 1.2, 4.0 Hz, 1H). dC
4.4.6. Synthesis of 5,7-bis(p-tert-butylphenyl)-8-
benzyloxyquinoline (4f)
(100.4 MHz, CDCl3):
d (ppm) 74.05, 116.53, 121.83, 124.80 (2C),
126.65, 127.69, 128.15 (2C), 128.34 (2C), 128.65 (2C), 129.89, 131.21,
133.96, 134.73, 137.16, 143.66, 145.83, 149.61, 150.14 (2C), 150.24
(2C), 152.72. ESI-MS (M þ H)þ calcd for C26H19N3O: 389.15, found:
390.28.
The specific amount of chemical used is: 4-tert-butylphe-
nylboronic acid (2.99 g, 16.8 mmol). The crude product was
extracted with benzene, recrystallized from ethanol, and dried
under vacuum to give 4f (3.40 g, 89.2%) as an orange powder. Mp.:
149.0e149.2 ꢂC. IR (KBr) nmax in cmꢀ1: 3010, 2830, 1637, 1368, 756.
4.4.2. Synthesis of 5,7-bis(p-nitrophenyl)-8-benzyloxyquinoline (4b)
The specific amount of chemical used is: 4-nitrophenyl boronic
acid (2.23 g, 16.8 mmol). The crude product was extracted with
benzene, recrystallized from ethanol, and dried under vacuum to
give 4b (2.63 g, 82.5%) as a tan powder. Mp.: 162.1e163.8 ꢂC. IR
(KBr) nmax in cmꢀ1: 3010, 2977, 1595, 1346, 845. 1H NMR (400 MHz,
1H NMR (400 MHz, CDCl3):
d (ppm) 1.40 (s, 9H), 1.41 (s, 9H), 5.18 (s,
2H), 7.18e7.21 (m, 5H), 7.37 (dd, J ¼ 4.0, J ¼ 8.4 Hz, 1H), 7.44 (d,
J ¼ 8.4 Hz, 2H), 7.45 (d, J ¼ 8.4 Hz, 2H), 7.52 (d, J ¼ 8.4 Hz, 2H), 7.58
(s, 1H), 7.61 (d, J ¼ 8.4 Hz, 2H), 8.32 (dd, J ¼ 1.6, J ¼ 8.4 Hz, 1H), 9.01
(dd, J ¼ 1.6, J ¼ 4.0 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm) 31.45
(6C), 34.63, 34.67, 76.47, 120.84, 125.03 (2C), 125.41 (2C), 127.27,
127.54, 127.91 (2C), 128.61 (2C), 129.68 (2C), 129.81 (2C), 133.92,
134.63 (2c), 135.27, 135.82, 136.34, 137.63, 143.70, 149.63, 150.30,
150.48, 151.14. ESI-MS (M þ H)þ calcd for C36H37NO: 499.69, found:
500.30.
CDCl3):
d
(ppm) 5.54 (s, 2H), 7.08 (m, 5H), 7.44 (dd, J ¼ 4.4,
J ¼ 8.4 Hz,1H), 7.62 (d, J ¼ 8.4 Hz, 2H), 7.67 (s,1H), 7.68 (d, J ¼ 8.4 Hz,
2H), 8.08 (dd, J ¼ 1.6, J ¼ 8.8 Hz,1H), 8.20 (m, 2H), 8.35 (d, J ¼ 8.4 Hz,
2H), 9.00 (dd, J ¼ 1.6, J ¼ 4.4 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm)
76.57, 116.49, 121.89, 122.30, 123.23, 123.86 (2C), 126.84, 128.09e
128.52 (5C), 128.66 (2C), 128.78 (2C), 130.82 (2C), 131.42, 134.24,
137.13, 144.43, 144.62, 145.46, 150.06, 150.37, 152.78. ESI-MS
(M þ H)þ calcd for C28H19N3O5: 477.47, found: 477.85.
4.4.7. Synthesis of 5,7-bis(p-methoxyphenyl)-8-benzyloxyquinoline
(4g)
The specific amount of chemical used is: 4-methoxy
phenylboronic acid (2.55 g, 16.8 mmol). The crude product was
extracted with benzene, recrystallized from ethanol, and dried
under vacuum to give 4g (2.40 g, 70.3%) as a pale yellow solid. Mp.:
147.1e147.9 ꢂC. IR (KBr) nmax in cmꢀ1: 3019,1609, 1351, 1026, 723, 1H
4.4.3. Synthesis of 5,7-bis(p-chlorophenyl)-8-benzyloxyquinoline (4c)
The specific amount of chemical used is: 4-chloro-phenyl
boronic acid (2.63 g, 16.8 mmol). The crude product was extracted
with benzene, recrystallized from ethanol, and dried under vacuum
to give 4c (1.80 g, 50.2%) as an orange powder. Mp.: 119.1e121.2 ꢂC.
IR (KBr) nmax in cmꢀ1: 3009, 2967, 1637, 1343, 787. 1H NMR
NMR (400 MHz, CDCl3):
d (ppm) 3.87 (s, 3H), 3.89 (s, 3H), 5.17 (s,
2H), 6.99 (d, J ¼ 8.8 Hz, 2H), 7.05 (d, J ¼ 8.8 Hz, 2H), 7.24e7.30 (m,
5H), 7.36 (dd, J ¼ 4.4, J ¼ 8.4 Hz, 1H) 7.42 (d, J ¼ 8.8 Hz, 2H), 7.53 (s,
1H), 7.66 (d, J ¼ 8.8 Hz, 2H), 8.27 (dd, J ¼ 1.8, J ¼ 8.4 Hz,1H), 9.01 (dd,
(400 MHz, CDCl3):
d (ppm) 5.23 (s, 2H), 7.20 (m, 5H), 7.36 (m, 1H),
7.38 (d, J ¼ 8.4 Hz, 2H), 7.41 (d, J ¼ 8.4 Hz, 2H), 7.44 (s, 1H), 7.48 (d,
J ¼ 1.8, J ¼ 4.4 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm) 55.34, 55.43,
J ¼ 8.4 Hz, 2H), 7.55 (d, J ¼ 8.4 Hz, 2H), 8.19 (dd, J ¼ 1.6, J ¼ 8.6 Hz,
76.13, 113.95 (2C), 114.05 (2C), 120.84, 127.22, 128.03 (2C), 128.54
(2C), 129.59, 129.62, 130.56, 131.14, 131.20 (2C), 134.52 (2C), 134.86,
135.63, 137.61, 141.73, 149.70, 150.70, 159.04, 159.17. ESI-MS
(M þ H)þ calcd for C30H25NO3: 447.52, found: 448.38.
1H), 9.03 (dd, J ¼ 1.6, J ¼ 4.4 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm)
76.21, 121.40, 127.35, 127.79, 128.05 (2C), 128.30 (2C), 128.55 (2C),
128.76 (2C), 129.18, 131.25 (2C), 131.34 (2C), 132.77, 133.45, 133.84,

S.N. Al-Busafi et al. / Dyes and Pigments 103 (2014) 138e144
143
4.4.8. Synthesis of 5,7-bis(p-dimethylaminophenyl)-8-benzyloxy
quinoline (4h)
4.5.4. Synthesis of 5,7-diphenyl-8-hydroxyquinoline (5d)
The specific amount of chemicals used are: 5,7-diphenyl-8-
benzyloxyquinoline (4) (1.0 g, 2.58 mmol), Pd/C (0.794 g), cyclo-
hexa-1,4-diene (1.85 g, 23.0 mmol), and ethanol (25.2 mL). The
crude product was filtered and recrystallized from ethanol/water
and dried under vacuum to give 5d (0.511 g, 66.7%) as light yellow
crystals. Mp.: 136.1e136.5 ꢂC. IR (KBr) nmax in cmꢀ1: 3315, 3033,
The specific amount of chemical used is: 4-(dimethylamino)
phenylboronic acid (2.77 g, 16.8 mmol). The crude product was
extracted with benzene, recrystallized from ethanol, and dried
under vacuum to give 4h (1.98 g, 54.7%) as light yellow powder.
Mp.: 159.1e159.6 ꢂC. IR (KBr) nmax in cmꢀ1: 3012, 2967, 1521, 1086.
1H NMR (400 MHz, CDCl3):
d
(ppm) 3.013 (s, 6H), 3.014 (s, 6H), 5.48
1638, 1371. 1H NMR (400 MHz, CDCl3):
d (ppm) 7.39e7.43 (m. 2H),
(s, 2H), 6.79e6.87 (m, 4H), 7.31 (dd, J ¼ 4.0, J ¼ 8.0 Hz, 1H), 7.06e
7.47 (dd, J ¼ 4.0, 8.8 Hz, 1H), 7.49e7.55 (m, 6H), 7.67 (s, 1H), 7.89 (m,
7.24 (m, 5 H), 7.56 (s, 1H), 7.66 (m, 4H), 8.31 (dd, J ¼ 2.0, J ¼ 8.0 Hz,
2H), 8.31 (dd, J ¼ 1.6, 8.8 Hz, 1H), 8.83 (dd, J ¼ 1.6, 4.0 Hz, 1H). dC
1H), 8.96 (dd, J ¼ 2.0, J ¼ 4.0 Hz, 1H). dC (100.4 MHz, CDCl3):
d
(ppm)
(100.4 MHz, CDCl3): d (ppm) 121.68, 122.25, 125.88, 127.33, 127.36,
40.53 (2C), 40.62 (2C), 75.75,112.23 (2C),112.33 (2C), 121.20,126.71,
127.35 (2C), 127.46e128.31 (5C), 128.05, 130.91e130.60 (4C), 132.87,
134.64, 137.19, 140.62, 148.99, 149.77, 153.12 (2C). ESI-MS (M þ H)þ
calcd for C32H31N3O: 473.61, found: 474.41.
128.45 (2C), 128.58 (2C), 129.42 (2C), 129.97, 130.14, 130.72, 134.62,
137.60, 138.69, 139.30, 147.91, 148.23. ESI-MS (M þ H)þ calcd for
C21H15NO: 297.35, found: 298.06.
4.5.5. Synthesis of 5,7-dinaphthyl-8-hydroxyquinoline (5e)
4.5. General procedure for the synthesis of compounds 5aeh
The specific amount of chemicals used are: 5,7-dinaphthyl-8-
benzyloxyquinoline (8) (1.01 g, 2.05 mmol), Pd/C (0.63 g), cyclo-
hexa-1,4-diene (1.47 g, 18.2 mmol), and ethanol (20.0 mL). The
crude product was recrystallized from ethanol/water and dried
under vacuum to give 5e (0.57 g, 70.2%) as gold crystals. Mp.:
202.2e203.6 ꢂC. IR (KBr) nmax in cmꢀ1: 3433, 3046, 1631, 1193. 1H
A mixture of compound 4e11, Pd/C (10 wt%), cyclohexa-1,4-
diene, and absolute ethanol was refluxed under N2 for 5 h. The
mixture was filtered, and ethanol was evaporated under vacuum.
4.5.1. Synthesis of 5,7-bis(pyridin-4-yl)-8-hydroxyquinoline (5a)
The specific amount of chemicals used are: 5,7-bis(pyridin-4-
yl)-8-benzyloxyquinoline (11) (1.01 g, 2.57 mmol), Pd/C (0.79 g),
cyclohexa-1,4-diene (1.84 g, 22.8 mmol), and ethanol (25.0 mL). The
crude product was recrystallized from ethanol/water and dried
under vacuum to give 5a (0.512 g, 61.2%) as orange solid. Mp.:
p134.6e134.9 ꢂC. IR (KBr) nmax in cmꢀ1: 3409, 1508, 1334, 1257. 1H
NMR (400 MHz, CDCl3):
d (ppm) 7.46e7.62 (m, 7H), 7.91e7.96 (m,
7H), 7.34 (m, 1H), 7.64 (s, 1H), 7.84 (m, 1H), 8.86 (d, J ¼ 4.1 Hz,1H). dC
(100.4 MHz, CDCl3):
d (ppm) 121.80, 126.02, 128.03e128.55 (24C),
135.23, 148.09, 149.00. ESI-MS (M)þ calcd for C29H19NO: 397.47,
found: 397.99.
NMR (400 MHz, CDCl3):
d
(ppm) 7.38 (d, J ¼ 8.0 Hz, 2H), 7.77 (s, 1H),
4.5.6. Synthesis of 5,7-bis(p-tert-butylphenyl)-8-hydroxyquinoline
(5f)
7.78 (dd, J ¼ 4.4, 8.8 Hz, 1H), 7.79 (d, J ¼ 8.0 Hz, 2H), 8.06 (d,
J ¼ 6.8 Hz, 2H), 8.64 (dd, J ¼ 1.2, 8.6 Hz, 1H), 8.86 (d, J ¼ 6.8 Hz, 2H),
The specific amount of chemicals used are: 5,7-bis(p-tert-
butylphenyl)-8-benzyloxyquinoline (6) (1.50 g, 3.00 mmol), Pd/C
(0.92 g), cyclohexa-1,4-diene (2.15 g, 26.6 mmol), and ethanol
(22.0 mL). The crude product was recrystallized from ethanol/
water and dried under vacuum to give 5f (0.670 g, 65.1%) as linen
crystals. Mp.: 138.6e139.8 ꢂC. IR (KBr) nmax in cmꢀ1: 3489, 2954,
8.99 (dd, J ¼ 1.2, 4.4 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm) 111.92,
122.88, 125.51, 126.51, 126.98 (4C), 131.02, 133.89, 135.94, 136.14,
143.71 (4C), 147.16, 153.90, 154.40. ESI-MS (M þ H)þ calcd for
C
16H13N3O: 299.33, found: 300.02.
1637, 1361. 1H NMR (400 MHz, CDCl3):
d (ppm) 1.39 (s, 9H), 1.41
4.5.2. Synthesis of 5,7-bis(p-nitrophenyl)-8-hydroxyquinoline (5b)
The specific amount of chemicals used are: 5,7-bis(p-nitro-
phenyl)-8-benzyloxyquinoline (10) (1.02 g, 2.09 mmol), Pd/C
(0.64 g), cyclohexa-1,4-diene (1.50 g, 18.6 mmol), and ethanol
(20.4 mL). The crude product was recrystallized from ethanol/water
and dried under vacuum to give 5b (0.50 g, 61.7%) as brown solid.
Mp.: 122.2e122.5 ꢂC. IR (KBr) nmax in cmꢀ1: 3468, 3061, 1482, 1230.
(s, 9H), 7.39 (dd, J ¼ 4.4, 8.4 Hz, 1H), 7.42 (d, J ¼ 8.4 Hz, 2H), 7.52
(m, 4H), 7.66 (s, 1H), 7.80 (d, J ¼ 8.4 Hz, 2H), 8.35 (dd, J ¼ 1.2,
8.4 Hz, 1H), 8.81 (dd, J ¼ 1.2, 4.4 Hz, 1H). dC (100.4 MHz, CDCl3):
d
(ppm) 31.37 (3C), 31.43 (3C), 34.60, 34.63, 121.40, 122.13,
125.38 (2C), 125.43 (2C), 125.80, 128.97 (2C), 129.75 (2C), 129.89,
130.54, 134.63, 134.77, 136.34, 138.70, 147.75, 147.92, 150.13,
150.22. ESI-MS (M þ H)þ calcd for C29H31NO: 409.56, found:
410.23.
1H NMR (400 MHz, CDCl3):
(m, 1H), 7.38 (m, 2H), 7.62 (s, 1H), 7.68 (m, 2H), 8.30 (m, 1H), 8.95 (d,
(ppm) 115.0 (2C), 121.89,
d (ppm) 6.81 (m, 2H), 7.21 (m, 2H), 7.34
J ¼ 2.8 Hz, 1H). dC (100.4 MHz, CDCl3):
d
128.35, 128.64 (2C), 128.72 (2C), 130.42, 130.78 (2C), 131.95, 134.13,
138.01, 138.28, 1441.01, 144.66, 148.27, 148.91, 150.28. ESI-MS
(M þ H)þ calcd for C21H13N3O5: 387.35, found: 388.18.
4.5.7. Synthesis of 5,7-bis(p-methoxyphenyl)-8-hydroxyquinoline
(5g)
The specific amount of chemicals used are: 5,7-bis(p-methox-
yphenyl)-8-benzyloxyquinoline (5) (1.0 g, 2.23 mmol), Pd/C
(0.70 g), cyclohexa-1,4-diene (1.60 g, 20.0 mmol), and ethanol
(22.0 mL). The crude product was recrystallized from ethanol/
water and dried under vacuum to give 5g (0.689 g, 54.0%) as or-
ange crystals. Mp.: 118.2e119.3 ꢂC. IR (KBr) nmax in cmꢀ1: 3352,
4.5.3. Synthesis of 5,7-bis(p-chlorophenyl)-8-hydroxyquinoline (5c)
The specific amount of chemicals used are: 5,7-bis(p-chlor-
ophenyl)-8-benzyloxyquinoline (9) (1.01 g, 2.19 mmol), Pd/C
(0.67 g), cyclohexa-1,4-diene (1.57 g, 19.5 mmol), and ethanol
(21.4 mL). The crude product was recrystallized from ethanol/water
and dried under vacuum to give 5c (0.720 g, 89.7%) as yellow
crystals. Mp.: 168.1e168.5 ꢂC. IR (KBr) nmax in cmꢀ1: 3415, 1538,
3015, 1635, 1266. 1H NMR (400 MHz, CDCl3):
d (ppm) 3.87 (s, 3H),
3.89 (s, 3H), 7.03 (d, J ¼ 8.8 Hz, 2H), 7.05 (d, J ¼ 8.8 Hz, 2H), 7.37
(dd, J ¼ 4.0, 8.4 Hz, 1H), 7.41 (d, J ¼ 8.8 Hz, 2H), 7.58 (s, 1H), 7.80 (d,
J ¼ 8.8 Hz, 2H), 8.27 (dd, J ¼ 1.2, 8.4 Hz, 1H), 8.78 (dd, J ¼ 1.2,
1381. 1H NMR (400 MHz, CDCl3):
d (ppm) 7.39 (m, 1H), 7.44 (m, 2H),
7.53 (m, 2H), 7.70 (d, J ¼ 8.8 Hz, 2H), 7.74 (d, J ¼ 7.2 Hz, 2H), 7.83 (s,
1H), 8.90 (d, J ¼ 8.0 Hz, 1H), 9.03 (m, 1H). dC (100.4 MHz, CDCl3):
4.0 Hz, 1H). dC (100.4 MHz, CDCl3):
d (ppm) 55.34, 55.39, 113.90
d
(ppm) 120.35, 128.52, 128.69 (2C), 129.10 (2C), 129.85, 130.11 (2C),
(2C), 113.97 (2C), 121.34, 121.89, 125.76, 129.64, 129.99, 130.29,
130.50 (2C), 131.13 (2C), 131.70, 134.63, 138.70, 147.62, 147.78,
158.89, 158.99. ESI-MS (M)þ calcd for C23H19NO3: 357.40, found:
357.40.
131.22 (2C), 132.77, 133.59, 134.05, 134.43, 134.69, 141.70, 141.84,
144.81 (2C), 144.93. ESI-MS (M)þ calcd for C21H13Cl2NO: 366.24,
found: 366.18.

144
S.N. Al-Busafi et al. / Dyes and Pigments 103 (2014) 138e144
4.5.8. Synthesis of 5,7-bis(p-dimethylaminophenyl)-8-
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1353. 1H NMR (400 MHz, CDCl3):
d (ppm) 3.02 (s, 12H), 6.84 (d,
J ¼ 8.8 Hz, 2H), 7.20 (d, J ¼ 7.8 Hz, 2H), 7.25 (s,1H), 7.32 (d, J ¼ 8.8 Hz,
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We acknowledge, with thanks, financial support from the Sultan
Qaboos University (Grant #: IG/SCI/CHEM/09/05).
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