Fused Alq3 derivatives: Syntheses and photophysical characteristics

Article abstract of DOI:10.1039/c1jm12424b

Three new tetracyclic 8-hydroxyquinoline derivatives were synthesized by using a Pd catalyzed intramolecular direct arylation reaction in a key step. Furthermore, the new compounds were used as ligands in aluminium complexes and their photophysical proper

Full text of DOI:10.1039/c1jm12424b

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PAPER
Fused Alq3 derivatives: syntheses and photophysical characteristics†
a
Juha P. Heiskanen, Antti E. Tolkki,a Helge J. Lemmetyinena and Osmo E. O. Hormib
*
Received 30th May 2011, Accepted 18th July 2011
DOI: 10.1039/c1jm12424b
Three new tetracyclic 8-hydroxyquinoline derivatives were synthesized by using a Pd catalyzed
intramolecular direct arylation reaction in a key step. Furthermore, the new compounds were used as
ligands in aluminium complexes and their photophysical properties were studied in detail both in
solution and solid state by using absorption, steady-state, and time resolved fluorescence
spectroscopies. Results show especially that the aluminium complex of 11H-indolo[3,2-c]quinolin-4-ol
has the most blue-shifted emission maximum among the Alq3 derivatives to date and CIE chromaticity
coordinates locate on the deep blue area (0.16, 0.12). Moreover, the fluorescence quantum yield of this
compound is 3.1–3.5 times higher compared with the parent Alq3. Photophysical properties of the
complex did not show major differences between the solution and the solid states. The lack of melting
endotherm in DSC analysis indicates that the compound is amorphous. Based on the results, 11H-
indolo[3,2-c]quinolin-4-ol has promising features to be applied as a ligand for aluminium or other metal
ions in different applications.
molecular orbital (HOMO) on the phenoxide side.5 This obser-
1. Introduction
vation has been a key in the development of new derivatives with
8-Hydroxyquinoline is a bidentate ligand, which forms complexes
tailored photophysical properties. It has been experimentally
effectively with various metal ions. Tris-(8-hydroxyquinoline)
shown that emission properties can be effectively and systemat-
aluminium (Alq3) (Fig. 1) is a fluorescent octahedral complex
ically tuned by substituting either the 4-position or the 5-position
compound, which was used as a combined electron transport and
of the quinoline ring.6 In very recent studies, it has been shown
emitter layer in organic light emitting diode (OLED) devices for
that an amorphous tris-(4-piperidinyl-8-hydroxyquinoline)
the first time by Tang and VanSlyke in 1987.1 Since that, the
aluminium (Fig. 1) works as a superior emitting material in
parent Alq3 has become a standard material in OLED devices.
OLED devices and tris-(5-fluoro-8-hydroxyquinoline)aluminium
The parent Alq3 has also found an important role in the device
can increase device efficiency considerably when it is used as an
architectures of organic solar cells. It has been used as an effective
electron transport material in the Si-anode based OLED.7
buffer layer to prohibit undesired cathode diffusion from a metal
Substituting a polymerizable unit to 8-hydroxyquinoline
cathode to an organic layer and to increase the lifetime of devices
allows the incorporation of a Alq3 derivative into the polymer
by preventing penetration of oxygen and moisture.2 Moreover,
doping of Alq3 in either the donor or acceptor layer has been
observed to improve organic photovoltaic (OPV) cell perfor-
mance by increasing e.g. the power conversion efficiency.3 The
parent Alq3 has also been shown to work as a host material in an
organic solar concentrator in which Alq3 provides a polar envi-
ronment for a highly polar excited state of the dye molecule thus
reducing concentration quenching.4
Theoretical studies have shown that the lowest unoccupied
molecular orbital (LUMO) of the parent Alq3 is located mainly
on the pyridyl side of the organic ligand and the highest occupied
aDepartment of Chemistry and Bioengineering, Tampere University of
Technology, P.O. Box 541, FI-33101 Tampere, Finland. E-mail: juha.
heiskanen@tut.fi
bDepartment of Chemistry, University of Oulu, P.O. Box 3000, FI-90014,
Finland
† Electronic supplementary information (ESI) available: 1H and 13C
NMR spectra, HRMS data, TCSPC data and equations. See DOI:
10.1039/c1jm12424b
Fig. 1 8-Hydroxyquinoline and its derivatives as chelating ligands.
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aluminium and spectroscopic properties of the resulting Alq3
derivatives were studied in detail both in solution and solid state
by using absorption, steady-state, and time resolved fluorescence
spectroscopy. Especially, tris-(11H-indolo[3,2-c]quinolin-4-ol)
aluminium showed interesting properties compared with the
parent Alq3: three times higher photoluminescence quantum
yield and deep blue emission with CIE (Commission inter-
Scheme 1 Intramolecular Pd-catalyzed C-C bond formation
ꢀ
nationale de l’eclairage) coordinates (0.16, 0.12). This is the most
blue-shifted emission among the Alq3 derivatives so far and the
differential scanning calorimetry (DSC) data indicate that the
complex is amorphous. These properties make the Alq3 deriva-
tive and the synthesized ligand itself especially interesting for
different applications e.g. blue emission utilizing full-color
display and lighting applications.
backbone and emission properties of that Alq3-functionalized
polymer can be tuned by alternating the substituents in the 8-
hydroxyquinoline ligand (Fig. 1).8 Polymers with 8-hydroxy-
quinoline side chains can also complex boron in addition to
aluminium.9 Such boron quinolate-functionalized copolymers
have shown excellent emission properties and high electron
mobilities.9b A slightly different approach utilizes poly(bromo-p-
tert-butylphenylborylstyrene) to complex 8-hydroxyquinoline
(Fig. 1) and its derivatives.10 This methodology allows tuning the
chemical, physical, and photophysical properties simply by
varying the chelating 8-hydroxyquinoline ligand.
2. Results and discussion
2.1 Syntheses
4-Chloro-8-hydroxyquinoline 1 (Scheme 2) was synthesized by
using a previously reported method.13 On the first reaction step,
the hydroxyl group was protected with the benzyl group by
reacting compound 1 with benzyl bromide. 8-(Benzyloxy)-4-
chloroquinoline 2 was collected in good yield (82%) after flash
chromatography.
Also other highly versatile application possibilities have
increased researchers’ interest to apply 8-hydroxyquinoline and
develop synthetic methods to produce its new derivatives. Those
applications cover for example near-infrared emitting tris-(8-
hydroxyquinoline)lanthanide-functionalized mesoporous silica
materials as well as N,N0-bis((8-hydroxy-7-quinolinyl)methyl)-
1,10-diaza-18-crown-6 ether (Fig. 1) and its substituted deriva-
tives, which can be used as fluorescent chemosensors for different
divalent metal ions such as magnesium.11 Experimental research
including design and synthesis of new compounds is essential in
order to obtain exact knowledge about luminescence and other
photophysical properties of the compounds, because theoretical
methods often give just rough estimations or trends.12
In the literature, Fisher indole synthesis and ligand free Pd-
catalyzed arylation have been used to construct the 11H-indol
[3,2-c]quinoline skeleton.14 Both methods gave the desired
products in relatively low yields. Far more efficient method has
been presented lately by Maes et al.15 In their method, intermo-
lecular amination and intramolecular arylation are carried out by
using auto-tandem catalysis and product yields varying from
moderate to high (52–82%). Our synthetic protocol applies the
solvent free amination reaction and Pd-catalyzed direct arylation
method. Amination was performed by heating compound 2 in 2-
bromoaniline for 17 h. Pd-catalyzed intramolecular direct ary-
lation was done by using Pd(OAc)2 as a palladium source for the
In this paper, we present a novel strategy to synthesize new
tetracyclic 8-hydroxyquinoline derivatives by using a Pd-cata-
lyzed direct arylation in a key reaction step (Scheme 1). These
new 8-hydroxyquinoline derivatives were applied as ligands for
Scheme 2 Reagents and conditions: (a) (i) K2CO3 (2 equiv), DMF rt, 10 min; (ii) BnBr (1.1 equiv), rt, 18 h; (b) (i) 2-bromoaniline (10 equiv) 135 ꢀC, 17 h;
(ii) NaOH (aq) (3 equiv), acetone, reflux, 10 min; (iii) Pd(OAc) (5 mol%), PCy3-HBF4 (10 mol%), anhydrous K2CO3 (2.5 equiv), DMA 160 ꢀC, 3 h; (c)
Pd–C (10 wt%), H2, ethanol, reflux, 5 h; (d) (i) 2-bromo-N-methylbenzylamine (6.25 equiv) 135 ꢀC, 17 h; (ii) HCl (aq); (iii) NaOH (aq) (2 equiv), reflux,
15 min; (iv) TsCl (1 equiv), acetone rt, 1 h; (e) Pd(OAc) (10 mol%), PCy3-HBF4 (20 mol%), anhydrous K2CO3 (2.5 equiv), DMA 160 ꢀC, 4 h; (f) (i) NaOH
(aq) (5 equiv), ethanol, reflux, 21/2 h; (ii) HCl (aq).
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Scheme 3 Reagents and conditions: (a) (i) NaH (1.7 equiv), DMF rt, 5 min; (ii) 2-bromobenzyl bromide (1.5 equiv), rt, 24 h; (b) Pd(OAc) (5 mol%),
PCy3-HBF4 (10 mol%), anhydrous K2CO3 (2.5 equiv), DMA 160 ꢀC, 3 h; (c) (i) NaOH (aq) (3 equiv), ethanol/acetone, reflux, 21/2 h; (ii) HCl (aq).
catalysis. Air stable tricyclohexylphosphine tetrafluoroborate
(PCy3-HBF4) was used as a ligand and anhydrous K2CO3 as
a base. The same catalyst system has successfully been used in
various direct arylation reactions earlier by Fagnou et al.16
Reaction was monitored by thin layer chromatography (TLC)
analysis and it was observed that the use of 5 mol% catalyst
loading of Pd(OAc)2 gave total conversion of the starting
material within three hours.17 As a noteworthy observation, it
must be mentioned that it was necessary to protect the 8-
hydroxyl group before direct arylation reaction. Product
formation could not be observed when direct arylation was tried
right away after amination of compound 1. The tetracyclic
quinoline derivative 4-benzyloxy-11H-indol[3,2-c]quinoline 3
was collected in high yield (93%). Pd catalyzed hydrogenolysis of
compound 3 was carried out by using standard Pd–C (10 wt%) in
ethanol under H2 atmosphere. The procedure gave the final
ligand 4 in excellent yield (94%).
2-bromobenzyl bromide gave product 9 in good yield (76%).
Direct arylation of compound 9 was performed by using the
same method as for compound 2. Tetracyclic quinoline deriva-
tive 10 was collected in good yield (87%). Deprotection of
compound 10 with NaOH gave ligand 11 in quantitative yield
(>99%).
Complexes 12–14 (Fig. 2) were synthesized by using a previ-
ously reported method.6a New Alq3 derivatives were isolated in
1
good to high yields (72–92%). H NMR spectra show that also
the new derivatives exist as their meridional isomers similarly as
the parent Alq3 in solution at room temperature.20
2.2 Photophysical properties in solution
Absorption and emission (photoluminescence) spectra in the
steady state for the parent Alq3 and its derivatives (12–14) in
solution are shown in Fig. 3. Because of different solubility
properties between the prepared complexes, compound 12 was
measured in ethanol and compounds 13 and 14 in chloroform.
Reference solutions of the parent Alq3 were prepared in both
solvents. Fluorescence lifetimes (s) and corresponding ampli-
tudes (A) were obtained by using the time correlated single
photon counting (TCSPC) method. Measuring the decay curves
at a wide range of wavelengths provides an alternative way to
determine the ratio of emitted and absorbed photons (i.e.
quantum yield) for each compound. s was assumed to be
constant at each monitoring wavelength and the amplitudes were
obtained from the fittings of the decay curves at each wavelength
Compound 5 (Scheme 2) was prepared from compound 1 by
performing solvent free amination and tosylation reactions
consecutively. Compound 5 was collected as a pure product in
moderate yield (50%). Direct arylation of compound 5 was
accomplished by using 10 mol% of Pd catalyst and compound 6
was collected in 55% yield. Finally, detosylation of compound 6
gave the desired ligand 7 in high yield (84%) by using NaOH as
a deprotection agent.
4-Hydroxy-8-tosyloxyquinoline18,19 8 (Scheme 3) is readily
available and can be used as a starting material in the synthesis of
ligand 11. Alkylation of compound 8 in the presence of NaH and
Fig. 2 The chemical structures of the fused Alq3 derivatives 12–14.
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Fig. 3 Normalized steady state spectra in diluted solutions: absorption and emission of the parent Alq3 and fused derivatives 13 and 14 in CHCl3 (a),
and the parent Alq3 and 12 in EtOH (b). Emission band features were independent of the excitation wavelength.
and corrected according to the detectors wavelength sensitivity.
The product of s and the corresponding amplitude was summed
throughout the measured range (SAs), which gives the quantum
yields referred to the parent Alq3. In the time resolved experi-
ment, transmittance (T ¼ 1 ꢁ 10ꢁAbs.) was not equal for all the
samples at the excitation wavelength of 340 nm. Thus, this was
taken into account in calculations. Measured lifetimes (Table 1)
for the parent Alq3 in CHCl3 and in ethanol are comparable with
the values reported in the literature.21 Absolute data, which were
used in the determination of relative quantum yields, are shown
in the ESI† together with the decay curves, decay associated
spectra and calculation procedures.
(0.11621) the absolute fluorescence quantum yield for 12 is 0.35
and the radiative fluorescence rate constants are 1.3 ꢂ 107 sꢁ1 and
4.6 ꢂ 107 sꢁ1 for Alq3 and 12, respectively. Simultaneously with
the increased radiative fluorescence rate the non-radiative rate
constant of 12 (8.3 ꢂ 107 sꢁ1) decreased compared with Alq3
(9.8 ꢂ 107 sꢁ1).
In terms of CIE chromaticity coordinates (0.16, 0.12),
compound 12 shows deep blue emission. To the best of our
knowledge, the observed 77 nm blue-shift is the largest among the
Alq3 derivatives so far.23 Previously, it has been theoretically
predicted that attachment of EDG on the 4-position of the
quinoline ring causes rise of LUMO level leading to a wider energy
gap, and thus causing the blue-shifted emission.5 LUMO also has
a notable coefficient at the 3-position.24 This can be the reason for
the exceptionally high blue-shift of compound 12, in which
a strong electron donating nitrogen part at the 4-position is also
fully conjugated to the 3-position. On the other hand, electron
donating nitrogen and oxygen parts at the 4-position in
compounds 13 and 14 are isolated from the phenyl part attached
on the 3-position, which can be considered as an electron neutral
substituent in terms of Hammett substituent constants.25 Thus the
phenyl part at the 3-position is likely to increase the conjugation of
the quinoline ring, but does not shift electron density from the
electron donating part at the 4-position in compounds 13 and 14.
For compound 13 in chloroform, the relative fluorescence
quantum yields obtained both in the steady state and by the time-
resolved method are much lower than the quantum yield of
the parent Alq3. Fluorescence maximum was only slightly
blue-shifted and fluorescence decay was two exponential with
Generally, increased degree of conjugation causes the bath-
ochromic effect.22 However, compounds 12–14 have blue-shifted
absorption maxima (i.e. hypsochromic effect) and increased
molar extinction coefficients (i.e. hyperchromic effect) compared
with those of Alq3. The strong electron donating group (EDG) at
the 4-position of the quinoline ring seems to have a major
contribution to the absorption profile instead of the extended
conjugation sphere caused by the attached phenyl ring at the
3-position.
Tris-(11H-indolo[3,2-c]quinolin-4-ol)aluminium 12 has in
ethanol 3.1–3.5 times higher fluorescence quantum yield (F) than
the parent Alq3. Fluorescence lifetime (s) is somewhat shorter
compared to that with Alq3. By using the relative fluorescence
quantum yields and measured fluorescence lifetimes in Table 1,
one can calculate that the radiative rate constant for 12 is 3.5
times higher than that for Alq3. In addition, taking into account
the absolute fluorescence quantum yield of Alq3 in ethanol
Table 1 Photophysical parameters of the parent Alq3 and fused derivatives in solution
Compound
labsa/nm
3b
lPLc/nm
FWHM/nm
Fd
Stokes’ shift/cmꢁ1
se/ns
SAs/(1 ꢁ T)f
CIE/(x, y)g
h
Alq3
378
385
362
379
7.6 ꢂ 103
5.9 ꢂ 103
1.5 ꢂ 104
2.9 ꢂ 104
519
522
442
499
117
116
81
1
1
3.06
0.14
7190
6820
5000
6350
8.99
16.63
7.76
9.73 (15%)
1.81 (85%)
11.76
1
1
3.47
0.34
(0.32, 0.51)
(0.33, 0.52)
(0.16, 0.12)
(0.25, 0.41)
i
Alq3
12h
13i
106
14i
362
1.9 ꢂ 104
478
92
1.45
6700
2.14
(0.18, 0.28)
a
b
Absorption maximum. Molar extinction coefficient. Photoluminescence maximum. Relative fluorescence quantum yield. (The absolute
c
d
e
f
fluorescence quantum yields for Alq3 in ethanol and chloroform are 0.116 and 0.223 respectively.21) Fluorescence lifetime. Relative fluorescence
quantum yield by the TCSPC experiment (A ¼ amplitude, T ¼ transmittance). CIE chromaticity coordinates. h In EtOH. i In CHCl3.
g
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in the industrial scale. It has also become the current trend in
organic light emitting diode and solar cell research.27 Thus, we
demonstrated deposition of the thin films of Alq3 derivatives on
the quartz substrate by using the spin coating technique. The first
set of films was spin coated from a diluted solution (0.1 mM) and
produced very weak absorption (Fig. 5a). Therefore, concen-
tration was increased to 1 mM and another set of films was
prepared. Reference film (9.5 nm) was made from the parent Alq3
by evaporating in high vacuum, because a spin coated film of the
parent Alq3 showed neither detectable absorption nor emission.
The results are shown in Fig. 5 and Table 2.
For an unknown reason, the thin film of compound 12 had
very weak absorption (Fig. 5a and c). However, emission
measurements yielded clear signals (Fig. 5b and d) corresponding
to the ones observed in solutions (Fig. 3b). Compound 13 in thin
film was invisible in all fluorescence measurements, despite
relatively high absorbance of the layer (Fig. 5c). Fluorescence
lifetimes in the solid state, when excited at 340 nm, were resolved
only for the parent Alq3 and compound 12. Decays were fitted
with the two-exponential model. The appearance of the fast
component can be attributed to solid state interaction between
the molecules, which is not taking place in dilute solutions. The
two components have very similar lifetimes than what has been
reported in the literature for 3 mm thick crystalline film, although
the pre-exponential amplitudes were different.21
Fig. 4 The chemical structure of 4-alkoxy substituted Alq3 derivative,
tris-(4-benzyloxy-8-hydroxyquinoline)aluminium.6a
relative amplitudes of 0.15 and 0.85, and corresponding lifetimes
of 9.7 ns and 1.8 ns, respectively. Obviously, a concomitant
twisted intramolecular charge transfer (TICT) occurs which
would explain the observed second decay component.22 As was
calculated for compound 12, the absolute fluorescence quantum
yields and radiative fluorescence rate constants can be deter-
mined for 13. In chloroform, the absolute fluorescence quantum
yield for 13 is 0.03 (0.22321 for the parent Alq3 in chloroform) and
the radiative fluorescence rate constants are 1.3 ꢂ 107 sꢁ1 and
1.0 ꢂ 107 sꢁ1 for Alq3 and 13, respectively. The non-radiative
fluorescence rate constant of 13 (3.2 ꢂ 108 sꢁ1) increased notably
compared with Alq3 (4.7 ꢂ 107 sꢁ1).
In terms of CIE coordinates, it is interesting to note that
emission of the parent Alq3 was shifted to the yellowish-green
area while the solid state emission of compound 12 remained on
the deep blue area. For compound 12, the peak width (FWHM)
values of the thin films (Table 2) are close to the one obtained in
solution (Table 1) whereas FWHM values of the parent Alq3
showed major difference between the two states. For compound
14, the solid state emission spectrum was clearly broadened
compared with the solution state spectrum, which indicates
increased interaction between the molecules.21
Relative to the parent Alq3, emission maximum was blue-
shifted 23 nm, but CIE coordinates (0.25, 0.41) are located still
on the green area. Likely, the extended conjugation due to the
phenyl ring is a reason for the observed blue-shift of compound
13 which is smaller than that of piperidinyl and 4-methyl piper-
azinyl substituted Alq3 derivatives.7a In the case of compound 14,
emission maximum was blue-shifted 44 nm compared with the
parent Alq3. The observed blue-shift is the same order of
magnitude than those of tris-(4-alkoxy-8-hydroxyquinoline)
aluminium complexes (Fig. 4) reported earlier.6a
DSC analyses indicate that the synthesized Alq3 derivatives 12
and 13 are amorphꢀous. The parent Alq3 showed a sharp melting
endotherm at 417 C, which is consistent with earlier studies,28
whereas a melting endotherm could not be detected for
compounds 12 and 13 (Fig. 6). The parent Alq3 showed a glass
ꢀ
transition temperature (Tg) at 162 C, which is lower compared
with earlier reported values. Compounds 12 and 14 showed
slightly lower Tg values of 142 and 153 ꢀC, respectively, relative
to Alq3. Compound 14 showed also a sharp melting endotherm
at 194 ꢀC. Compound 13 can be considered thermally more
stable than the parent Alq3, because of the lack of a melting
endotherm and a higher Tg of 173 ꢀC. Generally, amorphous
materials have advantage over crystalline materials in various
organic electronic applications because of their good process-
ability, homogeneity, higher quantum efficiency in the solid state
and capability to form uniform films.29
The relative fluorescence quantum yield for 14 is considerably
higher compared with the parent Alq3 and its unfused analogue,
tris-(4-benzyloxy-8-hydroxyquinoline)aluminium6a (Fig. 4). The
absolute fluorescence quantum yield in chloroform for 14 is 0.32
and the radiative and non-radiative fluorescence rate constants
are 2.8 ꢂ 107 sꢁ1 and 5.8 ꢂ 107 sꢁ1, respectively. Increased fluo-
rescence quantum yield can be related to the fused tetracyclic
structure of new derivatives. The C–C bond between the aryl
group and the quinoline ring increases the rigidity of molecular
structures, which explains the increased F of compounds 12 and
14. Decreased Stokes’ shifts of the fused derivatives can also be
related to rigid molecular structures.26
In general, spin coating is not a well-suited processing tech-
nique for the studied solutions, because the thickness and
uniformity of the resulting films could not be accurately
controlled by using this method. However, results show the
potential of new derivatives to form thin films and if suitable
a deposition procedure is selected from the other available
solution-processing methods such as spray-on deposition, ink-jet
or roll-to-roll printing, the quality of films may be controlled
2.3 Solid state properties
Solution processing is a highly desired method because it allows
low-cost manufacturing techniques for organic electronic devices
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Fig. 5 Spectral characteristics of the parent Alq3 and its fused derivatives 12–14 in thin films. Absorption (a and c) and emission (b and d) spectra of the
parent Alq3 (evaporated film, 9.5 nm), derivative 12 (spin coated from ethanol) and derivatives 13 and 14 (spin coated from chloroform) spinned from
diluted solutions (0.1 mM, a and b) and concentrated solutions (1 mM, c and d) on quartz substrates. Emission band features were independent of the
excitation wavelength.
Table 2 Photophysical parameters of the parent Alq3 and fused derivatives in the solid state
Compound
labsa/nm
lPLb/nm
FWHM/nm
s1c/ns
s2d/ns
savge/ns
CIE/(x, y)f
g
Alq3
387
—
388
363
518
442
—
93
78,h 87j
—
27.00
3.81j
—
6.76
0.55j
—
10.77
0.77
—
(0.28, 0.53)
(0.18, 0.16)
12
13
14
480
95,i 112k
—
—
—
(0.23, 0.32)
a
b
Absorption maximum. Photoluminescence maximum. Fluorescence lifetime, long-living component. Fluorescence lifetime, short-living
c
d
e
f
g
h
component. Average fluorescence lifetime, savg ¼ (a1s1 + a2s2)/(a1 + a2). CIE chromaticity coordinates. Evaporated (9.5 nm). Spin coated (0.1
mM in EtOH). i Spin coated (0.1 mM in CHCl3). Spin coated (1 mM in EtOH). k Spin coated (1 mM in CHCl3).
j
more precisely. Especially, due to the observed deep blue emis-
sion of compound 12, as well as the increased fluorescence
quantum yield, one of the most likely application possibilities for
that aluminium complex is to use it as a fluorescent dopant in
OLEDs. The efficiency of the full-color OLED is highly depen-
dent on the deepness of blue emission i.e. deeper blue (smaller
value of y CIE coordinate) leads to decrease of power
consumption in the device.30 Forrest et al. have shown that by
using a fluorescent blue emitting dopant along with phospho-
rescent red and green dopants can considerably increase lumi-
nance efficiency in the white light OLED (WOLED) compared
with the all-phosphor doped device.31 Very recently, it has been
shown that blue fluorescent binaphthalene derivatives work
efficiently as host and light emitting materials in OLEDs without
problems faced by blue phosphorescent materials in OLEDs.30a
Lately, it has also been shown that doping the parent Alq3 in an
UV-emitting polymer matrix increases fluorescence efficiency of
the parent Alq3 caused by resonance energy transfer from the
polymer to the parent Alq3.32
3. Experimental section
3.1 Syntheses of quinoline derivatives
3.1.1 Synthesis of 8-(benzyloxy)-4-chloroquinoline (2). 4-
Chloro-8-hydroxyquinoline
1 (401 mg, 2.23 mmol) and
anhydrous K2CO3 (616 mg, 4.46 mmol) were mixed in dime-
thylformamide (DMF) (4 mL) under argon atmosphere for 10
min. Benzyl bromide (0.30 mL, 2.53 mmol) was added and the
reaction mixture was stirred for 18 h at room temperature.
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3.1.3 Synthesis
of
11H-indolo[3,2-c]quinolin-4-ol
(4).
Compound 3 (600 mg, 1.85 mmol) and 10 wt% Pd–C (122 mg)
were refluxed in ethanol (18 mL) under H2 atmosphere (balloon)
for 5 h. The hot reaction mixture was filtered, washed with hot
ethanol (35 mL) and the filtrate was evaporated to dryness. The
crude product was dissolved in ethanol (15 mL) and added
dropwise to distilled water (45 mL). The precipitate was filtered,
ꢀ
washed with distilled water and dried at 60 C. The procedure
gave the pure product as yellow powder (409 mg, 94%). Mp 254
1
ꢀC. H NMR dH (200 MHz; DMSO-d6; Me4Si) 7.09 (1H, dd, J
7.7, 1.1), 7.31–7.39 (1H, m), 7.46–7.56 (2H, m), 7.71 (1H, d, J
8.0), 7.92 (1H, dd, J 8.2, 1.2), 8.34 (1H, d, J 7.8), 9.55 (1H, s),
12.69 (1H, s, NH). 13C NMR dC (50 MHz; DMSO-d6; Me4Si)
110.5, 111.9, 112.0, 114.8, 117.7, 120.3, 120.7, 122.0, 125.7, 126.7,
135.5, 139.0, 140.1, 142.4, 153.9. HRMS: calcd for C15H11N2O
([M + H]+) 235.0871, found 235.0889.
Fig. 6 DSC thermograms of the parent Alq3 and compounds 12 and 13.
Solvent was removed by a rotary evaporator. The reaction
product was dissolved in acetone, filtered through a silica layer
and evaporated to dryness. The desired product was collected
after flash chromatography (1 : 1 ethyl acetate/n-hexane) as
3.1.4 Synthesis of 4-((2-bromobenzyl)(methyl)amino)quinolin-
8-yl 4-methylbenzenesulfonate (5). Compound 1 (503 mg, 2.80
mmol) was stirred in 2-bromo-N-methylbenzylamine (3.50 g,
17.5 mmol) under argon atmosphere for 17 h. The oil bath
1
white powder (492 mg, 82%). Mp 133 ꢀC. H NMR dH (200
ꢀ
MHz; DMSO-d6; Me4Si) 5.33 (2H, s, CH2), 7.32–7.47 (4H, m),
7.53–7.58 (2H, m), 7.63–7.81 (3H, m), 8.79 (1H, d, J 4.7). 13C
NMR dC (50 MHz; DMSO-d6; Me4Si) 70.1 (CH2), 110.9, 115.1,
122.1, 126.7, 127.9 (2C, Ph), 128.4, 128.4 (2C, Ph), 136.7, 140.7,
140.9, 148.8, 154.4. HRMS: calcd for C16H13NOCl ([M + H]+)
270.0686, found 270.0679.
temperature was adjusted to 135 C. The reaction mixture was
allowed to cool to room temperature. Ethyl acetate (5 mL) was
added and the solution was extracted with 6% HCl (aq) (25 mL).
Separated aqueous layer was allowed to stand at room temper-
ature overnight and for 30 min on an ice bath. The resulting
precipitate was filtered and washed with two 5 mL portions of 6%
HCl (aq) and distilled water (5 mL). The precipitate was dried at
60 ꢀC. The intermediate product (723 mg, 1.90 mmol)34 was
boiled in 1 M NaOH (aq) (3.80 mL) and distilled water (5 mL)
for 15 min. The mixture was allowed to cool to room tempera-
ture. p-Toluenesulfonyl chloride (363 mg, 1.90 mmol) in acetone
(15 mL) was added dropwise. The reaction mixture was stirred at
room temperature for 1 h. The mixture was concentrated by
evaporation to half. Distilled water (10 mL) was added and the
mixture was kept on an ice bath for 10 min. The precipitate was
filtered, washed with distilled water and dried at 60 ꢀC. The
procedure gaveꢀthe pure product as light brown powder (697 mg,
3.1.2 Synthesis of 4-benzyloxy-11H-indol[3,2-c]quinoline (3).
Compound 2 (390 mg, 1.45 mmol) was stirred in 2-bromoaniline
(2.60 g, 15.1 mmol) under argon atmosphere for 17 h. The oil
ꢀ
bath temperature was adjusted to 135 C. The reaction mixture
was allowed to cool to room temperature. Acetone (6.5 mL) was
added and the precipitate was filtered and washed with acetone
(35 mL). The crude product was boiled in a mixture of 1 M
NaOH (aq) (4.5 mL), acetone (2 mL) and distilled water (8 mL)
for 10 min. The mixture was cooled to room temperature. The
precipitate was filtered, washed with distilled water and dried at
60 ꢀC overnight. Dimethylacetamide (DMA) (8 mL) was
bubbled with argon for 15 min. Dried quinoline derivative33 (550
mg, 1.36 mmol), Pd(OAc)2 (17.5 mg, 0.069 mmol), PCy3-HBF4
(52.0 mg, 0.141 mmol) and anhydrous K2CO3 (471 mg, 3.41
mmol) were added to the reaction vessel against the argon flow.
The reaction mixture was stirred and heated (oil bath 160 ꢀC)
under argon atmosphere for 3 h. The hot reaction mixture was
filtered through a silica layer, silica was washed with acetone (50
mL) and the filtrate was evaporated to dryness. The crude
product was dissolved in acetone (8 mL) and the solution was
added to distilled water (25 mL) dropwise. The precipitate was
filtered, washed with distilled water and dried at 60 ꢀC. The
procedure gaveꢀthe pure product as light brown powder (434 mg,
1
50%). Mp 151 C. H NMR dH (200 MHz; DMSO-d6; Me4Si)
2.38 (3H, s, Me), 2.93 (3H, s, NMe), 4.50 (2H, s, CH2), 6.98 (1H,
d, J 5.1), 7.24–7.48 (6H, m), 7.57–7.68 (2H, m), 7.81–7.85 (3H,
m), 8.54 (1H, d, J 4.9). 13C NMR dC (50 MHz; DMSO-d6; Me4Si)
21.2 (Me), 59.3 (NMe), 65.6 (CH2), 109.1, 121.4, 123.0, 123.1,
124.0, 124.1, 128.1, 128.3 (2C, Ph), 129.5, 129.5, 129.8 (2C, Ph),
132.7, 133.0, 136.0, 142.7, 145.3, 145.4, 150.7, 155.9. HRMS:
calcd for C24H22N2O3SBr ([M + H]+) 497.0535, found 497.0531.
3.1.5 Synthesis of 5-methyl-5,6-dihydrodibenzo[c,h][1,6]naph-
thyridin-1-yl 4-methylbenzene-sulfonate (6). DMA (3.75 mL) was
bubbled with argon for 15 min. Compound 5 (251 mg, 0.505
mmol), Pd(OAc)2 (13.2 mg, 0.052 mmol), PCy3-HBF4 (38.8 mg,
0.105 mmol) and anhydrous K2CO3 (184 mg, 1.33 mmol) were
added to the reaction vessel against the argon flow. The reaction
mixture was stirred and heated (oil bath 160 ꢀC) under argon
atmosphere for 4 h. The hot reaction mixture was filtered
through a silica layer, silica was washed with acetone (50 mL)
and the filtrate was evaporated to dryness. The crude product
was boiled in acetone (1 mL) after flash chromatography and n-
hexane (4 mL) was slowly added. The mixture was cooled to
1
93%). Mp 282 C. H NMR dH (200 MHz; DMSO-d6; Me4Si)
5.36 (2H, s, CH2), 7.29–7.63 (10H, m), 7.71 (1H, d, J 8.0), 8.07
(1H, d, J 7.2), 8.31 (1H, d, J 7.8), 9.53 (1H, s), 12.65 (1H, s, NH).
13C NMR dC (50 MHz; DMSO-d6; Me4Si) 70.1 (CH2), 109.6,
111.9, 114.0, 114.7, 118.2, 120.2, 120.6, 121.8, 125.7, 126.0, 127.9,
128.0 (2C, Ph), 128.4 (2C, Ph), 137.1, 137.2, 138.9, 139.9, 143.1,
155.0. HRMS: calcd for C22H17N2O ([M + H]+) 325.1341, found
325.1347.
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room temperature and kept on an ice bath for 15 min. The
precipitate was filtered, washed with cold solvent mixture (3 mL
of acetone and 12 mL of n-hexane) and dried at 60 ꢀC. The
procedure gave the product as off-white powder (115 mg, 55%).
Mp 161 ꢀC. 1H NMR dH (200 MHz; DMSO-d6; Me4Si) 2.41 (3H,
s, Me), 2.99 (3H, s, NMe), 4.37 (2H, s, CH2), 7.33–7.57 (7H, m),
7.87 (2H, d, J 8.2), 8.05–8.09 (1H, m), 8.15 (1H, d, J ¼ 7.6), 9.30
(1H, s). 13C NMR dC (50 MHz; DMSO-d6; Me4Si) 21.2 (Me),
42.6 (NMe), 53.5 (CH2), 119.6, 121.4, 122.3, 123.6, 124.4, 125.3,
126.7, 128.0, 128.3 (2C, Ph), 128.5, 128.9, 129.9 (2C, Ph), 131.0,
132.7, 141.8, 145.4, 145.5, 147.1, 150.3. HRMS: calcd for
C24H20N2O3NaS ([M + Na]+) 439.1092, found 439.1104.
(5 mL) after flash chromatography (1 : 1 ethyl acetate/n-hexane)
and n-hexane (15 mL) was slowly added. The mixture was cooled
to room temperature and kept on an ice bath for 15 min. The
precipitate was filtered, washed with cold solvent mixture (10 mL
of acetone and 30 mL of n-hexane) and dried at 60 ꢀC. The
procedure gave the product as off-white powder (290 mg, 87%).
Mp 200 ꢀC. 1H NMR dH (200 MHz; DMSO-d6; Me4Si) 2.40 (3H,
s, Me), 5.53 (2H, s, CH2), 7.34–7.61 (7H, m), 7.85 (2H, d, J 8.2),
8.04–8.10 (2H, m), 9.32 (1H, s). 13C NMR dC (50 MHz; DMSO-
d6; Me4Si) 21.2 (Me), 68.8 (CH2), 113.5, 121.1, 121.5, 121.8,
122.4, 125.3, 126.1, 126.7, 128.3, 128.8, 128.9, 129.7, 130.0, 132.4,
141.7, 145.0, 145.5, 147.1, 156.0. HRMS: calcd for C23H18NO4S
([M + H]+) 404.0957, found 404.0950.
3.1.6 Synthesis of 5-methyl-5,6-dihydrodibenzo[c,h][1,6]naph-
thyridin-1-ol (7). Compound 6 (221 mg, 0.531 mmol), NaOH (aq)
(1 M, 2.65 mL, 2.65 mmol) and ethanol (10 mL) were refluxed for
21/2 h. Solvents were removed by a rotary evaporator. Distilled
water (5 mL) and ethanol (5 mL) were added and the pH was
adjusted to 7 with 6% HCl (aq). Distilled water (20 mL) was
added and the resulting precipitate was filtered. The solid
product was washed with distilled water and dried at 60 ꢀC. The
product was collected as greenish powder (117 mg, 84%). Mp 159
ꢀC. 1H NMR dH (200 MHz; DMSO-d6; Me4Si) 2.97 (3H, s,
NMe), 4.35 (2H, s, CH2), 7.03 (1H, d, J 7.43), 7.28–7.53 (4H, m),
7.62 (1H, d, J 8.22), 8.08 (1H, d, J 6.06), 9.27 (1H, s), 9.69 (1H, br
s, OH). 13C NMR dC (50 MHz; DMSO-d6; Me4Si) 43.5 (NMe),
54.9 (CH2), 112.3, 115.4, 120.7, 123.5, 124.9, 128.1, 128.1, 129.3,
129.5, 130.7, 132.3, 140.3, 145.5, 152.0, 155.1. HRMS: calcd for
C17H15N2O ([M + H]+) 263.1184, found 263.1181.
3.1.9 Synthesis of 6H-isochromeno[4,3-c]quinolin-1-ol (11).
Compound 10 (517 mg, 1.28 mmol), NaOH (aq) (1 M, 3.85 mL,
3.85 mmol), ethanol (12.5 mL) and acetone (12.5 mL) were
refluxed for 21/2 h. The solvents were removed by a rotary
evaporator. Distilled water (6 mL) was added. pH was adjusted
to 6 with 6% HCl (aq). The precipitate was filtered, washed with
distilled water and finally dried at 60 ꢀC. The procedure gave the
1
product as off-white powder (319 mg, >99%). Mp 192 ꢀC. H
NMR dH (200 MHz; DMSO-d6; Me4Si) 5.49 (2H, s, CH2), 7.08
(1H, d, J 7.4), 7.32–7.57 (5H, m), 8.08 (1H, d, J 7.2), 9.29 (1H, s),
9.82 (1H, br s, OH). 13C NMR dC (50 MHz; DMSO-d6; Me4Si)
68.6 (CH2), 111.4, 112.1, 113.2, 120.6, 121.7, 125.2, 127.3, 127.4,
128.5, 128.8, 129.7, 139.2, 144.1, 153.5, 156.4. HRMS: calcd for
C16H12NO2 ([M + H]+) 250.0868, found 250.0873.
3.1.7 Synthesis of 4-(2-bromobenzyloxy)quinolin-8-yl 4-
methylbenzenesulfonate (9). NaH in 60% mineral oil (105 mg,
2.63 mmol) was washed with n-hexane (2 mL) under argon
atmosphere. 4-Hydroxy-8-tosyloxyquinoline 8 (502 mg, 1.59
mmol) in DMF (5 mL) was added and reaction was allowed to
proceed for 5 min. 2-Bromobenzyl bromide (615 mg, 2.46 mmol)
was added and the reaction solution was mixed for 24 h at room
temperature. The reaction mixture was evaporated to dryness.
The product was collected as off-white powder (586 mg, 76%)
after flash chromatography (1 : 1 ethyl acetate/n-hexane). Mp
3.2 General procedure for syntheses of Alq3 derivatives
Ligand (3 equiv), anhydrous K2CO3 (3 equiv), and Al
(NO3)3$9H2O (1 equiv) were refluxed in ethanol for 23 h under
argon atmosphere. The reaction mixture was allowed to cool to
room temperature. The precipitate was filtered and washed
sequentially with ethanol, distilled water and ethanol. The
product was dried at 60 ꢀC.
3.2.1 Synthesis
of
tris-(11H-indolo[3,2-c]quinolin-4-ol)
ꢀ
1
163 C. H NMR dH (200 MHz; DMSO-d6; Me4Si) 2.38 (3H, s,
Me), 5.40 (2H, s, CH2), 7.21 (1H, d, J 5.3), 7.32–7.57 (6H, m),
7.69–7.75 (2H, m), 7.82 (2H, d, J 8.2), 8.09 (1H, dd, J 7.7, 2.1),
8.69 (1H, d, J ¼ 5.3). 13C NMR dC (50 MHz; DMSO-d6; Me4Si)
21.2 (Me), 70.0 (CH2), 102.9, 121.0, 122.3, 122.5, 123.3, 125.5,
128.1, 128.4, 129.9, 130.7, 130.8, 132.5, 132.9, 134.8, 142.0, 144.8,
145.4, 152.2, 160.1. HRMS: calcd for C23H19NO4SBr ([M + H]+)
484.0218, found 484.0208.
aluminium (12). The specific amounts of chemicals used:
compound 4 (60.2 mg, 0.257 mmol), anhydrous K2CO3 (43.0 mg,
311 mmol), Al(NO3)3$9H2O (32.3 mg, 0.086 mmol) and ethanol
(6 mL). The procedure gave the product as white powder (57.3
mg, 92%). 1H NMR dH (200 MHz; DMSO-d6; Me4Si) 6.75 (1H,
dd, J 7.14, 1.27), 6.98–7.04 (2H, m), 7.12 (1H, t, J 7.43), 7.28–7.73
(14H, m), 7.84 (1H, d, J 8.02), 8.22–8.28 (3H, m), 9.32 (1H, s),
9.55 (1H, s), 12.99 (3H, br s). HRMS: calcd for C45H27N6O3-
NaAl ([M + Na]+) 749.1858, found 749.1842.
3.1.8 Synthesis of 6H-isochromeno[4,3-c]quinolin-1-yl 4-
methylbenzenesulfonate (10). DMA (6 mL) was bubbled with
argon for 15 min. Compound 9 (402 mg, 0.830 mmol), Pd(OAc)2
(10.8 mg, 0.043 mmol), PCy3-HBF4 (32.3 mg, 0.088 mmol) and
anhydrous K2CO3 (287 mg, 2.08 mmol) were added to the
reaction vessel against the argon flow. The reaction mixture was
stirred and heated (oil bath 160 ꢀC) under argon atmosphere for
3 h. The hot reaction mixture was filtered through a silica layer,
silica was washed with acetone (50 mL) and the filtrate was
evaporated to dryness. The crude product was boiled in acetone
3.2.2 Synthesis of tris-(5-methyl-5,6-dihydrodibenzo[c,h][1,6]
naphthyridin-1-ol)aluminium (13). The specific amounts of
chemicals used: compound 7 (57.6 mg, 0.220 mmol), anhydrous
K2CO3 (30.7 mg, 0.222 mmol), Al(NO3)3$9H2O (27.5 mg, 0.073
mmol) and ethanol (5.75 mL). The procedure gave the product as
1
beige powder (42.7 mg, 72%). H NMR dH (200 MHz; CDCl3;
Me4Si) 3.29–3.43 (9H, m, NMe), 4.33–4.46 (6H, m, CH2), 7.03–
7.78 (22H, m), 9.16 (1H, s), 9.26 (1H, s). HRMS: calcd for
C51H40N6O3Al ([M + H]+) 811.2977, found 811.2981.
This journal is ª The Royal Society of Chemistry 2011
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3.2.3 Synthesis of tris-(6H-isochromeno[4,3-c]quinolin-1-ol)
aluminium (14). The specific amounts of chemicals used:
compound 11 (100 mg, 0.401 mmol), anhydrous K2CO3 (55.4
mg, 0.401 mmol), Al(NO3)3$9H2O (50.8 mg, 0.135 mmol) and
ethanol (10 mL). The procedure gave the product as off-white
powder (86.3 mg, 84%). 1H NMR dH (200 MHz; CDCl3; Me4Si)
5.28–5.54 (6H, m), 7.01 (1H, d, J 6.80), 7.11–7.50 (18H, m), 7.64–
7.69 (2H, m) 7.80 (1H, s), 9.15 (1H, s), 9.28 (1H, s). HRMS: calcd
for C48H30N3O6NaAl ([M + Na]+) 794.1848, found 794.1868.
which compound 12 was deposited in order to hydrophilize the
surface. In fluorescence measurements, the plates were aligned to
an angle (45–60ꢀ) with respect to the excitation, which yielded the
maximum signal intensity.
Fluorescence lifetimes (s) were obtained by using a time
correlated single photon counting (TCSPC) system (Piqoquant
GmBH) consisting of a Picoharp 300 controller and a PDL 800-B
driver. Pulsed LED (340 nm, 2.5–10 MHz) was used for excita-
tion and a microchannel plate photomultiplier (Hamamatsu
R3809U-50) for detection in 90ꢀ configuration. Time resolution
of a TCSPC measurement is about 300 ps estimated from the
FWHM of the instrumental response at 340 nm. Decay associ-
ated spectra (DAS) were measured by accumulating the signal
for 1 min at each monitoring wavelength (10 nm steps). Pre-
exponential amplitudes (A) and corresponding lifetimes (s) were
obtained by using an ordinary exponential fitting procedure.
Well-known models were used in the analysis.22 Equations and
fluorescence decay data together with DAS are shown in the
ESI†. Absolute absorption and emission spectra are shown in the
ESI† together with the decay curves, decay associated spectra
and calculation procedures.
3.3 Chemical characterization
1H and 13C NMR spectra were measured by using a Bruker
Avance DPX200 instrument. High resolution mass spectra were
measured by using a Micromass LCT device. Thermoanalyses
were carried out by using a Mettler Toledo DSC821e apparatus
equipped with a TSO800GC1 Gas Control system. The heating
rate was 20 ꢀC minꢁ1 and the nitrogen flow 50 mL minꢁ1. Melting
points are reported from the peaks and the glass transition
temperatures as on-set values from the third heating scan to 350
ꢀC after rapid cooling to 25 ꢀC.
3.4 Photophysical measurements
4. Conclusion
Compound 12 was soluble in ethanol and compounds 13 and 14
in chloroform. These were used as solvents in optical measure-
ments to prevent possible concentration quenching. Reference
solutions of the parent Alq3 (Sigma-Aldrich, 99.99%) were
prepared in both solvents. Concentrations were fixed in order to
find a wavelength, where the absorbances of compounds 12–14
and that of the parent Alq3 reference were the same. Thus the
fluorescence quantum yield, F, can be determined by comparing
directly the number of emitted photons (i.e. signal intensity, I)
throughout the measured spectrum (I f Nabs f 1 ꢁ T ¼ 1 ꢁ
10ꢁAbs.). The relative fluorescence quantum yield, F ¼ 1.0, was
given to the parent Alq3 and the fused Alq3 derivatives
(compounds 12–14) were referenced to that. Sample solutions
were kept in a 1 ꢂ 1 cm quartz cuvette during the experiments.
Absorption and emission spectra were measured by using stan-
dard spectrophotometers (Shimadzu UV-3600 UV-vis, Fluo-
rolog Jobin Yvon-SPEX). In each fluorescence measurement, 90ꢀ
configuration was used for detection.
Three new tetracyclic 8-hydroxyquinoline derivatives were
synthesized. Readily available 4-chloro-8-hydroxyquinoline 1
and 4-hydroxy-8-tosyloxyquinoline 8 were applied as starting
materials in the syntheses. Aminations were performed by using
solvent free amination reactions. The hydroxyl group at the 8-
position of the quinoline ring was protected with the tosyl or
benzyl group prior to intramolecular direct arylation reactions.
Direct arylation reactions were carried out efficiently by using Pd
(OAc)2 as a palladium source and air stable PCy3-HBF4 as
a ligand. Deprotection of the benzyl group or the tosyl group
gave the desired ligands in good to quantitative yields. Finally,
aluminium complexes were prepared from the synthesized
ligands and the spectroscopic properties of the complexes were
studied in detail both in solution and solid state.
All new tetracyclic Alq3 derivatives have blue-shifted
absorption maximum and show increased molar extinction
coefficients compared with the parent Alq3. A strong EDG on
the 4-position of the quinoline ring seems to affect the
absorption profile more than the extended conjugation sphere.
Derivatives have also blue-shifted emission and decreased
Stokes’ shifts compared with the parent Alq3. Evidently,
decreased Stokes’ shifts are related to rigid tetracyclic struc-
tures. Especially interesting observation is that the aluminium
complex of 11H-indolo[3,2-c]quinolin-4-ol 12 has 3.1–3.5 times
higher fluorescence quantum yield than the parent Alq3 and the
most blue-shifted emission maximum among the Alq3 derivatives
to date and CIE chromaticity coordinates locating on the deep
blue area (0.16, 0.12). Moreover, spectroscopic properties of
compound 12 did not show major differences between the solution
and the solid states. Obviously in the case of tris-(5-methyl-5,6-
dihydrodibenzo[c,h][1,6]naphthyridin-1-ol)aluminium 13, charge
transfer is taking place in the molecule which explains partly
that only the small blue-shift of emission occurs and a conse-
quent TICT state is likely to cause the observed second decay
of fluorescence. Compound 13 also has dramatically decreased
Films were deposited onto 12 ꢂ 36 mm quartz plates by using
a programmable spin-coater (WS-400B-6NPP/LITE, Laurell
Technologies Corp., 10–10 000 rpm). Concentrations of the
solutions (compound 12 in ethanol and compounds 13 and 14 in
chloroform) before casting were 0.1 mM and 1 mM in two
distinct sets. The spinning speed was 2000 rpm and the time
1 min. Substrates were cleaned prior to deposition by sonicating
1 h in CHCl3 and 1 h in sulfochromic acid followed by rinsing
with MilliQ water (Millipore, resistivity >18.0 MU cm) and
drying in vacuum at 110 ꢀC for 1 h. A test was made to deposit
a film by using thermal evaporation in a high vacuum (Edwards
AUTO 306). Compounds 12–14 were placed into a ceramic jar (5
mg) and the temperature was increased from 180 to 400 ꢀC, but
the layer growth was not observed. A thin film of the parent Alq3
(9.5 nm) was produced by using thermal evaporation in a high
vacuum (2–3 ꢂ 10ꢁ6 mbar) at 200 ꢀC. Additional N2 plasma
treatment (Harrick, 10 min) was applied for the plates, onto
14774 | J. Mater. Chem., 2011, 21, 14766–14775
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View Article Online
D. Petruzziello, L. Prodi, M. Sgarzi, C. Trombini and
N. Zaccheroni, J. Org. Chem., 2010, 75, 6275–6278.
12 (a) L.-L. Shi, Y. Geng, H.-Z. Gao, Z.-M. Su and Z.-J. Wu, Dalton
Trans., 2010, 39, 7733–7740; (b) C.-K. Tai, Y.-M. Chou and
B.-C. Wang, J. Lumin., 2011, 131, 169–176.
the fluorescence quantum yield compared with the parent Alq3.
In addition, emission could not be detected in the solid state.
Tris-(6H-isochromeno[4,3-c]quinolin-1-ol)aluminium 14 has
similar blue-shifted absorption and emission like its unfused
analogue
tris-(4-benzyloxy-8-hydroxyquinoline)aluminium6a
13 W. A. E. Omar, J. P. Heiskanen and O. E. O. Hormi, J. Heterocycl.
Chem., 2008, 45, 593–595.
but the fluorescence quantum yield is considerably higher
which can be explained by the rigid fused structure of the
ligands. Compound 14 shows pronounced emission broadening
in the solid state, which is attributed to the crystalline nature of
the compound in the solid state. DSC analyses indicate that
compounds 12 and 13 are amorphous whereas compound 14
and the parent Alq3 have sharp melting endotherms. Based on
the results, 11H-indolo[3,2-c]quinolin-4-ol 4 has especially
promising features to be applied as a ligand for aluminium or
other metal ions in different applications.
14 L. He, H.-X. Chang, T.-C. Chou, N. Savaraj and C. C. Cheng, Eur. J.
Med. Chem., 2003, 38, 101–107.
15 C. Meyers, G. Rombouts, K. T. J. Loones, A. Coelho and
B. U. W. Maes, Adv. Synth. Catal., 2008, 350, 465–470.
16 L.-C. Campeau, M. Parisien, A. Jean and K. Fagnou, J. Am. Chem.
Soc., 2006, 128, 581–590.
17 Use of 2.5 mol% Pd(OAc)2 gave incomplete conversion of the starting
material.
18 J. P. Heiskanen, W. A. E. Omar, M. K. Ylikunnari, K. M. Haavisto,
M. J. Juan and O. E. O. Hormi, J. Org. Chem., 2007, 72, 920–922.
19 The tosyl protective group was chosen to replace the benzyl protective
group in the syntheses of ligands 7 and 11 because both benzylamine
and benzyl ether structures do not last Pd catalyzed hydrogenolysis.
(See: Protective Groups in Organic Synthesis, ed. T. W. Greene and
P. G. M. Wuts, John Wiley & Sons, New Jersey, 4th edn, 2007, pp.
102–818.) On the other hand, the tosyl group could not be used as
Acknowledgements
€
The authors thank Mrs Paivi Joensuu for HRMS data and
a
protective group in the synthesis of ligand 4 because 2-
bromoaniline cleaved the protective tosyl group from 4-chloro-8-
tosyloxyquinoline similarly as pyrrolidine has been previously
observed to cleave the tosyl group (see ref. 13).
Finnish Cultural Foundation for funding.
20 M. Muccini, M. A. Loi, K. Kenevey, R. Zamboni, N. Masciocchi and
A. Sironi, Adv. Mater., 2004, 16, 861–864.
References and notes
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€
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whose structure was confirmed by 1H NMR.
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 14766–14775 | 14775