Synthesis, photophysical and electrochemical studies of acridone-amine based donor-acceptors for hole transport materials

Article abstract of DOI:10.1039/c5ra25115j

A series of new donor-acceptor molecules based on acridone-amine containing four aryl substituted 2,7-diaminoacridones (1-4) and morpholine substituted acridone compounds (5) were synthesized in good yields using palladium catalysed Buchwald-Hartwig C-N amination. Their absorption, photoluminescence and electrochemical properties were investigated in solution and in thin films. Photophysical properties were found to be affected by the electron donating capability of the substituents on the diaryl amines. Absorption showed intramolecular charge transfer transitions (ICT) in a range of 447-479 nm. These acridone amine derivatives emit in the green region (500-527 nm). Reversible oxidation waves were observed for compounds 1-5 in cyclic voltammetry. The HOMO (-4.95 to -5.11 eV) and LUMO (-2.36 to -2.56 eV) energy levels of 1-5 were calculated. The E_HOMO for compounds 1-5 are similar with the most widely used hole transporting materials NPD, TPD and spiro-OMe-TAD. Hence we believe that these compounds have the potential to be used as hole transporting materials in optoelectronic devices.

Full text of DOI:10.1039/c5ra25115j

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Synthesis, Photophysical and Electrochemical Studies of
AcridoneꢀAmine based DonorꢀAcceptors for Hole Transport
Materials
a
a
b
a
Bharat K. Sharma , Azam M. Shaikh , Neeraj Agarwal* and Rajesh M. Kamble*
a
Department of Chemistry, University of Mumbai, Santacruz (E), Mumbai, 400098, India
b
UMꢀDAE, Centre for Excellence in Basic Sciences, University of Mumbai, Santacruz (E),
Mumbai, 400098, India
eꢀmail: kamblerm@chem.mu.ac.in, na@cbs.ac.in
Abstract: A series of new donorꢀacceptor molecules based on acridoneꢀamine containing
four aryl substituted 2,7ꢀdiaminoacridones(1ꢀ4) and morphololine substituted acridone
compounds (5) were synthesized in good yields using palladium catalysed Buchwaldꢀ
Hartwig CꢀN amination. Their absorption, photoluminescence and electrochemical properties
were investigated in solution and in thin films. Photophysical properties were found to be
1

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affected by electron donating capability of substituents on diaryl amines. Absorption showed
an intramolecular charge transfer transitions (ICT) in a range of 447ꢀ479 nm. These acridone
amine derivatives emit in green region (500ꢀ527 nm). Reversible oxidation wave were
observed for compounds 1ꢀ5 in cyclic voltammetry. The HOMO (ꢀ4.95 to ꢀ5.11 eV) and
LUMO (ꢀ2.36 to ꢀ2.56 eV) energy levels of 1ꢀ5 were calculated. The EHOMO for compounds
1ꢀ5 are similar with the most widely used hole transporting materials NPD, TPD and spiroꢀ
OMeꢀTAD. Hence we believe that these compounds are having potential to be used as hole
transporting materials in optoelectronic devices.
Introduction
Development of active materials for organic electronics is highly active field of
research powered by the exciting applications inorganic light emitting devices (OLEDs),
1
organic field effect transistors (OFETs), solar cells, solid state detectors etc. Although
soluble conjugated polymers remain a major class of organic materials for solutionꢀprocessed
electronic devices, recent years have seen the upcoming of small molecules in applications
owing to their obvious advantages in well defined structures, ease of purification, reliable
2
reproducibility and better solubility in most of the organic solvents. Depending on the
structureꢀproperties relationship, small molecules also offer the control on photophysical and
electrochemical properties by having various electron donating or withdrawing
3
substituents. Low molecular weight, simple structure and good overall synthetic yield present
the advantage to be processable from solutions or by thermal evaporation under vacuum. It
has been shown recently that interesting photovoltaic performances can be obtained with
donorꢀacceptor molecules having triphenylamine (TPA) as donor unit. DonorꢀAcceptor
(D/A) design approach facilitates intramolecular charge transfer in the molecule leading to
4
smaller HOMOꢀLUMO energy band gap .Choice of suitable D/A unit could allow the
2

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5
simultaneous control of photophysical and electrochemical properties of such systems. A
variety of molecules based on donorꢀacceptor are available which emits in the visible region,
6
7
8
9
including blue, green, yellow, and red . Bipolar molecules can accept and transport both
holes and electrons along with good emission for applications in OLEDs. Many donor-
acceptor molecules derived from electron-deficient and electronꢀrich units such as
10
11
12
13
borane/amine,
quinoxaline/fluorine,
triazole/amine,
bathophenanthrooline/amine,
14
15
benzimidazole/amine and oxadiazole/carbazole have been synthesized for their possible
applications in electroluminescent devices. Acridone derivatives also have attracted a lot of
1
6a
research attention because of their successful biological applications as antimicoribial
16a
16b
16c
16d
fungicidal agents, anticancer, antiꢀinflammatory, chemosensor etc
. Some of these
acridone derivatives are shown in Figure 1.
Figure 1: Biologically active acridone derivatives
Recently, acridone derivatives found applications in organic electronics. Nitrogen
17
18a
substituted
triarylamines
acridone
derivatives,
2,7ꢀorganosilane
acridone,
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1
8b
18c
acridonediyneplatinum(II) complexes and quinacridone derivatives were synthesized and
used as host materials for phosphorescent dopants and as well as emitting materials in
OLEDs (Figure 2). To the best of our knowledge, substitution of groups affecting electronic
19
properties of acridone, at 2,7ꢀ positions are very rare and have not been studied extensively.
O
N
N
O
N
(
C H O) Si
Si(OC H )
2 5 3
2
5
3
Et P
Pt
PEt3
Pt
Et P
3
O
PEt3
3
N
C12H25
Figure 2: Literature reported acridone derivatives used in optoelectronic devices
There is no report on the synthesis and studies of 2,7ꢀdiarylamino acridone. Herein we
report the synthesis of 2,7ꢀdiarylamine substituted acridone derivatives, 1ꢀ4 and morpholine
substituted acridone derivative 5 (Figure 3) and study their photophysical, electrochemical
and thermal properties for their possible applications in organic electronic devices.
Morpholine amine was used to see the effect of rigid cyclic aliphatic amines on the properties
of acridone. The design of triarylamines based acridone derivatives is mainly based on the
considerations that triarylamine derivatives are well known hole transporting materials and
acridone is selected for its known electron injection/transporting abilities due to the presence
4

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17
of the electronꢀwithdrawing carbonyl group. Further the incorporation of arylamines at 2,7ꢀ
positions of acridone are expected to affect the electronic properties effectively.
O
O
N
N
N
N
N
N
1
2
H CO
OCH
3
H N
2
NH
2
3
O
O
N
N
N
N
N
N
OCH3
H CO
3
4
3
O
O
O
N
N
N
5
Figure 3: 2,7ꢀDiamine substituted acridone derivatives 1ꢀ5.
Results and discussion
The synthesis of the target compounds,1ꢀ5 is shown in Scheme 1. The building block,
,7ꢀdibromoꢀ10ꢀmethyl acridone was synthesized in two steps. The 9(10H)-acridone
2
possesses a low solubility in most of the organic solvents while Nꢀmethylation of acridone
increases the solubility effectively, therefore 9(10H)ꢀacridone was first methylated using
methyliodide and sodium hydride as a base to get 10ꢀmethylacridone (6). Further,
bromination of 6 was carried out with molecular bromine in acetic acid at reflux temperature
to get the desired 2,7ꢀdibromoꢀ10ꢀmethyl acridone (7) in overall 85% yield for these two
5

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2
0
steps. Acridone derivatives 1ꢀ5 were synthesized by BuchwaldꢀHartwig coupling reaction
of different diarylamines with 2,7ꢀdibromoꢀ10ꢀmethylacridone (7) in the presence of a
palladium catalyst, coꢀligand and strong base. The Pd
source of palladium catalyst. The SPhos (2-dicyclohexylphoshpino-2΄,6΄-dimethylbiphenyl),
XPhos (2ꢀdicyclohexylphosphinoꢀ2′,4′,6′ꢀtriisopropylbiphenyl) and DPPF (1,1'ꢀ
2 3
(dba) (5ꢀ8 mol%), was used as the
bis(diphenylphosphino)ferrocene) were tried as coꢀligands with bases such as sodium tꢀ
butoxide, potassium tꢀbutoxide and potassium phosphate however the best results were
obtained with SPhos and sodium tꢀbutoxide along with palladium catalyst. Further it was
observed that the yield of the reaction was significantly affected by the substituent attached to
the diarylamines. Amines with electronꢀdonating groups like ꢀOCH and ꢀNH were resulted
3
2
in better yield compared to electronꢀwithdrawing groups like Br, CN etc. It is worth to
mention that no coupling reaction was observed when rigid polycyclic heteroamines such as
phenothiazine, phenoxazine and carbazole were used in this reaction. The five target
compounds were obtained in 50ꢀ62 % yield as yellow to orange solids. Compounds 1ꢀ5
(except 4) showed good solubility in common organic solvents e.g. ~ 20 mg/ml in
dichloromethane and chloroform.
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O
O
N
O
N
CH I, NaH
3
Br , CH COOH
Br
Br
2
3
N
H
0
Reflux, 20h
DMF, 60 C
6
7
(
90%)
(
95%)
Pd (dba) , SPhos, RH, Toluene
2
3
o
NaOBut
1
00 C, 16-24 h
O
N
R
R
1
-5
(
50-62%)
H CO
OCH3
3
NH2
O
N
R =
N
N
N
N
1
2
3
4
5
Scheme 1: Synthesis of acridoneꢀamine derivatives 1ꢀ5
The identity and purity of all new compounds were confirmed by several
1
13
characterization methods such as HꢀNMR, CꢀNMR, MALDI mass, FTIR, elemental
1
13
analysis etc. Figure 4 shows the HꢀNMR and CꢀNMR of 2,7-bis(anisylamino)ꢀ10ꢀ
methylacridone (3) in CDCl A singlet of two hydrogens at 1,8ꢀpositions appeared at 8.04
3
.
ppm and shows the symmetric nature of molecule. A multiplet of four protons at ~7.41 ppm
is assigned for acridone hydrogens at ꢀ3,6 and ꢀ4,5 positions. 4ꢀMethoxyphenyl hydrogens
appeared at 7.00 and 6.81 ppm. The presence of a singlet at 3.83 ppm indicates the Nꢀmethyl
and four methoxy groups are shown at 3.77 ppm in compound 3. A characteristic signal for
13
carbonyl group was observed 176 ppm in CꢀNMR. Nꢀmethyl and methoxy carbons
13
appeared at 33 and 55 ppm respectively. All other peaks observed in CꢀNMR spectrum can
be assigned to aromatic carbons.
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1
13
Figure 4: HꢀNMR (above) and CꢀNMR (below) of compound 3 recorded in CDCl
3
Absorption and fluorescence properties of compounds 1-5 were studied in various
solvents and as neat solid film. The photophysical data for compounds 1ꢀ5 is summarized in
Table 1. The absorption spectra of compounds 1ꢀ5,in toluene and in neat solid films, are
shown in Figure 5. The 10ꢀmethylacridone (6) shows two absorption maxima at 376 and 396
*
nm due to πꢀπ transition. 1ꢀ5 showed absorption at 303ꢀ342 nm showing a blue shift of ~ 30ꢀ
*
6
5 nm as compared high energy transition of 6. The πꢀπ transitions were found at ~348-391
nm in 1ꢀ5. However, this transition was weak in compound 5 where aliphatic substituent,
morpholine, was used. All these new acridone derivatives showed a broad feature with
relatively low molar absorption coefficient in further lower energy region (~ 447ꢀ479 nm).
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This band is assigned to the transitions based on the intramolecular charge transfer transitions
originating from electronꢀdonating, arylamines in 1ꢀ4 and morpholine in 5, to electronꢀ
withdrawing acridone core. A set of solvents of different polarity was used to study the effect
of solvents polarity on photophysical properties of 1ꢀ5 and were correlated with their donorꢀ
acceptor architecture. Compounds 1ꢀ5 showed blue shift in the absorption peaks in
ethylacetate due to possible Hꢀbonding of acridone derivatives with solvent molecules.
Charge transfer band showed a bathochromic shift in 1ꢀ5 with increase of solvent polarity.
Absorption of compounds 1ꢀ3 and 5 in neat solid films was observed in a range of ~450ꢀ500
nm. The red shift observed in thin film absorption maxima along with broadening of peaks
suggests the intermolecular aggregation in these acridone derivatives.
Figure 5: Absorption spectra of acridone derivatives in (a) toluene and (b) neat solid film.
Compounds 1-5 showed emission in green region with emission maxima in range of
500-527 nm (Figure 6) in toluene. A red shift of ~ 65ꢀ90 nm was observed for 1ꢀ5 as compare
to unsubstituted 10ꢀmethylacridone, 6 (445 nm). Considerable Stokes shifts of about 50 nm
were observed for 1ꢀ5 which suggest the change in the ground and excited state geometry.
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We believe that a large change in the dipole moment is a result of intramolecular charge
transfer from donor to acceptor moieties in compounds 1ꢀ5. The Stokes shift were further
increased in the more polar solvents which suggests the charge transfer complex formation in
1ꢀ5 and interaction with the polar solvents (see supporting information Table 1). The lone
pair of electrons in nonꢀbonding orbitals of amines interacts strongly with polar solvents
which may lead to the stabilization of polarized molecules in the excited state by polar
solvent. The emission of compounds 1ꢀ3 and 5 (540ꢀ586 nm) in the neat solid film were
bathochromically shifted (upto ~60 nm) as compared to emission in toluene. It may be due to
21
intermolecular aggregations of molecule in the solid state. Compound 4 could not be used
in thin film absorption and emission studies as it did not produce uniform neat solid films due
to poor solubility in common organic solvents.
Figure 6: Emission spectra of 1ꢀ5 in (a) toluene and (b) neat solid films.
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Table 1: Photophysical data of compounds 1ꢀ5 in toluene and thin film
a
a
a
b
c
c
d
Comp
λ
(
abs ,nm
λ
em
,
Stokes shift ,
F
λ
abs ,nm
λ
em
,
E
g
−
1
−1 a
log εmaxM cm )
nm
nm
43
41
48
56
65
nm
eV
1
2
3
4
303 (5.52), 348 (5.67), 397 501
4.54), 458 (4.65)
338 (5.40), 360 (5.06), 459 500
4.45)
303 (5.55), 351 (5.66), 415 527
4.60), 479 (4.61)
342 (5.69), 391 (4.55), 462 518
4.68)
310 (5.07), 358 (3.83), 447 512
4.22)
0.41 358, 407,
477
0.19
540
545
586
ꢀ
2.41
2.50
2.32
ꢀ
(
354, 479
(
0.10 303, 353,
423, 494
0.01
(
ꢀ
(
5
0.25 311, 364,
583
2.31
(
456
a
b
c
in toluene, Quantum yield with reference to Fluorescein (Ф =0.79 in ethanol, in neat solid film,
optical band gap estimated using emission and excitation spectra in neat solid film form.
d
The quantum yields of 1-5 were calculated using Fluoresceine (Ф = 0.79 in ethanol)
as reference and are tabulated in table 1. Quantum yields were found to be dependent on the
electronꢀdonating nature of diarylamine at 2,7ꢀpositions. Substitution of strong electronꢀ
donating amine resulted in decrease in quantum yield. Compounds 1ꢀ5 showed red shift of
emission maxima and low quantum yields with increasing polarity of solvents (See Table 1,
supporting information). It can be explained according to energy gap law, which says, excited
state internal conversion efficiency and fluorescence is reduced with a decrease in energy gap
between ground and excited states. Fluorescence life time for compounds 1ꢀ5 were measured
on TCSPC and are summarized in supporting information. All the compounds show a
doubleꢀexponential decay. A short lifetime (1ꢀ2 ns) combined with a longer lifetime (10 ns)
components are observed. Interestingly, the short/long fluorescence lifetimes composition
seems to follow a trend related to the energy distribution of the emission spectrum.
Compounds 1ꢀ5 were studied by cyclic voltammetry (CV) and differential pulse
voltammetry (DPV) to get an insight on the redox properties and molecular orbital energy
levels (HOMO and LUMO). Thus, the electrochemical properties obtained by CV
measurements are reported in Table 2 and cyclic voltammogram for compound 1 is shown in
Figure 7. Cyclic voltammetry of 10ꢀmethyl acridone (6) showed an irreversible oxidation
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wave at 1.55 V whereas two reversible oxidation peaks were obtained for compounds 1ꢀ5.
Oxidation at lower potential (0.71 to 0.91 V) is assigned for the oxidation of peripheral
amines while other at higher potential (1.02 to1.78 V) is attributed to oxidation of 10ꢀ
methylacridone core. Additional peak at 0.58 and 0.66 V were observed in 3 and 5
respectively and these were assigned to the oxidation of aliphatic methoxy and morpholine
groups. First oxidation potentials decrease with the increasing electron donating ability of
substituents in 1ꢀ5. Compounds 1ꢀ5 did not show substantial changes in the peak potential
even after repeated scans, revealing that compounds 1ꢀ5 are electrochemically stable during
these oxidation conditions. None of these compounds showed electrochemical reduction and
decomposition of compounds was observed, which was visible by change in color (dark
brown) near the working electrode during negative scan hence no reduction wave was
observed. The energy levels of the highest occupied and lowest unoccupied molecular
orbitals (HOMO and LUMO) were calculated from first oxidation potential and optical band
gap and are found in the range ofꢀ4.95 to ꢀ5.11 eV and ꢀ2.36 to ꢀ2.56 eV, respectively.
Table 2: Electrochemical and thermal data of compounds 1ꢀ5:
a
c
d
e
Comp
(V)
E
ELUMO (eV)
Tm (°C)
d
T (°C)
HOMO
b
(
eV)
1
2
0.74, 1.02
0.73, 1.05
ꢀ5.11
ꢀ5.11
ꢀ2.56
ꢀ2.56
170
240
391
428
402
178
3
4
5
0.58, 0.78, 1.24
0.71, 1.42
ꢀ4.95
ꢀ5.04
ꢀ5.02
ꢀ2.51
ꢀ2.49
1
98
17
302
345
2
0.66, 0.91, 1.78
ꢀ2.36
a
b
+
c
d
oxidation peak potential, EHOMO = ꢀ (E w.r.t. Fc/Fc + 4.8) eV, E
= EHOMOꢀoptical band gap,
LUMO
ox
e
Melting points, decomposition temperature obtained from the onset of TGA.
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Figure 7: Cyclic voltammogram of compound 1 and ferrocene (Fc) in acetonitrile.
To know the thermal stabilty of compounds 1ꢀ5 they were subjected for the thermal
gravimetric analysis (TGA). Thermograms of 1ꢀ5 are given in supporting information.
Melting points of 1ꢀ5 were recorded using capillary method and were observed in the range
of 170ꢀ240 °C. Decomposition temperature for these compounds were calculated using the
onset of weight loss in TGA. 1ꢀ5 showed no decomposition in the range of their melting
points. It was found that these compounds are thermally stable and decompose > 300 °C.
These decomposition temperatures are much higher than the usually used hole transporting
15,22b
materials.
The EHOMO for compounds 1ꢀ5 are similar to that of most widely used hole
transporting material NPD (N,N′ꢀDi(1ꢀnaphthyl)ꢀN,N′ꢀdiphenylꢀ(1,1′ꢀbiphenyl)ꢀ4,4′ꢀ
diamine), TPD (N,N′ꢀBis(3ꢀmethylphenyl)ꢀN,N′ꢀdiphenylbenzidineand spiroꢀOMeꢀTAD
2
2
(2,2',7,7'ꢀTetrakis[N,Nꢀdi(4ꢀmethoxyphenyl)amino]ꢀ9,9'ꢀspirobifluorene.
Electrochemical
(HOMO energy levels) properties along with thermal stability of these compounds are
promising which make these acridone derivatives suitable for hole transporter for OLEDs.
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Figure 8 shows the schematic representation of energy levels of 1ꢀ5 along with well known
and widely used hole transporters NPD, TPD and spiroꢀOMeꢀTAD. We further believe that
these compounds may show better stability in solid state devices as the oxidation of these
compounds are reversible as observed in cyclic voltammetry. The combination of the holeꢀ
transporting arylamine moiety and the electronꢀtransporting acridone in 1ꢀ5 may provide
bipolar charge transport property.
Figure 8: Schematic representation of HOMO and LUMO energy levels of 1ꢀ5, spiroꢀOMeꢀ
TAD, NPD and TPD
Conclusions
Five new acridone/amine derivatives were synthesized in good yield under mild
conditions using palladiumꢀcatalyzed BuchwaldꢀHartwig amination. These compounds were
characterized by several spectroscopic methods and their photophysical and electrochemical
properties were studied in solution and thin films. It was observed that the absorption,
emission and electrochemical properties of these new compounds were affected by the
electroꢀdonative nature of the peripheral diarylamine substituents. All compounds were found
to emit in the green region (500ꢀ527 nm) in toluene. A broad absorption band was observed
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on substitution of aryl amines on acridone which was attributed to charge transfer transitions
from the electron donating peripheral arylamine to electron acceptor acridone.
Electrochemical studies reveal the stability of these compounds under oxidative conditions.
The HOMO energy levels of these compounds are found in the range of -4.95 to -5.11 V
which is very similar with well known hole transporter eg. NPD, TPD and spiroꢀOMeꢀTAD.
The combination of the holeꢀtransporting arylamine moiety and the electronꢀtransporting
acridone in 1ꢀ5 may provide bipolar charge transport property. Electrochemical properties
along with thermal stability of these compounds are promising which make these acridone
derivatives suitable hole transporter for OLEDs. We further believe that these compounds
may show better stability in solid state devices owing to their reversible oxidation potentials.
Experimental
General
All the reagents were purchased from commercial sources (Sigma Aldrich and Alfa
Aesar) and were used without any further purification. The organic solvents were of
analytical or spectroscopic grade and were dried and freshly distilled using the standard
1
13
procedures whenever anhydrous solvents were required. HꢀNMR (300 MHz) and CꢀNMR
75 MHz) spectra were recorded on a Bruker Avance II 300 MHz Ultrashield spectrometer
with tetramethylsilane (TMS) as internal reference and residual CHCl in CDCl as reference.
(
3
3
Fourier transform infrared (FTꢀIR) spectra were recorded on a Perkin Elmer Frontier 91579.
Mass spectrometric measurements were recorded using MALDIꢀTOF (Bruker). Melting
points of the products were determined by open capillary method. Elemental analyses were
obtained on Elemental AnalyserꢀEURO Vector Italy EAꢀ3000. Cyclic voltammetry and
differential pulse voltammetry were carried out on a computer controlled (CH instruments,
620D). Typically, a three electrode cell equipped with a glassy carbon working electrode,
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Ag/AgCl (non–aqueous) reference electrode and platinum (Pt) wire as counter electrode were
employed. The measurements were carried at room temperature in anhydrous acetonitrile
with tetrabutyl ammonium hexafluorophosphate solution (0.1 M) as supporting electrolyte
–
1
with a scan rate of 100 mVs . The potential of Ag/AgCl reference electrode was calibrated
by using ferrocene/ferrocenium redox couple. Absorption and fluorescence data were
ꢀ6
acquired using ~2 X 10 M solutions of 1ꢀ5. UVꢀVisible spectra were recorded on
SHIMADZU U.V‒A114548 and fluorescence studies were done on Horiba Flurolog 3 at
room temperature. The fluorescence quantum yields (Ф
F
) were calculated relative to
Fluorescein (Ф = 0.79 in 0.1 M H SO . Fluorescence life times were recorded on time
F
2
4
correlated single photon counter (TCSPC). The neat solid films of compounds 1ꢀ5 were
prepared by using spin coater (Holmarc HOꢀTHꢀ05) at 1000 rpm for 2 min using ~6 mg/mL
of sample in chloroform. Quartz substrate was used for neat solid film studies. Thermal
e
studies were performed on Star system Mettler Toledo TGA 1 with a heating rate of 10
°C/min under inert atmosphere.
Synthesis
10ꢀMethylacridone, (6).10ꢀMethylacridone (6) was synthesized according to the reported
18a
procedures. To a mixture of 9(10H)ꢀacridone (6.00 g, 30.7 mmol) in anhydrous DMF (240
mL) was added NaH (3.07 g, 60% oil dispersion, 76.7 mmol) at 0°C. The reaction
temperature was raised slowly to room temperature and later mixture was stirred at 60 °C.
After for 30 min, iodomethane (4.80 ml, 77.0 mmol) was added, and stirring was continued at
2
60 °C for 18 h. The reaction mixture was quenched by slow addition of H O. The resulting
solid obtained by vacuum filtration was washed thoroughly with ethanol to give title
1
compound 6 as lightꢀyellow solid (5.77 g, 95%). M.P. 205 °C; HꢀNMR (300 MHz, CDCl
3
,
3
δ, ppm): 3.82 (3H, s, CH ), 7.24 (2H, t, J = 7.1 Hz, aromatic), 7.47 (d, 2H, J = 8.7
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13
Hz,aromatic), 7.67 (2H, d, J = 8.7 Hz, aromatic), 8.53 (2H, d, J = 8.01 Hz, aromatic); Cꢀ
NMR (75 MHz, CDCl , δ, ppm): 33.57, 114.73, 121.20, 122.42, 127.66, 133.76, 142.49,
3
178.04.
2,7ꢀDibromoꢀ10ꢀmethylacridone, (7). Molecular bromine (31 g, 0.19 mol) was added dropꢀ
wise over 20 min to a solution of 10ꢀmethylacridone (5 g, 25.5 mmol) in acetic acid (45 ml).
The solution was stirred continuously and heated at reflux temperature for 20 h, after which
half of the solvent was removed by vacuum distillation. The reaction mixture was allowed to
cool and then poured over crushed ice to obtain the yellow colored solid. The resulting solid
was filtered and collected and washed with sodium bicarbonate solution and further treated
with 20% aqueous solution of sodium bisulfate. The obtained solid was then dried under
vacuum and purified using column chromatography to afford the title compound as yellow
1
solid (7.85 g, 90%). HꢀNMR (300 MHz, CDCl
3
, δ, ppm): 3.87 (3H, s, CH
3
), 7.42 (2H, d, J =
13
9
.18 Hz, aromatic), 7.80 (2H, d , J = 9.15 Hz, aromatic), 8.62 (2H, s, aromatic); CꢀNMR
(
75 MHz, CDCl , δ, ppm): 34.02, 115.13, 116.91, 123.69, 130.22, 136.88, 141.20, 178.28.
3
General method for the synthesis of compound 1-5:
In a three necked round bottom flask equipped with reflux condenser and argon inlet and
outlet ports, 2,7-dibromoꢀ10ꢀmethylacridone (1.0 mmol) and diarylamine (2.2 mmol) were
dissolved in anhydrous toluene (20 ml) under argon atmosphere. The palladium catalyst
[
2 3
Pd (dba) ] (5ꢀ8 mol%), 2-dicyclohexylphoshpino-2΄,6΄-dimethylbiphenyl (SPhos) (10ꢀ
15mol%) and sodiumꢀtꢀbutoxide (3.1 mol) were added to the reaction mixture. The reaction
mixture was thoroughly stirred under argon atmosphere while the temperature was slowly
0
raised to 100 C. Reaction Mixture was stirred at this temperature for 12-24 hr. Reaction
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mixture was cooled to room temperature and extracted with chloroform (3 x 50 ml) followed
by water wash (3 x 50 ml). All organic layers were combined and dried over anhydrous
Na
2 4
SO and evaporated to get the crude product which was further purified by silica gel
column chromatography.
2,7-Bisꢀ(N,Nꢀdiphenylamino)ꢀ10ꢀmethylacridone, (1). A mixture of 2,7-dibromoꢀ10ꢀ
methylacridone (0.37 g, 1 mmol) and diphenylamine (0.37 g, 2.2 mmol) were reacted in
toluene as mentioned in general method. The crude solid thus obtained was purified by
column chromatography using hexane / chloroform to obtain a bright yellow solid. Yield:
°
–1
0
.28 g (52%);mp 170 C; FTIR (KBr, ν/cm ): 692.79, 746.31, 1172.65, 1270.99, 1294.73,
1
1
481.69, 1583.91, 3033.31: HꢀNMR (300 MHz, CDCl3, δ ppm): 3.90 (3H, s,CH
3
), 6.99 (4 H,
t, J = 6.1 Hz, aromatic), 7.07 ( 8H, d, J= 7.0Hz, aromatic), 7.23 (8H, t, J= 6.1Hz, aromatic),
7.45 (2H, d, J = 7.7Hz, aromatic), 7.53 (2H, d, J = 5.35Hz, aromatic), 8.23 (s, 2H, aromatic);
1
3
CꢀNMR (75 MHz, CDCl , δ, ppm): 30.90, 116.17, 121.79, 122.75, 123.05, 123.72, 126.17,
3
+
1
29.32, 130.23, 131.54, 141.60, 176.20; MALDI-TOF: Mass calcd for C H N O [M ]:
38
29
3
5
43.66; found: 543.75; Anal. Calcd. forC38
4.28; H, 5.32; N, 7.68.
29 3
H N O: C, 83.95; H, 5.38, N, 7.73.Found : C,
8
2,7-Bisꢀ(NꢀnaphthylꢀNꢀphenylamino)ꢀ10ꢀmethylacridone (2). A mixture of 2,7ꢀdibromoꢀ10ꢀ
methylacridone (0.36 g, 1 mmol) and NꢀnaphthylꢀNꢀphenyl amine (0.48 g, 2 mmol) were
reacted in toluene as mentioned in general method. The crude solid thus obtained was
purified by column chromatography using chloroform to obtain a bright yellow solid. Yield:
°
–1
0
.33 g (50%); M.P. 240 C; FTIR (KBr,ν/cm ): 693.71, 748.09, 1174.97, 1273.18, 1484.09,
1
1
592.99, 2970.41, 3038.73; HꢀNMR (300 MHz, CDCl , δ, ppm): 3.78 (3H, s, CH ), 6.91
3
3
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(2H, t, J = 7.2Hz, aromatic), 6.98 (4H, d, J = 7.7Hz, aromatic), 7.16 (4H, t, J = 7.4Hz,
aromatic), 7.29ꢀ7.48 (14H, m, aromatic), 7.74 (2H, d, J = 8.1 Hz, aromatic), 7.86 (2H, d, J =
1
3
8
3
.1 Hz, aromatic), 7.94 (2H, d, J = 8.4 Hz, aromatic); CꢀNMR (75 MHz, CDCl , δ, ppm):
29.70, 115.86, 119.19, 121.02, 121.53, 122.82, 124.12, 126.11, 126.38, 126.60, 127.14,
128.46, 129.19, 129.52, 131.10, 135.39, 137.87, 142.37, 143.27, 148.50, 176.70; MALDI-
+
TOF: Mass calcd. for C44
H
33
N
3
O [M ]: 643.77; found: 644.11:Anal. Calcd. forC44
H
33
N
3
O: C,
85.82; H, 5.17; N, 6.53. Found : C, 86.12, H, 5.23, N, 6.49.
2,7-Bisꢀ(N,Nꢀdianisylamino)ꢀ10ꢀmethylacridone, (3). A mixture of 2,7-dibromo–10–
methylacridone (0.36 g, 1 mmol) and 4,4`methoxydiphenyl amine (0.50 g, 2 mmol) were
reacted in toluene as mentioned in general method. The crude solid thus obtained was
purified by column chromatography using hexane / chloroform to obtain a bright orange
°
–1
solid. Yield: 0.38 g (58%); M.P. 178 C; FTIR (KBr, ν/cm :): 721.11, 808.08, 1029.65,
1
1
172.27, 1234.21, 1499.72, 1593.89, 2832.08, 2928.79; HꢀNMR (300 MHz, CDCl
3
, δ,
ppm): 3.77 (12H, s, OCH ), 3.83 (3H, s, OCH ), 6.79 (8H, d, J = 8.7 Hz, aromatic), 7.02 (8H,
3
3
13
d, J = 8.4 Hz, aromatic), 7.34ꢀ7.42 (4H, m, aromatic), 8.04 (2H, s, aromatic); CꢀNMR (75
MHz, CDCl
3
, δ, ppm): 33.56, 55.51, 114.81, 115.63, 118.09, 127.76, 125.76, 129.00, 137.33,
+
141.12, 142.75, 155.65, 176.61; MALDI-TOF: Mass calcd for C42
H
37
N
3
O
5
[M ]: 663.76;
37 3 5
found: 663.79; Anal. Calcd. forC42H N O : C, 76.00; H, 5.62; N, 6.33.Found: C, 76.33, H;
5.74; N, 6.43.
2,7ꢀBisꢀ(Nꢀ(pꢀaminobenzene),Nꢀphenylamino)ꢀ10ꢀmethylacridone (4). A mixture of 2,7-
dibromoꢀ10ꢀmethylacridone (0.36 mg, 1 mmol) and N-phenyl-p-phenylenediamine (0.40 g,
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2.2 mmol) were reacted in toluene as mentioned in general method. The crude solid thus
obtained was purified by column chromatography using chloroform / ethylacetate as solvent
°
–1
to obtain a bright orange solid. Yield: 0.32 g (56%); M.P. 217 C; FTIR (KBr, ν/cm ):
690.67, 743.52, 804.56, 1175.16, 1224.62, 1286.89, 1489.49, 1519.86, 1589.36, 2922.97,
1
3
022.18, 3289.46, 3391.34; HꢀNMR (300 MHz, CDCl
3
, δ, ppm): could not be obtained
+
because of very poor solubility; MALDI-TOF: Mass calcd. for C38
H
31
N
5
O [M ]: 573.69;
31 5
found: 573.78; Anal. Calcd. forC38H N O: C, 79.56; H, 5.45; N, 12.21.Found: C, 79.83; H,
5.51; N, 12.31.
2,7ꢀBisꢀ(morpholino)ꢀ10ꢀmethylacridone, (5). A mixture of 2,7-dibromo–10–methylacridone
(0.36 g, 1 mmol) and morpholine (0.19 g, 2.2 mmol) were reacted in toluene as mentioned in
general method. The crude solid thus obtained was purified by column chromatography using
°
chloroform to obtain a bright yellow solid. Yield: 0.24 g (62%); M.P. 198 C; FTIR (KBr
–1
ν/cm ): 636.97, 726.17, 793.32, 908.81, 1114.03, 1210.84, 1264.28, 1495.94, 1586.24,
1
2
855.94, 2964.48, 3055.22; HꢀNMR (300 MHz, CDCl , δ, ppm): 3.25 (8H, t, J = 4.7Hz,
3
NCH
2
), 3.86 (3H, s, CH
3
), 3.91 (8H, t, J = 4.8 Hz,OCH
2
), 7.36ꢀ7.43 (4H, m, aromatic), 7.97
, δ, ppm): 33.44, 49.96, 66.91,
13
(2H, d, J = 2.7 Hz, aromatic); CꢀNMR (75 MHz, CDCl
3
111.22, 115.82, 122.38, 124.41, 136.82, 145.50, 177.17; MALDIꢀTOF: Mass calcd for
+
C
22
H
25
N
3
O
3
[M ]: 379.45; found: 379.54; Anal. Calcd. forC22
H
25
N
3
O
3
: C, 69.64; H, 6.64; N,
11.07.Found: C, 69.95; H, 6.71; N, 10.92.
1
13
Supporting information: HꢀNMR, CꢀNMR, MALDI mass, FTIR, absorbance and
emission spectra in different solvents, fluorescence life times and decay profiles, cyclic
voltammograms, thermograms etc. are provided in supporting information.
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Acknowledgement
BKS and AS thank the University Grant Commission, India for research fellowships. We
thank the MicroꢀAnalytical Laboratory, Department of Chemistry, University of Mumbai and
UMꢀDAE, Centre for Excellence in Basic Sciences, Mumbai for providing instrumentation
facility. We also thank the Bhabha Atomic Research Centre, Mumbai for TCSPC and Tata
Institute of Fundamental Research, Mumbai for MALDIꢀTOF facilities.
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