Synthesis of perylene dyes with multiple triphenylamine substituents

Article abstract of DOI:10.1002/chem.201201196

Perylene monoimide (PMI) was brominated to give tetra- and tribrominated molecules, which underwent a Suzuki coupling reaction with 4-(diphenylamino) phenylboronic acid to give PMI derivatives. The photophysical and electrochemical properties of the synthesized compounds were investigated, and theoretical calculations were performed. Single crystals of tetrasubstituted PMI were grown and studied in detail. The structure-property relationships were examined to reveal the effect of the position and number of substituents on the perylene core unit. All molecules showed a broad absorption up to 750 nm. Corresponding anhydrides of PMIs were used for fabrication of dye-sensitized solar cells. The molecule with four triphenylamine units on perylene monoanhydride showed the highest power conversion efficiency. Copyright

Full text of DOI:10.1002/chem.201201196

FULL PAPER
DOI: 10.1002/chem.201201196
Synthesis of Perylene Dyes with Multiple Triphenylamine Substituents
Ashok Keerthi,[a, b] Yeru Liu,[b, c] Qing Wang,[b, c] and Suresh Valiyaveettil*[a, b]
Abstract: Perylene monoimide (PMI)
was brominated to give tetra- and tri-
brominated molecules, which under-
went a Suzuki coupling reaction with 4-
(diphenylamino)phenylboronic acid to
give PMI derivatives. The photophysi-
cal and electrochemical properties of
the synthesized compounds were inves-
tigated, and theoretical calculations
were performed. Single crystals of tet-
rasubstituted PMI were grown and
studied in detail. The structure–proper-
ty relationships were examined to
reveal the effect of the position and
number of substituents on the perylene
core unit. All molecules showed a
broad absorption up to 750 nm. Corre-
sponding anhydrides of PMIs were
used for fabrication of dye-sensitized
solar cells. The molecule with four tri-
phenylamine units on perylene mono-
anhydride showed the highest power
conversion efficiency.
Keywords: density functional calcu-
lations · dyes/pigments · polycycles ·
solar cells · substituent effects
Introduction
with a wide absorption range covering most of the solar
spectrum up to the NIR region is interesting and used in the
current investigation.[2b,5f,11] Triphenylamine (TPA) is known
to be an efficient donor moiety that interacts electronically
with the perylene core to produce interesting intramolecular
charge transfer (ICT).[11] Herein, the design and synthesis of
a series of TPA-functionalized perylene monoanhydrides
(PMAs) from multibrominated perylene monoimides
(PMIs) is reported. The effects of the number and steric
crowding of TPA groups and overall conformation of the
PMI molecules on the photophysical and electrochemical
properties are investigated. Good-quality single crystals of
the four TPA-incorporated PMIs were grown and analyzed
to understand the influence of steric crowding on the confor-
mation and lattice packing of such a big molecule. Careful
separation of regioisomers of perylene is a key step involved
in synthesizing target molecules.
Recently, the design and synthesis of advanced materials
with the perylene chromophore has been an active area of
research.[1] Unique light-harvesting and redox properties
combined with high thermal stabilities of perylene dyes
offer potential applications in organic field-effect transis-
tors,[2] xerography,[3] organic light-emitting diodes,[4] and
photovoltaic devices.[5] In metal-free dyes, perylene deriva-
tives have been widely applied in various optical devices,[6]
light-harvesting arrays, and photosynthetic systems.[7] More
recently, perylene-based dyes were used in biological appli-
cations.[8] A rising interest is to use ruthenium-free dyes as
sensitizers for dye-sensitized solar cells (DSSCs),[9] because
such dyes hold many advantages over ruthenium-based dyes
such as a higher absorption coefficient, lower cost, and ease
of tuning molecular energy levels. However, to obtain a
single sensitizer that is capable of effectively capturing light
over the entire spectrum from the visible to near-infrared
(NIR) region and simultaneously fulfills all the requirements
for an efficient device remains a challenge.[10]
Results and Discussion
The strategy of incorporating multiple donor moieties on
to the single acceptor moiety to obtain a stable, soluble dye
The molecular structures of all synthesized target com-
pounds are given in Scheme 1. In compound 8, the TPA
units are attached to the PMA moiety through the 1,6,9 po-
sitions, whereas TPA is attached at the 1,9,10 positions in
compound 9 and the 1,6,9,10 positions in compound 10, thus
leading to incorporation of multiple donors into a single ac-
ceptor unit. All compounds have been isolated, purified,
and fully characterized.
Syntheses of target compounds were achieved through the
following route. N-(2-Ethylhexyl)perylene-3,4-dicarboximide
(1) was synthesized from 3,4,9,10-perylenetetracarboxylic
acid anhydride (PDA) by partial decarboxylation following
a modified procedure reported earlier.[12] The selective bro-
mination of the N-substituted (aryl/alkyl)perylene-3,4-dicar-
boximides was reported with bromine in chlorobenzene and
methylene chloride to give monobromination at the 9 posi-
[a] A. Keerthi, Prof. S. Valiyaveettil
Department of Chemistry, National University of Singapore
3 Science Drive 3, Singapore 117543 (Singapore)
E-mail: chmsv@nus.edu.sg
[b] A. Keerthi, Y. Liu, Dr. Q. Wang, Prof. S. Valiyaveettil
NUSNNI-NanoCore, T-Lab Building
National University of Singapore
5A Engineering Drive 1, Singapore 117411 (Singapore)
[c] Y. Liu, Dr. Q. Wang
Department of Materials Science and Engineering
Faculty of Engineering, National University of Singapore
Singapore 117574 (Singapore)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201201196.
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Scheme 1. Synthesis of functionalized PMI and PMA compounds.
tion,[13,14] and bromination under reflux conditions in chloro-
form gave threefold bromination at the 1,6,9 positions of N-
arylPMI.[11a,12,13c,14,15] In this study, the bromination of N-(2-
ethylhexyl)perylene-3,4-dicarboximide in chloroform under
reflux conditions gave tetrabromo- and tribromoPMI in
good yields. The crude brominated PMI showed two spots
on a thin-layer chromatography (TLC) plate with a mixture
of dichloromethane and hexane (1:1). The crude mixture
spectrum of the compound with an Rf value of 0.78 showed
two sets of peaks, which are assigned to 1,6,9,10-tetrabro-
moPMI (4) and 1,6,9-tribromoPMI (2); MALDI-TOF analy-
sis also confirmed the presence of both compounds.
1
The H NMR spectrum of a second compound with an Rf
value of 0.74 was assigned to 1,9,10-tribromoPMI (3). It was
found that the solubility of tribromo- and tetrabromoPMI
derivatives varies in common solvents. Repetitive precipita-
tion from hexane gave pure tetrabromoPMI, which was
1
was purified by column chromatography and the H NMR
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Perylene Dyes with Triphenylamine Substituents
FULL PAPER
1
used for further characterization. From the H NMR analy-
sis of the crude mixture, the mole ratio of compounds 2–4
was found to be 4:2:1, respectively.
The syntheses of TPA-substituted PMI compounds 5–7
are depicted in Scheme 1. The brominated crude mixture
was reacted with 4-(diphenylamino)phenylboronic acid by
the Suzuki coupling reaction to obtain compounds 5–7.
These compounds were successfully purified by column
chromatography and were then characterized.
Alkaline treatment of compounds 5–7 with KOH/tBuOH
afforded the target PMAs 8–10, respectively. All molecules
were highly soluble in common organic solvents, such as di-
chloromethane, chloroform, and tetrahydrofuran (THF).
Single crystals of tetra-TPA-substituted PMI (7) were ob-
tained by slow diffusion of hexane into a solution of the
compound in chloroform. The molecules were packed in tri-
¯
clinic space group P1. The asymmetric unit contains one
tetra-TPA-substituted PMI (7) molecule and two chloroform
molecules. Two molecules of compound 7 form a dyad in a
head-to-tail fashion through strong p–p interactions
(Figure 1) with a separation of 3.81 ꢁ. In the crystal struc-
ture, two naphthalene units of the perylene moiety are dis-
torted to an angle of 21.58 from planarity owing to the pres-
ence of bulky TPA substitution at the 1 and 6 positions of
the perylene core (bay positions). The individual benzene
rings of the naphthalene unit away from the imide group are
further distorted to an angle of 308 due to the steric hin-
drance from substitution at the 9 and 10 positions of the per-
ylene core (peri positions). The TPA groups interact with
molecules in the adjacent lattice to fill up the volume and
molecules are packed in an ABC pattern (Figures S6 and S7
in the Supporting Information). No strong interactions are
observed among the phenyl groups of the TPA units from
the adjacent molecules.
Figure 2. Absorption (solid lines) and emission (dotted lines) spectra of
PMI (A) and PMA (B) compounds (10À5 m) in chloroform at room tem-
perature.
The absorption spectra of PMA dyes in chloroform are
shown in Figure 2B. The broader absorption between 400
and 750 nm is attributed to an extended conjugation and
photoinduced ICT absorption of the perylene dye, which re-
sults from the orbital partitioning induced from substitution
of TPA on the perylene core.[11a–c] This ICT absorption band
was clearly visible in the case of TPA-substituted perylene
diimide systems.[11d,e] Compared to the trisubstituted PMAs,
tetrasubstituted PMA (10) shows broad absorption up to
sorption than 8, which indicates that the substitution at the
peri position improves the ICT absorption. The same trend
was also observed for the PMI compounds 5–7 with a blue-
shift on lmax values relative to their respective PMA dyes.
The absorption spectra of compounds 5 and 6 were similar,
with no influence from the position of substituents in these
tri-TPA-substituted compounds. All three PMA dyes dis-
played broader absorption properties across the visible
region of the spectrum.
750 nm
with
a
high
extinction
coefficient
of
56600mÀ1 m3 cmÀ1. Compound 9 showed slightly broader ab-
The emission spectra of PMA
dyes in CHCl3 were acquired by
excitation at their respective
lmax
,
and are presented in
Figure 2 and summarized in
Table 1. As expected the emis-
sion intensity was significantly
lower in all cases compared
with unsubstituted PMI.[16] This
can be rationalized by intramo-
lecular electron-transfer proc-
esses and vibrational relaxation
Figure 1. A) Crystal structure of compound 7, B) dyad formation, and C) schematic view of the dyad.
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S. Valiyaveettil et al.
Table 1. Summary of photophysical and electrochemical properties of TPA–PMI/
PMA dyes.
stituents as well as on the perylene core, whereas
the LUMOs are seen on the perylene core and on
the anhydride moiety, as expected. The calculated
HOMO and LUMO energy values were found to
be slightly higher, also as expected, and this trend
was in agreement with experimental values.[11a–d]
The twisting angle (q) of the perylene core of the
molecules 8–10 was different (Table 2). In the case
of compound 7, the twisting angle was 228, which is
in agreement with single-crystal data.
[a]
[a]
[b]
[b]
[e]
Compound lmax
lem
Eox
Ered
HOMO[c] LUMO[d] Eg
[nm]
[nm] [V]
[V]
[eV]
[eV]
[eV]
5
6
7
8
9
576, 483 667
582, 477 679
608, 497 700
582, 488 695
595, 488 714
624, 515 721
0.42, 0.52, 0.90 À1.34 À5.22
0.47, 0.59, 0.93 À1.35 À5.25
0.40, 0.60, 0.97 À1.39 À5.20
0.35, 0.54, 0.98 À1.30 À5.15
0.33, 0.53, 0.97 À1.29 À5.13
0.37, 0.56, 1.01 À1.27 À5.14
À3.46
À3.45
À3.41
À3.50
À3.51
À3.53
1.76
1.80
1.79
1.65
1.62
1.61
10
[a] Recorded in chloroform. [b] Versus ferrocene in 0.1m Bu4NPF6 in dichlorome-
thane, with a platinum disk as the working electrode and a scan rate of 100 mVsÀ1
.
In a preliminary test, DSSCs were fabricated by
immersing TiO2 electrodes in solutions of com-
pounds 8–10 in THF. The electrode had a double-
layer structure consisting of a 12 mm thick transpar-
[c] Calculated by using the relationship EHOMO =À(Eooxnset +4.8). [d] Calculated by using
the relationship ELUMO =À(Eorendset +4.8). [e] Electrochemical bandgap.
upon substitution of electron-donating TPA groups on the
electron-deficient perylene core.[5f,11a,d] The emission maxi-
mum of 8 appeared at 695 nm. The introduction of the TPA
moiety at the 9 and 10 positions of perylene resulted in a
bathochromic shift of the emission maxima to 714 and
721 nm for compounds 9 and 10, respectively. In the case of
compounds 6 and 7, a significant difference in emission max-
imum was observed (21 nm). A significant redshift in emis-
sion maximum was noticed for peri-substituted over bay-
substituted compounds.
ent layer with 20 nm TiO2 nanoparticles and a 4 mm thick
scattering layer of 400 nm TiO2 nanoparticles. The electro-
des were immersed in a 0.25 mm solution (THF) and left
overnight before being removed and rinsed in THF immedi-
ately before cell assembly. Photoanodes and platinized coun-
The electrochemical properties were investigated by cyclic
voltammetry and all PMA and PMI dyes showed ambipolar
redox behavior (Figure 3 and Figure S1 in the Supporting
Information). During the positive potential sweep, all dyes
showed three reversible oxidation peaks, for which the first
and second oxidation potentials were assigned to the oxida-
tion of TPA.[11d] The third oxidation peak may correspond to
perylene core oxidation.[13d] In the negative potential
regime, only one characteristic reduction wave of the pery-
lene moiety was observed.[11a] This was also supported by
theoretical calculations. The HOMO and LUMO energy
levels were determined from the oxidation and reduction
onset potentials (Table 1). Interestingly, dyes 8–10 possess a
similar energy gap (Eg) as the
Figure 3. Cyclic voltammograms of PMA dyes 8–10 in 0.1m Bu4NPF6 in
dichloromethane, with a platinum disk as working electrode at a scan
rate of 100 mVsÀ1 in dichloromethane. Fc/Fc+ =ferrocene/ferrocenium.
positions of the HOMO and
LUMO levels were not signifi-
cantly different.
To gain further insight into
the geometric, electronic, and
optical properties of perylene
dyes, hybrid density functional
theory (DFT) at the B3LYP
level with 6-31G(d) as the basis
set was used for geometry and
energy optimization. The opti-
mized structures of the respec-
tive molecules and the distribu-
tion of frontier orbitals were
calculated (Figure 4, Figures S2
and S3 in the Supporting Infor-
mation).
Surprisingly,
the
HOMOs of PMA/PMI dyes are
Figure 4. The optimized geometric structures of TPA–PMA dyes and their frontier orbitals were calculated by
distributed on the TPA sub- DFT at the B3LYP/6-31G(d) level.
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Perylene Dyes with Triphenylamine Substituents
FULL PAPER
Table 2. Theoretically calculated data of synthesized PMI/PMA dyes.
Conclusion
Compound
HOMO
[eV]
LUMO
[eV]
Eg
[eV]
Twisting angle
[q]
We have synthesized highly stable and soluble TPA-incorpo-
rated PMA dyes with interesting architectures. The number
and positions of TPA units on PMI/PMA were studied. The
tetrasubstituted compound showed a redshift in absorption
spectra and peri substitution broadened the absorption spec-
trum. Theoretical studies were in agreement with the photo-
physical and electrochemical studies. In the single-crystal
analysis of compound 7, two molecules were packed in a
head-to-tail motif by following the ABC packing pattern.
These compounds were used in the fabrication of DSSCs, in
which tetrasubstituted compound 10 gave the highest effi-
ciency. This finding highlights the fact that more donor
groups on a single acceptor unit may be better to enhance
the power conversion efficiency of future dyes. A detailed
investigation of regioselectivity in bromination of PMI and
optimization of DSSC performance of the synthesized mole-
cules are in progress in our laboratory.
1
5
6
7
8
À5.49
À4.84
À4.87
À4.76
À4.95
À4.98
À4.87
À2.77
À2.58
À2.61
À2.58
À2.77
À2.80
À2.74
2.72
2.26
2.26
2.18
2.18
2.18
2.13
0
21
17
22
23
17
22
9
10
ter electrodes were sealed together in a sandwich configura-
tion and were filled with an electrolyte (1m propylmethyli-
midazolium iodide, 0.1m I2, 0.1m lithium bis(trifluorometha-
ne)sulfonamide, and 0.5m N-methylbenzimidazole) by
vacuum back-filling. The current–voltage (I–V) characteris-
tics and power conversion efficiencies (h) were evaluated
for all three PMA dyes under simulated air mass (AM) 1.5
illumination and are presented in Figure 5 and Table 3.
Experimental Section
Materials: All chemicals and reagents were purchased from commercial
suppliers (Sigma–Aldrich and Merck) and used without further purifica-
tion. Solvents for spectroscopic measurements were spectral-grade quali-
ty. All reactions were monitored by TLC carried out on silica gel plates.
Preparative separations were performed by column chromatography on
silica gel grade 60 (0.040–0.063 mm) from Merck.
1
Instrumentation and characterization: H NMR spectra were recorded on
Bruker Avance AV300 (300 MHz) and AV500 (500 MHz) spectrometers.
The peaks are represented as s=singlet, d=doublet, t=triplet, m=mul-
tiplet, and br=broad. The chemical shifts are reported in ppm and refer-
enced to the residual solvent peak. MALDI-TOF mass spectra were ob-
tained on a Bruker Autoflex III spectrometer. Elemental analysis was
carried out on an Elementar Vario Micro Cube. UV/Vis and emission
spectra were measured on a Shimadzu UV-1601 PC spectrophotometer
and RF-5301PC Shimadzu spectrofluorophotometer. Current–voltage (I–
V) characteristics under simulated AM 1.5 illumination were measured
by using a Keighley Source Meter and the PVIV software package (New-
port). Simulated AM 1.5 illumination was provided by a Newport class A
solar simulator and light intensity was measured by using a calibrated Si
reference cell. The thickness of nanocrystalline TiO2 layers was deter-
mined by profilometry measurements made by means of an Alpha-Step
IQ surface profiler.
Figure 5. I–V characteristics of solar cells of TPA–PMA dyes under
AM 1.5 illumination.
Table 3. I–V data of TPA–PMA dyes.
Compound
Jsc
Voc
[V]
h
Fill factor
[%]
[mAcmÀ2
]
[%]
Cyclic voltammograms were recorded with a computer-controlled CHI
electrochemical analyzer at a constant scan rate of 100 mVsÀ1. Measure-
ments were performed in an electrolyte solution of 0.1m tetrabutylammo-
nium hexafluorophosphate dissolved in degassed dichloromethane. The
electrochemical cell consisted of a three-electrode system with a platinum
disk as the working electrode, a platinum rod as the counter electrode,
and a standard calomel electrode (SCE) as the reference electrode. The
potentials were calibrated by using ferrocene as the internal standard.
8
9
10
2.22
2.07
3.08
0.59
0.57
0.53
0.95
0.85
1.14
69.5
69.0
66.8
The low power conversion was on account of lower cur-
rent density (Jsc) values, which may be due to insufficient
dye loading on the electrodes, even though the dyes showed
broad absorption spectra. The open-circuit voltage (Voc)
values were not optimized and slightly lower than reported
values.[11a] The current values and efficiencies could be im-
proved by 1) increasing the dye loading on TiO2 by incorpo-
rating solubilizing groups on the molecule, 2) optimizing the
performance of the electrolyte and electrodes, and 3) lower-
ing the bulkiness of the substituents at the bay position.
onset
ox
onset
red
The onsets of oxidation (E ) and reduction (E ) were used to calcu-
late the HOMO and LUMO energy levels by using the relationships
onset
ox
E
HOMO =À
ACHTUNGTRENNUNG
optimizations were performed in Gaussian 09[17] at the DFT level with
the B3LYP functional and the 6-31G(d) basis set. The HOMO and
LUMO surfaces were generated from the optimized geometries by using
GaussView 5.[18]
N-(2-Ethylhexyl)perylene-3,4-dicarboximide (1): Following the literature
procedure,[12] samples of perylene-3,4,9,10-tetracarboxylic acid anhydride
(PDA; 2.5 g, 6.4 mmol), 2-ethylhexylamine (0.42 g, 3.3 mmol), Zn(OA-
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S. Valiyaveettil et al.
c)2·2H2O (0.39 g, 1.81 mmol), imidazole (13 g), and H2O (6 mL) were
placed in an autoclave. The mixture was heated at 1908C. After 24 h, the
reaction mixture was cooled to room temperature and poured into water
(30 mL). The resulting mixture was vacuum filtered and washed with
water (50 mLꢂ4) and methanol (50 mL). The isolated solid was purified
by flash column chromatography with chloroform as the eluent to give a
Synthesis of TPA-substituted PMI molecules by Suzuki coupling reac-
tion: The brominated mixture of PMI (0.336 g) and 4-(diphenylamino)-
phenylboronic acid (0.578 g, 2 mmol) was dissolved in THF (20 mL) in a
two-neck round-bottomed flask (100 mL) under a nitrogen atmosphere.
A nitrogen-purged aqueous solution of 1m K2CO3 (10 mL) was added to
this reaction mixture. Catalyst [Pd(PPh3)4] (0.058 g, 0.05 mmol) was
added and the mixture was stirred for 24 h at 808C under a nitrogen at-
mosphere. The reaction mixture was allowed to cool to room tempera-
ture and was extracted with dichloromethane. The collected organic layer
was dried over anhydrous sodium sulfate and filtered. The excess solvent
was removed under reduced pressure. The crude mixture showed three
spots on TLC plates with 5% ethyl acetate in hexane as the eluent, with
Rf values of 0.39, 0.35, and 0.32. The crude mixture was purified by
column chromatography by using 5% ethyl acetate in hexane as the
mobile phase and all three compounds were collected. The mole ratio of
compounds 5–7 was 4:2:1, respectively, which was also comparable to the
brominated crude mixture.
1
red compound (m.p. >3008C, 24%, 0.66 g). H NMR (300 MHz, CDCl3):
d=8.06 (d, J=7.20 Hz, 2H), 7.85 (d, J=7.80 Hz, 2H), 7.74 (d, J=
8.10 Hz, 2H), 7.61 (d, J=7.80 Hz, 2H), 7.31 (t, J1 =J2 =7.80 Hz, 2H),
4.05–4.00 (m, 2H; N-CH2), 1.94–1.90 (m, 1H), 1.44–1.34 (m, 8H), 0.99–
0.89 ppm (m, 6H); 13C NMR (75 MHz, CDCl3): d=163.9, 136.2, 133.8,
130.7, 130.4, 129.0, 128.5, 127.2, 126.5, 125.8, 123.0, 120.4, 119.5, 44.0,
38.1, 30.8, 28.8, 24.1, 23.2, 14.2, 10.7 ppm; FAB MS: m/z: 433.21 [M]+; el-
emental analysis calcd (%) for C30H27NO2: C 83.11, H 6.28, N 3.23;
found: C 83.21, H 6.34, N 3.17.
Bromination of N-(2-ethylhexyl)perylene-3,4-dicarboximide: N-(2-Ethyl-
hexyl)perylene-3,4-dicarboxydiimide (0.500 g, 1.15 mmol) was dissolved
in chloroform (30 mL) in a two-neck round-bottomed flask (100 mL),
bromine (3 mL, 58 mmol) was added, and the solution was heated at
reflux for 10 h. The reaction mixture was cooled to room temperature,
excess bromine was removed by passing through an aqueous solution of
sodium thiosulfate with an air pump, and solvent was removed on a
rotary evaporator. The crude brominated PMI (0.80 g) showed two close-
ly separated spots on a TLC plate by using an eluent of dichloromethane
and hexane (1:1). The crude mixture (100 mg) was purified by silica gel
column chromatography and the 1H NMR spectrum of the spot with an
Rf value of 0.78 (65 mg) showed two sets of peaks, which were assigned
to 1,6,9,10-tetrabromoPMI (4) and 1,6,9-tribromoPMI (2) present in a
ratio of approximately 1:4. The 1H NMR spectrum of a second spot with
an Rf value of 0.74 (0.26 mg) was assigned to 1,9,10-tribromoPMI (3).
The molar ratio of compounds 2–4 was approximately 4:2:1, respectively.
N-(2-Ethylhexyl)-1,6,9-tri(triphenylamine)perylene-3,4-dicarboximide (5):
Compound 5 (Rf = 0.39) was obtained as a dark blue solid (290 mg, m.p.
146–1488C). 1H NMR (300 MHz, CDCl3): d=8.56 (s, 2H; Per-H), 7.96
(d, J=8.07 Hz, 1H; Per-H), 7.88 (m, 2H; Per-H), 7.38–7.34 (m, 3H),
7.32–7.27 (m, 13H), 7.20–7.14 (m, 22H), 7.09–7.02 (m, 6H), 4.19–4.11 (m,
2H; N-CH2), 1.98 (m, 1H), 1.43–1.32 (m, 8H), 0.97–0.87 ppm (m, 6H);
13C NMR (75 MHz, CDCl3): d=164.4, 147.6, 147.51, 147.49, 147.36,
147.31, 141.6, 138.8, 138.6, 137.6, 137.5, 135.6, 135.3, 135.2, 133.3, 131.5,
130.9, 130.7, 130.5, 130.2, 130.1, 130.0, 129.4, 129.3, 128.8, 128.0, 127.7,
127.1, 126.3, 125.0, 124.7, 124.6, 124.5, 124.4, 123.3, 123.1, 123.0, 122.9,
120.0, 119.8, 44.0, 38.0, 30.8, 28.8, 24.1, 23.1, 14.1, 10.7 ppm; MALDI-
TOF MS: m/z: 1163.74 [M]+; elemental analysis calcd (%) for
C84H66N4O2: C 86.72, H 5.72, N 4.82; found: C 86.64, H 5.66, N 4.78.
N-(2-Ethylhexyl)-1,9,10-tri(triphenylamine)perylene-3,4-dicarboximide
(6): Compound 6 (Rf = 0.35) was obtained as a black solid (140 mg, m.p.
156–1588C). 1H NMR (300 MHz, CDCl3, ppm): d=8.59 (s, 1H; Per-H),
8.17 (d, J=8.22 Hz, 1H; Per-H), 8.10 (d, J=8.73 Hz, 1H; Per-H), 7.93 (d,
J=7.89 Hz, 1H; Per-H), 7.76 (d, J=8.22 Hz, 1H; Per-H), 7.53 (d, J=
8.88 Hz, 1H; Per-H), 7.45–7.40 (m, 3H), 7.37–7.29 (m, 15H), 7.21–7.10
(m, 15H), 7.08–7.03 (m, 10H), 4.17–4.12 (m, 2H; N-CH2), 1.97 (m, 1H),
1.42–1.32 (m, 8H), 0.97–0.87 ppm (m, 6H); 13C NMR (75 MHz, CDCl3):
d=164.50, 164.46, 147.8, 147.6, 147.5, 147.4, 147.3, 141.5, 141.0, 140.7,
137.6, 137.4, 137.0, 136.7, 136.7, 136.6, 135.4, 135.2, 135.0, 133.3, 133.2,
131.1, 131.0, 130.9, 130.7, 130.6, 130.2, 130.1, 129.9, 129.43, 129.40, 129.3,
129.2, 129.1, 128.4, 128.2, 127.9, 127.2, 126.4, 125.1, 124.9, 124.8, 124.7,
124.6, 124.5, 124.4, 124.0, 123.9, 123.4, 123.3, 123.2, 123.1, 122.9, 122.8,
119.8, 119.5, 44.1, 38.0, 30.8, 28.8, 24.0, 23.1, 14.1, 10.7 ppm; MALDI-
TOF MS: m/z: 1163.70 [M]+; elemental analysis calcd (%) for
C84H66N4O2: C 86.72, H 5.72, N 4.82; found: C 86.67, H 5.69, N 4.88.
N-(2-Ethylhexyl)-1,6,9,10-tetrabromoperylene-3,4-dicarboximide
(4):
Compound 4 was precipitated from a solution of the mixture of 2 and 4
in dichloromethane by using hexane, and the procedure was repeated
five times to give a red precipitate (m.p. >3008C) with a yield of 13%
(from 1H NMR analysis). 1H NMR (300 MHz, CDCl3): d=8.92 (d, J=
8.40 Hz, 2H; Per-H), 8.84 (s, 2H; Per-H), 8.10 (d, J=8.40 Hz, 1H; Per-
H), 4.14–4.10 (m, 2H; N-CH2), 1.96–1.90 (m, 1H), 1.40–1.30 (m, 8H),
0.96–0.87 ppm (m, 6H); MALDI-TOF MS: m/z: 749.69 [M]+; elemental
analysis calcd (%) for C30H23Br4NO2: C 48.10, H 3.09, Br 42.67, N 1.87;
found: C 48.02, H 3.18, Br 42.69, N 1.95.
N-(2-Ethylhexyl)-1,6,9-tribromoperylene-3,4-dicarboximide (2): After re-
petitive precipitation of compound 4 from the mixture, a small amount
of compound 2 was formed as a red compound (m.p. 2178C) from the re-
maining solution with a yield of 54%. 1H NMR (500 MHz, CDCl3): d=
9.22 (d, J=7.00 Hz, 1H; Per-H), 9.00 (d, J=8.20 Hz, 1H; Per-H), 8.81 (s,
1H; Per-H), 8.79 (s, 1H; Per-H), 8.37 (d, J=8.20 Hz, 1H; Per-H), 7.91
(d, J=8.20 Hz, 1H; Per-H), 7.30 (t, J1 =J2 =8.20 Hz, 1H), 4.16–4.07 (m,
2H; N-CH2), 1.93-1.91 (m, 1H), 1.41–1.30 (m, 8H), 0.96–0.88 ppm (m,
6H); 13C NMR (125 MHz, CDCl3): d=162.7, 138.0, 134.8, 134.6, 131.5,
130.7, 130.2, 129.7, 129.4, 128.7, 127.4, 126.8, 126.6, 126.3, 126.1, 120.9,
120.8, 119.1, 118.8, 44.4, 37.9, 30.7, 28.7, 24.1, 24.0, 14.1, 10.6 ppm;
MALDI-TOF MS: m/z: 670.21 [M]+; elemental analysis calcd (%) for
C30H24Br3NO2: C 53.76, H 3.61, Br 35.77, N 2.09; found: C 53.71, H 3.54,
Br 35.67, N 2.06.
N-(2-Ethylhexyl)-1,6,9,10-tetra(triphenylamine)perylene-3,4-dicarbox-
imide (7): Compound 7 (Rf = 0.32) was obtained as a dark-blue solid
(80 mg, m.p. 1698C). 1H NMR (300 MHz, CDCl3, ppm): d=8.58 (s, 2H;
Per-H), 7.90 (d, J=7.90 Hz, 2H; Per-H), 7.37–7.32 (m, 6H), 7.29–7.27
(m, 8H), 7.23–7.13 (m, 30H), 7.07–7.03 (m, 8H), 6.92 (d, J=8.55 Hz,
4H), 6.83 (d, J=8.55 Hz, 4H), 4.20–4.15 (m, 2H; N-CH2), 2.04–1.99 (m,
1H), 1.44–1.33 (m, 8H), 0.98–0.88 ppm (m, 6H); 13C NMR (75 MHz,
CDCl3): d=164.5, 147.5, 147.4, 147.3, 146.3, 142.3, 138.3, 137.6, 136.0,
135.6, 135.3, 133.0, 130.6, 130.1, 130.0, 129.9, 129.8, 129.3, 129.0, 127.7,
127.1, 125.1, 124.6, 124.5, 123.2, 123.1, 120.8, 119.7, 44.1, 38.0, 30.8, 28.8,
24.1, 23.1, 14.1, 10.7 ppm; MALDI-TOF MS: m/z: 1406.82 [M]+; elemen-
tal analysis calcd (%) for C102H79N5O2: C 87.09, H 5.66, N 4.98; found: C
87.13, H 5.60, N 5.01.
N-(2-Ethylhexyl)-1,9,10-tribromoperylene-3,4-dicarboximide (3): Com-
pound 3 was orange-red in color (m.p. 170–1728C) with a yield of 27%.
1H NMR (500 MHz, CDCl3): d=9.05 (d, J=8.20 Hz, 1H; Per-H), 8.85 (d,
J=8.20 Hz, 1H; Per-H), 8.71 (s, 1H; Per-H), 8.49 (d, J=8.20 Hz, 1H;
Per-H), 8.01 (d, J=9.45 Hz, 1H; Per-H), 7.84 (d, J=8.80 Hz, 1H; Per-H),
7.79 (d, J=8.20 Hz, 1H; Per-H), 4.16–4.08 (m, 2H; N-CH2), 1.96–1.94
(m, 1H), 1.41–1.32 (m, 8H), 0.96–0.88 ppm (m, 6H); 13C NMR
(125 MHz, CDCl3): d=163.4, 162.9, 137.7, 137.1, 135.1, 133.6, 131.2,
130.4, 129.8, 129.7, 129.6, 129.0, 128.6, 126.9, 126.8, 126.6, 125.4, 122.2,
121.2, 120.9, 117.8, 44.3, 38.0, 30.7, 28.7, 24.1, 23.1, 14.1, 10.6 ppm;
MALDI-TOF MS: m/z: 670.11 [M]+; elemental analysis calcd (%) for
C30H24Br3NO2: C 53.76, H 3.61, Br 35.77, N 2.09; found: C 53.73, H 3.58,
Br 35.69, N 2.05.
General procedure to synthesize PMAs: TPA-substituted PMI
(0.10 mmol) and KOH (560 mg, 10.0 mmol) were added to a solution of
tert-butyl alcohol (15 mL) and heated to reflux. After stirring for 2 h, the
reaction mixture was poured into a mixture of acetic acid (20 mL) and
1n HCl (20 mL) and stirred for 5 h at room temperature. The resulting
mixture was poured into
a biphasic mixture of dichloromethane
(100 mL) and H2O (50 mL). After separation, the organic layer was
washed with brine (100 mL) and dried over MgSO4. After filtration and
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Perylene Dyes with Triphenylamine Substituents
FULL PAPER
evaporation of the solvent, the residue was subjected to silica gel column
chromatography by using hexane/dichloromethane (1:3).
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N-(2-Ethylhexyl)(1,6,9-triphenylamine)perylene-3,4-dicarboxylic acid an-
hydride (8): Compound 8 was obtained as a black solid (72 mg, 69%,
m.p. 1778C). 1H NMR (300 MHz, CDCl3): d=8.53 (s, 2H; Per-H), 8.00
(d, J=8.40 Hz, 2H; Per-H), 7.92–7.88 (m, 2H), 7.37–7.34 (m, 2H), 7.33–
7.27 (m, 12H), 7.24–7.04 ppm (m, 30H); 13C NMR (75 MHz, CDCl3): d=
160.92, 147.8, 147.7, 147.6, 147.45, 147.40, 142.5, 139.1, 138.9, 137.4, 137.2,
137.0, 136.6, 136.5, 132.9, 131.5, 131.1, 131.0, 130.9, 130.7, 130.4, 129.8,
129.6, 129.4, 128.9, 128.3, 127.2, 126.4, 125.1, 124.8, 124.7, 124.6, 124.34,
124.3, 123.6, 123.4, 123.3, 122.7, 115.7, 115.5 ppm; MALDI-TOF MS: m/
z: 1052.55 [M]+; elemental analysis calcd (%) for C76H49N3O3: C 86.75, H
4.69, N 3.99; found: C 86.67, H 4.66, N 4.08.
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N-(2-Ethylhexyl)(1,9,10-triphenylamine)perylene-3,4-dicarboxylic
acid
anhydride (9): Compound 9 was obtained as a black solid (63 mg, 60%,
m.p. 2038C). 1H NMR (300 MHz, CDCl3): d=8.47 (s, 1H; Per-H), 8.11
(d, J=8.70 Hz, 1H; Per-H), 8.01 (d, J=8.22 Hz, 1H; Per-H), 7.88 (d, J=
8.07 Hz, 1H; Per-H), 7.63 (d, J=8.22 Hz, 1H; Per-H), 7.53 (d, J=
9.06 Hz, 1H; Per-H), 7.39 (d, J=8.55 Hz, 1H; Per-H), 7.36–7.28 (m,
16H), 7.25–7.00 ppm (m, 26H); 13C NMR (75 MHz, CDCl3): d=161.0,
160.8, 148.1, 147.9, 147.84, 147.80, 147.4, 147.3, 147.2, 142.8, 142.5, 142.0,
141.7, 139.3, 139.1, 137.9, 137.6, 137.1, 136.9, 136.7, 136.1, 136.0, 135.9,
135.8, 132.8, 132.7, 132.2, 131.4, 131.2, 131.0, 130.9, 130.74, 130.70, 130.3,
130.1, 130.0, 129.9, 129.5, 129.4, 129.3, 129.1, 128.9, 128.8, 128.3, 127.9,
127.6, 126.5, 125.2, 125.0, 124.9, 124.8, 124.7, 124.6, 124.1, 123.7, 123.6,
123.5, 123.4, 123.3, 122.8, 122.6, 115.6, 115.4, 114.9, 114.7 ppm; MALDI-
TOF MS: m/z: 1052.54 [M]+; elemental analysis calcd (%) for
C76H49N3O3: C 86.75, H 4.69, N 3.99; found: C 86.77, H 4.61, N 4.02.
N-(2-Ethylhexyl)-1,6,9,10-tetra(triphenylamine)perylene-3,4-dicarboxylic
acid anhydride (10): Compound 10 was obtained as a dark-blue solid
(87 mg, 67%, m.p. 1978C). 1H NMR (300 MHz, CDCl3): d=8.55 (s, 2H;
Per-H), 7.93 (d, J=8.10 Hz, 2H; Per-H), 7.34–7.27 (m, 12H), 7.24–7.13
(m, 30H), 7.09–7.02 (m, 8H), 6.92 (d, J=8.70 Hz, 4H), 6.83 ppm (d, J=
8.70 Hz, 4H); 13C NMR (75 MHz, CDCl3): d=161.0, 147.6, 147.4, 147.3,
146.5, 143.4, 138.6, 137.4, 137.0, 136.7, 135.6, 133.5, 130.6, 130.5, 130.0,
129.9, 129.6, 129.4, 129.3, 129.0, 127.2, 125.2, 124.9, 124.6, 124.4, 123.4,
123.3, 120.7, 115.3 ppm; MALDI-TOF MS: m/z: 1295.65 [M]+; elemental
analysis calcd (%) for C94H62N4O3: C 87.15, H 4.82, N 4.32; found: C
87.17, H 4.86, N 4.28.
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Acknowledgements
We thank the National University of Singapore for financial support and
facilities. We are grateful to Tan Geok Kheng, Hong Yimian, and Ragha-
vender Medishetty for solving the crystal structure. Both A.K. and L.Y.
acknowledge NanoCore and the National University of Singapore for
graduate scholarships.
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Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
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Received: April 9, 2012
Revised: June 4, 2012
Published online: && &&, 0000
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Perylene Dyes with Triphenylamine Substituents
FULL PAPER
Perylene Dyes
A. Keerthi, Y. Liu, Q. Wang,
S. Valiyaveettil* ............... &&&& — &&&&
Synthesis of Perylene Dyes with
Multiple Triphenylamine Substituents
Multiple donors: The design and syn-
thesis of a series of triphenylamine
(TPA)-functionalized perylene mono-
anhydrides from multibrominated per-
ylene monoimides (PMIs) is reported
(see figure). The number and position
of TPA groups and conformation of
the PMI molecules influence the pho-
tophysical and electrochemical proper-
ties of the compounds. The tetrasubsti-
tuted derivative gives the highest effi-
ciency in dye-sensitized solar cells.
Chem. Eur. J. 2012, 00, 0 – 0
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