Synthesis, photophysical and electrochemical properties of 1-aminoperylene bisimides

Article abstract of DOI:10.1016/j.dyepig.2011.06.023

1-Aminoperylene bisimides (1a-1c) were synthesized under mild condition in high yields, and were characterized by FT-IR, ¹H NMR, UV-Vis, HRMS spectra, cyclic voltammetry, differential scanning calorimetry, and thermogravimetric analyses. These

Full text of DOI:10.1016/j.dyepig.2011.06.023

Dyes and Pigments 92 (2011) 517e523
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, photophysical and electrochemical properties
of 1-aminoperylene bisimides
*
Kew-Yu Chen , Tzu-Chien Fang, Ming-Jen Chang
Department of Chemical Engineering, Feng Chia University, 40724 Taichung, Taiwan, R.O.C
a r t i c l e i n f o
a b s t r a c t
Article history:
1-Aminoperylene bisimides (1ae1c) were synthesized under mild condition in high yields, and were
characterized by FT-IR, 1H NMR, UVeVis, HRMS spectra, cyclic voltammetry, differential scanning calo-
rimetry, and thermogravimetric analyses. These compounds are stable up to 310 ꢀC according to ther-
mogravimetric analyses. They undergo two quasi-reversible one-electron oxidations and two quasi-
reversible one-electron reductions in dichloromethane at modest potentials. Their spectroscopic proper-
ties in various conditions and complementary density functional theory (DFT) calculations are reported.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 17 May 2011
Received in revised form
16 June 2011
Accepted 17 June 2011
Available online 29 June 2011
Keywords:
1-Aminoperylene bisimides
Intramolecular charge transfer
Purple dyes
Self-assembly
1. Introduction
Replacement of these halogens is readily achieved by traditional
substitution reactions or by metal-catalyzed cross-coupling reac-
Derivatives of perylene-3,4:9,10-bis(dicarboximide) (PDI) have
attracted considerable attention due to their applications in
molecular electronic devices, such as photovoltaic cells [1e8], light-
harvesting arrays [9,10], light-emitting diodes [11], organic field-
effect transistors (OFETs) [12e17], photochromic materials [18],
and LCD color filters [19]. These chromophores are advantageous
due to their high photochemical stability, ease of synthetic modi-
fication and reversible redox properties. Moreover, the electronic
characteristics of PDI can be fine-tuned by the substitution of the
conjugated aromatic core. Many perylene bisimide derivatives with
either electron-donating or electron-withdrawing groups have
been reported in the literature, such as (a) pyrrolidinyl-substituted
perylene bisimides [20], (b) piperidinyl-substituted perylene bisi-
mides [21], (c) alkoxy-substituted perylene bisimides [22], (d) aryl-
substituted perylene bisimides [23], (e) cyano-substituted perylene
bisimides [24], (f) nitro-substituted perylene bisimides [25], etc.
Furthermore, perylene bisimides modified with electron-donating
groups have been characterized as near-infrared fluorescent dyes
[26], and some with strong electron-withdrawing groups have
been used as air-stable n-type organic semiconductors [27,28]. To
date, a promising strategy for introducing substituents onto the PDI
core is chlorination or bromination of perylene dianhydride [29].
tions [30]. However, both of these methods are usually accompa-
nied by stringent reaction conditions such as high temperatures,
and absence of water and oxygen. More recently, alkyl amino-
substituted perylene bisimides have been synthesized based on
the above methods, and have been characterized as new photo-
active charge transport materials and as stable near-infrared fluo-
rescent dyes [31]. To expand the scope of chromophores available
for designing systems for self-assembly and colorful dyes based on
PDI, we have synthesized a series of amino-substituted perylene
bisimides, since previous studies have used either flexible alkyl
(DAPER3C) [32] or sterically bulky cyclic amines (5be5c) [33] as
electron-donating groups (Fig. 1). These chromophores (5be5c and
DAPER3C) show green or blue colors, both in the solid form and in
solution. We now report on the introduction of an amino group of
PDI affording chromophores that are intense purple in color and
that readily undergo two quasi-reversible one-electron oxidations
and two quasi-reversible one-electron reductions.
2. Experimental
2.1. Chemicals and instruments
All reagents such as perylene-3,4,9,10-tetracarboxyldianhydride,
cyclohexylamine, octylamine, butylamine, acetic acid, cerium (IV)
ammonium nitrate (CAN),1-methyl-2-pyrrolidinone (NMP), and tin
(II) chloride dihydrate (SnCl2$2H2O) were purchased from Aldrich
* Corresponding author. Tel.: þ886 4 24517250x3683; fax: þ886 4 24510890.
E-mail address: kyuchen@fcu.edu.tw (K.-Y. Chen).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.06.023

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K.-Y. Chen et al. / Dyes and Pigments 92 (2011) 517e523
Fig. 1. The structures of alkylamino-substituted (DAPER3C) and bulky cyclic amino-
substituted perylene bisimides (5ae5c).
Chemical Co.. These were used without further purification unless
otherwise noted. Solvents were dried and purified by fractional
distillation over sodium and handled in a moisture-freeatmosphere.
Column chromatography was performed using silica gel (Merk,
250e430 mesh).
Fig. 2. FT-IR spectra of 1a.
1H NMR spectra were recorded in CDCl3 on a Varian Mercury
400 MHz. FT-IR spectra were measured with a Horiba FT-720
infrared spectrophotometer. Mass spectra were recorded on
a VG70-250S mass spectrometer. The absorption and photo-
luminescence (PL) spectra were measured using a Jasco V-570
UVeVis spectrometer and a Hitachi F-4500 fluorescence spec-
trometer, respectively. Cyclic voltammetry (CV) was carried out
with a CH instruments (Electrochemical Workstation) at a potential
rate of 200 mV/s in a 0.1 M solution of tetrabutylammonium hex-
afluorophosphate (TBAPF6) in dichloromethane. A platinum wire
was used as the counter electrode and an Ag/AgNO3 electrode was
used as the reference electrode. Thermogravimetric analysis (TGA)
was conducted under nitrogen at a heating rate of 10 ꢀC/min with
a TA Instruments Thermogravimetric Analyzer 2050.
(150 mL) were stirred at 25 ꢀC under N2 for 2 h. The mixture was
neutralized with 10% KOH and extracted with CH2Cl2. After solvent
was removed, the crude product was purified by silica gel column
chromatography with eluent CH2Cl2 to afford 2a (2b or 2c) in 95%
yield. Characterization data: 2a: 1H NMR (400 MHz, CDCl3)
d 8.74 (d,
J ¼ 7.6 Hz, 1H), 8.62e8.69 (m, 4H), 8.55 (d, J ¼ 8.0 Hz, 1H), 8.18 (d,
J ¼ 7.6 Hz, 1H), 5.00 (m, 2H), 2.54 (m, 4H), 1.91 (m, 4H), 1.76 (m, 6H),
1.47 (m, 4H), 1.34 (m, 2H); IR (KBr): 2928, 2851, 1700, 1659, 1596,
1539, 1401, 1336, 1262, 1245, 1190, 809, 743 cmꢁ1; MS (FAB): m/z
(relative intensity) 600 (M þ Hþ, 100); HRMS calcd. for C36H30O6N3
600.2135, found 600.2141. Selected data for 2b: 1H NMR (400 MHz,
CDCl3)
d
8.79 (d, J ¼ 8.0 Hz,1H), 8.73e8.67 (m, 4H), 8.60 (d, J ¼ 8.0 Hz,
1H), 8.23 (d, J ¼ 8.0 Hz, 1H), 4.19 (m, 4H), 1.76 (m, 4H), 1.26e1.54 (m,
20H), 0.87 (t, J ¼ 6.5 Hz, 6H); MS (FAB): m/z (relative intensity) 660
(M þ Hþ, 100); HRMS calcd. for C40H42O6N3 660.3074, found
660.3076. Selected data for 2c: 1H NMR (400 MHz, CDCl3)
d 8.80 (d,
2.2. Synthesis and characterization
J ¼ 8.0 Hz, 1H), 8.79e8.68 (m, 4H), 8.62 (d, J ¼ 8.0 Hz, 1H), 8.25 (d,
J ¼ 8.0 Hz, 1H), 4.22 (m, 4H), 1.76 (m, 4H), 1.48 (m, 4H), 0.98 (t,
J ¼ 7.2 Hz, 6H); MS (FAB): m/z (relative intensity) 548 (M þ Hþ,100);
HRMS calcd. for C32H26O6N3 548.1822, found 548.1826.
2.2.1. General procedure for nitration
3a (3b or 3c) (1.8 mmol), cerium (IV) ammonium nitrate (CAN)
(1.2 g, 2.2 mmol), nitric acid (2.0 g, 31.7 mmol) and dichloromethane
Scheme 1. The synthetic routes of 1ae1c and 5a.

K.-Y. Chen et al. / Dyes and Pigments 92 (2011) 517e523
519
Table 2
Summary of optical absorption and emission properties of 5a in various solvents.
Compound 5a
labs (nm)/(
3
(Mꢁ1 cmꢁ1)a)
lem (nm)
Fb
Cyclohexane
Ethyl acetate
Dichloromethane
Acetonitrile
581
595
599 (43 600)
607
687
722
731
748
0.18
0.11
0.06
0.04
a
Measured at 2 ꢂ 10ꢁ5 M.
b
Determined with N,N0-dioctyl-3,4,9,10-perylenedicarboximide as reference
[36].
2.2.3. Synthesis of 1-(N-piperidyl)-N,N0-bis(cyclohexyl)-3,4:9,10-
perylenebis(dicarboximide) (5a)
1-bromoperylene bisimide (6a) (500 mg, 7.9 mmol) [33] was
dissolved in 50 mL piperidine. The solution was heated at 60 ꢀC
under nitrogen for 3 h with stirring. Excess piperidine was removed
on a rotary evaporator and the residue was purified by silica gel
column chromatography with dichloromethane/n-hexane (2/1) to
afford 5a (430 mg, 85%). Characterization data for 5a: 1H NMR
Fig. 3. Normalized absorption spectra of 1a (purple line), 2a (red line) and 5a (green
line) in dichloromethane solution.
2.2.2. General procedure for reduction
(400 MHz, CDCl3)
d
9.80 (d, J ¼ 8.0 Hz, 1H), 8.61 (d, J ¼ 7.6 Hz, 1H),
Tin chloride dihydrate (5.0 g, 22 mmol), and 2a (2b or 2c) (1.0 g,
1.7 mmol) were suspended in 50 mL of THF, and stirred 20 min. The
solvent was refluxed 80 ꢀC with stirring for 2 h. THF is removed at
the rotary evaporator, and the residue was dissolved in ethyl
acetate and washed with 10% sodium hydrate solution and brine.
The organic layer was dried over anhydrous MgSO4 and the filtrate
was concentrated under reduced pressure. The crude product was
purified by silica gel column chromatography with eluent ethyl
acetate/n-hexane (2/3) to afford 1a (1b or 1c) in 80% yield. Char-
8.59 (d, J ¼ 7.6 Hz,1H), 8.53 (s,1H), 8.46e8.49 (m, 3H), 5.07, (m, 2H),
3.44 (m, 2H), 2.93 (m, 2H), 2.55 (m, 4H), 1.74e1.90 (m, 14H),
1.20e1.46 (m, 8H); MS (FAB): m/z (relative intensity) 638 (M þ Hþ,
100); HRMS calcd. for C41H40O4N3 638.3019, found 638.3016.
Elemental analysis: Calcd for C41H39O4N3: C, 77.21; H, 6.16; N, 6.59.
Found C, 77.35; H, 6.08; N, 6.43.
3. Results and discussion
acterization data: 1a: 1H NMR (400 MHz, CDCl3)
d 8.62 (d,
3.1. Synthesis of dyes
J ¼ 8.0 Hz, 1H), 8.45 (d, J ¼ 7.6 Hz, 1H), 8.38 (d, J ¼ 8.0 Hz, 1H), 8.25
(d, J ¼ 7.6 Hz,1H), 8.18 (d, J ¼ 8.0 Hz,1H), 8.10 (d, J ¼ 8.0 Hz,1H), 7.98
(s, 1H), 5.03, (s, 2H), 4.99 (m, 2H), 2.55 (m, 4H), 1.91 (m, 4H), 1.74 (m,
6H),1.46e1.40 (m, 6H); IR (KBr): 3346, 3240, 2926,1694,1653,1372,
1338, 1260, 806, 747 cmꢁ1; MS (FAB): m/z (relative intensity) 570
(M þ Hþ, 100); HRMS calcd. for C36H32O4N3 570.2393, found
570.2396. Elemental analysis: Calcd for C36H31O4N3: C, 75.90; H,
5.49; N, 7.38. Found C, 75.74; H, 5.57; N, 7.52. Selected data for 1b:
Scheme 1 shows the chemical structures and synthetic routes of
compounds 1ae1c and 5a. The synthesis starts from an imidization
of perylene bisanhydride (4) by reaction with cyclohexylamine,
octylamine, or butylamine. The mono-nitration can be achieved by
a reaction of perylene bisimides (3ae3c) with cerium (IV) ammo-
nium nitrate (CAN) and HNO3 (or H2SO4) under ambient temper-
ature for 2 h, giving 2ae2c in high yields of ca. 90%. The reduction of
nitroperylene bisimides (2ae2c) by tin (II) chloride dihydrate
(SnCl2$2H2O) in refluxing THF obtained the corresponding 1-
aminoperylene bisimides 1ae1c. The presence of a single amino
1H NMR (400 MHz, CDCl3)
d
8.82 (d, J ¼ 8.0 Hz, 1H), 8.62 (d,
J ¼ 7.6 Hz, 1H), 8.59 (d, J ¼ 8.0 Hz, 1H), 8.49 (d, J ¼ 7.6 Hz, 1H), 8.44
(d, J ¼ 8.0 Hz, 1H), 8.41 (d, J ¼ 8.0 Hz, 1H), 8.10 (s, 1H), 5.04, (s, 2H),
4.18 (m, 4H), 1.88 (m, 4H), 1.23e1.74 (m, 26H); MS (FAB): m/z
(relative intensity) 630 (M þ Hþ, 100); HRMS calcd. for C40H44O4N3
630.3332, found 630.3330. Elemental analysis: Calcd for
substituent can be verified by the presence of a signal at
d 5.1 ppm
(eNH2) in 1H NMR spectrum and the absorption at 3343 and
3240 cmꢁ1 in FT-IR spectrum, corresponding to the stretching of
the primary amino group (Fig. 2). In addition, the nucleophilic
C
40H43O4N3: C, 76.28; H, 6.88; N, 6.67. Found C, 76.06; H, 6.96; N,
6.79. Selected data for 1c: 1H NMR (400 MHz, CDCl3)
d
8.80 (d,
J ¼ 8.0 Hz, 1H), 8.74 (d, J ¼ 7.6 Hz, 1H), 8.72 (d, J ¼ 8.0 Hz, 1H), 8.70
(d, J ¼ 7.6 Hz,1H), 8.67 (d, J ¼ 8.0 Hz,1H), 8.59 (d, J ¼ 8.0 Hz,1H), 8.11
(s, 1H), 5.12, (s, 2H), 4.20 (m, 4H), 1.77 (m, 4H), 1.47 (m, 4H), 1.00 (t,
J ¼ 7.2 Hz, 6H); MS (FAB): m/z (relative intensity) 518 (M þ Hþ, 100);
HRMS calcd. for C32H28O4N3 518.2080, found 518.2084. Elemental
analysis: Calcd for C32H27O4N3: C, 74.26; H, 5.26; N, 8.12. Found C,
74.08; H, 5.32; N, 8.28.
Table 1
Summary of optical absorption and emission properties of 1a in various solvents.
Compound 1a
labs (nm)/(
3
(Mꢁ1 cmꢁ1)a)
lem (nm)
Fb
Cyclohexane
Ethyl acetate
Dichloromethane
Acetonitrile
554
571
578 (41 200)
581
624
663
677
690
0.25
0.16
0.10
0.06
a
Measured at 2 ꢂ 10ꢁ5 M.
b
Determined with N,N0-dioctyl-3,4,9,10-perylenedicarboximide as reference
Fig. 4. Normalized emission spectra of 1a in cyclohexane (blue line) ethyl acetate
[36].
(green line), dichloromethane (red line) and acetonitrile (black line).

520
K.-Y. Chen et al. / Dyes and Pigments 92 (2011) 517e523
Table 3
Calculated and experimental parameters for perylene diimide derivatives 1ae1c and
5ae5c.
HOMOa
LUMOa
Eg
Eg
Twisting angle (ꢀ)
a
b
Compound
1a
1b
1c
ꢁ5.62
ꢁ5.65
ꢁ5.65
ꢁ5.54
ꢁ5.42
ꢁ5.41
ꢁ3.21
ꢁ3.24
ꢁ3.25
ꢁ3.21
ꢁ3.14
ꢁ3.13
2.41
2.41
2.40
2.33
2.28
2.28
2.24
2.24
2.25
2.13
2.12
2.12
9.23, 17.49
9.16, 17.57
9.19, 17.50
10.07, 18.03
10.11, 18.46
10.24, 18.22
5a
5bc
5cc
a
Calculated by DFT/B3LYP (in eV).
b
c
At absorption maxima (Eg ¼ 1240/lmax, in eV).
Reference [33].
increasing the solvent polarity (Tables 1 and 2 and Supplementary
data), which is consistent with the previous studies [31].
Fig. 5. LipperteMataga plots for 1a (purple line) and 5a (green line). The solvents are
The fluorescence spectra of 1a in various solvents are shown in
Fig. 4 and summarized in Table 1; the fluorescence spectra of 1be1c
can be found in the Supplementary data. The fluorescence spectra
shift significantly to the red upon increasing solvent polarity,
indicating strong intramolecular charge transfer (ICT) characteris-
tics for the excited states of 1ae1c. Using the well-established
fluorescence solvatochromic shift method [34], we measured the
stabilization of the excited states of 1a and compared these results
to those of 5a (Table 2). The emission lmax of each compound was
measured in four solvents with dielectric constants ranging from
2.02 to 37.50. The solvent polarity-dependent emission can be
expressed quantitatively derived from dielectric polarization,
specifying that the spectra shifts of the fluorescence upon
increasing the solvent polarity depend on the difference in
(1) cyclohexane, (2) ethyl acetate, (3) dichloromethane, (4) acetonitrile.
substitution of 1-bromoperylene bisimide (6a) with piperidine at
60 ꢀC [33] afforded the corresponding monopiperidinyl bisimide
(5a) as a deep green solid.
3.2. Photophysical properties of dyes
Fig. 3 shows the steady state absorption spectra of the purple dye
1a, the red dye 2a, and the green dye 5a in dichloromethane. The
spectra of 1b and 1c can be found in the Supplementary data. The
spectrum of 1a is dominated by a very broad, and nearly structure-
less, absorption band that spans a large part of the visible spectrum
(380e740 nm). This broad absorption band is red-shifted relative to
that of 2a, but it is blue-shifted relative to that of 5a (390e760 nm).
The main differences between the spectra are the absorption near
422 and 566 nm for 1a and the peaks at 445 and 607 nm in the
spectrum of 5a. These two features account for the large differences
in color observed by the naked eye. Moreover, the longest wave-
length absorption band of 1ae1c and 5a exhibits a red shift upon
ƒ!
permanent dipole moments between ground ð mg Þ and excited
ƒ!
ð
me Þ state [35]. The change of magnitudes for dipole moments
ƒ! ƒ!
between ground and excited states, i.e., Dm ¼ j me
ꢁ
mg j, can be
calculated by the LipperteMataga equation and expressed as:
ꢀ
ꢁ
2
2
hc
ya
ꢁ
yf
¼
me
ꢁ
mg aꢁ0 3Df þ const:
(1)
Fig. 6. Computed frontier orbitals of 1a and 5a. The upper graphs are the LUMOs and the lower ones are the HOMOs.

K.-Y. Chen et al. / Dyes and Pigments 92 (2011) 517e523
521
Table 4
Summary of half-wave redox potentials, HOMO and LUMO energy levels for 1ae1c
and 5a.
a
a
a
a
Compound
Eþ
E2þ
Eꢁ
E2ꢁ
1/2
EHOMO/ELUMO (eV)b
1/2
1/2
1/2
1a
1b
1c
5a
0.97
0.99
1.00
0.82
1.36
1.38
1.39
1.32
ꢁ0.97
ꢁ0.96
ꢁ0.96
ꢁ0.98
ꢁ1.09
ꢁ1.08
ꢁ1.07
ꢁ1.15
ꢁ5.57/ꢁ3.33
ꢁ5.59/ꢁ3.35
ꢁ5.60/ꢁ3.35
ꢁ5.44/ꢁ3.31
Fig. 7. DFT (B3LYP/6-31G**) geometry-optimized structures of 1a (left) and 5a (right)
shown with view along the long axis. For computational purposes, methyl groups
replace the cyclohexyl groups at the imide positions.
a
Measured in a solution of 0.1 M tetrabutylammonium hexafluorophosphate
(TBAPF6) in dichloromethane versus SCE (in V).
b
Calculated from EHOMO ¼ ꢁ4.88 ꢁ (Eoxd ꢁ EFc/Fcþ), ELUMO ¼ EHOMO þ Eg.
where h is the Planck constant, c is the speed of light, and a0
denotes the cavity radius in which the solute resides, calculated to
be 7.0 Å via HartreeeFock theories with 6-31G (d0, p0) basis, ya
ꢁ
yf
is the Stokes shift of the absorption and emission peak maximum,
and f is the orientation polarizability defined as:
3.4. Electrochemical properties of dyes
D
Fig. 8 shows that the cyclic voltammograms of 1a and 5a
undergo two quasi-reversible one-electron oxidations and two
quasi-reversible one-electron reductions in dichloromethane at
modest potentials. Table 4 summarizes the redox potentials and the
HOMO and LUMO energy levels estimated from cyclic voltammetry
(CV) for 1ae1c and 5a [38]. It appears that the first oxidation
potential of 5a is smaller than those of 1ae1c; this can be explained
by the fact that the piperidinyl substituent has better electron-
donating ability than the amino substituent. The HOMO and
LUMO energy levels of 1ae1c (5a) are estimated in the range
of ꢁ5.57 to ꢁ5.60 (ꢁ5.44) eV and ꢁ3.33 to ꢁ3.35 (ꢁ3.31) eV,
respectively. As expected, the HOMOeLUMO energy gap of 5a is
ꢀ
ꢁ
3
ꢁ 1
n2 ꢁ 1
D
f ¼ f ð
3
Þ ꢁ f n2
¼
ꢁ
(2)
2n2 þ 1
2
3
þ 1
The plot of the Stokes shift ya
ꢁ
yf as a function of
D
f is suffi-
ƒ! ƒ!
ciently linear for 1a and 5a (Fig. 5). Accordingly, Dm ¼ j me
ꢁ
mg
j
was deduced to be 7.4 D and 7.1 D for 1a and 5a, respectively. These
values of Dm are very close to that determined for alkylamino-
substituted perylene bisimides [31].
3.3. Quantum chemistry computation
To gain insight into the electronic properties of 1ae1c and
5ae5c, quantum chemical calculations were performed using
density functional theory (DFT) at the B3LYP/6-31G** level [37].
Fig. 6 shows the highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO) of 1a and 5a. The
HOMO of both 1a and 5a is delocalized mainly on the amino group
and the perylene core, while the LUMO is extended from the central
perylene core to the bisimide groups. The calculated and experi-
mental parameters are summarized in Table 3. The results indicate
that both the HOMO and LUMO energy levels of 1ae1c are similar
to those of 5ae5c. Furthermore, DFT (B3LYP/6-31G**) calculations
show that the ground-state geometries of the perylene core have
two core twist angles, i.e., approximate dihedral angles between
the two naphthalene subunits attached to the central benzene ring;
these are w9ꢀ and w17ꢀ for 1ae1c and 10ꢀ and 18ꢀ for 5ae5c
(Table 3 and Fig. 7). As a whole, the core twist angles of primary
amino-substituted perylene bisimides (1ae1c) are smaller than
those of sterically bulky piperidinyl-substituted perylene bisimides
(5ae5c).
Fig. 9. Thermogravimetric analysis graphs for 1a (purple line) and 5a (green line) in
nitrogen atmosphere at normal pressure. Heating rate, 10 ꢀC/min.
Fig. 10. Normalized absorption spectra of 1a at different concentrations in ethyl
acetate.
Fig. 8. The cyclic voltammograms of 1a (purple line) and 5a (green line) measured in
dichloromethane solution with ferrocenium/ferrocene, at 200 mV/s.

522
K.-Y. Chen et al. / Dyes and Pigments 92 (2011) 517e523
as good optical stability and reversible redox properties. Working
toward their applications on photoactive charge transport mate-
rials is in progress.
Acknowledgement
Financial support from the National Science Council of the
Republic of China is gratefully acknowledged (NSC 99-2113-M-035-
001-MY2).
Appendix. Supplementary data
Supplementary data (1H NMR spectra of 1ae1c and 5a;
absorption and emission spectra of 1b and 1c in various conditions;
absorption spectra of 1a at different concentrations in dichloro-
methane) associated with this article can be found, in the online
version, at doi:10.1016/j.dyepig.2011.06.023.
Fig. 11. Normalized absorption spectra of 1a at different temperatures in ethyl acetate.
smaller than those of 1ae1c, which is in good agreement with the
theoretical calculations.
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thermogravimetric analysis (TGA) and differential scanning calo-
rimetry (DSC). Thermogravimetric analyses revealed that 1ae1c
and 5a were thermally stable materials, and that the onset of
decomposition temperatures occurred above 300 ꢀC under
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alkyl chains are liquid crystalline (LC) [39]. However, according to
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The stacking behaviors of 1ae1c in methylcyclohexane (MCH),
dichloromethane, and ethyl acetate were investigated by
concentration-dependent UVeVis measurements (from 10ꢁ4 M to
10ꢁ6 M). Fig. 10 shows the absorption spectra of 1a at different
concentrations in ethyl acetate; those of 1be1c can be found in the
Supplementary data. At high concentrations, J-type stacks are
formed (w700 nm), whereas at low concentrations, the spectrum is
similar to the one in dichloromethane where no stacking takes
place (Supplementary data). Due to the low solubility of 1ae1c in
MCH (highest concentration is approximately 10ꢁ5 M), no
concentration-dependent UVeVis measurements were performed.
The stacking behaviors of 1ae1c in ethyl acetate were further
investigated by temperature-dependent UVevis measurements
(from 20 to 50 ꢀC). Upon cooling, a clear red shift was observed in
the UVevis measurements for all perylene bisimides 1ae1c, indi-
cating the formation of J-type aggregates (Fig. 11 and
Supplementary data).
4. Conclusions
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We have successfully synthesized a series of purple dyes based
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