1,7-Diaminoperylene bisimides: Synthesis, optical and electrochemical properties

Article abstract of DOI:10.1016/j.dyepig.2012.09.003

A series of blue dyes, 1,7-diaminoperylene bisimides (2a-2c), was synthesized under mild condition in high yields, and was characterized by ¹H NMR, UV-Vis, HRMS spectra, cyclic voltammetry, differential scanning calorimetry, and thermogravimetr

Full text of DOI:10.1016/j.dyepig.2012.09.003

Dyes and Pigments 96 (2013) 319e327
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
1,7-Diaminoperylene bisimides: Synthesis, optical and electrochemical properties
*
Hsing-Yang Tsai, Kew-Yu Chen
Department of Chemical Engineering, Feng Chia University, No. 100, Wenhwa Rd., 40724 Taichung, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of blue dyes, 1,7-diaminoperylene bisimides (2ae2c), was synthesized under mild condition in
high yields, and was characterized by 1H NMR, UVeVis, HRMS spectra, cyclic voltammetry, differential
scanning calorimetry, and thermogravimetric analyses. These molecules undergo an excited-state
intramolecular electron transfer reaction, resulting in a unique charge transfer emission. Upon excita-
tion, they show smaller dipole moment changes than those of the asymmetric 1-aminoperylene bisi-
mides (4ae4c); the dipole moments of these compounds have been estimated using the LipperteMataga
equation. Furthermore, they undergo two quasi-reversible one-electron oxidations and two quasi-
reversible one-electron reductions in dichloromethane at modest potentials. Their optical properties
in various conditions and complementary density functional theory (DFT) calculations are reported.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 10 July 2012
Received in revised form
5 September 2012
Accepted 6 September 2012
Available online 14 September 2012
Keywords:
1,7-Diaminoperylene bisimides
Blue dyes
Intramolecular charge transfer
LipperteMataga equation
DFT calculations
Self-assembly
1. Introduction
alkylaminoperylene bisimides [54,55] have been synthesized by
reaction of alkylamine with the corresponding dibromo
Perylene bisimides (PBIs) possess remarkable optical, thermal
and photochemical stabilities with high extinction coefficients [1e
6]. Their use has been explored for demanding applications in
molecular electronic devices, such as photochromic materials [7,8],
light-harvesting arrays [9,10], LCD color filters [11,12], light-
emitting diodes [13,14], photovoltaic cells [15e24], and organic
field-effect transistors (OFETs) [25e30]. Many perylene bisimide
derivatives with either electron-donating or electron-withdrawing
groups attached to the bay-positions (1,6,7,12-positions) have been
reported in the literature, such as (a) alkyl-substituted PBIs [31], (b)
ferrocenyl-substituted PBIs [32,33], (c) pyrrolidinyl-substituted
PBIs [34,35], (d) piperidinyl-substituted PBIs [36,37], (e) alkoxy-
substituted PBIs [38e42], (f) aryl-substituted PBIs [43,44], (g)
perfluoroalkyl-substituted PBIs [45,46], (h) cyano-substituted PBIs
[47,48], (i) nitro-substituted PBIs [49e51], etc. Furthermore, PBIs
modified with electron-donating groups have been characterized
as near-infrared absorbing and fluorescent dyes [37,52], and some
with strong electron-withdrawing groups have been used as air-
stable n-type OFETs [48,53]. More recently, 1,7- and 1,6-
compounds. These chromophores show green or blue colors, both
in the solid form and in solution. They have also been characterized
as new photoactive charge transport materials [54] and G-quad-
ruplex interactive telomerase inhibitors [55]. However, the above
reaction is accompanied by stringent reaction conditions such as
high temperatures and absence of water and oxygen. In an effort to
expand the scope of PBI-based chromophores available for
designing systems for colorful dyes and self-assembly [56e61], we
have synthesized a series of amino-substituted perylene bisimides
[62], since previous studies have used either flexible alkyl [54,55] or
sterically bulky cyclic amines [63] as electron-donating groups. We
now report on the introduction of two amino groups of PBIs
affording chromophores that are an intense blue 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
The starting materials such as perylene-3,4,9,10-tetracarboxy-
ldianhydride, butylamine, octylamine, cyclohexylamine, acetic
acid, cerium (IV) ammonium nitrate (CAN), 1-methyl-2-
* 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 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.09.003

320
H.-Y. Tsai, K.-Y. Chen / Dyes and Pigments 96 (2013) 319e327
pyrrolidinone (NMP), tetrahydrofuran (THF) and tin (II) chloride
dihydrate (SnCl2.2H2O) were purchased from Merk, ACROS and
SigmaeAldrich. Solvents were distilled freshly according to stan-
dard procedure. Column chromatography was performed using
silica gel Merk Kieselgel si 60 (40e63 mesh).
(m, 4H),1.75 (m, 4H),1.26e1.53 (m, 20H), 0.87 (t, J ¼ 6.4 Hz, 6H); MS
(FAB): m/z (relative intensity) 645 (M þ Hþ, 100); HRMS calcd. for
C40H45O4N4 645.3441, found 645.3447. Selected data for 2c: 1H
NMR (400 MHz, CDCl3)
d
8.87 (d, J ¼ 8.0 Hz, 2H), 8.40 (d, J ¼ 8.0 Hz,
2H), 8.10 (s, 2H), 4.92, (s, 4H), 4.19 (m, 4H), 1.76 (m, 4H), 1.48 (m,
4H), 0.90 (t, J ¼ 6.0 Hz, 6H); MS (FAB): m/z (relative intensity) 533
(M þ Hþ, 100); HRMS calcd. for C32H29O4N4 533.2189, found
533.2185.
1H NMR spectra were recorded in CDCl3 on a Bruker 400 MHz.
Mass spectra were recorded on a VG70-250S mass spectrometer.
The absorption and emission spectra were measured using a Jasco
V-570 UVeVis spectrophotometer and a Hitachi F-4500 fluores-
cence spectrophotometer, respectively. Cyclic voltammetry (CV)
was performed with a CH instruments at a potential rate of 200 mV/
s in a 0.1 M solution of tetrabutylammonium hexafluorophosphate
(TBAPF6) in dichloromethane. Platinum and Ag/AgNO3 electrodes
were used as counter and reference electrodes, respectively. Ther-
mogravimetric analysis (TGA) was conducted under nitrogen at
a heating rate of 10 ꢀC/min with a TA Instruments Thermogravi-
metric Analyzer 2050. DSC measurements were performed using
a PerkineElmer DSC-7 calorimeter at a heating rate of 10 ꢀC/min
under a nitrogen atmosphere.
2.2.3. Synthesis of 1,7-dipiperidinylperylene bisimide (1a)
1,7-dibromoperylene bisimide (7a) (300 mg, 0.2 mmol) was
dissolved in 30 ml piperidine. The solution was heated at 60 ꢀC
under nitrogen for 6 h with stirring. Excess piperidine was removed
on a rotary evaporator and the residue was purified by silica gel
column chromatography with eluent dichloromethane/n-hexane
(2/1) to afford 1a in 60%. Characterization data: 1a: 1H NMR
(400 MHz, CDCl3)
d
9.42 (d, J ¼ 8.4 Hz, 2H), 8.40 (s, 2H), 8.30 (d,
J ¼ 8.4 Hz, 2H), 5.06 (m, 2H), 3.45 (m, 4H), 2.86 (m, 4H), 2.58 (m,
4H), 1.80 (m, 8H), 1.74 (m, 12H), 1.35e1.54 (m, 8H); MS (FAB): m/z
(relative intensity) 721 (M þ Hþ, 100); HRMS calcd. for C46H49O4N4
721.3754, found 721.3758.
2.2. Synthesis and characterization
2.2.1. Synthesis of 1,7-dinitroperylene bisimides (5ae5c)
3. Results and discussion
9a (9b or 9c) (1.8 mmol), cerium (IV) ammonium nitrate (CAN)
(4.8 g, 8.8 mmol), nitric acid (8.0 g, 131.1 mmol) and dichloro-
methane (250 ml) were stirred at 25 ꢀC under N2 for 48 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 a mixture
of 1,7- and 1,6-dinitroperylene bisimides, and 1H NMR (400 MHz)
analysis revealed a 3:1 ratio. The regioisomeric 1,7- and 1,6-
dinitroperylene bisimides could not be separated by column
chromatography. Regioisomerically pure 1,7-dinitroperylene bisi-
mides (5ae5c) were obtained by repetitive crystallization. Char-
3.1. Synthesis of dyes
Scheme 1 shows the chemical structures and synthetic routes of
amino-substituted (2ae2c and 4ae4c) and piperidinyl-substituted
PBIs (1a and 3a). The synthesis starts from an imidization of PBIs by
reacting with cyclohexylamine, octylamine or butylamine. The
nitration of PBIs can then be achieved by the reaction of PBIs (9ae
9c) with cerium (IV) ammonium nitrate (CAN) and HNO3 under
ambient temperature. By controlling the reaction time, both mono-
and di-substituted nitroperylene bisimides (6ae6c and 5ae5c) can
be obtained. Among the dinitroperylene bisimides, a 3:1 mixture of
isomers (nitrated at the 1,7- or 1,6-positions) were indicated by 1H
NMR spectroscopy, as well as bromination of PBIs under mild
conditions reported by Rybtchinski [63]. Pure 1,7-regioisomer (5ae
5c) are obtained through repetitive crystallizations. The reduction
of 1-nitroperylene bisimides (6ae6c) and 1,7-dinitroperylene
bisimides (5ae5c) by tin (II) chloride dihydrate (SnCl2$2H2O) in
refluxing THF obtained the 1-aminoperylene bisimides (4ae4c)
and 1,7-diaminoperylene bisimides (2ae2c), respectively. In addi-
tion, the nucleophilic substitution of 1-bromoperylene bisimide
(8a) and 1,7-dibromoperylene bisimide (7a) with piperidine at
60 ꢀC [63] afforded the monopiperidinyl (3a) and dipiperidinyl
bisimides (1a), respectively. The symmetric structures of 1,7-
diaminoperylene bisimides (2ae2c) can be verified by the pres-
acterization data: 5a: 1H NMR (400 MHz, CDCl3)
d 8.78 (s, 2H), 8.67
(d, J ¼ 8.4 Hz, 2H), 8.28 (d, J ¼ 8.4 Hz, 2H), 4.99 (m, 2H), 2.51 (m, 4H),
1.92 (m, 4H), 1.74 (m, 6H), 1.46 (m, 4H), 1.36 (m, 2H); MS (FAB): m/z
(relative intensity) 645 (M þ Hþ, 100); HRMS calcd. for C36H29O8N4
645.1985, found 645.1981. Selected data for 5b: 1H NMR (400 MHz,
CDCl3)
d
8.82 (s, 2H), 8.71 (d, J ¼ 8.0 Hz, 2H), 8.30 (d, J ¼ 8.0 Hz, 2H),
4.20 (m, 4H), 1.75 (m, 4H), 1.26e1.53 (m, 20H), 0.87 (t, J ¼ 6.4 Hz,
6H); MS (FAB): m/z (relative intensity) 705 (M þ Hþ, 100); HRMS
calcd. for C40H41O8N4 705.2924, found 705.2923. Selected data for
5c: 1H NMR (400 MHz, CDCl3)
d
8.76 (s, 2H), 8.63 (d, J ¼ 8.0 Hz, 2H),
8.26 (d, J ¼ 8.0 Hz, 2H), 4.18 (m, 4H), 1.74 (m, 4H), 1.47 (m, 4H), 0.96
(t, J ¼ 6.0 Hz, 6H); MS (FAB): m/z (relative intensity) 593 (M þ Hþ,
100); HRMS calcd. for C32H25O8N4 593.1672, found 593.1674.
2.2.2. Synthesis of 1,7-diaminoperylene bisimides (2ae2c)
ence of three signals (one singlet and two doublet signals) at d 8.0e
Tin chloride dihydrate (1.0 g, 4.8 mmol), and 5a (5b or 5c) (0.5 g,
0.8 mmol) were suspended in 50 ml of THF, and stirred at 25 ꢀC
under N2 for 20 min. The solvent was refluxed 80 ꢀC with stirring
for 6 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 (4/5) to afford
2a (2b or 2c) in 82% yield. Characterization data: 2a: 1H NMR
9.0 ppm in 1H NMR spectrum, indicating that there are only three
different kinds of protons in the perylene core (Fig. 1). However,
there are seven sets of signals, including six doublets and one
singlet in asymmetric 1-aminoperylene bisimides (4ae4c).
3.2. Optical properties of dyes
Fig. 2 shows the steady state absorption spectra of 1ae5a in
dichloromethane. The absorption spectra of 1,7-dinitro- (5a) and 1-
nitroperylene bisimides (6a) are nearly identical with the spectrum
of the non-substituted perylene bisimide (9a), but they do not
exhibit fluorescence [50]. On the other hand, the reduction of 6
(5)e4 (2) switches the substituent from an electron-withdrawing
group to an electron-donating group and causes a distinct red
shift. The spectra of amino-substituted (2ae2c and 4ae4c) and
piperidinyl-substituted PBIs (1a and 3a) are dominated by very
(400 MHz, CDCl3)
d
8.87 (d, J ¼ 8.4 Hz, 2H), 8.43 (d, J ¼ 8.4 Hz, 2H),
8.14 (s, 2H), 5.04, (m, 2H), 4.94 (s, 4H), 2.61 (m, 4H), 1.93 (m, 4H),
1.74 (m, 6H), 1.36e1.54 (m, 6H); MS (FAB): m/z (relative intensity)
585 (M þ Hþ, 100); HRMS calcd. for C36H33O4N4 585.2502, found
585.2504. Selected data for 2b: 1H NMR (400 MHz, CDCl3)
d 8.89 (d,
J ¼ 8.4 Hz, 2H), 8.46 (d, J ¼ 8.4 Hz, 2H), 8.17 (s, 2H), 4.96, (s, 4H), 4.19

H.-Y. Tsai, K.-Y. Chen / Dyes and Pigments 96 (2013) 319e327
321
Scheme 1. The synthetic routes of 1a, 2ae2c, 3a and 4ae4c.
broad absorption bands that span a large part of the visible spec-
trum (400e800 nm). These broad bands are typical for perylene
bisimide derivatives N-substituted at the bay-core positions, due to
a charge transfer absorption [54]. The longest wavelength absorp-
tion band of the 1,7-diaminoperylene bisimide (2a: 620 nm) is red-
shifted relative to those of mono-substituted compounds (3a:
599 nm; 4a: 578 nm), but it is blue-shifted relative to that of the 1,7-
dipiperidinylperylene bisimide (1a: 696 nm). Obviously, the
inductive effect of the alkyl groups in 1a and 3a causes an addi-
tional red shift. Moreover, the longest wavelength absorption band
of 1e4 exhibits a red shift when the solvent polarity increases
(Tables 1 and 2), which is consistent with previous studies [54].
The fluorescence spectra of 2a in various solvents are shown in
Fig. 3. The fluorescence spectra of 1a, 3a and 4a can be found in the
Fig. 1. The 1H NMR spectra of 2a (top) and 4a (bottom).

322
H.-Y. Tsai, K.-Y. Chen / Dyes and Pigments 96 (2013) 319e327
Table 2
Summary of optical absorption and emission properties of 2a in various solvents.
(Mꢁ1 cmꢁ1)a)
lem (nm)
Fc
b
Compound 2a
labs (nm)/(
3
Cyclohexane
Ethyl acetate
Dichloromethane
Acetonitrile
587
613
620 (42,500)
624
638
675
693
701
0.18
0.13
0.09
0.04
a
Measured at 2 ꢂ 10ꢁ5 M.
lex w 590 nm.
Determined with N,N0-dioctyl-3,4,9,10-perylenedicarboximide as reference
b
c
[71].
functional theory (DFT) at the B3LYP/6-31G** level [67]. The highest
occupied molecular orbitals (HOMOs) and the lowest unoccupied
molecular orbitals (LUMOs) of 1a, 2a and 4a are shown in Fig. 5. The
HOMO of all compounds 1e4 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
experimental parameters for perylene bisimide derivatives 1e4 are
summarized in Table 3. The results indicate that both the HOMO
and LUMO energy levels increase as the number of amino groups
increase. Moreover, DFT (B3LYP/6-31G**) calculations show that
the ground-state geometries of the perylene core have a core twist
angles, i.e., approximate dihedral angles between the two naph-
thalene subunits attached to the central benzene ring; which is
20.0ꢀ for 1a and 19.2ꢀ for 2a (Table 3 and Fig. 6), yet both are larger
than those of 3a (10.1ꢀ and w18.0ꢀ) and 4a (9.2ꢀ and 17.5ꢀ). As
a whole, the core twist angles of di-substituted PBIs (1a and 2ae2c)
are larger than those of mono-substituted PBIs (3a and 4ae4c).
Fig. 2. Normalized absorption spectra of 1a (green line), 2a (blue line), 3a (cyan line),
4a (purple line) and 5a (red line) in dichloromethane solution. (For interpretation of
the references to color in this figure legend, the reader is referred to the web version of
this article.)
Supplementary data. The fluorescence spectra shift significantly to
the red upon increasing solvent polarity, indicating strong intra-
molecular charge transfer (ICT) characteristics for the excited states
of 1e4. We used the well-established fluorescence solvatochromic
shift method [64] to measure the stabilization of the excited states
of 1ae4a. The change of magnitudes for dipole moments between
ƒ! ƒ!
ground and excited states, i.e., Dm ¼ j: me
ꢁ
mg j:, can be calculated
by the LipperteMataga equation and expressed as:
3.4. Electrochemical properties of dyes
ꢀ
ꢁ
2
2
hc
ya
ꢁ
yf
¼
me
ꢁ
mg aꢁ0 3Df þ const:
(1)
The cyclic voltammograms of 4a and 2a with mono- and di-
amino substituents are illustrated in Fig. 7. These chromophores
(1e4) undergo two quasi-reversible one-electron oxidations and
two quasi-reversible one-electron reductions in dichloromethane
at modest potentials, which clearly indicates all these processes can
be attributed to successive removal or addition of electrons to the
orbitals. Table 4 summarizes the redox potentials and the HOMO
and LUMO energy levels estimated from cyclic voltammetry (CV)
for 1e4 [68]. It appears that both the first oxidation and the first
reduction potentials are shifted toward more negative values with
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
0
0
ꢀ
be 7.0 A via HartreeeFock theories with 6-31G(d ,p ) basis, ya
ꢁ
yf is
the Stokes shift of the absorption and emission peak maximum, and
Df is the orientation polarizability defined as:
ꢀ
ꢁ
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-
ꢁ
mg j: was
ƒ! ƒ!
ciently linear for 1ae4a (Fig. 4). Accordingly, Dm ¼ j: me
deduced to be 4.7 D, 5.2 D, 7.1 D and 7.4 D for 1ae4a. These values
indicate that the asymmetric compound 3a (4a) has larger dipole
moment change than that of the symmetric compound 1a (2a)
upon excitation, which are in good agreement with previous
reports [65,66].
3.3. Quantum chemistry computation
To gain more insight into the electronic properties of 1e4,
quantum mechanical calculations were performed using density
Table 1
Summary of optical absorption and emission properties of 1a in various solvents.
Compound 1a
labs (nm)/(
3
(Mꢁ1 cmꢁ1)a)
lemb (nm)
Fc
Cyclohexane
Ethyl acetate
Dichloromethane
Acetonitrile
646
679
696 (45,600)
699
720
765
789
799
0.16
0.11
0.08
0.03
Fig. 3. Normalized emission spectra of 2a in cyclohexane (black line), ethyl acetate
(blue line), dichloromethane (green line) and acetonitrile (red line). (For interpretation
of the references to color in this figure legend, the reader is referred to the web version
of this article.)
Measured at 2 ꢂ 10ꢁ5 M.
lex w 650 nm.
a
b
c
Determined with N,N0-dioctyl-3,4,9,10-perylenedicarboximide as reference [71].

H.-Y. Tsai, K.-Y. Chen / Dyes and Pigments 96 (2013) 319e327
323
Table 3
Calculated and experimental parameters for perylene bisimide derivatives.
HOMOa
LUMOa
Eg
Eg
Twisting angle (ꢀ)
a
b
Compound
1a
2a
2b
2c
3a
4a
4b
4c
9a
ꢁ5.09
ꢁ5.33
ꢁ5.35
ꢁ5.35
ꢁ5.54
ꢁ5.62
ꢁ5.65
ꢁ5.65
ꢁ5.94
ꢁ2.96
ꢁ3.05
ꢁ3.06
ꢁ3.07
ꢁ3.19
ꢁ3.21
ꢁ3.24
ꢁ3.25
ꢁ3.46
2.13
2.28
2.28
2.28
2.35
2.41
2.41
2.40
2.48
1.98
2.14
2.15
2.14
2.20
2.24
2.24
2.25
2.38
20.0
19.2
19.4
19.2
10.1, 18.0
9.2, 17.5
9.2, 17.6
9.2, 17.5
0
a
Calculated by DFT/B3LYP (in eV).
b
At absorption maxima (Eg ¼ 1240/lmax, in eV).
(DSC). The decomposition temperature of 2a is 320 ꢀC and that of
5a is 260 ꢀC; this shows that the amino-substituted perylene bisi-
mide 2a is more thermally stable than the nitro-substituted per-
ylene bisimide 5a (Fig. 8). The weight loss of about 7% for 5a is in
good agreement with the theoretical calculation of 7.1%, and is most
likely due to the fragmentation of the nitro group. Many perylene
bisimide derivatives with long alkyl side chains are liquid crystal-
line (LC) [69,70]. However, according to DSC analyses all of the
compounds 2ae2c had no observable liquid crystalline transitions
between ꢁ50 and 300 ꢀC.
Fig. 4. LipperteMataga plots for 1a (green line), 2a (blue line), 3a (cyan line) and 4a
(purple line). The solvents are (1) cyclohexane, (2) ethyl acetate, (3) dichloromethane,
(4) acetonitrile. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article.)
increasing numbers of substituted amino groups, while both the
HOMO and the LUMO energy levels increase with the trend. The
first oxidation of 1a (3a) is smaller than that of 2a (4a); this can be
explained by the fact that the piperidinyl substituent has better
electron-donating ability than the amino substituent. The HOMO/
LUMO energy levels of 1a, 2a, 3a and 4a are estimated to be ꢁ5.21/
ꢁ3.23, ꢁ5.39/ꢁ3.25, ꢁ5.49/ꢁ3.29 and ꢁ5.57/ꢁ3.33 eV, respec-
tively. As expected, the trend of the HOMOeLUMO energy gap is
4a > 3a > 2a > 1a, which is in good agreement with the theoretical
calculations.
3.6. Stacking behaviors of dyes in solution and solid state
The stacking behaviors of 2ae2c and 4ae4c in dichloromethane
and ethyl acetate were investigated by concentration-dependent
3.5. Thermal properties of dyes
The thermal properties of 1,7-diaminoperylene bisimide (2a)
and 1,7-dinitroperylene bisimide (5a) were investigated by ther-
mogravimetric analysis (TGA) and differential scanning calorimetry
Fig. 6. DFT (B3LYP/6-31G**) geometry-optimized structures of 2a (left) and 4a (right)
shown with view along the long axis. For computational purposes, methyl groups
replace the cyclohexyl groups at the imide positions.
Fig. 5. Computed Frontier orbitals of 1a, 2a and 4a. The upper graphs are the LUMOs and the lower ones are the HOMOs.

324
H.-Y. Tsai, K.-Y. Chen / Dyes and Pigments 96 (2013) 319e327
Fig. 7. The cyclic voltammograms of 2a (blue line) and 4a (purple line) measured in
dichloromethane solution with ferrocenium/ferrocene, at 200 mV/s. (For interpreta-
tion of the references to color in this figure legend, the reader is referred to the web
version of this article.)
Fig. 9. Normalized absorption spectra of 2a (inset) and 4a at different concentrations
in ethyl acetate.
Table 4
Summary of half-wave redox potentials, HOMO and LUMO energy levels for 1e4.
a
a
a
a
EHOMO/ELUMO (eV)b
2þ
E1þ=2
E
E1ꢁ=2
E
2ꢁ
Compound
1=2
1=2
1a
2a
2b
2c
3a
4a
4b
4c
0.61
0.79
0.79
0.80
0.89
0.97
0.99
1.00
0.88
1.17
1.17
1.18
1.32
1.36
1.38
1.39
ꢁ1.20
ꢁ1.15
ꢁ1.14
ꢁ1.14
ꢁ0.98
ꢁ0.97
ꢁ0.96
ꢁ0.96
ꢁ1.28
ꢁ1.24
ꢁ1.23
ꢁ1.22
ꢁ1.15
ꢁ1.09
ꢁ1.08
ꢁ1.07
ꢁ5.21/ꢁ3.23
ꢁ5.39/ꢁ3.25
ꢁ5.39/ꢁ3.24
ꢁ5.40/ꢁ3.26
ꢁ5.49/ꢁ3.29
ꢁ5.57/ꢁ3.33
ꢁ5.59/ꢁ3.35
ꢁ5.60/ꢁ3.35
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.
UVeVis measurements (from 10ꢁ4 M to 10ꢁ6 M). Fig. 9 shows the
absorption spectra of 2a and 4a at different concentrations in ethyl
acetate. At high concentrations, a clear red shift (w700 nm) was
observed for all 1-aminoperylene bisimides 4ae4c, indicating the
formation of J-type aggregates. At low concentrations, the spectra
resemble those of dichloromethane, in which no stacking takes
Fig. 10. Normalized absorption spectra of 1a (green line), 2a (blue line), 3a (cyan line),
4a (purple line) and 5a (red line) in neat film. (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of this article.)
Fig. 8. Thermogravimetric analysis graphs for 2a (blue line) and 5a (red line) in
nitrogen atmosphere at normal pressure. Heating rate, 10 ꢀC/min. (For interpretation of
the references to color in this figure legend, the reader is referred to the web version of
this article.)
Fig. 11. The absorption (red line) and emission (black line) spectra of 2a in concen-
trated HCl. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article.)

H.-Y. Tsai, K.-Y. Chen / Dyes and Pigments 96 (2013) 319e327
325
Scheme 2. One of the possible resonance structures for 2ae2c, explaining the disappearance of the charge transfer absorption band in concentrated HCl.
place. However, compounds 2ae2c show no significant red shift
transfer emission. Upon excitation, they show smaller dipole
both in dichloromethane and ethyl acetate; this can be explained by
moment changes than those of the asymmetric PBIs (4ae4c); the
dipole moments of these compounds have been estimated using
the LipperteMataga equation. All of the compounds from 2a to 2c
undergo two quasi-reversible one-electron oxidations and two
quasi-reversible one-electron reductions in dichloromethane at
modest potentials. Furthermore, they display good thermal
stability as well as good optical stability and reversible redox
properties. Research on their applications to organic photovoltaic
cells is in progress.
the fact that the big core twist angles of 2ae2c decrease the
pep
interactions (Fig. 6 and Table 3).
The absorption spectra recorded for the thin drop-cast films of
1ae5a are shown in Fig. 10. The shapes of the absorption spectra of
all the perylene dyes (1ae5a) in solid state and in solution show
drastic differences, in view of wavelength range (absorption of up
to 800 nm for 1ae4a) and peak positions. The absorption spectra of
all the drop-cast film chromophores were red-shifted as well as
broadened compared to their respective spectra in cyclohexane,
which indicates aggregation. This spectral change can be attributed
Acknowledgment
mainly to intermolecular pep interactions in the solid state.
Financial support from the National Science Council of the
Republic of China is gratefully acknowledged (NSC 101-2113-M-
035-001-MY2).
3.7. Influence of the acidic condition on the optical properties of
dyes
The effects of the acidic condition on the absorption and emis-
sion spectra of 1,7-diaminoperylene bisimides (2ae2c) were also
examined. Fig. 11 shows the absorption and emission spectra of 2a
in concentrated HCl. The absorption spectrum of 2a in such an
acidic condition loses its typical absorption band over 600 nm and
instead shows non-substituted perylene bisimide centered around
520 nm, as also demonstrated by the red color of the analyzed
solution. The most likely explanation is that the two nitrogen atoms
on the bay-core are protonated in the acidic condition, so that
charge transfer is no longer possible (Scheme 2). Furthermore,
Appendix A. Supplementary data
Supplementary data (1H NMR spectra of 1e6; emission spectra
of 1a, 3a and 4a in various solvents; absorption spectra of 2a at
different concentrations in dichloromethane) associated with this
article can be found, in the online version at http://dx.doi.org/10.
1016/j.dyepig.2012.09.003.
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