The synthesis of symmetric and asymmetric perylene derivatives and their optical properties

Article abstract of DOI:10.1016/j.dyepig.2009.10.001

Symmetric bisimidazole and asymmetric imide-imidazole derivatives having a perylene structure were synthesized. Long, hyperbranched alkyl groups, attached to the benzimidazole moeity, enhanced the solubility of the imidazole derivatives. Soluble asymmetric imide-imidazoles were prepared using 1,2-diaminophenyls which contained methoxy, nitro and ester groups. The effects of both electron-withdrawing and donating groups were examined optically and electronically using both absorption and emission spectroscopy. Photoluminescence spectroscopy revealed that the various perylene derivatives displayed varying quantum yield; frontier orbital energy levels were determined using cyclic voltammetric analysis. The asymmetric imide-imidazole displayed the transient, electronic and optical properties of symmetric bisimide and symmetric bisimidazole perylene derivatives. Nitro derivation reduced the LUMO energy level of the asymmetric perylene by 0.05?eV while methoxy derivation increased it by 0.07?eV, in comparison with that of the unsubstituted, asymmetric perylene. Either bathochromic or hypsochromic spectral shifts of the asymmetric imidazoles were observed in solid film, depending on electronic substituent.

Full text of DOI:10.1016/j.dyepig.2009.10.001

Dyes and Pigments 85 (2010) 37–42
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis of symmetric and asymmetric perylene derivatives
and their optical properties
Sang Hyun Oh a, Bong Gun Kim a, Sun Ju Yun a, Muchchintala Maheswara a,
,
Ketack Kim b, Jung Yun Do a
*
a Department of Chemistry Education, Pusan National University, 30 Jangjeong-Dong, Geumjeong-Gu, Busan, 609-735, Republic of Korea
b Battery Research Group, Korea Electrotechnology Research Institute Changwon, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Symmetric bisimidazole and asymmetric imide-imidazole derivatives having a perylene structure were
synthesized. Long, hyperbranched alkyl groups, attached to the benzimidazole moeity, enhanced the
solubility of the imidazole derivatives. Soluble asymmetric imide-imidazoles were prepared using 1,2-
diaminophenyls which contained methoxy, nitro and ester groups. The effects of both electron-with-
drawing and donating groups were examined optically and electronically using both absorption and
emission spectroscopy. Photoluminescence spectroscopy revealed that the various perylene derivatives
displayed varying quantum yield; frontier orbital energy levels were determined using cyclic voltam-
metric analysis. The asymmetric imide-imidazole displayed the transient, electronic and optical prop-
erties of symmetric bisimide and symmetric bisimidazole perylene derivatives. Nitro derivation reduced
the LUMO energy level of the asymmetric perylene by 0.05 eV while methoxy derivation increased it by
0.07 eV, in comparison with that of the unsubstituted, asymmetric perylene. Either bathochromic or
hypsochromic spectral shifts of the asymmetric imidazoles were observed in solid film, depending on
electronic substituent.
Received 17 June 2009
Received in revised form
30 September 2009
Accepted 2 October 2009
Available online 13 October 2009
Keywords:
Bisimidazole
Solar cell
Asymmetric perylene imidazole
Soluble perylene
Energy levels
Spectral shift
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
stability as well as electron transfer through p–p stacking [8]; many
perylene derivatives have been described [5,9–13].
Perylene derivatives with a planar structure have attracted
interest in the context of liquid crystal materials and light emitting
diodes [1,2]. The excellent charge transporting character of such
aligned perylenes is favorable fororganic thin films transistor(OTFT)
applications [3] as the electron transfer process is both rapid and
effective [4]. Recent organic photovoltaic research has adopted
perylene derivatives as the n-type semiconductor for the fullerene
derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) [5];
manyorganicsolarcellshavebeenfabricatedusing PCBM, despiteits
demerits of high synthesis cost, low solvent solubility and low
charge carrier mobility [6]. In terms the cascade of energy transfer
froman exited chromophore in a heterojunctionsolarcell, the LUMO
energy level of fullerenes has to be located between that of the
chromophore and the anode work function [7]. Fullerene derivation
is difficult and, synthetically, is limited to the maintenance of
A key issue for perylenes is their solvent solubility, this being of
significance in the context of film formation [9]; their nonpolar,
planar and rigid structure imparts very low solubility and necessi-
tates the use of vacuum evaporation for thin film fabrication [8]. The
introduction of a long chain alkyl substituent in perylene derivatives
enhances their solubility and many studies have involved the use of
perylene carboxylic dianhydride. Perylene bisimides are soluble
derivatives that contain long alkyl chains [14] which have also been
further derivatised to modify specific optical properties such as
electronic energy levels and absorption wavelength [10,15,16]. In
this context, amino and alkoxy groups extend absorption to longer
wavelengths or lower the band gap [9]. Such bulky substituent
distort the phenyl groups of the planar perylene structure and
induce aggregation, which diminishes the conductionchannel of the
electrons [9]. An imidazole derivative as a perylene imide analogue
was employed as an n-type semiconductor [10,17] in which, whilst
the novel, planar ring formation beyond the four phenyls of the
perylene constituent imparted longer wavelength absorption, it
worsened solubility. However, it is considered that modification of
such structures via perylene carboxylic dianhydride should be
possible employing an appropriate synthetic pathway.
p-conjugation. Perylenes are similar to fullerenes in character and
display reversible redox properties and good thermal and optical
* Corresponding author. Fax: þ82 51 581 2348.
E-mail address: jydo@pusan.ac.kr (J.Y. Do).
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.10.001

38
S.H. Oh et al. / Dyes and Pigments 85 (2010) 37–42
This paper concerns the selective synthesis of an asymmetric
with oxidizing agents and acids; 4.98 g, 19 mmol) in DMF (20 ml)
under N2. The mixture was stirred for 10 min and diethyl azodi-
carboxylate (DEAD) (caution: can explode if heated under
confinement; shock sensitive; decomposes vigorously >100 ꢀC;
incompatible with strong acids, strong bases, strong oxidizing
agents, strong reducing agents; light sensitive; 3.3 ml, 19 mmol)
was added dropwise at ꢁ15 ꢀC. The resulting mixture was stirred at
room temperature for 36 h. The reaction mixture was diluted with
ethyl acetate and washed with water. The organic layer was dried
over anhydrous MgSO4 and filtered. The solvent was removed by
rotary evaporation and the mixture was purified by column chro-
matography on silica gel with ethyl acetate/hexane (1/4) as an
eluent to yield 7.72 g (78%).
imide-imidazole derivative that exhibits the transient electronic
property of both symmetric imidazole and symmetric imide per-
elyne derivatives. All derivatives were analyzed in solution phaseso
as to suppress strong intermolecular interactions that inevitably
occur in solid films. The electronic energy levels of the asymmetric
perylene derivative that has undergone electronic modification via
imidazole rings are discussed.
2. Experimental
2.1. Materials and instrumentations
All reagents such as perylene-3,4,9,10-tetracarboxyldianhy-
dride, 4-nitro-o-phenylenediamine, methoxy-1,2-phenylenedi-
amine dihydrochloride, diaminobenzoic acid, and steric acid ethyl
ester were purchased from Aldrich 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-free atmosphere. Column chromatography
was performed using silica gel (Merck, 250–430 mesh).
1H NMR (CDCl3, 300 MHz): dppm ¼ 0.88–0.92 (t, 12H, CH3), 1.36–
1.47 (m, 16H, CH2), 1.53–1.71 (m, 2H), 3.80–3.82 (d, 4H, OCH2), 4.27
(s, 2H, OCH2), 6.40 (s, 1H), 6.55 (s, 2H), 6.70–6.73 (d, J ¼ 9 Hz, 1H),
7.52 (s,1H), 7.58–7.61 (d, J ¼ 9 Hz, 1H).
2.2.1.3. 2‘-Nonyloctadecyl -3,4-diaminobenzoate (3a) (52%). 1H
NMR (DMSO-d6, 300 MHz): dppm ¼ 0.79 (t, 6H, CH3), 0.94–1.78 (m,
48H), 1.99 (m, 1H, CH), 4.3 (d, 2H, OCH2), 4.6 (br, 2H, NH2), 5.2 (br,
2H, NH2), 6.46 (d, J ¼ 8.1 Hz, 2H), 7.03 (d, J ¼ 8.1 Hz, 2H), 7.10 (s, 1H).
1H NMR spectra were recorded in CDCl3 on a Varian Mercury
300 MHz. The absorption and photoluminescence (PL) spectra were
measured using a Jasco V-570 UV–Vis spectrometer and a Hitachi
F-4500 fluorescence spectrophotometer, respectively. Cyclic vol-
tammetry (CV) was carried out with a Bioanalytical Systems CV-
50W voltammetric analyzer at a potential scan rate of 100–150 mV/
s in a 0.1 M solution of tetrabutylammonium tetrafluoroborate
(Bu4NBF4) in anhydrous acetonitrile and tetrabutylammonium
hexafluorophosphate (Bu4NBPF6) in dichloromethane. A platinum
wire was used as the counter electrode and an Ag/AgNO3 electrode
was used as the reference electrode.
2.2.2. Synthesis of asymmetric anhydride-imide derivative
of perylene, N-(1- nonyldecyl)perylene-3,4,9,10-tetracarboxyl-3,
4-anhydride-9,10-imide (5)
Symmetric diimide (4, PDI) was prepared through a known
synthetic process [10]. Perylene-3,4,9,10-tetracarboxyldianhydride
(1.44 g, 3.7 mmol), and 10-nonyldecyl amine (2.667 g, 9.4 mmol)
with imidazole (caution: incompatible with acids, strong oxidizing
agents; protect from moisture; 6 g) were heated under N2 at 180 ꢀC
for 3 h. The reaction mixture was cooled, dispersed in 100 mL
ethanol, and then treated with 2 M HCl (300 mL) overnight. The
resulting red solid was filtered and washed with distilled water. The
solid was dried in vacuum at 100 ꢀC to give N,N0-bis(10-non-
yldecyl)perylene-3,4,9,10-tetracarboxyl bisimide (4)
2.2. Synthesis
2.2.1. Synthesis of alkyl 3,4-diaminobenzoate (3)
2.2.1.1. Synthesis of methyl 3,5-bis(2-ethylhexyloxy)benzoate. In
a 205-mL round flask, methyl 3,5-dihydroxybenzoate (5.04 g,
30.0 mmol), 3-(bromomethyl)heptane (30.66 g, 156 mmol), TBAB
(4.87 g, 15.0 mmol), and K2CO3 (16.6 g, 120 mmol) were dissolved
with 120 mL absolute acetone and stirred at 80 ꢀC for 48 h. The
reaction mixture was diluted with water and extracted with ethyl
acetate. The organic layers were washed several times further with
water, dried over anhydrous MgSO4 and filtered. The solvent was
removed by rotary evaporation and the mixture was purified (95%)
by column chromatography on silica gel.
In a 250-mL round flask, PDI (3.66 g, 5.24 mmol) was suspended
in t-BuOH (97 mL) and treated with solid KOH (85%, 982 mg,
17.5 mmol). The reaction mixture was heated with vigorous stirring
to reflux until the solution turned dark purple for ca. 30 min. The
mixture was cooled to room temperature, treated with acetic acid
(80 mL) and 2N HCl (40 mL), and stirred overnight. The dark red
precipitate was filtered, washed with distilled water, and dried at
130 ꢀC. This solid was suspended in 10% K2CO3 solution (150 mL)
and heated to reflux for 30 min. The mixture was cooled and
filtered. The filtered cake was rinsed with warm 10% K2CO3 until the
filtrate was clear, rinsed twice with 2 N HCl (100 mL), and dried at
130 ꢀC. The solid was then suspended in boiling water (100 mL) and
triethylamine was added until the solution presented a dark purple
color. The insoluble solid was filtered out and dark purple filtrate
was acidified with 2N HCl overnight. The resulting dark red
precipitate was filtered, rinsed with water, and dried at 130 ꢀC. The
resultant solid was further purified through the same process above
with water and triethylamine to yield 1.14 g (40%) of red solid (5).
1H NMR (4, CDCl3, 300 MHz): dppm ¼ 0.83 (t, 12H, CH3), 1.25 (m,
56H, CH2), 1.86 (m, 4H, CH2), 2.24 (m, 4H), 5.18 (m, 2H), 8.67 (m, 8H).
1H NMR (5, CDCl3, 300 MHz): dppm ¼ 0.73 (t, 6H, CH3), 1.11–1.81
(m, 28H), 1.98 (m, 2H), 2.31 (m, 2H), 5.12 (br, 1H, CHN), 8.61 (br, 8H).
1H NMR (CDCl3, 300 MHz): dppm ¼ 0.88–0.92 (t, 12H, CH3), 1.36–
1.47 (m, 16H, CH2), 1.53–1.71 (m, 2H), 3.86 (d, 4H, CH2), 3.90 (s, 3H,
OCH3), 6.64 (s, 1H), 7.16 (s, 2H); IR (KBr, cmꢁ1): 1697, 1661, 1593,
1426, 1305, 1347, 1343.
2.2.1.2. Synthesis of 3, 5-bis(20-ethylhexyloxy)benzyl-3,4-diamino-
benzoate (3b). In a 250-mL round flask, methyl 3,5-bis(2-ethyl-
hexyloxy)benzoate (10 g)was dissolved in90mlTHF. LiAlH4 (caution:
incompatible with heat, water, alcohols, acids, transition metal salts,
oxidizing agents, and a wide variety of other substances; violently
reacts with oxidants; corrosive, toxic; hazardous decomposition
products: 0.59 g, 15 mmol) was added slowly and the mixture was
stirred at room temperature for 40 min. The reaction was quenched
with water and then extracted with ethyl acetate. The organic layer
was dried over anhydrous MgSO4, filtered, and concentrated to give
3,5-bis(2-ethylhexyloxy)benzyl alcohol (1) with 74% yield.
2.2.3. Synthesis of asymmetric imide-imidazole derivatives
of perylene (6)
General procedure: In a 50-mL round flask, the anhydride-imide
(5) (1.32 g, 2.0 mmol), methoxy-1,2-phenylenediamine dihydro-
chloride (1.12 g, 4.8 mmol), and imidazole (15 g) were heated under
N2 at 180 ꢀC for 12 h. The cooled mixture was diluted with ethanol
A solution of 3,5-bis(2-ethylhexyloxy)benzyl alcohol (1) (7.28 g,
crude) in dried THF (40 ml) was added to 3,5-diaminobenzoic acid
(2.97 g, 19 mmol), and triphenylphosphine (caution: incompatible

S.H. Oh et al. / Dyes and Pigments 85 (2010) 37–42
39
6d (69% yield). MALDI-TOF MS: Calcd. for C73H89N3O7:1119.67,
Found: m/z ¼ 1119.65 [Mþ].
(20 mL), yielding a suspend mixture. The suspension was filtered
and washed with 5%-aqueous HCl (100 mL). The resulted mixture
was filtered and dried (10 h/2 torr/80 ꢀC) to afford PIZ2 (6b, 1.14 g,
75%). The product was further purified by silica gel-chromatog-
raphy with chloroform as an eluent.
2.2.4. Synthesis of symmetric imidazole derivative of perylene (7)
Perylene-3,4,9,10-tetracarboxyldianhydride (0.57 g, 1.45 mmol),
and 2-decyloctadecyl 3,4-diaminobenzoate (1.74 g, 3.19 mmol) in
imidazole (4 g) were heated under N2 at 180 ꢀC for 12 h. The
reaction mixture was cooled to room temperature, dispersed into
ethanol (100 mL), and mixed with 2 M HCl (300 mL) overnight.
The resulting solid was filtered and washed with distilled water.
The solid was dried in a vacuum at 100 ꢀC to give 1.23 g (60%).
1H NMR (CDCl3, 300 MHz): dppm ¼ 0.83 (t, 12H), 1.04–1.72 (m,
84H), 2.07 (m, 2H,-CH), 6.88–7.02 (m, 6H), 7.09 (s, 2H), 7.18–7.24 (d,
2H), 7.29–7.32 (m, 4H); IR (KBr, cmꢁ1): 1709,1694, 1594, 1282, 1240.
MALDI-TOF MASS: Calcd. For C94H128N4O6: 1408.98, Found: m/z ¼
1408.97 [Mþ].
1H NMR (6b,1/1-isomer mixture, CDCl3, 300 MHz): dppm ¼ 0.85 (m;
6H, CH3),1.19–1.21 (m; 28H),1.98–2.00 (m; 2H), 2.21–2.33 (m; 2H), 3.78
(s,1.5H, OCH3), 3.79 (s,1.5H, OCH3), 5.20 (m,1H, NCH), 6.65 (d, J ¼ 9 Hz,
0.5H), 6.74 (d, J ¼ 9 Hz, 0.5H), 6.94 (s, 0.5H), 7.37 (d, J ¼ 9 Hz, 0.5H), 7.43
(s,0.5H),7.81(d,J¼ 9 Hz, 0.5H), 8.41–8.62 (m, 8H); UV-Vismax ¼564nm
(CDCl3), 504 nm (film); IR (KBr, cmꢁ1): 1697, 1654, 1592. MALDI-TOF
MS: Calcd. for C50H53N3O4: 759.98, Found: m/z ¼ 759.20 [Mþ].
6a (82% yield) MALDI-TOF MS: Calcd. for C49H51N3O3: 729.39,
Found: m/z ¼ 729.27 [Mþ]
6c (70% yield). MALDI-TOF MS: Calcd. for C49H50N4O5: 774.38,
Found: m/z ¼ 774.34 [Mþ]
CH2OH
CO2CH3
(i) 95%
78%
H2N
CO2R
(ii) 74%
(iii)
3
O
OCH2CH(C2H5)C4H9
HO
OH
H2N
+
H3N
-
CH2CH(C2H5)C4H9
CO2
1
C9H19
R = CH2CH
3a
H2N
C16H33
2
OCH2CH(C2H5)C 4H9
C16H33
C10H21
OH
52%
3b R = CH
2
a
OCH2CH(C2H5)C 4H9
O
N
O
O
O
O
O
N
O
O
N
O
C9H19
C9H19
C9H19
C9H19
C9H19
(iv)
40%
C9H19
5
4 (PDI)
H2N
G
O
N
O
N
C9H19
C9H19
G
H2N
G= H
OCH3
NO2
(PIZ1)
(PIZ2)
(PIZ3)
6a
6b
6c
N
(v)
70%
O
6
OCH2CH(C2H5)C4H9
3b
69%
CO2CH2
G =
(vi)
OCH2CH(C2H5)C4H9
(PIZ4)
6d
b
N
N
N
N
O
O
O
O
O
O
G
G
(vi)
3a
60%
O
O
G = CO2CH2CH C10H21
C16H33
(PDZ)
7
(i) 2-ethylhexylbromide, K2CO3, Bu4NBr/acetone reflux
(ii) LiAlH4/tetrahydrofuran
(iii) 3,4-diaminobenzoic acid/Ph3P/DEAD
(iv) 85% KOH/t-BuOH reflux, 30min
(v) 1,2-diamino-4-nitrobenzene/ imidazole, 180 oC
(vi) 3a, imidazole, 180 oC
c
Fig. 1. Preparation of 3,4-diaminophenyl esters (a) and asymmetric (b) and symmetric perylene derivatives (c).

40
S.H. Oh et al. / Dyes and Pigments 85 (2010) 37–42
3. Results and discussion
PDI (525 nm)
PDZ (572 nm)
PIZ1 (574 nm)
PIZ2 (565 nm)
PIZ3 (570 nm)
PIZ4 (562 nm)
1.4
PIZ1
PDZ
Substituents in the bay area of perylene bisimides (1,6,7,12-
positions) have been demonstrated to enhance solvent solubility,
mainly due to a twisted phenyl system with a torsion angle
depending on the substituent size [9]. Electron enrichment on the
1.2
1.0
0.8
0.6
0.4
0.2
0.0
PIZ4
PIZ3
PDI
p-system of the perylene induced a red shift of the absorption
wavelength but loss of the flatness for fused rings may have affected
the electron mobility in solid film applications. The bay substituent
occasionally showed thermal instability by decomposing below
150 ꢀC [10]. The high-energy band gap (2.50 eV) of perylene [18] was
reduced by 2.13 eV with perylene bisimide derivation as a n-type
semiconductor. The high LUMO level of 3.69 eV of the diimide was
adequate to increase the driven voltage in a solar cell using poly-
thiophene [6]. The band gap was further reduced by an imidazole
derivative with 1.7 eV [10]. Two phenyl imidazole groups extended
the conjugation length of perylene structure but the decrement of
the LUMO level to 4.4 eV resulted in the disadvantage of reducing the
driven voltage. Because the voltage is determined from the energy
difference of LUMO level of an n-type material and HOMO level of
a p-type material, it is desired that the LUMO level of the perylene
derivatives is just below that of polythiophene. Furthermore, the
imidazole derivation of perylene degraded the solubility so that the
thin film processing was achieved through thermal evaporation.
Thus, an asymmetric derivation of perylene was considered with
both imide and imidazole functionalities. The phenyl attached,
asymmetric, imide-imidazole derivativewas previouslyreported for
photovoltaic applications [10]. It was soluble due to the alkyl-C19
attached on N-imide and evidently revealed a red-shifted absorp-
tion compared to a perylene bisimide. We tried to change the elec-
tronic polarity of the asymmetric derivative for further red-shifted
absorption. A convenient way of introducing a substituent on the
imidazole ring was employed. The synthesis beganwith bisimide (4)
and partially hydrolyzed anhydride-imide (5) was condensed with
1,2-phenylenediamine to afford the asymmetric imide-imidazole
(6a), as reported previously [10]. The continuous synthesis is out-
lined in Fig. 1.
PIZ2
400
450
500
550
600
650
700
750
800
850
Wavelength (nm)
Fig. 3. Emission spectra of perylene derivatives in chloroform irradiated at a wave-
length of the parentheses.
insufficient solubility during solution analysis. Thus, an exceedingly
long alkyl chain was designed. A primary alcohol from the aldol
condensation of decanal and ethyl stearate was coupled with
3,4-daminobenzoic acid to afford 3,4-diaminobenzoate 3a. Thermal
condensation of 3,4,9,10-perylenetetracarboxylic dianhydride and
two equimolar amount of 3a generated a symmetric perylene
imidazole 7, exhibiting a moderate solubility of ca. 30 mg/mL in
chloroform. A potential isomerism during the preparation of per-
ylene derivatives in Fig. 1 was expected and was observed on the 1H
NMR spectrum. The equal formation of two isomers of 6b was
defined with an integral ratio (1/1) of two singlet peaks (3.78 and
3.79 ppm) assigned to an unlikely placed methoxy group on the
imidazole phenyl. Six isomers are potentially possible for 7 due to
the ester positions as well as cis and trans-bisimidazole. However,
the chromatographic isolation of each isomer was unsuccessful due
to their similar polarities and the 1H NMR spectrum of isomeric
mixture 7 showed a complicated pattern. Infrared absorption bands
of imide carbonyls around 1694 cmꢁ1 and mass analysis substan-
tially proved the formation of 7.
A methoxy group to enrich the electrons and a nitro group to
induce an electron deficiency on the imidazole were employed for
6b and 6c, respectively. A hyperbranched alkyl was adapted to
attain a level of solvent solubility comparable to that of the bisimide
(4). 3,5-Ethylhexyloxybenzyl alcohol (1) was esterified with
3,5-diaminobenzoic acid under the Mitsunobu coupling condition
[19] to provide 6d. A symmetric imidazole derivative with 3b was
synthesized under refluxing imidazole solvent but it exhibited
The prepared soluble perylene derivatives were optically
analyzed and the absorption spectra were presented in Fig. 2. The
maximum peak of the symmetric imidazole (PDZ) appeared at
the longest wavelength among the derivatives as expected. The
asymmetric imide-imidazole derivatives (PIZs) were apparently
placed between a symmetric imide (PDI) and an imidazole
1.2
PDI
PIZ1
1.0
PIZ2
PIZ3
PIZ4
0.8
PDZ
0.6
0.4
0.2
0.0
400
450
500
550
600
650
700
750
800
850
Wavelength (nm)
Fig. 4. Comparison of UV–vis absorption spectra of
a thin film and chloroform
Fig. 2. UV–vis absorption spectra of perylene derivatives in chloroform.
solution.

S.H. Oh et al. / Dyes and Pigments 85 (2010) 37–42
41
Table 1
Summarized optical and electrical properties of the prepared perylene derivatives.
Perylene derivatives
UV–vis absorption, CHCl3
Emission
Energy level, eV
HOMOd
Egf,eV
3
*103, molar absorptivity
lpeak, nm CHCl3
FPL(%)c
LUMOe
a
lmax, nm
b
PDI
525 (489)b
574 (534)
565
528 (550)
524 (562)
602 (560)
58.0 (36.5)
31.5 (28.4)
24.0
23.5 (22.0)
30.0 (17.4)
27.0 (24.3)
553, 574
597, 638
652
572, 621
584, 628
658
77
28
2
25
36
40
5.82
5.72
5.60
5.54
5.65
5.80
3.69
3.72
3.65
3.77
3.75
3.86
2.13
2.00
1.95
1.77
1.90
1.94
PIZ1
PIZ2
PIZ3
PIZ4
PDZ
All UV–vis and emission spectra were measured with 1.0*10ꢁ5 mol/L-chloroform solution.
a
Irradiated at 525, 534, 490, 528, 524, 602 nm for PDI, PIZ1, PIZ2, PIZ3, PIZ4, PDZ respectively.
Second highest peak.
b
c
The PL quantum yields in chloroform solution were determined against 9,10-diphenylanthracene in ethanol as a standard (FPL ¼ 91%) [21].
d
e
f
Calculated using an optical band gap and LUMO level.
The energy levels were determined with CV analysis in the 0.1 M Bu4NBF4/CHCl3 (Supplementary Data).
Optical band gap was determined from the edge of absorption tail in chloroform solution.
derivative (PDZ) in the comparison of the maximum wavelengths.
bisimide and symmetric bisimidazole spectra. The electron-with-
drawing and -donating groups decreased and increased the LUMO
levels of the asymmetric perylene derivatives, respectively. These
asymmetric derivations contributed to the widening absorption
span of the solid films along with the elaborate adjustment of the
perylene energy levels. The absorptive spectral shifts occurred with
the solid films of the asymmetric perylene derivatives where
methoxy and nitro groups induced opposite shifts.
The introduction of polar substituents on the asymmetric deriva-
tives caused spectral shifts. The electronic contribution was
observed with a distinct emission band as shown in Fig. 3. When
the derivatives were excited with their maximum absorption
wavelengths, electron-withdrawing group derivatives (PIZ3 and
PIZ4) presented shorter emissive wavelengths than PIZ1 while the
methoxy derivative (PIZ2) presented longer wavelengths. PIZ3
exhibited a peculiar broad absorption tailed up to 745 nm. Many
perylene derivatives have been demonstrated to aggregate in solid
films where head-to-tail interaction and face-to-face packing
induced bathochromic and hypsochromic shifts, respectively [9].
Fig. 4 compares the absorption spectra of a solution and a solid
film of selected derivatives. The hypsochromic shift of the PIZ2 film
was conspicuous while the electron-withdrawn derivative (PIZ3)
exhibited a bathochromic shift. Electronic supplementation tends
Acknowledgments
This research was supported by the MKE (The Ministry of
Knowledge Economy), Korea, under the ITRC (Information Tech-
nology Research Center) support program supervised by the NIPA
(National Industry Promotion Agency (NIPA-2009-(C1090-0902-
0022))).
to induce a favorable intermolecular p-interaction of the perylenes.
The spans of these spectra were increased in the solid film, sug-
gesting the action of various interactions including face-to-face and
long alkyl-tails aggregation. Self-assembled perylene structures in
the solid film were promising for electronic applications accom-
panying charge conduction such as OTFT, organic light emitting
diodes, and solar cells [20]. The adjustment of the energy levels of
constituent organics is required for charge injection or collection
across metallic electrodes or heterojunction surface. The frontier
orbital energies were determined from a cyclic voltammetric
analysis of perylene derivative solutions and the results are
summarized in Table 1. The LUMO levels of the imidazole deriva-
tives were comparatively stabilized over bisimide (PDI). The
attachment of a nitro group on an asymmetric imidazole decreased
the LUMO level by 0.05 eV. The methoxy-donating group of PIZ2
increased the LUMO level over the unsubstituted derivative (PIZ1).
The addition of substituents is a convenient strategy to adjust the
energy levels of perylene imidazole derivatives.
Appendix. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.dyepig.2009.10.001.
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