The synthesis of novel, unsymmetrically substituted, chiral naphthalene and perylene diimides: Photophysical, electrochemical, chiroptical and intramolecular charge transfer properties

Article abstract of DOI:10.1016/j.dyepig.2009.04.014

A novel naphthalene monoimide and two unsymmetric chiral diimides (naphthalene and perylene) were synthesized; for comparison purposes, the perylene monoimide with the same substituent in the naphthalene monoimide was prepared. The naphthalene monoimide exhibited intramolecular charge transfer complexation in polar solvents. Excimer-like emissions were obtained in non-polar, polar protic and aprotic solvents in the cases of both the naphthalene monoimide and diimide. The specific optical rotation values of unsymmetrical chiral naphthalene and perylene diimides were -221.6 and -24, respectively at 20?°C. The Chiral naphthalene diimide showed prominent, negative Cotton effects centred at 362 and 382?nm in CH₃CN.

Full text of DOI:10.1016/j.dyepig.2009.04.014

Dyes and Pigments 84 (2010) 1–13
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis of novel, unsymmetrically substituted, chiral naphthalene
and perylene diimides: Photophysical, electrochemical, chiroptical
and intramolecular charge transfer properties
,
Suleyman Asir a, Ayhan S. Demir b, Huriye Icil a
*
a Department of Chemistry, Faculty of Arts and Science, Eastern Mediterranean University, Famagusta, N.Cyprus Mersin 10, Turkey
b Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel naphthalene monoimide and two unsymmetric chiral diimides (naphthalene and perylene) were
synthesized; for comparison purposes, the perylene monoimide with the same substituent in the naphthalene
monoimide was prepared. The naphthalene monoimide exhibited intramolecular charge transfer complexa-
tion in polar solvents. Excimer-like emissions were obtained in non-polar, polar protic and aprotic solvents in
the cases of both the naphthalene monoimide and diimide. The specific optical rotation values of unsym-
metrical chiral naphthalene and perylene diimides were ꢀ221.6 and ꢀ24, respectively at 20 ꢁC. The Chiral
naphthalene diimide showed prominent, negative Cotton effects centred at 362 and 382 nm in CH3CN.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 21 January 2009
Received in revised form
7 April 2009
Accepted 8 April 2009
Available online 20 May 2009
Keywords:
Unsymmetrical naphthalene diimides
Unsymmetrical perylene diimides
Chirality
Charge transfer
Exciplex
Cyclic voltammetry
1. Introduction
naphthalene and perylene diimides with strong CD (circular
dichroism) effects have been prepared with optimized optical prop-
Although significant advances in the synthesis of chiral naphtha-
lene and perylene diimides have been made, the synthesis of
macromolecules with inherently strong chiral properties remains
a challenge. The optical property of helically chiral compounds
depends strongly on the helical structure (conjugation and dihedral
angle). There has been a growing interest in the development of new
chiral molecular switches [1–3]. Moreover, the area using molecular
chirality to engineer useful properties in nanoscience materials is
fruitful and exciting, and represents an exceptionally strong promise
for future development. Many types of achiral, perylene and naph-
thalene diimides have been synthesised and their attractive properties
for photonic materials, molecular devices and biological applications
have been well reported in literature [4–14]. Chiral perylene and
naphthalene diimides are particularly very promising classes of dyes
for chiral molecular switches due to their excellent photochemical and
electrochemical properties, and good thermal stabilities.
erties [15–24]. Unsymmetric chiral perylene diimides have been
synthesized with the same method used for achiral unsymmetric
perylene dyes synthesis [25]. By substituent tuning the face-to-face
p
–
p
interaction of perylene dyes can be tailored in order to achieve
a balance between good solubility and the ability to form stacks with
extensive intermolecular orbital overlap, which is very important for
p
applications envisaged in the area of photonics [19,21]. Importantly,
enhancement of structural stability should be taken into account when
tailoring the structures in order to provide efficient chiroptical
switching. Recently, the first solution-processable nonracemic chiral
main-chain perylene polymers have been prepared which emerged as
a promising helical polymer for use in optoelectronic devices [23]. NDI
(naphthalene diimide) and PDI (perylene diimide) derivatives are able
to intercalate inside DNA [26–33]. Additionally, it is possible to increase
their binding property via conjugation to other binding species, nucleic
acids [28–33]. The facile reduction of these compounds has allowed
them to be used as electrochemical DNA biosensors for the detection of
Introduction of chirality into naphthalene and perylene diimides
remains a challenge and may lead to materials with optimized optical
properties that can emit circularly polarized light. Several helical
specific genes [29]. Naphthalene modified cyclic D, L–peptide nano-
tubes with interesting optical and electronic properties have been well
documented [34,35]. On the other hand, molecular recognition dyad
self-assembles in solvents to form helically stacking structures have
been described [36,37]. Notably, the chirality in the pendant tails is
* Corresponding author. Tel.: þ357 90 392 630 1085; fax: þ357 90 392 365 3641.
E-mail address: huriye.icil@emu.edu.tr (H. Icil).
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.04.014

2
S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
crucial to control the chiroptical responses of the self-assembled
structures [38–41]. Remarkably, use of chiral, self-assembled, donor
and acceptor chromophores substituting fibers in optoelectronic
devices, and prototypes and models for new nanoscale devices would
lead to very exciting future applications. Transfer of chirality from low
molecular chiral tectons to supramolecular assemblies has been
presented [41]. Donor and acceptor chromophores on naphthalene
and perylene diimide molecules revealed electron mobility via intra or
intermolecular charge transfer interactions and electron transfer
reactions [42–43]. Furthermore, results of similar studies on fluo-
rophores conjugated DNA could be extremely important for environ-
mental and biological applications [44].
In this paper, the synthesis of a novel naphthalene monoimide,
N-(4-hydroxyphenyl)-1,4,5,8-naphthalenetetracarboxylic-1,8-anhy-
dride-4,5-imide (1), as well as that of novel unsymmetrically substi-
tuted chiral naphthalene and perylene diimides 2 and 5, N-(4-hydro
xyphenyl)-N0-[(S)-1-phenylethyl]-1,4,5,8-naphthalenetetracarboxydi
imide and N-(4-hydroxyphenyl)-N0-[(S)-1-phenylethyl]-3,4,9,10-per-
ylenetetracarboxydiimide are reported and their photophysical, elec-
trochemical, chiroptical and intramolecular charge transfer properties
are explored; in addition, their solid state absorption are discussed. For
comparison, perylene-3,4,9,10-tetracarboxylic acid monoanhydride
monopotassium carboxylate (3) and N-(4-hydroxyphenyl)-3,4,9,10-
perylenetetracarboxylic-3,4-anhydride-9,10-imide (4) were synthe-
sized according to the methods given previously [11].
paraffin impregnated graphite electrodes (PIGEs) with a diameter of
5 mm. The solid compound was attached to the surface of PIGE by
scratching. The supporting electrolyte was 1 M HCl. The scan rate of
25–600 mVꢀ1 and the frequency 50–300 Hz were employed for solid
state cyclic and square-wave voltammetries, respectively. Fluores-
cence lifetime measurement was performed by time correlated single
photon counting technique (FLS920, from Edinburgh Instruments).
2.2. Novel synthetic compounds and procedures
The naphthalene monoimide (1) and two unsymmetric chiral
diimides (2: naphthalene, 5: perylene) were synthesized; for
comparison purposes, the perylene monoimide (4) with the same
substituent in naphthalene monoimide was prepared (Fig. 1). The
unsymmetrical chiral naphthalene diimide was prepared using a two-
step reaction process starting from 1,4,5,8-naphthalenetetracarboxylic
dianhydride. In the first stage, N-(4-hydroxyphenyl)-1,4,5,8-naph-
thalenetetracarboxylic-1,8-anhydride-4,5-imide (1) was synthesized
according to the literature [34]. In the final step, the chiral unsym-
metrical naphthalene diimide (2) was synthesized via condensation of
1 with (S)-(-)-a-methylbenzylamine using m-cresol and isoquinoline
as solvent mixture. The unsymmetrical chiral perylene diimide has
been synthesized from perylene-3,4,9,10-tetracarboxylic dianhydride
by a three-step reaction with the same amines (5). At the first and
second steps, perylene-3,4,9,10-tetracarboxylic acid monoanhydride
monopotassium carboxylate (3) and N-(4-hydroxyphenyl)-3,4,9,10-
perylenetetracarboxylic-3,4-anhydride-9,10-imide (4) were synthe-
sized and purified according to literature [21], respectively. Finally, the
unsymmetrical chiral perylene diimide (5) was synthesized via
2. Experimental
2.1. Chemicals and instruments
condensation of (S)-(-)-a-methylbenzylamine with 4 using m-cresol
1,4,5,8-naphthalenetetracarboxylic dianhydride, perylene-
3,4,9,10-tetracarboxylic dianhydride, 4-aminophenol, potassium
hydroxide, phosphoric acid and isoquinoline were obtained from
and isoquinoline as solvent mixture.
2.2.1. N-(4-hydroxyphenyl)-1,4,5,8-naphthalenetetracarboxylic-
1,8-anhydride-4,5-imide (1, Fig. 2)
Aldrich. (S)-(-)-a-methylbenzylamine, tetrabutylammonium hexa-
fluorophosphate (TBAPF6) and ferrocene were purchased from
Fluka. All organic solvents employed were of spectroscopic grade.
IR spectra were measured as KBr pellets using a Mattson Sattelite
FT-IR spectrometer. UV/vis spectra in solutions were recorded with
a Varian-Cary 100 spectrometer. UV/vis spectra of solid state were
measured in thin films using a Perkin–Elmer UV/VIS/NIR Lambda 19
spectrometer, equipped with solid accessories. Mass spectra were
recorded with a Thermo Finnigan ESI instrument. Data were pre-
sented in m/z (%) values. Emission spectra were measured using
a Varian-Cary Eclipse Fluorescence spectrometer. Optical rotations
were measured with a Dr. Kernchen Sucromat digital automatic
polarimeter, at 589 nm and 20 ꢁC. CD spectra were measured on
a JASCO 810 spectropolarimeter. Elemental analyses were obtained
from a Thermo Finigann 1112C, H, N analyzer. 1H and 13C NMR spectra
were measured with a Bruker AVANCE-500 spectrometer. Thermal
analyses were recorded with a Perkin Elmer/Pyris 1. The samples
were heated at 10 K/min. Cyclic and square-wave voltammetries in
solvents were performed using a three-electrode cell with a polished
2 mm glassy carbon as working and Pt as counter electrode; solutions
were 10ꢀ4 M in electroactive material and 0.1 M in supporting elec-
trolyte, tetrabutylammonium hexafluorophosphate (TBAPF6). Data
were recorded on an EG&G PAR 273A computer-controlled poten-
tiostat. Ferrocene was used as internal reference. The scan rate of
50–1000 mVꢀ1 and the frequency 60–150 Hz were employed for
cyclic and square-wave voltammetries, respectively. Cyclic and
square-wave voltammetries in solid state were performed using an
AUTOLAB system (Eco-Chemie, Utrecht, The Netherlands). The
reference electrode was an Ag/AgCl electrode (saturated NaCl) with
a potential of 0.200 V vs. SHE at 25 ꢁC. A platinum wire served as an
auxiliary electrode. A graphite rod (diameter: 0.5 cm) was used as
working electrode. Compound was immobilized at the surface of the
Following the procedure of Ghadiri 1,4,5,8-naphthalenete-
tracarboxylic dianhydride (2.0 g, 7.5 mmol), water (350 mL) and KOH
(1.0 M, 65 mL) were stirred for 2 h [34]. After the starting material had
dissolved, the solution was acidified to pH 6.4 with H3PO4 (1.0 M).
4-Aminophenol (0.8 g, 7.5 mmol) was added and the solution was
refluxed at 110 ꢁC for 28 h. The solution was filtered, and the filtrate
acidified with acetic acid (10%). The precipitate was collected by
vacuum filtration, washed with water and dried in vacuum at 100 ꢁC.
The crude product was extracted with acetone in a Soxhlet apparatus
during one day, in order to remove unreacted reactants. Yield (2.10 g,
78%); light-brown powder. FT-IR(KBr, cmꢀ1):
n
¼ 3430, 1783, 1709,
1660,1609,1591,1516,1439,1382,1351,1243,1163,1102, 956, 861, 824,
770, 646, 582, 535, 431. 1HNMR, dH (ppm) (500 MHz, DMSO-d6):
8.51–8.49 (d, J ¼ 6.7 Hz, 2 Ar-H, H-C(3), H-C(6)), 8.12–8.11(d, J ¼ 7.0 Hz,
2 Ar-H, H-C(2), H-C(7)), 7.15–7.14 (app d, J ¼ 7.7 Hz, 2 Ar-H, H-C(14),
H-C(18)), 6.88–6.86 (app d, J ¼ 7.7 Hz, 2 Ar-H, H-C(15), H-C(17)).
13CNMR, dC (ppm) (100 MHz, DMSO-d6): 169.55 (2C]O, C(9), C(10)),
163.53 (2 C]O, C(11), C(12)), 157.33 (1(C), C(16)), 139.48 (1(C), C(13)),
130.22 (2 Ar-CH, C(2), C(7)), 129.94 (2 Ar-CH, C(3), C(6)), 128.94 (1(C),
C(19)), 128.44 (2 Ar-CH, C(14), C(18)), 126.66 (2(C), C(1), C(8)), 125.68
(1(C), C(20)), 124.34 (2(C), C(4), C(5)), 115.54 (2 Ar-CH, C(15), C(17)).
UV/Vis (DMF): lmax (nm) (
3
) ¼ 356 (10850), 373 (11732). Fluorescence
(DMF): lmax (nm) ¼ 407. Fluorescence quantum yield (MeOH, refer-
ence Anthracene with Vf ¼ 27%, lexc. ¼ 360 nm) ¼ 0.2%. MS (EI): m/z:
359 [M]þ. Anal. Calcd. for C20H9NO6 (Mw, 359.3); C, 66.86; H, 2.52; N,
3.90. Found: C, 66.36; H, 2.54; N, 3.94.
2.2.2. N-(4-hydroxyphenyl)-N0-[(S)-1-phenylethyl]-1,4,5,8-
naphthalenetetracarboxydiimide (2, Fig. 2)
N-(4-hydroxyphenyl)-1,4,5,8-naphthalenetetracarboxylic-1,8-
anhydride-4,5-imide (1.0 g, 2.8 mmol), (S)-(-)-a-methylbenzylamine

S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
3
Fig. 1. 1,2,4 and 5 with a 3D model.
(1.1 mL, 8.4 mmol), m-cresol (40 mL) and isoquinoline (8 mL) were
stirred under argon at 80 ꢁCfor3h,at120ꢁCfor6h,at160ꢁCfor8hand
at 190 ꢁCfor 5h. Thewarm solutionwaspouredintomethanol(350mL)
and filtered. Hydrochloric acid (1.0 M) was added to the filtrate, and
a brown solid precipitated from the solution. The product was further
purified by crystallization from chloroform. The solid was collected by
vacuum filtration, washed with water and dried in vacuum at 100 ꢁC.
methanol (300 mL). The precipitate was collected by vacuum filtration,
washed with water and dried in vacuum at 100 ꢁC. The crude product
was extracted for 24 h with methanol then ethanol in order to remove
high boiling solvents and the unreacted reactants using a Soxhlet
apparatus. Yield (0.45 g, 92%); black-brownish powder. Rf (silica gel,
CHCl3) ¼ 0.25. ½a D
ꢂ
20: ꢀ24 (c 0.052, DMSO). FT-IR(KBr, cmꢀ1) :
¼ 3370,
n
3063, 3025, 2966, 2926, 1698, 1659, 1594, 1577, 1513, 1449, 1403, 1354,
1256, 1179, 1124, 960, 837, 810, 746, 697, 601, 531, 490, 430. 1HNMR, dH
(ppm) (400 MHz, Pyridine-d5) ¼ 8.92–8.48 (m, 8 Ar-H, H-C(1), H-C(2),
H-C(5), H-C(6), H-C(7), H-C(8)), 7.79–7.69 (m, 4 Ar-H, H-C(18), H-C(19),
H-C(21), H-C(22)), 7.43–7.25 (m, 5 Ar-H, H-C(26), H-C(27), H-C(28),
H-C(29), H-C(30)), 6.98 (s,1 OH, HO-C(20)), 6.85–6.80 (q, J ¼ 7.09,1 CH,
H-C(23)), 2.18–2.16 (d, J ¼ 6.85, 1CH3, H3-C(24)). UV/Vis (DMF): lmax
Yield (1.10 g, 85%); brown powder. Rf (silica gel, CHCl3) ¼ 0.54. ½a D20
ꢂ
:
ꢀ221.6 (c 0.0194, CHCl3), FT-IR(KBr, cmꢀ1):
¼ 3430, 3053, 3026, 2976,
n
1708, 1660, 1611, 1590, 1513, 1450, 1350, 1326, 1250, 1195, 1102, 1066,
1030, 974, 876, 829, 769, 697, 568, 405. 1HNMR, dH (ppm) (500 MHz,
CDCl3): 8.71–8.68 (d, 4 Ar-H, H-C(2), H-C(3), H-C(6), H-C(7)), 7.65–7.48
(m, 2 Ar-H, H-C(16), H-C(20)), 7.41–7.21 (m, 5 Ar-H, H-C(17), H-C(18),
H-C(19), H-C(22), H-C(26)), 7.13–6.85 (m, 2 Ar-H, H-C(23), H-C(25)),
6.54–6.50 (q, J ¼ 7.02, J ¼ 7.005, J ¼ 6.934, 1 C H, H-C(13)), 2.00–1.99
(d, J ¼ 7.382, 1 CH3, H3-C(14)). 13CNMR, dC (ppm) (100 MHz, CDCl3):
163.35 (2 C]O, C(11), C(12)), 162.84 (2 C]O, C(9), C(10)), 157 (1(C),
C(24)), 140.00 (1(C), C(15)), 139.9 (1(C), C(21)), 131.38 (2 Ar-CH, C(3),
C(6)), 131.13 (2 Ar-CH, C(2), C(7)), 129.36 (1 Ar-CH, C(18)),128.28 (2 Ar-
CH, C(22), C(26)), 127.34 (2 Ar-CH, C(17), C(19)), 127.25 (2 Ar-CH, C(16),
C(20)), 127.1 (1(C), C(27)), 126.9 (1(C), C(28)), 126.81 (2(C), C(4), C(5)),
(nm) (
3
) ¼ 459 (40606), 490 (58 465), 526 (70 000). Fluorescence
(DMF): lmax (nm) ¼ 539, 580. Fluorescence quantum yield (MeOH,
reference N, N0-didodecyl-3,4,9,10-perylenebis(dicarboxiimide) with
Vf ¼ 100%, lexc. ¼ 485 nm) ¼ 80%. MS (EI): m/z: 587.5 [M þ 1]þ. Anal.
Calcd. for C38H22N2O5 (Mw, 586.6); C, 77.81; H, 3.78; N, 4.78. Found: C,
77.52; H, 3.64; N, 4.43.
3. Results and discussion
126.5 (2(C), C(1), C(8)). UV/Vis (DMF): lmax (nm) (
3
) ¼ 345 (13714), 360
(17918), 381 (18318). Fluorescence (DMF): lmax (nm) ¼ 410, 458, 500.
Fluorescence quantum yield (DMF, reference Anthracene with
Vf ¼ 27%, lexc. ¼ 360 nm) ¼ 0.8%. MS (EI): m/z: 463.5 [M þ 1]þ. Anal.
Calcd. for C28H18N2O5 (Mw, 462.5); C, 72.72; H, 3.92; N, 6.06. Found: C,
73.08; H, 4.02; N, 6.24.
3.1. Synthesis and characterization of naphthalene and perylene
monoimides (1, 4) and diimides (2, 5)
Unsymmetrically substituted chiral naphthalene and perylene
diimides (2, 5) were prepared according to the synthetic routes
shown in Figs. 2 and 3, respectively. The diacid naphthalenete-
tracarboxylic acid monoanhydride was directly converted to naph-
thalene monoimide (1) via condensation with 4-aminophenol at
110 ꢁC for 10 h (Fig. 2). Compounds 3 and 4 were synthesized
according to the methods given in our previous works [11,17]. The
structures of the compounds were characterized by 1HNMR,13CNMR,
MS, IR and elemental analysis; the results clearly support the
predicted chemical structures of all the compounds (Fig. 1).
2.2.3. N-(4-hydroxyphenyl)-N0-[(S)-1-phenylethyl]-3,4,9,10-
perylenetetracarboxydiimide (5, Fig. 3)
N-(4-hydroxyphenyl)-3,4,9,10-perylenetetracarboxylic-3,4-anhy-
dride-9,10-imide (0.4 g, 0.8 mmol), (S)-(-)-a-methylbenzylamine
(0.2 mL, 1.8 mmol) and isoquinoline (40 mL) were stirred under argon
at 60 ꢁC for 2h, at 80 ꢁC for 3 h, at 120 ꢁC for 8 h, at 160 ꢁC for 10 h, at
180 ꢁCfor8handat200ꢁC for 18 h. Thewarm solutionwas poured into
Fig. 2. Synthesis of naphthalene monoimide (1) and unsymmetrical chiral naphthalene diimide (2).

4
S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
Fig. 3. Synthesis of perylene-3,4,9,10-tetracarboxylic acid monoanhydride monopotassium carboxylate (3), perylene monoimide (4) and unsymmetrical chiral perylene diimide (2).
All IR spectra were consistent with the assigned structures as
shown in Figs. 2, 3 and 4. The IR spectrum of 1 exhibited charac-
teristic absorption bands at 3430 (O–H stretch); 1783 (anhydride
C]O stretch); 1709, 1660 (imides C]O stretch); 1609, 1591
(conjugated C]C stretch); 1351 (C-N stretch); 1102 (C–O–C
stretch); 861 and 770 (C–H bend) cmꢀ1. In the IR spectrum of 2, the
characteristic bands of the anhydride carbonyl stretching bands
(1783 cmꢀ1) had disappeared and were replaced by the N-imide
carbonyl stretching bands (1708 and 1660 cmꢀ1). Similarly, the
characteristic band of the C–O–C stretching (1102 cmꢀ1) had dis-
appeared and was replaced by C–N stretching band (1350 cmꢀ1).
Other absorption bands of 2 were very similar to those of 1
(Fig. 4(a)). The IR spectrum of 4 exhibited characteristic absorption
bands at 3443 (O–H stretch); 3096 (aromatic C–H stretch); 1773,
1730 (anhydride C]O stretch); 1698, 1659 (imides C]O stretch);
1594 (conjugated C]C stretch); 1300 (C–N stretch); 1025 (C–O–C
stretch); 808 and 732 (C–H bend) cmꢀ1. In the IR spectrum of 5, the
characteristic bands of the anhydride carbonyl stretching bands
(1773 and 1730 cmꢀ1) had disappeared and were replaced by
N-imides carbonyl stretching bands (1698 and 1659 cmꢀ1). Simi-
atoms force the methyl and phenyl substituent out of the plane of
the molecule and thereby hamper the face-to-face stacking of
the 2 and 5 [21]. The sterically hindered chiral substituent prevented
the short contacts of the fluorophores and resulted in higher
solubility. With less rigid 2, these effects are more pronounced
comparing to 5 which contribute to the higher solubility. Similarly,
chiral 5 was poorly soluble compared to our previously reported
symmetrically substituted chiral perylene diimide [21].
The main fragmentation routes of the compounds 1, 2 and 5 are
shown in Fig. S1. The mass spectrum of the compound 1 showed the
corresponding molecular ion peak at 359 m/z, which was also the
base peak. The fragment of 250 m/z was produced by the breakage
of C6H4NO
(Fig. S1(a)). The base peak again coincided with the molecular ion
peak for compound 2 at 463.5 m/z (M þ 1) (Fig. S1(b)). The fragment
of 372.4 m/z was produced by the breakage of C7H7 (Fig. S1(b)). The
mass spectrum of 5 (Fig. S1(c)) showed the corresponding molecular
ion peak at 587.5 m/z (M þ 1). The base peak occurred at 302.3 m/z
was produced by the cleavage of C16H17N2O3.
p–p
p–p
larly, the characteristic band of the C–O–C stretching (1025 cmꢀ1
)
3.2. Absorption and fluorescence properties
had disappeared and was replaced by C–N stretching band
(1354 cmꢀ1). An additional band appeared at 2926 cmꢀ1 due to
aliphatic C–H stretching. Other absorption bands of 5 were very
similar to those of 4 (Fig. 4(b)).
The absorption and emission spectra of 1 in non-polar, polar
protic and aprotic solvents are shown in Fig. 5(a): absorption
spectra at 10ꢀ5 M concentration, (b): absorption spectra of filtered
Table 1 lists the solubility properties of 1, 2, 4 and 5. Solubility of
monoimides is lower than that of diimides which is depended on
intermolecular interactions that are affected by the rigidity and
symmetry. The presence of secondary carbon atoms next to nitrogen
solution through a 0.2
10ꢀ5 M concentration, (b): emission spectra of filtered solution
through a 0.2 m SPR microfilter. The absorbance is significantly
dependent on the solubility of the compound and the polarity of
mm SPR microfilter, (c): emission spectra at
m
Fig. 4. FT-IR spectra of (a) 1 and 2; (b) 4 and 5.

S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
5
Table 1
Solubility of 1, 2, 4 and 5.
of the HOMO-LUMO gap in the compound 1. Additionally, the lower
degree of symmetry of 1 may induce a higher number of vibronic
modes which results in a broader absorption band. The small
changes on absorption bands regarding to their initial shape upon
Solubilitya/Colour
1
2
4
5
filtration of the solutions through a 0.2 mm SPR microfilter (Fig. 5(b))
CHCl3
DCM
Pyridine
Acetone
EtOH
þ - Colorless
þ - Colorless
þ - Colorless
þ - Colorless
þ - Colorless
þ - Pale Yellow
þ - Colorless
þ - Colorless
þ Pale Yellow
þ Pale Yellow
þ - Colorless
þ Brown
þ Brown
þ Brown
þ Brown
þ Brown
þ Brown
þ Brown
þ Brown
þ Brown
þ Brown
-
-
-
-
-
þ - Orange
þ - Orange
þ Yellow
þ - Yellow
þ - Yellow
þ Red
indicate weak aggregated distributions in polar solvents except
CHCl3, DCM and CH3CN. The absorption and emission spectra of 2, 4
and 5 in the same non-polar, polar protic and aprotic solvents used
in the electronic spectra of 1 are shown in Fig. 6 (2; (a): absorption
spectra at 10ꢀ5 M concentration, (b): absorption spectra of filtered
-
NMP
þ Red
MeOH
CH3CN
DMF
DMSO
H2O
-
-
þ - Yellow
þ - Yellow
þ - Light Pink
þ - Red
solution through a 0.2
10ꢀ5 M concentration, (d): emission spectra of filtered solution
through a 0.2 m SPR microfilter) and S2 (4; (a): absorption spectra
at 10ꢀ5 M concentration, 4; (b): emission spectra at 10ꢀ5
mm SPR microfilter, (c): emission spectra at
þ Red
þ Red
-
m
-
M
concentration, 5; (c): absorption spectra at 10ꢀ5 M concentration, 5;
(d): emission spectra at 10ꢀ5 M concentration). In contrast to 1 the
compounds 2, 4 and 5 exhibit the characteristic three absorption
bands of the compound class in their absorption spectra (solvent:
DMSO; 2: 345, 360, 381 nm; 4 : 454, 482, 518 nm and 5 : 461, 492,
529 nm) indicating the absence of a strong charge-transfer inter-
action in the ground state. The values of the absorption wavelength
maxima for all solvents are nearly the same without charge transfer
complexation. Consequently, there is more intensive interaction
between 1 and solvent molecules so as to influence its shape of
absorption spectra which is not observed for 2, 4 and 5.
- insoluble at RT. DCM: dichloromethane; NMP: N-methylpyrrolidinone.
DMF: dimethylformamide; DMSO: dimethyl sulfoxide.
a
0.1 mg in 1.0 mL of solvent. þ soluble; þ - partially soluble.
solvent. Characteristically three absorption bands are observed in
solvents (non-polar and polar) where compound 1 dissolves rather
poorly such as CHCl3, DCM and CH3CN (in CHCl3: 334, 350 and
370 nm) which is in agreement with literature data for other
naphthalene diimides [4]. The broad long wavelength absorption
band of 1 in polar solvents EtOH, NMP, MeOH, DMF, DMSO and H2O
presents a solvent dependent charge transfer character corre-
sponding to a shift of the electron density from the electron rich
moiety (hydroxyl substituent) towards the imide carbonyls and it is
significantly red shifted compared to the bands in CHCl3, DCM and
CH3CN solvents (Fig. 6(a) and (b)). On the other hand, the lack of
a charge transfer band in the polar solvent acetonitrile is attributed
to the rather poor solubility of compound 1 in this solvent. The
Interestingly, all the emission spectra of 1 and 2 show charac-
teristically red shifted and broad excimer-like emissions (Figs. 5 and
6; lexc ¼ 360 nm) which have been thought as important indication
of weakly interacting p-stacks in solutions. The higher Stokes shift
(Figs. 5 and 6, Table 2; 1: 123 457 cmꢀ1, filtered solution through
a 0.2
m SPR microfilter (1*): 138 889 cmꢀ1, 2: 120 482 cmꢀ1 and
filtered solution through a 0.2
m SPR microfilter (2*): 121951 cmꢀ1
m
extension of the
p
conjugation system accounts for the narrowing
m
)
Fig. 5. (a) Absorption spectra of 1 in different solvents; (b) after filtration with 0.2
360 nm; (d) after filtration with 0.2 m microfilter.
mm microfilter; (c) emission spectra of 1 in different solvents at the excitation wavelength
m

6
S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
Fig. 6. (a) Absorption spectra of 2 in different solvents; (b) after filtration with 0.2
mm microfilter; (c) emission spectra of 2 in different solvents at the excitation wavelength
360 nm; (d) after filtration with 0.2 m microfilter. These spectra are offset in the ordinate for clarity.
m
value and broadest band for the spectrum taken in NMP showed the
presence of a relatively large amount of non-radiative energy lost.
filtration). All these unique properties indicate the similarity
between ground S0 and excited S1 states. As expected, dominance of
rigidity and planarity gave a small Stokes shift and greater
reabsorption.
The difference in Stoke shift between the solution taken at 10ꢀ5
M
concentration and filtered solution through a 0.2 mm SPR microfilter
was attributed to weak aggregation (Table 2). The emission spectra
of 1 and 2 were very similar to the excimer-like emissions usually
The emission spectra of compounds 1 and 2 were taken at
lexc ¼ 360 nm and the relative fluorescence quantum yields were
determined in DMF by using anthracene as a standard in EtOH. The
low fluorescence quantum yields of 1 and 2 are in good correlation
with literature data (1: 0.2% and 2: 0.8%) [4]. The emission spectra
of 4 and 5 was taken at lexc ¼ 485 nm and the relative fluorescence
observed for
p-stacked interacting molecules in solution. Besides
the well resolved absorption bands for 2, the excimer-like emission
of the compound has been thought as an important indication
of weaker interacting
the emission spectra and obtained peak maxima upon filtration of
the solutions through a 0.2 m SPR microfilter (Figs. 5 and 6(c) and
p-stacks in solution. Additionally, the shape of
´
quantum yields determined in DMF using N,N-didodecyl-3,4,9,10-
m
perylenebis(dicarboximide) in CHCl3 as standard. The lower fluo-
rescence quantum yield of 4 could be attributed to conformational
changes, torsional movement, or other non-radiative decays
(4: 60% and 5: 80%).
Fig. 7 shows the absorption spectra of 1, 2, 4 and 5 in the solid state
and Table 3 provides a summary of the experimental spectroscopic
(d)) indicates aggregated emission besides the excimer emission in
the excited state. The fluorescence spectra of 4 and 5 taken at
lexc ¼ 485 nm showed mirror images of their absorption spectra
with small Stokes shifts and the absence of excimer emission (Fig. S2,
Table 2; 4 and 5: 1 000 000–666 667 cmꢀ1 before and after
Table 2
Stokes shifts of 1, 2, 4 and 5.
Stokes Shift (cmꢀ1
1
)
1*
2
2*
4
4*
5
5*
CHCl3
DCM
EtOH
NMP
MeOH
CH3CN
DMF
DMSO
H2O
227273
285714
169492
123457
208333
270270
294118
285714
178571
222222
204082
144928
138889
277778
161290
217391
200000
232558
200000
84034
81301
120482
133333
91743
344828
120482
–
256410
172414
166667
121951
192308
120482
250000
156250
–
–
–
–
–
–
–
1000000
909091
714286
769231
666667
769231
769231
714286
–
1000000
909091
714286
769231
666667
769231
769231
714286
–
666667
–
–
666667
833333
–
666667
–
–
666667
833333
–
*after filtration with 0.2 mm microfilter.

S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
7
times of our equipment (100 ps). The fluorescence lifetime of 4 and
5 is observed experimentally as 3.9 and 4.2 ns, respectively
(
lexc ¼ 530 nm, Fig. 8). The singlet energies were calculated in kcal
molꢀ1 using equation Es ¼ 2.86 ꢃ 105/lmax, where lmax stands for
maximum absorption wavelength in angstroms [45]. The theoretical
radiative lifetimes s0 were calculated according to the formula:
s0 ¼ 3.5 ꢃ 108/(n2
ꢃ
3max
ꢃ
Dn1/2), where nmax stands for the
max
wavenumber in cmꢀ1
, 3max for the molar extinction coefficient at the
selected absorption wavelength and Dn1/2 indicates the half-width of
the selected absorption in units of cmꢀ1 [45]. Fluorescence lifetimes
were calculated from sf
¼
s0
ꢃ
Ff and the rates of fluorescence from
kf ¼ 1/ 0 (Table 3). The radiationless deactivation rate constants were
s
calculated from kd
¼
(kf/Ff)ꢀkf and oscillator strength from
3max [45]. The technique of time correlated
f ¼ 4.32 ꢃ 10ꢀ9
ꢃ
Dn1/2
ꢃ
single photon counting was used to record fluorescence lifetimes of
the compounds. The decay curves were multi-exponential and
analysed by using the standard method of iterative reconvolution and
non-linear least square fitting method (Fig. 8). The quality of calcu-
lated fits was judged using statistical parameters, the reduced c2
value and the residual data. Experimental radiative lifetimes, fluo-
rescence lifetimes, fluorescence rate constants, rate constant of
radiationless deactivation, and singlet energies data of all the
compounds in DMF were consistent with literature data [11].
Fig. 7. Solid state UV/vis absorption spectra of 1, 2, 4 and 5.
The specific optical rotation (½a D
ꢂ
20, alpha) of 2 anꢀd15 measured
data for them together with calculated values. An intermolecular
electron–donor–acceptor complex are formed for 1 in the solid state
which gives rise to an intermolecular charge transfer absorption at
354 nm as an unresolved band. The main difference between the uv
spectra in solid and solution states of 1 is the shoulder around 373 nm
in the solution spectra. Interestingly, the solid state uv spectra of 1,
and 2 are very similar to their spectra taken in solution which indi-
cate weakly interacting p-stacks in solid state and similar intermo-
lecular interactions in both states. It is worth noting that the solid
state spectra of 4 and 5 are different with respect to the absorption
at 20 ꢁC (Solvent: DMF; 2: c ¼ 0.0194 mg mL
in and 5:
c ¼ 0.052 mg mLꢀ1) as ꢀ221.6 and ꢀ24, respectively. Fig. 9 shows the
CD spectra of 2 in acetonitrile and ethanol, respectively. Compound 2
showed a prominent negative Cotton effect which corresponds to the
maximum absorption bands in the UV spectra recorded (acetonitrile:
362 and 382 nm, ethanol: 364 and 384 nm). No significant spectro-
scopic changes were observed in these two solvents. The CD signal
provides support for the helical conformation of the synthesized
compound. However no detectable Cotton effect was obtained for
compound 5, a feature which is probably due to the poor solubility
comparing to compound 2 in solution at room temperature.
maxima and band shapes which indicate different
solid state. A higher red shift of the 0ꢀ0 band was observed for 4
due to the stronger intermolecular -stacking interactions (for the
filtered solutions through a 0.2 m SPR microfilter; 4: 31 nm and 5:
p interaction in
p
m
25 nm in DMF). Solid state fluorescence of all the compounds could
not be obtained which is attributed to presence of aggregates and
excimers, which normally reduce quantum efficiencies of emission in
the solid state. Maximum absorption wavelengths (lmax in nm),
extinction coefficients (3max), oscillator strengths f, fluorescence
3.3. Thermal stability
The thermal behavior of 1, 2 and 5 was investigated by DSC and
TGA (TGA: heating rate 5 K minꢀ1, DSC: heating rate 10 K minꢀ1
,
Fig. 10 and S3). All compounds exhibit no glass transition tempera-
ture in the DSC run (1 and 2: 0ꢀ300 ꢁC and 5: 0ꢀ400 ꢁC). The curves
showed the high decomposition temperatures (Td) for the
compounds. Compounds 1, 2 and 5 were stable up to 323, 353 and
373 ꢁC, respectively. For compound 1, a rapid weight loss of 70% of the
initial weight was occurred between 323 and 415 ꢁC. When 1 was
heated to 900 ꢁC, 91% of the initial weight was lost, and about 9% char
yield observed. For compound 2, a rapid weight lost of 27% of the
initial weight occurred between 353 and 405 ꢁC When 2 was heated
to 650 ꢁC, 98% of the initial weight was lost rapidly and about 2% char
yield observed. Compound 2 showed higher thermal stability than
compound 1 that could be attributed to the intermolecular forces,
rigidity and symmetry of the structure. For compound 5, a rapid
quantum yields (Vf), radiative lifetimes
sf (ns), fluorescence rate constants kf, rate constant of radiationless
deactivation kd, optical activity and singlet energies Es (kcal molꢀ1
s0 (ns), fluorescence lifetimes
)
data of all the compounds in DMF, are given in Table 3. Notably, the
high solvent sensitivity of the emissions of compounds 1 and 2
indicates a polar character for the emitting species. The excimer-like
emissions and the low fluorescence quantum rate constant in
DMF supports the charge transfer complexes in solutions as well. The
fluorescence lifetime of 1 and 2 are calculated as 10 and 30 ps
respectively, which support the ultra fast intersystem crossing from
the singlet excited state. We were unable to measure fluorescence
lifetimes of the compounds which are shorter than the resolution
Table 3
Maximum absorption wavelengths lmax (nm), extinction coefficients 3max (l molꢀ1 cmꢀ1), oscillator strengths f, fluorescence quantum yields Ff
(
lexc. ¼ 360 nm for OH-NMI and
HC-NDI, lexc. ¼ 485 nm for HC-PDI), radiative lifetimes
s0 (ns), fluorescence lifetimes
s
f (ns), fluorescence rate constants kf (108 ꢀ1), rate constants of radiationless deactivation
s
kd (108
s
ꢀ1), optical activities ½a D
ꢂ
20, and singlet energies Es (kcal molꢀ1) data of 1, 2, 4 and 5 in DMF.
lmax
lmax (solid state)
3max
f
Ff
s0
5.34
3.63
13.4
10.6
sf
kf
kd
½
a 2D0
ꢂ
Es
1
373
381
518
526
354
387
488
551
11 732
18 318
71 000
70 000
0.4
0.6
0.3
0.4
0.002
0.008
0.60
0.01
0.03
8.04 (3.9)
8.48 (4.2)
1.9
2.8
0.7
0.9
948
341
–
76.7
75.1
55.2
54.4
2
ꢀ221.6
4a
5a
0.5
0.2
–
0.80
ꢀ24
a
Experimental values are given in parantheses.

8
S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
Fig. 9. CD spectra of 2 in acetonitrile and ethanol.
is the reduction of the neutral compound to radical anion (1ꢀ, 2ꢀ
and 5ꢀ) and the second reduction corresponds to the formation of
the dianion (12ꢀ, 22ꢀand 52ꢀ) as shown in Fig. 13. Similarly, for
Fig. 8. Fluorescence decay curves of (a) 10ꢀ5 M 4; (b) 10ꢀ5 M 5 (lexc. ¼ 530 nm and
lem ¼ 580 nm) in DMF.
compounds 1, 2 and 5 the values of the half-wave potential (E1/2
)
were found to be independent of the scan rate, as was expected for
a reversible system.
weight lost of 20% of the initial weight occurred between 373 and
423 ꢁC. When 5 was heated to 900 ꢁC, 44% of the initial weight was
lost, and about 56% char yield observed. Accordingly, 5 showed
highest thermal stability that could be attributed to the intermolec-
ular forces, rigidity and symmetry of the structure. Remarkably, the
compound 5 showed better thermal stability at elevated temperature
(symmetrical PDI: 2% char yield at 900 ꢁC) with higher char yield
compared with the symmetrical PDI bearing the same chiral
substituent.
3.4. Electrochemistry
The electrochemical characterization of all compounds were
studied in detail using cyclic (CV: 1, 2 and 5) and square-wave
(SWV: 5) voltammetries in different solvents containing 0.1 M
TBAPF6 as a supporting electrolyte and in solid state (Figs. 11 and
12) which summarized in Table 4, S1 and S2. Due to the poor
solubility of 4 in general organic solvents its electrochemical
characterization could not be determined. All the measured redox
potentials, HOMO (highest occupied molecular orbital)/LUMO
(lowest unoccupied molecular orbital) and band gap energy Eg
values obtained from those are tabulated in Table 4. All compounds
undergo two reversible one-electron reductions, the first of which
Fig. 10. Thermal gravimetric analysis (TGA) of compounds 1, 2, and 5.

S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
9
Fig. 11. Cyclic voltammograms of (a) 1 in dichloromethane; (b) 1 in acetonitrille, scan rates (mVsꢀ1): i (50), ii (100), iii (200), iv (300); (c) 2 in chloroform, scan rates (mVsꢀ1): i (50),
ii (100), iii (200); (d) 2 in DMSO, scan rate (mVsꢀ1): 50, supporting electrolyte: TBAPF6.
As shown in Figs.11 and 13, cyclic voltammogram of compound 1
has shown two fast reversible, one-electron reductions at ꢀ0.695
and ꢀ1.127 V (vs. Ag/AgNO3, scan rate: 100 mV sꢀ1) with peak
calculated to be approximately 3.21 and 3.15 eV for the compound 1
and 2, respectively where Eg was obtained from the edge of the
electronic absorption band with Eg (eV) ¼ hc/
l
(h ¼ 6.626 ꢃ 10ꢀ34 J s,
potential separations
DEp1 ¼ 67 mV and
DEp2 ¼ 60 mV, respectively
c ¼ 3 ꢃ 1010 cm sꢀ1, 1 eV ¼ 1.602 ꢃ 10ꢀ19 J). From this value, the
HOMO energies of 1 and 2 were estimated from the relationship
EHOMO ¼ ELUMOꢀEg, as ꢀ7.14 and ꢀ6.94 eV, respectively.
in CH2Cl2 (Fig. 11(a) and Table 4). The calculated
DEp in the range
60–70 mV for 1 shows that reversibility of electron transfer was
fairly well maintained in this system. The reduction couples for 1
were observed at E1/2 ¼ ꢀ0.790 and ꢀ1.205 V (vs. Ag/AgNO3, scan
rate: 100 mV sꢀ1) in more polar solvent CH3CN (Fig. 11(b) and Table
The electrochemical stability and reversibility of the redox
processes of 1 and 2 were examined using cyclic voltammetry
(Fig. 11 and Table S1) in different solvents (1: CH2Cl2 and CH3CN, 2:
CHCl3). Electrochemical stability of the compounds was examined
by measuring repeated cycles of redox processes. Compound 1
showed completely reversible reduction steps for the entire scan-
ning rate in a region of 50–300 mV sꢀ1. As shown in Table S1, the
S1,
D
Ep1 ¼ 68 mV and Ep2 ¼ 68 mV). Compound 2 displays two fast
D
reversible one-electron reductions at ꢀ0.776 and ꢀ1.176 V (vs. Ag/
AgNO3, scan rate: 100 mV sꢀ1) with peak potential separations
D
Ep1 ¼97 mV and
Table 4). These values were observed at ꢀ0.777 and ꢀ1.175 V at scan
rate of 50 mV sꢀ1 with peak potential separations
Ep1 ¼ 86 mV and
D
Ep2 ¼ 99 mV, respectively in CHCl3 (Fig.11(c) and
DEp was about 59–78 mV for each cycle of 1 in CH2Cl2. Similar
D
results were attained with the solvent CH3CN. Compound 2 showed
D
Ep2 ¼ 87 mV. The reduction couples for 2 were observed at E1/
completely reversible reduction steps for the entire scanning rate in
¼ ꢀ0.876 and ꢀ1.331 V (vs. Ag/AgNO3, scan rate: 50 mV sꢀ1) in the
a region of 50–200 mV sꢀ1. At the large
DEp values (114 mV at
2
more polar solvent DMSO (Fig. 11(d) and Table S1,
DEp1 ¼75 mV and
200 mV sꢀ1), which indicate the limitation due to charge transfer
kinetics, the reversibility of the compound 2 was poor. According to
standard reversibility criteria, each reduction process indicates
reversible, diffusion-controlled one-electron transfer. A plot of peak
current against square root of scan rate was found to be linear as
shown in Fig. S4 for compounds 1 and 2 (1: in CH2Cl2 R2 ¼ 0.99 and
CH3CN R2 ¼ 0.98, 2: in CHCl3 R2 ¼ 1.00), which fulfills the conditions
for diffusion-controlled processes.
D
Ep2 ¼ 75 mV). Notably, E1/2 shifts towards high negative potentials
in more polar solvents indicating a more difficult reduction probably
due to the stable complex formation (1: CH2Cl2 and CH3CN, 2: CHCl3
and DMSO, Table S1).
In order to calculate the absolute energies of LUMO level of 1 and
2 with respect to the vacuum level, the redox data are standardized
to the ferrocene/ferricenium couple which has a calculated absolute
energy of ꢀ4.8 eV [46,47]. The LUMO energies of the 1 and 2 were
calculated from cyclic voltammograms (Fig.11 and Table 4) as ꢀ3.93
and ꢀ3.79 eV, respectively. The optical band gap, Eg values, were
The diffusion coefficients D were measured by cyclic voltammetry
according to Randles-Sevcik equation [48]: ip ¼ (2.69 ꢃ 105) ꢃ n3/
ꢃ v1/2 ꢃ D1/2 ꢃ A ꢃ C, where ip is peak current (A), n is the number of
2

10
S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
Fig. 12. (a) Cyclic voltammograms of 5 in chloroform; supporting electrolyte: TBAPF6, scan rates (mVs-1): i (50), ii (100), iii (300), iv (600), v (800), vi (1000); (b) square-wave voltam-
mograms of 5 in chloroform; supporting electrolyte: TBAPF6,
(Hz): i (60), ii (100), iii (150); (c) solid state cyclic voltammograms of 5; supporting electrolye: HCl, scan rates (mVsꢀ1): i (25), ii
(50), iii (100), iv (200), v (400), vi (600); (d) solid state square-wave voltammograms of 5; supporting electrolyte: HCl,
(Hz): i (50), ii (100), iii (200), iv (300) at 25 ꢁC.
n
n
transferred electrons, v is the scan rate (V sꢀ1), D is the diffusion
coefficient (cm2 ꢀ1), A is the electrode area (cm2), C is the concen-
in their cyclic and square-wave voltammetries. Cyclic voltammo-
gram of compound 5 has shown two fast reversible, one-electron
reductions at ꢀ0.827 and ꢀ1.018 V (vs. Ag/AgNO3, scan rate:
s
tration of the electroactive species (mol cmꢀ3). The diffusion coeffi-
cients (D) of 1 and 2 in solution were estimated from the slope of the
plot ipc versus v1/2 (Fig. S4). Accordingly, the diffusion coefficients were
determined as 8.73 ꢃ 10ꢀ8 and 2.55 ꢃ10ꢀ7 cm2 sꢀ1 for 1 in CH2Cl2 and
CH3CN, respectively, and 2.63 ꢃ 10ꢀ6 cm2 sꢀ1 for 2 in CHCl3.
100 mV sꢀ1) with peak potential separations
DEp1 ¼ 76 mV and
D
Ep2 ¼ 72 mV, respectively in CHCl3 (Fig. 12(a), Table 4). For
compound 5, the calculated DEp in the range of 60–70 mV shows that
reversibility of electron transfer was fairly well maintained in this
system. The square-wave voltammograms of 5 (Fig. 12(b)) showed
reversible reduction potentials at ꢀ0.830 and ꢀ1.026 V (vs. Ag/
AgNO3, frequency: 60 Hz). Similar results were found via cyclic and
square-wave voltammetric studies. These properties are in agree-
ment with the literature data [11].
The electrochemical property of 5 was investigated using cyclic
(CV) and square-wave (SWV) voltammetries in chloroform con-
taining 0.1 M TBAPF6 as a supporting electrolyte and in solid state
containing HCI as a supporting electrolyte (Fig. 12, Table 4, S1 and
S2). All the measured redox potentials, HOMO/LUMO and band gap
energy Eg values obtained from those are tabulated in Table 4. As
shown in Figs. 12 and 13, compound 5 displays reduction processes
In order to investigate the solid state electrochemical properties
of compound 5 the voltammetry of immobilized microparticles was
Table 4
Cyclica voltammetry data and optical band gap energy Eg, HOMO, LUMO values of compounds 1, 2 and 5.
Epc/V
Epa/V
DEp/mV
E1/2/V vs. Ag/AgNO3
EFc/V vs. Ag/AgNO3
E1/2/V vs. Fc
Eg/eV
HOMO/eV
LUMO/eV
1b (DCM)
b (CHCl3)
5b (CHCl3)
ꢀ0.729
ꢀ1.157
ꢀ0.825
ꢀ1.226
ꢀ0.865
ꢀ1.054
ꢀ0.244
ꢀ0.662
ꢀ1.097
ꢀ0.728
ꢀ1.127
ꢀ0.789
ꢀ0.982
ꢀ0.378
67
60
97
99
76
ꢀ0.695
ꢀ1.127
ꢀ0.776
ꢀ1.176
ꢀ0.827
ꢀ1.018
ꢀ0.311d
0.172
0.172
0.234
0.234
0.196
0.196
0.360d
ꢀ0.867
ꢀ1.299
ꢀ1.010
ꢀ1.411
ꢀ1.023
ꢀ1.214
ꢀ0.671
3.21
ꢀ7.14
ꢀ3.93
2
3.15
2.28
1.92
ꢀ6.94
ꢀ6.06
ꢀ6.05
ꢀ3.79
ꢀ3.78
ꢀ4.13
72
134
5
c (solid state)
a
Scan rate of 100 mV sꢀ1
Supporting electrolyte: 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6).
Supporting electrolyte: 1 M HCl.
vs. Ag/AgCl.
.
b
c
d

S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
11
band gap energies and the HOMO/LUMO values obtained from
those are tabulated in Table 4. The cyclic voltammograms of
compound 5 showed one reversible reduction waves (Fig. 12(c)),
implying the formation of anions (5ꢀ) at ꢀ0.311 V (vs. Ag/AgNO3,
scan rate: 100 mV sꢀ1
) with a peak potential separation
DEp1 ¼ 134 mV (Table 4). Similarly, the square-wave voltammo-
grams of 5 (Fig. 12(d)) showed reversible reduction potential at
ꢀ0.325 V (vs. Ag/AgNO3, frequency: 50 Hz). Cyclic and square-wave
voltammetric results were in good agreement. The reduction
potential value is more positive than that observed for free 5 in
solution indicating the easier reduction with higher reduction rate
(Table 4). The compound 5 has shown lower solid state reduction
potentials compared to the reductions of CN-substituted naphtha-
lene and perylene derivatives [4]. On the other hand, the symmet-
rically substituted chiral perylene diimide bearing the same chiral
substituent with compound 5 has the same solid state reduction
potentials with it [21]. All solid state reduction potentials were
measured with similar way. This interesting difference in results
could be attributed to the intermolecular forces, rigidity and
symmetry of the structure.
The electrochemical stability and reversibility of the redox
processes of 5 was examined using cyclic voltammetry and
square-wave voltammetries in CHCl3 and solid state (Fig. 12(a–d),
Tables S1 and S2). Electrochemical stability in CHCl3 was exam-
ined by measuring repeated cycles of redox processes. 5 showed
completely reversible reduction steps for the entire scanning
rate in a region of 50–1000 mV sꢀ1. As shown in Table S1, the
calculated peak current ratio, ipa (anodic current)/ipc (cathodic
current) was equal to unity and the
for each cycle in CHCl3. Notably, higher
1000 mV
ꢀ1scanning rate shows more difficult reduction.
D
Ep was about 70–103 mV
D
Ep value (103 mV) at
s
According to standard reversibility criteria, each reduction
process indicates reversible, diffusion-controlled one-electron
transfer. Similarly, the solid state electrochemical stability and
reversibility of the redox processes of 5 was examined using
cyclic and square-wave voltammetries (Fig. 12(c) and (d), Table
S2). Electrochemical stability of 5 was examined by measuring
repeated cycles of redox processes. Compound
5 showed
completely reversible reduction steps for the entire scanning rate
in a region of 25–600 mV sꢀ1 and 50–300 Hz. All voltammograms
have shown only a slight shift of peak (SWV) or formal potentials
(CV) of all compounds by 10 mV which indicate the electro-
chemical reversibility of the investigated system. As shown in
Table S2, the calculated peak current ratio, ipa/ipc was equal to
Fig. 13. Proposed two-step reduction mechanism for (a) 1; (b) 2; and (c) 5.
applied. This technique is a simple and powerful tool for charac-
terizing the thermodynamics and elucidating the redox mecha-
nisms of electroactive compounds which are poorly soluble in
water [49–56]. The basic principle of the voltammetry of immobi-
lized microparticles comprises mechanical attachment of the
substance on the surface of the working electrode (paraffin
impregnated graphite electrode, i.e., PIGE), and immersing the
modified electrode in an aqueous electrolyte solution. If the
substance is electroactive, and if its product is also insoluble in
water, for reasons of charge neutrality, ions must be exchanged
with the solution. In case of a reduction, either anions, if available,
must leave the solid, or cations must be transferred from the
solution into the solid phase. The processes of coupled electron and
ion transfer occur simultaneously and give rise to a single vol-
tammetric response. A comprehensive database of the voltamme-
try on immobilized microparticles can be found elsewhere [56]. All
the voltammetric measurements were repeated several times and
the values of the reduction potentials were found to be reproduc-
ible within ꢄ3 mV.
unity and the
DEp was about 134–164 mV for each cycle.
A plot of peak current against square root of scan rate was found
to be linear as shown in Fig. S4 for compound 5 (in CHCl3 R2 ¼ 0.99,
in solid state R2 ¼ 0.96), which fulfills the conditions for diffusion-
controlled processes. Additionally, at the large
DEp values which
indicate the limitation due to charge transfer kinetics the revers-
ibility of the compound showed poor reversibility.
The LUMO energies of 5 in CHCl3 and solid state were calculated
from cyclic voltammograms (Fig. 12(c) and (d), Table 4) as ꢀ3.78
and ꢀ4.13 eV, respectively. The optical band gap, Eg values, were
calculated approximately 2.28 and 1.92 eV for the compounds,
respectively where Eg was obtained from the edge of the solid state
electronic absorption band. From these values, the HOMO energies
of 5 were estimated as ꢀ6.06 and ꢀ6.05 eV, respectively. Remark-
ably smaller LUMO and Eg value were obtained at the solid state
characterization of 5 as compared to those obtained from its
solution state (Fig. 14). The diffusion coefficients D of 5 in CHCl3 and
solid state were measured by cyclic voltammetry according to
Randles–Sevcik equation [48]. Accordingly, the diffusion coeffi-
cients were determined as 1.21 ꢃ10ꢀ5 and 1.62 ꢃ 10ꢀ6 cm2 sꢀ1 for 5
in CHCl3 and solid state, respectively.
The solid state electrochemical property of 5 was determined
with cyclic (CV) and square-wave voltammetries (CV and SWV:
Fig. 12(c), (d) and Table 4, S2). All the measured redox potentials,

12
S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
Appendix. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.dyepig.2009.04.014
References
[1] Todd EK, Wang S, Wan X, Wang ZY. Chiral imides as potential chiroptical
switches: synthesis and optical properties. Tetrahedron Letters 2005;46:587–90.
[2] Zhou Y, Zhang D, Zhang Y, Tang Y, Zhu DJ. Tuning the CD spectrum and optical
rotation value of a new binaphthalene molecule with two spiropyran units:
mimicking the function of a molecular ‘‘AND’’ logic gate and a new chiral
molecular switch. Journal of Organic Chemistry 2005;70:6164–70.
[3] Zhang J, Albelda MT, Liu Y, Canary JW. Chiral nanotechnology. Chirality
2005;17:404–20.
[4] Uzun D, Ozser ME, Yuney K, Icil H, Demuth MJ. Synthesis and photophysical
properties of N, N0-bis(4-cyanophenyl)-3,4,9,10-perylenebis(dicarboximide)
and N, N0-bis(4-cyanophenyl)-1,4,5,8-naphthalenediimide. Journal of Photo-
chemistry and Photobiology A – Chemistry 2003;156:45–54.
Fig. 14. Schematic energy diagram of 1, 2 and 5.
4. Conclusions
In conclusion, one new naphthalene monoimide (1) and two
unsymmetrically substituted chiral diimides (2 and 5) having large
-conjugated systems have been successfully synthesized. At the
p
same time, the perylene monoimide with the same substituent in
naphthalene monoimide (4) has been synthesized according to
the methods given in our previous works. Their structures have
been well characterized and the photophysical, thermal, electro-
chemical, chiroptical and intramolecular charge transfer properties
have been investigated. Imides 1, 2 and 5 showed high thermal
stability. Compound 1 exhibits an intramolecular charge transfer
complexation in its absorption spectrum in polar solvent corre-
sponding to a shift of the electron density from the electron rich
moiety (hydroxyl substituent) towards the imide carbonyls. Addi-
tionally, the lower degree of symmetry of 1 may induce a higher
number of vibronic modes which results in a broader absorption
bands. The difference in complex formation between polar and
non-polar solvents was attributed to the higher concentration of
free reactive compound 1. Excimer-like emissions were obtained in
non-polar, polar protic and aprotic solvents for 1 and 2. Interest-
ingly, all the emission spectra of 1 and 2 show characteristically red
shifted and broad excimer-like emissions. The large Stokes shifts
and broadest band for the spectrum taken in NMP showed the
presence of a relatively large amount of non-radiative energy lost.
Moreover, it indicates that the configurations and interaction with
the solvent of the excited and ground states are not similar. The
fluorescence spectra of 4 and 5 showed mirror images of their
absorption spectra with close and small Stokes shifts and absence
of excimer emission in the same solvents used in the electronic
spectra of 1 and 2 which proved the similarity between ground S0
and excited S1 states and high fluorescence quantum yield values.
Solid state fluorescence of chiral compound 5 could not be obtained
which is attributed to presence of excimers, which normally reduce
quantum efficiencies of emission in the solid state. The electro-
chemical characteristics of compounds were investigated from
dilute solution to solid state. In solution, compounds 1, 2 and 5
showed two one-electron reductions. However in the solid state,
chiral compound 5 has shown only one one-electron reduction
which is consistent with the high molecular symmetry. Chiral 2
showed prominent negative Cotton effect centred at 362 and
382 nm however, 5 did not possibly due to the poor solubility
comparing to the compound 2 at room temperature.
[5] Dou Z, Li X, Zhong S, Zhao C, Na H. The synthesis and characterization of
a
novel ternary polymer bisphenol A-4,40-difluorobenzophenone-bis(p-
hydroxyphenyl)-1,4,5,8-naphthalenetetracarboxylic diimide monomer. Poly-
mer Bulletin 2006;57:351–8.
[6] Figueiredo KM, Marcon RO, Campos IB, Nantes IL, Brochsztain S. Photoinduced
electron transfer between cytochrome c and a novel 1,4,5,8-naphthalenete-
tracarboxylic diimide with amphiphilic character. Journal of Photochemistry
and Photobiology B – Biology 2005;79:1–9.
[7] Nagao Y. Synthesis and properties of perylene pigments. Progress in Organic
Coatings 1997;31:43–9.
[8] Shchepinov MS, Korshun VA, Egeland RD, Southern EM. Tritylisation of pyr-
ene, perylene and coronene: a new family of switchable fluorescent labels.
Tetrahedron Letters 2000;41:4943–8.
[9] Langhals H, Ismael R, Yu¨ru¨ k O. Persistent fluorescence of perylene dyes by
steric inhibition of aggregation. Tetrahedron 2000;56:5435–41.
[10] Tomizaki K, Loewe RS, Kirmaier C, Schwartz JK, Retsek JL, Bocian DF, et al. Of
light-harvesting arrays comprised of a porphyrin bearing multiple perylene-
monoimide accessory pigments. Journal of Organic Chemistry 2002;67:6519–34.
[11] Pasaogullari N, Icil H, Demuth M. Symmetrical and unsymmetrical perylene
diimides: their synthesis, photophysical and electrochemical properties. Dyes
and Pigments 2006;69:118–27.
[12] Baffreau J, Leroy-Lhez S, Anh NV, Williams RM, Hudhomme P. Fullerene c60-
perylene-3,4:9,10-bis(dicarboximide) light-harvesting dyads: spacer-length
and bay-substituent effects on intramolecular singlet and triplet energy
transfer. Chemistry A European Journal 2008;14:4974–92.
[13] Hippius C, vanStokkum IHM, Gsa¨nger M, Groeneveld MM, Williams RM,
Wu¨rthner F. Sequential FRET processes in calix[4]arene-linked orange-red-
green perylene bisimide dye zigzag arrays. Journal of Physical Chemistry C
2008;112:2476–86.
[14] Veldman D, Chopin SMA, Meskers SCJ, Groeneveld MM, Williams RM,
Janssen RAJ. Triplet formation involving a polar transition state in a well-
defined intramolecular perylenediimide dimeric aggregate. Journal of Physical
Chemistry A 2008;112:5846–57.
[15] Gawron´ ski J, Brzostowska M, Kacprzak K, Ko1bon H, Skowronek P. Chirality of
aromatic bis-imides from their circular dichroism spectra. Chirality 2000;
12:263–8.
[16] Sterzel M, Pilch M, Pawlikowski MT, Gawron´ ski J. The circular dichroism (CD)
and absorption studies of 1,4,5,8-naphthalene tetracarboxydiimide dimer in
terms of vibronic coupling theory. Chemical Physics 2003;291:251–60.
[17] Langhals H, Gold J. Chiral bifluorophoric perylene dyes with unusually high CD
effects –- a simple model for the photosynthesis reaction center. Liebigs
Annalen 1997;1997:1151–3.
[18] Langhals H, Krotz O. Chiral, bichromophoric silicones: ordering principles of
structural units in complex molecules. Angewandte Chemie International
Edition 2006;45:4444–7.
[19] Sun R, Xue C, Owak M, Peetz RM, Jin S. Facile synthesis of chiral unsymmetric
perylene tetracarboxylic diimides involving
Letters 2007;48:6696–9.
a-amino acids. Tetrahedron
[20] Zheng J, Qiao W, Wan X, Ping Gao J, Wang ZY. Near-infrared electrochromic
and chiroptical switching materials: design, synthesis, and characterization of
chiral organogels containing stacked naphthalene diimide chromophores.
Chemistry of Materials 2008;20:6163–8.
In summary, the results could lead to further development of
sterically and stereochemically controlled conductive unsymmet-
rical diimides which could guide the design of important photo-,
electro-, and optoelectronic devices.
_
[21] Amiralaei S, Uzun D, Icil H. Chiral substituent containing perylene mono-
anhydride monoimide and its highly soluble symmetrical diimide: synthesis,
photophysics and electrochemistry from dilute solution to solid state.
Photochemical and Photobiological Sciences 2008;7:936–47.
[22] Osswald P, Reichert M, Bringmann G, Wu¨rthner F. Perylene bisimide atro-
pisomers: synthesis, resolution, and stereochemical assignment. Journal of
Organic Chemistry 2007;72:3403–11.
Acknowledgments
[23] Xue C, Chen M, Jin S. Synthesis and characterization of the first soluble non-
racemic chiral main-chain perylene tetracarboxylic diimide polymers. Poly-
mer 2008;49:5314–21.
The financial support from the Scientific and Technical Research
Council of Turkey (TUBITAK) is gratefully acknowledged.

S. Asir et al. / Dyes and Pigments 84 (2010) 1–13
13
[24] Dehm V, Chen Z, Baumeister U, Prins P, Siebbeles LDA, Wu¨rthner F. Helical
growth of semiconducting columnar dye assemblies based on chiral perylene
bisimides. Organic Letters 2007;9:1085–8.
[25] Tro¨ster H. Untersuchungen zur Protonierung von Perylen-3,4,9,10-tetra-
carbonsa¨urealkalisalzen. Dyes and Pigments 1983;4:171–7.
[26] Hopkins HP, Stevenson KA, Wilson WD. Enthalpy and entropy changes for the
intercalation of small molecules to DNA.I. Substituted naphthalene mono-
imides and naphthalene diimides. Journal of Solution Chemistry 1986;
15:563–79.
a chiral photochromic system using retro [4 þ 4] cycloaddition. Journal of
Organic Chemistry 2006;71:8037–44.
[41] Franke D, Vos M, Antonietti M, Sommerdijk NAJM, Faul CFJ. Induced
supramolecular chirality in nanostructured materials: ionic self-assembly
of perylene-chiral surfactant complexes. Chemistry of Materials 2006;18:
1839–47.
[42] Lukas AS, Miller SE, Wasielewski MR. Femtosecond optical switching of
electron transport direction in branched donorꢀacceptor arrays. Journal of
Physical Chemistry B 2000;104:931–40.
[27] Lokey RS, Kwok Y, Guelev V, Pursell CJ, Hurley LH, Iverson BL. A new class of
polyintercalating molecules. Journal of the American Chemical Society
1997;119:7202–10.
[43] Andric G, Boas JF, Bond AM, Fallon GD, Ghiggino KP, Hogan CF, et al. Spec-
troscopy of naphthalene diimides and their anion radicals. Australian Journal
of Chemistry 2004;57:1011–9.
[28] Gianolio DA, Segismundo JM, McLaughlin LW. Tethered naphthalene diimide-
based intercalators for DNA triplex stabilization. Nucleic Acids Research
2000;28:2128–34.
[44] Wilson JN, Gao J, Kool ET. Oligodeoxyfluorosides: strong sequence dependence
of fluorescence emission. Tetrahedron 2007;63:3427–33.
[45] Turro NJ. Molecular photochemistry. New York, W.A.: Benjamin, Inc; 1965. 4–48.
[46] Peng Z, Bao Z, Galvin ME. Polymers with bipolar carrier transport abilities for
light emitting diodes. Chemistry of Materials 1998;10:2086–90.
[47] Bredas JL, Silbey R, Boudreaux DS, Chance RR. Chain-length dependence of
electronic and electrochemical properties of conjugated systems: polyacetylene,
polyphenylene, polythiophene, and polypyrrole. Journal of the American
Chemical Society 1983;105:6555–9.
[29] Asseline U, Cheng E. Synthesis and binding properties of perylene-oligo-20-
deoxyribonucleotide conjugates. Tetrahedron Letters 2001;42:9005–10.
[30] Rahe N, Rinn C, Carell T. Development of donor-acceptor modified DNA
hairpins for the investigation of charge hopping kinetics in DNA. Chemical
Communications 2003;17:2120–1.
[31] Lewis FD, Zhang L, Kelley RF, McCamant D, Wasielewski MR.
A per-
ylenedicarboxamide linker for DNA hairpins. Tetrahedron 2007;63:3457–64.
[32] Haga M, Ohta M, Machida H, Chikira M, Tonegawa N. Point-to-point capture of
DNA with the aid of intercalation by immobilized rod-shaped Ru complexes at
solid surface towards nanowiring. Thin Solid Films 2006;499:201–6.
[48] Bard AJ, Faulkner LR. Electrochemical methods, fundamentals and applica-
tions. New York: Wiley & Sons Inc; 1980.
[49] Kahlert H, Retter U, Lohse H, Siegler K, Scholz F. On the determination of the
diffusion coefficients of electrons and of potassium ions in copper(II) hex-
[33] Zandonella G, Haalck L, Spener F, Faber K, Paltauf F, Hermetter A. Enantiomeric
perylene-glycerolipids as fluorogenic substrates for a dual wavelength assay of
lipase activity and stereoselectivity. Chirality 1996;8:481–9.
acyanoferrate(II) composite electrodes. Journal of Physical Chemistry
1998;102:8757–65.
[50] Lovric M, Scholz F. A model for the coupled transport of ions and electrons in
redox conductive microcrystals. Journal of Solid State Electrochemistry 1999;
3:172–5.
B
[34] Horne WS, Ashkenasy N, Ghadiri MR. Modulating charge transfer through
cyclic D, L a-peptide self-assembly. Chemistry 2005;11:1137–44.
[35] Ashkenasy N, Horne WS, Ghadiri MR. Design of self-assembling peptide
nanotubes with delocalized electronic states. Small 2006;2:99–102.
[36] Thalacker C, Wu¨rthner F. Chiral perylene bisimide-melamine assemblies:
hydrogen bond-directed growth of helically stacked dyes with chiroptical
properties. Advanced Functional Materials 2002;12:209–18.
[37] Schenning APHJ, Herrikhuyzen Jv, Jonkheijm P, Chen Z, Wu¨rthner F,
Meijer EW. Photoinduced electron transfer in hydrogen-bonded oligo(p-phe-
nylene vinylene)ꢀperylene bisimide chiral assemblies. Journal of the Amer-
ican Chemical Society 2002;124:10252–3.
[38] Herrikhuyzen Jv, Syamakumari A, Schenning APHJ, Meijer EW. Synthesis of
n-type perylene bisimide derivatives and their orthogonal self-assembly with
p-type oligo(p-phenylene vinylene)s. Journal of the American Chemical
Society 2004;126:10021–7.
[39] Wu¨rthner F, Chen Z, Hoeben FJM, Osswald P, You CC, Jonkheijm P, et al. Schoot
PPAMvd, Meijer EW, Beckers EHA, Meskers SCJ, Janssen RAJ. Supramolecular pꢀn-
heterojunctions by co-self-organization of oligo(p-phenylene vinylene) and per-
ylene bisimide dyes. Journal of the American Chemical Society 2004;126:10611–8.
[40] Masu H, Mizutani I, Kato T, Azumaya I, Yamaguchi K, Kishikawa K, et al. Fol-
damers with iminodicarbonyl linkers: their stabilities and application to
[51] Lovric M, Hermes M, Scholz F. Solid state electrochemical reactions in systems
with miscibility gaps. Journal of Solid State Electrochemistry 2000;4:394–401.
[52] Schro¨der U, Scholz F. The solid-state electrochemistry of metal octacyano-
molybdates, octacyanotungstates, and hexacyanoferrates explained on the
basis of dissolution and reprecipitation reactions, lattice structures, and
crystallinities. Inorganic Chemistry 2000;39:1006–15.
[53] Hermes M, Lovric M, Hartl M, Retter U, Scholz F. On the electrochemically
driven formation of bilayered systems of solid Prussian-blue-type metal hex-
acyanoferrates: a model for Prussian blue/cadmium hexacyanoferrate sup-
ported by finite difference simulations. Journal of Electroanalytical Chemistry
2001;501:193–204.
[54] Widmann A, Kahlert H, Petrovic-Prelevic I, Wulff H, Yakhmi JV, Bagkar N, et al.
Structure, insertion electrochemistry and magnetic properties of a new type of
substitutional solid solutions of copper, nickel and iron hexacyanoferrates/
hexacyanocobaltates. Inorganic Chemistry 2002;41:5706–15.
[55] Grygar T, Marken F, Schro¨der U, Scholz F. Electrochemical analysis of solids.
Collection of Czechoslovak Chemical Communications 2002;67:163–208.
[56] Entire database of bibliography on the voltammetry of immobilized micro-
particles is available on: http://www.chemie.uni-greifswald.de/wanalytik/