Regioisomers of perylenediimide: Synthesis, photophysical, and electrochemical properties

Article abstract of DOI:10.1021/jp210736x

A series of conjugation extended donor-acceptor 1,6- and 1,7-regiomers of perylenediimide were synthesized, separated, and characterized. The photophysical, electrochemical, and thermal properties of these compounds were investigated and compared. The absorption spectra of 1,6-substituted PDI showed blue shift as compared to its 1,7-substituted PDI. At the same time, the emission spectrum showed no significant differences among the regiomers. Both 1,6- and 1,7-regiomers were thermally stable up to 450 ?°C and showed different melting and crystallization transitions. The electrochemical studies did not show significant differences in oxidation and redox potentials owing to similar HOMO/LUMO gap of 1,6- and 1,7-regiomers, which is also supported by theoretical calculations. Comparison of properties of a series of 1,6- or 1,7-substituted PDIs showed significant differences. Such regiomerically pure compounds can offer certain advantages in applications, which are currently being investigated. ? 2012 American Chemical Society.

Full text of DOI:10.1021/jp210736x

Article
pubs.acs.org/JPCB
Regioisomers of Perylenediimide: Synthesis, Photophysical, and
Electrochemical Properties
Ashok Keerthi and Suresh Valiyaveettil*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore, and
NanoCore-NUSNNI, T-Lab Building, National University of Singapore, 5A Engineering Drive 1, Singapore 117411, Singapore
S
* Supporting Information
ABSTRACT: A series of conjugation extended donor−acceptor 1,6-
and 1,7-regiomers of perylenediimide were synthesized, separated, and
characterized. The photophysical, electrochemical, and thermal proper-
ties of these compounds were investigated and compared. The absorp-
tion spectra of 1,6-substituted PDI showed blue shift as compared to its
1,7-substituted PDI. At the same time, the emission spectrum showed
no significant differences among the regiomers. Both 1,6- and 1,7-
regiomers were thermally stable up to 450 °C and showed different melting
and crystallization transitions. The electrochemical studies did not show
significant differences in oxidation and redox potentials owing to similar
HOMO/LUMO gap of 1,6- and 1,7-regiomers, which is also supported
by theoretical calculations. Comparison of properties of a series of 1,6- or
1,7-substituted PDIs showed significant differences. Such regiomerically
pure compounds can offer certain advantages in applications, which are currently being investigated.
perylene core.44−47 Many research groups are working to
develop advanced materials with extended conjugation via bay
INTRODUCTION
Perylenediimides (PDIs) are known for their interesting optical
■
substitution of perylene oligomers and polymers for various
and electrical properties and belong to a class of n-type semi-
applications.2,8,48 However, dibromo PDI is the starting
conductors due to excellent electron acceptor ability with high
material for the synthesis of all these derivatives. Bromination
molar extinction coefficient, electron mobility, and thermal
stability.1−4 The bay substitution of PDI is an interesting
of perylenetetracarboxylic acid dianhydride (PDA) gave
approach to fine-tune properties5−7 and make them processable
dibrominated PDA, which was subsequently converted to
dibromo PDI.49 The latter was confirmed as a mixture of both
with common organic solvents. Tremendous scientific interests
1,6- and 1,7-dibromo PDI in 2004.50 However, there is no
have been focused on the modification of PDI structures to
report on separation of 1,6-dibromo PDI in pure form, although
enhance their optoelectronic and charge transport properties by
incorporating substituents.7−10 PDI and its derivatives have
been extensively utilized for a wide range of applications such as
organic and polymeric light emitting devices (OLEDs and
PLEDs),11−17 laser dyes,18,19 organic solar cells,20−23 optical
switches,24 organic field effect transistors (OFETs),25,26 logic
gates,27 photosensitizers,28 sensors,29,30 biological applica-
tions,31,32 light-harvesting arrays, and artificial photosynthetic
systems.33−38 Apart from their diverse and interesting proper-
ties, the relatively facile and reversible reduction of PDIs plays a
key role in many applications. These facile reductions, com-
bined with easily identifiable excited states have led to their
extensive use in fundamental research on photoinduced energy
and electron transfer processes.4,39,40
Currently, there is significant interest in the development of
PDI derivatives with extended conjugation, which are used in
field effect transistors and photovoltaic applications.41,42 Substi-
tution and functionalization at the bay region (1-, 6-, 7-, and 12-
positions) help to fine-tune the properties of PDIs (Figure 1).10,43
More recently, functionalization at the ortho region (2-, 5-,
8-, and 11-positions) of PDI modifies the properties of the
Wurthner’s method of recrystallization can remove the 1,6-
̈
regiomer to get 1,7-dibromo PDI. Thereafter, separation of pipe-
ridinyl and pyrrolidinyl substituted 1,6- and 1,7-regiomers of PDI
were reported, which showed different optical and electrochemical
properties, but phenoxy substituted 1,6- and 1,7-regiomers of PDI
showed no significant differences in their properties.51,52 Still there
was an ambiguity on properties of π-extented 1,6- and 1,7-PDI
systems, and more recenly, one report has published with alkyne
substitution at the bay positions, while our article was under
preparation.53 Here, we report a simple method to isolate 1,6- and
1,7-regiomers of π-extended PDI derivatives (Figure 2) and com-
pare the properties.
RESULTS AND DISCUSSION
Synthesis and Characterization. Synthesis of brominated
perylenetetracarboxylic acid dianhydride was achieved via
■
Received: November 8, 2011
Revised: March 13, 2012
Published: March 22, 2012
© 2012 American Chemical Society
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Figure 1. Labeling of position and region in perylene and its derivatives.
iodine-catalyzed bromination of 3,4,9,10-perylenetetracarbox-
ylicacid dianhydride in 98% concentrated sulfuric acid.49,50 The
crude brominated PDA (Scheme 1) was insoluble in common
solvents and subjected to further functionalization without puri-
fication. Imidization of the brominated PDA with 2-ethylhexyl-
amine was carried out in N-methyl pyrrolidone (NMP) in the
presence of acetic acid to produce diimide, which was a mixture
of mono-, di-, and tribrominated PDIs.7,50,54
1,6,7-Tribromo PDI (1,6,7-Br3PDI) and monobromo PDI
(Br-PDI) were separated in pure form. The dibromo PDI was
obtained as a mixture of 1,6- and 1,7-Br2PDI regiomers after
column chromatography with a ratio of ∼1:3, respectively.
Suzuki coupling between a regioisomeric mixture of dibromo
PDI and various boronic acid pinacol esters gave all compounds
in moderate to high yields. Separation of 1,6- and 1,7-regioisomers
was achieved via column chromatography using silica gel and a
mixture of solvents as eluent. All synthesized compounds were
soluble in common organic solvents such as chloroform, dichloro-
methane, tetrahydrofuran, toluene, and chlorobenzene.
was observed around 7.20 ppm with an integration of 8 protons
for 1,7-TPA and 12 protons for 1,6-TPA. A 13C NMR spectrum of
1,6-TPA showed two sets of aliphatic carbons as compared to that
of the 1,7- regiomer.
The reaction of 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9H-carbazole57 and dibromo PDI yielded a
mixture of N,N′-di(2-ethylhexyl)-1,6-bis(9-phenyl-9H-carbazol-
3-yl)perylene-3,4,9,10-tetracarboxydiimide (1,6-3CAR) and
N,N′-di(2-ethylhexyl)-1,7-bis(9-phenyl-9H-carbazol-3-yl)-
perylene-3,4,9,10-tetracarboxydiimide (1,7-3CAR). In an 1H
NMR spectrum of 1,7-3CAR, the perylene core showed one
broad singlet at 8.57 ppm, one broad doublet (8.22 ppm), and
one broad N−CH2 peak (at 4.25 ppm), whereas 1,6-3CAR
gave a broad doublet (8.10 ppm) instead of singlet and two
broad peaks (around 4.18 and 3.88 ppm) for the N−CH2
protons. The broadening of peaks may be due to rigidified
conformation of bulky 3-carbazole-9H-phenyl at the bay
positions (see Figure S-6 and S-7, Supporting Information).51
As expected, 13C NMR spectra of both regiomers were different:
1,6-3CAR showed two sets of aliphatic carbon peaks, whereas 1,7-
3CAR showed a single set of peaks.
The coupling reaction between 9-phenyl-2-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole (Scheme 2) and
dibromo PDI gave a mixture of N,N′-di(2-ethylhexyl)-1,6-bis(9-
phenyl-9H-carbazol-2-yl)perylene-3,4,9,10-tetracarboxydiimide
(1,6-2CAR) and N,N′-di(2-ethylhexyl)-1,7-bis(9-phenyl-9H-
carbazol-2-yl)perylene-3,4,9,10-tetracarboxydiimide (1,7-
2CAR), which were separated using silica gel column chroma-
tography using ethyl acetate in hexane (8% v/v) as the mobile
phase. 1H NMR spectra of the two regioisomers showed
a similar pattern in the aromatic region and only can be
differentiated in the case of the N−CH2 protons; 1,6-2CAR
showed two well-resolved multiplets (around 4.14 and 4.07 ppm).
Similarly,the 13C NMR spectrum of 1,6-2CAR showed two sets
of peaks for aliphatic carbons, and the rest are similar to those
of 1,7-2CAR.
Reaction of 9-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
phenyl]-9H-carbazole55 and dibromo PDI gave a mixture of
N,N′-di(2-ethylhexyl)-1,6-bis[4-(9H-carbazol-9-yl)phenyl]-
perylene-3,4,9,10-tetracarboxydiimide (1,6-CAR) and N,N′-
di(2-ethylhexyl)-1,7-bis[4-(9H-carbazol-9-yl)phenyl]perylene-
3,4,9,10-tetracarboxydiimide (1,7-CAR). These 1,6- and 1,7-
regiomers were separated on column chromatography using
dichloromethane and hexane (1:1) as eluent with 16% and 66%
1
yields, respectively. Peaks on H NMR spectra of both regiomers
in the aromatic region were the same, except that two doublets of
1,7-CAR (7.85 and 7.76 ppm) were merged in the case of 1,6-
CAR and that the N−CH2 protons of 1,6-CAR showed two
multiplets (at 4.22 and 4.10 ppm). In a similar manner, 13C NMR
spectra of both regiomers showed similar chemical shifts for
carbon atoms on the aromatic ring, but they were significantly
different with respect to aliphatic carbons. Compound 1,6-CAR
has two sets of peaks for aliphatic carbons with a small differ-
ence in chemical shift values (see NMR spectra in Supporting
Information).
In all cases, 1,6-regiomers were found to be different from
1
the corresponding 1,7-regiomers (Scheme 3) in H and 13C
2-(4-Diphenylaminophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane56 was attached to dibromo PDI via Suzuki coupling
reaction to give N,N′-di(2-ethylhexyl)-1,6-bis(4-diphenylamine)-
phenylperylene-3,4,9,10-tetracarboxydiimide (1,6-TPA) and N,N′-
di(2-ethylhexyl)-1,7-bis(4-diphenylamine)phenylperylene-3,4,9,10-
tetracarboxydiimide (1,7-TPA). The crude product was purified
using column chromatography with a mixture of dichloromethane
and hexane (1:1) to give 1,6- and 1,7-TPA with an isolated yield of
18% and 71%, respectively. 1H NMR spectra of 1,6- and 1,7-TPA
were identical, and the only difference was that the aromatic
protons were observed at 7.35 ppm with an integration of 12
protons for 1,7-TPA and 8 protons for 1,6-TPA. Another multiplet
NMR spectra due to the unsymmetrical nature of the pery-
lene core. Since Rf values of regiomers were close, significant
attention must be employed for the separation using column
chromatography.
Optical and Photophysical Properties. The absorption
spectra of all compounds were recorded in chloroform solution
(Figure 3), and solid-state absorption studies were done using
thin films obtained via drop-casting the solution on quartz plate
(Figure 4). The optical band gap was calculated based on
the absorption onset. Optical properties such as absorption
maxima, molar absorption coefficients, emission maxima, fluo-
rescence lifetime, and optical band gap were presented in Table 1.
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Figure 2. Chemical structure of synthesized PDI regiomers.
The PDI derivatives showed absorption maxima at 526 nm,
which is attributed to the perylene core π−π* transition with
characteristic vibronic fine structure.10
Compound 1,7-CAR showed two absorption maxima at 561
and 523 nm indicating better π-orbital overlapping with the
perylene core. This leads to a significant red-shift (35 nm) in
the absorption maximum (λmax) as compared to unsubstituted
PDI. Compound 1,6-CAR showed a λmax at 551 nm, which is
10 nm blue-shifted as compared to 1,7-CAR. An absorption
maximum was observed for both compounds at 523 nm, which
indicates a π−π* transition from the PDI core. In the solid
state, a blue shift was seen from 565 nm (1,7-CAR) to 558 nm
(1,6-CAR), whereas a second peak was red-shifted from 507 nm
(1,7-CAR) to 522 nm (1,6-CAR). The molar absorption
coefficient (ε) was found to be higher for 1,7-CAR as compared
to 1,6-CAR (Table 1). The calculated optical band gaps of
regiomers were more or less similar.
Compounds 1,7- and 1,6-TPA showed two absorption maxima
and lower wavelength peak had a high absorption coefficient value.
The low energy band was accounted to the charge transfer
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Scheme 1. Bromination and Diimidization of Perylenetetracarboxylic Acid Dianhydride (PDA)
Scheme 2. Synthesis of Compound 3
Scheme 3. Synthesis of 1,6- and 1,7-Substituted PDIs; (a) 2 M K2CO3, THF, Pd(PPh3)4, 24 h
absorption involving the electronic transition from the triphenyl-
amine to the electron-deficient perylene core, and the high energy
band was assigned to the perylene π−π* transition of characteristic
vibronic coupling pattern.58 In the case of 1,7-TPA, a low energy
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Figure 3. Absorption spectra of the regiomers in chloroform solution at room temperature.
Figure 4. Solid-state absorption spectra of drop casted films on quartz plate at room temperature.
band at 645 nm was red-shifted as compared to 1,6-TPA
(606 nm). The second high energy peak was unchanged at
510 nm for both regiomers, which confirms that the high
energy absorption band was originated from the perylene
moiety. Even though there were significant differences in the
absorption maxima, similar optical band gaps were observed
for 1,6- and 1,7-TPA compounds.
The solution state λmax of 1,6-3CAR was blue-shifted by
46 nm from that of 1,7-3CAR (609 nm). Here, the second λmax
was found to be same for both regiomers at 472 nm, which is
originated from PDI core, and an ε value of 1,6-3CAR was low
in comparison to that of 1,7-3CAR. The same trend was also
observed in the solid-state absorption spectra, where the
absorption maximum for 1,7-3CAR was red-shifted as compared
to that of the 1,6-3CAR regiomer. There was no significant differ-
ence in the optical band gap values observed for both 1,6- and 1,7-
3CAR compounds.
The absorption spectrum of 1,7-2CAR showed a λmax of 577 nm
at the low energy region, whereas λmax for 1,6-2CAR appeared at
567 nm. The second absorption peak for 1,6-2CAR at 507 nm
was red-shifted as compared to that of 1,7-2CAR. The molar
absorption coefficient (ε) of 1,7-2CAR was found to be higher
than that of 1,6-2CAR. The optical band gap values were
similar for both 1,6-2CAR and 1,7-2CAR regiomers.
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Table 1. Optical Properties of PDI Regiomers
absorption maxima (nm)
in chloroform
molar abs. coefficient
absorption maxima in
solid state (nm)
emission maxima in
chloroform (nm)
fluorescence
lifetime τ (ns)
optical band
gap (eV)
cmpd
(104 mol−1·dm3·m−1
)
1,6-CAR
551
523
561
523
606
510
645
510
563
472
609
472
567
507
577
429
4.010
3.961
4.494
4.100
2.569
5.346
2.384
5.774
2.849
2.263
3.104
2.905
3.335
3.064
3.485
2.781
558
522
565
507
632
512
652
513
562
477
604
482
564
508
557
437
651
3.3
3.4
1.85
1.87
1.61
1.59
1.76
1.74
1.87
1.84
1,7-CAR
1,6-TPA
651
1,7-TPA
1,6-3CAR
1,7-3CAR
1,6-2CAR
1,7-2CAR
663
689
644
647
4.1
3.9
13.2
8.8
Figure 5. Emission spectra of the regiomers in chloroform solution at room temperature.
Figure 6. Fluorescence decays of regiomers in chloroform solution.
Compound 1,7-TPA showed broad absorption up to 800 nm,
whereas the analogous compound 1,7-CAR showed narrow
absorption (up to 680 nm), which was due to electron donating
and charge transfer properties of the triphenylamine group. The
same trend was observed in the case of 1,6-TPA and 1,6-CAR.
The compound 1,7-3CAR (Figure 2, carbazole moiety is linked
through position 3) showed significant red shift as compared to
the compound 1,7-2CAR (carbazole moiety is linked through
position 2), which is expected due to a high resonance effect
from the carbazole functionalized at position 3. To our surprise,
1,6-3CAR and 1,6-2CAR had no significant differences in
absorption maxima.
maximum at 689 nm with a Stokes shift of 80 nm, whereas 1,6-
3CAR showed a Stokes shift of 100 nm. In the case of 1,7- and
1,6-2CAR, there was no significant difference in emission
spectra with λemis around 646 nm. As expected, carbazole-
substituted PDIs showed weak fluorescence intensity as
compared to unsubstituted PDI, and no fluorescence was observed
for triphenylamine-substituted PDI regiomers.43,58 In comparison
to 1,7-2CAR, the emission maximum of 1,7-3CAR was red-shifted
by 42 nm, whereas 1,7-CAR showed no significant difference. A
similar trend was observed in 1,6-regiomers.
Furthermore, the fluorescence lifetimes of 1,6- and 1,7-
regiomers were measured at an excitation wavelength of 560 nm
(pulse width of 250 ps) and probing emission maximum of
respective regiomers in chloroform solution (Figure 6). The
compounds 1,6- and 1,7-CAR showed similar decay profiles,
while 1,6-2CAR and 1,7-2CAR showed different fluorescence
lifetimes. This may be due to the difference in lifetime of charge
separated states of the excited molecules.
Steady-State Emission Properties and Fluorescence
Decay. The emission spectra were recorded in chloroform for
all molecules using the higher absorption wavelength (λmax
)
values as excitation wavelength (Figure 5). The emission spectra of
both 1,7-CAR and 1,6-CAR showed λemis at 651 nm with a Stokes
shift of 100 nm. The compound 1,7-3CAR showed emission
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In comparison, compound 1,7-CAR and 1,7-3CAR showed
insignificant differences in fluorescence lifetime, whereas 1,7-
2CAR showed higher fluorescence lifetime (Table 1). The
same trend was observed in the case of 1,6-regiomers. It is
understood that the substitution of the carbazole moiety linked
through position 3 to PDI enhances the charge transfer to the
PDI core as compared to the carbazole linked through position
2 to PDI.
Electrochemical Properties. Cyclic voltamograms (CV)
of all compounds were recorded in 0.1 M tetrabutylammonium
hexafluorophosphate solution of dichloromethane using a standard
calomel electrode (SCE) as the reference electrode at 100 mV/s
scan rate (Figure 7). CV of all compounds were calibrated with
(0.88 V). However, the HOMO and LUMO levels were found
to be similar for both 1,6- and 1,7-CAR. A small difference in
electrochemical band gap for both regiomers was observed.
Similarly, compounds 1,7- and 1,6-TPA showed similar one-
electron reduction potentials. A small difference (30 mV) in the
second one-electron reduction potentials of regiomers was
observed. Compound 1,6-TPA showed the first oxidation potential
at 0.58 V, which was 20 mV higher than that of 1,7-TPA. Inter-
estingly, both regiomers did not show a second oxidation peak
within the potential window of electrolyte. The HOMO−LUMO
gap was found to be similar for both regiomers.
The first reduction peak for compound 1,6-3CAR (−1.15 V)
was 20 mV lower than that of 1,7-3CAR. The second reduction
peak of 1,6-3CAR (−1.38 V) was shifted negatively by 20 mV
as compared to 1,7-3CAR. However, the first oxidation peak
was found to be similar for 1,6-3CAR (0.80 V) and 1,7-3CAR
(0.81 V), and the second oxidation of 1,6−3CAR was 30 mV
lower than that of 1,7-3CAR (1.07 V). The HOMO and
LUMO levels for both 1,6- and 1,7-3CAR were found to be
similar, which indicated no significant differences for both
regiomers in the energy levels.
The first one electron reduction of 1,7-2CAR (−1.09 V) was
observed to be 30 mV higher than corresponding the 1,6-
regiomer, and the second one electron reduction value of 1,6-
2CAR was 40 mV lower than that of 1,7-2CAR (−1.34 V). The
first one electron loss for 1,7-2CAR (0.82 V) was 20 mV higher
than that of 1,6-2CAR, and the second one electron loss was
40 mV more than that of 1,6-2CAR (0.98 V). The HOMO
levels for 1,6- and 1,7-2CAR were similar, but the LUMO levels
were slightly different (Table 2). Surprisingly, the compounds
with carbazole linked through 2 and 3 positions to PDI showed
similar electrochemical properties, even though they exhibited
considerable differences in optical properties.
The HOMO and LUMO energy level values for 1,7-CAR
and 1,7-TPA were found to be similar, and an analogous trend
was also observed for 1,6-CAR and 1,6-TPA. Both compounds,
1,7-3CAR and 1,7-2CAR showed similar oxidation and
reduction potentials with the same electrochemical band gap.
A similar trend was observed in the case of 1,6-3CAR and 1,6-
2CAR. The first reduction potentials of regiomers were generated
from reduction of the perylene core and gave rise to the LUMO
energy level.
Figure 7. Cylicvoltammograms of regiomers in dichloromethane
containing 0.1 M t-Bu4NPF6 at the scan rate of 100 mV/s.
ferrocene/ferrocenium ion (Fc/Fc+) redox couple as the internal
standard. The oxidation and reduction potentials, and HOMO and
LUMO levels, were depicted in Table 2. All compounds showed
Table 2. Electrochemical Properties of PDI Regiomers
Thermal Properties. Thermogravimetric analyses (TGA)
and differential scanning calorimetry (DSC) studies were
carried out under nitrogen atmosphere. TGA studies revealed
that all compounds were stable up to 450 °C (see Figure S-1,
Supporting Information). However, DSC traces were found to
be different for both regiomers. Compound 1,7-CAR showed a
glass transition temperature (Tg) at 169 °C and a crystallization
temperature (Tcryst) at 226 °C, but 1,6-CAR did not show Tg or
Tcryst. Compound 1,6-TPA showed a very sharp melting peak at
250 °C with no glass transition temperature or crystallization
peak, whereas 1,7-TPA showed a melting point (Tm) at 233 °C
(Figure 8).
In the case of 1,6-3CAR, Tg was observed at 150 °C with no
crystallization peak (Tcryst), whereas the Tg and Tcryst of 1,7-
3CAR were observed at 191 and 294 °C, respectively.
Compound 1,7-3CAR melted at 319 °C, but the corresponding
1,6-regiomer did not show a sharp melting peak. Compound
1,7-2CAR showed slightly higher Tm, Tg, and Tcryst in contrast
to the 1,6-regiomer (Table 3).
a
b
oxi-1 oxi-2 red-1 red-2 HOMO
LUMO
(eV)
Eg
cmpd
(V)
(V)
(V)
(V)
(eV)
(eV)
1,6-CAR
1,7-CAR
1,6-TPA
1,7-TPA
0.57
0.58
0.58
0.56
0.92 −1.13 −1.30
0.88 −1.04 −1.29
−1.12 −1.35
−5.31
−5.30
−5.26
−5.27
−5.40
−5.41
−5.40
−5.43
−3.80
−3.82
−3.78
−3.81
−3.70
−3.73
−3.70
1.51
1.48
1.48
1.46
1.70
1.68
1.70
1.68
−1.12 −1.38
1,6-3CAR 0.80
1,7-3CAR 0.81
1,6-2CAR 0.80
1,7-2CAR 0.82
1.04 −1.15 −1.38
1.07 −1.13 −1.36
1.02 −1.12 −1.38
0.98 −1.09 −1.34
−3.75
a
onset
Calculated using the relationship EHOMO = −(E
+ 4.8).
oxi
b
onset
red
Calculated using the relationship ELUMO = −(E
+ 4.8).
two prominent one-electron reduction peaks. The first
reduction peak for compound 1,6-CAR (at −1.13 V) was
lower by 90 mV to that of 1,7-CAR, whereas the second
reduction peak was similar for both 1,6- and 1,7-CAR com-
pounds. No significant difference was found in the first oxida-
tion potential of both regiomers, while the second oxidation
potential for 1,6-CAR (0.92 V) was higher than that of 1,7-CAR
Thermal studies revealed that 1,6-regiomers showed higher
melting points as compared to 1,7-regiomers. The compound
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Figure 9. Schematic view of twisting angle of (A) bay-substituted, (B)
1,7-substituted, and (C) 1,6-substituted PDIs.
Figure 8. DSC traces of PDI regiomers recorded at a heating rate of
10 °C min−1 under nitrogen atmosphere.
Table 4. Theoretical Calculations of PDI Regiomers
Table 3. Thermal Characteristics of PDI Regiomers
cmpd
av α (Θ) HOMO (eV) LUMO (eV) band gap (eV)
1,6-Br2PDI
1,7-Br2PDI
1,6-CAR
22.58
22.14
20.47
20.09
20.79
20.27
20.70
20.20
20.03
19.55
−6.12
−6.12
−5.47
−5.47
−5.09
−5.09
−5.36
−5.33
−5.47
−5.44
−3.59
−3.57
−3.43
−3.43
−3.18
−3.18
−3.13
−3.13
−3.18
−3.18
2.53
2.55
2.04
2.04
1.91
1.91
2.23
2.20
2.29
2.26
cmpd T (10 wt % loss) (°C) Td (°C) Tm (°C) Tg (°C) Tcryst (°C)
1,6-CAR
1,7-CAR
1,6-TPA
1,7-TPA
1,6-3CAR
1,7-3CAR
1,6-2CAR
1,7-2CAR
451
455
389
427
458
432
475
465
400
420
360
381
413
412
418
398
382
322
250
233
362
319
310
321
169
226
118
1,7-CAR
1,6-TPA
84
1,7-TPA
150
191
170
181
1,6-3CAR
1,7-3CAR
1,6-2CAR
1,7-2CAR
294
215
230
1,7-3CAR had higher Tg and Tcryst than 1,7-2CAR and 1,7-
CAR. For the compound 1,7-TPA, Tcryst was observed to be
significantly low compared to that of 1,7-CAR. In the case of
1,6-regiomers, Tcryst was not observed except for in 1,6-2CAR.
Theoretical Calculations. The Gaussian calculations were
carried out on Gaussian09 at the density functional theory
(DFT) level with the B3LYP function using 6-31G* as a basis
set. The geometry optimized structures (see Supporting
Information) and frontier orbital energy levels were calculated.
The twisting angle (α) between two naphthalene units of the
substituted perylene core was calculated (Figure 9), and all
results were depicted in Table 4. The twist angles (α) of
bromo-substituted PDI were 22.6° and 22.1° for both regio-
isomers 1,6- and 1,7-Br2PDI, respectively, which was close to
the previously reported angle 21.0° for 1,7-Br2PDI.6 The HOMO
energy levels of both regiomers were the same (at −6.12 eV), and
the LUMO energy levels were slightly different for 1,6- and 1,7-
Br2PDI. As a result, the HOMO−LUMO gap was almost the
same for 1,6- and 1,7-Br2PDI.
The calculated HOMO and LUMO levels for both 1,6- and
1,7-CAR were at −5.47 and −3.43 eV. In the case of 1,6- and
1,7-2CAR, the LUMO level exists at −3.18 eV, whereas the
HOMO level was located at −5.47 and −5.44 eV, respectively.
There was no difference in LUMO energy levels of both 1,6-
and 1,7-3CAR; however, the HOMO energy levels were at
−5.36 and −5.33 eV, with a small difference. The twist angle
(α) values were at 20.7° and 20.2° for both 1,6- and 1,7-3CAR,
respectively. No significant difference in HOMO and LUMO
energy levels was observed for both 1,6- and 1,7-TPA. In the
case of carbazole linked through the second position (1,6- and
1,7-2CAR) and third position (1,6- and 1,7-3CAR) to PDI, the
HOMO orbitals were evenly distributed on carbazole as well as
the perylene core, while the LUMO orbitals were located on
the PDI core (Figure 10). In the case of phenylene-bridged
carbazole (1,6- and 1,7-CAR) and triphenylamine-substituted
PDIs (1,6- and 1,7-TPA), the HOMO was mostly localized on
the phenyl carbazole and triphenylamine, and the LUMO was
fully localized on the PDI core. The twist angle (α) for 1,6-
regiomers was always higher than the corresponding 1,7-
regiomers, which indicates that two substitutions on the same
naphthalene unit of PDI causes more twisting of the molecule.
EXPERIMENTAL METHODS
■
General Considerations. Materials. All chemicals and
reagents were purchased from commercial suppliers and used
without further purification. Solvents used for spectroscopic
measurements were spectral grade quality. Tetrahydrofuran
(THF) was distilled in the presence of metallic sodium. The
compounds 9-phenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)-9H-carbazole,57 9-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
2-yl)phenyl]-9H-carbazole,55 2-bromo-9H-carbazole,59 and 2-(4-
diphenylaminophenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane56
were synthesized by following literature reports. All reactions
were monitored by thin-layer chromatography (TLC) on silica
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Article
Figure 10. Frontier orbitals of PDI regiomers calculated using density functional theory (DFT) at the B3LYP/6-31G (d) level.
onset
gel plates. Preparative separations were performed by column
(E ) were used to calculate HOMO and LUMO energy
red
onset
chromatography on silica gel grade 60 (0.040−0.063 mm).
levels using the relationship EHOMO = −(4.8 + E
) and
ox
1
onset
Instrumentation and Characterization. H NMR spectra
ELUMO = −(4.8 + E ), respectively. Geometry optimizations
red
were performed in Gaussian0960 at the density functional
theory (DFT) level with the B3LYP functional and a 6-31G*
basis set. The HOMO and LUMO surfaces were generated
from the optimized geometries using Gaussview 5.61
were recorded on a Bruker ACF300 (300 MHz) spectrometer.
The chemical shifts were reported in ppm and referenced to the
residual solvent peak: s = singlet, d = doublet, t = triplet, m =
multiplet, and b = broad. FAB-mass spectra were obtained on a
Finnigan MAT95XL-T and Micromass VG7035 mass spec-
trometer. Elemental analysis was carried out on Elementar
Vario Micro Cube. The UV−vis and emission spectra were
measured on a UV-1601PC Shimadzu spectrophotometer and
RF-5301PC Shimadzu spectrofluorophotometer. Fluorescence
lifetimes were measured by using TCSPC (Horiba Jobin Yvon
IBH ltd) by exciting with NanoLED of wavelength 560 nm
(pulse width of 250 ps). Thermal data were recorded under
nitrogen atmosphere on a TA Instruments Q100.
A cyclic voltammogram was recorded with a computer
controlled CHI electrochemical analyzer at a constant scan rate
of 100 mV/s. Measurements were performed in an electrolyte
solution of 0.1 M tetrabutylammonium hexafluorophosphate
dissolved in degassed dichloromethane. The electrochemical
cell consists of three electrode systems with a platinum disk as
the working electrode, platinum rod as the counter electrode,
and a standard calomel electrode (SCE) as the reference elec-
trode. The potentials were calibrated using ferrocene as the
internal standard. The onset of oxidation (Eooxnset) and reduction
9-(Phenyl)-2-bromo-9H-carbazole (2). A mixture of 2-
bromo-9H-carbazole (1) (5.0 g, 20.3 mmol), 4-iodobenzene
(4.5 g, 22.1 mmol), and K2CO3 (4.16 g, 30 mmol) in DMSO
(70 mL) was stirred under N2 for 30 min (Scheme 3).
Followed by the addition of CuI (0.40 g, 2.1 mmol) and
L-proline (0.48 g, 4.2 mmol), the mixture was refluxed at 120 °C
under nitrogen for 24 h. After cooling to room temperature, the
reaction mixture was poured into water, and the product was
extracted using diethyl ether. The crude product was purified
by column chromatography using hexane as the eluent to give a
white product (4.57 g, 70% yield). 1H NMR (300 MHz, CDCl3,
δ ppm): 8.11 (d, J = 7.80 Hz, 1H), 7.99 (d, J = 8.40 Hz, 1H),
7.65−7.60 (m, 2H), 7.55−7.52 (m, 4H), 7.43−7.37 (m, 3H),
7.32−7.30 (m, 1H). 13C NMR (75 MHz, CDCl3, δ ppm):
141.7, 141.1, 137.0, 130.0, 127.8, 127.1, 126.3, 123.0, 122.8,
122.2, 121.4, 120.3, 120.2, 119.4, 112.7, 109.9. MS (EI) m/z:
321.1. Anal. Calcd for C18H12BrN: C, 67.10; H, 3.75; N, 4.35;
Br, 24.80. Found: C, 67.16; H, 3.70; N, 4.27; Br, 24.91.
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9-(Phenyl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)-9H-carbazole (3). N-Butyl lithium (2 M solution in
cyclohexane) (2.5 mL, 5 mmol) was added slowly to compound
2 (1.28 g, 4 mmol) in dried THF solution at −78 °C and stirred
for 20 min. To this mixture, 2-isopropoxy-4,4,5,5-tetramethyl-
[1,3,2] dioxaborolane (1.0 g, 5.4 mmol) was added slowly and
stirred for 2 h at −78 °C and then stirred overnight at room
temperature (Scheme 2). The reaction mixture was quenched
with water and extracted with diethyl ether. The crude product
was purified by column chromatography using 5% ethyl acetate
retention factor (Rf) of 1,6-TPA and 1,7-TPA are 0.54 and 0.44,
respectively. The amount of 1,6-TPA obtained was 0.085 g
(18%). 1H NMR (300 MHz, CDCl3, δ ppm): 8.61 (s, 2H, Per-H),
8.25 (d, J = 8.40, 2H, Per-H), 8.02 (d, J = 8.40, 2H, Per-H),
7.36−7.27 (m, 8H), 7.24−7.18 (m, 12H), 7.14−7.07 (m, 8H),
4.19−4.14 (m, 2H, N−CH2), 4.10−4.06 (m, 2H, N−CH2),
1.96−1.92 (m, 2H), 1.42−1.31 (m, 16H), 0.96−0.87 (m, 12H).
13C NMR (75 MHz, CDCl3, δ ppm): 163.97, 163.96, 148.4,
147.2, 142.0, 135.6, 135.2, 134.8, 132.6, 129.8, 129.6, 129.5,
129.3, 128.4, 126.8, 125.0, 123.9, 123.6, 122.2, 121.8, 44.2, 38.0,
30.8, 30.7, 28.8, 28.7, 24.1, 24.01, 23.1, 23.1, 14.1, 10.7, 10.6.
FAB-MASS (+VE): (m/z) 1101.527. Anal. Calcd for
C76H68N4O4: C, 82.88; H, 6.22; N, 5.09. Found: C, 82.56; H,
6.30; N, 4.97.
1
in hexane to give a white solid (0.83 g, 56% yield). H NMR
(300 MHz, CDCl3, δ ppm): 8.18−8.14 (m, 2H), 7.84 (s, 1H),
7.76 (d, J = 7.80 Hz, 1H), 7.65−7.60 (m, 4H), 7.59−7.56 (m,
1H), 7.51−7.36 (m, 2H), 7.31−7.28 (m, 1H), 1.36 (m, 12H).
13C NMR (75 MHz, CDCl3, δ ppm): 141.5, 140.5, 137.7, 129.9,
127.5, 127.4, 126.1, 125.8, 124.2, 123.1, 120.8, 119.8, 119.5,
116.0, 109.9, 83.7, 24.9. MS (EI) m/z: 369.2. Anal. Calcd for
C24H24BNO2: C, 78.06; H, 6.55; N, 3.79. Found: C, 78.16; H,
6.61; N, 3.69.
N,N′-Di(2-ethylhexyl)-1,7-bis[(4-diphenylamine)phenyl]-
perylene-3,4,9,10-tetracarboxydiimide (1,7-TPA). The
1
amount of 1,7-TPA obtained was 0.385 g (71%). H NMR
(300 MHz, CDCl3, δ ppm): 8.61 (s, 2H, Per-H), 8.23 (d, J =
9.00, 2H, Per-H), 8.04 (d, J = 9.00, 2H, Per-H), 7.40−7.31 (m,
12H), 7.21−7.18 (m, 8H), 7.15−7.07 (m, 8H), 4.18−4.09 (m,
4H, N−CH2), 1.97−1.93 (m, 2H), 1.41−1.31 (m, 16H), 0.96−
0.87 (m, 12H). 13C NMR (75 MHz, CDCl3, δ ppm): 163.9,
148.5, 147.2, 140.8, 135.4, 135.2, 135.1, 132.3, 129.9, 129.6,
129.5, 129.3, 129.1, 127.5, 125.1, 123.8, 123.7, 122.1, 121.7,
44.2, 38.0, 30.8, 28.7, 24.1, 23.1, 14.1, 10.6. FAB-MASS: (m/z)
1101.527. Anal. Calcd for C76H68N4O4: C, 82.88; H, 6.22; N,
5.09. Found: C, 82.79; H, 6.19; N, 4.87.
Bromination and Imidization of Perylenetetracarboxyli-
cacid Dianhydride.7,49,50,54 Perylene tetracarboxylic acid
anhydride (10.0 g, 25.4 mmol) was dispersed in conc. H2SO4
(150 mL) with a catalytic amount of I2 (25 mg). To the
reaction mixture, bromine (9.4 g, 58.5 mmol) was added slowly
within a period of 0.5 h and stirred at 85 °C for 24 h (Scheme 1).
The reaction mixture was cooled to room temperature and
slowly poured into water (1 L). The precipitate was filtered,
washed with water and methanol, and dried in vacuum. This
crude brominated perylenetetracarboxylicacid dianhydride
(Br-PDA) was directly used for the imidization reaction. The
crude Br-PDI (5.5 g, 10 mmol) was dispersed in 100 mL of
N-methyl pyrrolidone (NMP), and to this, 2-ethylhexylamine (2 g,
23.0 mmol) and acetic acid (5.0 mL) were added in nitrogen
atmosphere. The reaction mixture was stirred for 24 h at 90 °C.
After cooling to room temperature, the mixture was poured in
to water and filtered. The precipitate was washed with water,
methanol, and purified by column chromatography on silica gel
using chloroform and hexane (2:1) mixture as eluent. At first
elution, 1,6,7-tribromo-N,N′-di(2-ethylhexyl)-perylene-3,4,9,10-
tetracarboxydiimide (1,6,7-Br3PDI) (0.054 g, 0.7% yield) was
obtained as a minor product, the mixture of 1,6- and 1,7-
dibromo-N,N′-di(2-ethylhexyl)-perylene-3,4,9,10-tetracarboxy-
diimide (5.5 g, 71% yield) was obtained during the second
elution, and 1-bromo-N,N′-di(2-ethylhexyl)-perylene-3,4,9,10-
tetracarboxydiimide (Br-PDI) (0.10 g, 1% yield) was obtained
on the third elution as a minor product.
N,N′-Di(2-ethylhexyl)-1,6-bis[4-(9H-carbazol-9-yl)phenyl]-
perylene-3,4,9,10-tetracarboxydiimide (1,6-CAR). The crude
compound was purified by column chromatography using 1:1
hexane and dichloromethane as the eluent. The Rf of 1,6-CAR
and 1,7-CAR are 0.33 and 0.26, respectively. The amount of
1
1,6-CAR obtained was 0.087 g (16%). H NMR (300 MHz,
CDCl3, δ ppm): 8.77 (s, 2H, Per-H), 8.31 (d, J = 9.00, 2H, Per-H),
8.19 (d, J = 6.00, 4H, Car-H), 8.06 (d, J = 9.00, 2H, Per-H),
7.73 (m, 8H, Ph-H), 7.52−7.50 (m, 8H, Car-H), 7.38−7.33
(m, 4H, Car-H), 4.25−4.20 (m, 2H, N−CH2), 4.13−4.08 (m,
2H, N−CH2), 2.02 (m, 1H), 1.93 (m, 1H), 1.44−1.31 (m,
16H), 1.01−0.87 (m, 12H). 13C NMR (75 MHz, CDCl3, δ
ppm): 163.74, 163.72, 141.5, 141.1, 140.6, 138.2, 135.4, 134.1,
133.1, 130.5, 129.9, 129.7, 129.6, 128.8, 128.7, 128.5, 127.4,
126.3, 123.6, 122.5, 122.4, 120.5, 120.4, 109.6, 44.36, 44.30,
38.05, 37.99, 30.8, 30.7, 28.8, 28.6, 24.1, 24.0, 23.07, 23.06,
14.12, 14.08, 10.7, 10.6. FAB-MASS (−VE): (m/z) 1096.495.
Anal. Calcd for C76H64N4O4: C, 83.18; H, 5.88; N, 5.11.
Found: C, 83.30; H, 6.04; N, 5.10.
General Condition for Suzuki Coupling Reaction. To a
100 mL two-neck round-bottom flask under nitrogen atmo-
sphere, the dibromo PDI (0.386 g, 0.5 mmol) and respective
boronic acid pinacol ester (1.2 mmol) were dissolved in 20 mL
of tetrahydrofuran (THF). To this reaction mixture, 10 mL of
prepurged 2 M K2CO3 aqueous solution and catalyst Pd(PPh3)4
(0.058 g, 0.05 mmol) were added and stirred for 24 h at 80 °C
under nitrogen atmosphere (Scheme 3). The reaction mixture
was allowed cool to room temperature and was extracted with
dichloromethane. The collected organic layers were dried over
anhydrous sodium sulfate. The solvent was removed under
reduced pressure. The crude product was purified by silica gel
column chromatography (see details below).
N,N′-Di(2-ethylhexyl)-1,7-bis[4-(9H-carbazol-9-yl)phenyl]-
perylene-3,4,9,10-tetracarboxydiimide (1,7-CAR). The yield of
the compound was 66% (0.359 g). 1H NMR (300 MHz, CDCl3,
δ ppm): 8.76 (s, 2H, Per-H), 8.33 (d, J = 8.07, 2H, Per-H),
8.19 (d, J = 6.00, 4H, Car-H), 8.09 (d, J = 8.10, 2H, Per-H),
7.85 (d, J = 9.00, 4H, Ph-H), 7.76 (d, J = 9.00, 4H, Ph-H),
7.53−7.51 (m, 8H, Car-H), 7.38−7.33 (m, 4H, Car-H), 4.22−
4.13 (m, 4H, N−CH2), 1.99−1.96 (m, 2H), 1.43−1.33 (m,
16H), 0.98−0.88 (m, 12H). 13C NMR (75 MHz, CDCl3, δ
ppm): 163.75, 163.68, 141.1, 140.6, 140.2, 138.3, 135.4, 134.8,
132.6, 130.7, 130.3, 129.6, 129.4, 128.7, 128.0, 126.3, 123.7,
122.6, 122.4, 120.5, 120.4, 109.6, 44.3, 38.0, 30.8, 28.1, 24.1,
23.1, 14.1, 10.7. FAB-MASS (−VE): (m/z) 1096.494. Anal.
Calcd for C76H64N4O4: C, 83.18; H, 5.88; N, 5.11. Found: C,
82.98; H, 6.07; N, 5.04.
N,N′-Di(2-ethylhexyl)-1,6-bis(4-diphenylamine)-
phenylperylene-3,4,9,10-tetracarboxydiimide (1,6-TPA). The
crude compound was purified by column chromatography
using 1:1 hexane and dichloromethane as the eluent. The
N,N′-Di(2-ethylhexyl)-1,6-bis(9-phenyl-9H-carbazol-3-yl)-
perylene-3,4,9,10-tetracarboxydiimide (1,6-3CAR). The crude
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Article
compound was purified by column chromatography using 10%
ethyl acetate in hexane as the eluent. The Rf of 1,6-3CAR and
1,7-3CAR were 0.67 and 0.75, respectively. The amount of 1,6-
3CAR obtained 0.098 g (18%). 1H NMR (300 MHz, CDCl3, δ
ppm): 8.73 (d, J = 20, 2H, Per-H), 8.38 (b, 1H, Car-H), 8.23
(d, J = 6.90, 1H, Per-H), 8.11 (d, J = 6.75, 1H, Per-H), 7.97 (b,
2H, Per-H), 7.87−7.80 (m, 3H, Car-H), 7.65 (m, 8H, Car-H),
7.53−7.46 (m, 8H, Car-H), 7.38−7.32 (m, 4H, Car-H), 4.21−
4.12 (m, 2H, N−CH2), 3.96−3.86 (m, 2H, N−CH2), 2.00 (m,
1H), 1.83 (m, 1H), 1.46−1.29 (m, 16H), 1.01−0.84 (m, 12H).
13CNMR (75 MHz, CDCl3, δ ppm): 164.0, 163.8, 142.8, 142.7,
141.4, 140.6, 137.2, 135.9, 134.8, 134.7, 134.2, 134.0, 132.8,
130.0, 129.8, 129.4, 128.9, 128.3, 127.8, 127.2, 126.8, 126.6,
124.9, 123.1, 121.6, 120.8, 120.5, 111.3, 110.2, 44.3, 44.1, 38.9,
37.8, 30.9, 30.7, 29.7, 28.6, 24.2, 24.0, 23.07, 23.03, 14.12,
14.07, 10.7, 10.6. FAB-MASS (+VE): (m/z) 1097.495. Anal.
Calcd for C76H64N4O4: C, 83.18; H, 5.88; N, 5.11. Found: C,
82.99; H, 6.03; N, 4.97.
Anal. Calcd for C76H64N4O4: C, 83.18; H, 5.88; N, 5.11.
Found: C, 82.98; H, 5.77; N, 4.98.
CONCLUSIONS
■
A series of donor−acceptor systems of substituted perylenedii-
mides with an extended π−system were synthesized. All
regioisomers of 1,6- and 1,7-disubstituted PDIs were separated
using conventional column chromatography and characterized.
A red shift in the absorbance maxima of 1,7-regiomers was
observed as compared to 1,6-regiomers. No significant differ-
ences in electrochemical properties of 1,6- and 1,7-disubstituted
PDIs were observed. Thermal properties such as melting point,
glass transition temperature, and crystallization temperature of
regiomers were found to be different, while retaining the high
thermal stabilities of perylenediimides. It is clear that energy
levels of 1,6- and 1,7-regiomers did not differ greatly, so the
applications where the energy levels were considered may not
be affected. The photovoltaic and organic field effect transistor
studies are underway in our laboratory.
N,N′-Di(2-ethylhexyl)-1,7-bis(9-phenyl-9H-carbazol-3-yl)-
perylene-3,4,9,10-tetracarboxydiimide (1,7-3CAR). The yield
1
of the compound was 65% (0.354 g). H NMR (300 MHz,
ASSOCIATED CONTENT
■
CDCl3, δ ppm): 8.57 (s, 2H, Per-H), 8.51 (s, 2H, Car-H), 8.22
(d, J = 24.00, 2H, Per-H), 8.05 (d, J = 8.02, 2H, Per-H), 7.62
(b, 10H, Car-H), 7.47 (b, 10H, Car-H), 7.21−7.17 (m, 2H,
Car-H), 4.25 (b, 4H, N−CH2), 1.97 (m, 2H), 1.42−1.30 (m,
16H), 0.98−0.90 (m, 12H). 13C NMR (75 MHz, CDCl3, δ
ppm): 163.8, 163.5, 141.4, 140.7, 137.2, 135.5, 134.4, 133.6,
131.5, 130.0, 129.7, 128.9, 128.7, 127.7, 127.1, 126.9, 126.6,
125.43, 125.41, 123.42, 123.40, 123.36, 121.8, 121.3, 121.1,
120.7, 110.1, 44.4, 38.0, 30.9, 28.8, 24.2, 23.1, 14.2, 10.7. FAB-
MASS (+VE): (m/z) 1097.499. Anal. Calcd for C76H64N4O4:
C, 83.18; H, 5.88; N, 5.11. Found: C, 82.89; H, 5.84; N, 5.00.
N,N′-Di(2-ethylhexyl)-1,6-bis(9-phenyl-9H-carbazol-2-yl)-
perylene-3,4,9,10-tetracarboxydiimide (1,6-2CAR). The crude
compound was purified by column chromatography using 10%
ethyl acetate in hexane as the eluent. The Rf of 1,6-2CAR and
1,7-2CAR were 0.71 and 0.76, respectively. The amount of 1,6-
S
* Supporting Information
1H NMR, 13C NMR, and TGA data and geometry optimized
structures for all compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*Phone: (+65) 65164327. Fax: (+65) 67791691. E-mail: chmsv@
nus.edu.sg.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the support of Department of
Chemistry, National University of Singapore, for providing facilities
and NUS computer center for high performance computation. A.K.
thanks NUS NanoCore for a graduate scholarship.
1
2CAR obtained was 0.077 g (12%). H NMR (300 MHz,
CDCl3, δ ppm): 8.67 (s, 2H, Per-H), 8.18 (d, J = 7.2, 4H,
Car-H), 8.05 (d, J = 8.10, 2H, Per-H), 7.80 (d, J = 9.00, 2H,
Per-H), 7.60−7.57 (m, 6H, Car-H), 7.48−7.46 (m, 10H, Car-
H), 7.38−7.33 (m, 4H, Car-H), 4.17−4.12 (m, 2H, N−CH2),
4.09−4.03 (m, 2H, N−CH2), 1.93 (m, 2H), 1.39−1.30 (m,
16H), 0.96−0.88 (m, 12H). 13C NMR (75 MHz, CDCl3, δ
ppm): 163.9, 163.7, 142.8, 142.1, 141.7, 140.2, 137.3, 135.5,
134.6, 133.1, 130.0, 129.9, 129.8, 129.5, 128.8, 128.2, 127.7,
127.1, 126.9, 126.6, 123.4, 122.8, 122.1, 122.0, 121.8, 120.8,
120.6, 120.5, 110.0, 109.9, 44.3, 44.2, 38.0, 37.9, 30.8, 30.7,
28.7, 28.6, 24.1, 24.0, 23.1, 23.0, 14.1, 10.6. FAB-MASS (+VE):
(m/z) 1097.498. Anal. Calcd for C76H64N4O4: C, 83.18; H,
5.88; N, 5.11. Found: C, 83.24; H, 5.21; N, 4.96.
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