Helical assembly induced by hydrogen bonding from chiral carboxylic acids based on perylene bisimides

Article abstract of DOI:10.1021/jp2064968

The control over self-assembly behavior becomes absolutely critical because it is dependent on the orientation and morphology. The motivation is focused on borrowing the help of O-H???O hydrogen bonding interactions to realize the control in chiral self-a

Full text of DOI:10.1021/jp2064968

ARTICLE
pubs.acs.org/JPCB
Helical Assembly Induced by Hydrogen Bonding from Chiral
Carboxylic Acids Based on Perylene Bisimides
Xinyu Lu, Zhiqian Guo, Chunyu Sun, He Tian, and Weihong Zhu*
Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced Materials and Institute of Fine Chemicals,
East China University of Science & Technology, Shanghai 200237, P. R. China
S Supporting Information
b
ABSTRACT: The control over self-assembly behavior becomes
absolutely critical because it is dependent on the orientation and
morphology. The motivation is focused on borrowing the help
of OꢀH O hydrogen bonding interactions to realize the
3 3 3
control in chiral self-assembly. A series of perylene bisimide
(PBI) dyes 3aꢀ3d bearing chiral amino acid derivatives on the
imide N atoms and four phenoxy-type substituents at the bay
positions of the perylene core were synthesized. Optical proper-
ties and aggregation behavior of PBIs were investigated by
absorption, fluorescence, circular dichroism (CD), and 1H NMR spectroscopy. Except for the chiral ester 3c and achiral 3d, chiral
dyes 3a and 3b show bisignated CD signals, indicating that the chiral carboxylic acid-functionalized PBI systems are found to be
spontaneously self-assembled into supramolecular helices via intermolecular hydrogen bonding rather than πꢀπ stacking.
Furthermore, the chirality-controlled helical superstructures are strongly dependent on several factors, such as solvent polarity,
concentration, and temperature. The supramolecular helical chirality can be well-controlled by the chiral amino acid residues in the
PBI system; that is, the assembled clockwise (plus, P) or anticlockwise (minus, M) helices can be induced by L- or D-isomers,
respectively.
’ INTRODUCTION
obtain PBIs bearing the self-assembly unit of carboxylic groups,
chiral R-amino acid is an obviously good choice to the building
block with an easy imidation to incorporate carboxylic groups
and retain the original chiral center of amino acid; (ii) to in-
corporate the substitute of 4-methylphenoxy to their bay-region
at PBI to prevent the competitive H- or J-aggregation during the
interaction process of hydrogen bonding;11 and (iii) to attempt to
realize helical arrangement via the chiral center control with two
exact enantiomers of L- and D-phenylalanine. For taking insight
into the effect on the intermolecular hydrogen bonding induced
by carboxyl groups, we further utilized the corresponding ester 3c
as reference (Scheme 1). The apolar solvent CCl4 and moderately
polar solvent CHCl3 were used in the studies, whereas MeOH
was used as the breaking or blocking agent of hydrogen bond.
Interestingly, the chiral carboxylic-acid-functionalized PBI sys-
tems (3a and 3b) are found to self spontaneously-assemble
into the supramolecular helices, which are strongly dependent
on several factors, such as solvent polarity, concentration, and
temperature. Moreover, the supramolecular helical chirality can
be well-controlled by the chiral amino acid residues in PBI system;
that is, the assembled clockwise (Plus, P) or anticlockwise
(Minus, M) helices can be induced by L- or D- isomers, re-
spectively.
Supramolecular helical architectures have received great inter-
est in recent years, especially in arising from the intermolecular
self-assembly with small molecular chiral building blocks.1ꢀ8
Perylene bisimides (PBIs) exhibit a pronounced tendency to self-
organization with the help of molecular stacking, metal coordina-
tion, or hydrogen bonding under conditions, even forming unique
chiral supramolecular helices,9ꢀ12 but many PBI helical assem-
blies are formed with the help of the intermolecular πꢀπ inter-
actions because of their big planar structures.13ꢀ17 To date,
several PBI supramolecular architectures containing NꢀH
O
3 3 3
hydrogen bonding interactions have been realized by the
W€urthner group.11,16 However, little attention has been paid to
the OꢀH O hydrogen bonding interactions in the PBI
3 3 3
system,18 although the conventional hydrogen bonding in car-
boxylic acids is particularly strong in solutions, on surface, and in
crystal with high sensitivity to various environmental factors.19ꢀ21
With this in mind, our motivation is focused on borrowing the
help of OꢀH O hydrogen bonding interactions to realize the
3 3 3
control in chiral self-assembly. Undoubtedly, the control over
their self-assembly behavior becomes absolutely critical because
it is dependent on the orientation and morphology. Moreover,
chirality has been utilized as a guiding element to induce self-
assembly processes with the assistance of circular dichroism (CD)
to assign the helical assemblies.22,23 For this purpose, we con-
struct the target chiral R-amino acid system based on PBI chromophore
(3a and 3b in Scheme 1) with the following considerations: (i) to
Received: July 9, 2011
Revised:
August 5, 2011
Published: August 10, 2011
r
2011 American Chemical Society
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The Journal of Physical Chemistry B
ARTICLE
Scheme 1. Molecular Structure of Chiral Functionalized PBIs 3aꢀ3c and the Reference 3d
Table 2. Absorption Ratios A0f0/A0f1 of PBIs 3aꢀ3d versus
Concentration
A
0f0/A0f1 (in CCl4 solution)
5 ꢁ 10ꢀ6
1 ꢁ 10ꢀ5
2.5 ꢁ 10ꢀ5
5 ꢁ 10ꢀ5
1 ꢁ 10ꢀ4
PBI
M
M
M
M
M
3a
3b
3c
3d
1.69
1.70
1.70
1.65
1.69
1.69
1.71
1.65
1.68
1.69
1.70
1.62
1.57
1.56
1.55
1.47
1.45
1.45
1.39
1.31
such molecular aggregation can be ruled out in the concentration
range from 5 ꢁ 10ꢀ6 to 1 ꢁ 10ꢀ4 M (Table 2). In contrast with
the systems studied previously,27 there is only a very small shift
by 1 to 2 nm in the absorption peak among acids 3a, 3b, and ester
3c in CCl4 solution, even upon a small amount addition of
MeOH (5 vol %, Table 1), indicative of less of a solvent polarity
effect on the absorption spectra. A larger red shift by 8ꢀ10 nm is
observed in the maximal absorption of acids 3a, 3b, and ester 3c
with respect to that of 3d (Figure 1, inset), suggesting that the
higher electronegative carboxylic or ester group can depress the
electronic densities in the PBI core more than the butyl group,
which is consistent with those previously reported.28
Figure 1. Absorption spectra of 3aꢀ3d in CCl4 (1.0 ꢁ 10ꢀ5 M). Inset:
expansion of the 550 to 600 nm region.
Table 1. UV/vis-Absorption Data of PBIs 3aꢀ3d (1.0 ꢁ
10ꢀ5 M)
in CCl4
in MeOHꢀCCl4 (5/95, v/v)
λabs εmax
A0f0
(nm) (Mꢀ1 cmꢀ1
λabs
εmax
A0f0
A0f1
/
/
(nm) (Mꢀ1 cmꢀ1
)
)
A0f1
PBI
Unlike absorption spectra, there is an additional red shift in
fluorescence peak with an increasing concentration (λex
=
3a 580
3b 580
3c 580
3d 572
54 100
54 100
57 000
53 400
1.68
1.66
1.70
1.65
581
581
582
574
53 600
53 500
55 500
53 400
1.66
1.67
1.70
1.64
538 nm). As a case illustrated in Figure 2a, the fluorescence
peak of 3a is red-shifted by 15 nm from 607 to 622 nmꢀu4pon
increasing the concentration from 5 ꢁ 10ꢀ6 to 1 ꢁ 10
M.
Similarly, the fluorescence band of its corresponding ester 3c is
red-shifted by 12 nm from 607 to 619 nm with the same
increment of concentration (Figure 2c). Obviously in the
fluorescence band upon increasing concentration, a larger red-
shifting by 3 nm for acid 3a is observed with respect to the
corresponding ester 3c. Here the red-shifting in the fluorescence
of ester 3c is mainly caused by molecular collision at increased
concentrations, whereas the red-shifting in the fluorescence of
acid 3a upon the increasing concentration might have resulted
from the cooperating interactions of both molecular collision and
hydrogen bonding.29 Interestingly, such difference could be
eliminated. That is, when adding 5 vol % MeOH to the CCl4
solution, the fluorescence band of acid 3a is blue-shifted by 4 nm
from 622 to 618 nm (Figure 2a), but there is no distinct shift for
the corresponding ester 3c. The similar tendency was also
observed in 3b (Figure 2b). Additionally, the fluorescence
quantum yields of 3aꢀ3c in CCl4 were 0.64, 0.64, and 0.66,
respectively, determined by comparing the integrated area of the
’ RESULTS AND DISCUSSION
The PBIs 3a and 3b and the reference compounds 3c and 3d
were synthesized from the commercially available starting ma-
terial of 1,6,7,12-tetra-(4-methyl-phenoxy)perylene-3,4:9,10-tetra-
carboxylic acid dianhydride17 (Scheme 1). Their chemical struc-
tures were fully characterized by H NMR, 13C NMR, and
1
HRMS, as shown in the Supporting Information.
The absorption spectra of 3aꢀ3c in CCl4 exhibit a close
apparent absorption coefficients (molar extinction coefficients)
and typical spectroscopic features similar to that of the tetra-
aryloxy-substituted PBI 3d (Figure 1 and Table 1). As in the case
of 3a, there exist three main characteristic peaks at 449, 538, and
580 nm, arising from the typical transitions of PBI chromo-
phore.16 The value of 1.69 for A0f0/A0f1 ratios of PBI 3a in
concentration of 1.0 ꢁ 10ꢀ5 M is indicative of the mostly non-π-
stacked dominance instead of H- or J-aggregations,24ꢀ26 and
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Figure 3. Concentration-dependent 1H NMR spectra of 3a in CDCl3 at
25 °C. Inset: chemical shifts of ꢀCOOH protons (Ha) and protons on
perylene ring (Hb) of 3a versus concentration.
in a decrease in the electron densities of carboxylic protons and a
chemical shift of NMR signal to lower magnetic field. However,
no obvious shift or broadening was observed in the protons on the
perylene ring (Hb) with an increase in concentration, also indicative
of no H-aggregation of 3a in CDCl3 medium (Figure 3, inset).31,32
In general, the CD spectrum is the absorption difference in
circularly polarized left and right light, and the signed order of
bisignate CD Cotton effects (CEs) can be used to predict the
relative orientation based on the exciton chirality theory.33 As
expected, the reference compound of 3d is CD-silent because of
its optically inactive normal butylamine residues (Figure 4a).
Interestingly, PBIs 3a and 3b show two exact opposite CD signal
response (Figure 4a). For instance, the positive CEs at 344, 393,
446, and 587 nm and negative CEs at 530 and 562 nm (with zero
crossing at 467 and 577 nm) were observed in the CD curve for
3a in CCl4. Here the fairly strong bisignate CE (with zero
crossing at 577 nm) as well as a strong nonbisignate CE at
530 nm and a smaller nonbisignate CE at 446 nm are corresponding
to the absorption region of 480ꢀ600 nm (S0ꢀS1 transition), and
380ꢀ480 nm (S0ꢀS2 transition) from PBI, respectively.34
Moreover, in contrast with 3a and 3b, the corresponding ester
3c shows a much weaker and nonbisignate CD curve at 577 nm
(Figure 4a). Consequently, considering the difference in chemi-
cal structures between 3a (containing chiral carboxylic group)
and 3c (containing chiral ester group), the enhancement in
Cotton effect might have arisen from the possible assembly via
the intermolecular hydrogen bonding between neighboring chiral
carboxylic groups. Accordingly, MeOH is utilized as the breaking
agent of the intermolecular hydrogen bonds. Surprisingly, the
CD signals of 3a and 3b become rather decreased (Figure 4b),
and the remaining weak nonbisignated band (also include 3c in
CCl4) from 480 to 600 nm might be caused by a combinational
expression of the R-carbon chirality and the axial chirality originating
from the nonplanar structure of bay-substituted PBIs.34ꢀ36
Figure 2. Normalized fluorescence emission spectra of (a) 3a, (b) 3b,
and (c) 3c in CCl4 at the concentrations of 5 ꢁ 10ꢀ6 and 1 ꢁ 10ꢀ4 M
(before and after the addition of 5 vol % MeOH).
corrected emission spectrum with a reference of N,N0-di(2,6-di-
n-butyl)-1,6,7,12-tetrakis[4-tert-phenoxy]perylene-3,4:9,10-tet-
racarboxylic acid bisimides.30 Here the very similar fluorescence
quantum yields of 3a and 3b with 3c further rule out the pos-
sibility of πꢀπ stacking. Accordingly from the fluorescent
change, the possible intermolecular hydrogen-bonding through
chiral carboxylic group in the system of 3a and 3b can take place
upon increasing concentration in apolar solvent CCl4, whereas
MeOH can disassociate the hydrogen bonding.
Further evidence of intermolecular hydrogen bonding of PBI
In general, the positive bisignated CD signal (a first long-
wavelength positive CE, followed by a short-wavelength negative
CE) is expected that chiral excitonic couplings in PBI chromo-
phores are assembled in close proximity with their transi-
tion dipoles and oriented in a right-handed, clockwise P-helical
fashion.1,36 In this view, the extraordinarily intense exciton couplet
of 3a has a positive component at 586 nm and a negative
1
3a was gathered from H NMR analysis in a moderately polar
solvent CDCl3 (Figure 3). Interestingly, the acid protons (Ha)
were found to be significantly shifted downfield from 12.47 to
13.25 ppm with the concentration of 3a increased from 1.2 to
20 mM. It is exactly in accord with the strong intermolecular
hydrogen bonding between neighboring carboxylic groups, resulting
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ARTICLE
Figure 4. (a) CD spectra of 3aꢀ3d in CCl4 (5 ꢁ 10ꢀ5 M) at 25 °C. (b) CD spectra of 3a and 3b in MeOHꢀCCl4 (5/95, v/v) and 3c in CCl4 solution
(5 ꢁ 10ꢀ5 M). (c) Changes in CD spectra of 3a and 3b in CCl4 solution at various concentrations. (d) Changes in CD spectra of 3a in CCl4 solution
(5 ꢁ 10ꢀ5 M) from 25 to 60 °C.
Figure 5. Proposed P-helical assembly of PBI 3a via intermolecular hydrogen bonding.
component at 563 nm, attributable to the preferential formation
of a P-helix, and the mirror-image CD curve of 3b (the enantiomer
of 3a) is indicative of generating an anticlockwise M-helix.
Accordingly, the exact opposite CD signals of 3a and 3b in
CCl4 show the tendency that the enantiomeric chiral amino
residues can control the helical sense of the PBI assembling,
resulting in a chiral bias toward homochiral assembly.
The stabilization behavior of the supramolecular helical
assembly was furthered investigated with the concentration- and
temperature-dependent CD spectra. As shown in Figure 4c,
nearly four-fold increments in ellipticity values of both enantiomers
(3a and 3b) are observed with a concentration increase from
1 ꢁ 10ꢀ5 to 5 ꢁ 10ꢀ5 M, consistent with an increased degree of
intermolecular hydrogen bonding to the enhancement in the
hydrogen-bonding helical assemblies. Moreover, the CD inten-
sity of 3a becomes gradually decreased when increasing tem-
perature from 25 to 60 °C (Figure 4d), indicating the breakdown
of the hydrogen-bonding helices at high temperature. Interest-
ingly, the thermodynamic CD behavior of 3a is fully reversible
because the hydrogen-bonding helical assembly process is de-
pendent on temperature. That is, upon cooling the sample to
room temperature, the initial CD signal can be recovered.
Accordingly, a proposed mode is shown in Figure 5 that refers
to a recent calculations.37 The exact helical assembly based on
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The Journal of Physical Chemistry B
ARTICLE
two exact PBI enantiomers 3a and 3b can be realized through the
possible intermolecular hydrogen bonding between neighboring
chiral carboxylic groups, most probably with a strong tendency of
the carboxylic acid residue to form cyclic hydrogen bonded
dimers of type R22 (8)19 rather than the hydrogen-bonded catemers
PBI 3a at different temperatures (25 to 65 °C) in CCl4 at
wavelengths ranging from 300 to 650 nm was recorded.
General Procedure for PBIs 3a∼3d. A mixture of the amino
acid (0.6 mmol), 1,6,7,12-tetra(4-methylphenoxy)perylene-
3,4:9,10-tetracarboxylic acid dianhydride (0.12 mmol), and triethy-
lamine (0.2 mL) in isopropanol (8 mL) were refluxed under
nitrogen for 12 h. After being cooled to room temperature, the
reaction mixture was diluted with 2 M HCl (80 mL). The
resulting suspension was allowed to coagulate for 1 h and then
filtered on a B€uchner funnel. The residue was washed succes-
sively with water (3 ꢁ 50 mL) and dried in vacuo. The products
as dark-red powders were purified by column chromatography
on silica gel, as described below.
or imide carboxlic acid hydrogen binding motif in rare cases.38
3 3 3
Exactly, we envision that the helical stacking in the system of PBIs 3a
and 3b can be modulated by intermolecular hydrogen bonding of
the carboxylic acid units as well as van der Waals interaction of the
four bulky bay substituents.
’ CONCLUSIONS
N,N0-Di((S)-1-carboxy-1-benzyl)-1,6,7,12-tetra(4-methyl-
phenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bisimide
(3a). Purification: ethyl acetate/n-hexane (30:70); yield 125 mg
In summary, the supramolecular helices of PBIs containing
chiral amino acid residues have been successfully realized in CCl4
via hydrogen-bonding-driven self-assembly. In this way, the
fluorescence from the PBI unit does not change so much, which
is in contrast with the πꢀπ arrangement, resulting in serious
quenching in fluorescence. By fluorescence, CD, and NMR-
studies, the intermolecular hydrogen bonding can be well-devel-
oped with increasing concentration in apolar solvents but
perturbed upon the addition of MeOH or increasing tempera-
ture. The use of chiral amino acid residues may provide a new
strategy for the construction of chirality-confined superstructures
to organic chromophores with potential application in chiral
molecular recognition and guest encapsulation.
1
(0.56 mmol, 94%). Dark-red powder. Mp > 250 °C. H NMR
(400 MHz, CDCl3, δ): 13.09 (s, 2H, ꢀCOOH), 8.02 (s, 4H,
perylene-H), 7.08ꢀ7.15 (m, 10H, Ph-H), 7.05 (d, J = 8.4 Hz, 8H,
Ph-H), 6.79 (d, J = 8.4 Hz, 8H, Ph-H), 5.94 (dd, J1 = 9.2 Hz, J2 =
5.6 Hz, 2H, ꢀNCHCOOH), 3.63 (dd, J1 = 14 Hz, J2 = 5.6 Hz,
2H, PhCHHꢀ), 3.36 (dd, J1 = 14.4 Hz, J2 = 9.2 Hz, 2H,
PhCHHꢀ), 2.31 (s, 12H, Ph-CH3). 13C NMR (100 MHz, CDCl3,
δ): 20.85, 34.78, 54.44, 119.26, 119.57, 120.24, 120.30, 121.74,
126.65, 128.43, 129.19, 130.61, 132.75, 134.47, 137.16, 152.65,
156.36, 162.84, 175.36. HRMS (TOF-ESI+): calcd for C70H50-
N2O12Na+ [M + Na+], 1133.3261; found, 1133.3257.
N,N0-Di((R)-1-carboxy-1-benzyl)-1,6,7,12-tetra(4-methyl-
phenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bisimide
(3b). Purification: ethyl acetate/n-hexane (30:70); yield 120 mg
’ EXPERIMENTAL SECTION
1
(0.55 mmol, 91%). Dark-red powder. Mp > 250 °C. H NMR
General. L-Phenylalanine, L-phenylalanine methylester hydro-
(400 MHz, CDCl3, δ): 13.35 (s, 2H, ꢀCOOH), 8.01 (s, 4H,
perylene-H), 7.08ꢀ7.15 (m, 10H, Ph-H), 7.05 (d, J = 8.4 Hz, 8H,
Ph-H), 6.79 (d, J = 8.4 Hz, 8H, Ph-H), 5.93 (dd, J1 = 9.6 Hz, J2 =
5.6 Hz, 2H, ꢀNCHCOOH), 3.62 (dd, J1 = 14 Hz, J2 = 5.6 Hz,
2H, PhCHHꢀ), 3.35 (dd, J1 = 14.0 Hz, J2 = 9.6 Hz, 2H,
PhCHHꢀ), 2.31 (s, 12H, Ph-CH3). 13C NMR (100 MHz,
CDCl3, δ): 20.85, 34.79, 54.46, 119.26, 119.57, 120.24, 120.30,
121.75, 126.65, 128.43, 129.19, 130.62, 132.76, 134.47, 137.17,
152.66, 156.36, 162.85, 175.36. HRMS (TOF-ESI+): calcd for
C72H54N2O12Na+ [M + Na+], 1133.3261; found, 1133.3260.
N,N0-Di((S)-1-carbomethoxy-1-benzyl)-1,6,7,12-tetra(4-
methylphenoxy)perylene-3,4:9,10-tetracarboxylic Acid Bi-
simide (3c). Purification: dichloromethane/n-hexane (60:40),
yield 150 mg (0.13 mmol, 33%). Dark-red needle. Mp > 250 °C.
1H NMR (400 MHz, CDCl3, δ): 8.08 (s, 4H, perylene-H),
7.14ꢀ7.21 (m, 10H, Ph-H), 7.11 (d, J = 8.4 Hz, 8H, Ph-H), 6.85
(d, J = 8.4 Hz, 8H, Ph-H), 5.92ꢀ5.96 (m, 2H, ꢀNCHCO-
OCH3), 3.71 (s, 6H, COOCH3), 3.68ꢀ3.69 (m, 2H, Ph-CH2),
3.56ꢀ3.42 (m, 2H, Ph-CH2), 2.36 (s, 12H, Ph-CH3). 13C NMR
(100 MHz, CDCl3, δ): 20.85, 35.06, 52.60, 54.61, 119.31, 119.57,
120.22, 120.36, 121.90, 126.62, 128.43, 129.22, 130.63, 132.80,
134.55, 137.39, 152.69, 156.38, 162.92, 170.01. HRMS (TOF-
ESI+): calcd for C70H50N2O12Na+ [M + Na+], 1161.3574; found,
1161.3579.
chloride, and D-phenylalanine were purchased from Fluka. All
1
solvents were purified using standard procedures. H and 13C
NMR in CDCl3 were recorded on a Bruker Avance-400 spectro-
meter with tetramethylsilane (TMS) as internal reference. HRMS
were measured on a Waters LCT Premier XE spectrometer.
Melting points were determined with a hot stage apparatus and
are uncorrected. TLC analyses were performed on silica-gel
plates, and flash chromatography was conducted using silica-
gel column packages purchased from Qing-dao Haiyang Chemi-
cal (China).
Absorption, Emission, and Circular Dichroism Spectros-
copy. UV/vis absorption spectra were obtained by using a Varian
Cary 500 spectrophotometer (1 cm quartz cell) at 25 °C.
Fluorescence spectra were recorded on a Varian Cary Eclipse
fluorescence spectrophotometer (1 cm quartz cell) at 25 °C. The
slit width was 5 nm for both excitation and emission. A set of
absorption and fluorescence spectra for 3a∼3d was recorded at
different concentrations (from 5 ꢁ 10ꢀ6 to 1 ꢁ 10ꢀ4 M). CD
spectra were recorded on a JASCO J-810 spectropolarimeter at
25 °C (1 cm quartz cell). The stock solution of PBIs (1 ꢁ 10ꢀ3 M)
was prepared by directly dissolving PBIs in CCl4 and then filtered
with a 0.2 μm PTFE membrane filter disc to remove the insoluble
particles. During the measurements of CD spectra, a few milli-
liters of the sample solutions were injected into a cell, followed by
intense stirring for 10 s prior to the measurement and then
rotated 90° around the light axis for the consecutive measure-
ment to exclude the macroscopic anisotropic orientation. Each
spectrum was collected with a scanning rate of 100 nm minꢀ1, a
bandwidth of 2 nm, and a response time of 1 s. Six scans were
averaged and blank-subtracted to give the spectrum. The ellip-
ticity (θ) was expressed in millidegrees. A set of CD spectra for
N,N0-Dibutyl-1,6,7,12-tetra(4-methylphenoxy)perylene-
3,4:9,10-tetracarboxylic Acid Bisimide (3d).17 Dark-red pow-
der. Mp > 250 °C. 1H NMR (400 MHz, CDCl3, δ): 8.12 (s, 4H,
perylene-H), 7.08 (d, J = 8.4 Hz, 8H, Ph-H), 6.84 (d, J = 8.4 Hz,
8H, Ph-H), 4.10 (t, J = 7.2 Hz, 4H, ꢀNCH2), 2.33 (s, 12H,
Ph-CH3), 1.60ꢀ1.68 (m, 4H, ꢀNCH2CH2), 1.33ꢀ1.43 (m,
4H, ꢀCH2CH3), 0.91ꢀ0.94 (t, J = 7.2 Hz, 6H, ꢀCH2CH3).
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13C NMR (100 MHz, CDCl3, δ): 13.77, 20.31, 20.78, 30.14,
40.34, 119.23, 119.46, 120.11, 122.46, 130.51, 132.76, 134.28,
152.93, 156.28, 163.41.
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’ ASSOCIATED CONTENT
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Supporting Information. 1H NMR, 13C NMR, and
S
b
HRMS (TOF-ESI+) spectra of compounds 3a, 3b, 3c, and 3d
and normalized concentration-dependent absorption spectra of
3a and 3b in CCl4. This material is available free of charge via the
Internet at http://pubs.acs.org.
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’ AUTHOR INFORMATION
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Loosdrecht, P. H. M.; van Esch, J. H.; Feringa, B. L. Org. Biomol. Chem.
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Corresponding Author
*E-mail: whzhu@ecust.edu.cn. Fax: (+86) 21-6425-2758.
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’ ACKNOWLEDGMENT
This work was supported by NSFC/China, National 973
Program (2011CB808400), the Oriental Scholarship, SRFDP
200802510011, and the Fundamental Research Funds for the
Central Universities (WK1013002).
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