Synthesis and self-assembly of perylenetetracarboxylic diimide derivatives with helical oligo(l -lactic acid)n segments

Article abstract of DOI:10.1021/la303061r

Three perylenetetracarboxylic diimide (PDI) derivatives consisting of a short oligo(l-lactic acid)_n (O-LLA) segment at one imide nitrogen were synthesized. The polymers were characterized by ¹H NMR and gel permeation chromatography (GPC). Their properties were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) experiments, scanning electron microscopy (SEM), electronic absorption, and circular dichroism (CD) spectroscopy. The self-assembly behavior of these PDIs in molten state as well as in solvent was examined. It was found that the structure and the morphology of the self-assembly of these polymers depend on the relative length of the O-LLA segment. The PDIs with longer O-LLA chains present liquid crystal properties with an obvious phase transition from disordered phase to an ordered (α) phase, which cannot be found for the PDIs with short O-LLA segments. The long O-LLA segments also caused a left-handed helicity for the aggregates of the PDIs from solution. This research demonstrated that one can control the order, aggregation mode, and morphology of the molecular aggregates by changing the length of the O-LLA chains. This information can be useful in the design of new organic materials that exhibit molecular aggregation.

Full text of DOI:10.1021/la303061r

Article
pubs.acs.org/Langmuir
Synthesis and Self-Assembly of Perylenetetracarboxylic Diimide
Derivatives with Helical Oligo(L‑lactic acid)n Segments
Jun Zhou,† Lin Xue,† Yan Shi,† Xiyou Li,*,† Qingbin Xue,*,† and Shuangqing Wang*,‡
†Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, Department of Chemistry, Shandong University, Jinan
250100, China
‡Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
S
* Supporting Information
ABSTRACT: Three perylenetetracarboxylic diimide (PDI) derivatives consist-
ing of a short oligo(L-lactic acid)n (O-LLA) segment at one imide nitrogen were
synthesized. The polymers were characterized by 1H NMR and gel permeation
chromatography (GPC). Their properties were investigated by differential
scanning calorimetry (DSC), X-ray diffraction (XRD) experiments, scanning
electron microscopy (SEM), electronic absorption, and circular dichroism (CD)
spectroscopy. The self-assembly behavior of these PDIs in molten state as well
as in solvent was examined. It was found that the structure and the morphology
of the self-assembly of these polymers depend on the relative length of the O-
LLA segment. The PDIs with longer O-LLA chains present liquid crystal
properties with an obvious phase transition from disordered phase to an
ordered (α) phase, which cannot be found for the PDIs with short O-LLA
segments. The long O-LLA segments also caused a left-handed helicity for the
aggregates of the PDIs from solution. This research demonstrated that one can control the order, aggregation mode, and
morphology of the molecular aggregates by changing the length of the O-LLA chains. This information can be useful in the
design of new organic materials that exhibit molecular aggregation.
from the self-assembly of amphiphilic PDI has also been
prepared by the same group. It can be used to separate
nanoparticles by size.18 The self-assembly of PDI has also been
used to fabricate a gas sensor, which shows high sensitivity
toward explosives.19,20 PDIs connected with DNA chains were
prepared by Li and co-workers. The resulted thermophilic
foldable polymer shows significant changes in fluorescence due
to the unfolding driven by the DNA hybridization, and
therefore can be used as DNA sensor.21 Other amphiphilic
diimide chromophores have also been reported recently, which
can controllably self-assemble into nanotubes and might be
promising functional components for mesoscopic scale opto-
electronics.22,23
Poly(L-lactide) (PLLA) is a biodegradable semicrystalline
polymer, which is widely investigated as a biomedical and
biocompatible material. The mechanical properties of PLLA
depend on the crystalline−amorphous structure, which vary
with the crystallization conditions from the melt.24−26 The
structure of the crystals was first determined by De Santis and
Kovacs27 as left-handed 103-helices (10 LLA units formed three
circles) in quasi-hexagonal manner into an orthorhombic unit
cell. Slight distortions of the basic helical conformation due to
interchain forces were observed by vibrational spectrosco-
INTRODUCTION
■
Perylenetetracarboxylate diimides (PDI) are currently being
investigated for use in a variety of photoactive organic materials
because of their low light and thermal fading rates, unique
optoelectronic properties, and high luminescence efficiency.1−3
They were widely used in light-harvesting solar cells, organic
field-effect transistors, and light-emitting diodes as robust
organic dyes.4−9 They were also proved to be excellent building
blocks for self-organized molecular materials with highly
ordered structure due to the strong π−π interactions between
the planar PDI rings.10−13
Recently, different functional groups have been introduced to
the imide nitrogen atoms or the bay (1, 2, 6, or 7) positions of
PDI ring aimed at modifying the micro structures as well as the
morphology of the molecular aggregates. Shinkai and co-
workers have prepared a series of PDI compounds by
connecting cholesterol groups at the imide nitrogen positions,
which can form an organic gel with light-harvesting function.14
Wurthner and co-workers have reported a highly fluorescent
̈
organic gel based on a PDI compound functionalized with urea
groups.15 Vesicular nanocapsules prepared from amphiphilic
PDI can serve as a pH sensor based on an intramolecular
energy transfer mechanism.16 Rybtchinski has prepared an
amphiphilc PDI compound by connecting a long hydrophilic
chain at the bay positions. This compound can form linear
molecular aggregates and perform different response toward
multiple outer stimuli.17 A recyclable membrane fabricated
Received: January 5, 2012
Revised: September 6, 2012
Published: September 18, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of the Initiator PDIOH and Polymers PDI-OLLAn
py.28,29 Among them, helical morphologies in different length
scales such as chiral centers, helical chain conformations, helical
aggregations, and helical agglomerates have all been demon-
strated.30−37
Table 1. Molecular Weight and Degree of Polymerization of
PDI-OLLAn Obtained by H NMR and GPC Methods
1
theoretical
1H NMR
GPC
n
Mn
n
Mn
Mn
Mw
Mw/Mn
In this Article, a series of PDI-OLLA polymers with different
lengths of the O-LLA segments were prepared by typical ring-
opening polymerization (ROP) sequence (Scheme 1). The
objective of this research is to examine the effects of liquid
crystal OLLA segments on the aggregation behavior of PDI
molecules, which might bring a new entry to vary the optical
properties of PDIs in solid films by outer stimulus, such as
temperature. On the basis of molecular weight, these polymers
were labeled as PDI-OLLAn, with n representing the average
numbers of the repeating unit for OLLA chains. The self-
assembly behavior of these PDI-OLLAn polymers with different
length of OLLA segments was comparatively investigated,
revealing the effect of the length of the OLLA chains covalently
linked to the PDI on the structure and morphology of the self-
assembled nanostructures. The finding of this research will be
helpful in the design of new PDI-based functional materials
with controllable microstructure and morphology.
PDI-OLLA10
PDI-OLLA30
PDI-OLLA50
10
30
50
2206
3646
5086
10
31
46
2206
3722
4798
1938
3122
4550
2532
4500
6201
1.31
1.44
1.36
Thermal Behavior of PDI-OLLAn. The thermal behavior of
these polymers was evaluated by DSC measurements. Two heat
scans were performed for each sample, and the results are listed
in Table 2 and Figure 1.
Table 2. Phase Transitions of PDI-OLLAn Observed by DSC
(°C)
a
samples
Tg
Tm
Ti
ΔHm (J/g)
χc (%)
PDI-OLLA10
PDI-OLLA30
PDI-OLLA50
36.2
48.2
52.5
140.0
143.7
146.9
157.2
159.6
160.8
1.7
16.6
28.4
6.0
27.9
53.0
a
The ΔHm of the complete crystal of PLLA is 93.7 J/g.
RESULTS AND DISCUSSION
■
ROP of L-LA. Stannous octoate, SnOct2, was redistilled
three times, and L-lactide (L-LA) was purified by two times
recrystallization from ethyl acetate and one more time
recrystallization from toluene and vacuum-dried to constant
weight to remove any possible impurities containing OH
groups. The ROP reaction usually is completed in 10 h at 100
°C in toluene. The synthetic procedures are shown in Scheme
1.
In the first scan, PDI-OLLA10 and PDI-OLLA30 present three
endothermic transitions, which correspond to structural
relaxation associated with glass transition temperature at
lower temperature range, and one transition corresponds to
the melting behavior of PDI segment. Besides the three
transitions observed for PDI-OLLA10 and PDI-OLLA30 in the
low temperature range, PDI-OLLA50 presents one more
endothermic transition at about 149 °C, which corresponds
to the melting behavior of the crystallized OLLA segment. In
the second scan, the melting of this crystallized OLLA is not
observed, as the system had a short time to undergo structural
relaxation and crystallization during the cooling course after the
first scan. The endothermic transition at about 159 °C can be
assigned to the melting behavior of PDI segments. The Tg
values are more evident for the second scan than for the first
Molecular Weight of PDI-OLLAn. The molecular weights
of PDI-OLLAn were determined by 1H NMR and GPC
methods. The results are summarized in Table 1. The measured
1
molecular weights by H NMR and GPC methods were in
good agreement with the theoretical prediction and found to be
well controlled by the feed molar ratios of L-LA to PDIOH
(Table 1).
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Figure 2. Absorption (−) and fluorescence (− − −) spectra (excited
at 430 nm) of PDI-LLA10 in chloroform (5 × 10−6 mol L−1).
The molten sample (at 230 °C) was cooled to room
temperature with a controlled speed (2 °C/min). The films
prepared in this way were designed as molten film. The
solution-precipitated aggregates were prepared by injecting a
polymer solution (2 mg/mL, 1 mL) in dichloromethane into a
large volume of methanol (100 mL). The resulted mixture was
aged at room temperature overnight, and then the suspension
of the molecular aggregates was transferred to the glass
substrate by a dropper. After the solvents were evaporated to
dryness at room temperature, the samples were subjected to
spectroscopic and morphology examination. The solids
prepared in this way are designed as aggregates. The absorption
spectrum of PDI normally shows three pronounced peaks in
the range of 350−575 nm, which correspond to the 0−0, 0−1,
and 0−2 vibronic transitions, respectively. Yet the absorption
spectra of the molten films and the aggregates of these three
compounds changed dramatically from their monomer, Figure
3A and B. The transitions from ground state to the higher levels
of vibration states (0−1 and 0−2) are enhanced as compared to
the 0−0 transition. Such a spectral change implies strong
molecular stacking between the PDI skeletons in the solid-state
molten films and aggregates. Meanwhile, the pronounced
absorption band at longer wavelength (575 nm) is also a typical
indication of the effective π−π interactions in cofacially
arranged molecular stack.47 The polarized absorption spectra
of these polymers in molten film are recorded under both
parallel or vertical polarized incident light. The spectra are
shown in Figures S9−12 in the Supporting Information. The
small difference between the absorption spectra of different
polarized light suggests that the PDI units in the molten film do
not pack with long-range order in one direction. This point is
also supported by the SEM images as shown later.
Figure 1. DSC scans of PDI-OLLAn.
one as indicated by the increase in heat capacity reflected by the
step of the traces.
Additionally, the crystallinity of the samples can be estimated
on the basis of the melting enthalpy via the following equation:
ΔHm
χ =
× 100%
ΔHm0 ·w
where ΔHm is the melting enthalpy of the sample, ΔH0m is the
melting enthalpy of 100% crystalline OLLA (93.7 J/g),38 and w
is the weight fraction of OLLA in the polymers. Apparently the
χc39 values increased with the increase of OLLA chain length,
indicating a stronger crystallization tendency for higher
molecular weight OLLA.
Absorption Spectra, Circular Dichroism Spectra, and
Fluorescence Spectra. UV−vis absorption and fluorescence
spectra of PDIs are sensitive to the interchromophore
orientation and distance40,41 and have been widely used to
study their π−π stacking.42−44 The absorption and fluorescent
spectra of these compounds in chloroform are similar, and
those of PDI-OLLA10 are shown in Figure 2 as a representative.
The absorption spectra of these four compounds in chloroform
exhibit typical spectroscopic features that are expected for
monomeric diphenoxy-substituted PDI chromophores.13,45 The
spectra show two peaks at 550 and 515 nm, which correspond
to the 0−0 and 0−1 transitions, respectively.46 The emission
spectrum presents a maximum emission peak at 585 nm, which
is similar to that of monomeric PDI and suggests that the PDI
molecules in chloroform do not show any interactions between
each other in diluted solution. Yet these polymers show
significant aggregation in mixed solvents of CHCl3/CH3OH as
indicated by the blue-shifted absorption maximum and
broadened absorption band (Supporting Information, Figures
S1−S8).
The fluorescence spectra of the molten films of these three
polymers show a broad emission band at about 670 nm, Figure
4A. The fluorescence lifetime measurement revealed longer
fluorescence lifetimes for this emission band, Table 3. This
band can be assigned to the emission of excimer.13 Small
differences were identified between the emission spectra of
these three polymers. The maximum emission peak of PDI-OH
molten film is found at 678 nm, but this peak blue-shifted to
668 nm for PDI-OLLA10 molten film, 665 nm for PDI-OLLA30
molten film, and 659 nm for PDI-OLLA50 molten film. This
change in the maximum emission peak can be ascribed to the
influence of OLLA on the micro stacking manner of PDI units.
The absorption and emission spectra of these polymers are
also measured in their molten thin solid films or precipitated
aggregates from solution. The thin solid films are prepared by
depositing the polymer solids on a glass substrate, and then the
glass substrate was heated on a hot plate to melt the sample.
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Figure 3. Absorption (A,B) and circular dichroism spectra (C,D) spectra of PDI-OLLA10, in molten film (A,C) and solution precipitated aggregates
films (B,D). The dashed lines are the spectra of PDIOH in solution.
excimer emission of these three polymers in relation to that of
PDIOH might be ascribed to the deviation of the stacked
structure of PDI units from a strictly face-to-face stacking to a
slipped face-to-face stacking. The larger OLLA group will cause
larger blue shift of the emission peak and more significant
deviation from strictly face-to-face stacked structure. This
means the aggregation of these polymers in molten films is
affected significantly by the OLLA chains.
The fluorescence spectra of the aggregates of these three
polymers are shown in Figure 4. A small emission band at about
580 nm, which can be assigned to the emission from
monomeric PDI, is found for PDIOH, PDI-OLLA10, and
PDI-OLLA30. The maximum emission bands at about 660 nm
of these three polymers are similar and can be assigned to the
emission of excimer based on the maximum emission
wavelength and the lifetime measured.13 This emission band
show a small blue shift in comparison with that of PDIOH.
This result suggests that the micro structure of the stacked
PDIs in the precipitated aggregates is less sensitive to the length
of the OLLA chain than that in the molten films. In another
word, the aggregation process of these molecules during the
Figure 4. Fluorescence spectra of the molten films (A) and
precipitation from solution is probably dominated by the PDI
■
precipitated aggregates (B) of compounds PDIOH ( ), PDI-
parts of the molecules instead of the OLLA chains. More
interestingly, the maximum emission band of the aggregates
precipitated from solution of PDIOH is significantly blue-
shifted relative to that of molten films. This means that the PDI
units of PDIOH in the solution-precipitated aggregates do not
form a strictly face-to-face stacked structure, but a slipped or
twisted stacked structure instead. Similarly, the emission bands
of these three polymers blue-shifted a little bit in relation to
that of molten films. This indicates also that the PDI in the
aggregates adapted a more slipped or twisted stacked structure
than that in molten films.
◆
( ).
●
▲
), and PDI-OLLA50
OLLA10 ( ), PDI-OLLA30
(
Table 3. Fluorescence Quantum Yields (Φf) and Lifetimes
(τ)
in chloroform
aggregates
molten films
a
a
a
compounds
Φf
τ
Φf
τ
Φf
τ
PDIOH
0.77
0.63
0.62
0.61
4.37
4.40
4.32
4.45
0.18
0.09
0.08
0.08
14.6
17.1
15.8
16.3
0.11
0.04
0.04
0.03
15.8
15.3
15.0
14.2
PDI-OLLA10
PDI-OLLA30
PDI-OLLA50
The fluorescence quantum yields for PDIOH, PDI-OLLA10,
PDI-OLLA30, and PDI-OLLA50 are measured, and the results
are summarized in Table 3. It can be found that the
fluorescence quantum yields (Φf) of these compounds in
solution are large, which suggest that no aggregation in solution
happened. Yet in the solid states, the fluorescence quantum
yields decrease significantly. This can be ascribed to the
a
τ values are measured at 680 nm.
A PDI dimer with rigid face-to-face stacked structure shows an
excimer emission at about 705 nm,41 but a similar dimer with
relatively flexible face-to-face stacked structure shows excimer
emission at about 625 nm.48 Therefore, the blue shift of the
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Figure 5. SEM images of the solution-precipitated aggregates of PDI-OLLA10 (A,D), PDI-OLLA30 (B,E), and PDI-OLLA50 (C,F).
formation of H-type molecular aggregates. More importantly,
the fluorescence quantum yields for the aggregates precipitated
from solution show relatively larger Φf than that of molten
films. This indicates that the stacking structure for the PDI
units in the solution precipitated aggregates is more seriously
slipped or twisted from the face-to-face stacking, which
corresponds very well with the results of fluorescence spectra
as shown in Figure 4.
with the change in the length of OLLA chains. Longer OLLA
caused the formation of short nanoribbons with large width,
whereas short OLLA segments induce the formation of long
fibers with small width. It is clear that these ribbons consist of
bundles of single, twisted strands. The morphology of the
molten films shows a flat surface; no fine structure or veins can
be identified from the SEM images.
X-ray Diffraction Patterns of the Aggregates. To
obtain information about the internal structure of the thin solid
films and the aggregates precipitated from solution, XRD
experiments are performed on these solids. The XRD patterns
are compared in Figure 6. In the wide-angle region of the X-ray
diffraction patterns obtained for the molten films, a broad peak
in the region of 15−30°, with d space around 0.40 nm, can be
found, which can be attributed to the liquid-like order of the
alkyl chains.52 In the diffraction pattern of PDI-OLLA10, a
broad diffraction peak appeared at 2θ = 19.06°, which can be
ascribed to the formation of PLLA crystals with small crystallite
size.53 This peak becomes more apparent for PDI-OLLA30 and
PDI-OLLA50 molten films. A group of sharp diffraction peaks
found in the same region for PDI-OLLA30 and PDI-OLLA50
molten films can be assigned to the (110), (100), (203), and
(205) diffractions of the α-form crystal of PLLA as have been
reported by Miyata.39 The diffraction peak at about 2θ = 5.45°,
corresponding to a d space of about 1.60 nm, can be assigned to
the length of the PDI units as shown in Figure 5. The intensity
of this diffraction peak decreases obviously along with the
increase in the size of OLLA segment. This result suggests that
the longer OLLAn segments cut down the packing order of PDI
units in the molten films.
In the diffraction profile of the precipitated aggregates, the
broad diffraction peak around 2θ = 21° and d = 0.40 nm is not
found, which suggests that the packing of the long alky chains
in these precipitated aggregates is orderless. Yet the diffraction
peak at 2θ = 28.5°, with d = 0.31 nm, corresponding to the
distance between the PDI rings of the adjacent molecules,54 is
more significant than that for the molten films. A diffraction
peak at 2θ = 16.4° with d = 0.54 nm is observed in the
diffraction pattern of the precipitated aggregates of PDI-
OLLA50, which is missing in the diffraction of PDI-OLLA10 and
PDI-OLLA31 and can be attributed to the α-form crystal of
PLLA as reported by Miyata.39
In the CD spectra of the aggregates, Figure 3C and D,
negative bisignate Cotton effects [570(−)/476(+)] are
observed in the absorption region of PDI units for all three
polymers in molten films as well as in precipitated aggregates,
which indicates the presence of left-handed chirality of the
dipole moment (negative chirality)49 in the solid state.
However, we do not find any CD signals in dilute chloroform
solutions. According to Meskers and Aida,50 the CD signals can
be induced by the linear alignment of molecules in thin solid
film. To find out the origin of these CD signals of these
polymer thin solid films, we measured the CD spectra of
stacked two-layer polymer films with different rotated angles of
one layer against the other one following the method described
by Meskers. Bisignate CD effects are observed, whose intensity
depends on the angle of rotation of one layer film against the
other, but the negative bisignate Cotton effects do not change
(Supporting Information Figure S13). This phenomenon is
similar to that observed for a chiral oligo(p-phenylene vinylene)
compound and suggests that the CD signals obtained for the
thin solid films of these three polymers are caused by both
linear alignment and left-handed helical arrangement of the
molecules in molten films and aggregates.50a,51 These results
confirm the effect of the long OLLA segment on tuning the
PDI chromophore packing mode and supramolecular chirality
in molecular aggregates. All of the compounds show similar
behavior in the CD spectra; no obvious difference can be
identified between these three polymers.
Morphology of the Aggregates. The morphologies of
the precipitated aggregates are examined by scanning electron
microscopy (SEM). As can be found in Figure 5, these
polymers self-assemble into long, twisted fibrous nanostruc-
tures with approximately several tens of micrometers in length
and hundreds of nanometers in width. Further careful
inspection over these nanoribbons revealed that the dimensions
of these one-dimensional nanostructures were changed along
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Figure 6. XRD scans of PDI-OLLA10, PDI-OLLA30, and PDI-OLLA50.
By comparing the XRD profile of the precipitated aggregates
with that of the molten thin solid film, we can conclude that the
PDI aromatic rings in solution-precipitated aggregate packed
with high order. However, during the cooling process from a
molten state to a solid state, the aggregation of the polymer
molecules is dominated by the long alkyl chains and the OLLA
segment and results in a highly ordered alkyl chain packing and
OLLA packing in the thin solid film. This phenomenon might
be caused by the ordered alignment of OLLA segment in
molten state, which drives the PDI units to change their
packing structure accordingly. This results corresponding well
with the results of absorption and fluorescence spectra as
mentioned above.
CONCLUSION
■
A series of PDI compound connected with L-lactic acid
oligimers of different length have been prepared successfully.
The attachment of low molecular weight L-lactic acid oligomers
can significantly affect the self-assembly properties of PDI. The
helicity of the L-lactic acid segments induces left-hand
arrangement of the PDI units in the molten films or solution-
precipitated aggregates. During the cooling process from
molten state to solid state, the OLLA segment as well the
long alkyl chains packed together with long-range order and
had larger effects on the aggregation of PDI units and affect the
fluorescence spectra significantly. However, during the
precipitating from solution, both the alkyl chains and the
OLLA chains do not form ordered structure. The aggregation
behavior can be schematically described by Figure 7. The
present results reveal that introducing liquid crystal OLLA
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Figure 7. Comparison of the aggregation behavior of these polymers in solution-precipitated aggregates or molten films.
N-Amino-1-hexanol-1,7-di(p-t-butyl)phenoxy-perylene-3,4-dicar-
boxylic anhydride- 9,10-dicarboxyimide. 1,7-Di(p-t-butyl-phenoxyl)-
3,4,9,10-tetracarboxylic dianhydride (500 mg, 0.73 mmol) was
dissolved in 30 mL of pyridine, and a solution of 6-amino-1-hexanol
(85 mg, 0.73 mmol) in 20 mL of pyridine was added dropwise. The
mixture was refluxed at 116 °C for 1.5 h. After being cooled to room
temperature, the solvent was evaporated. The residue was purified by
column chromatography on silica gel (CH2Cl2 as eluent) (57.4 mg,
10%). 1H NMR (300 MHz, CDCl3): δ = 9.65 (m, 2H), 8.65 (m, 2H),
8.35 (d, 2H), 7.50−7.53 (d, 4H), 7.13 (d, 4H), 4.15 (t, 2H), 3.63 (t,
2H), 1.25−1.71 (m, 26H). MS (MALDI-TOF): m/z, calculated for
C50H45NO8, 787.32; found, 787.90 [M+].
segment to a PDI derivative could introduce a special
aggregation behavior for the PDI units during the solidification
from a molten state. This finding might be useful for the design
of novel thermal-sensitive fluorescent PDI compounds.
EXPERIMENTAL SECTION
■
1
Measurements and Characterization. H NMR spectra were
recorded on a Bruker DPX 300 spectrometer (300 MHz) in CDCl3.
Spectra were referenced internally by using the residual solvent
resonance (δ = 7.26 for CDCl3) relative to SiMe4. GPC measurements
were performed on an HPLC equipped with 515HPLC pump and
HR3/HR4/HR6 columns at 1.00 mL/min using THF as eluent under
40.0 °C with polystyrene as standard (Shodex Standard SL-105,
Japan). Differential scanning calorimeter (DSC) measurements were
performed on a DSC-SP (Rheometric Scientific Inc., NJ) from −50−
200 °C under inert N2 atmosphere with a scanning rate of 10 °C/min.
Typically, samples weighting about 5.0 mg were heated (10 °C/min)
in Al crucibles from −50 to 200 °C. Normally two circles of heating at
same scan rate were performed. Low-angle X-ray diffraction (XRD)
measurements were carried out on a Rigaku D/max-γB X-ray
diffractometer with a Cu Kα sealed tube (λ = 0.15406 nm) at 293
K. Scanning electronic microscopy (SEM) images were obtained using
a JEOL JSM-6700F field-emission scanning electron microscopy. For
SEM imaging, Au (1−2 nm) was sputtered onto the grids to prevent
charging effects and to improve image clarity. UV−vis absorption
spectra were recorded on a Hitachi 4100 spectrometer. Fluorescence
spectra and fluorescence lifetimes were recorded on a K2 system of
ISS. The absolute fluorescence quantum yields of these compounds in
solution as well as in films or solid aggregates were measured on a
Hamamatsu Quantaurus QY instrument. Circular dichroism (CD)
spectra were recorded on a J-810-150 L spectropolarimeter (Jasco,
Japan).
N-Amino-1-hexanol-N′-(2-aminoethyl)-3,4,5-tris(dodecyloxy)
Benzamide-1,7-di(p-t-butylphenoxy)perylene-3,4;9,10-tetracarbox-
ylate Diimide. A mixture of N-amino-1-hexanol-1,7-di(p-t-butyl)-
phenoxy-perylene-3,4-dicarboxylic anhydride-9,10-dicarboxyimide
(200 mg, 0.254 mmol), N-(2-aminoethyl)-3,4,5-tris(dodecyloxy)
benzamide (500 mg, 0.70 mmol), and pyridine (15 mL) was heated
to 116 °C under N2 atmosphere. The reaction mixture was stirred
continuously for 60 min at this temperature until the reaction finished
from the detection of TLC. The solvent was evaporated under reduced
pressure, and the residue was purified by column chromatography on
silica gel with chloroform as eluent. The main fraction contains
product HOPDI (302.2 mg, yield 80%). MALDI-TOF MS (m/z):
1
calcd for C95H127N3O11, 1485.95; found, 1487.03. H NMR (CDCl3,
300 MHz): δ 9.57−9.53 (m, 2H), 8.65−8.62 (m, 2H), 8.29 (s, 1H),
8.26 (s, 1H), 7.47 (d, 4H), 7.09 (d, 4H), 6.9 (d, 2H), 4.55 (t, 2H),
4.12 (t, 2H), 3.99−3.84 (b, 8H), 3.60 (b, 2H), 1.83−1.66 (b, 6H),
1.59 (m, 2H), 1.25−1.22 (m, 54H), 0.88 (t, 9H).
Ring-Opening Polymerization of L-LA. A general procedure for
the ring-opening polymerization (ROP) of L-LA was shown in Scheme
1. The feed ratios of LLA to HOPDI and SnOct2 were adjusted to get
oligomers/polymers of different molecular weight. The procedure was
briefly described as follows:58 the proper amount of L-LA, HOPDI
were vacuum-dried at near 50 °C for 3 h and then mixed with SnOct2
solution in toluene with a typical ratio (x:1:1, x = 5, 15, 25) and
toluene. After being stirred for 10 h at 100 °C, the viscous mixture was
cooled and evaporated to dry. Next, the residual was dissolved in
CH2Cl2 and washed with 1 M HCl aqueous and water, respectively.
After being concentrated under reduced pressure to a third of the
volume, the solution was then poured into petroleum ether. The
precipitate was collected as the targeted compounds.
Materials. L-Lactide (LLA) was purified by repeat recrystallization
from ethyl acetate and toluene, respectively, and then with vacuum-
drying at room temperature to constant weight. Stannous octoate,
SnOct2, was redistilled three times as reported in ref 55. Toluene
(AR) was refluxed over Na for 24 h, and then distilled under nitrogen
atmosphere just before use. 1,7-Di(p-t-butyl-phenoxyl)-3,4,9,10-
tetracarboxylic dianhydride56 and N-(2-aminoethyl)-3,4,5-tris-
(dodecyloxy) benzamide57 were synthesized following the previously
reported methods. All other chemicals were purchased from
commercial source. Column chromatography was carried out on silica
gel (Merck, Kieselgel 60, 70−230 mesh) with the indicated eluent. All
other reagents and solvents were used as received without further
purification.
PDIOPLLA10. 1H NMR (CDCl3, 300 MHz): δ 9.60 (q, 2H), 8.69−
8.59 (m, 2H), 8.38 (d, 1H), 8.28 (s, 1H), 7.47 (d, 4H), 7.09 (d, 4H),
6.92 (d, 2H), 5.23−5.01 (m, 10H), 4.52 (d, 2H), 4.38−4.32 (m, 1H),
4.11 (m, 2H), 3.99−3.92 (b, 6H), 3.60 (b, 2H), 1.78−1.68 (m, 6H),
1.37 (s, 9H), 1.25−1.22 (m, 54H), 0.87(t, 9H).
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Article
PDIOPLLA30. 1H NMR (CDCl3, 300 MHz): δ 9.66 (q, 2H), 8.69−
8.58 (m, 2H), 8.38 (d, 1H), 8.28 (s, 1H), 7.47 (d, 4H), 7.09 (d, 4H),
6.92 (d, 2H), 5.25−5.10 (m, 31H), 4.56 (d, 2H), 4.38−4.32 (m, 1H),
4.14 (m, 2H), 4.02−3.92 (b, 6H), 3.60 (b, 2H), 1.78−1.68 (m, 6H),
1.37 (s, 9H), 1.25−1.23 (m, 54H), 0.87 (t, 9H).
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PDIOPLLA50. 1H NMR (CDCl3, 300 MHz): δ 9.60 (q, 2H), 8.69−
8.59 (m, 2H), 8.38 (d, 1H), 8.28 (s, 1H), 7.47 (d, 4H), 7.09 (d, 4H),
6.92 (d, 2H), 5.20−5.13 (m, 43H), 4.57 (d, 2H), 4.38−4.32 (m, 1H),
4.12 (m, 2H), 3.98−3.92 (m, 6H), 3.60 (m, 2H), 1.80−1.68 (m, 6H),
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ASSOCIATED CONTENT
* Supporting Information
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Organogel Composed of Cholesterol-Based Perylene Derivatives.
Angew. Chem., Int. Ed. 2004, 43, 1229−1233.
■
S
Absorption spectra of PDI-OLLAn in chloroform with different
contents of methanol. Polarized absorption spectra of the
solution precipitated aggregates and the molten films. CD
spectra of two-layer stacked molten films at different rotation
angles between the two layers. This material is available free of
charge via the Internet at http://pubs.acs.org.
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Bisimide Dye. Org. Lett. 2005, 7, 967−970.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: xiyouli@sdu.edu.cn.
Notes
■
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
Financial support from the Natural Science Foundation of
China (21073112, 21173136) and the Natural Science
Foundation of Shandong Province (ZR2010EZ007) is grate-
fully acknowledged.
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