Structural and property comparison between the di-piperidinyl- and di-pyrrolidinyl-substituted perylene tetracarboxylic diimides

Article abstract of DOI:10.1002/poc.1799

Four compounds 1-4 connected with cyclic amino groups at the bay positions of perylenetetracarboxylic diimide (PDI) have been prepared and the isomers with 1,7- and 1,6-substituted PDIs were successfully separated by conventional column chromatography. Th

Full text of DOI:10.1002/poc.1799

Research Article
Received: 31 March 2010,
Revised: 15 August 2010,
Accepted: 25 August 2010,
Published online in Wiley Online Library: 22 October 2010
(wileyonlinelibrary.com) DOI 10.1002/poc.1799
Structural and property comparison
between the di-piperidinyl- and
di-pyrrolidinyl-substituted perylene
tetracarboxylic diimides
Junqian Fenga,b, Delou Wanga, Hailong Wanga, Daopeng Zhanga,
Liangliang Zhanga and Xiyou Lia
*
Four compounds 1–4 connected with cyclic amino groups at the bay positions of perylenetetracarboxylic diimide (PDI)
have been prepared and the isomers with 1,7- and 1,6-substituted PDIs were successfully separated by conventional
column chromatography. The structures of 1,7-dipyrrolidinyl-substituted PDI (1) and 1,7-dipiperidinyl-substituted PDI
(3) were further characterized by single crystal X-ray diffraction experiments. The crystal structure revealed that the
small difference in the molecular structure has caused significant difference on the absorption and emission spectra as
well as the electrochemical properties. The shorter bond length of C1—N3, together with the more sp2 hybrid atomic
orbital characteristics of the nitrogen atom in pyrrolidine relative to those in piperidine is found to be responsible for
this large property difference between 1 and 3. Copyright ß 2010 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this paper.
Keywords: crystal structure; perylene tetracarboxylic diimide; photophysical properties; pyrrolidine; piperidine
pyrrolidine or piperidine leads inevitably to the formation of a
mixture of 1,7 and 1,6 isomers.[32] Fortunately, these two isomers
INTRODUCTION
Perylenetetracarboxylic diimides (PDIs) have attracted much
interest and found wide range applications in diverse fields of
current research because of their excellent thermal- and
photostability, high luminescence efficiency, and novel opto-
electronic properties.[1–4] Because the low solubility of PDIs in
conventional organic solvents always induces difficulties on the
synthesis and purification, bay substitution is recently popularly
employed as an efficient way to improve the solubility of PDI
compounds. Furthermore, bay substitution has been found to be
very efficient on varying the physical properties of PDIs.
Therefore, developing new PDI compounds for different
particular applications by introducing different side groups at
bay positions has attracted a lot of attention in the past decade.
Amino group substituted PDIs represent a very important
category of these PDIs derivatives, which are characterized with
their blue–green color, long wavelength absorption and
emission, as well as environmental sensitive photophysical
property. The application researches of these compounds as
photosensitizers in photodynamic therapy,[5] molecular
switches,[6] light-harvesting antenna arrays,[7,8] and dye sensi-
tized solar cell,[9–12] and other functional materials have been
reported in literatures.[13–30]
can be separated by column chromatography and the molecular
structure can be fully characterized by 1H NMR and mass spectra.
Tian et al. prepared regioisomerically pure 1,6-dipyrrolidine PDI
first and found that it presents significantly different properties
from its 1,7 isomer.[33] Wasielewski compared the properties of
1,6- and 1,7-bis(n-octylamino)-substituted PDIs.[34] The electron
paramagnanetic resonance (EPR) study together with the Density
Functional Theory (DFT) calculation revealed that the substitution
pattern strongly affects the electronic structure of the radical
cations of these amine-substituted PDIs. Champness has
successfully prepared 1,6- and 1,7-dimorpholino PDIs[35] and
observed an unusual two-electron oxidation process for the
1,7-isomer.
Ever since the first time successful preparation of 1,7-dipyrrolidinyl
or piperidinyl-substituted PDIs in 1999,[31] the significant differences
on the absorption spectra between pyrrolidinyl- and piperidinyl-
substituted PDIs were noticed but without further discussion. The
large difference on the absorption spectra is interesting because of
*
Correspondence to: X. Li, Department of Chemistry, Shandong University,
Jinan 250100, China.
E-mail: xiyouli@sdu.edu.cn
1,7-Dipyrrolidinyl- or piperidinyl-substituted PDIs had been
prepared firstly by Wasielewski in 1999 by the nucleophilic
substitution of 1,7-dibromo PDI by pyrrolidine or piperidine,
respectively.[31] Because 1,7-dibromo PDI is always contaminated
with 1,6-dibromo isomer, which cannot be separated by column
chromatography, the nucleophilic substitution of dibromo PDI by
a
J. Feng, D. Wang, H. Wang, D. Zhang, L. Zhang, X. Li
Department of Chemistry, Shandong University, Jinan, China
b
J. Feng
College of Shandong Policeman, Jinan, China
J. Phys. Org. Chem. 2011, 24 621–629
Copyright ß 2010 John Wiley & Sons, Ltd.

J. FENG ET AL.
their very similar molecular structure. Further understanding on this
difference might be helpful to reveal the origin of the effects
of the bay substituents on the properties of PDI compounds.
However, the detailed comparison between the properties
of 1,7-dipyrrolidinyl- or piperidinyl-substituted PDIs has never
been made. The present paper focuses on the difference
of the structural and photophysical properties of the dipyrro-
lidinyl- or dipiperidinyl-substituted PDIs at 1,7 or 1,6 positions.
For this purpose, four PDI compounds, namely, N,N0 -dibutyl -
1,7-dipyrrolidinyl-3,4:9,10-perylenetetra carboxylic diimide (1),
N,N0-dibutyl-1,6-dipyrrolidinyl-3,4:9,10-perylene tetra carboxylic dii-
mide (2), N,N0-dibutyl-1,7 -dipiperidinyl -3,4:9,10 -perylenetetra-
carboxylic diimide (3), and N,N0 -dibutyl -1,6-dipiperidinyl-
3,4:9,10-perylene-tetra carboxylic diimide (4) were prepared
(Scheme 1). The single crystals for 1,7-disubstituted compounds
1 and 3, which are large enough for single crystal X-ray diffraction
experiments, are obtained. The minor difference on the structure
between pyrrolidine and piperidine leads to significant difference
on the photophysical properties and bulky packing behavior
between 1 and 3 as well as 2 and 4 as revealed in crystal structure
and DFT calculation. We believe that the finding of this research
will be helpful for the design of novel PDIs that maybe useful for
molecular optoelectronic devices.
Figure 1. The absorption spectra of compounds 1–4 in CH2Cl2 com-
pared with that of standard compound 5 in the same solvent (10ꢀ5M)
chromatography.[32,33] The structures of these compounds were
fully characterized by different spectroscopic methods, including
1H and 13C NMR, MALDI-TOF mass spectrometry, and elemental
analysis.
UV–vis absorption
RESULTS AND DISCUSSION
Figure
1 compares the electronic absorption spectra of
compounds 1–4 with model compound N,N0-dibutyl-perylene
-3,4:9,10-tetracarboxylic diimide (5) in dichloromethane. The
measured spectral parameters are summarized in Table 1. All of
these compounds show intense absorption in the UV–vis region.
The maximum absorption band of compounds 1, 2, 3, and 4 is
red-shifted for about 175, 158, 157, 127 nm, respectively, relative
to that of 5 because of the introduction of pyrrolidinyl or
Synthesis
The isomeric mixture N,N0-dibutyl-dibromo-3,4:9,10 -perylene
-tetracarboxylic diimide was heated in pyrrolidine or piperidine
to give the corresponding dipyrrolidinyl- or dipiperidinyl-
substituted PDI isomeric mixture, respectively. The mixtures
can be separated from each other by conventional column
Scheme 1. Synthesis of compounds 1–4
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PROPERTY COMPARISON BETWEEN TWO PDIS
Table 1. The spectral parameters of compounds 1–4 and model compound 5
Compounds
1
2
3
4
5
labs (nm)
lem (nm)
Ff (430) (%)
698
739
681
735
<0.01
<0.01
0.05
—
680
757
650
761
<0.01
<0.01
<0.01
—
523
532
100
100
100
3.84
3.82
3.82
Toluene
THF
CH2Cl2
Toluene
THF
0.25
0.16
0.79
2.63
1.93
1.98
0.015
0.016
0.08
1.85
1.15
1.23
tf (ns)
—
—
—
—
CH2Cl2
piperidinyl group at the bay positions. It can be ascribed to the
strong electron donating ability which promotes the conjugation
of the entire molecule. Pyrrolidinyl or piperidinyl groups at the
1,6- and 1,7-positions of PDI show significantly different effect on
the absorption spectra. The red-shift of the maximum absorption
band of 1 is 17 nm larger than that of 2, and similarly, the red-shift
of 3 is 30 nm larger than that of 4. In another word, the
substitutents at 1,7 positions red-shifted the maximum absorp-
tion band more significantly than those at 1,6 positions. This
might be attributed to the large degree distortion of the perylene
core caused by the substituents at the 1,6-positions of PDI, which
disturbs the conjugation system of PDI ring and thus brings small
red-shift on the maximum absorption band.
Both pyrrolidine and piperidine are cyclic secondary amines,
which have very similar structures. But pyrrolidinyl and
piperidinyl group at the same position of PDI show evidently
different effect on the absorption spectra as shown in Fig. 1 and
Table 1. In compounds 1 and 3, the pyrrolidinyl or piperidinyl
groups are similarly connected at 1,7-positions of PDI ring, but
the maximum absorption band of compound 1 is centered at
about 698 nm, which red-shits for about 18 nm relative to that of
compound 3. Similarly, compound 2, in which pyrrolidinyl groups
are connected at 1,6 positions, presents a maximum absorption
band at 681 nm, while compound 4 with piperidinyl groups
substituted at the same positions show maximum absorption
band at about 650 nm. The red-shift for the maximum absorption
band of 2 is as large as 31 nm relative to that of 4. These results
indicate that pyrrolidinyl groups are more efficient on red-shift of
the maximum absorption band than piperidinyl group. It is worth
noting that cyclic primary amino groups substituted at 1,7
positions of PDI[34] can red-shift the maximum absorption band
more efficiently than linear primary amino groups[36] attached at
the same positions, suggesting that the steric hindrance might be
an important source for this huge difference between the
absorption spectra of pyrrolidinyl- and piperidinyl-substituted
PDIs.
piperidine units. The maximum emission bands of compounds
1, 2, 3, and 4 are red-shifted for about 207, 203, 225, 229 nm,
respectively, relative to that of 5. Though the same substituents at
the different positions of perylene bay region created significant
different effect on the absorption spectra of the PDI isomers as
mentioned above, but they did not show significant influence on
their emission spectra. For example, the maximum emission
wavelength of compound 1 with pyrrolidinyl groups at the
1,7-positions is only 4 nm longer than that of compound 2 with
pyrrolidinyl group at the 1,6-positions. Similarly, difference of
4 nm between the maximum emission wavelength of com-
pounds 3 and 4 was found, but with the 1,6-isomer 4 the longer
wavelength emission was shown. Similar emission properties
have also been found for a pair of linear amino groups substituted
PDI isomers.[34]
Although the maximum absorption wavelengths of dipyrro-
lidinyl-substituted PDIs 1 and 2 are larger than that of
dipiperidinyl-substituted PDIs 3 and 4, but the maximum
emission wavelengths of 1 and 2 are significantly shorter than
that of 3 and 4. This leads to large difference on their Stock’s shifts
between the dipyrrolidinyl- and dipiperidinyl-substituted PDIs.
The Stock’s shifts of dipyrrolidinyl-substituted PDIs are signifi-
cantly smaller than that of dipiperidinyl-substituted PDIs. As the
Stock’s shift reflects directly the structure relaxing during the
photo-excitation, larger Stock’s shift corresponds to larger
structure difference between the ground states and the excited
states. Therefore, the smaller Stock’s shift of 1 and 2 relative to
those of 3 and 4 suggests that the structure relaxing during the
Fluorescence
The fluorescence spectra of these series compounds are recorded
in dichloromethane with excitation at 430 nm. Fluorescence
quantum yields (Ff) are calculated with model 5 as standard. The
spectra and experimental results are summarized in Fig. 2 and
Table 1. Similar to that observed for the absorption spectra, the
maximum emission bands of compounds 1–4 red-shifted
significantly relative to that of model 5. This can be ascribed
to the electron-donating properties of the pyrrolidine or
Figure 2. Fluorescence spectra of 1–4 compared with that of 5 in
dichloromethane
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J. FENG ET AL.
photo-excitation of 1 and 2 are significantly smaller than those of
3 and 4, which indicates that the molecular structure of 1 and 2
are more rigid than those of 3 and 4.
corresponds well to the electron-donating nature of pyrrolidinyl
and piperidinyl groups. The negative shift of both first oxidation
and reduction potentials of the compounds with pyrrolidinyl
groups (1 and 2) are much more significant than that of the
compounds with piperidinyl groups (3 and 4), which suggests
again that the pyrrolidinyl groups interact with the perylene core
more strongly than the piperidinyl groups connected at the same
positions. The difference on the redox potentials between 1 and 3
as well as 2 and 4 revealed that the same group at different
positions shows different effects on the redox potentials too. The
side groups connected at 1,7 positions seem to be more efficient
than the groups at 1,6 positions on negative shifting the
oxidation or reduction potentials.
The fluorescence quantum yields of compounds 1, 2, 3, and 4
are distinctively smaller relative to that of standard compound 5
because of the introduction of pyrrolidine or piperidine. Due to
the very strong electron-withdrawing nature of the PDI core,
introducing electron-donating side groups onto the bay positions
of the PDI core leads to charge transfer characteristic in the
excited states of the PDI molecules, which in turn results in a
significant decrease in the fluorescence quantum yield (Table 1).
This corresponds well with the results found for other PDI
compounds.[34,36] The fluorescence quantum yields of 1 and 3 are
significantly larger than that of 2 and 4. This might be attributed
to the larger steric hindrance introduced by the side groups at 1,6
positions relative to that at 1,7 positions, which induce larger
degree of distortion of the perylene core.[37] Compound 1
presents distinctively larger fluorescence quantum yields than
compound 3, which might be induced again by the more rigid
molecular structure of compound 1 relative to 3 because of the
different side groups as mentioned above. The rigid molecular
structure could significantly reduce the proportion of nonradia-
tive decay of the excited states through structure relaxing and,
therefore, could increase the fluorescence quantum yields.
The fluorescence lifetimes of compounds 1 and 3 are shorter
than that of standard compound 5 due to the electron transfer
characteristic in the excited states. The measured fluorescence
lifetimes are found to be sensitive to the solvent polarity. In polar
solvents, the fluorescence lifetimes of 1 and 3 are reduced
significantly probably because of the enhanced electron transfer
characteristics of the excited states caused by the solvention. The
fluorescence lifetimes of compounds 2 and 4 cannot be
measured accurately because of the very weak emission intensity.
Crystal structure
For the purpose of deep understanding the relation between the
molecular structure and the physical properties, the single
crystals of compounds 1 and 3 suitable for X-ray diffraction
analysis were grown by diffusion of methanol into a solution of 1
or 3 in CH2Cl2. Compound 1 belongs to C2c space group with
calculated density Dc ¼ 1.208 g/cm3 (Table S1, Supporting
Information). The crystal structure of compound 1 is shown in
Fig. 3A. The steric effect of two pyrrolidinyl substituents performs
on the perylene core, leads to a twisting conformation for the two
naphthalene subunits, and therefore, 1 gives a distorted
molecular conformation. As a consequence, the characteristic
torsion angles at the bay position of 1 are 20.188 (for
C8-C9-C10-C11) and 20.058 (for C18-C19-C20-C1), which are in
consistence with those observed for other substituted PDI
derivatives.[35] The dihedral angle (a) of the two planes of the
naphthalene subunit is 20.468 (Fig. 3B). The two pyrrolidinyl
groups attached at the diagonal positions of the perylene core
diminishes the symmetry to C1 symmetry, leading to intrinsic
chirality for the whole PDI molecule. The two enantiomers (L and
D) with different chiral molecular conformation in mole ration 1:1
were observed in the crystal. The neighboring twisted molecules
with the same chiral molecular conformation form a pseudo-
dimer (L-L or D-D) in a clasp-like structure through inter-
molecular p–p interaction (Fig. 3B). It is worth noting that these
two PDI molecules arranged is nonparallel with the dihedral
angle (u) of two planes through the axis atoms
(N1-C21-C22-C23-C24-N2) of perylene cores amounting to
45.918 (Fig. 3C). This packing behavior is different from that
previously reported for fluorinated PDIs[38] and can be assigned
to the steric hindrance caused by the pyrrolidinyl groups. The cell
unit of 1 contains eight PDI molecules (Fig. 3D). The adjacent
pseudo-dimers are further linked by the intermolecular p–p
interaction between the PDI core of the neighboring enantio-
Electrochemical properties
The electrochemical behaviors of these compounds are
investigated by cyclic voltammetry (CV) and differential pulse
voltammetry (DPV). The half-wave redox potential values versus
Saturated calomel electrode (SCE) of 1–4 together with that
of model compound 5 are summarized in Table 2. Within the
electrochemical window of CH2Cl2, these compounds undergo at
least one reversible one-electron oxidation and reduction.
The introduction of pyrrolidinyl or piperidinyl groups at the
positions of PDI bay region induces negative shift for first
oxidation and reduction potentials of compounds 1–4. This
Table 2. Half-wave redox potentialsa (mV vs. SCE) of 1–4 and
5 in CH2Cl2 containing 0.1 M TBAP
˚
topic PDI molecules (L-D) separated in 3.39 A, forming an infinite
1D chain-like supramolecular structure (-L-L-D-D-) (Fig. 3E).
The di-piperidinyl-substituted compound 3 crystallizes in
triclinic system with Pꢀ1 space group. In comparison with the
calculated density of 1, the calculated density of 3 (Dc ¼ 1.192 g/
cm3) is slightly smaller, which may be ascribed to the looser
packing mode than that of 1 as a result of the different side
groups connected. As shown in Fig. 4A and B, there are two kinds
of independent PDI molecules in the asymmetric unit due to the
different bending direction of the piperidinyl groups. The
characteristic torsion angles at the bay position of 3 are 20.068
(for C8-C9-C10-C11) and 17.388 (for C18-C19-C20-C1) in one PDI
molecule and 18.098 (for C50-C51-C52-C53) and 18.228 (for
b
Compounds Oxd3 Oxd2 Oxd1 Red1
Red2 DE81/2
1
2
3
4
5
0.75 ꢀ0.87 ꢀ1.00
1.62
1.65 1.21 0.85 ꢀ0.83 ꢀ0.97
1.68
1.62
1.71
2.21
0.86 ꢀ0.76 ꢀ0.96
1.91 1.43 0.97 ꢀ0.74 ꢀ0.95
1.63 ꢀ0.58 ꢀ0.82
a Values obtained by DPV in dry CH2Cl2 with 0.1 M TBAP as the
supporting electrolyte and Fc/Fcþ as internal standard.
b E81/2 ¼ Oxd1ꢀRed1.
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PROPERTY COMPARISON BETWEEN TWO PDIS
Figure 3. Single crystal structure of 1 with labels (A), pseudo-dimer (B and C), packing diagram (D), and side view on the stacks (E, only the perylene core
is shown for clarity)
Figure 4. Single crystal structure of 3 with labels (A and B), packing diagram (C), and side view on the stacks (D, only the perylene part is shown for
clarity)
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J. FENG ET AL.
Figure 5. The bond length and bond angles around the nitrogen atom in compounds 1 (A) and 3 (B)
˚
C60-C61-C62-C43) in the other one. The dihedral angle (a) of the
two planes of the naphthalene subunits in 3 is 18.508 on average,
which is slightly smaller than that observed for 1, indicating that
smaller steric hindrance from piperidinyl groups than that from
pyrrolidinyl groups. Similar to compound 1, intrinsic chirality for
the whole PDI molecule is also found in 3. The enantiomers L and
D was observed in 3 in mole ratio 1:1. Despite the formed
pseudo-dimers with u ¼ 32.228, the tetramer (L-L-D-D) bridged
by the intermolecular p–p interaction between the neighboring
PDI cores (L–D) separated in 3.61 A are found in crystal of 3
instead of the 1D supramolecular chain of 1, which may be
assigned to the much bigger volume of piperidinyl groups than
that of pyrrolidinyl groups.
As shown in Table S2 (Supporting Information), the bond
˚
length between C1 and N3 in compound 1 is 1.377 A, which is
˚
distinctively smaller than that in compound 3 (1.391 A). The
measured bond angles of the bonds connected to the nitrogen
atom of the pyrrolidinyl or piperidinyl groups in the crystal
Figure 6. Minimized structures of compounds 1 (A) and 3 (B)
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PROPERTY COMPARISON BETWEEN TWO PDIS
structures of 1 and 3 are shown in Fig. 5. In the five member ring
of pyrrolidine in 1, the bond angles between the bonds around
the nitrogen atom are 120.878 and 120.798, respectively. But in
the six member ring of piperidine in compound 3, the
corresponding bond angles are 116.618 and 117.518, which are
smaller than those observed for compound 1. So, nitrogen atoms
of pyrrolidinyl groups of 1 have larger sp2 hybrid orbital
characteristics, whereas nitrogen atoms of piperidinyl groups of 3
have more sp3 hybrid orbital characteristics, which suggests that
there are double bond characteristics between C1 and N3 in
compound 1 (Fig. 5A), otherwise, there are more single bond
characteristics between C1 and N3 in compound 3 (Fig. 5B).
Because the pyrrolidine group in compound 1 cannot rotate
freely due to the double bond characteristic of C1—N3, it creates
larger steric hindrance between the pyrrolidinyl group and the
neighboring naphthalene ring of perylene core and, therefore,
results in larger torsion angle between the two naphthalene
subunits. All the structure characteristics as mentioned above
indicate that the electron lone pair on the nitrogen atom in the
pyrrolidinyl groups of 1 conjugated with the PDI core stronger
than that in piperidinyl groups of 3. This is in accordance with the
conclusion deduced from the absorption and emission spectra as
mentioned above.
and LUMO of 1 is 2.11 eV, which is slightly smaller than that of 3
(2.13 eV) as shown in Fig. 7. This is in accordance with the
recorded red-shifted maximum absorption band of 1 relative to 3
in the absorption spectra. Both the HOMO and LUMO of 1 and 3
are extended successfully to the nitrogen atoms, indicating the
contribution of the nitrogen atoms to the frontier molecular
orbital and the interaction between the side groups and the PDI
core. The contribution of nitrogen atom to the HOMO is obviously
larger than that to the LUMO, which suggests that the nitrogen
atom affected the HOMO more significantly than the LUMO; this
has been proved by the fact that the introduction of side groups
has induced more significant changes on the oxidation potentials
than that on the reduction potentials, because the former is
related closely with the HOMO while the later correlated with the
LUMO closely.
CONCLUSION
Four PDI derivatives connected with cyclic amino groups at the
bay positions were synthesized and the isomers with 1,7 and 1,6
substitution patterns were successfully separated by conven-
tional column chromatography. Single crystals of the 1,7
disubstituted compounds (1 and 3) with proper size, which
can be utilized in single crystal diffraction experiments, were
obtained for the first time. The more double bond characteristics
of C1—N3 in compound 1 relative to that in compound 3 caused
stronger interactions between the pyrrolidinyl groups and the
perylene core, which is the origin of the significantly different
physical properties presented by compounds 1 and 3. This
information is meaningful not only for the design of novel PDI
compounds, but also useful for the design of the new molecules
with amino groups.
DFT calculation
For the purpose of further understanding of the proper-
ty–structure relation of PDI compounds, the molecular structures
as well as the molecular orbital are calculated based on DFT
method. The minimized molecular structures of compounds 1
and 3 are shown in Fig. 6. The minimized molecular structures
correspond well to the crystal structure. For instance, the twist
angle between the two naphthalene plans (a) in the calculated
structure of 1 is 21.468, which is similar to the measured result
(20.468). The calculated twist angle for 3 is 18.608, which is also
close to the measured twist angle (18.508) in the crystal. The
comparison results between the minimized structure and the
crystal structure as mentioned above also suggest that the DFT
calculation is reliable.
EXPERIMENTAL SECTION
1H NMR spectra were recorded on a Bruker DPX 300 spectrometer
(300 MHz) using SiMe4 as reference. MALDI-TOF mass spectra
were taken on a Bruker BIFLEX III mass spectrometer with
a-cyano-4-hydroxycinnamic acid as the matrix. Electronic
The frontier molecular orbital maps of compounds 1 and 3 are
calculated at DFT/B3LYP/6–31g(d) level. Figure 7 shows the
frontier orbital maps of 1 and 3 together with their energy levels
as representative. The calculated energy gap between the HOMO
absorption spectra were recorded on
a Hitachi U-4100
spectrophotometer, whereas the fluorescence spectra and
fluorescence lifetime were recorded on ISIS K2 system. Elemental
analyses were performed by the Institute of Chemistry, Chinese
Academy of Sciences. Electrochemical measurements were
carried out on a BAS CV-50W voltammetric analyzer with a
glassy carbon disk working electrode (2.0 mm in diameter), a
silver-wire counter electrode, and an Ag/Agþ reference electrode.
The experiments were carried out under nitrogen at room
temperature. Tetrabutylammonium perchlorate in freshly dis-
tilled CH2Cl2 (0.1 mol dmꢀ3) was used as the electrolyte solution.
Ferrocene was employed as the reference redox system
according to IUPAC’s recommendation. Crystal data for these
three complexes were collected on a Bruker SMART APEXII CCD
diffractometer with graphite monochromatic Mo Ka radiation
˚
(l ¼ 0.71073 A) using the SMART and SAINT programs at 298 K,
and the structures were solved by the direct method (SHELXS-97)
and refined by full-matrix least-squares (SHELXL-97) on F2.
Anisotropic thermal parameters were used for the nonhydrogen
atoms and isotropic parameters for the hydrogen atoms.
Hydrogen atoms were added geometrically and refined using
Figure 7. Frontier molecular orbital maps and energy levels of compounds
1 (left) and 3 (right)
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J. FENG ET AL.
a riding model. Crystallographic data and other pertinent
information for all the complexes are summarized in Table S1
(Supporting Information). Selected bond distances and their
estimated standard deviations are listed in Table S2 (Supporting
Information). CCDC 752512 and 752513 for 1 and 3, respectively,
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
4H), 1.40–1.91(m, 20H), 0.98 (m, 6H); 13C NMR (100Hz, CDCl3) d
163.8, 163.7, 153.2, 136.0, 131.7, 130.7, 128.8, 128.0, 123.8, 123.2,
123.1, 122.3, 120.7, 120.2, 53.1, 40.3, 40.2, 30.3, 30.2, 25.8, 23.8, 20.5,
20.4, 13.9, 13.8; MALDI-TOF MS(m/z) 668.8, Calcd for C42H44N4O4
(m/z) 668.8. Anal. Calcd. for C42H44N4O4: C, 75.42; H, 6.63; N, 8.38.
Found: C, 75.38; H, 6.61; N, 8.43.
N,N0-dibutyl-dibromo-3,4:9,10-perylene -tetracarboxylic dii-
mide[39] and N,N0 -dibutyl-dibromo-3,4:9,10- perylene-
tetracarboxylic diimide(5)[37] were prepared following the
Acknowledgements
The authors acknowledge the financial support from the natural
science foundation of China (grant no. 20771066 and
20640420467), Ministry of education.
1
literature method and characterized by H NMR, 13C NMR, and
MALDI-TOF mass spectra. Synthesis of compounds 1–4 is
described in the following. All other chemicals are purchased
from commercial source. Solvents were of analytical grade and
were purified by the standard method before use.
REFERENCES
N,N(-dibutyl-1,7-dipyrrolidinyl-3,4:9,10-perylenetetra-car-
boxylic diimide (1), and N,N(-dibutyl-1,6 -dipyrrolidinyl-
3,4:9,10-perylenetetracarboxylic diimide (2): A mixture of
N,N0-dibutyl-1,6-dibromo-3,4:9,10 -perylenetetracarboxylic dii-
mide and N,N0 -dibutyl-1,7 -dibromo -3,4:9,10- perylenetetracar-
boxylic diimide (1 g, 1.51 mmol) was dissolved in 30 ml
pyrrolidine. The solution was heated at 608 under dry nitrogen
for 24 h with stirring. Excess pyrrolidine was removed on a rotary
evaporator. The solid collected was purified by column
chromatography on silica gel using CHCl3 as eluent. 1: green
solid; 603 mg, yield 58%; mp. > 300 8C; 1H NMR (300 MHz, CDCl3) d
8.37 (s, 2H), 8.31 (d, 2H), 7.53 (d, 2H), 4.24 (t, 4H), 3.68 (m, 4H), 2.76
(m, 4H), 1.99(m, 8H), 1.76(m, 4H), 1.48(m, 4H), 0.98 (t, 6H); 13C NMR
(100 Hz, CDCl3) d 164.0, 146.4, 134.1, 129.8, 126.6, 123.7, 122.1,
121.7, 120.7, 119.0, 118.0, 52.1, 40.3, 30.3, 25.8, 20.4, 13.9;
MALDI-TOF MS(m/z) 640.8, Calcd for C40H40N4O4 (m/z) 640.8.
Anal. Calcd. for C40H40N4O4: C, 74.98; H, 6.29; N, 8.74. Found: C,
74.95; H, 6.32; N, 8.71. 2: blue solid; 156 mg, yield 15%;
mp. > 300 8C; 1H NMR (300 MHz, CDCl3) d 8.65 (d, 2H), 8.31 (s,
2H), 7.85 (d, 2H), 4.23 (m, 4H), 3.68 (m, 4H), 2.77 (m, 4H), 2.00(m,
8H), 1.76(m, 4H), 1.49(m, 4H), 0.98 (t, 6H); 13C NMR (100 Hz, CDCl3)
d 164.3, 164.1, 149.9, 135.7, 131.1, 130.2, 128.5, 128.3, 123.3, 122.9,
117.8, 117.6, 117.0, 116.9, 52.1, 40.3, 40.2, 30.4, 30.3, 25.6, 20.5,
20.4, 13.9, 13.8; MALDI-TOF MS(m/z) 640.8, Calcd for C40H40N4O4
(m/z) 640.8. Anal. Calcd. for C40H40N4O4: C, 74.98; H, 6.29; N, 8.74.
Found: C, 74.93; H, 6.35; N, 8.72.
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A
mixture of
N,N0-dibutyl-1,6-dibromo-3,4:9,10- perylenetetracarboxylic dii-
mide and N,N0-dibutyl-1,7-dibromo -3,4:9,10 -perylenete tracar-
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stirring. Excess piperidine was removed on a rotary evaporator. The
solid collected was purified by column chromatography on silica
gel using 1:2 CH2Cl2/CCl4 as eluent. 3: green solid; 619 mg, yield
61%; mp. > 300 8C; 1H NMR (300MHz, CDCl3) d 9.29 (d, 2H), 8.24 (d,
2H), 8.17 (s, 2H), 4.24 (t, 4H), 3.34 (d, 4H), 2.76 (m, 4H), 1.36–1.88(m,
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