Cyclophanes of perylene tetracarboxylic diimide with different substituents at bay positions

Article abstract of DOI:10.1002/chem.200800136

Cyclophanes of perylene tetracarboxylic diimides (PDIs) with different substituents at the bay positions, namely four phenoxy groups at the Impositions (1), four piperidinyl groups at the 1,7-positions (2), and eight phenoxy groups at the 1,6,7,12-positions (3) of the two PDI rings, have been synthesized by the condensation of perylene dianhydride with amine in a dilute solution. These novel cyclophanes were characterized by ¹H NMR spectroscopy, MALDI-TOF mass spectrometry, electronic absorption spectroscopy, and elemental analysis. The conformational isomers of cyclophanes substituted with four piperidinyl groups at the 1,7-positions (2 a and 2 b) were successfully separated by preparative TLC. The main absorption band of the cyclophanes shifts significantly to the higher energy side in comparison with their monomeric counterparts, which indicates significant π-π interaction between the PDI units in the cyclophanes. Nevertheless, both the electronic absorption and fluorescence spectra of the cyclophanes were found to change along with the number and nature of the side groups at the bay positions of the PDI ring. Time-dependent DFT calculations on the conformational isomers 2a and 2b reproduce well their experimental electronic absorption spectra. Electrochemical studies reveal that the first oxidation and reduction potentials of the PDI ring in the cyclophanes increase significantly compared with those of the corresponding monomeric counterparts, in line with the change in the energy of the HOMO and LUMO according to the theoretical calculations.

Full text of DOI:10.1002/chem.200800136

DOI: 10.1002/chem.200800136
Cyclophanes of Perylene Tetracarboxylic Diimide with Different Substituents
at Bay Positions
Junqian Feng, Yuexing Zhang, Chuntao Zhao, Renjie Li, Wei Xu, Xiyou Li,* and
Jianzhuang Jiang[a]
Abstract: Cyclophanes of perylene tet-
racarboxylic diimides (PDIs) with dif-
ferent substituents at the bay positions,
namely four phenoxy groups at the 1,7-
positions (1), four piperidinyl groups at
the 1,7-positions (2), and eight phenoxy
groups at the 1,6,7,12-positions (3) of
the two PDI rings, have been synthe-
sized by the condensation of perylene
dianhydride with amine in a dilute so-
lution. These novel cyclophanes were
characterized by 1H NMR spectrosco-
py, MALDI-TOF mass spectrometry,
electronic absorption spectroscopy, and
elemental analysis. The conformational
isomers of cyclophanes substituted with
four piperidinyl groups at the 1,7-posi-
tions (2a and 2b) were successfully
separated by preparative TLC. The
main absorption band of the cyclo-
phanes shifts significantly to the higher
energy side in comparison with their
monomeric counterparts, which indi-
cates significant p–p interaction be-
tween the PDI units in the cyclo-
phanes. Nevertheless, both the elec-
tronic absorption and fluorescence
spectra of the cyclophanes were found
to change along with the number and
nature of the side groups at the bay po-
sitions of the PDI ring. Time-depen-
dent DFT calculations on the confor-
mational isomers 2a and 2b reproduce
well their experimental electronic ab-
sorption spectra. Electrochemical stud-
ies reveal that the first oxidation and
reduction potentials of the PDI ring in
the cyclophanes increase significantly
compared with those of the corre-
sponding monomeric counterparts, in
line with the change in the energy of
the HOMO and LUMO according to
the theoretical calculations.
Keywords: cyclophanes · dimers ·
perylenes · photophysical proper-
ties · supramolecular chemistry
Introduction
ular structures formed based on weak intermolecular inter-
actions. To investigate the dependence of the optical proper-
ties on the structure of supramolecular systems, the design
and synthesis of model systems with the chromophores
bonded into a rigid structure are necessary.
Spontaneous self-organization of organic chromophores has
been a very active field in supramolecular chemistry since
the important role of the chlorophyll aggregates in photo-
synthesis in purple bacteria was revealed.[1–6] Various supra-
molecular systems constructed from organic dyes including
porphyrins[7] and phthalocyanines[8] based on noncovalent
intermolecular interactions, such as hydrogen bonding,
metal coordination, dipole–dipole, electrostatic, and p–p in-
teractions, have been intensively studied.[9] However, investi-
gation towards understanding the relationship between
structure and spectroscopic as well as electrochemical prop-
erties has been retarded because of the flexible supramolec-
Perylene tetracarboxylic diimides (PDIs) have attracted
significant research interest because of their great applica-
tion potential in field-effect transistors,[10] solar cells,[11] and
light-emitting diodes.[12] One fascinating feature of this kind
of organic dye is the significant change in the relative inten-
sity of the 0!0 and 0!1 vibronic bands in the absorption
spectrum upon p–p stacking, which makes them the ideal
model for studying the structure–property relationships of
supramolecular systems. Wasielewski and co-workers have
prepared a PDI dimer linked by a xanthene spacer.[13,14] The
resulting dimer showed a significant blueshifted band in its
electronic absorption spectrum, which indicates a strong p–
p interaction between the two PDI rings with the transition
dipole moments parallel to each other. Li and co-workers
reported a series of PDI dimers or foldamers linked by long
and flexible ethylene oxide or single-stranded DNA.[15] The
intensity reversal between the 0!0 and 0!1 vibronic bands
[a] J. Feng, Y. Zhang, C. Zhao, R. Li, W. Xu, Prof. X. Li, Prof. J. Jiang
Key Lab for Colloid and Interface Chemistry of Education Ministry
Department of Chemistry, Shandong University
Jinan 250100 (China)
Fax : (+86)531-8856-4464
E-mail: xiyouli@sdu.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200800136.
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FULL PAPER
in the absorption spectra of these PDI dimers or foldamers
upon p–p stacking is solvent dependent, which indicates the
change in the molecular geometry of the stacked structure
in different solvents. Two PDI units linked by a flexible tria-
zine ring presented an equilibrium between the stacked and
unstacked conformation in solution, as revealed by the ab-
sorption and emission properties in different solvents.[16] The
only cyclized PDI dimer, that is, cyclophane of PDIs,
formed by two PDI rings linked by two long and flexible
alkyl chains at imide nitrogen atoms showed a conforma-
tional change from H to J aggregate upon photoexcitation,
as evidenced by the blueshifted absorption bands and red-
shifted emission bands.[17] Investigation towards establishing
direct correlation between the molecular structure and opti-
cal properties for all the above-mentioned PDI dimers is im-
possible due to their flexible molecular geometry. However,
a recent theoretical examination of PDI dimers with a face-
to-face stacked molecular structure by using time-dependent
density functional theory (TDDFT) clearly revealed the ef-
fects of the molecular conformation, including the interpla-
nar distance, lateral slippage along either the N–N axis or
the in-plane short axis of PDI, and the rotation of one sub-
number and species of side groups attached at the bay posi-
tions of the PDI rings in these cyclophanes induces different
degrees of slipping and/or rotation of the two PDI rings rel-
ative to each other. The electronic absorption and fluores-
cence spectroscopic results for the series of compounds are
revealed to depend on the geometry of the stacked struc-
ture, which is also confirmed by the results calculated by the
TDDFT method. To the best of our knowledge, this repre-
sents the first experimental effort towards constructing the
structure–property relationship for the face-to-face stacked
PDI dimer.
Results and Discussion
Molecular design and synthesis: To prepare a PDI dimer
with rigid structure and efficient p–p interactions between
the PDI rings, the spacer used to connect the PDI subunits
must be able to confine the two PDI rings in a parallel way
and keep the two subunits at a proper distance. 2,4-Diami-
no-1,3,5-triazine has been proved an ideal bridge for this
purpose on the basis of our previous research.[16] Therefore,
2,4-diamino-1,3,5-triazine was chosen as the spacer to con-
nect two PDI rings for this cyclophane compound. It has
been revealed that introducing substituents at the bay posi-
tions of the PDI ring is an effective way to tune the optical
and electrochemical properties of PDI compounds.[19] There-
fore, different numbers of phenoxy or piperidinyl groups are
incorporated into the bay positions of PDI rings. In addition,
introduction of side groups
ACHTREUNG
erties of four PDI cyclophanes with different substituents at
the bay positions of the PDI ring (Scheme 1, 1–3). Two PDI
rings are connected by two 2,4-diamino-1,3,5-triazine rings
and form a rigid cyclic structure. The difference in the
onto the PDI rings significantly
improves the solubility of cyclo-
phanes in conventional organic
solvents, which simplifies the
preparation and purification
procedure to a large degree.
Condensation of substituted
perylene tetracarboxylic di-
AHCTREUNG
AHCTREUNG
zine-1,3,5-trazine (7) in toluene
in the presence of imidazole
leads to the formation of cyclo-
phanes (Scheme 2). Note that a
dilute solution is employed in
the reaction to prevent poly-
merization.[20] Target cyclo-
phane compounds were purified
by column chromatography
and/or preparative TLC.
The reaction of 1,7-di(4-tert-
butylphenoxy)perylene-3,4:9,10-
tetracarboxylic dianhydride (8)
or
1,7-dipiperidinylperylene-
3,4:9,10-tetracarboxylic dianhy-
dride (9) with 7 induces the for-
mation of two conformational
Scheme 1. Molecular structure of cyclophanes 1–3 and the reference compounds 4–6. Labels of the carbon
atoms on the PDI ring are shown on the structure of 5.
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X. Li et al.
in the Supporting Information).
To identify the molecular struc-
ture, 2D COSY and ROESY
NMR spectra for both isomers
were recorded in CDCl3. For
the purpose of comparison, the
2D ROESY NMR spectrum of
a
monomeric PDI, namely
N,N’-di-n-butyl-1,7-dipiperidin-
yl-3,4:9,10-tetracarboxylic diim-
ide (11), was also recorded.
Figure 1 shows the 2D ROESY
spectrum of 2a. A cross peak
corresponding to the correla-
Scheme 2. Synthesis of the cyclophanes 1–3.
tion between the protons at po-
sitions 5 and 2 as well as the
isomers for cyclophanes 1 and 2 because of the blocked ro-
tation of the disubstituted perylene ring along the long mo-
lecular axis. We have indeed isolated a product from the re-
action mixture during the preparation of compound 1, which
gives a molecular mass corresponding well with the dimeric
structure. However, observation of two sets of proton signals
in its 1H NMR spectrum (see Figure S1 in the Supporting In-
formation) indicates the presence of two isomers with one
as the main product. The mole ratio calculated from the in-
tegral of the peaks for the protons at position 5 is 5:2 for
the two isomers. However, attempts to separate these two
isomers by various chromatographic methods have been un-
successful.
protons at positions 11 and 8 of the PDI rings appears in
this spectrum. However, a similar correlation signal was not
observed in the 2D ROESY of monomeric PDI 11 (see Fig-
ure S5 in the Supporting Information). As a consequence,
the cross peak in cyclophane 2a should result from the cor-
relation between the protons at position 5 of one PDI ring
and position 2 of another PDI ring as well as between the
protons at position 8 of one PDI ring and position 11 of the
other PDI unit, which also suggests a trans configuration for
the two PDI units. In addition, five signals indicating the
correlations of the protons at positions 5 and 11 of the PDI
rings with those on piperidinyl rings were also observed in
the 2D ROESY spectrum of 2a (Figure 1). Comparison with
the correlation signals in the 2D ROESY spectrum of
Fortunately, the isomers 2a and 2b (Scheme 3) have been
successfully separated by preparative TLC in the mole ratio
of 3:1. The first component is the main product, cyclophane
2a, which easily dissolves in most common organic solvents.
In contrast, the second isomer separated with low yield, cy-
clophane 2b, is hard to dissolve in organic solvents in com-
parison with 2a. As expected, the two isomers give identical
A
N
Information) indicates that these five signals are due to the
correlations of the protons at positions 5 and/or 11 of the
PDI ring with those protons on the piperidinyl rings con-
nected at the same PDI ring, as well as the protons of piper-
idinyl rings connected on the other PDI ring. These results
give additional support to the trans configuration of the PDI
units in cyclophane 2a. Note that in the 2D ROESY spec-
trum of the cis isomer 2b (see Figure S8 in the Supporting
Information), correlation of the protons at positions 2 and 8
of the PDI ring with the protons of its own piperidinyl sub-
stituent was also observed, as in its trans isomer 2a. Howev-
er, unlike the trans isomer, the PDI proton at position 5 (or
11) of the PDI ring can only correlate with one of the two
protons neighboring the nitrogen atom in the piperidinyl
groups attached to this PDI ring in the cis isomer 2b. These
results indicate a large repulsion between the two piperidin-
yl groups attached to two different PDI rings in cyclophane
2b, which forces the piperidinyl groups to bend away from
the plane of the PDI rings and therefore suggests a cis con-
figuration for the PDI units in this isomer.
1
mass but different H NMR spectra (see Figures S2 and S3
Reaction between 1,6,7,12-tetra(p-tert-butylphenxoyl)per-
ylene-3,4:9,10-tetracarboxylic dianhydride (10) and 2-di(n-
A
butyl)amino-4,6-dihydrazine-1,3,5-triazine (7) leads to the
isolation of cyclophane 3 in very low yield (3.1%), probably
due to the large steric hindrance between the eight bulky
phenoxy groups attached at two different PDI rings. This is
Scheme 3. Molecular structure of trans and cis isomers of cyclophane 2.
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Cyclophanes of Perylene Tetracarboxylic Diimide
FULL PAPER
Figure 1. 2D ROESY NMR spectrum of cyclophane 2a in CDCl3 at room temperature. Inset: correlation of the protons at positions 5 and 11 of one of
the PDI units to those at positions 2 and 8 of the other unit.
rationalized by the fact revealed previously that all the
1,6,7,12-tetrasubstituted PDI compounds form J aggregates
exclusively in their self-assembly.[21] Interestingly, broad
1
peaks without fine structure were observed in the H NMR
spectrum of cyclophane 3 (see Figure S4 in the Supporting
Information), which indicates the restricted rotation of the
ꢀ
phenoxy groups along the O C bond with a rate compara-
ble to the response of the NMR instrument due to the large
steric hindrance among the phenoxy groups.
Minimized structure: The minimized structures of these cy-
clophanes have been calculated by the B3LYP method and
6-31G(d) basis set in the Gaussian 03 program.[22] The struc-
ture of cyclophane 2b is shown in Figure 2 as a representa-
tive example. The calculated structures of other cyclophanes
are shown in Figure S9 in the Supporting Information. As
can be seen, in these cyclophanes the two triazine spacers
connect two PDI rings to form a cyclic rigid molecule in
which the two PDI rings employ a face-to-face stacked
structure. All the structure parameters, including the inter-
planar distance between the two PDI planes (d1), the side-
Figure 2. Top: The minimized structure of cyclophane 2b (hydrogen
ways slippage along the long axis of the PDI ring (d2), the
slippage along the short axis of the PDI ring (d3), the in-
plane torsion angle between the long axis of the two PDI
rings (a), and the dihedral between the PDI planes (b),
were calculated for both isomers of 1 and 2 together with
cyclophane 3 and the data are summarized in Table 1.
All the parameters except d1 for the trans isomer 1a are
close to zero (Table 1), thus indicating an ideal face-to-face
stacking for the two PDI units without any sideways slipping
atoms are omitted for clarity). Bottom: a schematic description of the
structure parameters.
or in-plane torsion of the PDI rings relative to each other.
However, in addition to the interplanar distance between
the two PDI planes, the in-plane torsion angle between the
long axis of the two PDI rings for the cis isomer 1b is no
longer zero. These results indicate a structure with zero side-
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X. Li et al.
Table 1. Parameters of the dimeric structure of PDI in cyclophanes 1–3.
mation between the two PDI planes (b) for this compound
indicate weakened interaction between its two PDI rings.
[a]
Compound
d1 [Š]
d2[b] [Š]
d3[b] [Š]
a [8]
b [8]
1a
1b
2a
2b
3
4.81
4.85
4.56
4.46
4.77
0
0
0
0
0.35
0
1.25
1.61
1.80
0
0
0
0
15.38
6.06
0
The UV/Vis absorption spectra: Figure 3 compares the elec-
tronic absorption spectra of cyclophanes 1–3 with those of
their monomeric counterparts 4–6 in dichloromethane. All
the main absorption bands of cyclophanes 1–3 are blueshift-
ed relative to those of their monomeric counterparts 4–6,
which confirms the face-to-face stacked molecular geometry
between the two PDI rings in these cyclophane com-
pounds.[23] In particular, cyclophane 3 appears to represent
the first example of a PDI dimeric structure in which the
14.96
14.70
0.72
8.11
[a] Four atoms (two imide nitrogen and 1,7-carbon) are selected in one
PDI ring and the distance from the selected atoms to their projections on
the opposite PDI ring are measured. The interplanar distance d1 was cal-
culated from the average of these four measured distances. [b] The slip-
page was measured at the molecule center (the cross point of the diago-
nals of the rectangle that links the four imide oxygen atoms in one PDI
ring).
two tetra(phenoxy)-substituted PDI rings form a face-to-
A
face geometry.
As shown in Figure 3A, cyclophane 1 (actually the mix-
ture of the two isomers 1a and 1b) presents a maximal ab-
sorption band at 512 nm, which corresponds to the transition
to the allowed higher-energy exciton-split LUMO of pery-
lene. Different from other PDI dimers constructed from two
PDI rings connected by a soft or rigid spacer,[13,24] the ab-
sorption due to the formally disallowed transition to the
lower-energy exciton-split LUMO of perylene at approxi-
mately 550 nm is almost negligible. Note that for the face-
to-face stacked PDI dimeric system, the transition to the
higher-energy exciton-split LUMO of perylene should have
the whole oscillator strength, whereas the transition to the
lower-energy exciton-split LUMO is symmetry forbidden ac-
cording to exciton theory. However, the latter transition
with significant oscillator strength is always observed in the
recorded electronic absorption spectra of dimeric PDI sys-
tems reported thus far. This finding has been explained on
the basis of vibronic coupling in the exciton states of the di-
meric systems, which relieves the symmetry restriction to
the transition to the lower-energy exciton-spilt LUMO ac-
cording to the simple exciton model.[25] The negligible band
corresponding to the transition to the lower-energy exciton-
split LUMO in the electronic absorption spectrum of cyclo-
phane 1 can be attributed to the strictly face-to-face stacked
structure in both trans isomer 1a and cis isomer 1b as de-
tailed above, which efficiently reduces the vibronic coupling
in the exciton states of cyclophane 1.
The main absorption band for the cyclophane trans
isomer 2a and cis isomer 2b appears at 632 and 617nm, re-
spectively, which is blueshifted by about 40 and 55 nm, re-
spectively, compared with that of their monomeric counter-
part 5. This agrees well with previous results on other PDI
dimeric systems.[14] In particular, the different blueshift of
the main absorption band for isomers 2a and 2b compared
with that of their monomeric counterpart 5 indicates differ-
ent p–p interaction strength between the two PDI rings, as-
sociated with the difference in the molecular structure of
these two isomers. To understand the difference in the elec-
tronic absorption spectra of the trans isomer 2a and cis
isomer 2b, their frontier orbitals were calculated by DFT.
Figure 4 displays the frontier molecular orbital maps togeth-
er with their energy levels for isomers 2a and 2b. As can be
seen, the HOMOꢀ1, HOMO, LUMO, and LUMO+1 of
ways slippage along both the short and long axes for the
PDI rings, and a parallel conformation between the two
PDI planes but distinct rotation of the PDI rings relative to
each other for the cis isomer. Furthermore, the calculated
results indicate a smaller energy of the minimized structure
for isomer 1a in comparison with isomer 1b, which suggests
that the trans isomer 1a is more thermodynamically pre-
ferred. This is also true for the two isomers of cyclophane 2.
It is therefore reasonable to assign the dominant isomer of
cyclophane 1 as trans isomer 1a. This result is further ration-
alized by the much higher yield of trans isomer 2a than cis
isomer 2b, as described above.
For both the trans 2a and cis 2b isomers, the sideways
slippage along the long axis of the PDI ring is calculated to
be 0 Š, which indicates no sideways slipping along the long
axis of the PDI rings (Table 1). In contrast, the large value
of d3 of 1.25 and 1.61 Š for 2a and 2b, respectively, reveals
noticeable sideways slipping along the short axis of the PDI
rings in these two isomers. Notably, the relatively smaller
value of d3 for the trans isomer 2a in comparison with that
for the cis isomer 2b suggests a relatively more intense in-
teraction between the two PDI rings in the former isomer, if
only in terms of the sideways slippage along the short axis
of the PDI ring.[18] However, both the larger values of the
interplanar distance between the two PDI planes (d1) and
the in-plane torsion angle between the long axis of the two
PDI rings (a) for the trans isomer 2a relative to those of cis
isomer 2b appear to induce weaker interaction between the
two PDI rings in the trans isomer. Additionally, contrary to
the two parallel PDI rings in the trans isomer 2a, a nonpar-
allel stacking of PDI rings was employed by the cis isomer
2b with a dihedral of 14.968.
As expected, eight bulky phenoxy groups attached to the
bay positions of the PDI rings in cyclophane 3 lead to signif-
icant distortion over the PDI rings in the molecular struc-
ture due to the large steric hindrance among the phenoxy
groups. The calculated results summarized in Table 1 reveal
that both the long and short axes of the PDI rings are not
parallel to each other again in this cyclophane. The large
value of the sideways slippages along the long and short
axes of the PDI ring (d2 and d3), the distinct in-plane torsion
angle of the two PDI rings (a), and the nonparallel confor-
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Cyclophanes of Perylene Tetracarboxylic Diimide
FULL PAPER
Figure 3. Absorption spectra of cyclophanes 1 (A), 2a (B), 2b (C), and 3 (D) (c) and of their monomeric counterparts 4–6 (a) in dichloromethane
at room temperature. The spectra were recorded at a concentration of 1”10ꢀ5 molLꢀ1 for all compounds.
trans isomer 2a are distributed equally on both PDI units,
with HOMOꢀ1 as the bonding orbital and HOMO the anti-
bonding orbital. The extremely small energy splitting be-
tween HOMOꢀ1 and HOMO (0.004 eV) and between
LUMO and LUMO+1 (0.021 eV) indicates relatively small
interaction between the two PDI units in the trans isomer
2a. However, calculations revealed that the HOMOꢀ1 and
LUMO are distributed on one of the two PDI units, whereas
the HOMO and LUMO+1 are on the other unit for the cis
isomer 2b. As a consequence, the energy splitting between
both HOMOꢀ1 and HOMO and between LUMO and
LUMO+1 for the cis isomer 2b (0.135 and 0.174 eV, re-
spectively) is significantly larger than that for the trans
isomer 2a, thus indicating the intensified p–p interaction be-
tween the two PDI units in the cis isomer 2b. As mentioned
above, the interaction between the two PDI rings in cyclo-
phane is determined by five factors. In the present case, the
smaller interplanar distance between the two PDI planes
(d1) and the smaller in-plane torsion angle between the long
axes of the two PDI rings (a) for the cis isomer 2b seem to
be responsible for the relatively stronger p–p interaction be-
tween the two PDI rings compared with that in the trans
isomer 2a, despite the larger sideways slippage along the
short axis of the PDI ring (d3).
tions from HOMO to LUMO+1 and from HOMOꢀ1 to
LUMO, for trans isomer 2a appears at the lower-energy
side of the cis isomer 2b at 625 nm. This result is also in line
with the relatively larger blueshift observed for the main ab-
sorption band of the cis isomer 2b in comparison with that
of the trans isomer 2a, as detailed above.
The main absorption band for cyclophane 3 was observed
at 537nm (Figure 3D), which is blueshifted by about 40 nm
compared with its monomeric counterpart, thus indicating
the face-to-face geometry for the two PDI rings in this cy-
clophane. Different from cyclophanes 1 and 2, an obvious
absorption at 575 nm corresponding to the transition to the
lower-energy exciton-split LUMO was found in the electron-
ic absorption spectrum of cyclophane 3. This result suggests
weaker p–p interaction between the two PDI rings in 3 than
in 1 and 2 because of the large degree of deviation from the
ideal face-to-face stacking geometry for the two PDI units
in cyclophane 3. This promotes the vibronic coupling in the
exciton states and relieves the symmetry restriction to the
transition to the lower-energy exciton-split LUMO of pery-
lene, according to the simple exciton model.
Fluorescence spectra and fluorescence lifetime: The fluores-
cence spectra of cyclophanes 1–3 in different organic sol-
vents were recorded and the fluorescence quantum yields
(Ff) were calculated with their monomeric counterparts as
standards. In addition, the fluorescence lifetimes (t) were
measured by a phase modulation method with a scattering
Figure 5 shows the simulated electronic absorption spectra
for isomers 2a and 2b. In good consistency with the experi-
mental results, our calculated results show that the lowest-
energy absorption at 632 nm, due to the electronic transi-
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X. Li et al.
solution as reference. The fluo-
rescence spectra of cyclophanes
1 and 3 are shown in Figure 6
and the fluorescence quantum
yields and lifetimes are sum-
marized in Table 2. Notably, no
emission was detected for
either of the two isomers of cy-
clophane 2, which indicates the
presence of charge separation
between the two PDI units in
this compound, as observed
previously by Wasielweski in a
noncyclic PDI dimer.[14]
As shown in Figure 6, an in-
tense emission band at 659 nm
appears in the fluorescence
spectrum of cyclophane 1 re-
corded in CH2Cl2, which shifts
to the lower-energy direction
by about 90 nm in comparison
with that of the monomeric
counterpart 4. This broad,
structureless band is attributed
to the excimerꢁs emission ac-
cording to previous reports.[13,23]
Comparison of the results
shown in Table 2 reveals that
the
fluorescence
quantum
yields of cyclophane 1 in organ-
ic solvents are significantly
smaller than those of the mono-
meric counterpart 4, which
meanwhile decrease along with
an increase in the polarity of
Figure 4. Frontier orbital maps and energy levels of isomers 2a (left) and 2b (right) calculated by DFT.
the organic solvent. These results suggest that the excited
states of cyclophane 1 have a remarkable electron-transfer
characteristic, which induces a mass of nonradioactive decay
of the excited states and in turn leads to a significant de-
crease in the fluorescence quantum yields. In addition, the
fluorescence lifetime of cyclophane 1 also shows depend-
ence on the polarity of the solvents due to the different sta-
bilization ability of solvents with different polarity to the ex-
cited states.[24] Interestingly, the fluorescence lifetime of cy-
clophane 1 in toluene, 38.1 ns, is significantly longer than
that of other PDI dimers connected by a spacer with a flexi-
ble structure in the same solvent,[13,16] most probably due to
the rigid molecular structure of both trans and cis isomers of
cyclophane 1 which hinders structural relaxation during the
decay of the excited states. In addition, this is the longest
fluorescence lifetime observed so far for a face-to-face
stacked PDI dimer.
Similar to its monomeric counterpart 6, the emission of
cyclophane 3 appears at 605 nm (Figure 6B). However, the
fluorescence lifetime of cyclophane 3 decreases along with
an increase in the polarity of the solvent, in line with the re-
sults for cyclophane 1. This is obviously different from the
Figure 5. Simulated (c) and experimental (a) absorption spectra of
cyclophanes 2a (A) and 2b (B) in chloroform. Bars indicate the contribu-
tion modes.
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Cyclophanes of Perylene Tetracarboxylic Diimide
FULL PAPER
Table 3. Half-wave redox potentials[a] (vs. SCE) of cyclophanes 1–3 and
their monomeric counterparts 4–6 in CH2Cl2.
[b]
Compounds
Ox2
Ox1
Red1
Red2
Red3
Eo
1/2
1
1.72
0.86
0.9
ꢀ0.55
ꢀ0.66
ꢀ0.63
ꢀ0.66
ꢀ0.67
ꢀ0.78
ꢀ0.72
ꢀ0.71
ꢀ0.81
ꢀ0.8
2.27
1.54
1.53
2.04
2.11
1.57
2.00
2a
2b
3
4
5
ꢀ0.98
ꢀ1.06
1.271.38
1.78
ꢀ0.85
ꢀ0.89
ꢀ0.96
ꢀ0.95
1.44
0.79
1.28
6
[a] Values obtained by DPV in dry CH2Cl2 with 0.1m tetrabutylammoni-
um phosphate (TBAP) as the supporting electrolyte and Fc/Fc+ as inter-
nal standard. [b] Eo1/2 =Ox1ꢀRed1.
Figure 6. Fluorescence spectra of cyclophanes 1 (A) and 3 (B) (c)
compared with those of compounds 4 (A) and 6 (B) (a) in dichloro-
methane (excited at 400 nm).
Table 2. Photophysical properties of compounds 1–6.
Compound labs
lem
Ff [%]
t [ns]
[nm] [nm]
toluene THF CH2Cl2 toluene THF CH2Cl2
1
512 660 5.53
1.45 1.10
38.09
–
15.38 13.25
2a
2b
3
4
5
632
–
–
–
–
–
–
617–
–
–
–
–
–
–
537605 5.51
1.32 0.89
100 100
11.36
4.63
3.85 2.39
4.69 4.64
540 569 100
672 730 3.41
576 602 81.2
1.35 6.8
82.0 80.1
3.64
6.19
1.97 2.46
6.80 6.78
6
Figure 7. CV (A) and DPV (B) plots of cyclophane 2a in dichlorome-
thane containing 0.1m TBAP.
behavior of its monomeric counterpart 6, which shows an
almost unchanged fluorescence lifetime at approximately
6.80 ns in different solvents. More importantly, analysis of
the fluorescence characteristics of cyclophane 3 in all three
solvents reveals a single exponential decay for the excited
states of this compound, and no component close to the
fluorescence lifetime of monomeric counterpart 6 is ob-
served. All these results indicate the dimeric-structure-origi-
nated nature of the emission at 605 nm for cyclophane 3, de-
spite the similar emission wavelength to its monomeric
counterpart.
Comparison of the first oxidation and reduction potentials
of cyclophane 1 with those of its monomeric counterpart 4
reveals that the face-to-face stacking of the PDI rings shifts
the half-wave potentials for the first oxidation and reduction
to the positive direction and makes cyclophane 1 harder to
oxidize and more easily reduced, which indicates the de-
crease in the energy of both the HOMO and LUMO of the
dimeric cyclophane 1. A similar positive shift for the first
oxidation and reduction potentials of cyclophanes 2 (includ-
ing both 2a and 2b) and 3 compared with their monomeric
counterparts 5 and 6, respectively, is also observed. This
finding is in line with DFT calculations on the energy of the
frontier molecular orbitals of both trans and cis isomers of
cyclophane 2 (Figure 4). In comparison with the almost
identical electrochemical property of the PDI dimer linked
by one triazine spacer with a flexible structure,[16] the above-
mentioned results reveal the crucial role of the rigid face-to-
face stacked geometry in cyclophanes 1–3 for the positive
shift of their first oxidation and reduction potentials. Fur-
thermore, the larger positive shift in the first oxidation and
reduction potentials for cyclophane 1 relative to its mono-
Electrochemistry: The electrochemical behavior of all the
newly synthesized cyclophanes was investigated by cyclic
voltammetry (CV) and differential pulse voltammetry
(DPV) in CH2Cl2. The half-wave redox potential values
versus SCE for cyclophanes 1–3 and their monomeric coun-
terparts 4–6 are summarized in Table 3. Figure 7shows the
cyclic and differential pulse voltammograms of cyclophane
2a as a typical representative of the series of compounds.
Within the electrochemical window of CH2Cl2, cyclophanes
1–3 undergo at least one reversible one-electron oxidation
process and two quasi-reversible one-electron reductions.
Chem. Eur. J. 2008, 14, 7000 – 7010
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7007

X. Li et al.
nyl)]perylene-3,4:9,10-tetracarboxylic diimide (5),[28] and [N,N’-dicyclo-
hexyl-1,6,7,12-tetra(p-tert-butyl)phenoxy]perylene-3,4:9,10-tetracarboxylic
diimide (6)[29] were prepared by following the literature methods. The di-
anhydrides 8–10 were prepared by the hydrolysis of compounds 4–6 in n-
propanol and potassium hydroxide according to published procedures.[30]
Other chemicals were purchased from commercial sources. Solvents were
of analytical grade and purified by the standard method.
meric counterpart 4 in comparison with that of cyclophane 3
indicates the relatively intense p–p interaction between the
two PDI rings in the former cyclophane. A similar conclu-
sion can also be drawn by comparing the electrochemical
properties of trans isomer 2a and cis isomer 2b.
2-N,N-Di
2,4,6-trichloro-1,3,5-triazine (5.43 g, 29.4 mmol) and N,N’-diisopropyl-
ethylamine (DIPEA; 6 mL) in THF (40 mL) was cooled to 0–58C in a
A
Conclusion
AHCTREUNG
ice-water bath. Dibutylamine (4.99 mL, 29.4 mmol) was added dropwise
in 30 min. The reaction mixture was stirred at 0–58C for another 30 min,
then warmed to room temperature and kept at that temperature for 2 h.
This reaction mixture was added slowly to a cooled mixture of THF
(50 mL) and hydrazine (85%, 10 mL) at ꢀ108C. The resulting reaction
mixture was further stirred at ꢀ108C for 6 h and then stirred continuous-
ly at room temperature for 24 h. After removing the solvent under re-
duced pressure, the residue was washed thoroughly with toluene, water,
and methanol. Compound 7 was collected as a white solid (5.29 g, 67%).
M.p. 1228C; 1H NMR (300 MHz, CDCl3, 258C, TMS): d=6.52 (br, 2H;
NH), 4.23 (br, 4H; NCH2), 3.48–3.56 (br, 4H; CH2), 1.52–1.64 (br, 4H;
CH2), 1.30–1.40 (br, 4H; CH2), 0.92 ppm (m, 6H; CH3); MS (70 eV): m/z
(%): 269.72 (100) [M+H]; elemental analysis calcd (%) for C11H24N8: C
49.23, H 9.01, N 41.75; found: C 49.18, H 8.87, N 41.43.
A series of cyclophanes 1–3, composed of two substituted
PDI rings connected by two triazine spacers with rigid face-
to-face dimeric structure, have been designed and prepared
for the first time. In particular, the successful separation of
the two isomers of cyclophane 2 has been achieved by TLC.
The trans and cis isomers, 2a and 2b, were structurally char-
acterized by 2D NMR spectroscopy. These cyclophanes with
rigid face-to-face dimeric structures render it possible to cor-
relate the molecular structure with optical and electrochemi-
cal properties. The structural parameters, including interpla-
nar distance, lateral sideways slippage along the short or
long axis of the PDI ring, and the in-plane torsion angle be-
tween the long axis of the PDI ring, seem to be the domi-
nating factors that affect the optical or electrochemical
properties definitively. Tiny structure differences will induce
significant changes in the optical or electrochemical proper-
ties. To the best of our knowledge, this represents the first
experimental effort towards understanding the correlation
of the dimeric structure with the optical properties of PDI
derivatives. The results will be useful for the design and
preparation of new supramolecular systems of PDIs with
novel structure and optical properties.
Cyclophane 1: A mixture of [N,N’-dicyclohexyl-1,7-di(p-tert-butylphen-
A
dianhydride
(8;
88 mg,
AHCTREUNG
zine-1,3,5-triazine (7; 35 mg, 0.129 mmol) in toluene (300 mL) was heated
to reflux under a nitrogen atmosphere and kept at reflux for 48 h. The
solvent was removed under reduced pressure and the residue was washed
with dilute hydrochloric acid (10%, 100 mL) and then water. The prod-
uct was purified by column chromatography on silica gel with chloroform
as eluent. After recrystallization from chloroform and methanol, the
product was collected as
1H NMR (300 MHz, CDCl3, 258C, TMS): d=9.54 (d, J
4H; perylene, isomer 1), 9.28 (d, (H,H)=8.4 Hz, 4H; perylene,
isomer 2), 8.31 (d, J(H,H)=8.1 Hz, 4H; perylene, isomer 1), 8.28 (d, J-
(H,H)=8.4 Hz, 4H; perylene, isomer 2), 8.11 (s, 4H; perylene, isomer 2),
a
red solid (9.8 mg, 8%). M.p. >3008C;
AHCTREUNG
J
ACHTREUNG
AHCTREUNG
AHCTREUNG
8.01 (s, 4H; perylene, isomer 1), 7.47 (m, 16H; phenyl, isomer 1+2), 7.07
(m, 16H; phenyl, isomer 1+2), 6.90 (s, 8H; NH, isomer 1+2), 3.52 (m,
16H; NCH2, isomer 1+2), 1.62 (m, 16H; CH2, isomer 1+2), 1.41–1.31
Experimental Section
(m, 88H; CH2 +C(CH3)3, isomer 1+2), 0.96 ppm (t, 24H; CH3,
A
isomer 1+2); MS (MALDI-TOF): m/z: 1842.1 [M+]; elemental analysis
calcd (%) for C110H104N16O12: C 71.72, H 5.69, N 12.17; found: C 71.35, H
5.51, N 11.89.
General method: 1H NMR spectra were recorded at 300 MHz with the
solvent peak as internal standard (in CDCl3). Electronic absorption spec-
tra were recorded in organic solvents at room temperature. Fluorescence
spectra and the fluorescence lifetime were measured on a multifrequency
phase and modulation fluorometer with the excitation at 400 nm. The
fluorescence lifetimes were measured by the multifrequency phase modu-
lation method with a scattering sample as standard.[26] Fluorescence
quantum yields were calculated with compound 4 as standard. MALDI-
TOF mass spectra were obtained on an ultrahigh-resolution Fourier
transform ion cyclotron resonance (FT-ICR) mass spectrometer. Electro-
chemical measurements were carried out under a nitrogen atmosphere
on an electrochemical workstation. The cell comprised inlets for a glassy
carbon disk working electrode 2.0 mm in diameter and a silver-wire coun-
ter electrode. The reference electrode was Ag/Ag+, which was connected
to the solution by a Luggin capillary, the tip of which was placed close to
the working electrode. It was corrected for junction potentials by being
Cyclophanes 2a and 2b: By using a similar procedure to that for prepar-
ing cyclophane 1, with [N,N’-dicyclohexyl-1,6,7,12-tetra(p-tert-butyl)phe-
noxy]perylene-3,4:9,10-tetracarboxylic diimide (10; 127mg, 0.129 mmol)
instead of 8 as starting material, cyclophane 2 was synthesized. The prod-
uct was purified by column chromatography on silica gel with chloroform
as eluent. The first fraction contained cyclophanes 2a and 2b, which
were further separated by preparative TLC. The first green fraction from
TLC was 2a (4 mg, 3.7%) and the second fraction was 2b (1.3 mg,
1.2%).
2a: M.p. >3008C; 1H NMR (300 MHz, CDCl3, 258C, TMS): d=9.66 (d,
J
N
N
8.4 Hz, 4H; perylene), 6.94 (s, 4H; NH), 3.61 (m, 8H; NCH2), 3.21 (t,
4H; piperidine), 2.72 (d, 4H; piperidine), 2.17 (m, 8H; CH2), 1.90 (m,
8H; CH2), 1.69 (m, 16H; piperidine), 1.42 (m, 16H; piperidine),
0.98 ppm (t, 12H; CH3); MS (MALDI-TOF): m/z: 1581.3 [M+]; elemen-
tal analysis calcd (%) for C90H92N20O8: C 68.34, H 5.86, N 17.71; found: C
68.21, H 5.79, N 17.69.
referenced internally to the Fe+/Fe couple [E1/2
SCE]. Typically, a solution (0.1 moldmꢀ3) of [Bu4N]
ACHTREUNG
AHCTREUNG
thane containing the sample (0.5 mmoldmꢀ3) was purged with nitrogen
for 10 min, then the voltammograms were recorded at ambient tempera-
ture. The scan rates were 20 and 10 mVsꢀ1 for CV and DPV, respectively.
TDDFT calculations with the B3LYP method and 6-31G(d) basis set
were carried out to study the molecular structures, molecular orbitals,
and electronic absorption spectra of these cyclophanes.
2b: M.p. >3008C; 1H NMR (300 MHz, CDCl3, 258C, TMS): d=9.84 (d,
J
N
N
8.4 Hz, 4H; perylene), 6.99 (s, 4H; NH), 3.58 (m, 8H; NCH2), 3.23 (t,
4H; piperidine), 2.86 (m, 4H; piperidine), 2.35 (m, 8H; CH2), 1.96 (m,
8H; CH2), 1.65 (m, 16H; piperidine), 1.40 (m, 16H; piperidine),
1.03 ppm (t, 12H; CH3); MS (MALDI-TOF): m/z: 1581.5 [M+]; elemen-
Materials:
[N,N’-dicyclohexyl-1,7-di(p-tert-butylphenoxy)]perylene-
3,4:9,10-tetracarboxylic diimide (4),[27] [N,N’-dicyclohexyl-1,7-di(piperidi-
7008
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Cyclophanes of Perylene Tetracarboxylic Diimide
FULL PAPER
tal analysis calcd (%) for C90H92N20O8: C 68.34, H 5.86, N 17.71; found:
C 68.12, H 5.85, N 17.69.
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Cyclophane 3: By employing a similar procedure to that for cyclophane
1, with [N,N’-dicyclohexyl-1,6,7,12-tetra(p-tert-butyl)phenoxy]perylene-
3,4:9,10-tetracarboxylic diimide (10; 127mg, 0.129 mmol) instead of 8 as
starting material, cyclophane 3 was prepared. The product was purified
by column chromatography on silica gel with chloroform as eluent. The
first red fraction contained cyclophane 3 (5 mg, 3.1%). M.p. >3008C;
1H NMR (300 MHz, CDCl3, 258C, TMS): d=8.08 (b, 4H; perylene), 7.88
(b, 4H; perylene), 7.08 (b, 16H; perylene), 6.80 (s, 4H; NH), 6.64 (b,
8H; phenyl), 6.41 (b, 8H; phenyl), 3.39 (b, 8H; NCH2), 1.60–1.43 (m,
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Financial support from the Natural Science Foundation of China (Grant
Nos. 20571049, 20771066, 20431010), Ministry of Education of China, and
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