Novel pyromellitic diimide-based macrocycle with a linear π-electronic system and bis(phenylethynyl)pyromellitic diimide: Syntheses, structures, photophysical properties, and redox characteristics

Article abstract of DOI:10.1021/jo800283r

(Chemical Equation Presented) We report the syntheses, structures, photophysical properties, and redox characteristics of the [2 + 2] pyromellitic diimide-based macrocycle with a linear π-electronic system 2 as well as the 3,6-bis(phenylethynyl)pyromellitic diimide derivative 3. The interesting solid state structural properties of the clathrates of 3 with π-donors are also reported. The macrocycle 2 was synthesized by the direct cyclocondensation followed by the Sonogashira coupling reaction. X-ray crystallographic studies showed that the phenylacetylene moieties in 2 formed the intramolecular benzene dimer structures, and the bis(phenylethynyl)pyromellitic diimide moieties in both 2 and 3 were stacked in a parallel and slanted arrangement. Theoretical calculations for 2′ and 3 suggested the existence of electrostatic interactions between the bis(phenylethynyl)pyromellitic diimide moieties. The UV/vis spectral measurements and TDDFT calculations of 2, 2′, and/or 3 were performed to understand their electronic transitions. The fluorescence spectral measurements showed that 2 and 3 have visible fluorescence properties and 2 displays an excimer fluorescence at ca. 590 nm. The cyclic voltammetry measurements revealed that the electrostatic repulsion between the diimide moieties in 2 is greater than that in 1 according to the extension of the π-electronic systems. X-ray crystallography of the clathrates of 3 with various π-donors demonstrated the formation of the segregated donor-acceptor structures, indicating the strong aggregation ability of the bis(phenylethynyl)pyromellitic diimide moiety.

Full text of DOI:10.1021/jo800283r

Novel Pyromellitic Diimide-Based Macrocycle with a Linear
π-Electronic System and Bis(phenylethynyl)pyromellitic Diimide:
Syntheses, Structures, Photophysical Properties, and Redox
Characteristics1
Shin-ichiro Kato,†,‡ Yasuhiro Nonaka,†,‡ Toshiaki Shimasaki,†,‡ Kenta Goto,† and
Teruo Shinmyozu*,†
Institute for Materials Chemistry and Engineering (IMCE) and Department of Molecular Chemistry,
Graduate School of Sciences, Kyushu UniVersity, Hakozaki 6-10-1 Higashi-ku, Fukuoka 812-8581, Japan
shinmyo@ms.ifoc.kyushu-u.ac.jp
ReceiVed February 13, 2008
We report the syntheses, structures, photophysical properties, and redox characteristics of the [2 + 2]
pyromellitic diimide-based macrocycle with a linear π-electronic system 2 as well as the 3,6-
bis(phenylethynyl)pyromellitic diimide derivative 3. The interesting solid state structural properties of
the clathrates of 3 with π-donors are also reported. The macrocycle 2 was synthesized by the direct
cyclocondensation followed by the Sonogashira coupling reaction. X-ray crystallographic studies showed
that the phenylacetylene moieties in 2 formed the intramolecular benzene dimer structures, and the
bis(phenylethynyl)pyromellitic diimide moieties in both 2 and 3 were stacked in a parallel and slanted
arrangement. Theoretical calculations for 2′ and 3 suggested the existence of electrostatic interactions
between the bis(phenylethynyl)pyromellitic diimide moieties. The UV/vis spectral measurements and
TDDFT calculations of 2, 2′, and/or 3 were performed to understand their electronic transitions. The
fluorescence spectral measurements showed that 2 and 3 have visible fluorescence properties and 2 displays
an excimer fluorescence at ca. 590 nm. The cyclic voltammetry measurements revealed that the electrostatic
repulsion between the diimide moieties in 2 is greater than that in 1 according to the extension of the
π-electronic systems. X-ray crystallography of the clathrates of 3 with various π-donors demonstrated
the formation of the segregated donor-acceptor structures, indicating the strong aggregation ability of
the bis(phenylethynyl)pyromellitic diimide moiety.
1. Introduction
material and supramolecular chemistry. In the past years,
functionalized NDIs and PBIs2 were tailored for applications
in various research fields. Aromatic diimides are easily revers-
ibly reduced to form stable radical anion species. Due to their
n-type semiconducting properties, functionalized NDIs and PBIs
Aromatic diimides, particularly naphthalene diimides (NDIs)
and perylene bisimides (PBIs), are important compounds for
* To whom correspondence should be addressed. Phone: +81-92-642-2720.
Fax: +81-92-642-2735.
† Institute for Materials Chemistry and Engineering.
‡ Department of Molecular Chemistry, Graduate School of Sciences, Kyushu
University.
(2) (a) Wu¨rthner, F. Chem. Commun. 2004, 1564–1579. (b) Grimsdale, A. C.;
Mu¨llen, K. Angew. Chem., Int. Ed. 2005, 44, 5592–5629. (c) Wasielewski, M. R.
J. Org. Chem. 2006, 71, 5051–5066. (d) Wu¨rthner, F. Pure Appl. Chem. 2006,
78, 2341–2350.
(1) Molecular Tubes and Capsules, Part 4. For Part 1-3, see refs 17a-c.
10.1021/jo800283r CCC: $40.75
Published on Web 04/23/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 4063–4075 4063

Kato et al.
have been of much interest as the active layer in organic field-
effect transistors (OFETs).3,4 In this context, the preparation of
core-substituted naphthalene dianhydrides as versatile precursors
has been most recently explored to develop the NDI-based future
functional materials by Wu¨rthner et al.5 In supramolecular
chemistry, aromatic diimides with both an electron-withdrawing
property and extended π-surface, which exploit the charge-
transfer (CT) interactions between aromatic π-systems, i.e.,
alkoxynaphthalenes, have been used in the design of a plethora
of supramolecular architectures, such as [2]catenanes,6,7 [2]ro-
taxanes,8 folded aedamers,9 and macrocycle-tweezer com-
plexes.10 Additionally, the aggregation of PBIs with solubilizing
3,4,5-trialkoxyphenyl and 3,4,5-trialkylphenyl substituents at the
imide functional groups were achieved both in solution and in
the condensed phase on the basis of their strong π-stacking
interactions and van der Waals interactions.11 Afterward, it was
recently reported that NDIs and PBIs, which enable π-stacking
interactions, hydrogen bonding, and van der Waals interactions,
formed robust 1D organogel structures.12 Thus, the created
supramolecular structures could be regarded as candidates for
the attractive functional materials due to the presence of
photophysically and electrochemically active aromatic diim-
ides.13
Pyromellitic diimides, which have only a central benzene
core, are the smallest moieties among the class of aromatic
diimides. Pyromellitic diimides also have a sufficient electron
affinity and can interact with electron-rich π-systems by CT
interactions in solution and the solid state regardless of the
smallness of their core π surfaces relative to NDIs and PBIs.
Therefore, the creation of supramolecular architectures,14 es-
pecially [2]catenanes7a–f and [2]rotaxanes,8b–d and their applica-
tions to molecular receptors15 have been achieved due to their
peculiar properties similar to those of the NDIs and PBIs.
Although the functionalized pyromellitic diimides would be
important compounds in terms of their optoelectronic and
electrochemical properties, only a limited number of them have
been reported.16
We have been investigating the molecular recognition proper-
ties of pyromellitic diimide-based macrocycles, which were
synthesized by the cyclocondensation of commercially available
pyromellitic dianhydride and alkoxy-substituted bis(amino-
methyl)arenes.17 Recently, we reported the first example of
“cyclophanes within cyclophanes” based on CT interactions as
the driving force, which has been confirmed by X-ray
crystallography.17a Furthermore, we have more recently syn-
thesized the macrocycle 1, and 1 constructs 1D and 2D
supramolecular assemblies with naphthols in the solid states with
the regioselectivity of the hydroxyl groups of the naphthols and
exhibits redox modulations via noncovalent interactions with
the naphthols (Figure 1).17b As a part of our continuing effort
to develop this type of pyromellitic diimide-based macrocycle,
we planned to synthesize a macrocycle with a linear π-electronic
system 2 and bis(phenylethynyl)pyromellitic diimide 3 in which
the phenylethynyl groups were introduced at the core benzene
rings because of the interest in the effect of the elongated
π-system in the pyromellitic diimide moiety on their optoelec-
tronic and electrochemical properties (Figure 1). Compounds 2
and 3 are regarded as aromatic acetylene analogues which are
now recognized as ideal materials for advanced applications.18,19
We now report the synthesis of 2 and 3 and their electronic
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compounds based on pyromellitic diimide moiety, N,N′-di(2-tert-butylphenyl)-
3,6-di(4-chlorophneyl)pyromellitic diimide, by the approach different from ours.
See: Dong, Z.; Liu, X.; Yap, G. P. A.; Fox, J. M. J. Org. Chem. 2007, 72,
617–625.
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K.; Shimasaki, T.; Goto, K.; Shinmyozu, T. J. Org. Chem. 2006, 71, 4723–
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4064 J. Org. Chem. Vol. 73, No. 11, 2008

NoVel Pyromellitic Diimide-Based Macrocycles
FIGURE 1. Structures of the [2 + 2] pyromellitic diimide-based macrocycle 1, macrocycle with a linear π-electronic system 2, and
bis(phenylethynyl)pyromellitic diimide 3.
properties, based on their electronic and fluorescence spectra,
and redox potentials. The structures of 2 and 3 and the unusual
aggregation ability of the bis(phenylethynyl)pyromellitic diimide
moiety in the solid state are also discussed on the basis of the
X-ray crystallographic analyses, theoretical calculations, and
MALDI-TOF mass spectrum. Finally, the formation of the CT
complexes and segregated donor-acceptor crystal structures of
3 with various π-donors are demonstrated in UV/vis titration
studies and X-ray crystallography results, respectively.
6 by ICl at room temperature (92%). The cyanation of 6 with
CuCN in NMP afforded the dinitrile 7 (59%), which was
converted into the diamine 8 by reduction with DIBAL-H at
110 °C (53%). The cyclocondensation of 8 and 3,6-dibromopy-
romellitic dianhydride (9), which was prepared from durene in
3 steps,22,23 followed by dehydration with NaOAc and Ac2O
gave the [2 + 2] tetrabromo-substituted macrocycle 10 (12%).
1
The H NMR spectrum of the macrocycle 10 is very simple,
exhibiting a pair of two singlets at 6.49 and 6.52 ppm in CDCl3
due to the spacer benzene protons in line with its D2h-symmetric
structure. Although the solubility of the macrocycle 10 in
organic solvents was very poor, it was purified by silica gel
column chromatography (CHCl3/hexane) because the higher
oligomers, such as [3 + 3] and [4 + 4] macrocycles, were not
isolated. Finally, the Sonogashira coupling reaction24 of 10 with
phenylacetylene in the presence of PdCl2(PPh3)2 as a catalyst
afforded the desired 2 (23%).25 For the comparison of the
photophysical and electrochemical properties of the macrocycle
2, the acyclic reference compound, N,N′-di-n-butyl-3,6-bis(phe-
nylethynyl)pyromellitic diimide 3, was prepared from the
anhydride 9 by a similar procedure for the synthesis of 2.
Compounds 2 and 3 have been fully characterized by various
2. Results and Discussion
Synthesis. The synthesis of the [2 + 2] pyromellitic
diimide-based macrocycle with a linear π-electronic system
2 was achieved by cyclocondensation followed by Sono-
gashira coupling as the key reactions (Scheme 1). The
solubilizing octyloxy groups were engineered into 2 to
alleviate the anticipated solubility problems. 1,3-Bis(ami-
nomethyl)-4,6-dioctyloxy-benzene (8) was prepared from
resorcinol (4) by a similar series of reactions reported for the
preparation of 1,3-bis(aminomethyl)-4,6-di-n-butoxybenzene.17b,20
1,3-Di-n-octyloxybenzene (5)21was transformed into the diiode
(19) For recent reviews of aromatic acetylenes, see: (a) Diederich, F.; Gobbi,
L. Top. Curr. Chem. 1999, 201, 43–79. (b) Haley, M. M.; Pak, J. J.; Brand,
S. C. Top. Curr. Chem. 1999, 201, 81–130. (c) Bunz, U. H. F.; Rubin, Y.; Tobe,
Y. Chem. Soc. ReV. 1999, 101–119. (d) Youngs, W. J.; Tessier, C. A.; Bradshaw,
J. D. Chem. ReV. 1999, 99, 3153–3180. (e) Bunz, U. H. F. Chem. ReV. 2000,
100, 1605–1644. (f) Tour, J. M. Acc. Chem. Res. 2000, 33, 791–804. (g) Simsen,
P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int. Ed. 2000, 39, 2632–
2657. (h) Diederich, F. Chem. Commun. 2001, 219–227. (i) Zhao, D.; Moore,
J. S. Chem. Commun. 2003, 807–818. (j) Spitler, E. L.; Johnson, C. A.; Haley,
M. M. Chem. ReV. 2006, 106, 5344–5386. (k) Orita, A.; Otera, J. Chem. ReV.
2006, 106, 5387–5412.
(22) Suh, D. H.; Chung, E. Y.; Hong, Y.-T; Choi, K.-Y. Angew. Makromol.
Chem. 1998, 254, 33–38.
(23) To our knowledge, the detailed procedures of 9 have not been described
in the literature.22 Thus, our procedure was described in the Experimental Section.
The use of unpurified 9 significantly decreased the cyclocondensation yield (less
than 1%) probably due to the side reactions.
(24) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
16, 4467–4470. (b) Sonogashira, K. J. Organomet. Chem. 2002, 653, 46–49.
(25) We also prepared the tetrabromide 12 with the dibutoxy substituents at
the benzene linkers (Experimental Section) by the cyclocondensation of the
anhydride 9 and 1,3-bis(aminomethyl)-4,6-di-n-butoxybenzene and attempted
the Sonogashira reaction of 12 with phenylacetylene under the same reaction
conditions for the synthesis of 2. However, the reaction resulted in the quantitative
recovery of 12 due to the poor solubility of 12 in common organic solvents.
(20) Sasaki, S.; Mizuno, M.; Naemura, K.; Tobe, Y. J. Org. Chem. 2000,
65, 275–283.
(21) (a) Mohr, B.; Enkelmann, V.; Wegner, G. J. Org. Chem. 1994, 59, 635–
638. (b) Higuchi, T.; Satake, C.; Hirobe, M. J. Am. Chem. Soc. 1995, 117, 8879–
8880.
J. Org. Chem. Vol. 73, No. 11, 2008 4065

Kato et al.
SCHEME 1. Synthesis of Pyromellitic Diimide-Based Macrocycle with Linear π-Electronic System 2 and Bis(phenylethynyl)-
pyromellitic Diimide 3a
a Reagents and conditions: (a) 1-bromooctane, NaI, K2CO3, acetone, reflux for 48 h; (b) ICl, AcOH, rt for 3 h; (c) CuCN, NMP, 150 °C for 10 h; (d)
DIBAL-H, toluene, 110 °C for 4 h; (e) compound 9, THF, 50 °C for 24 h; (f) NaOAc, Ac2O, rt for 3 h to 100 °C for 1 h; (g) phenylacetylene, PdCl2(PPh3)2,
CuI, Et3N, THF, 75 °C for 36 h; (h) n-butylamine, THF, rt for 12 h; (i) NaOAc, Ac2O, 100 °C for 1 h; (j) phenylacetylene, PdCl2(PPh3)2, CuI, Et3N, THF,
75 °C for 12 h.
spectroscopic methods and elemental analysis,26 and finally by
X-ray crystallographic analyses as described below.
facing benzene ring was only 2.8°. The transannular distance
between the benzene rings of the diimide moieties was only
4.09 Å, and this indicated a significant decrease (ca. 20%) in
the distance compared to the corresponding distance of 1 (5.06
Å). It is well documented that the attractive interaction in the
benzene dimer would increase in the perpendicular T-shaped
and parallel-displaced geometries.28 The observed benzene dimer
geometry of 2 almost satisfied this geometrical requirement to
maximize the attractive interactions, which can compensate for
the destabilization caused by the deformation of the pyromellitic
diimide moieties. However, the deformation of the pyromellitic
diimide moieties of 2 was not observed in the optimized
structure calculated at the B3LYP/6-31G* level of theory (Figure
S30, Supporting Information).29 Therefore, the crystal packing
force also would contribute to the geometry of 2 observed in
the X-ray crystallography spectrum.
Structural Properties. Single crystals of 2 suitable for an
X-ray crystallographic analysis were obtained by recrystalliza-
tion from DMF. We reported that 1 formed a clathrate
compound with DMF (1:DMF ) 1:2),17b but DMF was not
included in the single crystals of 2 (Figure 2). The transannular
pyromellitic diimide moieties with phenylacetylene units of 2
were set in parallel (Figure 2a). The phenyl rings of the
phenylacetylene units of 2 were slightly twisted against the
benzene ring of the diimide moieties with the dihedral angles
for C1-C10-C29-C30 and C4-C5-C21-C26 of -12.3° and
15.1°, respectively. The dihedral angle between the benzene ring
of the diimide moiety and the benzene ring of the xylyl moiety
was 80.6°. Interestingly, the phenyl rings of the phenylacetylene
units were stacked in a parallel-displaced geometry with the
distance between the centers of the two facing benzene rings
of 3.39 Å and formed the benzene dimer (Figure 2b). The angle
between the plane of the benzene ring and the stacking axis
was 64.0°. The transannular distance (3.39 Å) of the benzene
rings was almost equal to the sum of the van der Waals radii of
the two sp2 carbons (2 × 1.7 Å) or the value of the common
stacked π-system (3.4 Å).27 In the benzene dimer structure, the
incline of the benzene ring of the phenylacetylene unit and the
Figure 3a shows the side view of the packing arrangement
of 2, and the molecules were packed in a parallel and slanted
arrangement with the intermolecular distance between the center
of the benzene ring of the pyromellitic diimide moiety and the
(28) For review of high-accuracy quantum mechanical studies in benzene
dimers, see: Sinnokrot, M. O.; Sherrill, C. D. J. Phys. Chem. A 2006, 110, 10656–
10668.
(29) In the optimized structure of 2′ at the B3LYP/6-31G* level, the
transannular distance between the benzene rings of the diimide moieties is 5.17
Å: This value is clearly larger than the experimental value. It is pointed out that
the underestimation of attractive π-π interaction is common to anthracene-
acetylene oligomers at the B3LYP/6-31G level by Toyota et al, see: Ishikawa,
T.; Shimasaki, T.; Akashi, H.; Toyota, S. Org. Lett. 2008, 10, 417–420.
(30) The stacking in the parallel and slanted arrangement was not observed
in 1·(DMF) clathrate, where DMF served as an adhesive that bound the diimide
molecules to form the 1D network.17b
(26) Unfortunately, we could not carry out the variable-temperature 1H NMR
experiments for 2 and 10 due to their solubility problem in CD2Cl2. The
macrocycle 2 easily crystallized below 0 °C and 10 did not dissolve in common
organic solvents.
(27) The standard van der Waals radii are taken from: Bondi, A. J. Phys.
Chem. 1964, 68, 441–451.
4066 J. Org. Chem. Vol. 73, No. 11, 2008

NoVel Pyromellitic Diimide-Based Macrocycles
the b-axis with an H · · ·O distance of 2.67 (A of Figure 3c) and
2.42 (B of Figure 3c) Å, respectively.
Single crystals of 3 for an X-ray crystallographic analysis
were obtained by recrystallization from p-xylene as a clathrate
with p-xylene having a 2:1 stoichiometry. As shown in Figure
4b, the ORTEP drawing of 3 exhibited a nearly planar structure
with the dihedral angles for C6-C9-C21-C26 and C7-C12-
C29-C30 of -9.6° and 5.3°, respectively, and the trans
conformation of the butyl groups on the nitrogen atoms.
The acyclic 3 also packed in a parallel and slanted arrange-
ment as in the case of the macrocycle 2, although two kinds of
stacking arrangements were observed (Figure 5a).32 The closest
intermolecular distances between the center of the one diimide
molecule and the π-face of another one of 3.21 (R-ꢀ of Figure
5a) and 3.23 (ꢀ-R of Figure 5a) Å were observed. The angle
between the plane of the diimide molecule and the stacking axis
was 42.5° (R-ꢀ of Figure 5a) and 43.0° (ꢀ-R of Figure 5a),
and these values were almost consistent with that of 2 in the
crystalline state. This finding was also indicative of the electronic
interaction between the diimide 3 and the calculation of the
Mulliken charge of 3 that was also conducted by the DFT
method (B3LYP/6-311G**//B3LYP/6-31G*). As expected, the
carbon atoms at the 3- and 6-positions, the adjacent sp2 carbon
atoms of phenylacetylene, and the carbonyl oxygen atoms of 3
were negatively charged with the values of -0.29, -0.20, and
-0.31, respectively. On the other hand, the carbonyl carbon
atoms and the adjacent sp carbon atoms of the diimide moiety
were found to be positively charged with the values of +0.45
and +0.14, respectively. Thus, the packing arrangement of 3 is
also interpreted by the possible electrostatic interaction caused
by the introduction of the phenylacetylene moiety, in which the
difference in the electrostatic interactions in 3 would provide
the two kinds of stacking patterns of R-ꢀ and ꢀ-R in Figure
5a. In addition to the analogous contacts in the case of 2,
the further electrostatic interaction between the carbon atom at
the 3-position in the diimide and the adjacent sp carbon atom
was observed in the stacking pattern of R-ꢀ in 3.
The packing diagram of (3)2 ·p-xylene in Figure 5b shows
that 3 exhibited a slanted stacking aligned a-axis and the
multipoint C-H· · ·O interactions between the carbonyl oxygen
and the phenyl hydrogen atoms with the C-H· · ·O distance of
2.47 (A of Figure 5b) and 2.60 (B of Figure 5b) Å. The p-xylene
molecules served as adhesive to interact with 3 by C-H· · ·π
interactions33 with the distance of 2.94 (C of Figure 5b) and
2.88 (D of Figure 5b) Å.
Photophysical Properties. The UV/vis and fluorescence
spectra of 1-3 were measured in CHCl3 and toluene to
investigate the influence of the solvent polarity on the optical
properties. These data are summarized in Table 1. The UV/vis
spectra in CHCl3 of 1-3 are shown in Figure 6. Compared to
1, the longer wavelength absorption maxima of 2 and 3 were
significantly shifted bathochromically by ca. 70 nm, and their
absorption coefficients (ꢀ) dramatically increased due to the
linear 1D π-system on the pyromellitic diimide moiety. The
macrocycle 2 [359 (ꢀ 89400), 380 (ꢀ 78000), 427 (ꢀ 8700, sh)]
and acyclic 3 [356 (ꢀ 47600), 376 (ꢀ 66800), 414 (ꢀ 5800, sh)]
in CHCl3 solution exhibited similar spectra with two absorption
maxima (λmax) and one shoulder above 400 nm. The transannular
FIGURE 2. (a) ORTEP drawing of the top view of 2. Thermal
ellipsoids are drawn at the 50% probability level; (b) X-ray crystal
structure of the side view of 2. Hydrogen atoms and octyl groups of 2
are omitted for clarity.
plane of facing molecule of 3.25 Å and with an angle between
the plane of the diimide and the stacking axis of 42.5°. This
distance is shorter than the common distance between the
stacked π-system (3.4 Å), strongly indicating the electronic
interaction between these π-systems.30 To examine the nature
of the intermolecular interaction, the Mulliken charge was
calculated for 2′, in which the octyloxy groups were replaced
with methoxy groups in 2, by the DFT method (B3LYP/6-
311G**//B3LYP/6-31G*).31 As expected from the features of
the carbonyl group, the carbonyl carbon atoms and oxygen
atoms were found to be positive (+0.43) and negative (-0.30),
respectively (Figure 3b). The adjacent sp2 benzene carbon atom
bearing an acetylene moiety was negatively charged (-0.20).
The closest intermolecular distances were observed between the
carbonyl carbon and the C-1 carbon atom of the benzene ring
in the phenylacetylene unit as well as between the carbonyl
carbon and oxygen atoms (Figure 3a). Thus, the electrostatic
interactions might play an important role in the parallel and
slanted packing of the molecules and provide that the intermo-
lecular electrostatic repulsion between the diimide moieties was
negligible.
Figure 3c shows the molecular packing of 2. The macrocycle
2 packed by aligning in the a-axis in a parallel and slanted
arrangement as described above. In addition, the intermolecular
C-H· · ·O interactions between the carbonyl oxygen atoms and
the phenyl hydrogen atoms were observed as being aligned in
(31) The crystal packing of dehydro[12]annulene fused with tetrafluoroben-
zne, in which one of the tetrafluorobenzene rings faced the annulene core of
another molecule, was rationalized with its Mulliken charge by using B3LYP/
6-31G(d) level of theory by Komatsu et al., see: Nishinaga, T.; Nodera, N.;
Miyata, Y.; Komatsu, K. J. Org. Chem. 2002, 67, 6091–6096.
(32) It was reported that N,N′-di(2-tert-butylphenyl)-3,6-di(4-chlorophneyl)-
pyromellitic diimide did not exhibit the intermolecular π-π interactions in the
crystalline state due to the bulky tert-butylphenyl groups.16
(33) Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π interactions; Wiley-
VCH: New York, 1998.
J. Org. Chem. Vol. 73, No. 11, 2008 4067

Kato et al.
FIGURE 3. (a) Side view of packing arrangement of 2. Dotted lines show within the sum of van der Waals radius and possible electrostatic
interactions. (b) Sketches with the Mulliken charge of 2′ at the B3LYP/6-311G**//B3LYP/6-31G* level: light and dark colors indicate positively
and negatively charged atoms, respectively; the diameters of the circles are in proportion to the values of charge distribution. (c) Packing diagram
of 2. Dotted lines show C-H· · ·O interactions. Octyl groups of 2 are omitted for clarity. Selected distances (Å) of dotted lines: A, 2.67; B, 2.42.
2 appeared at almost the same positions as those of 3, whereas
the intensities of the absorption bands of 2 were higher than
those of the corresponding bands of 3. The λmax values of 2
and 3 were scarcely changed between the nonpolar toluene and
more polar CHCl3 (Table 1).
The electronic transitions of the pyromellitic diimide-based
π-conjugated compounds structurally modified at the 3- and
6-positions have not been studied in detail, while those in the
pyromellitic diimide chromophore were well-documented by
Gawron´ski, Gawron´ska, Koput, and Rychlewska’s group.34
Therefore, we calculated the frontier molecular orbitals (FMOs)
of 2′ and 3 and their electronic transitions by the TDDFT method
at the B3LYP/6-31G* level of theory for their optimized
structures (B3LYP/6-31G*). As summarized in Table 1, this
level of calculations almost reproduced the UV/vis spectra of 2
and 3, predicting the absorption at 389 and 498 nm in 2 and
397 and 498 nm in 3. It is considered that the observed split of
the absorption bands around 340-400 nm in 2 and 3 was
derived from the vibrational structures.
Figure 7 shows the relationship between the electronic
transitions and the FMO plots of 2′ and 3. For 3, the calculations
predicted that the absorption bands around the shorter and longer
wavelength regions were essentially assigned to the transition
from the HOMO delocalized over the bis(phenylethynyl)py-
romellitic diimide moiety to the similarly delocalized LUMO+1
and the transition from the HOMO to the LUMO mainly
localized on the pyromellitic diimide moiety, respectively. The
larger oscillator strength of the HOMO f LUMO+1 transition
compared to that of HOMO f LUMO agreed well with the
trend in the observed ꢀ values. The FMOs of 2′ closely
FIGURE 4. ORTEP drawing of the (a) top view and (b) side view of
(3)2 ·p-xylene. Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms and the p-xylene molecule are omitted for clarity.
interaction of the pyromellitic diimide moieties in 2 might be
(34) Gawron´ski, J.; Brzostowska, M.; Gawron´ska, K.; Koput, J.; Rychlewska,
negligible in the ground state because the absorption bands of
U.; Skowronek, P.; Norde´n, B. Chem. Eur. J. 2002, 8, 2484–2494.
4068 J. Org. Chem. Vol. 73, No. 11, 2008

NoVel Pyromellitic Diimide-Based Macrocycles
FIGURE 5. (a) Side view of the packing arrangement of (3)2 ·p-xylene. Dotted lines show within the sum of van der Waals radius and possible
electrostatic interactions. (b) Packing diagram of (3)2 ·p-xylene. Dotted red and blue lines show C-H· · ·O and C-H· · ·π interactions, respectively.
Butyl groups of 3 are omitted for clarity. Selected distances (Å) of dotted lines: A, 2.47; B, 2.60; C, 2.94; D, 2.88.
TABLE 1. Electronic Absorption and Emission Data for 1-3
λmax [nm]
calcd λmax [nm]
(f)a
compd solvent (ꢀ [M-1 cm-1])
λem [nmb] (Φf)
1
2
CHCl3 285 (10600),
305 (5400)c
CHCl3 359 (89400),
380 (78000),
488 (0.001)d
389 (2.513),
498 (0.095)e
461, 592 (0.002)f
427 (sh, 8700)
toluene 357 (98200),
378 (83600),
442, 467, 583
(0.004)f
427 (sh, 9300)
CHCl3 356 (47600),
376 (66800),
3
397 (1.446),
498 (0.051)
492 (0.11)f
414 (sh, 5800)
toluene 353 (47300),
375 (67500),
477 (0.11)f
414 (sh, 7500)
a TDDFT (TD/B3LYP/6-31G*) calculations were carried out with use of
optimized structures at the B3LYP/6-31G* level of theory. b Measured in 1
× 10-6 M solution. c Reference 17b. d Fluorescence quantum yield
relative to anthracene. e In 2′, which replaced the octyloxy groups in 2
with methoxy groups. f Fluorescence quantum yield relative to quinine
bisulfate.
FIGURE 7. Selected frontier molecular orbitals for 2′ (left) and 3 (right)
calculated at the B3LYP/6-311G**//B3LYP/6-31G* level of theory.
Absorption wavelength and oscillator strength were calculated by
TDDFT (TD/B3LYP/6-31G*).
MO+3, respectively, of 2′. Analogous to the electronic transi-
tions of 3, the absorption bands around the shorter and longer
wavelength regions of 2 were ascribed to the transitions of
HOMO-3 f LUMO+2 and HOMO-2 f LUMO+3 and the
transitions of HOMO-3 f LUMO and HOMO-2 f LUMO+1,
respectively. Meanwhile, the HOMO and HOMO+1 of 2′ were
localized on the electron-rich xylyl moieties.
Figure 6 also shows the fluorescence spectra of 2 and 3 in
toluene and CHCl3. The acyclic 3 emitted a green fluorescence
at the wavelength region of ca. 470-540 nm with a moderate
FIGURE 6. Electronic absorption of 1-3 in CHCl3 solution and
emission spectra of 2 and 3.
resembled those of 3 but the three FMOs of 3, HOMO, LUMO,
and LUMO+1, split into the six FMOs of 2′ presumably due
to the inversion of the orbitals of the bis(phenylethynyl)pyro-
mellitic diimide moiety across the xylyl moiety; the HOMO,
LUMO, and LUMO+1 of 3 corresponded to HOMO-3 and
HOMO-2, LUMO and LUMO+1, and LUMO+2 and LU-
J. Org. Chem. Vol. 73, No. 11, 2008 4069

Kato et al.
fluorescence quantum yield (Φf 0.11 in both toluene and CHCl3).
With the increasing solvent polarity, the emission maxima (λem)
of 3 showed a bathochromic shift from 477 nm in toluene to
492 nm in CHCl3, suggesting that the excited state was slightly
stabilized by solvation in the relatively polar CHCl3. Contrary
to the absorption process, the fluorescence properties were
significantly different between 2 and 3. The macrocycle 2
showed a fluorescence in the significantly longer wavelength
region of 583 nm in toluene and 592 nm in CHCl3 in addition
to the shorter wavelength fluorescence that might essentially
correspond to that of 3. Furthermore, the Φf values of 2 in both
toluene (0.004) and CHCl3 (0.002) were dramatically lower than
those of 3. To investigate the effect of the macrocyclic structure
or phenylacetylene groups of 2 on its fluorescence properties,
we also measured the fluorescence spectra of the macrocycle 1
and N,N′-di-n-butylpyromellitic diimide.35,36 The fluorescence
spectrum of 1 was similar to that of the N,N′-di-n-butylpyro-
mellitic diimide and the additional longer wavelength fluores-
cence was not observed in 1 up to 700 nm despite its
macrocyclic structure (Figure S17 and Table S1, Supporting
Information). The Φf values of both 1 and N,N′-di-n-butylpy-
romellitic diimide were very small (0.001-0.005). Considering
these findings, one can conclude that the observed fluorescence
in the longer wavelength region of 2 was ascribed to the excimer
emission of the bis(phenylethynyl)pyromellitic diimide moieties
because the intramolecular aromatic interactions are expected
to be due to the rotation of the sp carbons of the phenylacetylene
groups. These spectroscopic data are in good agreement with
the structural features found in the X-ray crystallography of 2
as already described. The fluorescence emission of 2 in toluene
was observed as a mirror image of the absorption at 442 and
467 nm, which might be caused by the rigid macrocyclic
structure of 2.
Redox Properties. To examine the effect of the 1D π-system
on the redox behavior of the pyromellitic diimide derivatives,
cyclic voltammetries of 1-3 and N,N′-di-n-butylpyromellitic
diimide were conducted in CH2Cl2 with tetra-n-butylammonium
hexafluorophosphate as the supporting electrolyte at room
temperature. The voltammograms are shown in Figure 8 and
the values of the reduction potentials and LUMO energies are
summarized in Table 2. It has been well-documented that
pyromellitic diimide derivatives form the radical anion and
dianion as stable species by two reversible one-electron reduc-
tions.36 For example, N,N′-di-n-butylpyromellitic diimide ex-
hibited two reversible one-electron reductions at -1.35 and
-1.92 V vs Fc/Fc+, and the first and second waves were
ascribed to the radical anion and dianion species, respectively
(Figure 8). Reversible redox processes were also observed in
1-3. In 3, two analogous reversible one-electron reductions
were observed at -1.28 and -1.84 V, which were more positive
potentials relative to those of the N,N′-di-n-butylpyromellitic
diimide by ca. 70-80 mV, but the DFT calculations (B3LYP/
6-311G**//B3LYP/6-31G*) indicated that the calculated LUMO
level of 3 was slightly higher than that of N,N′-di-n-butylpy-
romellitic diimide by ca. 0.19 eV as summarized in Table 2.
Thus, these observations might be attributed to the solvation
that causes the shift of the reduction potentials.
FIGURE 8. CV traces for 1 (dashed blue line), 2 (solid blue line),
N,N′-din-butylpyromellitic diimide (dashed black line), and 3 (solid
black line).
TABLE 2. Potentials (V vs Fc/Fc+) for the Reduction Processesa
and LUMO Levels at the B3LYP/6-311G**//B3LYP/6-31G* Level of
1-3 and N,N′-Di-n-butylpyromellitic Diimide
compd
1E1/2
2E1/2 LUMO (eV)
1
2
-1.28 -1.35 -1.96 -3.240
-1.21 -1.34 -2.03 -2.967b
N,N′-di-n-butylpyromellitic diimide -1.35
-1.28
-1.92 -3.324
-1.84 -3.132
3
a All electrochemical measurements were performed in CH2Cl2
solution containing 0.10 M tetra-n-butylammonium hexafluorophosphate
at a scan rate of 200 mV s-1 b In 2′, which replaced the octyloxy
groups in 2 with methoxy groups.
.
electrostatic repulsion between the radical anion and the neutral
pyromellitic diimide moiety. The macrocycle 2 also exhibited
a reduction wave similar to that of 1. However, the split range
of the first reduction wave of 2 increased compared to that of
1 by ca. 60 mV and the second reduction wave of 2 shifted
toward a more negative potential by ca. 70 mV than that of 1.
These observations indicated that the increase in the number of
π-electrons in 2 provided a stronger electrostatic repulsion
between the radical anion and the neutral diimide in the first
reduction process and between the further reduced species in
the second reduction process; the electrostatic repulsions of the
radical anion-radical anion and dianion-radical anion were
expected.
Complexation Studies. It is well-known that the pyromellitic
diimide derivatives form the CT complexes with π-donors in
solution. Consequently, we carried out the UV/vis spectral
titration experiments with 3 in the presence of various π-donors
in concentrated CHCl3 solution (3: 1.0 × 10-3 M) to investigate
the effect of the linear 1D π-system on the CT complex
formation. As π-donor guests, aniline, p-dimethoxybenzene,
R-naphthol, and indole were chosen. Additional CT bands
should appear in the intermolecular CT complex between 3 as
an acceptor and a donor guest. In every case, the addition of an
excess amount of the π-donors to 3 produced an enhancement
in the end absorption around 480-550 nm, which was assigned
to the CT band from the π-donors to 3. For example, the UV/
vis spectral change in Figure 9a showed a monotonic growth
of the diagnostic CT absorbance upon the incremental addition
of the indole to 3 at 25 °C. These findings indicated the CT
complex formation between 3 and aniline, p-dimethoxybenzene,
In our previous study, we found that the first two-electron
reduction wave of 1 was split into two waves due to the
(35) Buchwalter, S. L.; Iyengar, R.; Viehbeck, A.; O’Toole, T. R. J. Am.
Chem. Soc. 1991, 113, 376–377.
(36) Carroll, J. B.; Gray, M.; McMenimen, K. A.; Hamilton, D. G.; Rotello,
V. M. Org. Lett. 2003, 5, 3177–3180.
4070 J. Org. Chem. Vol. 73, No. 11, 2008

NoVel Pyromellitic Diimide-Based Macrocycles
to those of 1 with various π-donors as previously reported by
our group.17b It is considered that the low KCT values are related
to the finding that the LUMO of 3, which interacts with the
HOMOs of the π-donors during the CT complex formation
process, localizes at the pyromellitic diimide moiety (Figure 7)
and the phenylacetylene groups scarcely affect the stabilization
of their CT complexes.
Clathrate Compounds of 3 and π-Donors. Since the UV/
vis spectral experiments strongly suggested the CT complex
formation with 3 and various π-donors, we examined the solid
state structures. Slow recrystallization of 3 from the aniline
solution gave single crystals of 3·aniline suitable for an X-ray
crystallographic analysis. The slow evaporation of the CH2Cl2
solution of 3 in the presence of p-dimethoxybenzene gave 3·(p-
dimethoxybenzene)2. Similarly, the recrystallization of 3 from
CHCl3 in the presence of R-naphthol and indole by vapor
diffusion with hexane gave 3·R-naphthol and 3·(indole)2,
respectively. We presumed that a coprecipitation effect con-
tributed to the formation of the clathrate compounds because
the 1:1 CT complexes were expected in CHCl3 solution based
on the UV/vis spectral titration study. In the crystal of 3·R-
naphthol, R-naphthols exhibited a 50% static disorder.
Figure 10 shows the packing diagram of the clathrate
compounds of 3 with the π-donors of aniline, p-dimethoxy-
benzene, R-naphthol, and indole (Figure S21-S24 for their
ORTEP drawings, Supporting Information). On the basis of
the investigation of the UV/vis spectral titration study, a D
(donor)-A (acceptor) orbital overlap was expected as in the
case of the clathrates of 117b or N,N′-bis(2-tert-butylphe-
nyl)pyromellitic diimide.38 However, the X-ray crystal-
lographic analyses disclosed unexpected packing patterns, in
which 3 as an acceptor stacked in a parallel and slanted
arrangement formed the segregated D-A structures in all
cases. The angles between the plane of the diimide 3 and
the stacking axis were 43.1° and 43.2° in 3 · aniline, 42.5 and
42.6° in (3)2 · p-dimethoxybenzene, 41.9° in 3 · R-naphthol,
and 45.3° in 3 · (indole)2. The intermolecular distances (d)
between the center of the diimide and the π-face of the facing
diimide were shorter than the sum of the van der Waals radii
of the two sp2 carbons: d ) 3.20 and 3.21 Å in 3 · aniline,
3.21 and 3.27 Å in (3)2 · p-dimethoxybenzene, 3.16 Å in 3 · R-
naphthol, and 3.21 Å in 3 · (indole)2. In all cases, the donor
molecules were located in close proximity to 3 (Figures
S25-S28, Supporting Information). For the aniline and
R-naphthol clathrates, which are hydrogen bonding donors,
the hydrogen bonding was observed with the N-H · · · O
distance of 2.54 Å and the O-H · · · O distance of 1.93 Å in
3 · aniline (Figure S25, Supporting Information) and 3 · R-
naphthol (Figure S27), respectively. In addition to the
hydrogen bonding, there were C-H · · · O interactions with
the C-H (aromatic) · · · O (carbonyl) distances of 2.65 and
2.79 Å in 3 · aniline (Figure S25, Supporting Information)
and with the C-H (aromatic) · · · O (hydroxy) distance of 2.54
Å in 3 · R-naphthol (Figure S27, Supporting Information).
Similarly, the C-H · · · O interactions were observable with
theC-H(aromatic) · · · O(carbonyl)andtheC-H(methyl) · · · O
(carbonyl) distances being 2.46 and 2.56 Å, respectively, in
(3)2 · p-dimethoxybenzene (Figure S26, Supporting Informa-
tion), and were also observable with the C-H (aromatic) · · · O
(carbonyl) distances being 2.37 Å in 3 · (indole)2 (Figure S28,
Supporting Information). However, the interactions between
the π-donors in these crystals depended on the size of their
FIGURE 9. (a) Absorption spectra of 3 in CHCl3 at 1 × 1013 M in the
presence of 0-500 equiv of indole. (b) Benesi-Hildebrand plot.
TABLE 3. Charge-Transfer Association and HOMO/LUMO
Energy Levels of 3 and π-Donorsa
b
compd
KCT
HOMO (eV)
LUMO (eV)
3
-6.092
-5.639
-5.508
-5.683
-5.666
-3.132
+0.121
-0.300
-1.084
-0.410
aniline
0.1 (0.1c)
0.2 (0.3d)
0.4 (1.0d)
0.2 (1.0d)
p-dimethoxybenzene
R-naphthol
indole
a HOMO and LUMO energy levels were calculated by using the B3LYP/
6-311G**//B3LYP/6-31G* level of theory. b In CHCl3 containing 1 mM 3
and 50-6000 mM π-donors at 25 °C, whereas the value in parentheses
is for 1. c Reference 17c. d Reference 17b.
R-naphthol, and indole (Figures S18-S20, Supporting Informa-
tion). The HOMO and LUMO energies of 3 and the π-donors
are summarized in Table 3. The observed CT complex formation
was rationalized by the calculated HOMO and LUMO energy
levels. Thus, the calculated HOMO energy of 3 was lower than
those of aniline, p-dimethoxybenzene, R-naphthol, and indole,
while the LUMO energy of 3 was remarkably lower than those
of the π-donors. For qualitative analysis of the CT interaction
in solution, the spectrophotometric changes were treated by the
Benesi-Hildebrand procedures37 as shown in Figure 9b, which
extracted the association constants (KCT) of 3 with the π-donors:
KCT ) 0.1 for aniline, 0.2 for p-dimethoxybenzene, 0.4 for
R-naphthol, and 0.2 for indole (Table 3), which were comparable
(37) (a) Benesi, H. A.; Hildebrand, J. J. J. Am. Chem. Soc. 1949, 71, 2703–
2707. (b) Person, W. B. J. Am. Chem. Soc. 1965, 87, 167–170.
J. Org. Chem. Vol. 73, No. 11, 2008 4071

Kato et al.
FIGURE 10. Packing diagrams of clathrate compounds of 3 with π-donors: (a) 3·aniline (light blue), (b) (3)2 ·p-dimethoxybenzene (pink), (c)
3·R-naphthol (orange), and (d) 3·(indole)2 (light green).
π surfaces. In the crystal of 3 · aniline, the aniline molecules
adopted an aniline dimer geometry (anilines A and B in
Figure 10a) by self-complementary N-H · · · π interactions
with the shortest N-H · · · C (aromatic) distance of 2.99 Å
(Figure S25, Supporting Information). The distance between
the centers of the aniline π-planes (aniline B and C in Figure
10a) was 5.87 Å and the closest C-C distance was 3.69 Å,
indicating that the electronic interaction between these aniline
dimer structures might be negligibly small if any. In the
crystal of (3)2 · p-dimethoxybenzene, the electronic interaction
between two p-dimethoxybenzenes should be entirely neg-
ligible (Figure 10b and Supporting Information Figure S26).
In contrast, there were definite interactions between the
π-donors in the crystals of 3 · R-naphthol and 3 · (indole)2. In
3 · R-naphthol, the angle of the centers of the R-naphthol
π-planes and the stacking axis was 38.9° and the distance of
the π-planes was about 3.4 Å, indicating an electronic
interaction between the R-naphthols (Figure 10c and Sup-
porting Information Figure S27). In 3 · (indole)2, the indole
molecules were shown to have a zigzag geometry by a
combination of the N-H · · · π interactions with the short
N-H · · · C distances of 2.45 and 2.48 Å and C-H · · · π
interactions with the short C-H · · · C distances of 2.45, 2.48,
and 2.84 Å (Figure 10d and Supporting Information Figure
S28).
Considering the finding that 3 in these clathrates stacked in
a parallel and slanted arrangement with the interfacial distance
below the sum of the van der Waals radii of two sp2 carbons
even in the presence of π-donors, this was indicative of the
strong aggregation ability of 3 in the solid state. Thus, the
stabilization by this type of attractive π-π interaction of 3 in
the solid state, which clearly resembled that in the (3)2 ·p-xylene,
would exceed the stabilization by the expected D-A orbital
interactions regardless of the size of their π-surfaces. The crystal
packing of 3 in these clathrates also could be interpreted by the
possible electrostatic interactions expected from the Mulliken
charge of 3 by DFT calculations as is the case of the (3)2 ·p-
xylene (Figure 11b). For example, in 3·aniline, the closest
intermolecular contacts were observed between the carbonyl
FIGURE 11. (a) Side view of the arrangement of 3·aniline. Dotted
lines show within the sum of van der Waals radius and possible
electrostatic interactions. Butyl groups of 3, aniline molecules, and
hydrogen atoms are omitted for clarity. (b) Sketches with the Mulliken
charge of 3 calculated at the B3LYP/6-311G**//B3LYP/6-31G* level:
light and dark colors indicate positively and negatively charged atoms,
respectively; the diameters of the circles are in proportion to the values
of the charge distribution.
carbons (+0.45) and the carbonyl oxygens (-0.31), and between
the carbonyl carbons and the sp2 benzene carbons (-0.20)
(Figure 11a). Similar intermolecular contacts were observable
in all cases, although their stacking arrangements slightly
differed depending on the π-donors (Figure S29, Supporting
Information). The strong aggregation tendency of the bis(phe-
nylethynyl)pyromellitic diimide moiety was also supported by
the MALDI-TOF mass spectrum of 3, in which the apparent
intensity peak was observed at three multiples (1584) of the
parent ions at m/z 528 (Figure S30, Supporting Information).
In contrast to the observed aggregation in the solid state, the
monomeric form of 3 was present in the solution even at 10
mM as revealed by the 1H NMR spectra of 3 in CDCl3 at room
temperature (Figure S31, Supporting Information). The signal
of the aromatic protons at 7.33-7.38 and 7.75 ppm showed no
4072 J. Org. Chem. Vol. 73, No. 11, 2008

NoVel Pyromellitic Diimide-Based Macrocycles
6.4 Hz, 8 H), 4.82 (s, 8 H), 6.14 (s, 2 H), 6.43 (s, 2 H), 6.98-7.11
(m, 12 H), 7.44 (d, J ) 6.6 Hz, 8 H); 13C NMR (75 MHz, CDCl3)
δ 14.1, 22.7, 26.1, 29.25, 29.30, 29.38, 29.7, 31.8, 36.6, 68.4, 80.9,
106.3, 114.6, 115.0, 120.7, 121.7, 128.0, 129.6, 132.7, 135.5, 156.0;
MALDI-TOF-MS (dithranol) m/z calcd for C100H100N4O12 1548.73
(M+), found 1548.62. Anal. Calcd for C100H100N4O12 ·0.15CHCl3:
C, 76.72; H, 6.43; N, 3.57. Found: C, 76.75; H, 6.42; N, 3.65.
significant shifts indicating the existence of only a weak π-π
interaction in solution.
3. Conclusions
In conclusion, we have synthesized a novel pyromellitic
diimide-based macrocycle with a linear π-electronic system
2 and N,N′-di-n-butyl-3,6-bis(phenylethynyl)pyromellitic di-
imide 3. The X-ray crystal structures and theoretical calcula-
tions of 2, 2′, and/or 3 and the clathrate formations of 3 with
π-donors indicated the presence of significant electrostatic
interactions between the bis(phenylethynyl)pyromellitic di-
imide moiety in the solid state, which was supported by the
MALDI-TOF mass spectral measurement of 3. The transan-
nular π-π interactions of the bis(phenylethynyl)pyromellitic
diimide moieties in 2 were expected to be very weak in the
ground state, but 2 and 3 showed quite different excited state
properties. The macrocycle 2 showed an excimer fluorescence
in toluene and CHCl3. Furthermore, the cyclic voltammetry
measurements for 1-3 and N,N′-di-n-butylpyromellitic di-
imide revealed that an increase in the number of π-electrons
in this type of macrocyclic structure provided the enhance-
ment of their electrostatic repulsion between the diimide
moieties. On the basis of the observed results, we expect the
bis(phenylethynyl)pyromellitic diimide moiety with elongated
π-system, aggregation ability, and electronic affinity as a new
n-type structural motif for the preparation of organic field-
effect transistor (OFET) materials. We also plan to prepare
a new covalent organic nanotube39 with an extended 1D
π-system by the introduction of ethynyl-substituted pyro-
mellitic diimide derivatives to the tetrabromide 10. Our
synthetic study is now in progress and the results will be
reported elsewhere. We believe that the present study
provides valuable information for the creation of pyromellitic
diimide-based π-electron materials.
N,N′-Di-n-butyl-3,6-bis(phenylethynyl)pyromellitic Diimide
(3). A flask was charged with the dibromide 11 (473 mg, 0.97
mmol), PdCl2(PPh3)2 (41 mg, 0.058 mmol), and CuI (22 mg, 0.12
mmol) in THF/Et3N (1:1, 30 mL). The mixture was degassed by
bubbling nitrogen for 30 min and a solution of phenylacetylene
(227 mg, 2.23 mmol) in THF (3 mL) was added. After the mixture
was heated at 75 °C for 12 h under a nitrogen atmosphere, the
reaction mixture was concentrated in vacuo to dryness, suspended
in CH2Cl2 (100 mL), and filtered through a bed of silica gel. The
filtrate was concentrated and purified by silica gel column chro-
matography eluting with CHCl3/hexane (4:1, v/v) and preparative
TLC eluting with CHCl3/hexane (1:4, 1:3, 2:3, v/v) to give 3 in
72% yield (315 mg, 0.60 mmol) as a yellow powder. An analytical
sample was obtained by recrystallization from CH2Cl2/hexane: mp
>300 °C; IR (KBr) νmax 3457, 2932, 2212 (νCt C), 1765 (νCdO),
1707 (νCdO), 1507, 1402, 1369, 1340, 1170, 1058 cm-1; 1H NMR
(300 MHz, CDCl3) δ 0.90 (t, J ) 7.3 Hz, 6 H), 1.35 (qt, J ) 7.3
Hz, 4 H), 1.66 (tt, J ) 7.3 Hz, 4 H), 3.69 (t, J ) 7.3 Hz, 4 H),
7.33-7.38 (m, 6 H), 7.75 (pseudo dd, J ) 2.0, 7.2 Hz, 4 H); 13C
NMR (75 MHz, CDCl3) δ 13.6, 20.2, 30.5, 38.4, 81.5, 105.1, 115.0,
122.9, 128.5, 130.0, 132.7, 136.2, 164.8; FAB-MS (NBA, positive)
529 [(M + H)+]. Anal. Calcd for C34H28N2O4: C, 77.25; H, 5.35;
N, 5.30. Found: C, 77.08; H, 5.35; N, 5.30.
1,3-Di-n-octyloxy-4,6-diiodobenzene (6). To a solution of 1,3-
dioctoxybenzene 5 (50.0 g, 146 mmol) in AcOH (800 mL) was
added dropwise iodine monochloride (50.0 g, 308 mmol) and the
solution was stirred at room temperature for 3 h. The reaction
mixture was poured into water (800 mL) and extracted with CHCl3.
The combined organic layers were washed with aqueous Na2S2O3
and saturated aqueous NaHCO3, dried over anhydrous MgSO4, and
evaporated in vacuo to dryness. The residue was purified by silica
gel column chromatography eluting with hexane, followed by
recrystallization from hexane to give 6 in 92% yield (78.7 g, 134
mmol) as colorless needles: mp 63-64 °C; IR (KBr) νmax 2954,
2927, 2854, 1567, 1556, 1483, 1456, 1403, 1388, 1355, 1272, 1199,
4. Experimental Section
Phenylethynyl-Substituted [2 + 2] Pyromellitic Diimide-
Based Macrocycle (2). A flask was charged with the macrocycle
10 (150 mg, 0.10 mmol), PdCl2(PPh3)2 (14 mg, 2.06 µmol), and
CuI (7 mg, 3.29 µmol) in THF/Et3N (1:1, 12 mL). The mixture
was degassed by bubbling nitrogen for 30 min and a solution of
phenylacetylene (63 mg, 0.62 mmol) in THF (1 mL) was added.
After the mixture was heated at 75 °C for 36 h under a nitrogen
atmosphere, the reaction mixture was concentrated in vacuo to
dryness. The residue was purified by silica gel column chroma-
tography eluting with CHCl3/hexane (2:1, v/v) and preparative TLC
with CHCl3/hexane (1:4, 1:3, 1:2, 2:3, v/v) to give 2 in 23% yield
(35 mg, 0.023 mmol) as a yellow powder. An analytical sample
was obtained by recrystallization from CHCl3/hexane: mp >300
°C; IR (KBr) νmax 3471, 2925, 2855, 2210 (νCt C), 1766 (νCdO),
1725 (νCdO), 1623, 1510, 1385, 1303, 1184, 1115 cm-1; 1H NMR
(300 MHz, CDCl3) δ 0.81 (t, J ) 7.0 Hz, 12 H), 1.23-1.38 (m, 32
H), 1.38-1.50 (m, 16 H), 1.78 (tt, J ) 6.4 Hz, 8 H), 3.97 (t, J )
1
1064, 1033 cm-1; H NMR (300 MHz, CDCl3) δ 0.99 (t, J ) 7.3
Hz, 6 H), 1.49-1.62 (m, 4 H), 1.77-1.86 (m, 4 H), 3.99 (t, J )
6.4 Hz, 4 H), 6.32 (s, 1 H), 8.02 (s, 1 H); 13C NMR (75 MHz,
CDCl3) δ 14.3, 22.8, 26.2, 29.2, 29.3, 29.4, 69.7, 76.2, 98.0, 146.8,
159.2; FAB-MS (NBA, positive) 586 (M+). Anal. Calcd for
C22H36I2O2: C, 45.18; H, 6.15. Found: C, 45.07; H, 6.19.
1,3-Di-n-octyloxy-4,6-dicyanobenzene (7). A solution of the
iodide 6 (12.0 g, 20.5 mmol) and CuCN (5.50 g, 61.4 mmol) in
NMP (40 mL) was heated at 150 °C for 10 h under a nitrogen
atmosphere. The reaction mixture was poured into a 1.2 N HCl
solution (150 mL) of iron chloride (33.5 g, 205 mmol) and stirred
at 60 °C for 4 h. The precipitates were collected by filtration and
washed well with water. To this precipitate was added CHCl3 (200
mL) and the solution was stirred for 1 h. The insoluble material
was removed by filtration through Celite, and the filtrate was washed
with aqueous Na2S2O3, saturated NaHCO3, and brine, dried over
anhydrous MgSO4, and evaporated in vacuo to dryness. The residue
was purified by silica gel column chromatography eluting with
CHCl3/hexane (3:2, v/v) to give 7 in 59% yield (4.65 g, 12.1 mmol)
as a white powder: mp 28-29 °C; IR (KBr) νmax 2923, 2854, 2227
(38) Kishikawa, K.; Tsubokura, S.; Kohmoto, S.; Yamamoto, M.; Yamaguchi,
K. J. Org. Chem. 1999, 64, 7568–7578.
(39) For covalent organic nanotubes, see: (a) Harada, A.; Li, J.; Kamachi,
M. Nature 1993, 364, 516–518. (b) Ikeda, A.; Shinkai, S. Chem. Commun. 1994,
2375–2376. (c) Kammermeiter, S.; Herges, R. Angew. Chem., Int. Ed. 1996,
35, 2669–2671. (d) Kim, S. K.; Sim, W.; Vicens, J.; Kim, J. S. Tetrahedron
Lett. 2003, 44, 805–809. (e) Kim, Y.; Mayer, M. F.; Zimmerman, S. C. Angew.
Chem., Int. Ed. 2003, 42, 1121–1126. (f) Organo, V. G.; Leontiev, A. V.; Sgarlata,
V.; Dias, H. V. R.; Rudkevich, D. M. Angew. Chem., Int. Ed. 2005, 44, 3043–
3047. (g) Jin, W.; Fukushima, T.; Kosaka, A.; Niki, M.; Ishii, N.; Aida, T. J. Am.
Chem. Soc. 2005, 127, 8284–8285. (h) Organo, V. G.; Sgarlata, V.; Firouzbakht,
F.; Rudkevich, D. M. Chem. Eur. J. 2007, 13, 4014–4023.
(νCt N), 1616, 1560, 1506, 1434, 1400, 1319, 1220, 1114, 993 cm-1
;
1H NMR (300 MHz, CDCl3) δ 0.89 (t, J ) 7.0 Hz, 6 H), 1.28-1.52
(m, 20 H), 1.88 (tt, J ) 6.4 Hz, 4 H), 4.12 (t, J ) 6.4 Hz, 4 H),
6.43 (s, 1 H), 7.71 (s, 1 H); 13C NMR (75 MHz, CDCl3) δ 14.0,
22.6, 25.7, 28.6, 29.0, 29.1, 31.7, 69.9, 95.0, 96.4, 114.7, 138.8,
165.4; HR-FAB-MS (NBA, positive) m/z calcd for C24H37N2O2
J. Org. Chem. Vol. 73, No. 11, 2008 4073

Kato et al.
385.2855 [(M
+
H)+], found 385.2858. Anal. Calcd for
with CH2Cl2 to give 11 in 73% yield (473 mg, 0.97 mmol) as a
white powder: mp >300 °C; IR (KBr) νmax 2959, 1767 (νCdO),
C24H36N2O2: C, 74.96; H, 9.44; N, 7.28. Found: C, 75.10; H, 9.53;
N, 7.31.
1712 (νCdO), 1439, 1401, 1364, 1351, 1339, 1181, 1169, 1070 cm-1
;
1,3-Bis(aminomethyl)-4,6-dioctyloxybenzene (8). To a solution
of the nitrile 7 (2.00 g, 5.21 mmol) in dry toluene (10 mL) was
added 1.0 M diisobutylaluminum hydride solution (52 mL, 52.0
mmol) at room temperature under a nitrogen atmosphere. After the
mixture was heated at 110 °C for 4 h, the reaction mixture was
diluted with toluene and treated with KF (12.1 g, 208 mmol) and
water (2.80 g, 156 mmol) at 0 °C. After being vigorously stirred at
room temperature for 30 min, the suspension was filtered and
washed with toluene. The filtrate was dried over anhydrous MgSO4
and evaporated in vacuo to dryness to give 8 in 53% yield (1.08 g,
2.76 mmol) as a colorless oil. Without further purification, it was
used in the next reaction: IR (NaCl) νmax 3376 (νNH ), 3290 (νNH ),
1H NMR (300 MHz, CDCl3) δ 0.96 (t, J ) 7.4 Hz, 6 H), 1.38 (qt,
J ) 7.4 Hz, 4 H), 1.69 (tt, J ) 7.4 Hz, 4 H), 3.74 (t, J ) 7.4 Hz,
4 H); 13C NMR (75 MHz, CDCl3) δ 13.6, 20.0, 30.2, 38.8, 114.0,
136.2, 163.5; FAB-MS (NBA, positive) 486 (M+). Anal. Calcd for
C18H18Br2N2O4: C, 44.47; H, 3.73; N, 5.76. Found: C, 44.54; H,
3.71; N, 5.75.
[2 + 2] Tetrabromo-Substituted Macrocycle (12). According
to similar procedures reported for 10, 12 was obtained in 12%
yield from the anhydride 9 and 1,3-bis(aminomethyl)-4,6-di-n-bu-
toxybenzene17b,20 as a pale yellow powder: mp >300 °C; IR
(KBr) νmax 2958, 2871, 1772 (νCdO), 1720 (νCdO), 1621, 1595,
1
1513, 1437, 1388, 1307, 1193, 1114, 954 cm-1; H NMR (300
2
2
1614, 1589, 1506, 1467, 1417, 1378, 1290, 1193, 1110, 1058 cm-1
;
MHz, CD2Cl2) δ 1.02 (t, J ) 7.4 Hz, 12 H), 1.52-1.61 (m, 8
H), 1.86 (tt, J ) 6.3 Hz, 8 H), 4.07 (t, J ) 6.3 Hz, 8 H), 4.86
(s, 8 H), 6.49 (s, 2 H), 6.52 (s, 2 H); 13C NMR (75 MHz, CD2Cl2)
δ 13.7, 19.4, 35.5, 68.6, 97.0, 114.0, 115.7, 124.9, 135.9, 156.8,
163.0; FAB-MS (NBA, positive) 1241 [(M + H)+]. Anal. Calcd
for C52H48Br4N4O12: C, 50.34; H, 3.90; N, 4.52. Found: C, 50.40;
H, 3.86; N, 4.57.
Preparation of Clathrate Crystals. Recrystallization of 3 (4
mg, 7.6 × 10-3 µmol) from the aniline solution (500 µL) at 15 °C
gave yellow crystals on standing for 5 d. The CH2Cl2 solution (2
mL) of 3 (5 mg, 9.5 × 10-3 µmol) in the presence of p-
dimethoxybenzene (19 mg, 1.4 × 10-1 µmol) was allowed to
evaporate very slowly at 15 °C for 4 d to give yellow crystals.
Recrystallization of 3 (4 mg, 7.6 × 10-3 µmol) from the CHCl3
solution (2 mL) in the presence of R-naphthol (8 mg, 5.3 × 10-2
µmol) by vapor diffusion with hexane (4 mL) at room temperature
gave yellow crystals on standing for 3 d. Recrystallization of 3 (4
mg, 7.6 × 10-3 µmol) from the CHCl3 solution (2 mL) in the
presence of indole (7 mg, 5.3 × 10-2 µmol) by vapor diffusion
with hexane (4 mL) at room temperature gave yellow crystals on
standing for 2 d.
1H NMR (300 MHz, DMSO-d6) δ 0.85 (t, J ) 6.8 Hz, 6 H),
1.20-1.64 (m, 20 H), 1.67 (tt, J ) 6.4 Hz, 4 H), 3.33 (s, 4 H),
3.95 (t, J ) 6.4 Hz, 4 H), 6.51 (s, 1 H), 7.13 (s, 1 H); 13C NMR
(75 MHz, DMSO-d6) δ 14.0, 22.1, 25.6, 28.6, 28.7, 28.8, 31.3,
40.8, 67.7, 97.1, 123.4, 127.8, 155.5.
3,6-Dibromopyromellitic Dianhydride (9). Preparation of this
compound has been reported already,22 but we describe here the
revised procedures. A mixture of 3,6-dibromopyromellitic acid (9.89
g, 24 mmol), AcOH (90 g, 1.50 mol), and Ac2O (5.00 g, 49 mmol)
was heated at 140 °C for 3 h under a nitrogen atmosphere. The
precipitate was collected by filtration, washed well with AcOH,
and dried at 100 °C under vacuum, then purified by sublimation
with Kugelrohr apparatus (280 °C/5 Pa) to give 9 in 57% yield
(5.10 g, 13.6 mmol) as colorless needles: mp >300 °C; 13C NMR
(75 MHz, acetone-d6) δ 117.4, 138.7, 159.0. Anal. Calcd for
C10Br2O6: C, 31.95. Found: C, 31.64.
[2 + 2] Tetrabromo-Substituted Pyromellitic Diimide-Based
Macrocycle (10). A solution of the anhydride 9 (1.06 g, 2.71 mmol)
in dry THF (180 mL) and a solution of the amine 8 (1.01 g, 2.71
mmol) in dry THF (180 mL) were simultaneously added to dry
THF (50 mL) at 50 °C over a period of 4 h with stirring under a
nitrogen atmosphere. After the addition, the reaction mixture was
stirred at 50 °C for 24 h, and the reaction mixture was evaporated
in vacuo to dryness to give the amic acid. A suspension of the
amic acid and NaOAc (889 mg, 10.8 mmol) in Ac2O (40 mL) was
stirred at room temperature for 3 h under a nitrogen atmosphere,
then heated at 100 °C for 1 h. The reaction mixture was poured
into water, and the precipitate was collected by filtration. The
precipitate was continuously extracted with CH2Cl2 in a Soxhlet
extractor, and the extract was evaporated in vacuo to dryness. The
residue was purified by silica gel column chromatography eluting
with CHCl3/AcOEt (50:1, v/v) and recrystallization from CHCl3/
hexane to give 10 in 12% yield (235 mg, 0.16 mmol) as a pale
yellow powder: mp >300 °C; IR (KBr) νmax 2925, 2856, 1772
(νCdO), 1718 (νCdO), 1621, 1594, 1513, 1436, 1392, 1307, 1193,
Determination of Association Constants (KCT). In the presence
of a large amount of π-donors, KCT values of the CT complexes
were determined in CHCl3 by a spectrophotometric procedure
based on the Benesi-Hildebrand relationship37 at 25 °C. In all
cases, linear correlations were observed, indicating a 1:1 molar
ratio for the CT complexes. From the linear plot of ∆absorbance
against [π-donor]-1, consisting of at least eight points, the slope
was estimated as (KCTꢀCT) )
-1 and the intercept as (ꢀCT -1. Linear
fits obtained by the least-squares had a correlation coefficient
of >0.999.
X-ray Crystallographic Structural Analysis. Data are sum-
marized in the Supporting Information.
Theoretical Methods. All calculations were performed with the
Gaussian 0340 suite of programs. Optimized structure, frequency
calculations, and single-point energy calculations were performed
with the Becke’s three-parameter hybrid functional (B3)41 with the
correlation functional of Lee, Yang, and Parr (LYP).42,43 Restricted
1114, 954 cm-1; H NMR (300 MHz, CDCl3) δ 1.02 (t, J ) 7.4
1
Hz, 12 H), 1.52-1.61 (m, 8 H), 1.86 (tt, J ) 6.3 Hz, 8 H), 4.07 (t,
J ) 6.3 Hz, 8 H), 4.86 (s, 8 H), 6.49 (s, 2 H, ArH), 6.52 (s, 2 H);
13C NMR (75 MHz, CD2Cl2) δ 13.7, 19.4, 35.5, 68.6, 97.0, 114.0,
115.7, 124.9, 135.9, 156.8, 163.0 (one signal of alkyl carbon
overlaps with that of other ones); FAB-MS (NBA, positive) 1464
(M+). Anal. Calcd for C68H80Br4N4O12: C, 55.75; H, 5.50; N, 3.82.
Found: C, 55.74; H, 5.47; N, 3.83.
(40) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.;
Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski,
J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;
Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
N,N′-Di-n-butyl-3,6-dibromopyromellitic Diimide (11). To a
solution of the anhydride 9 (505 mg, 1.34 mmol) in dry THF (65
mL) was added a dry THF solution (5 mL) of butylamine (294
mg, 4.03 mmol) at room temperature under a nitrogen atmosphere.
After the mixture was stirred for 12 h, the reaction mixture was
evaporated in vacuo to dryness to give the amic acid. A suspension
of the amic acid and NaOAc (439 mg, 5.36 mmol) in Ac2O (20
mL) was heated at 100 °C for 1 h, the reaction mixture was poured
into water, and the precipitate was collected by filtration. The
precipitate was purified by silica gel column chromatography eluting
(41) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(42) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785–789.
4074 J. Org. Chem. Vol. 73, No. 11, 2008

NoVel Pyromellitic Diimide-Based Macrocycles
calculations were performed, as all relevant species were closed
shell molecules.
Professor Dr. Tsutomu Ishi-i (Kurume National College of
Technology) for the fluorescence spectroscopic measurement.
Acknowledgment. S.K. thanks the JSPS for a Research
Fellowship for Young Scientists. This work was supported
by a Theme Project (Prof. Tahsin J. Chow) from the Institute
of Chemistry, Academia Sinica, Taiwan R.O.C., as well as
a Grant-in-Aid for Scientific Research (B) (No. 18350025)
and the Global COE program, “Science for Future Molecular
Systems” from the Ministry of Education, Culture, Sports,
Science and Technology of Japan. We are grateful to
Supporting Information Available: General experimental
1
methods, H and 13C NMR spectra of 2, 3, 6-8, 10, 11, and
12, fluorescent properties of 1 and N,N′-di-n-butylpyromellitic
diimide, complexation studies with 3 and π-donors, X-ray
crystallographic structure analysis, MALDI-TOF-MS spectrum
of 3, concentration-dependent 1H NMR spectra of 3, and
theoretical calculations of 2, 2′, and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
(43) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
157, 200–206.
JO800283R
J. Org. Chem. Vol. 73, No. 11, 2008 4075