Bishexa-peri-hexabenzocoronenyl: A 'superbiphenyl'

Article abstract of DOI:10.1021/ja000850e

The alkyl-substituted bishexa-peri-hexabenzocoronenyls 3a and 3b as well as the related alkyl-substituted dihexa-peri-hexabenzocoronenyldodecane 4 were synthesized. The good solubility of these compounds allowed a comprehensive spectroscopic characterization in solution. Both 3a and 4 form liquid crystalline phases, while only in the case of 4 could a highly ordered columnar structure with a hexagonal superstructure be observed. Photophysical studies in solution revealed a strong intramolecular interaction of the aromatic cores of 3a, in contrast to 4, where only weak intramolecular interactions could be observed. Compound 3a forms monomolecular adsorbate layers on graphite which were characterized by scanning tunneling microscopy.

Full text of DOI:10.1021/ja000850e

7698
J. Am. Chem. Soc. 2000, 122, 7698-7706
Bishexa-peri-hexabenzocoronenyl: A “Superbiphenyl”
Shunji Ito,† Peter Tobias Herwig,† Thilo Bo1hme,‡ Ju1rgen P. Rabe,‡ Wolfgang Rettig,§ and
Klaus Mu1llen*,†
Contribution from the Max-Planck-Institut fu¨r Polymerforschung, Ackermannweg 10,
D-55128 Mainz, Germany, Institut fu¨r Physik, Humboldt UniVersita¨t zu Berlin, InValidenstrasse 110,
D-10115 Berlin, Germany, and Institut fu¨r Chemie, Fach-Institut fu¨r Physikalische und Theoretische
Chemie, Humboldt UniVersita¨t zu Berlin, Bunsenstrasse 1, D-10117 Berlin, Germany
ReceiVed March 9, 2000
Abstract: The alkyl-substituted bishexa-peri-hexabenzocoronenyls 3a and 3b as well as the related alkyl-
substituted dihexa-peri-hexabenzocoronenyldodecane 4 were synthesized. The good solubility of these com-
pounds allowed a comprehensive spectroscopic characterization in solution. Both 3a and 4 form liquid crystalline
phases, while only in the case of 4 could a highly ordered columnar structure with a hexagonal superstructure
be observed. Photophysical studies in solution revealed a strong intramolecular interaction of the aromatic
cores of 3a, in contrast to 4, where only weak intramolecular interactions could be observed. Compound 3a
forms monomolecular adsorbate layers on graphite which were characterized by scanning tunneling microscopy.
Introduction
Chart 1
Hexa-peri-hexabenzocoronenes (HBCs, 1) are readily avail-
able upon oxidative cyclodehydrogenation of the corresponding
hexaphenylbenzene precursors.1-3 Alkyl substitution is impor-
tant to render HBC soluble in organic solvents. HBCs carrying
n-alkyl substituents give rise to discotic mesophases over a broad
temperature range2 and prove as photoconductors with very high
charge carrier mobilities.4 Furthermore, they furnish monomo-
lecular adsorbate layers on highly oriented pyrolytic graphite
(HOPG) which can be characterized by scanning tunneling
microscopy.1 HBCs are also important electrophores and upon
alkali metal reduction afford extended redox sequences ranging
from the monoanions to the tetraanions.5 It appears from solid-
state ESR measurements that the charged anions possess high-
spin states. This spin multiplicity is closely related to the possible
degeneracy of HBC frontier orbitals, which follows from the
hexagonal symmetry of the π-system. If from an electronic point
of view HBC can thus be regarded as a homologue of benzene,
i.e., as “superbenzene”, it seems challenging to use HBC as a
building block of more complex π-structures. As an example
of an extensively fused polycyclic aromatic hydrocarbon
(PAH),6 we have recently synthesized “supernaphthalene” 27
(see Chart 1).
Herein, we introduce the bishexa-peri-hexabenzocoronenyl
3 as an example of the “superbiphenyl” and the related dihexa-
peri-hexabenzocoronenyldodecane 4 in which two HBC units
are linked by a flexible alkyl chain. Compounds 3 and 4 are
structural homologues of biphenyl 5 and 1,n-diphenylalkanes
6 together with their naphthalene and anthracene derivatives
7-10.
* Corresponding author: (fax) +49 6131 379 350; (e-mail) muellen@mpip-
mainz.mpg.de.
(6) For further examples of extended polycyclic aromatic hydrocarbons,
see: (a) Clar, E. Aromatische Kohlenwasserstoffe-Polycyclische Systeme;
Springer, Berlin, 1952. (b) Clar, E. The Aromatic Sextet; Wiley: London,
1972. (c) Dias, J. R. Handbook of Polycyclic Hydrocarbons-Part a:
Benzenoid Hydrocarbons; Elsevier: Amsterdam, 1987. (d) Fetzer, J. C.
Polycycl. Aromat. Comput. 1996, 11 (1-4), 317; (e) Diederich, F.; Rubin,
Y. Angew. Chem. 1992, 104, 1123; Angew. Chem., Int. Ed. Engl. 1992, 31,
1101. (f) Hudgins, D. M.; Allamandola, L. J. J. Phys. Chem. 1995, 99,
3033. (g) Scott, L. T.; Cheng, P.-C.; Hashemi, M. M.; Bratcher, M. S.;
Meyer, D. T.; Warren, H. B. J. Am. Chem. Soc. 1997, 119, 10963. (h) Faust,
R. Angew. Chem. 1995, 107, 1559; Angew. Chem., Int. Ed. Engl. 1995, 34,
1429. (i) Mu¨ller, M.; Petersen, J.; Strohmaier, R.; Gu¨nther, C.; Karl, N.;
Mu¨llen, K. Angew. Chem. 1996, 108, 947; Angew. Chem., Int. Ed. Engl.
1996, 35, 886. (j) Tong, L.; Lau, H.; Ho, D. M.; Pascal, R. A., Jr. J. Am.
Chem. Soc. 1998, 120, 6000. (k) Debad, J. D.; Bard, A. J. J. Am. Chem.
Soc. 1998, 120, 2476.
† Max-Planck-Institut fu¨r Polymerforschung.
‡ Institut fu¨r Physik, Humboldt Universita¨t zu Berlin.
§ Institut fu¨r Chemie, Humboldt Universita¨t zu Berlin.
(1) Stabel, A.; Herwig, P.; Mu¨llen, K.; Rabe, J. P. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1609. Mu¨ller, M.; Ku¨bel, C.; Mu¨llen, K. Chem. Eur. J.
1998, 4, 2099.
(2) Herwig, P.; Kayser, C. W.; Mu¨llen, K.; Spiess, H. W. AdV. Mater.
1996, 8, 510.
(3) Herwig, P. T.; Enkelmann, V.; Schmelz, O.; Mu¨llen, K. Chem. Eur.
J., in press.
(4) van de Craats, A. M.; Warman, J. M.; Mu¨llen, K.; Geerts, Y.; Brand,
J. D. AdV. Mater. 1998, 10, 36.
(5) Gherghel, L.; Brand, J. D.; Baumgarten, M.; Mu¨llen, K. J. Am. Chem.
Soc. 1999, 121, 8104.
10.1021/ja000850e CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/26/2000

Bishexa-peri-hexabenzocoronenyl
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7699
Scheme 1. Synthesis of Bis-HBC’s 3a and 3ba
Chart 2
a Reaction conditions: (a) [Ni(COD)2], COD, 2,2′-bipyridyl, toluene,
60 °C.
“superbiphenyl” 3a can be compared with ordinary biphenyl
or other biaryls in order to study the interaction between the
two aromatic submoieties. (iii) Fluorescence spectroscopy is a
very valuable and sensitive tool to discover the aggregation
behavior of the species.
Chart 3
(3) Adsorption Layers. 3a can be considered as a soluble
graphene segment. Adsorbed to graphite it serves as a model
for small terraces or islands of graphite, which is of interest for
a better understanding of the transition from molecular to solid-
state electronic behavior in this class of materials. Extended
polycyclic aromatic hydrocarbons such as 1, 2, and 3 can be
regarded as 2D nanoparticles, which raises the exciting question
of their single-molecule visualization and manipulation. This
can finally lead to the use of single molecules as functional
units in molecular electronics. Scanning tunneling microscopy
(STM) was therefore employed to examine adsorption and
electronic properties of 3a on the basal plane of graphite.
Results and Discussion
Synthesis. The synthesis of the bis-HBCs 3a and 3b is
outlined in Scheme 1. The key step was the reductive coupling
of the bromo-substituted HBCs 11a and 11b, respectively, under
Yamamoto conditions. The syntheses of 11a and 11b are
described elsewhere.10 Thus, reaction of 11a with [Ni(COD)2]
in the presence of 2,2′-bipyridyl and COD in toluene afforded
bis-HBC 3a in 85% yield after recrystallization from tetrachlo-
roethane.11
Not surprisingly, the solubilization of the title compounds 3
and 4 (Chart 2) requires alkyl substitution, where in the case of
3, both the deca-n-dodecyl derivative 3a and the deca-tert-butyl
derivative 3b were synthesized. It is remarkable that the new
bis-HBCs 3a, 3b, and 4 are obtained from different routes where
the key synthetic question is at what stage the hexaphenylben-
zene precursor is transformed into the HBC disk.
The field desorption mass spectrum of 3a shows a signal at
m/z 2726.7 of M(3a)+, which unequivocally proves the coupling
of 11a under these conditions. Due to the low solubility of this
compound in common organic solvents at room temperature,
high-boiling solvents, such as tetrachloroethane or 1,4-dichlo-
1
robenzene, were necessary to obtain H NMR spectra of 3a.
The aryl protons (1,4-dichlorobenzene, 140 °C) at the positions
adjacent to the junction of the HBC unit (H-1, H-1′, H-3, H-3′)
give a single peak at δ ) 9.41 (4 H), while the remaining aryl
protons appear at δ ) 8.99 (4 H), 8.81 (4 H), 8.76 (4H), 8.69
Next to the synthetic challenge there are obvious structural
reasons to investigate 3a and 4:
(1) Phase Formation. Oligomers consisting of rigid discotic
cores interconnected directly or with flexible spacers are
expected to display liquid crystalline order significantly different
from that of the monomeric discotic cores. The bulk phase
behavior of 3a and 4 was therefore examined by polarizing
microscopy, differential scanning calorimetry and X-ray dif-
fractometry.
(2) Photophysical Properties. (i) The parent 1a or 1b has a
6-fold symmetry comparable to benzene, and it can be asked
whether similar consequences such as a highly forbidden lowest
singlet absorption and emission will be found.8,9 (ii) The
(8) Birks, J. B. Photophysics of Aromatic Molecules; Wiley: London
1970.
(9) Harris, D. C.; Bertolucci, M. D. Symmetry and Spectroscopy: An
introduction to Vibrational and electronic spectroscopy; Dover Academic
Press: New York, 1989.
(10) Ito, S.; Wehmeier, M.; Brand, J. D.; Ku¨bel, C.; Epsch, R.; Rabe, J.
P.; Mu¨llen, K. Chem. Eur. J., in press.
(11) Yamamoto, T.; Morita, A.; Miyazaki, Y.; Maruyama, T.; Wakayama,
H.; Zhou, Z.; Nakamura, Y.; Kanbara, T.; Sasaki, S.; Kubota, K.
Macromolecules 1992, 25, 1214.
(12) (a) Cassar, L. J. Organomet. Chem. 1975, 93, 253. (b) Dieck, H.
A.; Heck, F. R. J. Organomet. Chem. 1975, 93, 259. (c) Sonogashira, K.;
Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467.
(13) Kovacic, P.; Koch, F. W. J. Org. Chem. 1965, 30, 3176.
(7) Iyer, V. S.; Wehmeier, M.; Brand, J. D.; Keegstra, M. A.; Mu¨llen,
K. Angew. Chem., Int. Ed. Engl. 1997, 36, 1604.

7700 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Scheme 2. Alternative Synthesis of 3ba
Ito et al.
1
nation, as well as by H NMR spectroscopy. As in the case of
3a, the low solubility of 3b in organic solvents at room
temperature required the use of a high-boiling solvent (tetra-
chloroethane, 140 °C) to obtain a 1H NMR spectrum. In contrast
to 3a, the resonances of 3b appear as sharp peaks. Furthermore,
the absorptions of the aromatic protons are markedly downfield
shifted compared to those of 3a. Thus, protons H-1, H-1′, H-3,
and H-3′ resonate at δ ) 10.05 and the remaining protons
resonate at δ ) 9.66 (4 H), 9.40 (4 H), 9.35 (4 H), 9.32 (4 H),
and 9.27 (8 H). Both the significant downfield shift (i.e., a small
or negligible intermolecular shielding of the aromatic cores) and
the sharpness of the signals (i.e., a fast isotropic rotation of the
molecules) indicate that the bulky tert-butyl groups prevent a
pronounced aggregation of the aromatic cores of 3b in solu-
tion.
The spacer linked bis-HBC 4 was prepared similarly to 3b
using the cycloaddition and cyclodehydrogenation sequence as
shown in Scheme 3. First, the diacetylene compound 17 was
coupled with 4-bromoiodobenzene (18) providing 19 (88%).12
19 was then hydrogenated to give 20 in a yield of 79%. Coupling
of 20 with 4-n-dodecylphenylacetylene afforded diacetylene 22
in a low yield (42%).12 Reaction of 22 with tetra(n-dodecyl-
phenyl)cyclopentadienone in refluxing diphenyl ether gave the
hexaphenyl derivative 24 (73%), which was finally cyclodehy-
drogenated to 4 by treatment with FeCl3 in CH2Cl2 (72%).
The field desorption mass spectrum of 4 shows the clean loss
of 24 hydrogen atoms from the oligophenylene precursor 24
upon cyclodehydrogenation with FeCl3 without any chlorination
of the aromatic core. Compared to 3a and 3b, 4 exhibits a fairly
good solubility in various organic solvents even at room
temperature. Due to the aggregation of the aromatic cores, the
1H NMR spectrum of 3 shows a considerable signal broadening
at room temperature. However, the signals become gradually
sharper with increasing temperature. The 13C NMR spectrum
shows only 8 signals in the aromatic region and 17 signals in
the aliphatic region.
a Reaction conditions: (a) 4,4′-dibromobiphenyl (13), [Pd(PPh3)4],
CuI, piperidine, 80 °C; (b) tetra(4-tert-butylphenyl)cyclopentadienone
(15), diphenyl ether, reflux; (c) FeCl3, CH2Cl2, room temperature.
(4H), and 8.65 (4H), respectively. The benzylic protons of the
n-dodecyl chains exhibit broad absorptions at δ ) 3.56 (8 H),
3.35 (8 H), and 3.25 (4 H), respectively. The signal broadening
suggests a strong aggregation of the extended HBC cores even
at higher temperatures (see below). Following the above method,
the tert-butyl substituted homologue of 3a, 3b, was prepared
by homocoupling of 11b in a yield of 75%.
Alternatively, 3b was obtained by oxidative cyclodehydro-
genation of the oligphenylene precursor 16 (Scheme 2).
The synthesis started with 4-tert-butylphenylacetylene (12),
which was coupled with 4,4′-dibromobiphenyl (13) to yield 14
(81%).12 The Diels-Alder reaction of 14 with an excess of tetra-
(4-tert-butylphenyl)cyclopentadienone (15) in refluxing diphenyl
ether afforded 16 in a yield of 85%. Finally, 16 was cyclode-
hydrogenated with FeCl3 in CH2Cl2 to furnish the target
compound 3b (81%).13 The structure of 3b was confirmed by
field desorption mass spectrometry, which proves the loss of
24 hydrogen atoms during the course of the cyclodehydroge-
Scheme 3. Synthesis of 4a
a Reaction conditions: (a) 4-bromoiodobenzene (18) [Pd(PPh3)4], CuI, piperidine, room temperature; (b) H2, Pd/C, THF, room temperature; (c)
4-n-dodecylphenylacetylene (21), [Pd(PPh3)4], CuI, piperidine, 80 °C; (d) tetra(4-n-dodecylphenyl)cyclopentadienone (22), diphenyl ether, reflux;
(e) FeCl3, CH2Cl2, room temperature.

Bishexa-peri-hexabenzocoronenyl
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7701
Table 2. Gel Formation of 3b and 4
Table 1. Phase Transition Temperatures and Enthalpy Data (J/g in
Parentheses) of 1b, 3a, and 4 from DSC (Measurements Are for the
Second Heating Run)
system
n-heptane
CHCl3
toluene
THF
3a
4
3 g/L
10 g/L
no
no
5 g/L
10 g/L
no
no
system
Tm (°C)
Ti (°C)
phase width (K)
339
LC phase
1b
3b
4
60
124
53
399
Dho
370
317
Dho
Figure 2. Absorption and fluorescence spectra of HBC 1b and the
bis-HBCs 4 and 3a ) in 1,2-dichlorobenzene at room temperature.
is revealed by the alkyl chain halo. Remarkably, the LC phase
behavior of bis-HBC 4 shows only slight differences to the one
of the HBC 1b.2
Gel Formation. The bis-HBC derivatives 3a and 4 were
found to form gels with certain organic solvents such as
n-heptane and toluene, immobilizing the solvent at very low
concentrations, whereas with better solvents such as chloroform
and tetrahydrofuran neither 3a nor 4 formed good gels at low
concentrations. Table 2 summarizes the minimum concentrations
of 3a and 4 required for the gel-forming process.14
Organic gels composed of low-molecular-weight organic
compounds are of interest as a novel class of organic materials
that behave macroscopically as solids but contain a liquid
inside.15 Both intermolecular aggregation of the HBC cores and
covalent linkage of two HBC units are responsible for the gel
formation.
Fluorescence Studies in Solution. Figure 2 shows the
combined absorption and fluorescence spectra of 1b, 4, and 3a
in 1,2-dichlorobenzene. This solvent was found to lead to a
sufficient solubility of 3a, the least soluble of the investigated
compounds, such that the concentration dependence could be
studied.
Figure 1. Texture of a sample of 4 between crossed polarizers at 300
°C. Magnification, 200×.
Bulk Properties. The bulk phase behavior of the new bis-
HBCs 3a and 4 was established by means of polarization
microscopy and differential scanning calorimetry (DSC) as well
as X-ray diffractometry. The DSC data are summarized in Table
1. 3a shows a peak at 124 °C, which corresponds to the
transition from the solid state into the mesophase, while the
DSC curve of bis-HBC 4 indicates a melting point at 53 °C.
Both phase transitions are reversible with a little supercooling.
The LC phase of 3a is extraordinarily wide (317 °C) and is
comparable to the one of 1b.2 In analogy to 1b, the bis-HBC 4
exhibits a Dh-like texture in the mesophase which is manifested
by polarization microscopy (Figure 1).
The LC columnar structure of 3a was established by X-ray
diffraction. The alkyl chain halo manifests the disordered liquid
character of the mesophase of 3a. However, the X-ray diffrac-
togram shows that 3a does not form a well-defined monotropic
Dh mesophase. Apparently, the direct linkage of the two HBC
units prevents a perfect self-organization of this compound.
The X-ray diffractogram of bis-HBC 4 proves the formation
of an ordered columnar structure with a hexagonal superstruc-
ture. The intercolumnar distance was determined from the (100)
reflections and amounts to 28.0 Å, the (001) reflections indicate
an intramolecular distance of 3.66 Å. The (110) reflections prove
the hexagonal superstructure of the columnar discotic phase.
Finally, the disordered liquid character of the mesophase of 4
The spectra for 1b are highly structured. The main peaks of
absorption and fluorescence are collected in Table 3, allowing
the comparison of the vibrational spacings.
The structure loss observed for the absorption spectrum of 4
is accentuated in the fluorescence spectrum, and some red-shift
is observed with respect to 1b (Figure 2). In parallel with the
(14) The gelation test was carried out as follows: A 10 mg sample of
3a and 4, respectively, was dissolved in an organic solvent (1, 2, 3, and 4
mL) by heating. The resulting solution was then cooled to room temperature.
The gel formation was confirmed by observing that the sample did not
flow when the sample was inverted.
(15) Miles, J. M. In DeVelopments in Crystalline Polymers; Bassett, D.
C., Ed.; Elsevier: Amsterdam, 1987; Vol. 2.

7702 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Ito et al.
Table 3. Absorption and Fluorescence Maxima of 1b in
1,2-Dichlorobenzene
λ (nm)
ν (cm-1
)
∆ν(0-0)
Absorption
28 736
27 473
348
364
394
3355
2092
“0”
25 381
Fluorescence
21 322
20 790
20 450
20 080
19 084
18 727
469
481
489
498
524
534
“0”
532
872
1242
2238
2595
Figure 3. Fluorescence spectra of bis-HBC 3a in 1,2-dichlorobenzene
at elevated temperatures as indicated.
at 577 nm), 1,2-dichlorobenzene (578 nm), and benzonitrile (579
nm), however, leads to the conclusion that charge separation is
not involved in this case.
broadened and red-shifted absorption, 3a also shows a strongly
red-shifted and structureless fluorescence spectrum which is
independent of concentration in a range up to the maximum
solubility (∼5 ×10-6 mol L-1).
The nature of the relaxation coordinate that leads to the
strongly red-shifted spectrum of 3a was further investigated
using high-temperature fluorescence spectroscopy (Figure 3).
As evident from the spectra, an initial temperature increase does
not change the structureless and red-shifted appearance of the
spectra. Only at 60 °C, some additional blue fluorescence
component appears which gains importance and is the major
contribution at 88 °C. Some vibronic structure is visible,
especially on the blue major side. This temperature dependence
indicates that at room temperature the emitting species are not
monomers of 3a, but aggregates (dimers or higher clusters);
further, from the lack of temperature dependence between 22
and 40 °C, and the observed concentration independence, it can
be concluded that the equilibrium is totally in favor of the
aggregates at room temperature. From the structuring of the
fluorescence spectrum at high temperatures, a vibronic progres-
sion with a spacing of ∼430 cm-1 can be analyzed and
compared to that of 1b, which shows a similar average spacing
of 430 cm-1 (Table 3). The first prominent shoulder is situated
at 473 nm, to be compared with the first prominent band of 1b
at 469 nm (Table 3). Unfortunately, the corresponding excitation
spectra showed only a weak vibronic structuring which could
not be analyzed. Our comparison of 1b and 3b therefore rests
upon the fluorescence spectrum only.
If the first prominent bands of 1b at 469 nm and 3a at 473
nm correspond to the same quantum of a vibronic ladder, then
the red-shift for 3a can be used to extract a rough estimate of
the mutual electronic interaction between the two HBC moieties
in 3a. According to the Fo¨rster exciton model, this interaction
will red-shift both absorption and fluorescence spectra. A similar
analysis has been described for bianthryl and biperylenyl,18 with
the experimental red-shift (exciton interaction) for bianthryl
amounting to ∼0.13 eV. The exciton splitting for 3a is calculated
on this basis to be very small (∼0.02 eV). A possible reason
for this small interaction may be the large size of the HBC
moieties, which results in a large distance of the interacting
transition dipoles and in small molecular orbital coefficients and
hence small interaction energies.
As 1b is the annelated analogue of benzene, it is interesting
to compare the spectra of both compounds, which have in
common the high 6-fold symmetry. For benzene, this high
symmetry leads to a strongly forbidden S1 absorption and
emission which is weakened by vibronic coupling.8 Thus, the
0-0 band is absent, but vibrational progressions can be observed
that are built upon “false origins” resulting from coupling with
one quantum of a symmetry-reducing vibration.8,9 The absence
of the 0-0 band leads to a large energy gap between absorption
and emission. The same qualitative features are observed for
1b, and from the approximate mirror image relationship between
absorption and emission, the 0-0 band can be situated around
430-435 nm, i.e., considerably red-shifted from that of benzene
(at 270 nm in cyclohexane solution).8 The comparison of the
spacing of the optically active vibrations in the fluorescence
spectrum of 1b (average of 430 cm-1; see Table 3) and benzene
(955 cm-1) leads to the conclusion that the force constant is
much smaller in 1b.8
The loss of structure in the absorption spectrum of 4, as
compared to 1b, together with the close energetic similarity of
the spectra indicates that the HBC moieties in 4 are not
undisturbed, but probably interact weakly in an intermolecular
or intramolecular way. The latter possibility may be favored
given that the spectra do not depend on concentration. On the
other hand, the high-temperature results for 3a (see below)
indicate strong ground-state clustering, which is probably also
present for 4. This tendency for chromophore clustering is
increased in the excited state as evidenced by the further loss
of structure and the red-shift of the fluorescence spectrum, which
can be understood as a significant contribution of excimer
fluorescence from intra- or intermolecular clusters.
The strongly broadened and red-shifted absorption of 3a with
respect to that of 1b (Figure 3) indicates a much larger
interaction between the two chromophores as compared to 4.
The fluorescence of 3a is also strongly red-shifted and com-
pletely structureless, which suggests a large structural rear-
rangement prior to fluorescence or the formation of intermo-
lecular complexes. Some large biaryl compounds are known to
show polar solvent-induced excited-state charge separation. A
well-known example is 9,9′-bianthryl (8), which exhibits dual
fluorescence in polar solvents with a structured excitonic
component and a red-shifted charge-transfer (CT) compo-
nent.16,17 Even larger biaryls with solvent polarity effects on
the fluorescence are biperylenyl18,19 and bibenzpyrenyl. The fact
that the unstructured fluorescence is virtually not red-shifted
for 3a in solvents of different polarity such as toluene (maximum
Another relevant aspect concerns the angle of torsion about
the inter-ring bond, which results from the interplay of the steric
hindrance and the resonance interaction between the two HBC
moieties in 3a. This is usually different for ground and excited
(16) Rettig, W.; Paeplow, B.; Herbst, H.; Mu¨llen, K.; Desvergne, J.-P.;
Bouas-Laurent, H. New J. Chem. 1999, 23, 453.
(17) Rettig, W.; Zander, M. Ber. Bunsen-Ges. Phys. Chem. 1983, 87,
1143.
(18) Dobkowski, J.; Rettig, W.; Paeplow, B.; Koch, K. H.; Mu¨llen, K.;
Lapouyade, R.; Grabowski, Z. R. New J. Chem. 1994, 18, 525.
(19) Zander, M.; Rettig, W. Chem. Phys. Lett. 1984, 110, 602.

Bishexa-peri-hexabenzocoronenyl
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7703
Figure 5. Molecular modeling results for 3a: (a) the global energy
minimum structure of the isolated molecule, (b) the minimum structure
of the isolated molecule under the constraint of a torsion angle of 0°,
and (c) the molecule on the basal plane of graphite.
Figure 4. STM current image at constant height of a monolayer of 3a
at the interface between the basal plane of HOPG and an organic
solution. The positions of the aromatic disks can be assigned to areas
of high tunneling currents, which appear bright, whereas the darker
regions are attributed to the alkyl side chains giving rise to a lower
tunneling probability.20 The chemical formula for the aromatic core is
superimposed on the STM image and gives a better impression of the
molecule’s orientation and the associated contrast. Tip bias, +1.1V;
current set point, 180 pA; scan rate, 976 nm/s.
However, STM imaging does not provide this information
unambiguously; therefore, energy minimization calculations
based on a pcff force field approach have been carried out. They
reveal that the HBC disks are bent into saddlelike structures
with a torsion angle of 46° between them (Figure 5).22 The
difference in energy between this minimum structure and a
minimized geometry with a restrained torsion angle of 0° is
5.5 kcal/mol, indicating a rather shallow shape of the potential
surface. For comparison, the benzene rings of the biphenyl
molecule are rotated relative to each other by 36°, and the
structure with the restrained angle of 0° is 1.6 kcal/mol higher
in energy.
When 3a is adsorbed to graphite, the aromatic moieties are
flattened (Figure 5) and the gain in energy relative to the global
minimum of the isolated molecule is calculated to be ∼120 kcal/
mol, which is more than 1 order of magnitude larger than the
difference in energy between the 0 and 46° conformation. Even
though the major parts of the aromatic cores lie flat on the
graphite substrate, the torsion angle in this arrangement is 27.5°
and the participating atoms protrude out of plane. Furthermore,
the minimization has shown that the aromatic regions of the
adsorbed molecule orient like additional graphene segments on
the substrate no matter what the starting position of the molecule
relative to the graphite substrate was.
states of a biaryl molecule. In the case of substituted biphenyls,
planar model compounds enabled a quantitative fluorescence
conformational analysis in both ground and excited states,20 with
the result that biphenyls are completely planarized in the excited
state, while they are somewhat twisted in the ground state.
Although such a detailed analysis is not possible here, the
vibronic structure observed in the high-temperature fluorescence
spectrum of 3a (Figure 3) is consistent with an excited-state
flattening and partial rigidization of the carbon skeleton in this
case, too. The molecular modeling calculations reported below
indicate, however, that the planarization forces are considerably
weaker than for biphenyl. This is in line with the small exciton
splitting as concluded above.
Scanning Tunneling Microscopy. 3a was investigated in
monolayers, self-assembled at the interface between the basal
plane of HOPG and a solution in 1,2,4-trichlorobenzene. Figure
4 displays a STM current image at a resolution that allows one
to clearly identify two aromatic moieties per molecule.21
Each exhibits typically one bright spot in the middle which
is surrounded by a ringlike pattern; the distance between adjacent
center spots is 1.3 nm, which corresponds to the distance
between the aromatic centers within one biaryl molecule. As
one would expect, the submolecular patterns in the aromatic
regions are symmetric with respect to the long molecular axis,
and in cases of lower contrast, the patterns are smeared out into
stripes with the molecule’s symmetry maintained. The alkyl
chains are not resolved, indicating a high conformational
mobility at room temperature.
Coming back to the experimental results, Figure 4 shows that
the molecules pack along rows. Comparison with the orientation
of the underlying graphite lattice indicates that the aromatic
cores of the adsorbate molecules are oriented like additional
graphene layers to the graphite substrate. As illustrated in Figure
6, this results in a 30° angle between the long molecular axis
and a zigzag row in graphite (graphite axis).
In such a configuration, the packing of the alkyl side chains
parallel to the graphite axes is easily possible and agrees with
Since the structure of the isolated molecule 3a is far from
planar, one may wonder about its shape on a solid substrate.
(22) The torsion angle is defined by the two carbons forming the single
bond between both aromatic regions plus the next two carbons to the left
and to the right of the single bond, which are part of the adjacent benzoic
subunits. Due to the warping of the aromatic moieties, the given torsion
angle does not represent the angle between the two aromatic planes.
However, this definition of the torsion angle is quite useful in order to get
an impression to what degree the whole structure is distorted.
(20) Maus, M.; Rettig, W.; Bonafoux, D.; Lapouyade, R. J. Phys. Chem.
A 1999, 103, 3388.
(21) Smith, D. P. E.; Ho¨rber, J. K. H.; Binnig, G. Science 1989, 245,
43. Lazzaroni, R.; Calderone, A.; Bre´das, J. L.; Rabe, J. P. J. Chem. Phys.
1997, 107, 99.

7704 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Ito et al.
Chart 4
Conclusions
Following the chemical functionalization of HBC, this
exciting molecule can now be used as a building block of more
complex π-structures and a broad chemistry of “superbenzene”
can be developed. The size of the resulting molecular objects
becomes a key feature, with the opportunity of single-molecule
investigation by STM as an important consequence. Self-
assembly at the interface between the basal plane of graphite
and an organic solution allowed crystallization of 3a epitaxially
in different 2D modifications. Submolecularly resolved STM
in situ revealed a contrast, which reflects the structure of the
aromatic parts of the molecule, and which shows that the
aromatic moieties are oriented like a graphene layer in graphite.
Benzene rings are well known to serve as subunits not only
of oligomers such as biphenyl or oligophenyls but also of
structurally related polymers such as polyparaphenylene. Having
available para-disubstituted HBCs, like 2510 (Chart 4), we have
now synthesized polyarylenes and polyarylenealkylenes from
HBC building blocks26 and considered the interplay of intra-
and intermolecular π-π-interactions.
Figure 6. Schematic view of the proposed orientation of 3a with
respect to the underlying graphite substrate. The long molecular axis
forms an angle of 30° with the zigzag rows in graphite.
their favored orientation, as observed for other molecules
containing long alkyl chains.23-25 Due to the anisotropic shape
and the size of 3a, the alignment of its aromatic region with
respect to the underlying graphite could be resolved unambigu-
ously. According to the present STM data and the force field-
based minimizations, the major driving force for the observed
orientation with respect to the graphite substrate can be attributed
to the interaction between the aromatic core and the substrate
underneath. Even though the alkyl side chains are in a favorable
position relative to graphite, they are probably not dominating
the aromatic orientation. Due to their distance to each other, a
tight, crystalline packing of the alkyl parts is not possible, and
one can understand that due to their flexibility their images are
smeared out in the STM.
Experimental Section
General Information. All reactions were carried out under an
atmosphere of argon with freshly distilled solvents under anhydrous
conditions. Melting points were determined on a micro melting point
apparatus and are uncorrected. NMR spectra were recorded at ambient
or specified temperatures on Varian Gemini 2000, Bruker AM 300, or
Bruker AMX 500 instruments and calibrated with the solvent as the
internal reference. Mass spectra were recorded on VG TRIO 2000 EI
or ZAB2-SE-FPD equipment. Absorption spectra were recorded on a
ATI Unicam UV4 UV-visible spectrophotometer; corrected fluores-
cence spectra were taken on a Aminco Bowman 2 fluorometer. STM
was carried out in the constant-height mode in situ at solid-liquid
interfaces23 using a homemade beetle-type low-current STM27 interfaced
to Omicron electronics (Omicron Vakuumphysik GmbH). Images were
recorded with Pt/Ir tips and are presented without digital image
processing. The graphite lattice was used as internal calibration standard
for correcting the images for distortion and drift. For this purpose, the
tunneling parameter were changed (tip bias, +0.1 V; current set point,
600 pA) in order to resolve graphite after an image of the monolayer
of 3a was recorded. Solvents were of spectroscopic quality. Elemental
analyses were performed by the Institut fu¨r Organische Chemie,
Johannes Gutenberg-Universita¨t in Mainz, Germany. Molecular model-
ing was performed using the Software Package Discover 4.0.0 (1996)
by Molecular Simulation Inc., USA with the force field pcff, nonbond
interactions atom based, cutoff distance 0.95 nm, final convergence
0.001 kcal mol-1 Å-1. The minimized structure of the isolated molecule
with no alkyl side chains attached to the aromatic cores was obtained
as follows: A number of different starting geometries were chosen in
order to scan a sufficient area of the potential surface for local
minimums. All minimizations started from planar aromatic structures,
The unit cell’s parameters of the spontaneously formed 2D
crystal are |ba| ) 2.9 ( 0.1 nm, |Bb| ) 4.0 ( 0.1 nm, R ) 85 (
2°, and A ) 11.5 ( 0.7 nm2, with one molecule of 3a per unit
cell. This value is larger than the spatial requirements for a single
molecule lying flat on a surface (foot print), which is ap-
proximately 9-10 nm2 based on the van der Waals radii. The
remaining area provides a certain degree of freedom for the
flexible alkyl chains to move thermally; it also provides space
to be filled to some extent by solvent molecules. This picture
is consistent with molecular dynamics (MD) calculations, based
on the same pcff force field approach mentioned above. The
calculations indicate that the alkyl chains are adsorbed to
graphite, however, not in straight all-trans conformations but
rather bent at certain positions along the carbon backbone, which
allows the alkyl chains to fit into the unit cell without leaving
too much empty space on the surface. The resulting molecular
packing exhibits neither any significant chain interdigitation nor
crystallization.
Finally, small coexisting areas of a second polytype with the
same occupied area per molecule (within the experimental error)
were observed (Figure 4, upper right corner). Here, the
molecular rows are shifted relative to each other as indicated
in the STM image. Still, the orientation of the aromatic disks
with respect to the underlying graphite remains the same.
(23) Rabe, J. P.; Buchholz, S. Science 1991, 253, 424.
(24) Claypool, Ch. L.; Faglioni, F.; Goddard, W. A., III; Gray, H. B.;
Lewis, N. S.; Marcus, R. A. J. Phys. Chem. B 1997, 101, 5978.
(25) Strawasz, M. E.; Sampson, D. L.; Parkinson, B. A. Langmuir 2000,
16, 2326.
(26) Watson, M.; Mu¨llen, K., to be published.
(27) Samori, P.; Francke, V.; Mu¨llen, K.; Rabe, J. P. Chem. Eur. J. 1999,
5, 2312.

Bishexa-peri-hexabenzocoronenyl
J. Am. Chem. Soc., Vol. 122, No. 32, 2000 7705
differing only in the above-defined torsion angle and led to various
minimums on the potential surface. The geometries with a starting
torsion angle of 50, 60, and 70°, respectively, resulted in the same
minimum with the torsion angle of 46°, which could be identified as
the global minimum.
(FD) m/z (%) 1603.30 (100) [M+]. Anal. Calcd for C124H114
(1604.27): C, 92.84; H, 7.16. Found: C, 92.34; H, 7.05.
1,12-Di(4-bromophenyl)dodeca-1,11-diyne (19). To a solution of
18 (10.0 g, 35.4 mmol), CuI (161 mg, 0.847 mmol), and [Pd(PPh3)4]
(931 mg, 0.805 mmol) in piperidine (150 mL) was added 17 (2.62 g,
16.1 mmol). The resulting mixture was stirred at room temperature for
3 h. The reaction mixture was poured into NH4Cl solution and extracted
with CH2Cl2. The organic layer was washed with NH4Cl solution and
water and then dried (MgSO4). After the solvent was removed in vacuo,
the residue was purified by column chromatography on silica gel with
CH)2Cl2/petroleum ether (1/5) to afford 19 as colorless plates (6.70 g,
2,2′-Bis(5,8,11,14,17-penta-n-dodecylhexa-peri-hexabenzocorone-
nyl) (3a). To a deoxygenated mixture of 1,5-cycloctadiene (3 mL) in
toluene (25 mL), [Ni(COD)2] (116 mg, 0.422 mmol) and 2,2′-dipyridyl
(68 mg, 0.42 mmol) were added. After the mixture was stirred at room
temperature for 1 h, a deoxygenated solution of 11a (501 mg, 0.347
mmol) in toluene (50 mL) was added. The resulting mixture was heated
at 60 °C for 20 h. The mixture was allowed to cool to room temperature;
the precipitated crystals were collected by filtration and washed with
CH2Cl2. Recrystallization from tetrachloroethane afforded pure 3a as
yellow crystals (400 mg, 85%): mp 124 °C; 1H NMR (500 MHz, C2D2-
Cl4, 140 °C) δ 8.57 (br, 4 H), 8.26 (br, 4 H), 8.22 (br, 8 H), 8.07 (br,
4 H), 7.95 (br, 4 H), 3.11 (br, 8 H), 2.95 (br, 8 H), 2.71 (br, 4 H), 2.09
(br, 8 H), 2.05 (br, 8 H), 1.89-1.17 (m, 184 H), 0.94 (br, 18 H), 0.83
1
88%): mp 87.5 °C; H NMR (200 MHz, CDCl3) δ 7.40 (d, J ) 8.4
Hz, 4 H), 7.24 (d, J ) 8.4 Hz, 4 H), 2.39 (t, J ) 6.8 Hz, 4 H), 1.71-
1.28 (m, 12 H); 13C NMR (50 MHz, CDCl3) δ 133.49, 131.88, 123.59,
122.03, 92.18, 80.16, 29.49, 29.35, 29.09, 19.92; IR (KBr) ν ) 2929,
2851, 1484, 1463, 1454, 1392, 1066, 1010, 823, 521 cm-1; MS (FD)
m/z (%) 472.1 (100) [M+]. Anal. Calcd for C24H24Br2 (472.02): C,
61.04; H, 5.12; Br, 33.84. Found: C, 61.06; H, 5.01; Br, 33.50.
1,12-Di(4-bromophenyl)dodecane (20). A mixture of 19 (6.00 g,
12.7 mmol) and palladium on activated carbon (10%, 1.83 g) in THF
(600 mL) was stirred at room temperature for 2 h under an atmosphere
of hydrogen. After the catalyst had been removed by filtration, the
solvent was removed under reduced pressure. The residue was purified
by column chromatography on silica gel (CH2Cl2/petroleum ether 1/20)
affording 20 as colorless plates (4.85 g, 79%): mp 40.0 °C; 1H NMR
(500 MHz, CDCl3) δ 7.36 (d, J ) 8.4 Hz, 4 H), 7.02 (d, J ) 8.4 Hz,
4 H), 2.53 (t, J ) 7.5 Hz, 4 H), 1.56 (p, J ) 7.5 Hz), 1.33-1.18 (m,
16 H); 13C NMR (125 MHz, CDCl3) δ 141.84, 131.25, 130.16, 119.25,
35.35, 31.28, 29.60, 29.53, 29.44, 29.17; IR (KBr) ν 2922, 2850, 1488,
1468, 1072, 1009, 797 cm-1; MS (FD) m/z (%) 480.2 (100) [M+]. Anal.
Calcd for C24H32Br2 (480.09): C, 60.01; H, 6.72,; Br, 33.27. Found:
C, 61.03; H, 5.73; Br, 31.33.
1
(br, 12 H); H NMR (500 MHz, 1,4-dichlorobenzene-d4, 140 °C) δ
9.41 (br, 4 H), 8.99 (br, 4 H), 8.81 (br, 4 H), 8.76 (br, 4 H), 8.69 (br,
4 H), 8.65 (br, 4 H), 3.56 (br, 8 H), 3.35 (br, 8 H), 3.25 (br, 4 H), 2.54
(br, 8 H), 2.42 (br, 8 H), 2.26 (br, 4 H), 2.17-1.46 (m, 92 H), 1.19
(br, 18 H), 1.08 (br, 12 H); IR (KBr) ν 2919, 2850, 1610, 1467, 858,
852 cm-1; UV-vis (CHCl3) λmax (lg ꢀ) 279 (4.83 sh), 323 (4.76 (sh),
344 (4.94 sh), 365 (5.05), 395 (5.06), 431 (4.79 sh), 453 nm (4.40 sh);
MS (FD) m/z (%) 2726.7 (100) [M+]. Anal. Calcd for C204H274
(2726.15): C, 89.87; H, 10.13. Found: C, 89.35; H, 9.79.
4,4′-Di(4-tert-butylphenylethinyl)biphenyl (14). At room temper-
ature, 13 (5.0 g, 16.00 mmol) was added to a solution of [Pd(PPh3)4]
(1.84 g, 1.60 mmol) and CuI (0.61 g, 3.20 mmol) in piperidine (300
mL). After being stirred for 20 min, 12 (7.59 g, 48.00 mmol) was added
and the mixture was heated to 80 °C for 6 h. After the reaction mixture
had been allowed to cool to room temperature, the precipitate was
filtered off and washed with piperidine. Recrystallization from tetra-
chlorethane gave pure 14 as off-white crystals (6.04 g, 81%): mp 181
°C; 1H NMR (500 MHz, C2D2Cl4, 100 °C) δ 7.57 (s, 8 H), 7.47 (m, 4
H), 7.36 (m, 4 H), 1.33 (s, 18 H); 13C NMR (125 MHz, C2D2Cl4, 100
°C) δ 152.27, 140.33, 132.47, 131.86, 127.17, 125.68, 123.41, 120.68,
91.19, 89.21, 35.07, 31.54; MS (FD) m/z (%) 466.4 (100) [M+]. Anal.
Calcd for C36H34 (466.67): C, 92.66; H, 7.34. Found: C, 92.76; H,
7.31.
1,12-Bis[4-(4-n-dodecylphenylethynyl)phenyl]dodecane (22). To
a solution of 20 (2.00 g, 4.17 mmol), CuI (105 mg, 0.549 mmol), and
[Pd(PPh3)4] (485 mg, 0.420 mmol) in piperidine (100 mL)was added
21 (4.54 g, 16.8 mmol). The resulting mixture was stirred at 80 °C for
24 h. The reaction mixture was poured into NH4Cl solution. The
precipitate was filtered off and washed with CH2Cl2. Recrystallization
from n-heptane afforded 22 as colorless needles (1.49 g, 42%): mp
1
117.5 °C; H NMR (500 MHz, CDCl3) δ 7.41 (d, J ) 8.1 Hz, 8 H),
7.13 (d, J ) 8.1 Hz, 8 H), 2.59 (t, J ) 7.4 Hz, 8 H), 1.59 (p, J ) 7.4
Hz, 8 H), 1.34-1.19 (m, 52 H), 0.87 (t, J ) 6.9 Hz, 6 H); 13C NMR
(125 MHz, CDCl3) δ 143.21, 131.45, 128.42, 120.65, 88.94, 35.90,
31.92, 31.24, 29.66, 29.64, 29.61, 29.57, 29.54, 29.48, 29.34, 29.25,
4,4′′′′′-Di-tert-butyl-2′,3′,5′,6′,2′′′′,3′′′′,5′′′′,6′′′′-octa(4-tert-butyl-
phenyl) sexiphenyl (16). A mixture of 14 (0.5 g, 1.07 mmol) and 15
(1.56 g, 2.57 mmol) in diphenyl ether (10 mL) was heated at reflux
for 3 h. The reaction mixture was then cooled to 50 °C and ethanol
(80 mL) was added. Filtration of the precipitate and washing with
ethanol afforded analytically pure 16 as a white microcrystalline powder
(1.48 g, 85%): mp 221 °C; 1H NMR (500 MHz, CDCl3) δ 6.85 (m, 4
H), 6.77 (m, 24 H), 6.65 (m, 20 H), 1.07 (s, 90 H); 13C NMR (125
MHz, CDCl3) δ 147.55, 147.39, 147.31, 140.66, 140.47, 140.23, 139.53,
139.31, 137.98, 137.91, 137.32, 131.89, 131.12, 131.05, 124.60, 123.17,
122.99, 122.95, 34.05, 34.01, 31.22, 31.18; MS (FD) m/z (%) 1627.5
(100) [M+]. Anal. Calcd for C124H138 (1628.46): C, 91.46; H, 8.54.
Found: C, 91.30; H, 8.45.
22.68, 14.10; IR (KBr) ν 2920, 2847, 1516, 1469, 842, 816, 803 cm-1
;
MS (FD) m/z (%) 858.4 (100) [M+]. Anal. Calcd for C64H90 (858.70):
C, 89.44; H, 10.56. Found: C, 89.40; H, 10.58.
1,12-Bis{4,4′-bis[penta(4-n-dodecylphenyl)phenyl]phenyl}-
dodecane (24). A mixture of 22 (1.01 g, 1.18 mmol) and 23 (2.46 g,
2.33 mmol) in diphenyl ether (5 mL) was heated at reflux for 20 h.
After cooling to room temperature, the mixture was chromatographed
on silica gel with CH2Cl2/petroleum ether (1/9) to afford 5 as pale
yellow crystals (2.45 g, 73%): mp 38.5 °C; 1H NMR (500 MHz, CDCl3)
δ 6.64 (d, J ) 8.1 Hz, 24 H), 6.59 (d, J ) 8.1 Hz, 24 H), 2.32 (t, J )
7.5 Hz, 24 H), 1.37 (p, J ) 7.5 Hz), 1.31-1.06 (m, 196 H), 0.87 (t, J
) 6.9 Hz, 30 H); 13C NMR (125 MHz, CDCl3) δ 140.29, 139.02,
138.30, 131.41, 126.44, 35.36, 31.94, 31.24, 29.87, 29.77, 29.75, 29.69,
29.62, 29.56, 29.39, 29.02, 28.89, 28.86, 22.69, 14.09; IR (KBr) ν 2956,
2925, 2852, 1516, 1467, 1456, 1021, 834, 721 cm-1; MS (FD) m/z
(%) 2919.4 (100) [M+]. Anal. Calcd for C216H322 (2918.53): C, 88.88;
H, 11.12. Found: C, 88.76; H, 11.12.
1,12-Bis[2,2′-bis(5,8,11,14,17-penta-n-dodecylhexa-peri-hexaben-
zocoronenyl)]dodecane (4). To a stirred solution of 24 (1.01 g, 0.346
mmol) in CH2Cl2 (200 mL), a solution of FeCl3 (13.2 g, 81.1 mmol)
in nitromethane (30 mL) was added dropwise. A stream of argon was
bubbled during the reaction mixture throughout the reaction. After being
stirred for a further 30 min, the reaction was quenched with MeOH
(30 mL). The resulting mixture was poured into water and extracted
with hot toluene. The organic layer was washed with water, dried
(MgSO4), and concentrated under reduced pressure. Purification by
column chromatography on silica gel with warm toluene/petroleum ether
2,2′-Bis(5,8,11,14,17-penta-tert-butylhexa-peri-hexabenzocorone-
nyl) (3b). Method A. 3b was prepared similarly to 3a by heating 11b
(50 mg, 0.0566 mmol), 1,5-cyclooctadiene (0.48 mL), [Ni(COD)2]
(18.68 mg, 0.0566 mmol), and 2,2′-dipyridyl (10.60 mg, 0.0679 mmol)
for 48 h in toluene (8 mL). Recrystallization of the crude product from
1-methylnaphthalene furnished pure 3b as a yellow microcrystalline
powder (37.50 mg, 75%).
Method B. Anhydrous FeCl3 (0.62 g, 3.86 mmol) was added to a
solution of 16 (0.5 g, 0.307 mmol) in CH2Cl2 (250 mL). The resulting
green reaction mixture was stirred for 2 h at room temperature and
then quenched with MeOH (10 mL). The precipitate was filtered off
and washed with 5 N hydrochloric acid and MeOH. The crude material
was recrystallized twice from 1-methylnaphthalene affording pure 3b
(405 mg, 81%): mp >300 °C; 1H NMR (500 MHz, C2D2Cl4, 140 °C)
δ 10.05 (s, 4 H), 9.66 (s, 4 H), 9.40 (s, 4 H), 9.35 (s, 4 H), 9.32 (s, 4
H), 9.27 (br, 8 H), 1.88 (s, 36 H), 1.83 (s, 36 H), 1.82 (s, 18 H); MS

7706 J. Am. Chem. Soc., Vol. 122, No. 32, 2000
Ito et al.
(1/1) afforded 4 as yellow crystals (723 mg, 72%): mp 53 °C; 1H NMR
(500 MHz, C2D2Cl4, 140 °C) δ 8.38 (br, 4 H), 8.36 (br, 8 H), 8.34 (br,
4 H), 8.28 (br, 8 H), 3.10 (br, 20 H), 3.02 (br, 4 H), 2.07 (br, 24 H),
1.79-1.25 (m, 196 H), 0.90 (br, 30 H); 13C NMR (125 MHz, C2D2Cl4,
140 °C) δ 139.97, 139.88, 129.96, 129.89, 123.44, 123.38, 121.29,
119.50, 37.38, 36.94, 32.04, 32.01, 31.37, 30.22, 30.02, 29.98, 29.91,
29.83, 29.43, 29.37, 28.96, 28.81, 28.67, 22.69, 13.96; IR (KBr) ν 2953,
2921, 2850, 1610, 1583, 1466, 1372, 859, 719 cm-1; UV-vis (CHCl3)
λ
max (lg ꢀ) 271 (4.71 sh), 322 (4.66 sh), 357 (5.25), 368 (5.11 sh), 398
(4.71), 414 (4.36 sh), 424 nm (4.06); MS (FD) m/z (%) 2895.6 (100)
[M+]. Anal. Calcd for C216H298 (2894.34): C, 89.62; H, 10.38. Found:
C, 89.27; H, 9.91.
JA000850E