Oligomers of hexa-peri-hexabenzocoronenes as "super- oligophenylenes": Synthesis, electronic properties, and self-assembly

Article abstract of DOI:10.1021/jo0490301

Hexa-peri-hexabenzocoronene (HBC) is a remarkable polycyclic aromatic hydrocarbon and is often called "superbenzene" because of its similarity to benzene. In this article we present the facile synthesis of oligomers of HBC, up to trimers (3, 4, 5a-c) with

Full text of DOI:10.1021/jo0490301

Oligomers of Hexa-peri-hexabenzocoronenes as
“Super-oligophenylenes”: Synthesis, Electronic Properties, and
Self-assembly
Jishan Wu, Mark D. Watson,† Natalia Tchebotareva,‡ Zhaohui Wang, and Klaus Mu¨llen*
Max-Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
muellen@mpip-mainz.mpg.de
Received June 9, 2004
Hexa-peri-hexabenzocoronene (HBC) is a remarkable polycyclic aromatic hydrocarbon and is often
called “superbenzene” because of its similarity to benzene. In this article we present the facile
synthesis of oligomers of HBC, up to trimers (3, 4, 5a-c) with different modes of connection. UV-
vis and fluorescence spectroscopy studies reveal that the oligomers are electronically decoupled.
This arises from the small atomic orbital coefficients of the bridge-head carbon atoms, the large
torsion angle between the HBC units, and the large distance of interacting transition dipoles due
to the size of the HBC chromophore. For comparison, a methylene-bridged HBC dimer 6, so-called
“superfluorene”, was prepared. The induced planarity improves π-conjugation and suppresses the
geometrical relaxation of the backbone upon electronic excitation, leading to a prominent 0-0
transition band in the fluorescence spectra. The self-assembly of the oligomers and of superfluorene
6 was studied by wide-angle X-ray diffraction (WAXD) in the bulk state, and ordered columnar
stacking occurs in the HBC dimer 3, p-HBC trimer 4, and superfluorene 6. Measurements of shear-
aligned samples show that, despite increasing aspects ratio by linear entrainment of disks, the
anitropic element that is subject to alignment by shear is the supramolecular columns.
Introduction
strong steric hindrance results in a very weak electronic
coupling between the aromatic units, as convincingly
proven by UV-vis spectroscopy and electrochemistry.
Surprisingly, the 2,7-connected oligopyrenes show some
Oligoarylenes have attracted great interest because
they serve as (i) model compounds for related poly-
arylenes, (ii) active semiconducting materials in organic
electronic devices, and (iii) “molecular wires” in molecular
scale electronics.1 Depending on the topology and geom-
etry of the connected arylene units, the oligoarylenes are
either electronically coupled2 (such as oligophenylenes,
oligothiophenes, oligopyrrols, etc.) or decoupled3 (such as
2, 7-oligopyrene and 9,10-oligoanthrylenes). In the elec-
tronically coupled (conjugated) neutral and charged oligo-
arylenes, the electronic structure and optical properties
such as the lowest-energy absorption onset strongly
depend on the chain length and finally converge to those
of related polymers.4 The conjugation between the aro-
matic units is dramatically diminished when steric
hindrance is induced between the units.5,2k In the oligo-
(1, 4-naphthylene)s 3d-f and oligo(9, 10-anthrylene)s,3b the
larger size of the aromatic units in combination with the
(2) For examples of oligophenylenes, see: (a) Berlman, I. B.; Wirth,
H. O.; Steingraber, O. J. J. Phys. Chem. 1971, 75, 318-325. (b)
Nakanishi, H.; Sumi, N.; Aso, Y.; Otsubo, T. J. Org. Chem. 1998, 63,
8632-8633. (c) Kern, W.; Seibel, M.; Wirth, H.-O. Makromol. Chem.
1959, 29, 164. (d) Heitz, W.; Ulrich, R. Makromol. Chem. 1966, 98,
29. (e) Liess, P.; Hensel, V.; Schlu¨ter, A. D. Liebigs Ann. 1996, 1037.
(f) Meerholz, K.; Heinze, J. J. Am. Chem. Soc. 1989, 111, 2325-2326.
For examples of oligothiophenes, see: (g) ten Hoeve, W.; Wynberg, H.;
Havinga, E. E.; Meijer, E. W. J. Am. Chem. Soc. 1991, 113, 5887-
5889. (h) Ba¨uerle, P.; Fischer, T.; Bidlingmaier, A.; Stabel, J.; Rabe,
J. P. Angew. Chem., Int. Ed. Engl. 1995, 34, 303. (i) Ba¨uerle, P.;
Wu¨rthner, F.; Go¨tz, G.; Effenberg, F. Synthesis 1993, 1099. (j) Tour,
J. M.; Wu, R. Macromolecules 1992, 25, 1901-1907. (k) Ba¨uerle, P.;
Segelbacher, U.; Maier, A.; Mehring, M. J. Am. Chem. Soc. 1993, 115,
10217-10223. For examples of oligopyrroles, see: (l) Kauffmann, T.;
Levy, H. Chem. Ber. 1981, 403, 41-43. (m) Groenendaal, L.; Peerlings,
H. W. I.; van Dongen, J. L. J. Macromolecules 1995, 28, 116-123. (n)
Martina, S.; Schlu¨ter, A. D. Macromolecules 1992, 25, 3607-3608.
(3) (a) Kreyenschmidt, M.; Baumgarten, M.; Tyutyulkov, N.; Mu¨llen,
K. Angew. Chem., Int. Ed. Engl. 1994, 33, 1957. (b) Mu¨ller, U.;
Baumgarten, M. J. Am. Chem. Soc. 1995, 117, 5840-5850. (c) Rettig,
W.; Zander, M. Ber. Bunsen-Ges. Phys. Chem. 1983, 87, 1141-1149.
(d) Bohnen, A.; Ra¨der, H. J.; Mu¨llen, K. Synth. Met. 1992, 42, 37. (e)
Bohnen, A.; Koch, K.-H.; Lu¨ttke, W.; Mu¨llen, K. Angew. Chem., Int.
Ed. Engl. 1990, 29, 525. (f) Baumgarten, M.; Mu¨ller, M.; Bohnen, A.;
Mu¨llen, K. Angew. Chem., Int. Ed. Engl. 1992, 31, 448.
* To whom correspondence should be addressed. Fax: 0049 6131
379 350.
† New address: University of Kentucky, Department of Chemistry,
Lexington, KY 40506-0055.
‡ New address: Laboratory of Macromolecular and Organic Chem-
istry, Eindhoven University of Technology, P.O. Box 513, 5600 MB
Eindhoven, The Netherlands.
(4) (a) Khanna, R. K.; Jiang, Y. M.; Creed, D. J. Am. Chem. Soc.
1991, 113, 5451-5453. (b) Bejonne, D.; Cornil, J.; Friend, R. H.;
Janssen, R. A. J.; Bre´das, J. L. J. Am. Chem. Soc. 1996, 118, 6453-
6461. (c) Bohnen, A.; Heitz, W.; Ra¨der, H. J.; Schenk, R. Makromol.
Chem. 1991, 192, 1679. (d) Ba¨uerle, P. Adv. Mater. 1992, 4, 102. (e)
van Haare, J. A. E. H.; Groenendaal, L.; Havinga, E. E.; Janssen, R.
A.; Meijer, E. W. Angew. Chem., Int. Ed. Engl. 1996, 35, 638. (f) Rohde,
N.; Eh, M.; Greissler, U.; Hallensleben, M. L.; Voigt, M. Adv. Mater.
1995, 7, 401.
(1) (a) Mu¨llen, K.; Wegner, G. Electronic Materials: The Oligomer
Approach; Wiley-VCH: Weinheim, 1998. Also see review papers: (b)
Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999, 38, 1350-
1377. (c) Tour, J. M. Chem. Rev. 1996, 96, 537-553. (d) Schwab, P. F.
H.; Levin, M. D.; Michl, J. Chem. Rev. 1999, 99, 1863-1933. (e) Roncali,
J. Chem. Rev. 1997, 97, 173-205. (f) Berresheim, A. J.; Mu¨ller, M.;
Mu¨llen, K. Chem. Rev. 1999, 99, 1747-1785.
10.1021/jo0490301 CCC: $27.50 © 2004 American Chemical Society
Published on Web 11/02/2004
8194
J. Org. Chem. 2004, 69, 8194-8204

Super-oligophenylenes
CHART 1. Molecular Structures of Oligo- and
Polysuperphenylenes
electronic decoupling of the subunits due to the small
atomic orbital coefficients of C-2 and C-7 in the frontier
orbitals.3a Oligoarylenes therefore lead to high spin states
upon charging.
Hexa-peri-hexabenzocoronenes (HBCs)6 carrying solu-
blizing alkyl chains are gaining increasing attention as
discotic liquid crystalline materials for organic electronic
devices such as field effect transistors (FETs),7 photovol-
taic cells,8 and light-emitting diodes (LEDs)9 as a result
of their high tendency to form long-range ordered meso-
phases and very high charge carrier mobility along the
columnar axis.10 From an electronic point of view, HBC
is regarded as an aromatic “superbenzene”,11 which
suggests the synthesis of the corresponding oligomers as
“super-oligophenylenes”. Attempts to prepare poly-p-
“superphenylenes” such as 1 (Chart 1) from the p-
dibromo-substituted HBC by a Yamamoto coupling re-
action, however, only gave an insoluble polymeric
material.12 The poor solubility even when branched
solublizing alkyl chains are attached to the HBC core
suggests strong interchain π-π stacking. Interestingly,
the UV-vis spectra of the soluble part of the polymers
disclosed a spectrum similar to that of the HBC monomer
2 (Chart 1), indicating that the conjugation of the HBC
units is interrupted. To understand the electronic proper-
ties of the HBC-containing polymers, we set out to make
monodispersed oligomers such as the HBC dimer 3 and
the para-connected HBC trimer 4 (Chart 1). The better
solubilizing branched, racemic alkyl chains instead of
n-alkyl chains were introduced in the hope of obtaining
sufficient solubility and better resolved electronic absorp-
tion/emission spectra.13 Two ortho-connected HBC tri-
mers 5a,b were also prepared and served as models for
the corresponding poly-o-superphenylenes. The active
iodo groups in compound 5b were designed to facilitate
(5) (a) Horowitz, G.; Yassar, A.; Bardeleben, T. H. Synth. Met. 1994,
62, 245. (b) Laguren-davidson, L.; van Pham, C.; Zimmer, H.; Mark,
H. B.; Ondrus, D. J. J. Electrochem. Soc. 1988, 135, 1406.
(6) (a) Watson, M.; Fechtenko¨tter, A.; Mu¨llen, K. Chem. Rev. 2001,
101, 1267-1300. (b) Herwig, P.; Kayser, C.; Mu¨llen, K.; Spiess, H. W.
Adv. Mater. 1996, 8, 510-513. (c) Stabel, A.; Herwig., P.; Mu¨llen, K.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1609-1611. (d) Fechtenko¨tter,
A.; Saalwa¨chter, K.; Harbison, M. A.; Mu¨llen, K.; Spiess, H. W. Angew.
Chem., Int. Ed. 1999, 38, 3039-3042. (e) Fechtenko¨tter, A.; Tche-
botareva, N.; Watson, M.; Mu¨llen, K. Tetrahedron 2001, 57, 3769-
3783.
(7) (a) van de Crass, A.; Stutzmann, M. N.; Bunk, O.; Nielsen, M.
M.; Watson, M. D.; Mu¨llen, K.; Chanzy, H. D.; Sirringhaus, H.; Friend,
R. H. Adv. Mater. 2003, 15, 495-499. (b) Kraft, A. ChemPhysChem
2001, 2, 163-165. (c) Katz, H. E.; Lovinger, A. J.; Johnson, J.; Kloc,
C.; Siegrist, T.; Li, W.; Lin, Y.-Y.; Dodabalapur, A. Nature 2000, 404,
478-481.
(8) (a) Schmidt-Mende, L.; Fechtenko¨tter, A.; Mu¨llen, K.; Moons,
E.; Friend, R. H.; MacKenzie, J. Science 2001, 293, 1119-1122. (b)
Tang, C. W. Appl. Phys. Lett. 1986, 48, 183-185.
(9) (a) Christ, T.; Glu¨sen, B.; Greiner, A. J.; Kettner, A.; Sander,
R.; Stu¨mpflen, V.; Tsukruk, V.; Wendorff, J. H. Adv. Mater. 1997, 9,
48-52. (b) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51,
913-915.
(10) van de Craats, A. M.; Warman, J. M.; Fechenko¨tter, A.; Brand,
J. D.; Harbison, M. A.; Mu¨llen, K. Adv. Mater. 1999, 11, 1469-1472
(11) (a) Clar, E. Aromatische Kohlenwasserstoffe-Polycyclische Sys-
teme; Springer: Berlin, 1952. (b) Clar, E. The Aromatic Sextet; Wiley:
London, 1972.
an intramolecular coupling giving a fused tris-HBC 25
(Chart 2) or intermolecular coupling to afford higher
oligomers. As an alternative of the twisted oliogmers, a
nearly planar HBC dimer 6, in which a methylene unit
bridges the two neighboring disks, was synthesized. From
an electronic and topological point of view 6 can be
regarded as a “superfluorene”. Our synthesis of HBCs6
utilizes the oxidative cyclodehydrogenation of corre-
sponding hexaphenylbenzene derivatives, and this con-
cept has been extended here to the synthesis of HBC
oligomers. The electronic and photophysical properties
of the oligomers were studied by steady-state UV-vis
absorption spectroscopy and fluorescence spectroscopy.
(12) MALDI MS was conducted on the insoluble materials with
TCNQ as matrix, and a series of peaks assigned to 4-18 HBC repeat
units were observed. Synthetic details follow the literature: Yamamoto,
T.; Morita, A.; Miyazaki, Y.; Maruyama, T.; Wakayama, H.; Zhou, Z.-
H.; Nakamura, Y.; Kanbara, T.; Sasaki, S.; Kubota, K. Macromolecules
1992, 25, 1214-1223.
(13) Ito, S.; Herwig, P. T.; Bo¨hme, T.; Rabe, J. P.; Rettig, W.; Mu¨llen,
K. J. Am. Chem. Soc. 2000, 122, 7698-7706.
J. Org. Chem, Vol. 69, No. 24, 2004 8195

Wu et al.
CHART 2. Molecular Structure of Fused HBC
Trimer 25
methysilyl)benzene boronic acid (9) gave the extended
oligophenylene 10, in which the trimethylsilyl (TMS)
groups serve as precursors for iodo groups. After treat-
ment with iodine monochloride, compound 10 was con-
verted to the related iodide 11 in 94% yield. Standard
Hagihara-Sonogashira coupling18 between 11 and 4-(3,7-
dimethyloctanyl)phenyacetylene6e provided the extended
hexaphenylbenzene 12 with two diphenylacetylene arms.
Diels-Alder cycloaddition of 12 with tetrakis[4-(3,7-
dimethyloctanyl)phenyl]cyclopentadionene (13)7e afforded
the branched oligophenylene 14 in 78% yield. The soluble
precursor 14 was then fused to the related p-HBC trimer
4 by oxidative cyclodehydrogenation with FeCl3 in nearly
quantitative yield (Scheme 2). Compound 14 was ob-
tained as a yellow powder after repeated washing with
hot methanol and was slightly soluble in chloroform and
THF.
SCHEME 1a
The synthesis of the ortho-connected HBC trimers 5a,b
was based on a similar concept as shown in Scheme 3.
An o-dibromo-substituted hexaphenylbenzene 17 was
first synthesized by Diels-Alder cycloaddition between
tetraphenylcyclopentadionene 1519 and 4,4′-dibromoto-
lane (16) in 95% yield. After Suzuki coupling with
4-(trimethylsilyl)benzene boronic acid (9), compound 17
was converted in 82% yield to the extended hexphenyl-
benzene 18, which was treated with iodine monochloride
to afford the related di-iodide 19 in 92% yield. Compound
19 was subjected to Hagihara-Sonogashira coupling with
either phenylacetylene or 4-(trimethylsilyl)phenylacety-
lene to afford compounds 20 and 21, respectively. After
Diels-Alder cycloaddition with 15, compounds 20 and
21 were converted into the branched oligophenylenes 22
and 23, respectively. The TMS groups of compound 23
were transformed to iodo groups with iodine monochlo-
ride, affording two potential coupling sites in compound
24. Under the above cyclodehydrogenation conditions,
precursors 22 and 24 were easily converted to the related
ortho-connected HBC trimers 5a and 5b, respectively.
The cyclodehydrogenation of compound 23 with FeCl3,
however, gave a mixture of HBC trimers with two TMS
groups or one TMS group (i.e., one TMS was removed
under the Lewis acidic conditions) and 5a (loss of two
TMS). The mixture was treated by tetrabutylammonium
fluoride in hot THF overnight to afford clean compound
5a. The identical spectroscopic properties of compound
5a made from compound 23 and a sample prepared by
direct cyclodehydrogenation of compound 22 suggests
that 5a is a twisted HBC trimer rather than a planar
tris-HBC 25, i.e., the possibility of intramolecular cou-
pling in 5a to planar molecule 25 during the cyclodehy-
drogentation of compound 22 can be excluded. It is of
interest whether the planar tris-HBC 25 can be prepared
by intramolecular coupling of compound 5b in dilute
solution, or if higher oligomers can be made by intermo-
lecular coupling. Several attempts at Yamamoto coupling
reactions of compound 5b failed to give either compound
25 or higher oligomers but rather starting materials as
well as some partially dehalogenated compounds. It
seems that the intramolecular and intermolecular cou-
plings meet with too strong steric interactions. The high
a (i) Ni(COD)2, COD, 2,2′-bipyridine, toluene/DMF, 80 °C, 87%.
The self-assembly behavior of these oligomers is another
important issue. Polyarylenes with flexible alkyl substit-
uents can be regarded as “hairy-rod” polymers,14 and
depending on nature of the alkyl chains, two different
packing models were observed: (i) layered structures via
significant interchain π-π stacking between the aryl
units, if the polymers carry linear alkyl chains,15 and (ii)
a hexagonal packing, if the polymers carry short, branched
alkyl chains that partially suppress the interchain π-π
interactions.16 Poly-p-superphenylenes can be regarded
as “hairy-rod-disc” polymers where strong interchain π-π
interaction of the HBC units could be more prominent.
In this work, the self-assembly behavior of the mechani-
cally aligned HBC oligomers and superfluorene was
studied by wide-angle X-ray diffraction (WAXD) mea-
surements in the bulk state.
Results and Discussion
Synthesis. The HBC dimer 3 was prepared by a
Yamamoto13 homocoupling of mono-bromo-substituted
6e
HBC 7 in 87% yield (Scheme 1). The key aspect for
the synthesis of higher oligomers is the molecular design
of branched oligophenylene precursors for the cyclode-
hydrogenation. Scheme 2 presents the synthesis of the
p-HBC trimer 4. A two-fold Suzuki coupling17 between
p-dibromo-substituted hexaphenylbenzene 8 6e and 4-(tri-
(14) (a) Bockstaller, M.; Fytas, G.; Wegner, G. Macromolecules 2001,
34, 3497-3499. (b) Stepanyan, R.; Subbotin, A.; Knaapila, M.; Ikkala,
O.; ten Brinke, G. Macromolecules 2003, 36, 3758-3763. (c) Andriko-
poulos, K.; Vlassopoulos, D.; Voyiatzis, G. A.; Yiannopoulos, Y. D.;
Kamitsos, E. I. Macromolecules 1998, 31, 5465-5473.
(15) Ballaff, M. Angew. Chem. 1989, 101, 961.
(16) Vahlenkamp, T.; Wegner, G. Macromol. Chem. Phys. 1995, 195,
1933.
(17) (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981,
11, 513. (b) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457-2483.
(18) Taskahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627.
(19) Iyer, V. S.; Wehmeier, M.; Brand, J. D.; Keegstra, M. A.; Mu¨llen,
K. Angew. Chem. 1997, 109, 1676-1679.
8196 J. Org. Chem., Vol. 69, No. 24, 2004

Super-oligophenylenes
SCHEME 2a
a (i) Pd(PPh3)4, K2CO3, toluene, 95 °C, 87%; (ii) ICl, chloroform, room temperature, 94%; (iii) 4-(3,7-dimethyloctanyl)phenylacetylene,
Pd(PPh3)4, CuI, piperidine, 92%; (iv) Ph2O, reflux, 78%; (v) FeCl3, CH3NO2/dichloromethane, 45 min, 83%.
solubility of 5a,b, in contrast with that of their para-
connected counterpart 4 suggests less aggregation in
solution.
trimer 3 also has similar emission bands with lower
fluorescence quantum yield. At the same time, the bands
are broadened with a long wavelength emission tail. The
ortho-connected HBC trimer 5a shows an emission band
similar to that of para-connected HBC trimer 4 (Figure
4b), however, with a small blue-shift. Omitting the issue
of the band broadening and red-shift due to intermolecu-
lar stacking, the similarity of emission bands of these
oligomers further supports the electronic decoupling of
the oligosuperphenylenes.
Alkylated HBC are known to show a strong tendency
to aggregate even in very dilute solution (to 10-9 M in
toluene),20 and thus the spectroscopic properties of HBC
materials strongly depend on the concentration and
solvents.21 Herein upon increasing the concentration, the
extinction coefficients (ꢀ) of 2, 3, 4, 5a,b, and 6 gradually
decrease (see S-Figure 3 in Supporting Information), a
consequence of intermolecular π-stacking of HBC units.21
On the other hand, upon increasing the number of the
HBC units, i.e., upon going from monomer to the para-
connected trimer, the UV-vis absorption spectra re-
corded at the same HBC unit concentration became broad
and showed smaller extinction coefficients, suggesting
that the tendency to aggregate becomes stronger (Figure
1a). Compared to the para-connected HBC trimer 4, the
ortho-connected HBC trimer 5a,b has larger ꢀ values at
the same concentration (Figure 1b), which can be ex-
plained by the more twisted conformation in 5a,b. The
interchain π-π interactions also led to broadening and
The methylene-bridged HBC trimer 6 was synthesized
by similar cyclodehydrogenation of the oligophenylene
precursor 28 as shown in Scheme 4. The synthesis started
with a two-fold Hagihara-Sonogashira coupling reaction
between commercially available 2,7-dibromofluorene and
4-(3,7-dimethyloctanyl)phenylacetylene6e to give com-
pound 27, which was followed by a two-fold Diels-Alder
cyclodehydrogenation with compound 13 to afford pre-
cursor 28.
All intermediate and target compounds were purified
by standard column chromatography (except for com-
pound 4 because of low solubility) and were fully char-
acterized by mass spectroscopy (see Supporting Infor-
mation), 1H NMR and 13C NMR spectroscopy, and
elemental analysis.
UV-vis and Fluorescence Spectra in Solution.
The UV-vis absorption and fluorescence spectra of the
novel oligosuperphenylenes were measured in 1,2,4-
trichlorobenzene. For comparison, the HBC unit concen-
tration of the oligomers was controlled at 2.0 × 10-6, 2.0
× 10-7, and 2.0 × 10-8 M, respectively. Similar to other
nonconjugated oligoarylenes,3 the λmax,ab values of the
oligosuperphenylenes were shifted relative to one another
by only a few wavelengths (0-8 nm) (Figure 1), suggest-
ing that the HBC units are electronically decoupled.
The normalized fluorescence spectra of HBC monomer
2, dimer 3, and trimer 4 at [HBC] ) 2 × 10-8 M in 1,2,4-
TCB are presented in Figure 2a. The HBC dimer 3 has
emission bands similar to those of HBC monomer 2 with
a small red-shift, further proving the very weak coupling
interaction between two HBCs. The para-connected HBC
(20) Fleming, A. J.; Coleman, J. N.; Dalton, A. B.; Fechtenko¨tter,
A.; Watson, M. D.; Mu¨llen, K.; Byrne, H. J.; Blau, W. J. J. Phys. Chem.
B 2003, 107, 37-43.
(21) Biasutti, M. A.; Rommens, J.; Vacs, A.; Feyter, S. De.; De
Schryver, F. D.; Herwig, P.; Mu¨llen, K. Bull. Soc. Chim. Belg. 1997,
106, 659-664.
J. Org. Chem, Vol. 69, No. 24, 2004 8197

Wu et al.
SCHEME 3a
a (i) Ph2O, reflux, 95%; (ii) Pd(PPh3)4, K2CO3, toluene, 95 °C, 86%; (iii) ICl, chloroform, room temperature, 92%; (iv) phenylacetylene or
4-trimethylsilylphenylacetylene, Pd(PPh3)4, CuI, piperidine, 88% and 91%, respectively; (v) 15, Ph2O, reflux, 72% for 22 and 94% for 23;
(vi) FeCl3, CH3NO2/dichloromethane, 45 min, 92% for 5a and 80% for 5b; (vii) (a) FeCl3, CH3NO2/dichloromethane; (b) TBAF, THF, 60
°C, overnight.
red-shift of the fluorescence band (Figure 2a), and this
phenomenon was usually observed in conjugated poly-
mers and oligomers in which strong interchain interac-
tions exist.22,23 The strongly twisted conformation in the
ortho-connected HBC trimers 5a,b diminishes the inter-
chain interactions, leading to a blue-shift of the emission
bands with respect to their para-connected counterpart
4.
It is also known that the parent poly-p-phenylenes
adopt a twisted conformation with a distortion angle of
23° between adjacent building blocks in solution, and the
substituted derivatives display even larger torsional
angle of 60-80°.23 As a result of the twisted structure,
only a weak π-conjugation among the rings was ob-
served.24 The ground-state geometric optimization of the
oligomers of HBC by different calculation methods (e.g.,
pcff 3.00 force field level, AM1, or B3LYP 6-31G**)
disclosed that the HBC dimer 2 and trimers (4 and 5a)
(22) (a) Lemmer, U.; Heun, S.; Mahrt, R. F.; Scherf, R. F.; Hopmeier,
M.; Siegner, U.; Go¨bel, E. O.; Mu¨llen, K.; Ba¨ssler, H. Chem. Phys. Lett.
1995, 240, 373-378. (b) Samuel, I. D. W.; Rumbles, G.; Collison, C. J.
Phys. Rev. B 1995, 52, 11573-11576. (c) Webster, S.; Batchelder, D. N.
Polymer 1996, 54, 13713. (d) Gomes da Costa, P.; Conwell, E. M. Phys.
Rev. B 1993, 48, 1993-1996. (e) Bre´das, J. L.; Street, G. B. Acc. Chem.
Res. 1985, 18, 309-315. (f) Su, W. P.; Schrieffer, J. R.; Heeger, A. J.
Phys. Rev. Lett. 1979, 42, 1698-1701. (g) Conil, J.; Beljonne, D.; Heller,
C. M.; Campbell, I. H.; Laurich, B. K.; Smith, D. L.; Bradley, D. D. C.;
Mu¨llen, K.; Bre´das, J. L. Chem. Phys. Lett. 1997, 278, 139-145.
(23) (a) Elsenbaumer, R. L.; Shacklette, L. W. In Handbook of
Conducting Polymers; Skotheim, T. A., Ed.; Marcel Dekker: New York,
1986; Vol. 1, Chapter 7. (b) Park, K. C.; Dodd, L. R.; Levon, K.; Kwei,
T. K. Macromolecules 1996, 29, 7149-7154.
(24) Werncke, W.; Pfeiffer, M.; Hohr, T.; Lau, A.; Ju¨pner, H.-J.
Chem. Phys. 1995, 199, 65-72. (b) Migashita, K.; Kaneto, M. Makro-
mol. Chem. Rapid Commun. 1994, 15, 511. (c) Kohler, B. E.; West, B.
J. Chem. Phys. 1983, 79, 583.
8198 J. Org. Chem., Vol. 69, No. 24, 2004

Super-oligophenylenes
SCHEME 4a
a (i) 4-(3,7-Dimethyloctanyl)phenylacetylene, Pd(PPh3)4, CuI, piperidine, 78%; (ii) Ph2O, reflux, 27%; (iii) FeCl3, CH3NO2/dichloromethane,
55%.
FIGURE 1. UV-vis spectra of 2, 3, 4, 5a,b in 1,2,4-trichlorobenzene with [HBC] ) 2 × 10-6 M.
FIGURE 2. Fluorescence spectra of 2, 3, 4, 5a in 1,2,4-trichlorobenzene with [HBC] ) 2 × 10-8 M. All are excited at 370 nm.
possessed a large dihedral angle (above 40°) between the
HBC units. The large torsional angle induced by the
repulsion between 2,2′-hydrogens as well as the alkyl
chains of the neighboring HBC units is thus one impor-
tant reason explaining the weak electronic coupling in
the oligosuperphenylenes. Another possible reason for the
weak electronic coupling in the oligosuperphenylenes is
the large size of HBC building blocks, which results in a
large distance of the interacting transition dipoles.
The atomic orbital coefficients of the bridged-head
atoms in the oligoarylenes also play an important role.3
Calculations (AM1 method) disclose that the atomic
orbital coefficients (F) of the bridge-head carbon atoms
in the HBC dimer 2 are very small (F ) 0.13), and on
J. Org. Chem, Vol. 69, No. 24, 2004 8199

Wu et al.
for the first-order transition. For the other oligomers as
well as superfluorene, however, no phase transitions were
observed even up to 300 °C, suggesting either a thermally
stable ordered phase for the para-connected HBC trimer
and superfluorene due to strong π-π interaction or an
amorphous state in the ortho-connected HBC trimer.
The WAXD measurements29 were conducted on ex-
truded fibers of the oligomers and compound 6. Figure 4
presents a 2D diffractogram together with the intensity
distribution in the equatorial direction for the HBC-dimer
3 at room temperature. The wide-angle reflection peaks
between the meridian and equator leave no doubt that
HBC dimer 3 forms a columnar phase, and that it is the
columns, not the molecules themselves, that are aligned
in the direction of shear. The disks in the columns are
tilted at arcos (0.37 nm/0.53 nm) ) 45° with respect to
the fiber axis. The main repeating distance along the
fiber (0.53 nm) corresponds to the distance between tilted
disks in the column. As indicated by the above model
calculation, an intracolumnar coplanar conformation
seems to be unlikely because of steric hindrance, so
column formation is only possible if the dimer molecules
are stacked on top of each other, i.e., if a face-to-face
double-column stack is formed (Figure 4). As a result of
the twist of the two HBC disks, the columnar axes of the
two stacked HBC columns are also tilted to each other.
Integration in the equatorial direction reveals a strong
two-dimensional correlation in directions lateral to the
columnar axes, and the observed reflexes can be matched
relatively well to an orthorhombic 2D unit cell with cell
parameters a ) 2.74 nm, b ) 2.17 nm.
The p-HBC trimer 4 shows a similar diffractogram
(Figure 5). The reflex along the meridian and equator
again implies a tilted columnar stacking and can be
correlated to the intracolumn disc-disk distance (0.38
nm, i.e., the disks are tilted by 24° with respect to the
fiber axis). Integration along the equatorial direction
reveals a series of reflection maxima that could ap-
proximately be fitted to a monoclinic 2D unit cell with
the cell parameters a ) 4.27 nm, b ) 2.99, and γ ) 60°.
The 2D WAXD patterns of an oriented fiber of super-
fluorene 6 also reveal a tilted columnar phase; however,
only one obvious reflex on the equatorial direction was
observed (see Supporting Information), making the elu-
cidation of a 2D unit cell difficult. The ortho-connected
HBC trimers 5a,b cannot form a columnar phase on the
basis of their 2D WAXD measurement, possibly because
the twisted conformation prohibits columnar stacking.
When compared to the twisted dimer, 3, it is particular
surprising that the supposed nearly planar superfluorene
does not form a more ordered columnar phase.
FIGURE 3. Emission (exited at 370 nm) and excitation
spectra (excited at 480 nm) of compound 3 and 6 in 1,2,4-
trichlorobenzene with [HBC] ) 2 × 10-8 M.
the basis of the calculated torsional angle of about 45°
in the HBC dimer 2 (comparable to that of biphenyl22),
the interaction between the HBC units, expressed by F2
cos θ, is very weak.25
Significant improvement of conjugation in poly-p-
phenylenes came from the synthesis of “stepladder” and
“ladder” polymers.26,27 The induced planarity in molecule
6 significantly changes the optical properties of the HBC
dimer as shown in Figure 3. The fluorescence spectra of
the molecule 6 are obviously different from that of
molecule 2. The forbidden 0-0 transition in the HBC
dimer 228 is now allowed and becomes prominent in
superfluorene 6. The bathochromic shift and broadening
of the UV-vis absorption and fluorescence spectra of
superfluorene 6 compared to those of HBC dimer 2
suggest an improved conjugation induced by the in-
creased planarity.
WAXD Studies on the HBC Oligomers in the Bulk
State. The above UV-vis and fluorescence measure-
ments clearly show that the HBC oligomers have a high
tendency to aggregate by π-π interactions. Another point
of interest is to understand how these oligomers stack
in the bulk state and whether they can still form a
columnar stacking as the normal alkyl-substituted HBCs.
The phase behavior of the oligomers was investigated by
differential scanning calorimetry (DSC) and wide-angle
X-ray diffraction (WAXD). The DSC curves of HBC dimer
3 showed a second-order (probably glass) transition at
57 °C and a first-order endothermic (on heating) transi-
tion at 238 °C. Both transitions were reversible and were
observed on the cooling scan with a hysteresis of 70 °C
(25) Baumgarten, M.; Gherghel, L.; Friedrich, J.; Jurczok, M.; Rettig,
W. J. Phys. Chem. A 2000, 104, 1130-1140.
The single-crystal structures of parent p-oligophen-
ylenes reveal a planar conformation in the main chain
with a herringbone-type packing at room temperature.30
The alkyl-substituted PPPs, however, adopt twisted
conformations due to the induced steric hindrance and
the main chains are separated by a layer of side chains,
suggesting less importance of the interchain π-π inter-
(26) (a) Kreyenschmidt, M.; Uckert, F.; Mu¨llen, K. Macromolecules
1995, 28, 4577-4582. (b) Scherf, U.; Mu¨llen, K. Makromol. Chem.
Rapid Commun. 1991, 12, 489. (c) Grell, M.; Bradley, D. D. C.;
Inbasekaran, M.; Woo, E. P. Adv. Mater. 1997, 9, 798. (d) Fukuda, M.;
Sawada, K.; Yoshino, K. J. Polym. Sci. Polym. Chem. 1993, 31, 2465-
2471.
(27) (a) Stampfl, J.; Graupner, W.; Leising, G.; Scherf, U. J. Lumin.
1995, 63, 117. (b) Gru¨ner, J.; Wittmann, H. F.; Hamer, P. J.; Friend,
R. H.; Huber, J.; Scherf, U.; Mu¨llen, K.; Moratti, S. C.; Holmes, A. B.
Synth. Met. 1994, 67, 181-184.
(28) (a) Birks, J. B. Photophysics of Aromatic Molecules; Wiley:
London, 1970. (b) Harris, D. C.; Bertolucci, M. D. Symmetry and
Spectroscopy: An Introduction to Vibrational and Electronic Spectros-
copy; Dover Academic Press: New York, 1989.
(29) Fischbach, I.; Pakula, T.; Minkin, P.; Fechtenko¨tter, A.; Mu¨llen,
K.; Spiess, H. W. J. Phys. Chem. B 2002, 106, 6408-6418.
(30) (a) Baker, K. N.; Fratini, A. V.; Resch, T. Polymer 1993, 34,
1571. (b) Tzusuki, S.; Tanabe, T. J. Phys. Chem. 1991, 95, 139-144.
8200 J. Org. Chem., Vol. 69, No. 24, 2004

Super-oligophenylenes
FIGURE 4. 2D X-ray diffractogram of an extruded fiber of HBC dimer 3 at room temperature. The integrated reflex along the
equatorial direction reveals an orthorhombic 2D unit cell. Insert is the proposed top-to-top packing of the HBC disks to form a
dimeric column.
FIGURE 5. Room temperature 2D X-ray diffractogram of an extruded fiber of HBC trimer 4. Integration along the equatorial
direction discloses an approximate monoclinic 2D unit cell (insert).
actions.31 In the present cases, the strong intermolecular
interactions between the HBC disks drive the para-
connected oligomers of HBC and molecule 6 into a stable
columnar stacking in a microcrystalline phase. The self-
assembled dimeric or trimeric columns form multiple
hole-transfer tunnels, thus making them promising
electronic materials for organic devices.
the HBC multi-columns. Although poly-p-superphen-
ylenes and poly-o-superphenylenes are not readily avail-
able by transition-metal-catalyzed polymerization of the
corresponding monomers as a result of either their poor
solubility or the strong steric hindrance between the HBC
units, the meta-connected polysuperphenylenes and re-
lated oligo-m-superphenylenes could be made by a similar
synthetic strategy based on m-dibromo-substituted HBC.
The weaker steric hindrance between the HBC units in
poly-m-superphenylenes is expected to allow formation
of high molecular weight polymers, and the remaining
twisted conformation could diminish the intermolecular
π-stacking, thus leading to good solubility. Synthesis and
characterization of such kind of polymers and oligomers
is a subject of future research.
Conclusion
Oligomers of “superbenzene” (HBC) up to a trimer with
different geometries were successfully prepared by either
Yamamoto coupling or oxidative cycodehydrogenation
from corresponding branched oligophenylenes. These
oligomers represent a new kind of electronically de-
coupled oligoarylenes and serve as model compounds of
corresponding poly-p-(o-)“superphenylenes”. The reduc-
tion of these oligomers by an active metal such as
potassium offers the possibility toward high-spin oligo-
radical anion formation.32 The strong aggregation ten-
dency of HBC leads to a columnar stacking of the HBC
dimer 3, trimer 4, and superfluorene 6 in the bulk state,
allowing one to study the charge carrier transport along
Experimental Section
General Experimental Methods. 1H NMR and 13C NMR
spectra were recorded in deuterated solvents such as CD2Cl2
and 1,2-dichlorobenzene-d4. UV-vis and fluorescence spectra
of the oligomers were recorded in dilute solution at room
temperature. FD mass spectra were obtained with a working
voltage of 8 KV. MALDI TOF mass spectra were recorded
using a 337 nm nitrogen laser with TCNQ as matrix. Dif-
ferential scanning calorimetry (DSC) was measured with
heating and cooling rate of 10 K/min. 2D wide-angle X-ray
diffraction measurements of oriented fibers were conducted
using a rotating anode (Rigaku, 18 kw) X-ray beam (CuKR,
pinhole collimation, double graphite monochromator) and a
CCD camera.
(31) (a) Farmer, B. L.; Chapman, B. R.; Dudis, D. S.; Adams, W. W.
Polymer 1993, 34, 1588-1601. (b) Remmers, M.; Neher, D.; Gruener,
J.; Friend, R. H.; Gelinck, G. H.; Warman, J. M.; Quattrocchi, C.; dos
Santos, D. A.; Bredas, J.-L. Macromolecules 1996, 29, 7432-7445.
(32) Gherghel, L.; Brand, J. D.; Baumgarten, M.; Mu¨llen, K. J. Am.
Chem. Soc. 1999, 121, 8104-8105.
J. Org. Chem, Vol. 69, No. 24, 2004 8201

Wu et al.
Unless otherwise noted, all starting materials were used as
received. Toluene for water-free reactions was refluxed over
potassium under argon and freshly distilled before use.
dimethyloctanyl)phenylene acetylne, 20 mg of Pd(PPh3)4, 6.3
mg of CuI, and 4 mL of piperidine were mixed together. The
mixture was degassed by two freeze-pump-thaw cycles and was
stirred at room temperature for 16 h. The reaction was
quenched with 20 mL of saturated aqueous ammonium
chloride, and the product was extracted by diethyl ether. The
organic layer was washed with water three times and dried
over magnesium sulfate. The solvent was removed under
reduced pressure, and the residue was purified by column
chromatography (silica gel, PE/DCM ) 8:1) to give 530 mg of
compound 12 as a colorless solid in 92% yield. 1H NMR (CD2-
Cl2, 250 MHz): δ ppm 7.42-7.33 (m, 12H), 7.10 (d, J ) 8.8
Hz, 4H), 7.07 (d, J ) 8.8 Hz, 4H), 6.83 (d, J ) 8.8 Hz, 4H),
6.68 (d, J ) 8.2 Hz, 8H), 6.61 (d, J ) 8.2 Hz, 8H), 2.53 (m,
4H), 2.28 (m, 8H), 1.47-0.75(m, 72 H). 13C NMR (CD2Cl2, 62.5
MHz): δ ppm 143.8, 140.7, 140.3, 140.2, 139.9, 137.8, 136.2,
131.9, 131.6, 131.2, 128.3, 126.4, 126.3, 124.6, 121.8, 120.2,
89.9, 88.4, 39.2, 38.5, 36.9, 33.2, 32.7, 32.4, 31.9, 27.8, 24.5,
22.3, 22.2, 19.2. FD MS (8kv): m/z (%) ) 1728.5 (100%), calcd
1728.77. Elemental analysis: found C 90.24, H 9.60; calcd C
90.32, H 9.68.
HBC Dimer 3. To a deoxygenated mixture of 1,5-cyclooc-
tadiene (COD, 3 mL) in toluene (25 mL) were added Ni(COD)2
(116 mg, 0.42 mmol) and 2,2′-dipyridyl (68 mg, 0.42 mmol).
After the mixture was stirred at room temperature for 1 h, a
deoxygenated solution of 2-bromo-5,8,11,14,17-penta(3,7-di-
methyloctanyl)-hexa-peri-hexabenzocoronene (7) (0.45 g, 0.35
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, and the precipitated product was filtered
and washed with toluene, dibromoethane, and methanol. The
product was purified by recrystallization from toluene to give
3 as a yellow solid in 87% yield. MALDI TOF MS (TCNQ as
1
matrix): m/z (%) ) 2444.57 (100%), calcd 2445.92. H NMR
(500 MHz, 1,2-dichlorobenzene-d,4 443 K): δ ppm 9.78 (s, 4H),
9.19 (s, 4H), 8.92 (s, 4H), 8.84 (s, 4H), 8.81 (s, 4H), 8.76(s, 4H),
3.39-3.25 (m, 20H, R-CH2), 2.30-0.73 (m, 190H). 13C NMR
(125 MHz, C2D2Cl4, 413 K): δ ppm 141.9, 141.8, 141.4, 131.8,
131.5, 131.3, 131.2, 125.9, 125.0, 124.7, 122.9, 122.8, 122.7,
122.6, 122.4, 121.3, 121.0, 120.7, 41.0, 40.8, 40.7, 39.1, 38.9,
36.3, 36.1, 36.0, 34.8, 34.7, 34.5, 29.4, 29.1, 26.3, 26.2, 26.1,
24.0, 23.9, 23.7, 23.7, 21.3, 21.2. Elemental analysis: found C
90.21, H 9.34; calcd C 90.36, H 9.64.
para-Connected Hexaphenylbenzene Trimer 14. A
500-mg portion of compound 12 and 820 mg of tetra[4-(3,7-
dimethyloctanyl)phenyl]cyclopentadienone (13) were dissolved
in 2.0 mL of diphenyl ether. The mixture was degassed under
vacuum, filled back with argon, and heated to reflux for 19 h.
After cooling, the diphenyl ether was removed under high
vacuum, and the residue was purified by column chromatog-
raphy (PE/DCM ) 8:1) to afford 803 mg of compound 14 as a
colorless waxy product in 78% yield. MALDI-TOF MS (dithra-
1,2,4,5-Tetrakis[4′-(3′′,7′′-dimethyloctanyl)phenyl]-3,6-
bis[4′-(trimethylsilyl)biphenyl] Benzene (10). A 1.25-g
portion of p-dibromo-substituted hexaphenylbenzene 8, 775 mg
of 4-trimethylsilylbenzene boronic acid (9), and 58 mg of
catalyst Pd(PPh3)4 were dissolved in 15 mL toluene, and then
10 mL 1 M K2CO3 aqueous solution was added. The mixture
was degassed by two freeze-pump-thaw cycles and heated to
reflux for 24 h. After cooling, 150 mL of acetyl acetate was
added to extract the product. The organic layer was washed
with water three times and dried over magnesium sulfate. The
solvent was removed under reduced pressure, and the residue
was purified by column chromatography (silica gel, PE/DCM
) 10:1) to afford 1.45 g of compound 10 as a white solid in
87% yield. FD MS (8kv): m/z (%) ) 1392.4 (100%), calcd
1392.35. 1H NMR (CD2Cl2, 250 MHz): δ ppm 7.51 (d, J ) 8.2
Hz, 4H), 7,41 (d, J ) 8.2 Hz, 4H), 7.14 (d, J ) 8.2 Hz, 4H),
6.90 (d, J ) 8.2 Hz, 4H), 6.77 (d, J ) 7.9 Hz, 8H), 6.70 (d, J )
7.9 Hz), 2.42 (m, 8H), 1.56-0.80 (m, 76H), 0.27(s, 18H). 13C
NMR (CD2Cl2, 62.5 MHz): δ ppm 140.7, 140.2, 139.9, 139.8,
138.6, 137.8, 137.0, 133.4, 131.7, 131.1, 126.3, 125.6, 124.6,
39.1, 38.5, 36.9, 32.6, 31.9, 27.7, 24.4, 22.2, 22.2, 19.1, -1.7.
Elemental analysis: found C 86.06, H 9.62; calcd C 86.26, H
9.70, Si 4.03.
1
nol as matrix): m/z (%) ) 3562.11 (100%), calcd 3563.88. H
NMR (CD2Cl2, 500 MHz): δ ppm 6.91 (d, J ) 7.6 Hz, 8H),
6.78 (d, J ) 7.6 Hz, 8H), 6.66 (m, 56H), 2.39-2.32 (m, 28H),
1.40-0.78 (m, 266H). 13C NMR (CD2Cl2, 125 MHz): δ ppm
140.9, 140.8, 140.6, 140.4, 140.3, 140.2, 140.1, 140.0, 138.6,
138.4, 132.2, 131.6, 126.9, 126.7, 124.8, 39.7, 39.2, 37.4, 33.2,
32.6, 32.5, 28.4, 25.1, 22.9, 22.8, 19.8, 19.7, Elemental analy-
sis: found C 89.57, H 10.21; calcd C 89.65, H 10.35.
para-Connected HBC Trimer 4. A 220-mg portion of
precursor 14 was dissolved in 60 mL of fresh dichloromethane,
and the solution was degassed by bubbling argon for 20 min.
Then 720 mg of FeCl3 dissolved in 5 mL of nitromethane was
slowly added by syringe. The mixture was bubbled through
argon over 35 min and then quenched by adding 200 mL of
methanol. The yellow precipitate was collected and washed
by methanol until the filtrate is colorless. The powder was
further stirred in hot methanol (50 °C) overnight to remove
residual iron inside. After filtering and drying, 180 mg of
yellow powder was obtained (83% yield, MALDI-TOF mass
spectra of crude compound indicate quantitative conversion,
the low yield here because of the loss of product during
purification). MALDI-TOF MS (TCNQ as matrix): m/z (%) )
3528.11 (100%), calcd [M+] 3527.60. 1H NMR (1,2-dichloroben-
zene-d4, 500 MHz, 443 K): δ ppm 9.86 (s, 6H), 9.18-8.67 (m,
28H), 3.54-3.28 (m, 28H), 2.28-0.76 (m, 266H). Elemental
analysis: found C 90.02, H 9.34; calcd C 90.57, H 9.43.
1,2-Bis(4′-bromophenyl)-4,5-bis(4′-dodecylphenyl)-3,6-
bis(4′-tert-butylphenyl) Benzene (17). A 2.6-g portion of
compound 15, 1.05 g of 4,4′-dibromotolane (16), and 3 mL of
diphenyl ether were mixed together. The mixture was degassed
under vacuum, filled back with argon, and heated to reflux
for 17 h. After cooling, 50 mL of methanol was added to
precipitate the product. The white precipitate was washed by
methanol to remove diphenyl ether, dried under vacuum, and
afforded 3.4 g of pure compound 17 as a pale yellow solid (95%).
FD MS (8 kV): m/z (%) ) 1141.2 (100%), calcd [M+] 1141.37.
1H NMR (CD2Cl2, 250 MHz): δ ppm 6.95 (d, J ) 8.5 Hz, 4H),
6.89 (d, J ) 8.2 Hz, 4H), 6.73-6.66 (m, 16H), 2.35 (t, J ) 7.6
Hz, -CH2-C11H23, 4H), 1.27 (m, -CH2-(CH2)10-CH3, 20H), 1.14
(s, tert-butyl, 18H), 0.89(t, -(CH2)11-CH3, 6H). 13C NMR (CD2-
Cl2, 125 MHz): δ ppm 148.7, 141.5, 140.8, 140.3, 140.1, 139.0,
138.3, 137.8, 133.5, 131.5, 131.4, 130.1, 126.9, 123.8, 119.72,
1,2,4,5-Tetrakis[4′-(3′′,7′′-dimethyloctanyl)phenyl]-3,6-
bis(4′-iodobiphenyl)Benzene (11). A 1.10-g portion of com-
pound 10 was dissolved in 200 mL of fresh chloroform. The
solution was degassed by bubbling argon for 15 min, and 3.16
mL of iodine monochloride solution in dichloromethane (1 M)
was added. After stirring at room temperature for 45 min, the
reaction was quenched by adding 100 mL of 2 M aqueous
sodium sulfite. The organic layer was washed with water three
times and dried over magnesium sulfate. The solvent was
removed, and the residue was purified by column chromatog-
raphy (silica gel, PE/DCM ) 9:1) to give 1.4 g of compound 11
as a colorless solid in 94% yield. FD MS (8kv): m/z (%) )
1
1499.40 (100%), calcd 1499.78. H NMR (CD2Cl2, 250 MHz):
δ ppm 7.65 (d, J ) 8.5 Hz, 4H), 7.16(d, J ) 8.5 Hz, 4H), 7.07
(d, J ) 8.5 Hz, 4H), 6.88 (d, J ) 8.5 Hz, 4H), 6.73 (d, J ) 8.2
Hz, 8H), 6.67 (d, J ) 8.2 Hz, 8H), 2.34 (m, 8H), 1.42(m, 4H),
1.2-0.74(m, 72 H). 13C NMR (CD2Cl2, 62.5 MHz): δ ppm 141.4,
140.9, 140.7, 140.6, 140.5, 138.5, 138.1, 136.59, 132.57, 131.8,
128.9, 127.1, 125.2, 39.9, 39.2, 37.6, 33.3, 32.6, 28.4, 25.1, 23.0,
23.0, 19.9. Elemental analysis: found C 75.18, H 7.86; calcd
C 75.28, H 7.80, I 16.92.
1,2,4,5-Tetrakis[4′-(3′′,7′′-dimethyloctanyl)phenyl]-3,6-
bis[4′-(3′′,7′′-dimethyloctanyl)diphenylethynyl] Benzene
(12). A 500-mg portion of compound 11, 242 mg of 4-(3,7-
8202 J. Org. Chem., Vol. 69, No. 24, 2004

Super-oligophenylenes
35.70, 34.4, 32.3, 31.8, 31.3, 30.1, 30.0, 29.9, 29.8, 29.3, 23.1,
14.3. Elemental analysis: found C 77.86, H 8.13; calcd C 77.87,
H 8.12, Br 14.00.
78.1(-CCH), -1.0 (SiMe3). Elemental analysis: found C 75.65,
H 8.21; calcd C 75.79, H 8.10, Si 16.11.
1,4-Bis(4′-tert-butylphenyl)-2,3-bis(4′-dodecylphenyl)-
5,6-bis[4′- (trimethylsilyl) diphenylethynyl] Benzene (21).
Following the synthetic procedure for compound 20, Hagihara
coupling between compound 19 and 4-(trimethylsilyl)phenyl
acetylene gave compound 21 as a pale yellow solid in 91% yield
after column chromatography (silica gel, PE/DCM ) 4:1). FD
MS (8 kV): m/z (%) ) 1480.5 (100%), calcd 1480.38. 1H NMR
(CD2Cl2, 250 MHz): δ ppm 7.55-7.51 (m, 8H), 7.48 (d, J )
8.5 Hz, 4H), 7.39 (d, J ) 8.5 Hz, 4H), 7.16 (d, J ) 8.5 Hz, 4H),
6.99 (d, J ) 8.2 Hz, 4H), 6.92 (d, J ) 8.2 Hz, 4H), 6.81 (d, J )
8.5 Hz, 4H), 6.77 (d, J ) 8.5 Hz, 4H), 6.69 (d, J ) 8.2 Hz, 4H),
2.38 (t, J ) 7.2 Hz, -CH2-C11H23, 4H), 1.30 (m, CH2-(CH2)10-
CH3, 20H), 1.13 (s, tert-butyl, 18H), 0.91 (t, -(CH2)11-CH3, 6H),
0.29 (s, SiMe3, 18H).13C NMR (CD2Cl2, 125 MHz): δ ppm 147.9,
141.1, 140.7, 140.6, 140.4, 140.3, 139.4, 138.0, 137.6, 136.4,
133.1, 131.9, 131.6, 131.1, 130.9, 130.3, 126.4, 126.3, 124.7,
123.3, 123.1, 121.5, 35.1, 33.8, 31.8, 31.2, 30.8, 29.5, 29.4, 29.3,
29.2, 28.7, 22.5, 13.7, -1.8. Elemental analysis: found C 87.16,
H 8.64; calcd C 87.63, H 8.58, Si 3.79.
1,4-Bis(4′-tert-butylphenyl)-2,3-bis(4′-dodecylphenyl)-
5,6-bis[4′-(trimethylsilyl)biphenyl] Benzene (18). Follow-
ing the procedure of the synthesis of 10, compound 18 was
obtained in 86% yield after purification with column chroma-
tography (silica gel, PE/DCM ) 9:1). FD MS (8 kV): m/z (%)
1
) 1281.0 (100), calcd 1281.1. H NMR (CD2Cl2, 250 MHz): δ
ppm 7.19 (d, J ) 8.2 Hz, 4H), 7.14 (d, J ) 8.2 Hz, 4H), 7.12-
6.71 (m, 24H), 2.42 (t, J ) 7.2 Hz, -CH2-C11H23, 4H), 1.34 (m,
CH2-(CH2)10-CH3, 20H), 1.25 (s, tert-butyl, 18H), 0.95 (t,
-(CH2)11-CH3, 6H), 0.29 (s, SiMe3, 18H). 13C NMR (CD2Cl2, 125
MHz): δ ppm 141.3, 141.0, 140.8, 140.3, 140.0, 139.2, 138.7,
138.3, 137.9, 134.1, 132.5, 131.8, 131.6, 130.2, 127.0, 126.4,
125.5, 123.8, 123.7, 119.3, 35.8, 34.5, 32.4, 31.9, 31.5, 30.2, 30.1,
30.0, 29.9, 29.4, 23.2, 14.4, -1.0. Elemental analysis: found
C 85.78, H 8.85; calcd C 86.32, H 9.29, Si 4.39.
1,4-Bis(4′-tert-butylphenyl)-2,3-bis(4′-dodecylphenyl)-
5,6-bis(4′-iodobiphenyl) Benzene (19). Following the syn-
thetic procedure for compound 11, compound 19 was obtained
as a slightly yellow solid in 92% yield. FD MS (8 kV): m/z (%)
) 1388.1 (100), calcd 1387.56. 1H NMR (CD2Cl2, 250 MHz): δ
ppm 7.63 (d, J ) 8.5 Hz, 4H), 7.12 (d, J ) 8.2 Hz, 4H), 7.09 (d,
J ) 7.6 Hz, 4H), 6.95 (d, J ) 8.2 Hz, 4H), 6.89 (d, J ) 8.2 Hz,
4H), 6.79-6.86 (m, 12H), 2.37 (t, J ) 7.2 Hz, -CH2-C11H23, 4H),
1.28 (m, CH2-(CH2)10-CH3, 20H), 1.11 (s, tert-butyl, 18H), 0.90
(t, -(CH2)11-CH3, 6H). 13C NMR (CD2Cl2, 125 MHz): δ ppm
140.6, 140.0, 139.9, 138.5, 138.2, 138.0, 136.7, 132.5, 131.6,
131.5, 130.1, 128.9, 126.9, 125.2, 123.7, 35.7, 34.4, 32.4, 31.8,
31.4, 30.1, 30.0, 29.9, 29.8, 29.3, 23.1, 14.3. Elemental analy-
sis: found C 74.02, H 7.42; calcd C 74.44, H 7.26, I 18.29.
1,4-Bis(4′-tert-butylphenyl)-2,3-bis(4′-dodecylphenyl)-
5,6-bis(4′-diphenylethynyl) Benzene (20). A mixture of 556
mg of compound 19, 13.8 mg of Pd(PPh3)4, and 4.6 mg of CuI
in 4 mL of piperidine was degassed by two freeze-pump-thaw
cycles, and then 122 mg of phenyl acetylene was added. The
mixture was stirred at 40 °C for 2 h. After cooling, the mixture
was poured into saturated aqueous ammonium chloride and
extracted by diethyl ether. The organic layer was washed with
water three times and dried over magnesium sulfate. The
solvent was removed under vacuum, and the residue was
purified by column chromatography (silica gel, PE/DCM ) 4:1)
to give 470 mg of compound 20 as a pale yellow powder (88%).
FD MS (8 kV): m/z (%) ) 1335.8 (100%), calcd 1336.01. 1H
NMR (CD2Cl2, 250 MHz): δ ppm 7.55-7.54 (m, 4H), 7.49 (d,
J ) 8.5 Hz, 4H), 7.41 (d, J ) 8.8 Hz, 4H), 7.38-7.34 (m, 4H),
7.17 (d, J ) 8.5 Hz, 4H), 6.99 (d, J ) 8.2 Hz, 4H), 6.91 (d, J )
8.5 Hz, 4H), 6.80 (d, J ) 8.5 Hz, 4H), 6.76 (d, J ) 8.2 Hz, 4H),
6.69 (d, J ) 8.2 Hz, 4H), 2.38 (t,, J ) 7.3 Hz, -CH2-C11H23,
4H), 1.29 (m, CH2-(CH2)10-CH3, 20H), 1.13 (s, tert-butyl, 18H),
0.91 (t, -(CH2)11-CH3, 6H).13C NMR (CD2Cl2, 125 MHz): δ ppm
140.9, 140.0, 138.6, 138.2, 137.0, 132.5, 132.2, 131.9, 131.7,
131.5, 128.8, 128.7, 126.9, 125.4, 123.8, 123.7, 122.1, 90.2, 89.7,
35.8, 34.4, 32.4, 31.8, 31.4, 30.5, 30.1, 29.9, 29.8, 29.4, 23.1,
14.3. Elemental analysis: found C 91.65, H 8.32; calcd C 91.70,
H 8.30.
ortho-Connected Hexaphenylbenzene Trimer 22. A
200-mg portion of compound 20 and 500 mg of compound 15
were dissolved in 1 mL of diphenyl ether. The mixture was
degassed under vacuum, filled back with argon, and heated
to reflux for 4 h. After cooling, 10 mL of methanol was added,
and the precipitate was further purified by column chroma-
tography (silica gel, PE/DCM ) 4:1) to give 320 mg of pure
compound 22 as a pale yellow solid in 72% yield. MALDI-TOF
MS (dithranol as matrix): m/z (%) ) 2945.82 (100), calcd
1
2946.68. H NMR (CD2Cl2, 250 MHz): δ ppm 6.84-6.63 (m,
aromatic rings, 74H), 2.36 (t, J ) 7.3 Hz, -CH2-C11H23, 12H),
1.28 (m, CH2-(CH2)10-CH3, 60H), 1.13-1.11 (overlapped, tert-
butyl, 54H), 0.90 (t, -(CH2)11-CH3, 18H). 13C NMR (CD2Cl2, 125
MHz): δ ppm 140.2, 140.1, 139.9, 138.6, 138.2, 137.4, 132.2,
131.9, 131.7, 131.5, 126.8, 125.0, 123.6, 35.7, 34.4, 32.4, 31.8,
31.4, 30.1, 30.0, 29.9, 29.8, 29.3, 23.1, 14.3. Elemental analy-
sis: found C 89.44, H 9.61; calcd C 90.49, H 9.51.
ortho-Connected Hexaphenylbenzene Trimer 23. Fol-
lowing the synthetic procedure for compound 22, Diels-Alder
cycloaddition between compound 21 and 15 gave compound
23 as a slightly yellow solid in 94% yield after column
chromatography (silica gel, PE/DCM ) 5:1). FD MS (8 kV):
1
m/z (%) ) 3091.2 (100), calcd 3091.06. H NMR (CD2Cl2, 250
MHz): δ ppm 7.35-6.61 (m, aromatic rings, 72H), 2.35 (t, J
) 7.3 Hz, -CH2-C11H23, 12H), 1.27 (m, CH2-(CH2)10-CH3, 60H),
1.11-1.10 (overlapped, tert-butyl, 54H), 0.89 (t, -(CH2)11-CH3,
18H), 0.10 (s, SiMe3, 18H). 13C NMR (CD2Cl2, 125 MHz): δ
ppm 140.9, 139.9-137.72(m), 132.2-131.1(m), 130.1, 126.8,
125.1, 124.6, 123.6, 123.5, 35.7, 34.4, 32.3, 31.8, 31.4, 31.3, 30.1,
30.0, 29.9, 29.8, 29.3, 23.1, 14.3, -1.1. Elemental analysis:
found C 88.42, H 9.61; calcd C 88.60, H 9.59, Si 1.82.
ortho-Connected Hexaphenylbenzene Trimer 24. Fol-
lowing the synthetic procedure for compound 11, compound
24 as a pale yellow solid was obtained in 92% yield after
column chromatography (silica gel, PE/DCM ) 5:1). FD MS
(8 kV): m/z (%) ) 3198.2 (100), calcd 3198.48. 1H NMR (CD2-
Cl2, 250 MHz): δ ppm 7.35-6.57 (m, aromatic rings, 72H),
2.35 (t, J ) 7.2 Hz, -CH2-C11H23, 12H), 1.27 (m, CH2-(CH2)10-
CH3, 60H), 1.15-1.11 (overlapped, tert-butyl, 54H), 0.89 (t,
-(CH2)11-CH3, 18H. 13C NMR (CD2Cl2, 125 MHz): δ ppm 140.2,
140.0, 139.9, 139.8, 139.5, 139.3, 138.6, 138.4, 138.3, 138.1,
138.0, 137.8, 137.5, 137.3, 137.1, 136.0, 134.8, 133.9, 132.3,
132.2, 131.6, 131.4, 130.1, 126.9, 126.3, 125.3, 125.1, 125.0,
124.3, 123.8, 123.7, 123.2, 119.2, 35.7, 34.4, 32.3, 31.8, 31.4,
30.1, 30.0, 29.9, 29.8, 29.3, 23.1, 14.3. Elemental analysis:
found C 83.28, H 8.62; calcd C 83.37, H 8.70, I7.94.
4-Trimethylsilyphenyl Acetylene. A 6.88-g portion of
1-brom-4-trimethylsilylbenzene, 315 mg of Pd(PPh3)2Cl2, and
172 mg of CuI were mixed together with 50 mL of piperidine.
The mixture was degassed by two freeze-pump-thaw cycles,
and then 4.42 g of trimethylsilylacetylene was added. The
mixture was heated to 80 °C overnight (ca. 16 h). The solvent
was removed under vacuum, and the residue was stirred in
60 mL of methanol with 12.4 g of K2CO3 for 1 h. The mixture
was poured into 200 mL of water and extracted with 50 mL of
diethyl ether. Under standard workup and column chroma-
tography (silica gel, PE), 5.0 g of pale yellow liquid was
obtained in 95% yield. 1H NMR (CD2Cl2, 250 MHz): δ ppm
7.58 (m, 4H), 3.21 (s, -CCH, 1H), 0.37(s, SiMe3,9H). 13C NMR
(CD2Cl2, 125 MHz): δ ppm 142.4, 133.8, 131.7, 122.9, 84.3,
ortho-Connected HBC Trimer 5a. Following the syn-
thetic procedure for compound 4, cyclodehydrogenation of 22
with 72 equiv of FeCl3 over 35 min gave compound 5a as a
yellow-to-orange solid in 92% yield after column chromatog-
raphy (silica gel, PE/DCM ) 2:1). MALDI-TOF MS (TCNQ as
J. Org. Chem, Vol. 69, No. 24, 2004 8203

Wu et al.
1
matrix): m/z (%) ) 2909.32 (100%), calcd 2910.37. H NMR
cedure for compound 14, Diels-Alder cycloaddition between
compound 27 (200 mg, 0.31 mmol) and 13 (585 mg, 0.62 mmol)
in 1 mL of diphenyl ether afforded 210 mg of compound 28 as
a slightly yellow solid in 27% yield after column chromatog-
raphy (silica gel, PE/DCM ) 85:15). FD MS (8 kV): m/z (%) )
2482.6 (100), calcd 2482.12. 1H NMR (CD2Cl2, 250 MHz): δ
ppm 7.06-6.65 (br, Ar-H, 46H), 3.15 (s, bridged methylene,
2H), 2.39-2.33 (br, 20H), 1.53-0.78 (overlapped, 166H). 13C
NMR (CD2Cl2, 62.5 MHz): δ ppm 140.5, 140.2, 140.0, 139.7,
138.7, 138.6, 138.5, 131.7, 130.7, 128.7, 128.5, 126.9, 126.8,
117.9, 39.8, 39.2, 39.0, 37.5, 33.2, 32.6, 28.4, 25.1, 22.8, 19.8.
Elemental analysis: found C 89.38, H 10.37; calcd C 89.52, H
10.48.
(1,2-dichlorobenzene-d4, 443 K, 700 MHz): δ ppm 10.43, 9.61,
9.37, 9.06, 8.79, 8.59, 8.41, 7.65 (overlapped, Ar-H, 38H),
3.47-3.37 (overlapped, -CH2-C11H23, 12H), 2.37-1.27 (over-
lapped, 174H), 0.88 (t, J ) 7.6 Hz, -(CH2)11-CH3,18H). 13C NMR
(1,2-dichlorobenzene-d4, 403 K, 700 MHz): δ ppm 147.8 (br),
139.5 (br), 136.0-117.6 (br), 36.6 (br), 35.0, 34.5, 31.1-29.1
(br), 21.8, 12.9. Elemental analysis: found C 91.14, H 8.67;
calcd C 91.62, H 8.38.
ortho-Connected HBC Trimer 5b. Following the syn-
thetic procedure for compound 4, cyclodehydrogenation of 24
with 36 equiv of FeCl3 for 35 min gave compound 5b as a
yellow-to-orange solid in 80% yield after column chromatog-
raphy (silica gel, PE/DCM ) 2:1). MALDI-TOF-MS (TCNQ as
matrix): m/z (%) ) 3161.53 (100), calcd 3162.20. 1H NMR (1,2-
dichlorobenzene-d4, 443 K, 700 MHz): δ ppm 10.5-7.45
(overlapped, Ar-H, 36H), 3.48-3.32 (overlapped, -CH2-C11H23,
12H), 2.32-1.22 (overlapped, 174H), 0.85 (t, J ) 7.6 Hz,
-(CH2)11-CH3,18H). 13C NMR (1,2-dichlorobenzene-d4, 403 K,
125 MHz): δ ppm 148.0 (br), 139.6 (br), 136-118.0 (br), 36.5
(br), 34.3 (br), 34.3-228.2 (br), 21.5, 12.6. Elemental analy-
sis: found C 83.91, H 7.71; calcd C 84.32, H 7.65, I 8.03.
2,7-Bis[4′-(3′′,7′′-dimethyloctanyl)phenylethynyl]fluor-
ene (27). A mixture of 500 mg of 2,7-dibromofluorene (26, 1.54
mmol), 785 mg of 4-(3,7-dimethyloctyl)phenylacetylene (3.24
mmol), 178 mg of Pd(PPh3)4 (5 mol % per Br), 31 mg of CuI,
and 10 mL of piperidine was degassed by bubbling argon for
20 min and heated to reflux (80 °C in bath) overnight. After
cooling, the mixture was poured into saturated NH4Cl aqueous
solution and extracted by dichloromethane three times. The
organic layer was washed with water and dried over magne-
sium sulfate. After removing the solvent, the residue was
purified by column chromatography (silica gel, PE/DCM ) 10:
1) to give 778 mg of compound 27 as a colorless solid in 78%
yield. FD MS (8 kV): m/z (100) ) 647.1, calcd 647.01. 1H NMR
(CD2Cl2, 250 MHz): δ ppm 7.75 (d, J ) 7.9 Hz, 2H), 7.70 (s,
2H), 7.56 (d, J ) 7.9 Hz, 2H), 7.48 (d, J ) 8.2 Hz, 4H), 7.21 (d,
J ) 8.2 Hz, 4H), 3.91 (s, 2H), 2.66 (m, 4H), 1.65-1.14 (m, 20H),
0.98-0.89 (m, 18H, CH3). 13C NMR (CD2Cl2, 62.5 MHz): δ ppm
144.4, 144.2, 141.5, 131.8, 130.9, 128.9, 128.4, 122.3, 120.8,
120.4, 111.4, 90.3, 89.7, 39.7, 39.1, 37.5, 37.0, 33.8, 32.95, 28.4,
25.1, 22.9, 22.8, 19.8. Elemental analysis: found C 90.84, H
8.86; calcd C 90.96, H 9.04.
Superfluorene 6. Following the synthetic procedure for
compound 4, cyclodehydrogentation of 28 (120 mg, 0.048 mmol)
with 565 mg of FeCl3 (24 equiv) in 30 mL of dichloromethane
gave 65 mg of pure product (55%) after column chromatogra-
phy (silica gel, toluene). MALDI-TOF MS (TCNQ as matrix):
1
m/z (%) ) 2457.56 (100), calcd 2457.93. H NMR (1,2-dichlo-
robenzene-d4, 448 K, 500 MHz): δ ppm 9.59, 9.30-8.70 (br,
Ar-H), 5.23, 3.86-3.37 (br), 2.45-0.96 (br, alkyl chains).
Elemental analysis: found C 89.52, H 9.36; calcd C 90.40, H
9.60.
Acknowledgment. This work was financially sup-
ported by the Zentrum fu¨r Multifunktionelle Werkstoffe
und Miniaturisierte Funktionseinheiten (BMBF 03N
6500) and the Deutsche Forschungsgemeinschaft (Schw-
erpunkt Feldeffekt Transistoren), as well as EU project
DISCEL (G5RD-CT-2000-00321) and MAC-Mes (Grd2-
2000-30242). We thank Prof. Dr. Uwe H. F. Bunz, P.D.
Dr. Martin Baumgarten, and Dr. Nigel Lukas for helpful
discussions.
Supporting Information Available: Selected MALDI-
TOF MS and NMR spectra of the oligomers; concentration-
dependent UV-vis spectra of compound 2, 3, 4 and 5a,b in
1,2,4-TCB solution; WAXD diffractogram for compound 6 in
the solid state. This material is available free of charge via
the Internet at http://pubs.acs.org.
2,7-Bis{2′,3′,4′,5′,6′-penta[4”-(3′′′,7′′′-dimethyloctanyl)-
phenyl]phenyl} Fluorene 28. Following the synthetic pro-
JO0490301
8204 J. Org. Chem., Vol. 69, No. 24, 2004