Oligoindenopyrenes: A new class of polycyclic aromatics

Article abstract of DOI:10.1021/jo0613939

(Graph Presented) A new class of polycyclic aromatic hydrocarbons - oligoindenopyrenes - has been synthesized featuring a Pd-catalyzed Suzuki - Heck coupling cascade. The oligoindenopyrenes are robust, highly colored substructures of C₇₀ and have properties that might prove useful in new organic materials or devices. After excitation, the tetraindenopyrene derivative 3d undergoes efficient deactivation (99%) by internal conversion to the ground state. The small fluorescence quantum yield (0.004) is in accordance with the short (0.6 ns) fluorescence decay time.

Full text of DOI:10.1021/jo0613939

Oligoindenopyrenes: A New Class of Polycyclic Aromatics
Hermann A. Wegner,†,‡ Helge Reisch,‡ Karsten Rauch,† Attila Demeter,§,
Klaas A. Zachariasse,§ Armin de Meijere,† and Lawrence T. Scott*,‡
Institut fu¨r Organische und Biomolekulare Chemie, Georg-August-UniVersita¨t Go¨ttingen,
Tammannstrasse 2, 37077 Go¨ttingen, Germany, Boston College, Merkert Chemistry Center,
Chestnut Hill, Massachusetts 02467-3860, Max-Planck-Institut fu¨r biophysikalische Chemie, Abt.
Spektroskopie und Photochemische Kinetik, Am Fassberg 11, 37077 Go¨ttingen, Germany, and Institute of
Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, P.O. Box 17,
1525 Budapest, Hungary
lawrence.scott@bc.edu
ReceiVed July 5, 2006
A new class of polycyclic aromatic hydrocarbonssoligoindenopyrenesshas been synthesized featuring
a Pd-catalyzed Suzuki-Heck coupling cascade. The oligoindenopyrenes are robust, highly colored
substructures of C70 and have properties that might prove useful in new organic materials or devices.
After excitation, the tetraindenopyrene derivative 3d undergoes efficient deactivation (99%) by internal
conversion to the ground state. The small fluorescence quantum yield (0.004) is in accordance with the
short (0.6 ns) fluorescence decay time.
Introduction
anomalous fluorescence,4,5 and the carcinogenicity exhibited by
other nonalternant PAHs.6,7 Herein we report the previously
unknown diindenopyrenes 3a and 3b, triindenopyrene 3c, and
tetraindenopyrene 3d. The tert-butyl groups on 3c and 3d were
incorporated to enhance the solubility of these large PAHs. An
overview of the properties of these new hydrocarbons, including
their absorption and fluorescence spectra, fluorescence quantum
yields, and decay times, is presented first, and a summary of
the synthetic procedures used then follows.
Information on the class of indenopyrenes is scarce. To date,
only indeno[1,2,3-cd]pyrene (1) has been reported.1-3 Structur-
ally similar compounds, such as benzo[b]fluoranthene, show
strong carcinogenic effects in animals and are suspected to act
similarly in humans. We have begun exploring synthetic routes
to the other members of this interesting family of aromatics,
the di-, tri-, and tetraindenopyrenes, to learn what unusual
properties they might have. Special interest in these nonalternant
polycyclic aromatic hydrocarbons (PAHs) stems from their
identity as partial structures of C70-fullerene (2) and its higher
homologues, their potential to show unusual physical and
photophysical properties, e.g., high electron affinities and
Results and Discussion
Properties of the Indenopyrenes. In 2002, Havenith and
co-workers reported extensive calculations on all the cyclopenta-
(4) Gooijer, C.; Kozin, I.; Velthorst, N. H.; Sarobe, M.; Jenneskens, L.
W.; Vlietstra, E. J. Spectrochim. Acta, Part A 1998, 54, 1443-1449 and
references therein.
(5) (a) Necula, A. Ph.D. Thesis, Boston College, Chestnut Hill, MA,
1996. (b) Sarobe, M. Ph.D. Thesis, Utrecht University, Utrecht, The
Netherlands, 1998.
* To whom correspondence should be addressed. Fax: +1-617-552-6454.
† Georg-August-Universita¨t Go¨ttingen.
‡ Boston College.
§ Max-Planck-Institut fu¨r biophysikalische Chemie.
Hungarian Academy of Sciences.
(1) Cho, B. P.; Harvey, R. G. J. Org. Chem. 1987, 52, 5668-5678.
(2) (a) Rice, J. E.; Cai, Z. W. J. Org. Chem. 1993, 58, 1415-1424. (b)
Rice, R. E.; Cai, Z. W. Tetrahedron Lett. 1992, 33, 1663-1678.
(3) Harvey, R. G. Polycyclic Aromatic Hydrocarbons; Wiley-VCH: New
York, 1997.
(6) Sarobe, M.; Jenneskens, L. W.; Wesseling, J.; Wiersum, U. E. J.
Chem. Soc., Perkin Trans. 2 1997, 703-708 and references therein.
(7) (a) Lowe, J. P.; Silverman, B. D. Acc. Chem. Res. 1984, 17, 332-
338. (b) Ball, L. M.; Warren, S. H.; Sangaiah, R.; Nesnow, S.; Gold, A.
Mutat. Res. 1989, 224, 115-125.
10.1021/jo0613939 CCC: $33.50 © 2006 American Chemical Society
Published on Web 10/21/2006
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J. Org. Chem. 2006, 71, 9080-9087

Polyindenopyrenes
of 3d in solution; the signal returns to the expected region when
the spectrum is recorded on very dilute solutions. A more
thorough discussion of the NMR spectra of the neutral oligo-
indenopyrenes and of their dianions and other charged states is
reported in a separate publication.10
One property of these new compounds that adds to their
attractiveness for possible uses in material science is their
extreme stability. Diindenopyrene 3a remains solid up to 250
°C, and decomposition of 3b begins only at 240 °C. The melting
points for 3c and 3d are both over 325 °C.
FIGURE 1. Monoindenopyrene (1) and tetraindenopyrene mapped
onto C70 (2).
Absorption Spectra of the Indenopyrenes. In their absorp-
tion spectra, the diindenopyrenes 3a and 3b exhibit two main
absorption maxima (Figure 2), appearing at 267 (log ꢀ ) 1.94)
and 307 nm (log ꢀ ) 2.44) for 3a and at 264 (log ꢀ ) 3.01)
and 316 nm (log ꢀ ) 2.56) for 3b. These correlate with the
absorption maxima for pyrene itself at 242 (log ꢀ ) 8.84) and
273 nm (log ꢀ ) 5.36), but are shifted to longer wavelengths.11
The red colors of the diindenopyrenes result from their extended
π-systems, which give rise to additional lower intensity maxima
at 388 (log ꢀ ) 1.08) and 411 nm (log ꢀ ) 1.24) for 3b and at
even longer wavelength for 3a at 410 (log ꢀ ) 0.77), 429 (log
ꢀ ) 0.77), and 455 nm (log ꢀ ) 0.97). Monoindenopyrene 1
shows long wavelength absorptions also in this region at 376
(log ꢀ ) 1.40) and 386 nm (log ꢀ ) 1.16), which emphasizes
the trend: the more indeno groups attached, the further the
maxima shift to longer wavelength. This trend continues with
the higher homologues of the indenopyrenes. The triindenopy-
rene 3c exhibits strong maxima in its UV-vis spectrum at 276
nm (log ꢀ ) 1.43), 312 nm (log ꢀ ) 1.92), and up to 325 nm
(log ꢀ ) 1.00) and also in the region from 400 nm to beyond
500 nm. The tetraindenopyrene 3d shows distinct absorption
maxima well beyond 500 nm (545 nm (log ꢀ ) 0.21)) and an
fused pyrenes, which represent truncated substructures of the
indenopyrenes considered here.8 Besides interesting magnetic
and electronic properties, all of the structural parameters were
also predicted. Interestingly, tetracyclopenta[cd,fg,jk,mn]pyrene
was computed to be bowl shaped. To date, however, no
synthesis of this compound has been published. Our own
calculations (B3LYP/6-31G*)9 predict a curved structure as well
for tetraindeno[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-jk:1′′′,2′′′,3′′′-mn]-
pyrene 3d. The slightly longer o-phenylene bridges, however,
relax the pinching effect of the five-membered rings and lower
the calculated inversion barrier to just 0.33 kcal/mol. With
derivative 3d now in hand, it should be possible to test these
calculations. Unfortunately, we have so far been unable to obtain
a single-crystal suitable for X-ray analysis.
The NMR spectra of the indenopyrenes are unexceptional.
Incorporation of successive indeno groups causes only minor
changes in the chemical shifts of the remaining hydrogens
attached to the pyrene core. The only apparent exception to this
behavior is seen with the tetraindenopyrene 3d; in this case,
the signal for the remaining two equivalent hydrogens on the
pyrene core shifts upfield by ca. 0.8 ppm. Eventually, however,
we learned that the unusual shift is a consequence of aggregation
FIGURE 2. Absorption spectra in CHCl3 at room temperature of diindeno[1,2,3-cd:1′,2′,3′-jk]pyrene (3a) (top left), diindeno[1,2,3-cd:1′,2′,3′-fg]-
pyrene (3b) (top right), 2,7,11-tri-tert-butyltriindeno[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-jk]pyrene (3c) (bottom left), and 2,7,11,16-tetra-tert-butyltetraindeno-
[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-jk:1′′′,2′′′,3′′′-mn]pyrene (3d) (bottom right).
J. Org. Chem, Vol. 71, No. 24, 2006 9081

Wegner et al.
FIGURE 3. Absorption (ABS) and fluorescence (FLU) spectra of 2,7,-
11,16-tetra-tert-butyltetraindeno[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-jk:1′′′,2′′′,3′′′-
mn]pyrene (3d) in n-hexane at 25 °C. The excitation wavelength for
the fluorescence spectrum (550 nm) is indicated by an arrow.
TABLE 1. Fluorescence Quantum Yields Φf, Lifetimes τ, and
Energies E(S1) of the First Excited Singlet State S1 of 3d in Three
Solvents at 25 °Ca
solvent
n-hexane
toluene
diethyl ether
Φf
0.0037
0.610
16590
14720
18445
165
0.0043
0.606
16500
14590
18320
141
0.0043
0.618
16600
14708
18465
144
τ/ns
E(S1)b)/cm-1
flu max/cm-1
first abs max/cm-1
τf/ns
a The fluorescence (flu) and absorption (abs) maxima are also listed.
The radiative lifetime τf is equal to the reciprocal of the radiative rate
constant kf ) Φf/τ. b Determined from the crossing point of the normalized
absorption and fluorescence spectra of 3d in Figure 3.
absorption tail that extends beyond 600 nm. These long
wavelength absorption bands make the indenopyrenes appealing
as candidates for new dyes and photoelectronic materials.12
Absorption and Fluorescence Spectra of the Tetrainde-
nopyrene 3d. The absorption spectrum of 3d in n-hexane at
25 °C (Figure 3) is similar to that of the other indenopyrenes
3a-c in Figure 2, with the predominant pyrene features around
32 000 cm-1 (313 nm) and a considerably weaker low-energy
maximum at 18 445 cm-1 (542 nm). The fluorescence spectrum
of 3d, with a maximum at 14 720 cm-1 (679 nm) and vibrational
structure (progression of approximately 1350 cm-1), shows a
mirror-image with respect to the lowest energy absorption band
in n-hexane and also in the two other solvents (toluene and
diethyl ether) investigated (Table 1). This is an indication that
the molecular structure of 3d does not undergo a substantial
change upon excitation to the equilibrated lowest excited singlet
state S1, similar to what is observed for alternant aromatic
hydrocarbons such as pyrene as well as for the nonalternant
hydrocarbon fluoranthene. Practically no change occurs in the
fluorescence spectra of 3d in toluene and diethyl ether upon
cooling (Figure 4). In n-hexane, only a room temperature
spectrum is available because of solubility problems at lower
temperatures.13
FIGURE 4. Fluorescence spectra of 3d in n-hexane, toluene, and
diethyl ether at 25 °C. For toluene and diethyl ether, fluorescence spectra
are also presented for lower temperatures (dashed curves). Such a low-
temperature spectrum is absent for n-hexane, because of solubility
problems with 3d in this solvent upon cooling.
Triplet-triplet transient absorption laser measurements with
3d in n-hexane (XeCl, 308 nm) over a detection range covering
the entire spectrum (350-750 nm) did not reveal the presence
of a triplet state, indicating that the quantum yield of intersystem
crossing ΦISC is effectively zero. This shows that the S1 state
of 3d is mainly (more than 99%) deactivated by internal
conversion (IC), as ΦIC ) 1 - Φf - ΦISC. The efficiency of
the IC deactivation channel is due to the relatively small S1-
S0 energy gap (16 590 cm-1 in n-hexane, Table 1) of 3d, which
leads via kIC ) ΦIC/τ to an IC rate constant of 1.6 × 109 s-1
.
Deactivation by IC in the series of aromatic hydrocarbons
from benzene to hexacene is likewise governed by the energy
gap law.14 In cyclohexane at 25 °C, the IC rate constant kIC
increases from 8 × 102 (benzene) to 6.3 × 108 s-1 (hexacene),
with a decrease of the energy E(S1) of the first excited singlet
state from 37 080 to 14 500 cm-1 14c
For anthracene, with E(S1)
.
Internal Conversion of the Tetraindenopyrene 3d. The
fluorescence quantum yield Φf of 3d is very small: 0.0037 in
n-hexane at 25 °C, and 0.0043 in toluene and diethyl ether at
this temperature (Table 1). Upon cooling, a small increase of
Φf occurs, for example, to 0.005 for 3d in toluene at -91 °C.
) 26 580 cm-1, the IC yield ΦIC under these conditions is still
practically zero (ΦIC ) 1.6 × 10-3), as calculated from kIC (3.5
× 105 s-1) and the fluorescence lifetime τ (4.7 ns) by using the
expression ΦIC ) kICτ.14c Not before an energy gap between S1
and S0 of 20 950 cm-1 (tetracene) is reached is an appreciable
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Polyindenopyrenes
radiative lifetime τf of around 150 ns (Table 1). With pyrene in
cyclohexane τf ) 690 ns, due to its symmetry-forbidden S1 state
(Lb), whereas for fluoranthene τf ) 210 ns has been found.15
These data show that the bowl shaped form of 3d (see
Introduction) has only a small impact on internal conversion.
Syntheses of the Indenopyrenes. Our first synthesis of
indenopyrenes begins with a Suzuki coupling of a brominated
pyrene 4 with o-methoxybenzeneboronic acid (5a) (Scheme 1).
To enhance the solubility of the final products, 5-tert-butyl-2-
methoxybenzeneboronic acid (5b) was used for the synthesis
of tri- and tetraindenopyrenes. After the coupling, the ether 6
was demethylated with BBr3, and the resulting phenol 7 was
converted to the corresponding triflate 8 with triflic anhydride.
Palladium-catalyzed cyclization gave the desired oligoinde-
nopyrene 3. A similar four-step sequence has recently been used
by Echavarren for the synthesis of other polycyclic aromatic
hydrocarbons.16
For the synthesis of diindeno[1,2,3-cd:1′,2′,3′-jk]pyrene (3a)
and diindeno[1,2,3-cd:1′,2′,3′-fg]pyrene (3b), a mixture of 1,6-
and 1,8-dibromopyrene (4a and 4b) was subjected to the Suzuki
coupling, and the isomeric coupling products 6a and 6b were
subsequently separated by a simple treatment with acetone.
The 2,7,11-tri-tert-butyltriindeno[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-
jk]pyrene (3c) and 2,7,11,16-tetra-tert-butyltetraindeno[1,2,3-
cd:1′,2′,3′-fg:1′′,2′′,3′′-jk:1′′′,2′′′,3′′′-mn]pyrene (3d) were syn-
thesized by the same procedure. The starting materials,
tribromopyrene (4c) and tetrabromopyrene (4d), were prepared
by selective bromination of pyrene.17
Unfortunately, the final cyclization reactions give low yields,
especially for the tri- and tetraindenopyrenes. Therefore, efforts
were undertaken to improve the synthesis by replacing the
triflate with a bromine atom and then making use of the one-
step methodology developed in our labs, which had been
successfully applied to the synthesis of the monoindenopyrene
(1) (Scheme 2).18
When applied to a mixture of the two dibromopyrenes 4a
and 4a, however, this reaction furnished a mixture of diinde-
nopyrenes (3a and 3b) that could not be separated. To obtain
3a and 3b separately, therefore, a two-step variant was pursued.
After the first Suzuki coupling, the isomeric bis(2-bromophen-
yl)pyrenes 11a and 11b could be separated by fractional
crystallization (Scheme 3). Subsequent optimization of the
cyclization conditions revealed that Pd(PPh3)2Cl2 (10 mol
%/cyclization) and DBU in DMF at 155 °C gave the best results
and boosted the yield to 44% for the diindeno[1,2,3-cd:1′,2′,3′-
fg]pyrene (3a).
FIGURE 5. Fluorescence decay of 3d in n-hexane at 25 °C. The decays
τi were obtained by using picosecond laser excitation at 298 nm, with
10.03 ps/channel. The decay times and their preexponential factors Ai
are given. The decay time in parentheses (3.342 ns) is considered to
be an impurity. The weighted deviations, expressed as 3σ (expected
deviations), the autocorrelation function A-C, and the value for ø2
are also indicated.
yield ΦIC observed, rapidly increasing as E(S1) becomes
smaller: 0.083 (tetracene, 20 950 cm-1), 0.75 (pentacene, 17 000
cm-1), and 0.95 (hexacene, 14 500 cm-1).14c
Fluorescence Decays of the Tetraindenopyrene 3d. The
fluorescence decay of 3d in n-hexane is single exponential, with
a decay time τ of 610 ps at 25 °C (Figure 5). Similar decay
times are observed in toluene (606 ps) and diethyl ether (618
ps) (Table 1). The fluorescence decay times become somewhat
longer upon cooling, 705 ps in toluene at -91 °C, for example,
corresponding with the minor increase in the corresponding
fluorescence quantum yields mentioned above.
The observation of these relatively short decay times (similar
values around 600 ps in toluene and diethyl ether at 25 °C,
Table 1) is in line with the absence of ISC, as the forbidden
character of the singlet to triplet ISC generally leads to ISC
rates of the order of 10 ns or slower.15 The forbidden character
of the fluorescence of 3d can be seen from the values for the
(8) Havenith, R. W. A.; Jiao, H.; Jenneskens, L. W.; van Lenthe, J. H.;
Sarobe, M.; Schleyer, P. v. R.; Kataoka, M.; Necula, A.; Scott, L. T. J.
Am. Chem. Soc. 2002, 124, 2363-2370.
(9) Calculations on tetraindenopyrene were performed at the B3LYP/6-
31G* level of theory, using Spartan 02 (Linux version) from Wavefunction,
Inc., Irvine, CA 92612. The C2V structure was found to be an energy
minimum (zero imaginary frequencies), whereas the D2h structure was found
to be the transition state for bowl-to-bowl inversion (one imaginary
frequency).
(10) Aprahamian, I.; Wegner, H. A.; Sternfeld, T.; Rauch, K.; de Meijere,
A.; Sheradsky, T.; Scott, L. T.; Rabinovitz, M. Chem.-Asian J. In press.
(11) Kracher, W.; Fordham, R.; DuBois, J.; Gloude, P. Spectral Atlas of
Polycyclic Aromatic Compounds; D. Reidel: Dordrecht, The Netherlands,
1985; Fluoranthene, pp 72-73.
(12) Zollinger, H. Color Chemistry-Syntheses, Properties, and Applica-
tions of Organic Dyes and Pigments, 3rd ed.; Wiley-VCH: Weinheim,
Germany, 2003.
With these improved conditions, the synthesis of tetrainde-
nopyrene 3d was reexamined. Different substituents on the
phenyl groups were assayed (H, OMe, OEt), but only the tert-
butyl groups enhanced the solubility enough to allow purification
of the cyclized product by column chromatography. The tert-
butyl-substituted 2-bromobenzeneboronic acid 10b required for
this synthesis was prepared in four steps starting from 4-tert-
butylbromobenzene (12) (Scheme 4).
(15) Birks, J. B. Photophysics of Aromatic Molecules; Wiley-Inter-
science: London, UK, 1970.
(13) Berlman, I. B. Handbook of Fluorescence Spectra of Aromatic
Molecules; Academic Press: New York, 1971.
(14) (a) Englman, R.; Jortner, J. Mol. Phys. 1970, 18, 145-164. (b)
Druzhinin, S. I.; Demeter, A.; Galievsky, V. A.; Yoshihara, T.; Zachariasse,
K. A. J. Phys. Chem. A 2003, 107, 8075-8085. (c) Nijegorodov, N.;
Ramachandran, V.; Winkoun, D. P. Spectrochim. Acta 1997, 53A, 1813-
1824.
(16) Go´mez-Lor, B.; Gonza´lez-Cantalapiedra, E.; de Frutos Marta Ruiz,
OÄ ; Ca´rdenas, D. J.; Santos, A.; Echavarren, A. E. Chem. Eur. J. 2004, 10,
2601-2608.
(17) Vollmann, H.; Becker, H.; Corell, M.; Streeck, H.; Langbein, G.
Justus Liebig Ann. Chem. 1937, 531, 1-159.
(18) Wegner, H. A.; Scott, L. T.; de Meijere, A. J. Org. Chem. 2003,
68, 883-887.
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Wegner et al.
SCHEME 1. General Synthetic Route for the Preparation of Indenopyrenes 3
SCHEME 2. Synthesis of Monoindenopyrene (1) in a One-Pot Reaction
The one-pot preparation of the tetraindenopyrene 3d was
ultimately achieved reproducibly in 1% yield. Using the
pinacolboronic ester of 10b did not further improve the yield.
Likewise, increasing the equivalents of boronic acid from 1.2
to 5.0 had no effect. Application of this methodology to the
synthesis of the triindenopyrene 3c gave the desired product in
4% yield.
improve the result with 1,3,6,8-tetrabromopyrene (4d); the
reaction had a similar outcome as with 2-bromobenzeneboronic
acid (10a).
Conclusions
The syntheses reported here for oligoindenopyrenes, a new
class of polycyclic aromatics, demonstrate the utility of pal-
ladium-catalyzed cross-coupling reactions, especially the Suzuki
coupling. The tetraindenopyrene derivative 3d in its first excited
singlet state undergoes efficient deactivation (99%) by internal
conversion to the ground state. The short (0.6 ns) fluorescence
decay time is in line with the small fluorescence quantum yield
(0.004). The intense red colors of the oligoindenopyrenes along
One side product of the one-pot indenoannelation process is
the replacement of Br with H. Interestingly the use of o-
chlorobenzeneboronic acid (17) in the model system 1,4-
dibromonaphthalene (16) gave nearly quantitatively the desired
product 18, compared to 51% with o-bromobenzeneboronic acid
(10a) (Scheme 5).18 Unfortunately, this modification did not
9084 J. Org. Chem., Vol. 71, No. 24, 2006

Polyindenopyrenes
SCHEME 3. Synthesis of Diindenopyrenes 3a and 3b from 1,6- and 1,8-Dibromopyrene 4a and 4b
SCHEME 4. Synthesis of
and 0.10 at the maximum of the first band in the absorption
2-Bromo-5-tert-butylbenzeneboronic Acid (10b)
spectrum, were deaerated by bubbling with nitrogen for 15 min.
The fluorescence spectra were measured with a quantum-corrected
(modified)19 spectrofluorometer. The fluorescence quantum yields
Φf, with an estimated reproducibility of 5%, were determined with
quinine sulfate in 1.0 N H2SO4 as a standard (Φf ) 0.546 at 25
°C),20 with equal optical density at the excitation wavelength. The
difference in refractive index between the standard solution and
the alkanes was not taken into account. The fluorescence decay
times were obtained with a picosecond laser (λexc: 296 nm) single-
photon counting (SPC) setup described elsewhere.21
1,6-Bis(2-methoxyphenyl)pyrene (6a) and 1,8-Bis(2-methoxy-
phenyl)pyrene (6b). A mixture of 1,6-dibromopyrene and 1,8-
dibromopyrene17 (0.600 g, 1.66 mmol, isomer ratio ∼1:2), 2-meth-
oxybenzeneboronic acid (0.607 g, 4.01 mmol), K2CO3 (2.30 g, 16.7
mmol), and Pd(PPh3)4 (0.385 g, 0.333 mmol) in 10 mL of anhydrous
and oxygen-free DMF was stirred at 155 °C for 24 h. After cooling
to ambient temperature the mixture was diluted with CH2Cl2,
washed with HCl (10%), NaHCO3, and water, and dried over
MgSO4. After evaporation under reduced pressure the crude product
was treated with acetone (15 mL). The precipitate was filtered and
yielded 0.399 g (0.963 mmol) of 1,6-bis(2-methoxyphenyl)pyrene.
The residue was purified by column chromatography (silica gel,
CH2Cl2/n-pentane 1:2) to give 0.220 g (0.531 mmol) of 1,8-bis(2-
methoxyphenyl)pyrene as a pale yellow solid (90% total yield).
SCHEME 5. Improved Yield of the Pd-Catalyzed
Indenoannelation Reaction with o-Chlorobenzeneboronic
Acid (17)
1,6-Bis(2-methoxyphenyl)pyrene (6a): mp 242 °C; IR (KBr)
ν 3041, 3002, 2956, 2930, 2829, 1596, 1582, 1504, 1484, 1459,
1430, 1298, 1272, 1234, 1177, 1111, 1052, 1026, 1006, 845, 822,
795, 765, 707 cm-1; 1H NMR (300 MHz, C2D2Cl4, 125 °C) δ 3.78
(s, 6H), 7.10-7.18 (m, 4H), 7.40-7.52 (m, 4H), 7.84 (d, 3J ) 9.2
3
3
Hz, 2H), 7.93 (d, J ) 8.0 Hz, 2H), 7.99 (d, J ) 9.2 Hz, 2H),
8.18 (d, 3J ) 8.0 Hz, 2H); 13C NMR (75.5 MHz, C2D2Cl4, 125 °C,
additional APT) δ 55.8 (+), 112.2 (+), 120.6 (+), 123.9 (+), 124.8
(-), 125.5 (+), 126.7 (+), 128.0 (+), 128.7 (+), 129.4 (-), 130.2
(-), 130.5 (-), 132.2 (+), 134.4 (-), 157.6 (-); MS (70 eV, EI),
with their thermal stabilities make them potentially useful as
long wavelength dyes for special high-temperature applications.
Experimental Section
(19) Druzhinin, S. I.; Ernsting, N. P.; Kovalenko, S. A.; Pe´rez Lustres,
L.; Senyushkina, T.; Zachariasse, K. A. J. Phys. Chem. A 2006, 110, 2955-
2969.
(20) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991-1024.
(21) Druzhinin, S. I.; Demeter, A.; Galievsky, V. A.; Yoshihara, T.;
Zachariasse, K. A. J. Phys. Chem. A 2003, 107, 8075-8085.
Spectroscopic Studies on the Oligoindenopyrenes. The tet-
raindenopyrene derivative 3d was purified by HPLC. The solvent
n-hexane was used as received. Diethyl ether was chromatographed
over alumina, and toluene was refluxed from potassium in a nitrogen
atmosphere. The solutions, with an optical density between 0.02
J. Org. Chem, Vol. 71, No. 24, 2006 9085

Wegner et al.
m/z (%) 414 (100) [M+], 384 (16) [M - OMe], 353 (7) [M - 2
OMe]; C30H22O2 calcd 414.1620 (correct HRMS).
Hz, 2H), 8.18 (d, J ) 8.0 Hz, 2H), 8.21 (s, 2H); 13C NMR (75.5
MHz, C2D2Cl4, 125 °C) δ 120.1, 120.4, 121.1, 122.2, 122.6, 127.7,
128.5, 128.6, 131.48, 131.54, 135.4, 136.6, 140.4, 141.8; MS (70
eV, EI), m/z (%) 351 (28) [M+], 350 (100) [M], 277 (6), 200 (18)
[M + 2H - 2 × C6H4]; C28H14 calcd 350.1096 (correct HRMS).
1-Bromo-4-tert-butyl-2-nitrobenzene (13). Concentrated sul-
furic acid (31.6 mL, 594 mmol) was added slowly to nitric acid
(27.4 mL, 396 mmol) at 0 °C. This cold mixture was added carefully
to 4-bromo-tert-butylbenzene (56.2 g, 264 mmol). The temperature
was kept below 10 °C, and the mixture was stirred for an additional
20 h at ambient temperature, then poured into water (750 mL).
The organic layer was separated, and the water layer was washed
with Et2O (200 mL). The combined organic phases were dried over
MgSO4. Removal of the solvents under reduced pressure and
distillation (bp 190 °C, at 40 mbar) gave 62.7 g of the title
compound (243 mmol, 92%): 1H NMR (250 MHz, CDCl3) δ 1.33
(s, 9H), 7.44 (dd, 3J ) 7.4 Hz, 4J ) 1.9 Hz, 1H), 7.63 (d, 3J ) 7.4,
3
1,8-Bis(2-methoxyphenyl)pyrene (6b): mp 98-103 °C; IR
(KBr) ν 3026, 2937, 2831, 1596, 1575, 1486, 1461, 1434, 1263,
1236, 1180, 1121, 1048, 1027, 853, 827, 754 cm-1; 1H NMR (300
MHz, C2D2Cl4, 125 °C) δ 3.72 (s, 6H), 7.10-7.20 (m, 4H), 7.40-
7.55 (m, 4H), 7.81 (s, 2H), 8.00 (d, 3J ) 8.0 Hz, 2H), 8.17 (s, 2H),
8.25 (d, 3J ) 8.0 Hz, 2H); 13C NMR (75.5 MHz, C2D2Cl4, 125 °C,
additional APT) δ 55.8 (+), 112.2 (+), 120.6 (+), 124.0 (+), 124.8
(-), 125.2 (+), 127.0 (+), 127.9 (+), 128.7 (+), 129.0 (-), 130.3
(-), 130.6 (-), 132.2 (+), 134.3 (-), 157.5 (-); MS (70 eV, EI),
m/z (%) 415 (32) [M+], 414 (100) [M], 384 (16) [M - OMe], 353
(5) [M - 2 × OMe]; C30H22O2 calcd 414.1620 (correct HRMS).
1,6-Bis(2-hydroxyphenyl)pyrene (7a). A mixture of 1,6-bis(2-
methoxyphenyl)pyrene (6a) (402 mg, 0.97 mmol) in 20 mL of
anhydrous CH2Cl2 and 10 mL of a 1 M solution of BBr3 (10.0
mmol) in CH2Cl2 was stirred at -78 °C for 14 h. The reaction
mixture was quenched with water, and the organic phase was dried
over MgSO4. Evaporation of the solvent gave 347 mg (0.898 mmol,
93%) of the product as a yellow solid: mp 233 °C dec; IR (KBr)
ν 3538, 3038, 1576, 1482, 1456, 1330, 1280, 1227, 1195, 1096,
4
1H), 7.83 (d, J ) 1.9 Hz, 1H); 13C NMR (62.9 MHz, CDCl3) δ
30.9, 34.9, 111.1, 122.7, 130.6, 134.5, 152.5, 157.2; C10H12BrNO2
(258.1). The analytical data agreed with those reported in the
literature.22
1
1007, 850, 754 cm-1; H NMR (300 MHz, C2D2Cl4, 125 °C) δ
2-Bromo-5-tert-butylaniline (14). A mixture of 1-bromo-4-tert-
butyl-2-nitrobenzene (13) (59.1 g, 229 mmol) and Na2S2O4 (146.4
g, 841 mmol) in glycol monomethyl ether (350 mL) and water (350
mL) was heated under reflux for 6 h. Water (300 mL) and
concentrated hydrochloric acid (300 mL) were added to the warm
solution; then the mixture was heated under reflux for 15 min and
poured into ice water (500 mL). Solid Na2CO3 was added until the
mixture was basic. The organic layer was separated and the water
layer extracted with Et2O (200 mL). The combined organic phases
were dried over MgSO4. Removal of the solvents under reduced
pressure and distillation of the residue (bp 153 °C, at 35 mbar)
gave 42.3 g (185 mmol, 81%) of the title compound: IR (KBr) ν
3473, 3382, 2963, 2905, 2869, 1616, 1487, 1416, 1394, 1363, 1312,
1241, 1203, 1159, 1114, 1090, 1017, 935, 861, 801, 701, 667, 641
cm-1; 1H NMR (250 MHz, CDCl3) δ 1.29 (s, 9H), 3.96 (br s, 2H),
7.08-7.12 (m, 4H), 7.34-7.43 (m, 4H), 7.93 (d, 3J ) 9.3 Hz, 2H),
8.00 (d, 3J ) 7.8 Hz, 2H), 8.07 (d, 3J ) 9.3 Hz, 2H), 8.25 (d, 3J )
7.8 Hz, 2H); 13C NMR (75.5 MHz, C2D2Cl4, 125 °C, additional
APT) δ 115.8 (+), 120.6 (+), 125.0 (-), 125.1 (+), 126.9 (-),
127.8 (+), 128.4 (+), 129.4 (+), 129.6 (-), 131.0 (-), 131.4 (+),
131.9 (-), 153.2 (-); MS (70 eV, EI), m/z (%) 386 (100) [M+],
368 (10) [M - H2O], 292 (17) [M - phenyl - OH]; C28H18O2
(386.5).
1,6-Bis(2-trifluoromethylsulfonylphenyl)pyrene (8a). A mix-
ture of 1,6-bis(2-hydroxyphenyl)pyrene (7a) (301 g, 0.780 mmol)
in 50 mL of anhydrous CH2Cl2, pyridine (5 mL, 62.1 mmol), and
Tf2O (3 mL, 18.3 mmol) was stirred at -78 °C for 14 h. The
reaction was quenched with water, and the mixture was diluted
with CH2Cl2. The organic phase was washed with HCl (10%),
NaHCO3, and water and dried (MgSO4). After evaporation of the
solvents the crude product was purified by column chromatography
(silica gel, CH2Cl2/n-hexane 1:4) to yield 374 mg (0.575 mmol,
74%) of the product as a pale yellow solid: mp 198 °C; IR (KBr)
ν 3045, 2965, 1610, 1580, 1481, 1414, 1400, 1248, 1211, 1149,
3
4
4
6.48 (dd, J ) 7.4 Hz, J ) 1.9 Hz, 1H), 6.80 (d, J ) 1.9 Hz,
1H), 7.33 (d, J ) 7.4 Hz, 1H); 13C NMR (62.9 MHz, CDCl3) δ
3
31.2, 34.4, 106.3, 113.1, 117.0, 132.0, 143.5, 151.8; C10H14BrN
(228.1). The analytical data agreed with those reported in the
literature.23
1
1093, 1042, 889, 846, 818, 783, 772 cm-1; H NMR (300 MHz,
1-Bromo-2-iodo-4-tert-butylbenzene (15). A solution of NaNO2
(13.3 g, 193 mmol) in water (40 mL) was added dropwise to a
mixture of 2-bromo-5-tert-butylaniline (14) (40.0 g, 175 mmol) in
water (275 mL) and concentrated hydrochloric acid (66.2 mL)
below 5 °C, and the mixture was stirred for 10 min. Then a solution
of potassium iodide (43.7 g, 263 mmol) in water (67 mL) was
added. The mixture was stirred for 15 min without cooling, then at
50 °C for 15 min and at 80 °C for 15 min. After that the mixture
was cooled to 0 °C, and a solution of 5% aqueous sodium sulfite
(50 mL) was added. The organic layer was separated, and the water
layer extracted with Et2O (200 mL, 3 times). The combined organic
phases were dried over MgSO4. After removal of the solvents under
reduced pressure the crude product was purified by column
chromatography (silica gel, n-pentane) to yield 47.6 g of the title
compound (141 mmol, 80%): IR (KBr) ν 2963, 2905, 2868, 1576,
1547, 1475, 1452, 1375, 1272, 1257, 1203, 1118, 1006, 881, 848,
819, 753, 704, 657, 583 cm-1; 1H NMR (250 MHz, CDCl3) δ 1.28
(s, 9H), 7.22 (dd, 3J ) 7.4 Hz, 4J ) 1.9 Hz, 1H), 7.50 (d, 3J ) 7.4
Hz, 1H), 7.83 (d, 4J ) 1.9 Hz, 1H); 13C NMR (62.9 MHz, CDCl3)
δ 31.0, 34.4, 101.1, 126.3, 126.9, 132.1, 137.4, 152.0; MS (70 eV,
EI), m/z (%) 341 (5), 340 (55), 339 (4), 338 (53) [M+], 326 (8),
325 (98), 324 (6), 323 (100) [M+ - CH3], 297 (16), 295 (15), 277
(12), 198 (16), 196 (14), 127 (12), 117 (28) [M+ - CH3 - Br -
I], 115 (31); C10H12BrI (339.0).
C2D2Cl4, 125 °C) δ 7.66-7.48 (m, 8H), 7.81 (d, 3J ) 9.3 Hz, 2H),
7.95 (d, 3J ) 7.8 Hz, 2H), 8.04 (d, 3J ) 9.3 Hz, 2H), 8.21 (d, 3J )
7.8 Hz, 2H); 13C NMR (75.5 MHz, C2D2Cl4, 125 °C, additional
APT) δ 121.5 (+), 124.4 (+), 124.6 (-), 124.9 (+), 127.7 (+),
127.8 (+), 128.0 (+), 129.3 (+), 129.4 (-), 130.7 (-), 131.0 (-),
133.5 (+), 134.4 (-), 147.5 (-) (O3SCF3 is missing because of
coupling with F); MS (70 eV, EI), m/z (%) 650 (100) [M - H],
517 (16) [M - SO2CF3], 383 (80) [M+ - 2SO2CF3], 355 (17),
292 (8); C30H16F6O6S2 (650.6).
Diindeno[1,2,3-cd:1′,2′,3′-jk]pyrene (3a). An oxygen free solu-
tion of dry LiCl (150 mg, 3.54 mmol), 1,6-bis(2-trifluoromethyl-
sulfonylphenyl)pyrene (8a) (75.0 mg, 0.115 mmol), Pd(PPh3)2Cl2
(16.2 mg, 23.1 µmol), PPh3 (24.2 mg, 92.2 µmol), and 0.75 mL of
DBU in 5 mL of anhydrous DMF was stirred in a sealed thick-
walled Pyrex flask at 170 °C for 24 h. After cooling to ambient
temperature the reaction mixture was diluted with 50 mL of
CH2Cl2 and stirred with 30 mL of H2O2 (15%) for 3 h. Then the
mixture was washed with 50 mL of HCl (10%), 50 mL of NaHCO3,
and 50 mL of H2O. After drying over MgSO4 the solvent was
removed under reduced pressure. The crude product was treated
with 5 mL of CHCl3, and the resulting precipitate was filtered off
to yield 6 mg (17.3 µmol, 15%) of the product as a red solid: mp
>250 °C; IR (KBr) ν 3033, 2960, 1652, 1437, 1258, 1077, 826,
740 cm-1; UV λmax (CHCl3) nm (log ꢀ) 455 (0.97), 429 (0.77),
410 (0.77), 389 (0.35), 334 (0.45), 307 (2.44), 298 (2.14), 267
(22) Tashiro, M.; Yamato, T. J. Org. Chem. 1979, 44, 3037-3041.
(23) Welzel, P.; Dietz, C.; Eckhardt, G. Chem. Ber. 1975, 108, 3550-
3565.
1
(1.94), 260 (1.81), 248 (1.76); H NMR (300 MHz, C2D2Cl4, 125
°C) δ 7.29 (m, 4H), 7.79 (m, 2H), 7.88 (m, 2H), 8.01 (d, 3J ) 8.0
9086 J. Org. Chem., Vol. 71, No. 24, 2006

Polyindenopyrenes
2-Bromo-5-tert-butylbenzeneboronic Acid (10b). To a solution
of 1-bromo-2-iodo-4-tert-butylbenzene (15) (0.460 g, 1.36 mmol)
in 40 mL of a mixture of THF and Et2O (1:1) was added dropwise
at -78 °C isopropylmagnesium bromide (2.3 m in Et2O, 0.59 mL,
1.36 mmol). After the mixture was stirred for 2 h at that temperature
B(OiPr)3 (588 mg mL, 3.13 mmol) was added. The solution was
warmed to room temperature overnight; then 40 mL of HCl (10%)
was added, and the resulting mixture was stirred for 30 min at room
temperature. The aqueous layer was extracted with Et2O (50 mL,
3 times). Drying over Na2SO4 and evaporation of the solvent gave
300 mg of the crude product (86%).
For spectroscopic characterization the crude product was treated
with pinacol (355 mg, 3.00 mmol) in dioxane (50 mL) to give a
quantitative yield of 2-(2-bromo-5-tert-butylphenyl)-4,4,5,5-tetra-
methyl[1,3,2]dioxaborolane: mp 71 °C; 1H NMR (250 MHz,
CDCl3) δ 1.30 (s, 9H), 1.39 (s, 12H), 7.26 (dd, 3J ) 8.5 Hz, 3J )
2.6 Hz, 1H), 7.49 (d, 3J ) 8.5 Hz, 1H), 7.57 (d, 4J ) 2.6 Hz, 1H);
13C NMR (62.9 MHz, CDCl3) δ 24.8, 31.2, 34.2, 84.2, 124.8, 129.2,
132.2, 133.0, 149.1 (C-1, is missing because of coupling with B);
MS (70 eV, EI), m/z (%) 341 (5), 340 (36), 339 (14), 338 (34),
337 (6) [M+], 326 (15), 325 (100), 324 (40), 323 (98), 322 (23)
[M+ - CH3], 259 (33), 239 (11), 225 (19), 223 (18), 197 (8), 161
(12); C16H24BBrO2 (339.08).
CH3], 465 (4), 464 (13), 563 (40), 462 (90) [M+ - 2 × tBu -
CH3 - H], 449 (3), 448 (11), 447 (32) [M+ - 2 × tBu - 2 CH3
- H]; C46H40 calcd 592.3130 (correct HRMS).
2,7,11,16-Tetra-tert-butyltetraindeno[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-
jk:1′′′,2′′′,3′′′-mn]pyrene (3d) (one-pot procedure). A 50 mL
Schlenk flask was equipped with a magnetic stirring bar, Pd2(dba)3
(1.88 g, 1.82 mmol), P(Cy)3 (2.11 g, 7.53 mmol), 1,3,6,8-
tetrabromopyrene17 (4d) (2.44 g, 4.71 mmol), and 2-bromo-5-tert-
butylbenzeneboronic acid (7.26 g, 28.3 mmol) in DMF (60 mL).
After degassing the mixture, DBU (18 mL) was added. The resulting
mixture was stirred at 155 °C for 36 h. After dilution with 300 mL
of CH2Cl2, the mixture was washed twice with 150 mL of HCl
(10%) and once each with 150 mL of NaHCO3 and 50 mL of H2O.
Drying of the organic phase over MgSO4 and evaporation of the
solvent gave the crude product, which was subjected to chroma-
tography on flash silica gel, eluting with pentane/CH2Cl2 (3:1). The
isolated red product (Rf 0.28) was then further purified by column
chromatography on flash silica gel, eluting with pentane/CH2Cl2
(3:1) and then suspended in pentane (5 mL) in the sonicator
followed by separation in a centrifuge. This procedure was repeated
three times. The resulting solid was dissolved in CH2Cl2 (10 mL)
and then precipitated by adding pentane (30 mL). The product was
then again suspended in pentane (5 mL) in the sonicator followed
by separation in a centrifuge. This procedure was repeated until
the pentane fraction was colorless (six times) to yield 18 mg of 3d
(1%): mp >325 °C; UV λmax (CHCl3) nm (log ꢀ) 278 (1.55), 288
(1.38), 298 (1.44), 312 (1.72), 333 (1.16), 363 (0.82), 397 (0.35),
419 (0.43), 437 (0.24), 467 (0.25), 545 (0.21); 1H NMR (300 MHz,
C2D2Cl4, 125 °C) δ 1.57 (s, 36H), 7.27 (dd, 3J ) 8.0 Hz, 4J ) 1.5
Hz, 4H), 7.39 (s, 2H), 7.58 (d, 3J ) 8.0 Hz, 4H), 7.62 (d, 4J ) 1.5
Hz, 4H); 13C NMR (75 MHz, C2D2Cl4, 125 °C) δ 31.1, 34.7, 118.9,
119.0, 124.2, 125.65, 125.72, 133.1, 137.6, 139.4, 143.6, 152.1,
2,7,11-Tri-tert-butyltriindeno[1,2,3-cd:1′,2′,3′-fg:1′′,2′′,3′′-jk]-
pyrene (3c) (one-pot procedure). A 50 mL Schlenk flask was
equipped with a magnetic stirring bar, Pd2(dba)3 (894 mg, 0.976
mmol), P(Cy)3 (1.09 g, 3.90 mmol), 1,3,6-tribromopyrene17 (4c)
(1.07 g, 2.44 mmol), and 2-bromo-5-tert-butylbenzeneboronic acid
(3.76 g, 14.6 mmol) in DMF (30 mL). After degassing the mixture,
DBU (9.1 mL) was added. The resulting mixture was stirred at
155 °C for 36 h. After dilution with 300 mL of CH2Cl2, the mixture
was washed three times with 50 mL each of HCl (10%) and once
each with 50 mL of NaHCO3 and twice 50 mL of H2O. Drying of
the organic phase over MgSO4 and evaporation of the solvent gave
the crude product, which was subjected to chromatography on flash
silica gel, eluting with pentane/CH2Cl2 (10:1) and then (6:1). The
isolated red product (Rf 0.28) was then further purified by column
chromatography on flash silica gel, eluting with pentane/CH2Cl2
(6:1) and then suspended in pentane (10 mL) in the sonicator
followed by separation in a centrifuge. This procedure was repeated
until the pentane fraction was colorless (five times) to yield 60 mg
of 3c (4%): mp >325 °C; UV λmax (CHCl3) nm (log ꢀ) 259 (1.18),
276 (1.43), 298 (1.41), 312 (1.92), 325 (1.00), 354 (0.60), 371
153.8; MS (70 eV, EI), m/z (%) 723 (3) [M+], 708 (3) [M+
-
CH3], 481 (10), 421 (22), 393 (15), 309 (28), 268 (14), 222 (16),
167 (18), 153 (19), 139 (26), 125 (37), 111 (55), 97 (98), 57 (100);
C56H50 calcd 722.39125 (correct HRMS).
Acknowledgment. This work was supported by the State
of Niedersachsen (Germany) and the U.S. National Science
Foundation. H.A.W. is indebted to the German National Merit
Foundation (Studienstiftung des Deutschen Volkes) as well as
the Fonds der Chemischen Industrie for a graduate fellowship.
Generous gifts of chemicals by BASF, Bayer, Degussa-Hu¨ls
AG, and Chemetall GmbH have been provided. We thank Mr.
J. Bienert (MPIfbC, Go¨ttingen) for HPLC purification of the
2,7,11,16-tetra-tert-butyltetraindenopyrene (3d) used for the
fluorescence and absorption measurements.
1
(0.42), 413 (0.34), 438 (0.48), 451 (0.32), 487 (0.11); H NMR
(300 MHz, C2D2Cl4, 125 °C) δ 1.52 (s, 9H), 1.54 (s, 9H), 1.58 (s,
9H), 7.22-7.41 (m, 3H), 7.43-7.58 (m, 1H), 7.68-7.85 (m, 2H),
7.88-7.95 (m, 2H), 7.96-8.05 (m, 2H), 8.07-8.22 (m, 3H); 13C
NMR (75.5 MHz, C2D2Cl4, 125 °C, additional APT) δ 31.0 (+),
31.16 (+), 31.21 (+), 34.7 (-), 34.75 (-), 34.82 (-), 112.4 (+),
118.9 (+), 119.05 (+), 119.13 (+), 119.3 (+), 119.9 (+), 122.3
(+), 123.9 (+), 124.9 (+), 125.8 (+), 125.9 (+), 128.0 (+), 129.0
(+), 131.28 (-), 131.32 (-), 131.68 (-), 131.73 (-), 131.8 (-),
131.9 (-), 135.5 (-), 136.6 (-), 136.7 (-), 136.8 (-), 137.8 (-),
138.1 (-), 138.3 (-), 143.1 (-), 143.3 (-), 144.1 (-), 152.0 (-),
152.49 (-), 152.54 (-); MS (70 eV, EI), m/z (%) 595 (7), 594
(20), 593 (46), 592 (100) [M+], 579 (3), 578 (13), 577 (25) [M+ -
Supporting Information Available: Experimental procedures
1
for 3b-d, 6b-d, 7b-d, and 8b-d and H and 13C NMR spectra
for 3a-d, 6a-d, 7a-d, 8a-d, and the pinacol ester of 15. This
material is available free of charge via the Internet at http://
pubs.acs.org.
JO0613939
J. Org. Chem, Vol. 71, No. 24, 2006 9087