Heteroatom-annulated perylenes: Practical synthesis, photophysical properties, and solid-state packing arrangement

Article abstract of DOI:10.1021/jo8012622

(Chemical Equation Presented) A practical strategy for the preparation of a series of heterocyclic annulated perylenes in good yields is presented. UV-vis absorption spectra indicate hypsochromic shift of the absorption maxima relative to the corresponding parent perylene. Single-crystal X-ray diffraction analysis reveals that they all adopt planar conformation, but the solid-state packing arrangements are significantly altered by annulation of various heterocycles.

Full text of DOI:10.1021/jo8012622

properties.3 Incorporating heteroatoms into its skeleton is an
intriguing target because the introduction of heteroatoms would
induce a variety of intermolecular interactions, such as van der
Waals interactions and heteroatom-heteroatom interactions
(S· · ·S or Se· · ·Se interactions), which is essential to achieve
highly ordered supramolecular self-assembled structure,4 and
eventually excellent device performance.5
Heteroatom-Annulated Perylenes: Practical
Synthesis, Photophysical Properties, and
Solid-State Packing Arrangement
Wei Jiang,†,‡ Hualei Qian,†,‡ Yan Li,†,‡ and
Zhaohui Wang*,†
Beijing National Laboratory for Molecular Sciences, Key
Laboratory of Organic Solids, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100190, China, and
Graduate School of the Chinese Academy of Sciences,
Beijing 100190, China
S-heterocyclic annulated perylene, namely perylo[1,12-
b,c,d]thiophene (PET, 3), which has first prepared from 3,4:9,
10-perylenetetracarboxylic dianhydride by Rogovik,6 has been
synthesized by several groups in harsh conditions such as flash
vacuum pyrolysis (FVP).7 However, its electrical property is
rarely studied, probably due to the difficulties in scale-up, long
reaction sequences, and poor yields. Recently, we reported its
extraordinary solid-state packing arrangement with marked
S· · ·S short contacts of 3.51 Å between the neighboring columns
and the likelihood of double-channel superstructure, which is
responsible for effective intermolecular carrier transport.5c
Herein, we describe our endeavors to develop a new and
practical synthetic route toward PET up to gram-scale success-
fully. Furthermore, Se-heterocyclic annulated perylene is syn-
thesized by incorporating selenium into the perylene skeleton.
Accordingly, detailed investigation of photophysical properties
and single-crystal analysis of heterocyclic annulated perylenes
is presented to fully explore the influence of different heteroa-
toms on the inherent electronic properties and solid-state packing
arrangement.
wangzhaohui@iccas.ac.cn
ReceiVed June 12, 2008
A practical strategy for the preparation of a series of
heterocyclic annulated perylenes in good yields is presented.
UV-vis absorption spectra indicate hypsochromic shift of
the absorption maxima relative to the corresponding parent
perylene. Single-crystal X-ray diffraction analysis reveals that
they all adopt planar conformation, but the solid-state packing
arrangements are significantly altered by annulation of
various heterocycles.
The key starting material is 1-nitroperylene 2. Previous
synthetic reports8 of 2 were unsatisfactory in that the yield of
the regiospecific mononitration of perylene at position 1 was
rather low or the reaction was irreproducible.9 Successful
preparation of 2 from perylene is achieved in a modified
mononitration of the perylene process, by which the temperature
is reduced and the reaction time is shortened to 25-30 min.
There are three main fractions in the crude products. The first
(2) (a) Dopper, J. H.; Wynberg, H. J. Org. Chem. 1975, 40, 1957–1966. (b)
Klemm, L. H.; Hall, E.; Cousins, L.; Klopfenstein, C. E. J. Heterocycl. Chem.
1987, 24, 1749–1755. (c) Klemm, L. H.; Hall, E.; Cousins, L.; Klopfenstein,
C. E. J. Heterocycl. Chem. 1989, 26, 345–348. (d) Lawson, J.; DuVernet, R.;
Boekelheide, V. J. Am. Chem. Soc. 1973, 95, 956–957. (e) DuVernet, R.; et al.
J. Am. Chem. Soc. 1978, 100, 2457–2464. (f) Langhals, H.; Kirner, S. Eur. J.
Org. Chem. 2000, 365–380.
(3) (a) Werner, T. C.; Chang, J.; Hercules, D. M. J. Am. Chem. Soc. 1969,
92, 5560–5565. (b) Rathore, R.; Kumar, A. S.; Lindeman, S. V.; Kochi, J. K. J.
Org. Chem. 1998, 63, 5847–5856. (c) Shkrob, I. A. J. Phys. Chem. A 1998,
102, 4976–4989.
(4) Qian, H.; Liu, C.; Wang, Z.; Zhu, D. Chem. Commun. 2006, 4587–4589.
(5) (a) Briseno, A. L.; Miao, Q.; Ling, M.; Reese, C.; Meng, H.; Bao, Z.;
Wudl, F. J. Am. Chem. Soc. 2006, 128, 15576–15577. (b) Wu, Y.; Li, Y.;
Gardner, S.; Ong, B. S. J. Am. Chem. Soc. 2005, 127, 614–618. (c) Sun, Y.;
Tan, L.; Jiang, S.; Qian, H.; Wang, Z.; Yan, D.; Di, C.; Wang, Y.; Wu, W.; Yu,
G.; Yan, S.; Wang, C.; Hu, W.; Liu, Y.; Zhu, D. J. Am. Chem. Soc. 2007, 129,
1882–1883. (d) Zhou, Y.; Liu, W.; Ma, Y.; Wang, H.; Qi, L.; Cao, Y.; Wang,
J.; Pei, J. J. Am. Chem. Soc. 2007, 129, 12386–12387. (e) Yamamoto, T.;
Takimiya, K. J. Am. Chem. Soc. 2007, 129, 2224–2225. (f) Usta, H.; Lu, G.;
Facchetti, A.; Marks, T. J. J. Am. Chem. Soc. 2006, 128, 9034–9035.
(6) Rogovik, V. I. J. Org. Chem. (USSR) 1974, 10, 1072.
Highly π-extended heteroarenes, which contain chalcogen,
nitrogen, etc. in fused aromatic rings, are the subjects of
considerable current research interest due to their fundamental
optoelectronic properties and their potential applications such
as organic field-effect transistors (OFETs), light emitting diodes
(LEDs), photovoltaic devices, and other organic optoelectronic
devices.1 Attempts to construct bay-region heterocyclic annu-
lated polycyclic aromatic hydrocarbons (PAHs) such as triph-
enylene, pyrene, perylene, and perylene bisimides have been
performed during the past decades.2 However, due to the
difficulty in the establishment of efficient and practical synthetic
protocols, further investigation of structure/properties relation-
ship of the heterocyclic annulated PAHs is rather limited.
Perylene is unique in the family of PAHs and has been
extensively studied due to its excellent optical and electronic
(7) (a) Imamura, K.; Hirayama, D.; Yoshimura, H.; Takimiya, K.; Aso, Y.;
Otsubo, T. Tetrahedron Lett. 1999, 40, 2789–2792. (b) Bluemer, G. P.; et al.
Chem. Ber. 1977, 110, 269–272. (c) Solomentseva, T. I.; Rogovik, V. I.;
Chibisova, T. A.; Traven, V. F.; Stepanov, B. I. J. Org. Chem. (USSR) 1986,
943–946.
(8) Looker, J. J. J. Org. Chem. 1972, 37, 3379–3381.
(9) Eberson, L.; Radner, F. Acta Chem. Scand. B 1985, 39, 357–374.
† Institute of Chemistry, Chinese Academy of Sciences.
‡ Graduate School, Chinese Academy of Sciences.
(1) (a) Anthony, J. E. Chem. ReV 2006, 106, 5028–5048. (b) See a special
issue on organic electronics: Chem. Mater. 2004, 16,4381. (c) Takimiya, K.;
Jigami, T.; Kawashima, M.; Kodani, M.; Aso, Y.; Otsubo, T. J. Org. Chem.
2002, 67, 4218–4227.
10.1021/jo8012622 CCC: $40.75
Published on Web 08/09/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 7369–7372 7369

SCHEME 1. Preparation of Heterocyclic Annulated
Perylenesa
Crystals of 4, 5, and 7 suitable for single-crystal X-ray
analysis are obtained by slow evaporation of their dilute solution.
The crystal structure of perylo[1,12-b,c,d]selenophene 4 shows
almost planar molecular conformations, which are regularly
stacked along the b axis, with similar interplanar distances as
PET (3.47 Å).11 In addition, marked Se· · ·Se short contacts (3.49
Å) shorter than S · · ·S short contacts (3.51 Å) in PET molecules
are observed between molecules of neighboring stacks, indicat-
ing that 4 has a more compressed packing structure (Figure 1a).
This extraordinary double-channel superstructure makes 4 an
attractive candidate for device applications.
The introduction of nitrogen into the perylene backbone does
not induce a significant change in packing motif. The crystal
structure of 5 exhibits a nearly planar molecular conformation
with a packing arrangement consisting of edge-to-face dimers
(sandwich-herringbone packing, Figure 1b). The dimers adopt
an antiparallel manner, with an interplanar distance of 3.48 Å,
while the perylene molecules have interplanar distances of
3.47 Å.12
Differing from the packing motif of 4 and 5, the crystal
structure of 7 reveals a marked difference in solid-state packing
in which the dipole-dipole interaction is dominant over
chalcogen-chalcogen interactions and other factors. Recently,
a weak dipole-dipole interaction has been utilized for inducing
a columnar phase.13 In molecules of 7, the carboxylate-carbox-
ylate moiety would generate a dipole that would be expected
to organize the molecules in an antiparallel manner to produce
a columnar structure. The perpendicular separation between the
discs is 3.34 Å (Figure 1c). This π-stacked columnar struc-
ture represents a promising packing motif to explore its charge
transfer properties.14
The photophysical properties of heterocyclic annulated
perylenes 3-5 are summarized in Table 1, together with the
data of perylene 1 for comparison. The UV-vis absorption
spectra showed that they all exhibit well-defined vibronic π-π*
transition absorption bands with the longest maximum at 412.0,
416.5, and 425.0 nm for 3, 4, and 5, respectively. They are all
slightly blue-shifted relative to the corresponding parent com-
pound perylene (λmax ) 438.5 nm) as a reflection of the extended
aromatic core along the short molecular axis.15 Perylene
bisimides have proven to have a similar effect in which the
enlargement of the π system along the short molecular axis
always causes a hypsochromic shift.4 In comparison with 3, the
maximum absorption of 4 is bathochromically shifted about 4.5
nm. The heteroatom annulated perylenes presented here possess
small Stokes shifts of about 6, 7.5, and 11 nm for 3, 4, and 5,
respectively.
a Reagents and conditions: (a) fuming HNO3/H2O ) 1/1.6 (v/v), 1,4-
dioxane, 60 °C, 25-30 min; (b) sulfur powder, NMP, 180 °C, 5 h; (c)
selenium powder, 180 °C, 5 h; (d) triethyl phosphite, reflux, 2 h.
fraction is perylene, while the second and the third fractions
are determined to be 1-nitroperylene and 3-nitroperylene,
respectively. Notably, the yield of the desired product 2 is
improved up to 30% and can be obtained in 10-g scale, which
is a prerequisite for the synthesis of a series of heterocyclic
annulated perylenes and investigation of their material properties.
Chalcogen-annulated perylenes are prepared in high yield by
a surprisingly simple one-pot procedure from the readily
available precursor 2. The key step is carried out in N-
methylpyrrolidone (NMP) with sulfur or selenium powder at
180 °C in 5 h, following purification by column chromatography
to give the desired heteroatom-annulated products in 70% and
65% yield for 3 and 4, respectively (Scheme 1). Treatment of
1-nitroperylene with triethyl phosphite in reflux temperature in
2 h directly afforded the yellow-brown product 5 in high yield.8
The compounds 3-5 exhibit moderate solubility in common
solvents, such as dichloromethane and tetrahydrofuran. Their
structures are unambiguously characterized by mass spectrom-
etry, NMR spectroscopy, elemental analyses, and X-ray single-
crystal analysis.
As an extension of this synthetic methodology, heterocyclic
annulated benzoperylene bearing two carboxylate substituents
has been synthesized. The introduction of two carboxylate
substituents is expected to not only increase the solubility, but
also have a further influence on its solid-state packing mode.10
S-heterocyclic annulated benzoperylene 7 has been prepared
following the synthetic route shown in Scheme 2. Diels-Alder
reaction of 1-nitroperylene with diethyl maleate, following
dehydrogenation by chloranil affords 6 as bright yellow solids
(51%). The crucial final step with sulfur powder in NMP is the
same as the above-described, and 7 is obtained as light yellow
solids in a yield of 52%.
Cyclic voltammetry of 3-5 in acetonitrile shows a reversible
oxidation wave (for charts, see the Supporting Information). The
oxidation peaks (E1/2 values) of 3, 4, and 5 are found at 1.12,
1.08, and 0.89 V vs Ag/AgCl, respectively. Given the silver
(11) Santos, I. C.; Almeida, M.; Morgado, J.; Duarte, M. T.; Alcacer, L.
Acta Crystallogr. Sect. C: Cryst. Struct. Commun. 1997, 53, 1640–1642.
(12) Camerman, A.; Trotter, J. Proc. R. Soc. London, Ser. A 1964, 279, 129–
146.
(13) (a) Levitsky, I. A.; Kishikawa, K.; Eichhorn, S. H.; Swager, T. M. J. Am.
Chem. Soc. 2000, 122, 2474–2479. (b) Bushby, R. J.; Boden, N.; Kilner, C. A.;
Lozman, O. R.; Lu, Z. B.; Liu, Q. Y.; Thornton-Pett, M. A. J. Mater. Chem.
2003, 13, 470–474.
(14) (a) Naraso; Nishida, J.; Kumaki, D.; Tokito, S.; Yamashita, Y. J. Am.
Chem. Soc. 2006, 128, 9598–9599. (b) Moon, H.; Zeis, R.; Borkent, E.; Besnard,
C.; Lovinger, A.; Siegrist, T.; Kloc, C.; Bao, Z. J. Am. Chem. Soc. 2004, 106,
15322–15323.
(10) Wang, Z.; Enkelmann, V.; Negri, F.; Mu¨llen, K. Angew. Chem., Int.
Ed. 2004, 43, 1972–1975.
(15) (a) Colmsjo¨, A. L. Anal. Chem. 1982, 54, 1673–1677. (b) Nijegorodov,
N.; Mabbs, R.; Downey, W. S. Spectrochim. Acta, Part A 2001, 57, 2673–3685.
7370 J. Org. Chem. Vol. 73, No. 18, 2008

SCHEME 2. Synthesis of S-Heterocyclic Annulated Benzoperylene 7
TABLE 1. UV-vis and Electrochemical Data of 1 and 3-5
wire as a quasireference electrode and the ferrocene/ferrocenium
(Fc/Fc+) couple as the internal potential standard,16 HOMO
Together with Estimated HOMO Levels
compds
absmaxa/nm
fluomaxb/nm
E1/2 c/V
EHOMOd/eV
levels estimated by oxidation onsets are -5.42, -5.39, and
ox
-5.18 eV, respectively.17
1
3
4
5
438.5
412.0
416.5
425.0
443
418
424
436
1.05
1.12
1.08
0.89
-5.38
-5.42
-5.39
-5.18
In conclusion, we have developed a practical synthetic
procedure for the synthesis of heterocyclic annulated perylenes
and benzoperylene from the readily available 1-nitroperylene.
Single-crystal X-ray diffraction analysis demonstrates that
chalcogen-annulated perylenes have a similar slipped π-stacked
packing motif with marked chalcogen-chalcogen interactions
a Measured in dilute CHCl3 solution (1.0 × 10-5 M). b Excited at the
absorption maxima, and measured in dilute CHCl3 solution (1.0 × 10-6
c
M). Versus Fc/Fc+, performed in Bu4NPF6/CH3CN (0.1 M), scan rate
) 100 mV/s. d Estimated from the onset of the oxidation peak, ref 17.
between neighboring columns, which is expected to facilitate
effective charge transport. Further studies on the application of
these molecules to electronic devices such as OFETs are
currently underway.
Experimental Section
1-Nitroperylene (2). To a hot solution of perylene (30.0 g, 118.8
mmol) in 1,4-dioxane (1.2 L) was added a mixture of 24.0 mL of
water and 15.0 mL of nitric acid (d ) 1.5) dropwise. The resulting
solution was heated to 60 °C with vigorous stirring for 25-30 min,
and then cooled and poured into 5 L of water. The solid was
collected, washed, dried, and purified by column chromatography
on silica gel with petroleum ether as eluent to afford 2 (10.56 g,
1
30%) as a brick-red crystal. H NMR (DMSO, 400 MHz, ppm) δ
8.52 (dd, 2H), 8.01-7.93 (m, 4H), 7.81 (d, J ) 8.4 Hz, 1H), 7.76
(dd, 2H), 7.66 (t, J ) 7.6 Hz, 1H), 7.56 (t, J ) 8.0 Hz, 1H). 13C
NMR (DMSO, 100 MHz, ppm) δ 146.0, 134.3, 133.8, 131.3, 130.2,
129.0, 128.9, 128.8, 128.0, 127.8, 127.6, 127.2, 126.8, 125.6, 124.8,
122.8, 122.7, 122.2. EI-MS m/z (%) 297 (M+, 100%). Elemental
analysis calcd for C20H11NO2: C, 80.80; H, 3.73; N, 4.71. Found:
C, 80.55; H, 3.66; N, 4.74. Mp 170-171 °C.
Perylo[1,12-b,c,d]thiophene (3). Sulfur (1.72 g, 53.84 mmol)
was dissolved in N-methylpyrrolidone (NMP, 80 mL, 70 °C), then
1-nitroperylene 2 (1.6 g, 5.36 mmol) was added under argon. The
mixture was heated to 180 °C with vigorous stirring for 5 h until
the starting material could not be detected by TLC. Upon cooling
to room temperature, the reaction mixture was poured into 1 L of
2 M HCl, then the precipitate was collected by vacuum filtration,
washed with water, dried, and purified by column chromatography
on silica gel (petroleum ether/dichloromethane ) 5/1) to give 3
FIGURE 1. Crystal packing view of (a) the double-channel packing
mode of 4, (b) the sandwich-herringbone arrangement of 5, and (c) the
π-stacked columnar structure of 7.
1
(1.06 g, 70%) as a bright yellow needle. H NMR (DMSO, 400
MHz, ppm) δ 8.82 (d, J ) 7.6 Hz, 2H), 8.35 (d, J ) 8.8 Hz, 2H),
8.23 (d, J ) 8.0 Hz, 2H), 8.11 (d, J ) 9.2 Hz, 2H), 7.92 (t, J ) 7.6
Hz, 2H). EI-MS m/z (%) 282 (M+, 100%). Elemental analysis calcd
for C20H10S: C, 85.07; H, 3.57. Found: C, 85.02; H, 3.70. Mp
<280 °C.
Perylo[1,12-b,c,d]selenophene (4). This compound was synthe-
sized by a similar procedure as for the synthesis of 3. Selenium
(4.2 g, 53.84 mmol) was allowed to react with 2 (1.6 g, 5.36 mmol)
in NMP under argon for 5 h analogously to yield 4 as a yellow-
brown needle (1.15 g, 65%). 1H NMR (DMSO, 400 MHz, ppm) δ
8.76 (d, J ) 7.6 Hz, 2H), 8.38 (d, J ) 8.4 Hz, 2H), 8.16 (d, J )
8.0 Hz, 2H), 8.02 (d, J ) 8.8 Hz, 2H), 7.86 (t, J ) 7.6 Hz, 2H).
13C NMR (DMSO, 100 MHz, ppm) δ 136.5, 131.9, 131.0, 130.1,
126.7, 126.5, 125.7, 125.3, 121.1. EI-MS m/z (%) 330 (M+, 100%).
Elemental analysis calcd for C20H10Se: C, 72.96; H, 3.06. Found:
C, 72.85; H, 3.02. Mp 270-271.5 °C.
FIGURE 2. UV-vis absorption spectra of 1 (black line), 3 (red line),
4 (green line), and 5 (blue line) in CHCl3 at room temperature (1.0 ×
10-5 M).
J. Org. Chem. Vol. 73, No. 18, 2008 7371

6H-Phenanthro[1,10,9,8-c,d,e,f,g]carbazole (5). Compound 5
was synthesized according to the literature by J. J. Looker. 1H NMR
(DMSO, 400 MHz, ppm) δ 12.19 (s, NH, 1H), 8.76 (d, J ) 7.2
Hz, 2H), 8.19 (d, J ) 8.0 Hz, 2H), 7.98 (dd, 4H), 7.82 (t, J ) 8.0
Hz, 2H). 13C NMR (DMSO, 100 MHz, ppm) δ 130.6, 129.7, 128.3,
125.0, 124.5, 124.2, 123.5, 120.8, 116.9, 115.5. EI-MS m/z (%)
265 (M+, 100%). Elemental analysis calcd for C20H11N: C, 90.54;
H, 4.18; N, 5.28. Found: C, 90.23; H, 4.15; N, 5.21. Mp >280 °C.
Diethyl 7-Nitrobenzo[g,h,i]perylene-1,2-dicarboxylate (6). 1-Ni-
troperylene 2 (0.5 g, 1.68 mmol) was added to diethyl maleate (20
mL), the mixture was heated to 180 °C with vigorous stirring for
5 h and cooled to room temperature, then chloranil (1.0 g) was
added. The resulting mixture was stirred for another 24 h at 180
°C. Upon cooling to room temperature, the reaction mixture was
poured into 150 mL of hexane, and the precipitate was collected
by vacuum filtration, washed with hexane, dried, and purified by
column chromatography on silica gel (petroleum ether/dichlo-
romethane ) 1/1) to give 6 (400 mg, 51%) as bright yellow solids.
1H NMR (DMSO, 400 MHz, ppm) δ 8.61 (d, J ) 8.4 Hz, 1H),
8.55 (d, J ) 8.8 Hz, 2H), 8.51-8.46 (m, 4H), 8.43 (d, J ) 9.2 Hz,
1H), 8.17 (t, J ) 7.6 Hz, 1H), 4.63 (q, J ) 7.2 Hz, 4H), 1.46 (t, J
) 7.2 Hz, 6H). 13C NMR (CDCl3, 150 MHz, ppm) δ 168.1, 168.0,
146.0, 133.0, 131.2, 129.4, 129.2, 128.8, 128.7, 127.9, 127.0, 126.7,
126.5, 125.7, 125.4, 125.3, 125.0, 124.4, 124.3, 124.1, 123.8, 123.7,
122.4, 121.7, 62.49, 62.45, 14.44, 14.40. EI-MS m/z (%) 465 (M+,
100%). Elemental analysis calcd for C28H19NO6: C, 72.25; H, 4.11;
N, 3.01. Found: C, 72.15; H, 4.16; N, 3.13. Mp 210-211 °C.
vigorous stirring for 3 h until the starting material could not be
detected by TLC. Upon cooling to room temperature, the reaction
mixture was poured into 200 mL of 2 M HCl, then the precipitate
was collected by vacuum filtration, washed with water, dried, and
purified by column chromatography on silica gel (petroleum ether/
dichloromethane ) 1/1) to give 7 (100 mg, 52%) as light yellow
1
solids. H NMR (CDCl3, 400 MHz, ppm) δ 8.61 (d, J ) 9.2 Hz,
2H), 8.34 (t, J ) 8.8 Hz, 4H), 8.22 (d, J ) 8.4 Hz, 2H), 4.78 (q,
J ) 7.2 Hz, 4H), 1.66 (t, J ) 7.2 Hz, 6H). 13C NMR (CDCl3, 100
MHz, ppm) δ 168.4, 135.5, 128.3, 127.7, 126.7, 126.5, 124.5, 124.2,
123.2, 122.9, 121.2, 120.2, 62.1, 14.4. EI-MS m/z (%) 450 (M+,
100%). Elemental analysis calcd for C28H18O4S: C, 74.65; H, 4.03.
Found: C, 74.56; H, 4.05. Mp 225-226 °C.
Acknowledgment. For financial support of this research, we
thank the National Natural Science Foundation of China (Grants
20772131and20721061),the973Program(Grant2006CB932101),
and the Chinese Academy of Sciences.
Supporting Information Available: Futher experimental
details, NMR spectra for all new compounds, as well as
crystallographic data for 4, 5, and 7 presented in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JO8012622
(16) Bre´das, J. L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J. Am. Chem.
Soc. 1983, 105, 6555.
(17) (a) Li, Y.; Cao, Y.; Gao, J.; Wang, D.; Yu, G.; Heeger, A. Synth. Met.
1999, 99, 243. (b) Sun, Q.; Wang, H.; Yang, C.; Li, Y. J. Mater. Chem. 2003,
13, 800–806.
Diethyl Benzoperylo[7,8-b,c,d]thiophene-1,2-dicarboxylate (7).
Sulfur (138 mg, 4.3 mmol) was dissolved in N-methylpyrrolidone
(NMP, 10 mL, 70 °C), then benzoperylene 6 (200 mg, 0.43 mmol)
was added under argon. The mixture was heated to 180 °C with
7372 J. Org. Chem. Vol. 73, No. 18, 2008