Synthetic approach to and characterization of a fullerene-dtbt-fullerene triad

Article abstract of DOI:10.1055/s-0032-1316902

The synthesis of a new fullerene-dithienylbenzo[c]thiophene (DTBT)-fullerene triad is reported. The synthetic approach involves the synthesis of a DTBT unit, a Sonogashira reaction to introduce two acetylenic groups, and the coupling with fullerene. The p

Full text of DOI:10.1055/s-0032-1316902

LETTER
▌943
lSetyternthetic Approach to and Characterization of a Fullerene–DTBT–Fullerene
Triad
Fullerene–DTBT–Fullerene Triad
Maurizio D’Auria,*a Ambra Guarnaccio,a,b Rocco Racioppi,a Antonio Santagata,b Roberto Teghila
a
Dipartimento di Scienze, Università della Basilicata, Viale dell’Ateneo Lucano 10, 85100 Potenza, Italy
Fax +39(0971)205678; E-mail: maurizio.dauria@unibas.it
b
CNR-IMIP U.O.S. Potenza, Zona Industriale, 85100 Tito Scalo (PZ), Italy
Received: 01.03.2013; Accepted after revision: 17.03.2013
the most useful method is the ring closure of an ortho-di-
Abstract: The synthesis of a new fullerene–dithienylbenzo[c]thio-
ketone using Lawesson’s reagent (LR).5
phene (DTBT)–fullerene triad is reported. The synthetic approach
involves the synthesis of a DTBT unit, a Sonogashira reaction to in-
troduce two acetylenic groups, and the coupling with fullerene. The
product showed an absorption at λ = 485 nm and a fluorescence
band at λ = 575 nm.
DTBT was prepared in 37% overall yield in a three-step
synthesis (Scheme 1).6 The synthetic approach starts with
an in situ preparation of 2-thienylmagnesium bromide (2
mol equiv) for nucleophilic addition to commercial and
inexpensive ortho-phthalaldehyde (1) to give the interme-
diate secondary diol 2 in 76% yield. The oxidation of the
diol in the presence of two equivalents of pyridinium
chlorochromate (PCC)7 led to the desired diketone 3 in
49% yield and this was subsequently cyclized with
Lawesson’s reagent to afford the desired 1,3-bis(2-thie-
nyl)benzo[c]thiophene (4) as an orange solid (mp 100–
102 °C).8
Key words: alkynes, arylation, fullerenes, heterocycles, palladium
Organic thin film transistors (OTFT), light-emitting di-
odes (OLED), photovoltaic cells, sensors, and radio fre-
quency identification (RF-ID) tags are the main
application areas for the use of organic semiconductors in
low-cost, large-area electronics. The use of organic mate-
rials can bypass the need for expensive lithography and
vacuum-deposition steps necessary for silicon-based ma-
terials.
1.
PCC, CH2Cl2,
CHO
MgBr
S
r.t. 5 h
The main logic units in these circuits are field-effect tran-
sistors (FET), comprising a gate electrode, a gate dielec-
tric, a semiconductor, and a source/drain electrode.1 The
device is generally in an insulating state until a gate volt-
age is applied (relative to the source), which establishes a
‘channel’ of charge at the semiconductor–dielectric inter-
face, turns the device on, and allows conductivity between
the source and the drain.
49%
CHO 2. 0 °C to r.t., 3 h
3. NH4Cl (sat.)
1
S
S
OH HO
2
76%
1. LR, CH2Cl2, r.t. 4 h
S
2. EtOH, Δ, 1 h
S
S
O
O
S
S
99%
3
There are three basic types of semiconductor materials,
depending on their ability to conduct holes (p-type), elec-
trons (n-type), or both (ambipolar) under different gate
bias conditions. In semiconductor materials reduction of
the bandgap (Eg) will enhance the thermal population of
the conduction band and thus increase the number of in-
trinsic charge carriers. The decrease of Eg can led to true
organic metals showing intrinsic electrical conductivity.
There are several reviews on this field.2,3
4
Scheme 1 Reagents, conditions, and yields for the three-step syn-
thetic approach to DTBT backbone
Scheme 2 depicts the synthetic path by which we obtained
the alkynyl intermediate 6. In a first attempt, 1,3-bis(5-
bromo-2-thienyl)benzo[c]thiophene (5) was synthesized
by bromination of 1,3-bis(2-thienyl)benzo[c]thiophene
(4) with N-bromosuccinimide (NBS) according to
Mitschke et al.9 but using CHCl3–MeCO2H (1:1) as re-
ported by Kisselev et al.10 In that case, the reaction was
carried out at –40 °C while we tried to synthesize com-
In this letter we wish to report the synthesis and photo-
physical characterization of a new fullerene–dithienyl-
benzo[c]thiophene–fullerene donor–acceptor triad.
Several synthetic methods for the preparation of 1,3-di- pound 5 with ice-bath cooling. Under these conditions, we
thienylisothianaphthene (DTBT) derivatives are available observed a small amount of the undesired tetrabrominated
in the literature.4 Although several synthetic methods for byproduct that proved difficult to separate from the de-
the formation of the DTBT moiety have been proposed, sired product. Better results were obtained using DMF as
solvent at 0 °C in the dark as reported by Jung et al.11
when we obtained compound 5 in good yield with no tet-
rabrominated byproduct.
SYNLETT 2013, 24, 0943–0946
Advanced online publication: 05.04.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1316902; Art ID: ST-2013-D0187-L
© Georg Thieme Verlag Stuttgart · New York

944
M. D’Auria et al.
LETTER
1) C60, LHMDS, THF
r.t., 24 h
NBS, 0 °C
80%
S
S
S
2) TFA, r.t., 24 h
18% yield
S
S
S
S
S
S
4
Br
Br
5
6
1. TMSA, Pd(PPh3)2Cl2 (4 mol%);
CuI (6 mol%)
piperidine, toluene, Δ, 30 min
S
2. K2CO3, MeOH–THF, r.t., 2 h
80%
S
S
S
S
S
6
H
H
Scheme 2 Reagents, conditions, and yields for DTBT bromination
and Sonogashira cross-coupling reactions
Dibrominated DTBT (5) was then used as the substrate in
a Sonogashira cross-coupling reaction to achieve acety-
lene coupling in order to obtain 1,3-bis(5-ethynyl-2-thie-
nyl)benzo[c]thiophene (6), the pivotal material to perform
the key reaction. After assessing the optimal conditions
and reagents and combinations finally we obtained com-
pound 6 in a two-step protocol. An initial Sonogashira
cross-coupling using trimethylsilylacetylene (TMSA), pi-
peridine as base, bis(triphenylphosphine)palladium(II) di-
chloride as catalyst, and copper(I) iodide as co-catalyst in
dry toluene as solvent gave the corresponding trimethyl-
silyl derivative. This was then deprotected under standard
basic conditions in the presence of K2CO3 to furnish 6 in
80% yield over two steps.12
7
Scheme 3 Reagents, conditions, and yields for one-pot fullerene
ethynylation
acid to give a brownish slurry the crude product can be pu-
rified through a silica chromatographic column.
A similar substrate with respect to our isothianaphthenic
systems has been synthesized by Lafleur-Lambert et al.15
Taking into account this reported ethynylation we used a
slightly modified procedure. Firstly changed solvent be-
cause in THF, both at room temperature and at reflux,
fullerene has a poor solubility that compromised the for-
mation of the desired anionic intermediate. We chose
chlorobenzene as it is a better solvent for fullerene (solu-
bility of C60 in THF is 0.04 g/L while in chlorobenzene is
6.35 g/L). By this means the desired anionic intermediate
was readily formed. Subsequently, we used the standard
quenching procedure using TFA to obtain the desired
product 7 in 18% yield over the two steps.16
Oligothiophenes, which combine potential advantages
such as better photostability and smaller band gap than,
for instance, PPV derivatives, have been the most widely
used substrates for the synthesis of fullerene C60-deriva-
tized conjugated polymers. Covalent attachment of fuller-
ene C60 onto a poly- or oligothiophene structure was
initially investigated by Sannicolò et al.13 In our case, we
decided to carry out a one-pot ethynylation to allow the at-
tachment of a fullerene C60 to both terminal alkynes
(Scheme 3).
Figure 1 shows the UV-Vis absorption spectrum of a so-
lution of DTBT–(C60)2 (7) in CHCl3. We observed two
distinct absorption bands from the monomer backbone
Ethynylated fullerenes are generally prepared via a lithi-
um acetylide addition as first reported by Komatsu et al.14
Numerous acetylene derivatives of C60 have been success-
fully prepared by this general procedure on treating a son-
icated mixture of alkyne and excess C60 (ca. 2 equiv per
terminal alkyne) with lithium bis(trimethylsilyl)amide
(LHMDS, ca. 4 equiv) in dry THF under an inert atmo-
sphere.
LHMDS appears first to react with the fullerene to form a
more soluble and reactive intermediate. An indication that
the previous reaction is proceeding is the formation of a
dark red coloration. In general, this reaction proceeds
smoothly at ambient temperature and is completed within
few hours. After quenching with excess trifluoroacetic
Figure 1 DTBT–(C60)2 absorption UV-Vis spectrum of a 0.044 mM
solution in CHCl3
Synlett 2013, 24, 943–946
© Georg Thieme Verlag Stuttgart · New York

LETTER
Fullerene–DTBT–Fullerene Triad
945
with absorption maxima at 310 and 485 nm. The lower- tions show that the HOMO → LUMO transition is an
energy absorption band has been assigned to the π–π* electron-transfer process.
transition of the first excited singlet state (S1) of the π-con-
jugated system, while the higher-energy absorption band
has been attributed to the π–π* transition into the second
Acknowledgment
This paper draws on work undertaken as part of the Combined Laser
Nanotechnology (CLaN) project co-financed by the Operational
Programme ERDF Basilicata 2007-2013.
excited singlet state (S2).
Pumping the DTBT–(C60)2 system at the two different
wavelengths corresponding to each maximum absorption
band present in the UV-Vis spectrum we could detect two
different fluorescence bands. Pumping the system at λ =
320 nm we observed a fluorescence band centered around
λ = 390 nm, while pumping at λ = 480 nm we observed a
fluorescence centered around λ = 575 nm with a pro-
nounced shoulder at λ = 610 nm (Figure 2). We observed
a Stokes shift of λ = 90 nm.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
References and Notes
(1) Katz, H. E.; Bao, Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34,
359.
(2) (a) Waltman, R. J.; Bargon, J. Can. J. Chem. 1986, 64, 76.
(b) Patil, A. O.; Heeger, A. J.; Wudl, F. Chem. Rev. 1988, 88,
183. (c) Roncali, J. Chem. Rev. 1997, 97, 173. (d) Kraft, A.;
Brimsdale, A. C.; Holmes, A. B. Angew. Chem. Int. Ed.
1998, 37, 402. (e) McCullough, R. D. Adv. Mater. 1998, 10,
93. (f) Horowitz, G. Adv. Mater. 1998, 10, 365. (g) Garnier,
F. Acc. Chem. Res. 1999, 32, 209. (h) Roncali, J. J. Mat.
Chem. 1999, 9, 1875. (i) Bao, Z. Adv. Mater. 2000, 12, 227.
(j) Groenendaal, L. B.; Jonas, F.; Freitag, D.; Pielartzik, H.;
Reynolds, J. R. Adv. Mater. 2000, 12, 481. (k) Ma, H.; Jen,
A. K.-Y. Adv. Mater. 2001, 13, 1201. (l) Otsubo, T.; Aso, Y.;
Takimiya, K. Bull. Chem. Soc. Jpn. 2001, 74, 1789. (m) van
Mullekom, H. A. M.; Vekemans, J. A. J. M.; Havinga, E. E.;
Meijer, E. W. Mater. Sci. Eng. 2001, 32, 1. (n) Otsubo, T.;
Aso, Y.; Takimiya, K. J. Mater. Chem. 2002, 12, 2565.
(o) Kelly, T. W.; Baude, P. F.; Gerlach, C.; Ender, D. E.;
Muyres, D.; Haase, M. A.; Vogel, D. E.; Theiss, S. D. Chem.
Mater. 2004, 16, 4413. (p) Newman, C. R.; Frisbie, C. D.; de
Silva Filho, D. A.; Brédas, J.-L.; Ewbank, P. C.; Mann, K. R.
Chem. Mater. 2004, 16, 4436. (q) Ling, M. M.; Bao, Z.
Chem. Mater. 2004, 16, 4824. (r) Winder, C.; Sariciftci, N.
S. J. Mater. Chem. 2004, 14, 1077. (s) Barbarella, G.;
Melucci, M.; Sotgiu, G. Adv. Mater. 2005, 17, 1581.
(t) Facchetti, A.; Yoon, M.-H.; Marks, T. J. Adv. Mater.
2005, 17, 1705. (u) Perepichka, I. F.; Perepichka, D. F.;
Meng, H.; Wudl, F. Adv. Mater. 2005, 17, 2281. (v) Sun, Y.;
Liu, Y.; Zhu, D. J. Mater. Chem. 2005, 15, 53. (w) Anthony,
J. E. Chem. Rev. 2006, 106, 5028. (x) Roncali, J.; Leriche,
P.; Cravino, A. Adv. Mater. 2007, 19, 2045. (y) Murphy, A.
R.; Fréchet, J. M. J. Chem. Rev. 2007, 107, 1066.
Figure 2 DTBT–(C60)2 emission spectra of a 0.5 mM solution in
CHCl3 acquired pumping with a laser beam at λ = 480 nm
Calculations were performed at the DFT/B3LYP/6-
31G+(d,p) level on Gaussian 0917 and indicated that the
HOMO of DTBT–(C60)2 is found at –0.17177 H and it is
mainly localized on the dithienylbenzo[c]thiophene part
of the molecule; while the LUMO is found at 0.11032 H
and localized on the fullerene (Figure 3). These calcula-
(z) Bundgaard, W.; Krebs, F. C. Sol. Energy Mater. Sol.
Cells 2007, 91, 954.
(3) (a) Ong, B. S.; Wu, Y.; Li, Y.; Liu, P.; Pan, H. Chem. Eur. J.
2008, 14, 4766. (b) Arias, A. C.; MacKenzie, J. D.;
McCulloch, I.; Rivnay, J.; Salleo, A. Chem. Rev. 2010, 110,
3. (c) D’Auria, M. Adv. Heterocycl. Chem. 2011, 104, 127.
(4) (a) Lorcy, D.; Cava, M. P. Adv. Mater. 1992, 4, 562.
(b) Bauerle, P.; Gotz, G.; Emerle, P.; Port, H. Adv. Mater.
1992, 4, 564. (c) Mohanakrishnan, A. K.; Lakshmikantham,
M. V.; McDougal, C.; Cava, M. P.; Baldwin, J. W.; Metzger,
R. M. J. Org. Chem. 1998, 63, 3105. (d) Kiebooms, R.;
Hoogmartens, I.; Adriaensens, P.; Vanderzande, D.; Gelan,
J. Macromolecules 1995, 28, 4961.
(5) Ertasa, E.; Ozturkb, T. Tetrahedron Lett. 2004, 45, 3405.
(6) Musmanni, S.; Ferraris, J. P. J. Chem. Soc., Chem. Commun.
1993, 172.
(7) Piancatelli, G.; Scettri, A.; D’Auria, M. Synthesis 1982, 245.
(8) 1,2-Phenylenebis(2-thienylmethanol) (2)
1H NMR (400 MHz, CDCl3): δ = 7.44 (m, 2 H), 7.29 (m, 4
Figure 3 HOMO and LUMO of DTBT–(C60)2
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 943–946

946
M. D’Auria et al.
LETTER
H), 7.17 (m, 2 H), 6.85 (m, 2 H), 6.695 (m, 2 H), 6.14 (s, 2
H). 13C NMR (100 MHz, CDCl3): δ = 147.27, 140.58,
128.78, 127.92, 127.07, 125.68, 125.31, 70.04.
1,2-Di-(2-thienoyl)benzene (3)
7.35 (d, J = 5 Hz, 2 H), 7.25 (m, 4 H), 3.49 (s, 2 H). 13C NMR
(125 MHz, CDCl3): δ = 137.23, 135.67, 133.90, 126.44,
125.77, 125.02, 121.85, 121.47, 104.88, 82.94.
(13) Benincori, T.; Brenna, E.; Sannicolò, F.; Trimarco, L.; Zotti,
G.; Sozzani, P. Angew. Chem., Int. Ed. Engl. 1996, 35, 648.
(14) Komatsu, K.; Murata, Y.; Takimoto, N.; Mori, S.; Sugita, N.;
Wan, T. S. M. J. Org. Chem. 1994, 59, 6101.
(15) Lafleur-Lambert, A.; Rondeau-Gagné, S.; Soldera, A.;
Morin, J. F. Tetrahedron Lett. 2011, 52, 5008.
(16) 1,3-Bis(5-ethynyl-2-thienyl)benzo[c]thiophene–(C60)2 (7)
1H NMR (400 MHz, CDCl3): δ = 8.04 (m, 2 H), 7.93 (m, 2
H), 7.70, (m, 2 H), 7.38 (s, 2 H), 7.15 (m, 2 H), 6.98 (m, 2
H). 13C NMR (100 MHz, CDCl3): δ = 143.5, 142.3, 136.9,
134.8, 133.4, 130.4, 129.2, 129.1, 128.0, 128.8, 128.2,
128.1, 128.0, 127.9, 127.8, 127.6, 127.4, 127.3, 127.2,
127.1, 126.5, 126.3, 126.2, 126.27, 125.3, 125.31, 124.8,
124.6, 124.5, 125.5, 124.4, 124.1, 123.9, 123.7, 123.3,
123.2, 107.5, 79.5, 62.3, 54.9.
1H NMR (400 MHz, CDCl3): δ = 7.725 (m, 2 H), 7.635 (m,
4 H), 7.455 (m, 2 H), 7.055 (m, 2 H). 13C NMR (100 MHz,
CDCl3): δ = 188.50, 144.28, 139.55, 135.36, 135.18, 130.83,
129.44, 128.23. GC–MS (EI): m/z = 298.0 [M+]. FT-IR (KBr
pellet): νmax = 1620, 1585, 1570, 1510, 1410 cm–1.
1,3-Di-(2-thienyl)benzo[c]thiophene (4)
1H NMR (400 MHz, CDCl3): δ = 7.195 (m, 4 H), 7.195 (m,
3 H), 7.000 (m, 3 H). 13C NMR (100 MHz, CDCl3): δ =
135.57, 135.24, 127.86, 126.46, 125.57, 125.52, 124.76,
121.49. GC–MS (EI): m/z = 298.0 [M+]. UV-Vis (CHCl3):
λmax = 435 nm. FT-IR (KBr pellet): νmax = 1530, 1216, 1182,
841, 738 cm–1.
(9) Mitschke, U.; Bäuerle, P. J. Chem. Soc., Perkin Trans. 1
2001, 740.
(10) Kisselev, R.; Thelakkat, M. Chem. Commun. 2002, 1530.
(11) Jung, Y. K.; Kim, H.; Park, J.-H.; Lee, J.; Lee, S. K.; Lee, Y.
S.; Shim, H.-K. J. Polym. Sci., Part A: Polym. Chem. 2008,
46, 3573 .
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.;
Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.;
Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng,
G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda,
Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A. Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.;
Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam,
J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.;
Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
(12) 1,3-Bis(5-bromo-2-thienyl)benzo[c]thiophene (5)
1H NMR (400 MHz, CDCl3): δ = 7.87 (dd, J = 4 Hz, 2 H),
7.15 (d, J = 4 Hz, 2 H), 7.07 (m, 4 H). 13C NMR (100 MHz,
CDCl3): δ = 143.45, 136.99, 135.64, 130.95, 126.25, 125.50,
121.46, 112.59. GC–MS (EI): m/z = 455.8 [M+]. UV-Vis
(CHCl3): λmax = 440 nm. FT-IR (KBr pellet): νmax = 3062,
1529, 1489, 1433, 1190, 969, 788, 778, 734, 699, 582 cm–1.
1,3-Bis[5-(2-trimethylsilylethynyl-2-thienyl)]benzo[c]-
thiophene
1H NMR (CDCl3, 400 MHz): δ = 7.92 (dd, J = 4 Hz, 2 H),
7.22 (d, J = 4 Hz, 2 H), 7.15 (m, 4 H), 0.27 (s, 18 H). 13
NMR (100 MHz, CDCl3): δ = 137.18, 135.71, 133.58,
C
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski,
V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.;
Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision
A.1; Gaussian Inc: Wallingford (CT, USA), 2009.
126.70, 125.64, 125.24, 123.17, 121.78, 101.20, 97.50, 0.10.
1,3-Bis(5-ethynyl-2-thienyl)benzo[c]thiophene (6)
1H NMR (500 MHz, CDCl3): δ = 7.94 (dd, J = 5 Hz, 2 H),
Synlett 2013, 24, 943–946
© Georg Thieme Verlag Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not be copied or
emailed to multiple sites or posted to a listserv without the copyright holder's express written permission.
However, users may print, download, or email articles for individual use.