Benzodicarbomethoxytetrathiafulvalene derivatives as soluble organic semiconductors

Article abstract of DOI:10.1021/jo101817j

A series of new tetrathiafulvalene (TTF) derivatives bearing dimethoxycarbonyl and phenyl or phthalimidyl groups fused to the TTF core (6 and 15-18) has been synthesized as potential soluble semiconductor materials for organic field-effect transistors (OF

Full text of DOI:10.1021/jo101817j

pubs.acs.org/joc
Benzodicarbomethoxytetrathiafulvalene Derivatives as
Soluble Organic Semiconductors
†
Francisco Oton, Raphael Pfattner, Neil S. Oxtoby, Marta Mas-Torrent,*
†
†
,†
ꢀ
‡
§
†
ꢀ ^
Klaus Wurst, Xavier Fontrodona, Yoann Olivier, Jerome Cornil, Jaume Veciana, and
,†
ꢀ
Concepcio Rovira*
†
ꢁ
Institut de Ciencia de Materials de Barcelona (ICMAB-CSIC) and Networking Research Center on
Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Campus de la Universitat Autoꢁnoma de
Barcelona, Bellaterra E-08193 Barcelona, Spain, ‡Institut fu€r Allgemeine Anorganische und Theoretische
Chemie, Universita€t Innsbruck, A-6020, Innrain 52a, Innsbruck, Austria, §Serveis Tecnics de Recerca.
Universitat de Girona. Edifici Jaume Casademont (porta E), Pic de Peguera, 15 (La Creueta),
E- 17003 Girona, Spain, and Laboratory for Chemistry of Novel Materials, University of Mons,
Place du Parc 20, B-7000 Mons, Belgium
cun@icmab.es, mmas@icmab.es
Received September 16, 2010
A series of new tetrathiafulvalene (TTF) derivatives bearing dimethoxycarbonyl and phenyl or
phthalimidyl groups fused to the TTF core (6 and 15-18) has been synthesized as potential soluble
semiconductor materials for organic field-effect transistors (OFETs). The electron-withdrawing
substituents lower the energy of the HOMO and LUMO levels and increase the solubility and
stability of the semiconducting material. Crystal structures of all new TTF derivatives are also
described, and theoretical DFT calculations were carried out to study the potential of the crystals to
be used in OFET. In the experimental study, the best performing device exhibited a hole mobility up
to 7.5 ꢀ 10-3 cm2 V-1 s-1).
Introduction
of OFETs owing to their processability and high device
performance.4-10 OFETs using TTFs as semiconductors
have been prepared either from vacuum deposition or from
One of the most celebrated organic molecules for electro-
nics, tetrathiafulvalene (TTF), was independently reported
by Wudl in 1970 and by Coffen and Hunnig in 1971.1 TTF
and its derivatives have been thoroughly used as components
of organic conductors,2 or components for (opto)electronic
devices,3 but only recently, it has been shown that TTF
derivatives are very promising materials for the preparation
(4) (a) Mas-Torrent, M.; Rovira, C. J. Mater. Chem. 2006, 16, 433–436.
ꢀ
(b) Mas-Torrent, M.; Hadley, P.; Bromley, S. T.; Ribas, X.; Tarres, J.; Mas,
M.; Molins, E.; Veciana, J.; Rovira, C. J. Am. Chem. Soc. 2004, 126, 8546–
8553. (c) Mas-Torrent, M.; Durkut, M.; Hadley, P.; Ribas, X.; Rovira, C.
J. Am. Chem. Soc. 2004, 126, 984–985. (d) Bromley, S. T.; Mas-Torrent, M.;
Hadley, P.; Rovira, C. J. Am. Chem. Soc. 2004, 126, 6544–6545.
(5) Leufgen, M.; Rost, O.; Gould, C.; Schmidt, G.; Geurts, J.; Molenkamp,
L. W.; Oxtoby, N. S.; Mas-Torrent, M.; Crivillers, N.; Veciana, J.; Rovira, C.
Org. Electron. 2008, 9, 1101–1106.
(1) (a) Wudl, F.; Smith, G. M.; Hufnagel, E. J. J. Chem. Soc., Chem.
Commun. 1970, 1453–1454. (b) Coffen, D. L.; Chambers, J. Q.; Williams,
D. R.; Garrett, P. E.; Canfield, N. D. J. Am. Chem. Soc. 1971, 93, 2258–2268.
€
(c) Hunig, S.; Kiesslich, G.; Sceutzow, D.; Zhrandik, R.; Carsky, P. Int. J.
Sulfur Chem., C 1971, 109.
(2) See review papers in the issue: Chem. Rev. 2004, 104.
´
(3) (a) Delgado, J. L.; Bouit, P.-A.; Filippone, S.; Herranz, M. A.; Martın, N.
Chem. Commun. 2010, 46, 4853–4865. (b) Martin, N.; Sanchez, L.; Herranz,
M. A.; Illescas, B.; Guldi, D. M. Acc. Chem. Res. 2007, 40, 1015–1024. (c) Segura,
J. L.; Martın, N. Angew. Chem., Int. Ed. 2001, 40, 1372–1409.
´
(6) Takahashi, Y.; Hasegawa, T.; Horiuchi, S.; Kumai, R.; Tokura, Y.;
Saito, G. Chem. Mater. 2007, 19, 6382–6384.
(7) Mas-Torrent, M.; Hadley, P.; Bromley, S. T.; Crivillers, N.; Veciana,
J.; Rovira, C. Appl. Phys. Lett. 2005, 86, 012110/1–012110/3.
(8) (a) Naraso; Nishida, J.-I.; Ando, S.; Yamaguchi, J.; Itaka, K.;
Koinuma, H.; Tada, H.; Tokito, S.; Yamashita, Y. J. Am. Chem. Soc.
2005, 127, 10142–10143. (b) Naraso; Nishida, J.-I.; Kumaki, D.; Tokito,
S.; Yamashita, Y. J. Am. Chem. Soc. 2006, 128, 9598–9599.
ꢀ
154 J. Org. Chem. 2011, 76, 154–163
Published on Web 11/24/2010
DOI: 10.1021/jo101817j
r
2010 American Chemical Society

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Oton et al.
JOCArticle
SCHEME 1
solution. Soluble semiconductors are highly desired since
they are compatible with low-cost deposition techniques
(i.e., spin coating, inkjet printing, etc.) and they allow for
the synthesis of tailored materials. Although not suitable for
practical applications, single crystals represent the ideal class
of material in order to study the fundamental characteristics
of organic semiconductors such as charge carrier mobility.
The largest mobilities in TTF OFETs have been found for
single crystals prepared from solution of dithiophene-
tetrathiafulvalene (DT-TTF, μmax = 3.6 cm2 V-1 s-1),5
hexamethylene tetrathiafulvalene (HM-TTF, μmax = 10 cm2
Herein, we report the synthesis and crystal structure of a
new family of TTF derivatives containing methyl ester and
phthalimide groups. These molecules not only bear electron-
withdrawing groups fused to the TTF core to increase their
electron affinity12 but also incorporate carbomethoxy groups
that confer higher solubility in a larger range of solvents, which is
important for the fabrication of solution-processed devices. The
solid-state structures of all newly synthesized TTFs have also
been studied by single-crystal X-ray diffraction in order to assess
the preferential directions for charge transport with quantum-
chemical calculations.
V-1 s-1 6
) and dibenzotetrathiafulvalene (DB-TTF, μmax =
1cm2 V-1 s-1),7 which are among the largest reported for OFETs.
An important problem inherent to the TTF and other
semiconducting materials is the degradation during opera-
tion caused by moisture and oxygen.11 The high energy of the
orbitals implicated in the transport process is the cause of the
degradation, making the material more sensitive to air and
humidity. A possibility to avoid this problem in a hole
conducting material is to decrease the energy of the HOMO
orbitals. Therefore, the inclusion of electron-withdrawing
groups connected to the TTF core is a suitable approach to
decrease the HOMO energy and increase the stability of the
corresponding devices.8
Results and Discussion
Synthesis. The synthesis of 6 was carried out following a
different approach to the previously reported one14 (Scheme 1).
The phosponium salt 4 was synthesized by methods adapted
from the literature.13 Addition of triethylamine to an equi-
molar solution of compound 4 and 1,3-benzodithiolylium
tetrafluoroborate (5) in acetonitrile resulted in the formation
of the TTF 6. The synthesis of the TTFs bearing phthalimide
groups was achieved employing a different strategy. Initially,
reaction of the maleimides 7-10, prepared according to the
methodology described in the literature,15 with 3,4-bis-
(bromomethyl)dithioltione16 resulted in the formation of
Previous work10 demonstrated that attachment of phtha-
limide groups to tetrathiafulvalene resulted in higher
HOMO orbitals than dibenzotetrathiafulvalene (DB-TTF)
and stable devices. Nevertheless, the solubility of the com-
pounds was drastically reduced with respect to DB-TTF.
€
(12) (a) Almlof, J. E.; Feyereisen, N. W.; Jozefiak, T. H.; Miller, L. L. J.
Am. Chem. Soc. 1990, 112, 1206–1214. (b) Stanton, F. R.; Jozefiak, T. H.;
Miller, L. L. J. Org. Chem. 1990, 55, 4794–4801. (c) Stanton, F. R.; Miller,
L. L. J. Am. Chem. Soc. 1992, 114, 1388–1394. (d) Dumur, F.; Gautier, N.;
Gallego-Planas, N.; Sahin, Y.; Levillain, E.; Mercier, N.; Hudhomme, P.
J. Org. Chem. 2004, 69, 2164–2177. (e) Chen, M.-C.; Kim, C.; Chen, S.-Y.;
Chiang, Y.-J.; Chung, M.-C.; Facchetti, A.; Marks, T. J. J. Mater. Chem.
2008, 18, 1029–1036.
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Mater. 1998, 3, 330–334. (b) Baffreau, J.; Dumur, F.; Hudhomme, P. Org.
Lett. 2006, 8, 1307–1310.
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J. Heterocycl. Chem. 2007, 44, 831–836. (b) Spencer, H. K.; Cava, M. P.;
Garito, A. F. J. Chem. Soc., Chem. Comm. 1976, 23, 966–967. (c) Mizuno,
M.; Cava, M. P. J. Org. Chem. 1978, 43, 416–418.
(15) Reddy, P. Y.; Kondo, S.; Toru, T.; Ueno, Y. J. Org. Chem. 1997, 62,
2652–2654.
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Commun. 2006, 2750–2752. (b) Noda, B.; Katsuhara, M.; Aoyagi, I.; Mori,
T.; Taguchi, T. Chem. Lett. 2005, 34, 392–393.
(10) Gao, X.; Wang, Y.; Yang, X.; Liu, Y.; Qiu, W.; Wu, W.; Zhang, H.;
Qi, T.; Liu, Y.; Lu, K.; Du, C.; Shuai, Z.; Yu, G.; Zhu, D. Adv. Mater. 2007,
19, 3037–3042.
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Kamata, T.; Yase, K. J. Appl. Phys. 2004, 95, 5088–5093. (b) Abdou,
M. S. A.; Lu, X.; Xie, Z. W.; Orfino, F.; Deen, M. J.; Holdcroft, S. Chem.
Mater. 1995, 7, 631–641. (c) Abdou, M. S. A.; Orfino, F. P.; Son, Y.;
Holdcroft, S. J. Am. Chem. Soc. 1997, 119, 4518–4524. (d) Aguirre, C. M.;
Levesque, P. L.; Paillet, M.; Lapointe, F.; St-Antoine, B. C.; Desjardins, P.;
Martel, R. Adv. Mater. 2009, 21, 3087–3091.
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C. Synthesis 2007, 11, 1621–1623.
J. Org. Chem. Vol. 76, No. 1, 2011 155

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TABLE 1. Electrochemical and HOMO-LUMO Energies of Compounds 6 and 15-18
UV-vis/electrochemistry
DFT B3LYP/6-31G*
compd
E1/2 Ox1a (V)
E1/2 Ox2a (V)
EHOMO (eV)
ELUMOb (eV)
Eg (eV)
EHOMO (eV)
ELUMO (eV)
6
15
16
17
18
DB-TTF
0.31
0.39
0.46
0.47
0.46
0.17
0.78
0.78
0.76
0.80
0.81
0.59
-5.11
-5.19
-5.26
-5.27
-5.26
-4.97
-2.97
-3.02
-3.11
-3.17
-3.09
-2.61
2.14
2.17
2.15
2.10
2.17
2.36
-4.98
-5.30
-5.41
-5.41
-5.44
-4.70
-2.01
-2.43
-2.59
-2.58
-2.64
-1.1210
avs Fcþ/Fc, in CH2Cl2, tetrabutylammonium hexafluorophosphate as supporting electrolyte. bELUMO = EHOMO þ Eg (from UV-vis).
the phthalimide-fused precursors 11-14. Further reaction
with 3,4-methoxycarbonyldithioltione, in a reflux of freshly
distilled trimethylphosphite, led to the TTF derivatives
15-18 in a moderate yield due to the formation of homo-
coupling byproducts. The nature and purity of these com-
pounds were studied by the common spectroscopic techni-
ques (1H and 13C NMR, FTIR, MS, and elemental
analysis). Due to the low solubility of compound 18 in all
tested solvents, the 13C NMR spectrum could not be
registered.
UV-vis Spectroscopy. The UV-vis spectra of the TTF
diesters 6and 15-18 wasregisteredinCH2Cl2 (c=1ꢀ 10-4 M).
In all cases, two or three intense bands are observed in the
UV region (see Table S1 and Figures S10 and S11, Sup-
porting Information). In the case of 6, only one band
is observed in the visible region, which appears at λ =
441 nm. Compounds 15-18 show a band around λ = 385 nm
and a broad shoulder centered in the range of λ = 460-480 nm.
This band is more red-shifted in the fluorine-substituted mole-
cules 16-18 due to the more electron-withdrawing character of
the substituents.
The bands at lower energies are assigned to the HOMO
-LUMO transition, and thus, the onset of these bands
allows us to estimate the HOMO-LUMO gap17 that, in all
cases, is around 2.0 eV (see Table 1).
Electrochemical Properties. The redox behavior of all
synthesized compounds was studied by cyclic voltammetry
FIGURE 1. (a) Cyclic voltammogram (CH2Cl2, c = 10-3 M,
TBAHP) and (b) UV-vis spectrum (CH2Cl2, c = 10-4 M) of 15.
(CV). Cyclic voltammograms of compounds 6 and 15-18
showed two separate reversible one-electron oxidation waves
with half-wave potentials in the range E1/21 = 0.31-0.47 V
and E1/22 = 0.76-0.81 V vs Fcþ/Fc (CH2Cl2/0.1 M TBAHP)
(Table 1, Figure 1). The redox processes expected from the
reduction of the phthalimide groups in compounds 15-18
could not be clearly observed.
As expected, the most anodic potentials correspond to the
fluorine-substituted TTFs 16-18, where the oxidation peaks
appear at potentials approximately 0.15 V higher than the
potentials found for 6 (Table 1). In any case, the values of the
first oxidation potentials of all these compounds are con-
siderably higher than the first oxidation potential found for
the symmetric compound DB-TTF (E1/21 = 0.17 V vs Fcþ/
Fc),7 which can be explained by the fact that they incorporate
electron-withdrawing groups. As a consequence, these sys-
tems are expected to be more stable to oxygen exposure.
The CV experiments can be used as an experimental tool to
estimate the energy of the frontier orbitals of the molecules.
Therefore, from the onset of the first oxidation redox process
it is possible to calculate the value of the HOMO. The value
of the HOMO energy is found to be lower in the case of the
phthalimide-containing compounds. Since no reduction pro-
cesses were seen in the CV experiments, the estimation of the
LUMO was carried out by using the HOMO-LUMO gap
(Eg) obtained by UV-vis spectroscopy.17 These orbital
energy levels are listed in Table 1.
The energies of the HOMO levels are in the range of -5.11
to -5.27 eV, and the energies of the LUMOs vary from -2.97
to -3.17 eV. From these values, it should be noticed that the
imide moiety decreases the energy value of both HOMO and
LUMO. Further incorporation of fluorinated groups also
produces a small reduction of the energy of the frontier orbitals,
being lower than the ones of symmetric nonfluorinated diben-
zotetrathiafulvalene bisimides.10 The stabilization of HOMO is
evident when compared to the one of DB-TTF, which was
experimentally estimated to be around -4.97 eV.
(17) (a) Bando, Y.; Shirahata, T.; Shibata, K.; Wada, H.; Mori, T.;
Imakubo, T. Chem. Mater. 2008, 20, 5119–5121. (b) Yan, Q.; Zhou, Y.;
Ni, B.-B.; Ma, Y.; Wang, J.; Pei, J.; Cao, Y. J. Org. Chem. 2008, 73, 5328–
5339. (c) Tang, M. L.; Reichardt, A. D.; Siegrist, T.; Mannsfeld, S. C. B.; Bao,
Z. Chem. Mater. 2008, 20, 4669–4676. (d) Son, H.-J.; Han, W.-S.; Chun, J.-
Y.; Kwon, S.-N.; Ko, J.; Kang, S. O. Organometallics 2008, 27, 2464–2473.
156 J. Org. Chem. Vol. 76, No. 1, 2011

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Along with these measurements, DFT calculations were
performed with the B3LYP functional and the 6-31G* basis
set in vacuum. The geometries found for the TTFs are the
typical boat conformation which is usually reported in gas-
phase electron diffraction and theoretical calculations per-
formed for TTF and its derivatives.18 The HOMO of these
compounds is mainly located on the TTF core and the
LUMO on the electron-withdrawing groups, namely the
COOMe and the phthalimide groups (see Figures S14-S18
in the Supporting Information). This displacement in the
position of the LUMO clearly indicates the higher electron
affinity of the imide groups substituted with fluorinated
chains. The calculated energies found for the frontier orbitals
of the TTF derivatives are summarized in Table 1. If no
direct comparison between CV measurements and theoreti-
cal estimations of the frontier orbitals energies can be made,
the trends concerning the evolution of their values are well
correlated.
Molecular and Crystal Structures. Dark red single crystals
of 6 with platelike rectangular shape were grown via slow
evaporation of a chlorobenzene solution. Tetrathiafulvalene
6 crystallizes in the monoclinic system, space group P21/n,
and its structure consists of two crystallographically distinct
molecules. The two molecules that compose the asymmetric
unit cell are shown in Figure 2a. In both of them, the benzo
moiety and one methyl ester group are essentially coplanar
with the TTF core, and the other methyl ester group is
twisted to be nearly perpendicular (73.57 and 77.70ꢀ) with
respect to the TTF core. However, though one of these
molecules is fundamentally planar, the other presents a
significant bending of the TTF core in the side of the ester
groups (22.73ꢀ). These molecules form dimers in which the
two TTF cores are nearly parallel (the angle between the
FIGURE 2. (a) Molecular structure of the two distinct molecules of
6, along with the side views of them. (b) Packing structure of 6 along b.
The long axis of the rectangular crystal is parallel to the b-
crystallographic axis that exhibits numerous short intermo-
lecular interactions, with S S distances down to 3.606 A to
3 3 3
create an infinite 1D channel (Figure 2b). This can favor the
charge transfer along this axis which is probed in the OFET
measurements (see below).
Single crystals of the TTF-phthalimides 15-18 were also
obtained by slow evaporation of chlorobenzene solutions
(CHCl3 in case of 17). All of these compounds crystallize in
the triclinic system in the P-1 space group. However, whereas
the structures of 15, 16, and 18 are very similar and are
formed by one crystallographically distinct molecule, the
crystal structure of 17 is completely different with a unit cell
composed of two crystallographically different molecules.
The formation of these two types of crystal structures can be
in part due to the different nature of the solvent employed for
their crystallization.
Compounds 15, 16, and 18 exhibit conformations of the
conjugated system where all rings in the imide side of the
molecule are coplanar with the contiguous dithiol ring and
present a small angle between these planes and the ones that
contain the two other sulfur atoms and the carbon-carbon
double bond bearing the COOMe substituents. This bending
is more pronounced in 16 (11.63ꢀ). The ester groups are
twisted in all cases with angles that range from 7.50 to 56.61ꢀ.
As in the case of compound 6, phthalimide-substituted TTFs
15, 16, and 18 form head-to-tail dimers that stack into
columns. In all cases, there are similar intradimer and
interdimer distances (plane-to-plane distances between 3.50
and 3.69 A for all of them). Nevertheless, they differ in the
longitudinal shifting of the molecules in the intra- and
interdimers (see Figure 3), and as a consequence, there are
large differences in the sulfur-sulfur distances, which are
3.960, 3.714, and 3.807 A for the intradimer pairs for 15, 16,
planes is 2.73ꢀ) and interact via π-π and S S interactions,
3 3 3
with the closest S S distance of 3.773 A. These dimers form
3 3 3
stacks along the a* axis of the cell (Figure 2b). Taking the
four TTF sulfur atoms as a plane for each molecule, the
intradimer and the interdimer distances are 3.492 and 3.593 A,
respectively. The stacks further interact forming a herring-
bone pattern in the a-b plane (Figure 2b), in which several
lateral S S interactions occur between the stacks with
3 3 3
distances that range from 3.596 to 3.985 A. Simultaneously,
the herringbone sheets interact through weak hydrogen-
bonding interactions in the a-c plane. Although esters are
generally considered as hydrogen-bond acceptors, the methyl
protons of the carbomethoxy groups can also act as hydro-
gen-bond donors.19,20 Thus, it is interesting to note that
molecules of 6 exhibit weak C-H O hydrogen bonds
3 3 3
between the ester moieties in the herringbone sheets
[d(H(CH3) O(CdO) = 2.654-2.636 A; R(C-H O) =
3 3 3
3 3 3
170.28-109.12ꢀ; R(CdO H) = 175.44-148.70ꢀ].
3 3 3
ꢀ
(18) (a) Viruela, R.; Viruela, P. M.; Pou-AmeRigo, R.; Ortı
´
, E. Synth.
Met. 1999, 103, 1991–1992. (b) Berridge, R.; Serebryakov, I. M.; Skabara,
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P. J.; Ortı, E.; Viruela, R.; Pou-AmeRigo, R.; Coles, S. J.; Hursthouse, M. B.
´
J. Mater. Chem. 2004, 14, 2822–2830. (c) Terkia-Derdra, N.; Andreu, R.;
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Salle, M.; Levillain, E.; Orduna, J.; Garın, J.; Ortı, E.; Viruela, R.;
´ ´
Pou-AmeRigo, R.; Sahraoui, B.; Gorgues, A.; Favard, J.-F.; Riou, A.
ꢀ
Chem.;Eur. J. 2000, 6, 1199–1213.
(19) (a) Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290–296. (b) Desiraju,
G. R. Acc. Chem. Res. 1996, 29, 441–449. (c) Steiner, T.; Desiraju, G. R.
Chem. Commun. 1998, 891–892.
(20) Crivillers, N.; Mas-Torrent, M.; Bromley, S. T.; Wurst, K.; Veciana,
J.; Rovira, C. ChemPhysChem 2007, 8, 1565–1571.
and 18, respectively. However, there are no short S
distances in the interdimer structures or between different
S
3 3 3
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FIGURE 4. a-b plane structures of compounds 6 (a), 15 (b), and 16
(c) extracted from the X-ray spectra to calculate the transfer
integrals and charge carrier mobility values.
similar to the other phthalimide-TTF derivatives exhibiting a
columnar structure of dimers (Figure 5a), but the other
molecules form a layer of dimers with their face almost
perpendicular to the adjacent units of the columns (see
Figure S21, Supporting Information). Inside the columns,
the intradimer and interdimer S S distances are 3.998 and
3 3 3
4.541 A, and the plane-to-plane distances are 3.529 and 3.599 A,
respectively. These distances are slightly longer than in the
other phthalimide-substituted TTFs studied here. Despite the
fact that the packing of 17 is considerably more complex, the
nature of the hydrogen bonds is similar.
FIGURE 3. Views of the crystal structure of compounds (a) 15,
(b) 16, and (c) 18 showing the formation of columns of head to tail
dimers.
Indexation measurements of crystals of 17 show that the
longer axis of the crystal coincides with the crystallographic a
axis, which is the stacking direction of the columns.
Theoretical Characterization of Charge-Transport Proper-
ties. At a microscopic level, a hopping mechanism is often a
good starting point to describe theoretically charge transport
of organic semiconductors in operating devices.21 The
charge-transfer rate khop between two interacting molecules
can be evaluated with the help of Marcus-Levich-Jortner
(M-L-J) theory as22
columns. Probably the most significant difference in the
crystals is the lateral packing of the columns. Compound
15 exhibits an almost planar head-to-tail packing with the
nearest neighbor molecules in the adjacent stacks, whereas in
compounds 16 and 18 the packing is head-to-head (Figures
S19-S22, Supporting Information).
As found for 6, several weak hydrogen bonds are observed
in these crystals, especially between the imide CO groups and
the aromatic protons and the ester CO groups and the
terminal CH3 groups (choosing 15 as an example, this
khop
¼
Sn
compound exhibits weak C-H O hydrogen bonds between
3 3 3
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
"
#
imides and the phenyl rings [d(Ph-H OdC-N) = 2.409 A;
3 3 3
¥
2
ðΔG0þλSþnpωiÞ
X
2π
1
t2
expð- SÞ exp -
R(C-H O) = 125.25ꢀ], between the esters and phenyl rings
3 3 3
p
4πλSkBT n ¼ 0
n!
4λSkBT
[d(Ph-H OdC-O) = 2.288 A; R(C-H O) = 152.55ꢀ],
3 3 3 3 3 3
and between ester groups and the alkyl chain [d(CH-H O) =
3 3 3
The rate constant depends on several parameters accessi-
ble from quantum-chemical calculations: (1) The transfer
integral t depicts the strength of the interactions between the
electronic levels (HOMO for holes and LUMO for electrons)
of the molecules involved in the charge-transfer process. This
parameter has been calculated at the density functional
theory (DFT) level with the B3LYP functional and a TZP
2.596-2.627 A; R(C-H O) = 150.65-167.05ꢀ]). In com-
pounds 16 and 18, short F H interactions have been also
found.
3 3 3
3 3 3
Indexing measurements of crystals of 15, 16, and 18 show
that the longest axis of the crystal coincides with the growing
direction of the columns, whose relation with the crystal-
lographic axis is different in all cases.
Compound 17 has two crystallographically distinct mole-
cules that are fundamentally planar and form an angle of
71.7ꢀ between them. The packing of one of these molecules is
(21) Troisi, A.; Orlandi, G. Phys. Rev. Lett. 2006, 96, 86601.
(22) Jortner, J. J. Chem. Phys. 1976, 64, 4860–4867.
158 J. Org. Chem. Vol. 76, No. 1, 2011

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FIGURE 5. a-b plane structures of compounds 17 (a) and 18 (b) extracted from X-ray diffraction spectra to calculate transfer integrals and
charge carrier mobility values.
basis set, using the fragment approach implemented in the
ADF package with the methodology described in ref 23. (2) S
is the Huang-Rhys factor associated with a single effective
intramolecular vibrational mode (with a typical energy pω of
a stretching mode set here to 0.2 eV) that assists the charge
transfer by allowing for tunnelling across the energy barrier.
With a single mode, S is directly related to the internal
reorganization energy λi (= Spω) that reflects the degree
of geometric changes in the molecules upon addition of a
charge;24 λi is often computed at the DFT level with the
B3LYP functional and a 6-31G(d,p) basis set due to the good
agreement observed with values extracted from ultraviolet
photoemission spectroscopy spectra.25 (3) λs is the external
reorganization energy that accounts for the nuclear displace-
ments in the surrounding medium and the resulting electro-
nic effects.26 This parameter cannot be easily accessed from
quantum-chemical calculations, though values in the range
between 0.2 and 0.3 eV are obtained from simple models
based on a dielectric continuum.27 We will set λs equal to a
value 0.2 eV in all crystals; we stress that the main conclu-
sions of this work remain valid for other values of λs. (4)
When entropic contributions are neglected, the Gibbs energy
ΔG0 accounts for the difference in energy between the initial
and final states involved in the charge-transfer process. Since
a weak energetic disorder is expected in single crystals, we
have considered only the impact of the external electric field.
In this case, ΔG0 is expressed as ΔG0 = eFBdB, with FB and dB
representing the electric field and separation vectors between
mass centers, respectively.
deeper analysis of the bond-length modification upon oxida-
tion shows that the main changes are systematically located
over the TTF core leading to the appearance of a quinoid
structure. Note that such λi values are significantly larger
than that calculated at the same level of theory for pentacene
(∼100 meV)25 and DB-TTF (250 meV), a symmetric com-
pound of the family. However, a theoretical study on DT-
TTF showed that when the local molecular environment is
taken into account in DT-TTF (i.e., including in the calcula-
tion a cluster of molecules instead of a single one) and the
charge can be partially delocalized over several molecules,
the value of the reorganization energy is significantly re-
duced. This behavior can also be expected to take place in
other TTF derivatives.4d,28
Previous theoretical works27,29 have shown that the mag-
nitude of the transfer integral is driven by the shape of the
molecular orbitals as well as by the relative position of the
molecules involved in the charge transfer. We have thus
calculated the transfer integrals for all possible directions
in the crystalline structures and have reported hereafter only
the non-negligible contributions (larger than 1 meV).
Compound 6 exhibits its largest transfer integrals (on the
order of 20 meV) along the a and diagonal axes within the
a-b plane (Figure 4a). A slight difference is calculated along
the a axis between adjacent molecules due to the head-to-tail
configuration; this promotes transfer integrals of 18 meV
versus 23.5 meV for the intra- and interdimer jumps, respec-
tively. Although molecules 15, 16, and 18 display similar
crystalline structures (Figure 4b,c and 5b), the calculated
transfer integrals are sensibly different in magnitude and
have systematically their most important contributions
along the intracolumnar direction, with the larger value
obtained for the intradimer jump (24, 58, and 103 meV for
15, 16, and 18, respectively). The interdimer charge transfer
is also characterized by non-negligible transfer integral
values (12, 33, and 34 meV for 15, 16, and 18, respectively),
thus ensuring that the intracolumnar direction is a favorable
direction for charge transport. Smaller but non-negligible
transfer integrals are also calculated along the intercolumnar
direction (b and diagonal axes of the a-b plane for compound
The Marcus expression shows that high transfer rates
require large transfer integrals and small reorganization
energies. Interestingly, the internal reorganization energy
for positive polaron is found to be around 350 meV for each
compound. The addition of imide group or different side
chains has thus no significant impact on this parameter. A
(23) (a) Valeev, E. F.; Coropceanu, V.; da Silva, D. A.; Salman, S.;
ꢀ
Bredas, J.-L. J. Am. Chem. Soc. 2006, 128, 9882–9886. (b) Senthilkumar, K.;
Grozema, F. C.; Bickelhaupt, F. M.; Siebbeles, L. D. A. J. Chem. Phys. 2003,
119, 9809–9817.
(24) Coropceanu, V.; Cornil, J.; da Silva Filho, D. A.; Olivier, Y.; Silbey,
ꢀ
R.; Bredas, J.-L. Chem. Rev. 2007, 107, 926–952.
(25) Coropceanu, V.; Malagoli, M.; da Silva Filho, D. A.; Gruhn, N. E.;
ꢀ
Bill, T. G.; Bredas, J. L. Phys. Rev. Lett. 2002, 89, 275503.
(26) Marcus, R. A. J. Chem. Phys. 1965, 43, 679–701.
(27) Lemaur, V.; da Silva Filho, D. A.; Coropceanu, V.; Lehmann, M.;
Geerts, Y.; Piris, J.; Debije, M. G.; van de Craats, A. M.; Senthilkumar, K.;
ꢀ
Siebbeles, L. D. A.; Warman, J. M.; Bredas, J. L.; Cornil, J. J. Am. Chem.
Soc. 2004, 126, 3271–3279.
(28) Bromley, S. T.; Illas, F.; Mas-Torrent, M. Phys. Chem. Chem. Phys.
2008, 10, 121–127.
ꢀ
(29) (a) Bredas, J. L.; Calbert, J. P.; da Silva Filho, D. A.; Cornil, J. Proc.
Natl. Acad. Sci. U. S. A. 2002, 99, 5804. (b) Bredas, J. L.; Beljonne, D.;
ꢀ
Coropceanu, V.; Cornil, J. Chem. Rev. 2004, 104, 4971–5004.
J. Org. Chem. Vol. 76, No. 1, 2011 159

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FIGURE 6. Anisotropy mobility curves in the a-b plane of the crystalline structure of 6 (a) and 17 (b). The 0 degree orientation corresponds to
the a axis. The black arrows depict the intracolumnar direction. The mobility values are expressed in cm2 V-1 s-1
.
15 and directions d(1,3) and d(3,5) for compounds 16 and 18,
see Figures 4a,b and 5b).
simulation, the total time ttot of the simulation (linked to the
individual hopping times and hence inverse of the individual
transfer rates), and electric field norm:
As mentioned previously, compound 17 exhibits a quite
different packing compared with the other molecules
(Figure 5a). The a-b plane is made of a juxtaposition of
columns of different types promoting face-to-face or side-to-
side configurations. The transfer integrals in face-to-face
configurations are different for the intradimer (13 meV,
dimer 1-2) versus interdimer (67 meV, dimer 2-3) jump,
as expected from the head-to-tail geometry. Very small
contributions are found along the side-to-side direction (6
meV, dimer 6-7) whereas significant values are calculated
for the dimers 7-8 and 7-9. Moreover, intercolumnar
charge transfer is expected to occur in view of the significant
transfer integrals calculated in dimers 3-7, 4-7, and 5-7
(67, 30, and 13 meV, respectively). Note that the pathways
are equivalent in dimers 8-10, 8-11, 8-12 because of the
symmetry of the crystal. For all derivatives under study, it
turns out that transfer integrals between molecules located in
different layers are very small so that charge transport has
mainly a two-dimensional character.
dtot
μ ¼
ttot
F
The mobility anisotropy curve is then generated by repeat-
ing this scheme for different orientations of the electric field.
An electric field of 1000 V/cm similar in magnitude to that
typically applied in field-effect transistors is considered here.
As expected, compounds 15, 16, and 18 have their max-
imum hole mobility value (Figures S27-S29, Supporting
Information) along the intracolumnar direction. This is
driven by the large difference between the transfer integrals
along the intra- and intercolumnar directions, leading to a
ratio of the mobility around 4.5, 2, and 8, respectively. In
spite of the small transfer integral values along the inter-
columnar direction (b-axis) in 6, the mobility value is max-
imized along this axis (Figure 6a). The simulations indicate
that the holes migrate with a zigzag motion along the
diagonal axes to yield the largest mobility component along
the b axis. The anisotropy is weak for this compound since
the transfer integrals have the same order of magnitude along
the a and diagonal directions. In spite of the tight packing of
molecule 17 within the columns along the a axis, the simula-
tions reveal a mobility maximum along the intercolumnar
direction (deviation of 70ꢀ compared to the measurement
direction, see Figure 6b). This is rationalized by the presence
of efficient intercolumnar pathways, as discussed previously.
Single-Crystal Field-Effect Transistor Devices. OFETs were
fabricated on thermally oxidized silicon substrates. Crystals
were formed on the substrate by drop casting a solution of
0.5-1.0 mg of the compounds in 1 mL of toluene or chloro-
benzene and allowing the solvent to evaporate slowly under
darkness and reduced ambient humidity. Only 6 gave crystals
good enough to give reliable measurements. Some of the long
platelike crystals formed were connected with graphite paste
(Figure 7).
Several experimental studies30 have nicely shown that the
charge carrier mobility in single crystals is generally not
isotropic because of the high sensitivity of electronic cou-
plings to molecular packing. Monte Carlo simulations have
thus been performed in order to characterize the anisotropy of the
hole mobility for the different TTF derivatives. These simulations
propagate a single charge carrier in the crystals along directions
31
chosen according to the transfer probability pij
kij
P
pij
¼
kil
l
where kij is the transfer rate between molecules i and j and the
sum runs over all neighbors of the molecule supporting the
charge. The charge carrier mobility is ultimately evaluated
from the total distance dtot traveled by the charge during the
(30) Reese, C.; Bao, Z. Adv. Mater. 2007, 19, 4535–4538. (b) Sundar,
V. C.; Zaumseil, J.; Podzorov, V.; Menard, E.; Willett, R. L.; Someya, T.;
Gershenson, M. E.; Rogers, J. A. Science 2004, 303, 1644–1646. (c) Lee, J. Y.;
Roth, S.; Park, Y. W. Appl. Phys. Lett. 2006, 88, 252106.
ꢀ
(31) Olivier, Y.; Lemaur, V.; Bredas, J.-L.; Cornil, J. J. Phys. Chem. A
2006, 110, 6356–6364.
Figure 8 shows the source-drain current ISD of 6 versus the
applied source-drain voltage VSD across the two graphite
electrodes for different gate voltages VG applied to the silicon
substrate, which acts as a bottom gate. The resulting graphs
160 J. Org. Chem. Vol. 76, No. 1, 2011

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FIGURE 7. Optical microscopy photograph of the BDC-TTF 6
top-contact OFET with graphite source and drain electrodes. The
channel length and width are 122 and 20 μm, respectively.
are typical of a p-type semiconductor since as a more negative
VG is applied, more holes are induced in the semiconductor,
and the conductivity increases. When a -60 V gate voltage
is applied a clear saturation behavior at VSD = -20 V is
observed. The hole field-effect mobility was calculated accord-
ing to the formula described in the Experimental Section and
the mobility found in the saturation regime at VSD = -40 V
was of 7.5 ꢀ 10-3 cm2 V-1 s-1 (VTH = -27.6 V; on/off = 80),
which is on the order of the one predicted theoretically
(Figure 6a). The stability of these devices was tested by
measuring the electrical properties every week along a month
in which the devices were stored in room conditions. In this
period, no degradation of the mobility was observed, and only
a small doping effect caused the shifting of threshold voltage
from -27.6 to 28 V.
Interestingly, we should notice that the OFET measure-
ments were carried out along the longest crystal axis (parallel
to b) where the calculations predict the best transport path-
ways. This direction does not correspond to the face-to-face
packing of the molecules like in the high mobility semicon-
ductors DB-TTF and DT-TTF, but is promoted through a
diagonal zigzag pathway where one of the most prominent
FIGURE 8. (a) ISD vs VSD at VG (from top to bottom) 0, -10, -20,
-30, -40, -50, and -60 V for a single-crystal OFET based on 6. (b)
Transfer characteristics at VSD = -40 V for this device.
TTF derivatives that are symmetrically substituted such as
DB-TTF34 and dibenzotetrathiafulvalene bisimides,10 in
which regular columns of molecules are formed. The DFT
quantum-chemical calculations carried out point to relatively
high reorganization energy in all compounds. Furthermore,
the computed values of the transfer integrals show wide
variations with non-negligible transfer integrals calculated
along specific directions that not always correspond to the
π-π stacking of the molecules. In the tested conditions, the
best OFET performance with μ=7.5ꢀ 10-3 cm2 V-1 s-1 have
been found in devices prepared with a single crystal of 6 in a
top contact configuration using graphite paste as source and
drain electrodes. Undoubtedly, the search for novel soluble
organic semiconductors is a crucial step in order to progress in
the field.
features is the presence of short S S contacts. This result is
3 3 3
in agreement with the fact that π-stacking is not the only
assembly that can result in effective orbital overlap, as it has
31,32
ꢀ
been discussed by Bredas et al.
derivatives lateral S S have also been found to give rise to
Indeed, in other TTF
3 3 3
high charge carrier mobilities.4b,6,33
Conclusion
Experimental Section
In summary, we have described the synthesis and crystal
structure of a series of tetrathiafulvalene derivatives bearing
electron-withdrawing groups as esters and imides. These
groups contribute to reduce the energies of frontier orbitals
and the HOMO-LUMO gap of these compounds when
compared to other TTF derivatives used as semiconductors
such as DB-TTF and DT-TTF. The incorporation of the ester
groups have the additional advantage of imparting good
solubility to the compounds, permitting the preparation of
OFET devices with single crystals of the TTF derivatives
grown from solution, and giving an improved stability to de
prepared devices. In all cases, the crystal structure of the
compounds shows slip-stacks of dimers in contrast with the
Materials and Methods. All reactions were carried out under
Ar and using solvents which were dried by routine procedures.
Bis(bromomethyl)dithiolone,15 3,4-methoxicarbonyldithioltione,19
and phosphonium salt 413 were synthesized using procedures
reported in the literature. The synthesis and crystal structure of
compund 6 has previously been reported.14 Graphite paste XC-12
was purchased from Dotite and thermally grown silicon dioxide
was purchased from Si-Mat.
Reagents obtained from commercial sources were used without
further purification. Column chromatography was performed
using silica gel (60 A C.C. 35-70 μm, sds) as the stationary phase.
1H, 19F, and 13C NMR (250, 360, and 400 MHz) spectra were
recorded. The following abbreviations for stating the multiplicity
of the signals in the NMR spectra were used: s (singlet), d
(32) (a) Olivier, Y.; Muccioli, L.; Lemaur, V.; Geerts, Y. H.; Zannoni, C.;
ꢀ
(34) Brillante, A.; Bilotti, I.; Della Valle, R. G.; Venuti, E.; Milita, S.;
Dionigi, C.; Borgatti, F.; Lazar, A. N.; Biscarini, F.; Mas-Torrent, M.;
Oxtoby, N. S.; Crivillers, N.; Veciana, J.; Rovira, C.; Leufgen, M.; Schmidt,
G.; Molenkamp, L. W. CrystEngComm 2008, 10, 1899–1909.
Cornil, J. J. Phys. Chem. B 2009, 113, 1410. (b) Bredas, J.-L.; Beljonne, D.;
Coropceanu, V.; Cornil, J. Chem. Rev. 2004, 104, 4971–5004.
(33) Rovira, C. Chem. Rev. 2004, 104, 5289–5317.
J. Org. Chem. Vol. 76, No. 1, 2011 161

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Oton et al.
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(doublet), t (triplet), m (multiplet), q (quaternary carbon). The
MALDI-TOF MS spectra were also recorded. UV-vis-NIR
spectra were performed in CH2Cl2 (c = 1 ꢀ 10-4 M).
chlorobenzene or toluene solution on the substrate and allowing
the solvent to evaporate slowly in the dark at room temperature.
Electrical characterization was carried out under ambient con-
ditions (T = 24-26 ꢀC and RH = 45-55%) and darkness using
Cyclic voltammograms were performed with a conventional
three-electrode configuration consisting of platinum working
electrode and auxiliary electrodes and Ag/AgCl reference elec-
trode. The experiments were carried out with a 10-3 M solution
of the corresponding TTF derivative in CH2Cl2 containing 0.1
M (n-C4H9)4PF6 (TBAHP) as supporting electrolyte. Deoxy-
genation of the solutions was achieved by bubbling nitrogen for
at least 10 min and the working electrode was cleaned after each
run. The CVs were recorded with a scan rate increasing from
0.05 to 1.00 V s-1. Ferrocene was used as an internal reference
both for potential calibration and for reversibility criteria. All of
the potential values reported are relative to the Fcþ/Fc couple at
room temperature. Under these conditions the ferrocene has a
redox potential E0 = 0.440 V vs Ag/AgCl satd electrode and the
anodic-cathodic peak separation is 67 mV. Crystallographic
data of 6 were measured with monochromatic Mo KR (λ =
0.71073 A) radiation. Data were collected via φ and ω multi-
scans and reduced with the program DENZO-SMN without
absorption correction. The structure was solved with direct
methods SHELXS86 and refined against F2 with SHELXL97.
Crystallographic data of 15-18 were measured using graphite-
monocromated Mo KR radiation (λ = 0.71073 A) from an
X-ray tube. The measurements were made in the range 2.44 to
28.22ꢀ for θ. Full-sphere data collection was carried out with j
and ω scans. Programs used: data collection, Smart version
5.631 (Bruker AXS 1997-02); data reduction, Saint þ version
6.36A (Bruker AXS 2001); absorption correction, SADABS
version 2.10 (Bruker AXS 2001). Structure solution and refine-
ment was done by using SHELXTL Version 6.14 (Bruker AXS
2000-2003). The structure was solved by direct methods and
refined by full-matrix least-squares methods on F2. The non-
hydrogen atoms were refined anisotropically. The H-atoms
were placed in geometrically optimized positions and forced to
ride on the atom to which they are attached.
€
a Probe-station from Suss MicroTech and a Keithley 2612A
SourceMeter. A homemade Matlab-program using Instrument
Control Toolbox 2.0 was used to measure the current-voltage
characteristics. Field-effect mobilities were extracted in the
saturation regime from the transfer characteristics using the
formula.37
!
pffiffiffiffiffiffiffiffiffiffiffi
2
D
ID,sat
2L
μFE,sat
¼
VD ¼ const
3
WCi
DVG
Here, μFE,sat is the mobility, Ci the insulator capacitance per
unit area, and W and L the width and length of the crystal
between the electrodes, respectively. The effective channel width
W was determined by optical microscopy (see Figure 5).
Synthesis of BDC-TTF (6). A solution of 412 (3.234 g, 5.7mmol)
and 1,3-benzodithiolylium tetrafluoroborate (1.405 g, 5.8 mmol)
indry acetonitrile (45mL) was stirred for 30 minunder argon. Dry
triethylamine (5 mL) was added to this solution, and the resulting
mixture was stirred overnight. The red solid that precipitated was
filtered and recrystallized from methanol to yield a red crystalline
solid (1.097 g, 3.0 mmol, 51%) that was characterized as 6:14 yield
51%; mp 177-178 ꢀC; NMR δH (500 MHz; CDCl3; Me4Si) 7.25
(m, 2H), 7.13 (m, 2H), 3.84 (s, 6H); NMR δC (160.4 MHz; CDCl3)
160.1 (q), 136.4 (q), 132.1 (q), 126.3, 122.1, 113.2 (q), 107.4 (q),
53.5; IR νmax (KBr)/cm-1 3059, 1739, 1717, 1581, 1566, 1433,
1251, 1090, 1020, 767, 739, 676; MS m/z (MALDI) 369.9 (100,
Mþ). Anal. Calcd for C14H10O4S4: C, 45.39; H, 2.72; S, 34.62.
Found C, 45.48; H, 2.99; S, 34.37.
General Procedure for the Synthesis of Phthaloyldithiolones
11-14. A solution of the corresponding N-substituted malei-
mide (8.20 mmol), potassium iodide (8.20 mmol), and 3,4-bis-
(bromomethyl)dithiolone (4.10 mmol) in dry DMF (25 mL) was
refluxed for 8 h under argon. The solvent was partially removed
under vacuum and the residue mixed with water and extracted
with n-hexane/diethyl ether (8:2). The organic solvent was
removed under vacuum and the solid chromatographed on a
silica gel column (CH2Cl2, Rf = 0.4-0.6). The resulting white
solids were characterized as pure compounds 11-14.
Computational Details. Geometries were fully optimized with
tight convergence criteria at the DFT level with the Gaussian 03
package (E01 release),35 using the B3LYP36 functional and the
6-31G(d) basis set. All energies are not corrected for the zero-
point vibrational energy. The electronic structures and the
reorganization energies were calculated at the same level of
theory.
Device Preparation and Characterization. The devices were
prepared by using a bottom gate top contact graphite electrodes
on highly nþ2 doped silicon substrates with 200 nm of thermally
grown silicon dioxide. The source and drain graphite electrodes
were prepared by drawing with graphite paste the electrodes on
the crystal previously grown on the oxidized silicon wafer. The
crystals were formed in all cases by drop casting a drop of a
11: yield 61%; mp 225-226 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 7.97 (s, 2H), 3.67 (t, 2H, 3J(H,H) = 7.2 Hz), 1.73-1.67
(m, 2H), 0.95 (t, 3H, 3J(H,H) = 7.2 Hz); NMR δC (80.2 MHz;
CDCl3) 187.2 (q), 166.9 (q), 138.4 (q), 130.4 (q), 117.8, 40.0, 21.8,
11.3; IR νmax (ATR)/cm-1 3015, 2974, 1766, 1696, 1601, 1463,
1436, 1390, 1335, 1203, 1189, 1144, 1099, 1057, 973, 919, 875,
851, 765, 746; MS m/z (MALDI) 252 (100, Mþ - 27, þ H - CO).
Anal. Calcd for C12H9NO3S2: C, 51.60; H, 3.25; N, 5.01; S,
22.96. Found: C, 51.48; H, 3.19; N, 4.95; S, 22.80.
12: yield 45%; mp 161-162 ꢀC; NMR δH (250 MHz; CDCl3;
3
Me4Si) 8.02 (s, 2H), 4.30 (q, 2H, J(H,F)=8.5 Hz); NMR δC
(35) Gaussian 03, Revision E01: Frisch, M. J.; Trucks, G. W.; Schlegel,
H. B.; Scuseria, G. E.; Robb, M. A., Jr.; Cheeseman, J. R.; Montgomery,
J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.;
Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda,
R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski,
V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith,
T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian, Inc., Wallingford, CT, 2004.
(80.2 MHz; CDCl3) 186.7 (q), 165.2 (q), 139.5 (q), 129.6 (q),
123.0 (q, 1J(C,F) = 356.9 Hz), 118.4, 39.2 (CH2, q, 2J(C,F) =
46.9 Hz); NMR δF (376.3 MHz; CDCl3; CFCl3) -70.45; IR
ν
max( ATR)/cm-1 3010, 2983, 1779, 1757, 1722, 1651, 1417,
1387, 1333, 1260, 1208, 1162, 1066, 905, 890, 858, 834, 746; MS
m/z (MALDI) 292 (100, M - 27, þ H - CO). Anal. Calcd for
C11H4F3NO3S2: C, 41.38; H, 1.26; N, 4.49; C, 20.09. Found: C,
41.39, H, 1.17; N, 4.29; S, 19.99.
13: yield 33%; mp 126-127 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 8.06 (s, 2H), 4.38 (t, 2H, 3J(H,F) = 15.2 Hz); NMR δC
(80.2 MHz; CDCl3) 186.7 (q), 165.3 (q), 139.5 (q), 129.6 (q), 118.4,
37.4 (CH2, q, 2J(C,F) = 32.3 Hz); NMR δF (376.3 MHz; CDCl3;
(36) Bartolottiand, L. J.; Fluchick, K. Reviews in Computational Chem-
istry; VCH: New York, 1996; Vol. 7.
(37) Horowitz, G.; Hajlaoui, R.; Bouchriha, H.; Bourguiga, R.; Hajlaoui,
M. Adv. Mater. 1998, 10, 923–927.
162 J. Org. Chem. Vol. 76, No. 1, 2011

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CFCl3) -80.50 (t, 3J(F,F) = 10 Hz), -116.86 (m), -127.51 (m);
IR νmax (ATR)/cm-1 3096, 3014, 2968, 1786, 1732, 1660, 1418,
1386, 1354, 1314, 1282, 1228, 1181, 1122, 1068, 1029, 1011, 959,
928, 897, 834, 794, 750; MS m/z (MALDI) 392 (100, M - 27, þ
H - CO). Anal. Calcd for C13H4F7NO3S2: C, 37.24; H, 0.96; N,
3.34; S, 15.29. Found: C, 37.15; H, 0.95; N, 3.26; S, 15.16.
14: yield 49%; mp 187-188 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 8.09 (s, 2H), 7.77 (d, 2H, 3J(H,H) = 8.5 Hz), 7.62 (d, 2H,
3J(H,H) = 8.5 Hz); NMR δC (80.2 MHz; CDCl3) 190.5 (q),
176.6 (q), 134.5 (q), 130.9 (q, 2J(C,F) = 41.7 Hz), 126.5, 126.4,
126.3 (q), 126.1 (q), 124.1, 123.5 (q, 1J(C,F) = 349.3 Hz); NMR
δF (376.3 MHz; CDCl3; CFCl3) -62.85; IR νmax (ATR)/cm-1
2927, 1786, 1705, 1649, 1616, 1588, 1518, 1417, 1386, 1318, 1179,
1161, 1125, 1106, 1064, 1020, 956, 912, 882, 835, 769, 755; MS m/
z (MALDI) 354 (100, M - 27, þ H - CO). Anal. Calcd for
C16H6F3NO3S2: C, 50.39; H, 1.59; N, 3.67; S, 16.82. Found C,
50.28; H, 1.51; N, 3.78; S, 16.89.
General Procedure for the Synthesis of PDC-TTF (15-18). A
solution of the corresponding dithiolones 11-14 (0.58 mmol)
and 3,4-methoxycarbonyldithioltione (0.87 mmol) in freshly
distilled P(OCH3)3 (15 mL) was stirred for 6 h under argon.
The solvent was removed under reduced pressure, and the
residue was purified by column chromatography on a silica gel
(AcOEt/n-Hex 1:1, Rf = 0.5-0.7). The red-orange solids were
recrystallized from CHCl3.
15: yield 31%; mp 233-234 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 7.65 (s, 2H), 3.86 (s, 6H), 3.62 (t, 2H, 3J(H,H) = 7.2 Hz),
1.72-1.65 (m, 2H), 0.93 (t, 2H, 3J(H,H) = 7.2 Hz); NMR
δC (80.2 MHz; CDCl3) 167.1 (q), 159.6 (q), 143.3 (q), 131.8
(q), 130.4 (q), 116.2, 111.2 (q), 109.5 (q), 53.5, 39.8, 21.8, 11.3; IR
νmax (ATR)/cm-1 2952, 1761, 1734, 1699, 1573, 1434, 1391,
1365, 1287, 1229, 1206, 1189, 1053, 1015, 965, 907, 765, 745; MS
m/z (MALDI) 480 (100, M - 1). Anal. Calcd for C19H15NO6S4:
C, 47.39; H, 3.14; N, 2.91; S, 26.63. Found: C, 47.23; H, 3.06; N,
2.80; S, 26.51.
16: yield 21%; mp 253-254 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 7.72 (s, 2H), 4.27 (q, 2H, 3J(H,F) = 8.5 Hz), 3.87 (s, 6H);
NMR δC (80.2 MHz; CDCl3) 165.4 (q), 159.6 (q), 144.6 (q), 131.8
(q), 129.7 (q), 116.7, 112.1 (q), 108.8 (q), 53.5, 39.1 (2J(C,F) =
46.5 Hz); NMR δF (376.3 MHz; CDCl3; CFCl3) -70.52; IR νmax
(ATR)/cm-1 2950, 1780, 1728, 1634, 1436, 1385, 1264, 1164,
1067, 874, 748; MS m/z (MALDI) 521 (100, Mþ). Anal. Calcd for
C18H10F3NO6S4: C, 41.45; H, 1.93; N, 2.69; S, 24.59. Found: C,
41.39; H, 1.81; N, 2.60; S, 24.39.
1121, 1086, 1064, 1032, 956, 916, 886, 795, 772, 749, 734; MS m/z
(MALDI) 621 (100, Mþ). Anal. Calcd for C20H10F7NO6S4: C,
38.65; H, 1.62; N, 2.25; S, 20.64. Found: C, 38.61; H, 1.50; N, 2.16;
S, 20.50.
18: yield 18%; mp 251-252 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 7.78 (s, 2H), 7.76 (d, 2H, 3J(H,H) = 8.5 Hz), 7.62 (d, 2H,
3J(H,H) = 8.5 Hz), 3.87 (s, 6H); NMR δF (376.3 MHz; CDCl3;
CFCl3) -62.68; IR νmax (ATR)/cm-1 2957, 1773, 1738, 1716,
1615, 1579, 1436, 1361, 1320, 1288, 1265, 1171, 1115, 1068, 1037,
1020, 934, 905, 840, 769, 739; MS m/z (MALDI) 583 (100, Mþ).
Anal. Calcd for C23H12F3NO6S4: C, 47.33; H, 2.07; N, 2.40; S,
21.98. Found: C, 47.40; H, 2.00; N, 2.30; S, 22.07.
Crystal Structures. (For a more detailed description, see the
Supporting Information.) 6: C14H12O8S4, Mr = 370.46, mono-
clinic, P21/n, a = 8.3891(4) A, b = 10.8253(3) A, c = 34.158(1) A,
R=90ꢀ,β= 95.085(2)ꢀ,γ=90ꢀ,V= 3089.83(19) A3,Z=8,R1=
0.0461, wR2=0.0986, T=233(2) K. 15:C19H15NO6S4,Mr=481.56,
triclinic, P1, a=8.796(4) A, R=74.506(8)ꢀ, b=9.291(4) A3, β=
89.266(8)ꢀ, c=13.986(7) A3, γ=69.251(8)ꢀ, V=1025.8(8) A3, Z=2,
R1=0.0456, wR2=0.1272, T=300(2) K. 16: C18H10F3NO6S4,
Mr = 521.51, triclinic, P-1, a = 7.893(3) A, R = 92.716(7)ꢀ, b =
8.096(3) A, β=100.458(6)ꢀ, c=16.569(6) A, γ=107.625(6)ꢀ, V=
986.4(6) A3, Z=2, R1=0.0423, wR2=0.0894, T=300(2) K. 17:
C20H10F7NO6S4, Mr=621.53, triclinic, P-1, a=8.6082(10) A, R=
97.782(2)ꢀ, b=13.6635(16) A, β=90.026(2)ꢀ, c=21.298(3) A, γ=
102.338(2)ꢀ, V=2423.5(5) A3, Z=4, R1=0.0672, wR2=0.1771,
T=300(2) K. 18: C23H12F3NO6S4, Mr=583.62, triclinic, P-1, a=
7.9267(15) A, R=85.534(3)ꢀ, b=8.4428(16) A, β=78.675(3)ꢀ, c=
18.761(3) A, γ=76.174(3)ꢀ, V=1194.8(4) A3, Z=2, R1=0.0542,
wR2=0.1429, T=300(2) K.
Acknowledgment. We acknowledge the support of EU by
the EC FP7 ONE-P large-scale project (no. 212311), Marie
Curie EST FuMASSEC, DGI, Spain (Contract Nos.
CTQ2006-06333/BQU and CTQ2010-19501/BQU), Generalitat
de Catalunya, (2009SGR00516), and the programme “Juan de
la Cierva”(MICINN). We also thank Stefan T. Bromley for his
advice regarding the DFT calculations and CESGA for the use
of their installations. The work in Mons is also supported by the
European ONE-P project as well as by the Belgian National
Fund for Scientific Research (FNRS). Y.O. and J.C. are FNRS
research fellows.
17: yield 15%; mp 247-248 ꢀC; NMR δH (250 MHz; CDCl3;
Me4Si) 7.73 (s, 2H), 4.33 (t, 2H, 3J(H,F) = 15.2 Hz), 3.87 (s, 6H);
NMR δC (80.2 MHz; DMSO-d6) 166.0 (q), 159.4 (q), 143.7 (q),
131,3 (q), 129.8 (q), 118, 112.2 (q), 109.3 (q), 54.0; NMR δF
(376.3 MHz; CDCl3; CFCl3) -80.52 (t, 3J(F,F) = 10 Hz), -116.90
(t, 3J = 9.4 Hz), -127.54 (m); IR νmax (ATR)/cm-1 3017, 2961,
1781, 1744, 1726, 1588, 1577, 1436, 1386, 1351, 1264, 1223, 1176,
Supporting Information Available: NMR spectra of the
prepared compounds and electrochemical, UV-vis, and XRD
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
Note Added after ASAP Publication. Reference 32 (a) was
replaced in the version that reposted December 2, 2010.
J. Org. Chem. Vol. 76, No. 1, 2011 163