Molecular and crystal structure diversity, and physical properties of tetrathiafulvalene derivatives substituted with various aryl groups through sulfur bridges

Article abstract of DOI:10.1002/chem.201301819

A library of tetrathiafulvalene (TTF) derivatives (TTF-1-TTF-47) bearing aryl groups attached through sulfur bridges has been created. The peripheral aryl groups exert a significant influence on both the electronic and crystallographic properties of the resulting TTFs. These TTFs display broad absorption bands at 400-500 nm caused by intramolecular charge-transfer transitions between the aryl groups and central TTF core, and their first redox potentials increase with increasing electron-withdrawing ability of the aryl groups. In their crystal structures (22 examples), the central TTF cores adopt various conformations, including chair, half-chair, boat, and planar conformations. Moreover, the peripheral aryl groups exhibit multiple alignment modes with respect to the central TTF core, caused by their rotation about the two C-S bonds of the sulfur bridges. The packing motifs of these TTFs depend on both the nature of the aryl groups and their spatial alignment modes. Driven by intermolecular van der Waals forces and π-π interactions between the aryl groups and between the aryl groups and the TTF core, these TTFs adopt various packing structures. As a typical example, TTF-14, an achiral molecule, adopts a helical chain stack through intermolecular atomic close contacts. Moreover, the molecular geometries and packing motifs of these TTFs are sensitive to environmental variation, as exemplified by TTF-28, which adopts three distinct crystal modifications with diverse molecular geometries and stacking modes under different crystallization conditions. This work indicates that these TTFs are potential candidates as electronic materials, as well as functional building blocks for supramolecular assembly. Structural diversity due to flexible linkers: A thorough investigation of the properties and structural diversity of tetrathiafulvalene (TTF) derivatives substituted with various aryl groups through sulfur bridges is reported (see graphic). The aryl groups significantly affect both the electronic and crystallographic properties of the TTFs. These TTFs are candidates as electronic materials, as well as functional building blocks for supramolecular assembly. Copyright

Full text of DOI:10.1002/chem.201301819

FULL PAPER
DOI: 10.1002/chem.201301819
Molecular and Crystal Structure Diversity, and Physical Properties
of Tetrathiafulvalene Derivatives Substituted with Various Aryl Groups
through Sulfur Bridges
Jibin Sun,[a] Xiaofeng Lu,[a] Jiafeng Shao,[b] Xuexiang Li,[a] Shangxi Zhang,[a]
Baolin Wang,[a] Jinlian Zhao,[a] Yongliang Shao,[a] Ran Fang,[a] Zhaohui Wang,[c]
Wei Yu,[a] and Xiangfeng Shao*[a]
Abstract: A library of tetrathiafulva-
lene (TTF) derivatives (TTF-1–TTF-
47) bearing aryl groups attached
through sulfur bridges has been creat-
ed. The peripheral aryl groups exert a
significant influence on both the elec-
tronic and crystallographic properties
of the resulting TTFs. These TTFs dis-
play broad absorption bands at 400–
500 nm caused by intramolecular
charge-transfer transitions between the
aryl groups and central TTF core, and
their first redox potentials increase
with increasing electron-withdrawing
ability of the aryl groups. In their crys-
tal structures (22 examples), the central
TTF cores adopt various conforma-
tions, including chair, half-chair, boat,
and planar conformations. Moreover,
the peripheral aryl groups exhibit mul-
tiple alignment modes with respect to
the central TTF core, caused by their
packing structures. As a typical exam-
ple, TTF-14, an achiral molecule,
adopts a helical chain stack through in-
termolecular atomic close contacts.
Moreover, the molecular geometries
and packing motifs of these TTFs are
sensitive to environmental variation, as
exemplified by TTF-28, which adopts
three distinct crystal modifications with
diverse molecular geometries and
stacking modes under different crystal-
lization conditions. This work indicates
that these TTFs are potential candi-
dates as electronic materials, as well as
functional building blocks for supramo-
lecular assembly.
À
rotation about the two C S bonds of
the sulfur bridges. The packing motifs
of these TTFs depend on both the
nature of the aryl groups and their spa-
tial alignment modes. Driven by inter-
molecular van der Waals forces and p–
p interactions between the aryl groups
and between the aryl groups and the
TTF core, these TTFs adopt various
Keywords: electrochemistry · heli-
cal chains · photochemistry · poly-
morphism · TTF derivatives
Introduction
lic conductivity of the charge-transfer (CT) complex TTF-
TCNQ (TCNQ: tetracyano-para-quinodimethane)[3] and su-
perconductivity of (TMTSF)2X (TMTSF: tetramethyltetra-
selenofulvalene),[4] tremendous efforts have been devoted to
exploring multifunctional CT complexes of TTFs.[5] Recent-
ly, TTFs have been employed as building blocks for molecu-
lar devices such as switches,[6] sensors,[7] nonlinear optical de-
vices,[8] organic field-effect transistors,[9] rectifiers,[10] and or-
ganic photovoltaic cells.[11] This results from their good elec-
tron-donating ability and reversible one-electron oxidation
at accessible potentials, and these properties can be finely
tuned by peripheral substitution or chemical modification of
the TTF framework.[2]
Since they were first synthesized in the early 1970s,[1] tetra-
thiafulvalene (TTF) and its derivatives have remained
among the most extensively studied conjugated heterocyclic
systems in the materials sciences.[2] Stimulated by the metal-
[a] J. Sun, X. Lu, X. Li, S. Zhang, B. Wang, J. Zhao, Dr. Y. Shao,
Dr. R. Fang, Prof. Dr. W. Yu, Prof. Dr. X. Shao
State Key Laboratory of Applied Organic Chemistry
& School of Chemistry and Chemical Engineering
Lanzhou University, 222 Tianshui Southern Road
Lanzhou 730000 (P.R. China)
The peripheral substitution of TTF affords many interest-
ing materials.[2] For example, BEDT-TTF and BEDO-TTF,
derived from TTF by introducing bis(ethylenedithio) and bi-
s(ethylenedioxy) groups, respectively, show significant differ-
ences in the solid state. The former adopts various packing
patterns and has provided more than one-third of all organic
superconductors based on TTFs.[12] The latter has a self-as-
sembling nature and most of its salts are metallic.[13] Mean-
while, extension of the p-conjugation of TTF offers a prom-
ising means of adapting such materials for different applica-
Fax : (+86)0931-8915557
E-mail: shaoxf@lzu.edu.cn
[b] J. Shao
School of Physical Science and Technology, Lanzhou University
222 Tianshui Southern Road, Lanzhou 73000 (P.R. China)
[c] Prof. Dr. Z. Wang
Beijing National Laboratory of Molecular Sciences
Key Laboratory of Organic Solids, Institute of Chemistry
Chinese Academy of Science, Beijing 100089 (P.R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201301819.
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tions.[14] In this context, the attachment of aromatic systems
at the peripheral positions of the TTF framework would
seem to be especially intriguing because these may signifi-
cantly influence both the electronic and crystallographic
properties of the TTFs. Firstly, aromatic substituents can
modulate the electronic nature of the resulting TTFs
through extension of the p-conjugation and/or intramolecu-
lar charge transfer. Secondly, interactions between the pe-
ripheral aryl groups and between the peripheral aryl groups
and the central TTF core can lead to novel molecular pack-
ing motifs.
Most previously reported arylated TTFs have been ob-
tained by directly attaching aryl groups to the TTF frame-
[15]
À
work through C C bonds.
In these systems, rotational
Figure 1. UV/Vis spectra of selected TTFs in CH2Cl2. Measurement con-
freedom of the aryl groups has been limited due to steric
hindrance and/or conjugation. On the other hand, the at-
tachment of aryl groups to TTF through sulfur bridges could
increase the internal degrees of freedom of the molecule be-
cause the aryl groups would be able to rotate about the two
ditions: c=2ꢁ10À5 molLÀ1, 208C.
(CH2Cl2) at room temperature along with that of BEDT-
TTF as a reference. Figure 1 depicts the UV/Vis spectra of
selected TTFs, and those of the other compounds are pro-
vided in the Supporting Information (Figures S1a–S42a). In
comparison with that of BEDT-TTF, the UV/Vis absorption
spectra of the present TTFs display broad absorption bands
in the visible region. These absorption bands are progres-
sively red-shifted with increasing electron-withdrawing char-
acter of the respective aryl groups. For example, the absorp-
tion bands of TTF-5 (2-methoxyphenyl) and TTF-24 (2-ni-
trophenyl) are centered at 410 and 460 nm, respectively. To
understand the origin of this broad absorption band, we cal-
culated the HOMOs and LUMOs of the TTFs. As typical
examples, the HOMOs and LUMOs of TTF-1 and TTF-28
are shown in Figure 2. Theoretical calculations revealed that
the HOMO and LUMO are mostly localized on the TTF
À
C S bonds of the sulfur bridges. In addition, such sulfur
bridges would release steric hindrance. Consequently, the
supramolecular assembly diversity would be extended since
the molecules could easily adjust their geometries to adapt
to environmental variations. Under certain conditions, such
TTFs could form cavities capable of encapsulating guest
molecules of appropriate size, such as fullerene molecules.[16]
It is therefore highly desirable to carry out a thorough in-
vestigation of the electronic and crystallographic properties
of TTFs bearing aryl groups attached through sulfur bridges,
since this would provide insight concerning their potential
application as electronic materials and building blocks for
supramolecular assembly. To date, there have only been a
limited number of reports concerning such TTFs, presuma-
bly due to synthetic difficulties.[17–20] Recently, we reported a
facile and effective method for the attachment of aryl
groups to 1,3-dithiole-2-chalcogenones through sulfur
bridges,[21] which has enabled us to create a library of TTFs
with a broad range of aromatic substituents. To clarify the
electronic structures and aggregation modes of these TTFs,
we report herein their synthesis and a thorough study of
their properties and crystal structures. This work has mainly
been focused on the influence of the peripheral aryl groups
on the electronic properties, molecular geometries, and
packing modes of the obtained TTFs.
Results and Discussion
The TTF derivatives described in the title were synthesized
from the corresponding 1,3-dithiole-2-chalcogenones[21]
through the conventional phosphate-mediated coupling re-
action.[22] A total of 47 TTFs (TTF-1–TTF-47) were ob-
tained in good yields, as shown in Scheme 1. The synthetic
details are provided in the Supporting Information.
Photochemical properties: The UV/Vis absorption spectra
of TTF-1–TTF-47 were recorded in dichloromethane
Figure 2. Calculated HOMOs and LUMOs for a,b) TTF-1 and c,d) TTF-
28.
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Aryl-Substituted Tetrathiafulvalene Derivatives
FULL PAPER
Scheme 1. Chemical structures of the synthesized TTFs along with the yields of the isolated products. The synthetic route and experimental details are
provided in the Supporting Information.
core and peripheral aryl groups, respectively, and that the
broad visible absorption band corresponds to the HOMO–
LUMO transition. Therefore, this broad absorption band
originates from the intramolecular charge-transfer transition
between the aryl groups and the central TTF core, as in pre-
viously reported arylated TTFs.[15i,k,19d,20a]
(CV) and are summarized in Table 1. Figure 3 depicts the
voltammograms of some representative TTFs, and those of
the other compounds are provided in the Supporting Infor-
mation (Figures S1b–S42b). All of these TTFs display two
reversible redox potentials, which is typical electrochemical
behavior for the TTF framework. Among the functionalized
phenyl-substituted TTFs (TTF-1–TTF-26), the first redox
potential (E11 , 0.36 V) of TTF-8 is significantly lower than
Electrochemical properties: The electrochemical properties
=
2
of the present TTFs were investigated by cyclic voltammetry
that of BEDT-TTF (0.48 V), which may be ascribed to the
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12519

X. Shao et al.
Table 1. Electrochemical properties of the TTFs.[a]
chemical properties as those of
TTF-1. On the other hand, the
pyridyl-substituted TTFs, TTF-
28 (2-pyridyl) and TTF-29 (3-
pyridyl), exhibited quite differ-
ent electrochemical behavior.
E11
[V]
E12
[V]
DE
E11
[V]
E12
[V]
DE
E11
[V]
E12
=
2
[V]
DE
=
=
=
=
2
=
2
2
2
2
[V][b]
[V][b]
[V][b]
TTF-1
TTF-2
TTF-3
TTF-4
TTF-5
TTF-6
TTF-7
TTF-8
TTF-9
TTF-10
TTF-11
TTF-12
TTF-13
TTF-14
TTF-15
TTF-16
0.56
0.52
0.51
0.53
0.47
0.48
0.56
0.36
0.61
0.63
0.61
0.65
0.63
0.62
0.65
0.60
0.89
0.85
0.85
0.86
0.80
0.83
0.88
0.72
0.85
0.98
0.92
0.97
0.98
0.93
0.97
0.92
0.34
0.33
0.34
0.33
0.33
0.35
0.32
0.36
0.24
0.35
0.31
0.32
0.35
0.31
0.32
0.32
TTF-17
TTF-18
TTF-19
TTF-20
TTF-21
TTF-22
TTF-23
TTF-24
TTF-25
TTF-26
TTF-27
TTF-28
TTF-29
TTF-30
TTF-31
TTF-32
0.62
0.68
0.62
0.66
0.60
0.67
0.72
0.73
0.73
0.58
0.56
0.51
0.68
0.62
0.60
0.60
0.95
0.97
0.96
0.96
0.95
0.95
1.09
1.13
1.02
0.88
0.95
0.75
0.99
0.97
0.97
0.98
0.33
0.29
0.34
0.30
0.35
0.28
0.37
0.40
0.29
0.30
0.39
0.24
0.31
0.35
0.37
0.38
TTF-33
TTF-34
TTF-35
TTF-36
TTF-37
TTF-38
TTF-39
TTF-40
TTF-41
TTF-42
TTF-43
TTF-44
TTF-45
TTF-46
TTF-47
BEDT-TTF
0.60
0.60
0.61
0.59
0.65
0.60
0.53
0.53
0.53
0.53
0.62
0.68
0.60
0.68
0.68
0.48
0.98
0.96
0.96
0.91
0.98
0.94
0.81
0.81
0.81
0.82
0.96
1.03
0.97
1.00
1.00
0.89
0.38
0.36
0.35
0.32
0.33
0.34
0.28
0.28
0.28
0.29
0.34
0.35
0.37
0.32
0.32
0.41
The E11 values of TTF-28 and
=
TTF-292 were measured as 0.51
and 0.68 V, respectively. More-
over, the DE of TTF-28 is
smaller (0.24 V) than that of
TTF-29 (0.31 V), and both are
smaller than that for BEDT-
TTF. It is also worthy of note
that TTF-29 shows
a much
higher polarity than TTF-28,
with their respective Rf values
being 0.44 and 0.78 (CH2Cl2/
MeOH, 10:1 v/v), respectively.
These significant differences be-
tween TTF-28 and TTF-29 can
[a] Measurement conditions: solvent CH2Cl2, concentration 5ꢁ10À4 molLÀ1
,
supporting electrolyte
(nBu)4NPF6, working electrode Pt/C, counter electrode Pt, reference electrode SCE, scan speed 50 mVsÀ1
temperature 208C. [b] DE=E21 ÀE11 .
,
=
2
=
2
only be due to the positional effect of the pyridyl substitu-
ent. A relatively low E11 (ca. 0.53 V) and a small DE (ca.
=
2
0.28 V) were also observed for the other TTF derivatives
containing a 2-pyridyl group, TTF-39–TTF-42. These results
indicate that the attachment of a 2-pyridyl group to the TTF
skeleton through a sulfur bridge exerts little influence on
the first redox potential, even though 2-pyridyl is an elec-
tron-withdrawing substituent. The aryl-fused TTFs (TTF-30–
TTF-35) showed almost the same electrochemical behavior,
with E11 ꢀ0.60 and DEꢀ0.36 V, despite the variations in the
=
2
aryl system. The E11 and DE values of the cross-coupled
=
TTFs (TTF-36–TTF-238 and TTF-43–TTF-47) were found to
be intermediate between those of their pristine homo-cou-
pled TTFs.
The above results indicate that the incorporation of aryl
groups onto the TTF framework through sulfur bridges has
a strong influence on both the photochemical and electro-
chemical behavior of the resulting TTFs.
Figure 3. Cyclic voltammograms of selected TTFs. The dashed lines are
guides to the eye for E11 and E12 .
=
=
2
2
Crystal structures: By slowly evaporating the solvent, we ob-
tained single crystals of 22 TTFs suitable for single-crystal
X-ray diffraction measurement. The selected crystallograph-
ic data are provided in the Supporting Information (Ta-
bles S3–S6) and the detailed data have been submitted to
CCDC.[23] Instead of discussing in detail the crystal structure
of each TTF obtained, we only report the crystal structures
of three representative TTFs; those of the other TTFs can
be found in the Supporting Information (Figures S43–S62).
strong electron-donating ability of the N(Me)2 group. Simi-
lar behavior has been reported by Yorimitsu et al.[15i] The
E11 values of TTF-2–TTF-6 are comparable to that of
=
2
BEDT-TTF, whereas that of TTF-1 is slightly higher
(0.56 V). Positive shifts of more than 100 mV in E11 were ob-
=
2
served for TTF-7 and TTF-9–TTF-26, and the magnitude of
this shift increased with the electron-withdrawing ability of
the functional group on the phenyl substituent. On the other
hand, the differences between the first and second redox po-
tentials (E21 ) of these TTFs (DE) are smaller than that of
TTF-14: Red needle-like single crystals of TTF-14 were ob-
tained by slow evaporation of the solvent from a solution in
CH2Cl2 at room temperature. This compound crystallizes in
the chiral space group I2 with one molecule crystallographi-
cally unique. It should be noted that the structure of this
compound can also be solved with the C2 space group.
Figure 4 depicts the crystal structure of TTF-14. The central
=
2
BEDT-TTF (0.41 V). It should be noted that the position
(ortho-, meta-, para-) of the substituent on the phenyl group
has only a slight influence on the electrochemical behavior
of the corresponding TTFs (see Table 1).
In the case of heteroaryl-substituted TTF derivatives,
TTF-27 (2-thienyl) showed essentially the same electro-
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Aryl-Substituted Tetrathiafulvalene Derivatives
FULL PAPER
Figure 5. Solid-state CD spectra of TTF-14. The spectra were measured
from respective single crystals dispersed in KBr pellets.
from biological systems that achiral molecules can form heli-
cal chains through hydrogen bonds, as exemplified by DNA.
Recently, the spontaneous formation of chiral aggregate
morphologies at the nanoscale from achiral molecules in su-
pramolecular systems has received considerable attention.[25]
In the present case, TTF-14 as an achiral molecule forms a
helical chain of single-crystalline form through van der
Waals interactions. We have measured the CD spectrum of
single crystals of TTF-14 (Figure 5), the single-crystal sam-
ples for which were randomly picked from one crystal
batch. Positive and negative Cotton effects were observed at
325 and 400 nm, respectively. Remarkably, these samples
have almost identical CD spectra, but it may be premature
to conclude that the helical chain of TTF-14 always shows
the same chirality.
Figure 4. Crystal structure of TTF-14. a) Top and b) side views of the
TTF-14 molecule. The open, black-filled, and grey-filled circles represent
C, S, and Br atoms, respectively. c) Helical chain-type molecular packing
pattern along the a axis, in which TTF-14 molecules generated from dif-
ferent symmetry operations are drawn in black and grey. The dashed
À
lines represent the intermolecular atomic contacts: d1 =3.45 (Br C), d2 =
À
À
3.48 (S C), and d3 =3.53 ꢂ (Br C). Hydrogen atoms have been omitted
for clarity.
TTF core is almost planar (Figure 4a). Taking the short axis
of the TTF core as a reference plane, the two 4-bromophen-
yl moieties on one side are above whereas those on the
other side are below the mean plane of the TTF core. Close
atomic contacts, shorter than the sums of the van der Waals
radii of the two relevant atoms,[24] are observed between the
neighboring molecules along the crystallographic a axis (Fig-
TTF-28: This compound afforded three crystal modifica-
tions (I, II, and III) under different crystallization condi-
tions. Modifications I (Figure 6a), II (Figure 6b), and III
(Figure 6c) were obtained by slow evaporation of the sol-
vents CH2Cl2, CHCl3, and CS2, respectively. It is worth
noting that the crystals of III proved to be prone to collapse
À
À
ure 4c, Br C (3.45 and 3.53 ꢂ) and S C (3.48 ꢂ)). Consis-
tent with the chiral space group, TTF-14 molecules form a
helical chain-type arrangement along the a axis. It is known
Figure 6. Photographs of crystals (see Figure S64 in the Supporting Information for color photographs) and crystal structures of the three modifications
of TTF-28: a) modification I, b) modification II, and c) modification III. The crystal structures are depicted as top and side views of the central TTF skel-
eton for each modification, along with their packing motifs. The dotted and dashed lines are guides to the eye for the central C2S4 plane and terminal
C2S2 planes of the TTF core, respectively. q, q1, q2 are the dihedral angles between the terminal C2S2 planes and central C2S4 plane. The open, black-
filled, and grey-filled circles represent C, S, and N atoms, respectively. Hydrogen atoms have been omitted for clarity.
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X. Shao et al.
under ambient conditions. In the crystal structures of both I
and II, one TTF-28 molecule is crystallographically unique,
whereas half of TTF-28 and half of the CS2 solvent molecule
are independent in III. The molecular geometries and pack-
ing motifs of TTF-28 in I, II, and III are each quite differ-
ent, as shown in Figure 6. The diversity of molecular geome-
tries of TTF-28 arises from two factors: 1) the alignment of
the 2-pyridyl moieties with respect to the TTF core, and
2) the conformation of the TTF core. Referring to Fig-
ure 6a, the 2-pyridyl groups in I are all above the TTF core.
For the TTF core, both terminal C2S2 planes (dashed lines)
are bent upwards with respect to the central C4S4 plane
(dotted line) to form a boat conformation. Consequently,
the TTF-28 molecule forms an internal cavity. In the crystal
structure of II (Figure 6b), taking the long axis of the TTF
core as a reference plane, the 2-pyridyl groups on one side
are above whereas those on the other side are below the
TTF core. The TTF core adopts a half-chair conformation,
in which one terminal C2S2 plane is coplanar with the central
C2S4 plane and the other is bent upward. For III (Figure 6c),
the alignment of the 2-pyridyl groups is similar to that in
TTF-14 and the TTF core adopts a chair conformation. It is
noteworthy that the relative positions of the nitrogen atoms
of the 2-pyridyl groups reflect the different configurations in
I, II, and III (see the side view of each modification). These
results indicate that, as expected, the 2-pyridyl groups can
TTF-34: Another intriguing case is TTF-34, in the crystal
structure of which there are seven different molecules (A–
G). Molecules A–F have a similar conformation while mole-
cule G adopts a different one (see Figure 7). The TTF cores
of molecules A–F adopt a boat conformation (Figure 7b),
Figure 7. Crystal structure of TTF-34. a) Top view of TTF-34. b) Side
view of molecules A–F and c) side view of molecule G. The open, black-
filled, and grey-filled circles represent C, S, and O atoms, respectively.
Hydrogen atoms have been omitted.
and the dithiine rings are bent upwards with respect to the
C2S2 plane of the TTF core by 45–498 (q2). This conforma-
tion has pseudo-C2v symmetry and is similar to that of thie-
nodithiino-fused TTF.[20c,26] Molecule G has a chair-like TTF
core (Figure 7c) and its symmetry conforms to pseudo-C2h,
resembling those of BVDT-TTF and VDT-TTF.[27] Although
C2v and C2h symmetries of aryl-fused TTFs have been sepa-
rately observed in the solid state,[20c,26,27] the co-existence of
both conformations is only postulated in solution.[20c] To the
best of our knowledge, this is the first observation of the co-
existence of both C2v and C2h conformations in one crystal
of an aryl-fused TTF in the neutral state. DFT calculations
indicated that the C2v form is about 20 kcalmolÀ1 more
stable than the C2h form, similar to what has been found for
bis(thienodithiino)TTF.[20c] It is for this reason that six mole-
cules adopt C2v symmetry while only one molecule adopts
C2h symmetry in the crystal. In the packing structure of
TTF-34 (see Figure S57 in the Supporting Information),
molecules A–F form two kinds of trimers (A–B–F and C–
D–E), and G resides in the vacant space formed by the trim-
ers.
À
rotate freely about the two C S bonds of the sulfur bridges.
Structure I forms a unique aggregate that is difficult to
assign to the known packing motifs of neutral TTF deriva-
tives. Close atomic contacts are observed between the 2-pyr-
idyl group and the central TTF core of neighboring mole-
À
À
cules in TTF-28 (C C 3.39, C S 3.35 and 3.48 ꢂ). In both II
and III, the TTF-28 molecules form columnar packing
motifs along the crystallographic b axis, but their array
modes between the neighboring columns are different. In II,
the neighboring columns are tilted by an angle of 71.38 with
respect to the short axis of the TTF core, whereas in III
they are tilted by 66.88 with respect to the long axis of the
TTF core. Moreover, the intermolecular interactions are dif-
À
ferent for II and III. Within a packing column, two S S con-
À
tacts (3.51 and 3.58 ꢂ) between the TTF core and one C S
contact (3.38 ꢂ) between the TTF core and the 2-pyridyl
À
À
group are observed in II. In the case of III, no C C, C N,
À
À
À
C S, N S, or S S close contacts can be observed within or
between the columns, which is consistent with the unstable
nature of its crystals. On the other hand, the aryl groups and
TTF core in III are arranged to form cavities, which can ac-
commodate CS2 solvent molecules as shown in Figure 6c.
The differences between the molecular arrangements in I,
II, and III can be ascribed to the variation of aryl group
alignments, which significantly affect the intermolecular in-
teractions. These results also indicate that the geometry and
packing motif of TTF-28 are very sensitive to environmental
variation, with this sensitivity arising from the rotational
Structural comparison: As summarized in Table 2, the cen-
tral TTF core of the present TTFs adopts a variety of con-
formations, including chair, half-chair, boat, and planar con-
formations. The aryl group alignments in the tetraaryl-sub-
stituted TTFs give rise to various configurations due to the
À
rotational freedom of the aryl groups about the two C S
bonds of the sulfur bridges. The packing motifs of the pres-
ent TTFs depend on the nature of the peripheral aryl
groups and the alignment modes thereof. Moreover, when
an additional substituent is introduced onto the aryl groups
in different positions, the aryl group alignments, as well as
the molecular packing motifs, show significant differences,
as observed in TTF-2 and TTF-3, TTF-5 and TTF-6, TTF-11
À
freedom of the 2-pyridyl groups about the two C S bonds
of the sulfur bridges.
12522
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Chem. Eur. J. 2013, 19, 12517 – 12525

Aryl-Substituted Tetrathiafulvalene Derivatives
FULL PAPER
Table 2. The conformations of the central TTF cores along with the corresponding dihedral angles of the pre-
pared TTFs.[a]
the peripheral aryl groups, and
between the aryl groups and
TTF cores. In particular, TTF-
14, an achiral molecule, forms a
helical chain stack through in-
termolecular van der Waals
forces between the aryl groups
and between the aryl groups
and TTF core. The rotational
freedom of the aryl groups
Chair
Half-chair
Boat
Planar
À
about the C S bonds also
q1
q2
q
q1
q2
makes the solid-state structures
of TTFs sensitive to environ-
mental variations, allowing
them to create cavities that may
be capable of encapsulating
guest molecules of appropriate
size and symmetry, such as full-
erene.[16] Furthermore, function-
al groups attached to the pe-
ripheral aryl groups have the
potential to afford composite
materials, for example, through
coordination with transition
metals.[28] In fact, we have suc-
[8]
[8]
[8]
[8]
[8]
TTF-1
TTF-6
TTF-11
TTF-12
10.4
8.0
8.0
7.6
7.5
7.8
9.9
9.8
18.4
10.4
8.0
8.0
7.6
7.5
7.8
9.9
9.8
18.8
TTF-5
18.5
11.5
19.3
11.1
TTF-3
18.5
18.4
25.6–29.1
18.4
19.6–24.4
19.1
14.4
16.5
25.6–29.1
11.7
14.4–16.3
22.5
TTF-2
TTF-28, II[b]
TTF-38
TTF-28, I[b]
TTF-34, A–F[c]
TTF-41
TTF-14
TTF-19
TTF-20
TTF-27
TTF-33
TTF-39
TTF-15
TTF-42
TTF-46
TTF-17
TTF-28, III[b]
TTF-32
TTF-34, G[c]
[a] View along the short axis of the central C2S4 plane of the TTF skeleton; the geometries of the molecules
other than those in the main text can be found in the Supporting Information. [b] I, II, and III represent the
three crystal modifications of TTF-28. [c] A–G represent the seven different TTF-34 molecules in the crystal.
and TTF-12, and TTF-14 and TTF-15 (see the Supporting
Information). The rotational freedom of the peripheral aryl
groups makes the molecular geometry sensitive to environ-
mental variation, as observed for TTF-28, which in principle
would extend the diversity of supramolecular assembly.
Under certain conditions, these molecules have the potential
to form cavities. Cavities can be created by a single mole-
cule through rotation of the peripheral aryl groups as in
TTF-28 (modification I), TTF-41, TTF-42, and TTF-46 (see
the Supporting Information), or by the arrangement of adja-
cent molecules as in TTF-11, TTF-28 (modification III),
TTF-42, and TTF-46. Such cavities may be capable of en-
capsulating a guest molecule of appropriate size.
cessfully prepared inclusion complexes of these TTFs with
fullerenes, as well as their coordination complexes with tran-
sition metals, and these results will be submitted in due
course.
Experimental Section
General: Full synthetic details and spectroscopic data of the TTFs are
provided in the Supporting Information. All of the new compounds re-
1
ported herein have been characterized by H and 13C NMR spectroscopy,
mass spectrometry (EI, ESI, APCI, or HRMS), elemental analysis, and/
or single-crystal X-ray diffraction analysis.
UV/Vis spectra were recorded on
a Lambda 35 spectrophotometer
(Varian). Redox potentials were determined by cyclic voltammetry (CV)
on an RST 5000 electrochemical analyzer. X-ray diffraction measure-
ments were carried out on a SMART APEX II (Bruker) or SuperNova
(Agilent) diffractometer. Crystal structures were solved by direct meth-
ods using SIR2004[29a] and refined by full-matrix least-squares methods
against F2 by means of SHELXL-97.[29b] Solid-state CD spectra were
measured on a JASCO J-815 spectrometer.
Conclusion
We have synthesized 47 TTF derivatives bearing aryl groups
attached through sulfur bridges and have thoroughly investi-
gated their properties and solid-state structures. The aryl
groups exert a significant influence on the electronic proper-
ties of the resulting TTFs, as proved by the optical absorp-
tion spectra and electrochemical properties. X-ray crystallo-
graphic analysis has revealed that the molecular geometries
and packing patterns of these TTFs largely depend on the
nature of the aryl groups. The central TTF cores can adopt
various conformations, including chair, half-chair, boat, and
planar conformations. The rotational freedom of the periph-
All calculations were carried out with the Gaussian 09 suite of program-
s.[30a] For DFT calculations, we used the hybrid gradient corrected ex-
change functional of Lee, Yang, and Parr.[30b,c] A standardized 6-31G
basis set[30d] was used together with polarization (d) and (p) functions.
Acknowledgements
The authors acknowledge financial support from the National Natural
Science Foundation of China (NSFC 21003067, 21172104, and 21190034).
We are grateful to Prof. W. Xu (ICCAS, Beijing) for the measurement of
solid-state CD spectra.
À
eral aryl groups about the C S bonds allows these aryl
groups to align in multiple ways with respect to the central
TTF core, which in turn leads to a variety of packing struc-
tures determined by the intermolecular interactions between
Chem. Eur. J. 2013, 19, 12517 – 12525
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www.chemeurj.org
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Aryl-Substituted Tetrathiafulvalene Derivatives
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Received: May 13, 2013
Revised: June 11, 2013
Published online: August 5, 2013
Chem. Eur. J. 2013, 19, 12517 – 12525
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