Preparation, structures, and physical properties of tetrakis(alkylthio) tetraselenafulvalene (TTCn-TSeF, n = 1-15)

Article abstract of DOI:10.1246/bcsj.20090240

A series of tetrakis(alkylthio)tetraselenafulvalene compounds (TTC _n^-TSeF, n = 1-15) were prepared by a one-step reaction between dialkyl disulfide and tetralithiated TSeF. Molecular properties (redox potentials and optical absorptions in solution) and solid-state properties (thermal behaviors, electric conductivities, and molecular and crystal structures for n = 1 and 10) were studied. TTC_n-TSeF compounds are weak electron donor molecules and characterized by small on-site Coulomb repulsion. TTC₁-TSeF has a high-dimensional conduction network owing to the presence of highdimensional heteroatomic contacts, "Atomic-Wire Effect." The π-moieties of TTC₁₀-TSeF were fastened by the alkyl chains ("Fastener Effect") to form π-columns and there are a variety of short heteroatomic contacts resulting in two dimensional electronic structure. Electrical conductivity exhibited peculiar enhancement for n = 1 and 7 ≤ n ≤ 14 owing to the presence of high-dimensional conduction paths. These compounds may manifest high carrier mobility, and are good candidates for the field-effect transistor channel based on the advantageous features: low dark conductivity, low donor ability, on-site Coulomb repulsion energy, high-dimensional π-electron structure, and high solubility in organic solvents.

Full text of DOI:10.1246/bcsj.20090240

© 2010 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 83, No. 4, 335–344 (2010)
335
Preparation, Structures, and Physical Properties of
Tetrakis(alkylthio)tetraselenafulvalene (TTCn-TSeF, n = 1-15)
Gunzi Saito,*1,2,3 Yukihiro Yoshida,1,2 Hidenobu Murofushi,3,³ Naoko Iwasawa,3,³³
Takaaki Hiramatsu,4,5 Akihiro Otsuka,2,3,4 Hideki Yamochi,2,3,4 Kimio Isa,6 Eriko Mineo-Ota,7
Michiko Konno,7,³³³ Takehiko Mori,8,³³³³ Ken-ichi Imaeda,8,³³³³³ and Hiroo Inokuchi8,³³³³³³
1Research Institute, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502
2Division of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502
3Institute for Solid State Physics, The University of Tokyo, Roppongi, Minato-ku, Tokyo 106
4Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501
5Institute for Integrated Cell-Material Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501
6Faculty of Education and Regional Studies, University of Fukui, Bunkyo, Fukui 910-8507
7Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610
8Institute for Molecular Science, Myodaiji, Okazaki 444-8585
Received September 9, 2009; E-mail: gsaito@ccmfs.meijo-u.ac.jp
A series of tetrakis(alkylthio)tetraselenafulvalene compounds (TTCn-TSeF, n = 1-15) were prepared by a one-step
reaction between dialkyl disulfide and tetralithiated TSeF. Molecular properties (redox potentials and optical absorptions
in solution) and solid-state properties (thermal behaviors, electric conductivities, and molecular and crystal structures for
n = 1 and 10) were studied. TTCn-TSeF compounds are weak electron donor molecules and characterized by small
on-site Coulomb repulsion. TTC1-TSeF has a high-dimensional conduction network owing to the presence of high-
dimensional heteroatomic contacts, “Atomic-Wire Effect.” The ³-moieties of TTC10-TSeF were fastened by the alkyl
chains (“Fastener Effect”) to form ³-columns and there are a variety of short heteroatomic contacts resulting in two-
dimensional electronic structure. Electrical conductivity exhibited peculiar enhancement for n = 1 and 7 ¯ n ¯ 14 owing
to the presence of high-dimensional conduction paths. These compounds may manifest high carrier mobility, and are good
candidates for the field-effect transistor channel based on the advantageous features: low dark conductivity, low donor
ability, on-site Coulomb repulsion energy, high-dimensional ³-electron structure, and high solubility in organic solvents.
Some single-component organic compounds composed of
neutral closed shell molecules have evoked highly conductive
semiconductors with high carrier mobility and low solid-
state ionization potentials, by making use of the “Fastener
Effect”1-13 and/or heteroatomic contacts.14-18 In the “Fastener”
molecules consisting of a central ³-segment and peripheral
long alkyl chains, intermolecular van der Waals interactions
between the alkyl chains (paraffin part) assemble the ³-
segments to form ³-column and further enhance the intermo-
lecular interactions within the ³-column, as schematically
shown in Scheme 1.1 This results in the formation of robust
carrier paths for ³-electrons embedded in paraffin and the
compounds manifest intriguing behaviors in thermal, electron-
ic, transport, and structural properties (Fastener Effect). We
have reported these properties for the series of tetrakis(alkyl-
chalcogeno)tetrachalcogenafulvalene: TYCn-TXF, X is sulfur
(X = T); Y is sulfur (Y = T), selenium (Y = Se), or tellurium
(Y = Te); n = 1-18, Scheme 2).1-11,19-28
The n dependence of melting point (Tm) for TTCn-TTF is
seen in Figure 1.20,23 The melting point decreased drastically
with elongation of alkyl chains and showed a minimum at
n = 4-6 depending on X and Y. At higher n, the Fastener Effect
affords a gradual increase of melting point. The increased
intermolecular interactions enhanced both electric conductivity
³
Present address: New Business Development & Promotion
Center, Asahi Glass Co., LTD
³³
³³³
Present address: Department of Applied Chemistry,
Faculty of Science and Technology, Keio University
Present address: Department of Chemistry and Biochem-
istry, Graduate School of Humanities and Sciences,
Ochanomizu University
¹1
up to 10¹6 S cm (TTC10-TTF1,3 and TSeC8-TTF7) and bulk
¹1
carrier mobility up to 6-20 cm2 V¹1 s (TTCn-TTF, n = 8 and
³³³³ Present address: Department of Chemistry and Materials
Science, Tokyo Institute of Technology
³³³³³ Present address: Department of Applied Chemistry,
College of Engineering, Chubu University
10, time of flight (TOF) method).9 At low n region of TYCn-
TTF having bulkier Y, i.e., TTeC1-TTF,4 the presence of three-
dimensional heteroatomic contacts connecting the ³-moieties
¹1
³³³³³³ Present address: Japan Aerospace Exploration Agency
enhanced the electric conductivity up to 10¹5 S cm and bulk
Published on the web March 26, 2010; doi:10.1246/bcsj.20090240

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Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Tetrakis(alkylthio)tetraselenafulvalene (TTCn-TSeF)
(a)
(b)
Scheme 1. (a) Schematic view of the Fastener Effect. The van der Waals attractive intermolecular interactions between alkyl chains
(blue) enforce central ³-segments (red) to form a column with small interplanar distance. (b) Molecular packing of chair-shaped
TTC9-TTF molecules,19 where flat central C6S8 ³-segments form carrier path by the aid of van der Waals attractive force of alkyl
chains along the blue arrows.
H2n+1Cn-Y
H2n+1Cn-Y
Y-CnH2n+1
Y-CnH2n+1
H
H
H
H
X
X
X
X
X
X
X
X
X
X
X
X
HMTTF: X = sulfur
HMTSeF: X = selenium
HMTTeF: X = tellurium
TYCn-TXF
TTF: X = sulfur
TSeF: X = selenium
TTCn-TTF: X = Y = sulfur
TTCn-TSeF: X = selenium, Y = sulfur
TSeCn-TTF: X = sulfur, Y = selenium
TTeCn-TTF: X = sulfur, Y = tellurium
S
S
O
O
O
O
S
S
S
S
S
S
S
S
S
S
S
S
S
S
DBTTF
BEDT-TTF
BEDO-TTF
Scheme 2. Main molecules in text.
compounds concerning preparation, and thermal, physical, and
structural properties, and discuss in comparison with those of
TYCn-TTF compounds. We will emphasize that the increase in
size of the inner five-membered ring from TTF to TSeF has
enhanced the electronic dimensionality of the semiconductor
and thus TTCn-TSeF is anticipated to be a good candidate for
the field-effect transistor (FET) channel materials.
Experimental
Optical measurements were carried out on a Perkin-Elmer 1600
Series FT-IR spectrometer (400-4000 cm¹1, resolution 4 cm¹1) for
IR and near-IR regions, and on a Shimadzu UV-3100 spectrometer
for visible and ultraviolet (300-800 nm, UV-vis-NIR) regions. DC
conductivities of single crystals were measured between RT and
Tm by standard two-probe method using gold wires of 10 ¯m in
diameter with gold paste (Tokuriki, 8560-1A). Melting points
were determined using a Yanaco MP-500D micro melting point
apparatus. Differential scanning calorimetry (DSC) thermograms
were measured on a Shimadzu DSC-60 instrument equipped with
nitrogen cryostatic cooling. The samples were heated up to
150 °C for TTC1-TSeF and 100 °C for TTC10-TSeF (1st heating
in Figure 3), and then cooled down to ¹120 °C at a rate of
¹25 °C min¹1. After standing for 10 min, they were heated at a
rate of 10 °C min¹1 (2nd heating in Figure 3). While crystallization
(Tc), solid-solid transition (Ts), and Tm were taken as onset of peaks,
glass transition temperature (Tg) was taken as an onset of a heat
Figure 1. Melting points of TTCn-TSeF are compared with
those of TTCn-TTF.20,23 Minimum Tm’s are 24.6 °C at
n = 4 for TTCn-TTF and 22.9 °C at n = 5 for TTCn-TSeF.
¹1
carrier mobility up to 30 cm2 V¹1 s (®h = 29 and ®e = 19
cm2 V¹1 s¹1 for TTeC1-TTF).4 Atomic-Wire Effect is a concept
to represent this kind of enhancement of three-dimensional
intermolecular interactions by heteroatomic contacts.4,29 Here
we show an extension of our work to a series of TTCn-TSeF

G. Saito et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
337
H
H
H
LiS
LiS
SLi
SLi
H3CS
H3CS
SCH3
SCH3
Se
Se
Se
Se
Se
Se
Se
Se
Se
Se
Se
Se
(i-Pr)2NLi
S
MeI
(1)
H
TTC1-TSeF
RBr
(2)
(3)
S + NaOH
RS-SR (R = CnH2n+1)
EtOH
H
H
H2n+1CnS
SCnH2n+1
SCnH2n+1
Se
Se
Se
Se
Se
Se
Se
(i-Pr)2NLi
RS-SR
Se
H
H
H2n+1CnS
TTCn-TSeF
Scheme 3. Synthetic procedures of (1) TTC1-TSeF by a two-step method, (2) dialkyl disulfides, and (3) TTCn-TSeF by a one-step
method.
capacity change. The temperature was calibrated by water and
indium. Redox potentials were measured with supporting electro-
lyte of 0.1 M tetrabutylammonium tetrafluoroborate ((TBA)BF4) in
1,2-dichloroethane using Pt electrode vs. saturated calomel elec-
trode (SCE) at 22 °C. 1H NMR measurements were conducted on a
JEOL JNM-PMX60SI spectrometer operating at 60 MHz. The mass
spectra were obtained with a JEOL-O1SG-2 double focusing mass
spectrometer. Elemental analyses (C, H, N, S, Se, and halogen)
were carried out by the Microanalytical Laboratory, Division of
Chemistry, Graduate School of Science, The University of Tokyo.
X-ray diffraction data for TTCn-TSeF (n = 1 and 10) were
collected on a CCD diffractometer (Bruker SMART APEX II) with
graphite monochromated Mo K¡ radiation at room temperature
(RT). The absorption correction was carried out using the program
SADABS30 in Bruker APEX2 software by a numerical method
taking the crystal shape into consideration. The crystal structures
were solved by a direct method of SHELXS31 and refined by a full
matrix least-squares method of F2 by means of SHELXL.32 The
positional parameters of hydrogen atoms were calculated under a
fixed C-H bond length of 0.96 ¡ for methyl groups and 0.97 ¡ for
methylene groups with sp3 configuration of the bonding carbon
atoms. Crystallographic data have been deposited with Cambridge
Crystallographic Data Centre: Deposition numbers CCDC-746300
for TTC1-TSeF and CCDC-746301 for TTC10-TSeF. Copies of the
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge, CB2 1EZ, U.K.; Fax:
+44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
hampered by the formation of undesired and intractable by-
products. On the other hand, the direct and one-step introduc-
tion by dialkyl disulfide (Procedure 3 in Scheme 3) profoundly
improved the reaction and afforded TTCn-TSeF (n ¯ 15,
Supporting Information S1), where several dialkyl disulfides
(RSSR, R = CnH2n+1, n = 1-5, 7, and 10) were purchased and
other disulfides were synthesized (Procedure 2 in Scheme 3,
Supporting Information S2).35 The synthesized materials after
purification were characterized by elemental analysis, and
NMR, UV-vis, and mass spectra.
For TTC12-TSeF, elements except S and N are far from the
calculated values (Found: C, 53.62; H, 8.11; N, 0.00; S, 10.70;
Se, 27.81%. Calcd: C, 54.34; H, 8.45; N, 0.00; S, 10.75; Se,
26.46%) indicating the material is not purified enough and the
data for TTC12-TSeF in the text may include some uncertainty.
The same feature was seen for n = 15; the elemental analysis
indicates that the product has an excess of selenium (Found: C,
57.97; H, 8.96; N, 0.00; S, 9.44; Se, 24.00%. Calcd: C, 58.21;
H, 9.18; N, 0.00; S, 9.42; Se, 23.19%). The color, shape, yield,
and Tm of the TTCn-TSeF (n = 1-15) are summarized in
Table 1.
For n = 16-18 the products contained almost no TSeF
skeleton as indicated by the extremely low Se contents in the
elemental analysis (Found: less than 4%, Calcd: more than 20%,
Table S1). We will not discuss the compounds for n ² 16.
Molecular Properties. Redox Potentials: As for the
ionization potentials of the isolated TYCn-TTF molecules,
ultraviolet photoelectron spectroscopy in gas phase2,5 and
redox potentials in solution21,22,36 have been so far elucidated
and the latter is much conventional though the data includes
ambiguity caused by the solvation term. The first and second
The intermolecular overlap integrals (S) were calculated by
means of extended Hückel tight binding method with single-¦
parameters33 on the basis of the crystal structures. The 3d-orbitals
of the sulfur and selenium atoms were included in the calculation.
redox potentials (E1 and E21/2) and the difference between
1/2
Results and Discussion
them (¦E), which is a measure of the on-site Coulomb
repulsive energy of a molecule, of TTCn-TSeF are summarized
in Table 1. Similar to the series of TYCn-TTF com-
pounds,21,22,36 the redox data for TTCn-TSeF are insensitive
Synthesis. Among the TYCn-TSeF series, TSeC1-TSeF had
been synthesized by the electrochemical reduction of CSe2,
however the synthetic procedure is tedious with poor yield34
and cannot be applied to a series of TYCn-TSeF. In the previous
papers,22,28 we have noticed that the introduction of outer
methylthio groups to tetralithiated TSeF, which was prepared
by lithiation with lithium diisopropylamide for 1-2 h at
0 °C, by a two-step method (Procedure 1 in Scheme 3) was
to the length of the alkyl chains; E11/2 = 0.79 « 0.01 V, E2
=
1/2
1.07 « 0.02 V, ¦E = 0.28 « 0.02 V (Figure 2). It has been
known that the replacement of chalcogen atoms X in the TXF
skeleton in the order from S to Se or Te stabilizes the HOMO
level and gives rise to the increase of E11/2, that corresponds to

338
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Table 1. Characteristics of TTCn-TSeF
Tetrakis(alkylthio)tetraselenafulvalene (TTCn-TSeF)
Redox potentialc)
n
Color, shape
Yielda)/%
Tmb)/°C
E11/2/V
E21/2/V
¦E/V
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
orange, needle
purple, thin plate
red, plate
red, needle
red, needle
84.2
71.0
74.6
75.7
32.5
41.7
74.2
33.2
54.8
50.1
65.1
®
119.0-119.7
86.5-87.5
39.7-40.2
34.2-35.0
22.9
30.7-31.6
37.2-37.8
46.5-47.5
55.7-56.5
64.0-65.0
68.3-69.2
74.2-75.2
79.5-80.2
83.5-84.2
87.0-87.8
+0.78
+0.79
+0.79
+0.78
+0.78
+0.78
+0.78
+0.78
+0.78
+0.79
+0.78
+0.78
+0.80
+0.80
+0.80
+1.07
+1.08
+1.08
+1.05
+1.06
+1.07
+1.08
+1.07
+1.05
+1.07
+1.05
+1.05
+1.06
+1.06
+1.06
0.29
0.29
0.29
0.27
0.28
0.29
0.30
0.29
0.27
0.28
0.27
0.27
0.26
0.26
0.26
red, needle
red brown, needle
red brown, plate
red brown, thin plate
red brown, plate
red brown, thin plate
red brown, powder
brownish green, powder
brownish green, powder
brown, powder
45.2
58.3
®
a) ®: The yield of pure product could not be determined (see text). b) Tm (TSeF) = 135 °C. c) 0.1 M (TBA)BF4
in 1,2-dichloroethane, Pt, vs. SCE, 22 °C.
the decrease of donor ability.37 Accordingly, the E1 values
1/2
of TTCn-TSeF are higher by 0.15 V than those of TTCn-TTF
(0.64 V). The donor ability of TTCn-TSeF is a little weaker
than that of weak TTF analog DBTTF (E11/2 = 0.74 V). The
addition of the four alkylthio groups to TSeF skeleton changed
the E11/2 value from 0.59 V (TSeF) to 0.79 V (TTCn-TSeF) that
corresponds to the weakened donor ability by 0.20 V.
The most interesting point is that ¦E (0.28 V) of TTCn-TSeF
is smaller than those of TYCn-TTF (0.30-0.40 V) and is
comparable to that of HMTTeF (0.28 V), indicating very weak
on-site Coulomb repulsion. This feature stems from multiple
reasons. The C6X4 ³-moiety expands the own size in the
order of S ¼ Se ¼ Te, which causes a decrease of ¦E in
TSeF compounds compared with those of TTF compounds.
Furthermore, the increased atomic electronegativity of outer
chalcogen atom Y, which increases in the order of Te(2.1) ¼
Se(2.4) ¼ S(2.5), results in the decreased ³-electron density
on the central C6X4 moiety giving rise to a decrease of the
on-site Coulomb repulsive energy in the order of TTeCn-
TXF ¼ TSeCn-TXF ¼ TTCn-TXF as well as the decrease of
the donor ability in the same order.
Absorption Spectra: The absorption spectra of TTCn-
TSeF in chloroform are composed of three absorption bands
-1 = 311-314 nm (log ¾ = 4.19-4.23), -2 = 376-383 nm
(log ¾ = 3.55-3.58), and -3 = 477-507 nm (log ¾ = 2.28-
2.81) (see Supporting Information, Table S2), similar to that
observed for TSeF (293 (4.10), 368 (3.21), and 486 (2.12)).
No obvious dependence on the length of the alkyl chains
was observed concerning the absorption peaks and extinction
coefficients. The absorption band -3 originates from the
HOMO-LUMO transition and is known to appear very
weakly for TXF compounds.38 This band extends to longer
wavelength for TTCn-TSeF compared to those of conventional
TTF compounds (433-459 nm for DBTTF, BEDT-TTF, and
TTF in chloroform, and 483 nm for TTC10-TTF in hexane) and
is close to that of BEDO-TTF (518 nm). The threshold of the
absorption band is around 650 nm (1.9 eV).
Figure 2. Redox potentials (0.1 M (TBA)BF4 in 1,2-
dichloroethane, Pt, vs. SCE, 22 °C) of TTCn-TSeF are
compared with those of TTF and its analogs (see
Supporting Information, Table S3). Red circles and
arrows: E11/2, blue circles and arrows: E2
.
1/2
Solid-State Properties. Melting Point: Similarly to those
observed in the series of TYCn-TTF compounds,20-24 the
melting point (Table 1) was decreased drastically by the
addition of alkylchalcogeno groups to TSeF (Tm = 135 °C).
The Tm shows a minimum at n = 5 (Tm = 22.9 °C) and

G. Saito et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
339
(a)
(b)
1st heating
1st heating
Ts-s
Tm
Tc1
Tc2
Tm
Tg
2nd heating
2nd heating
Tm
100 150
Tm
50
-150 -100 -50
0
50
-150
-100
-50
0
100
T / °C
T / °C
Figure 3. DSC charts for (a) TTC1-TSeF and (b) TTC10-TSeF.
increases gradually for n ² 5 suggesting that the Fastener
Effect operates in this n region. It is interesting to note that
TTCn-TSeF (n = 5 and 6) shows Tm below 32 °C similarly to
TSeCn-TTF (n = 5 and 6): they are liquid electron donors near
RT with molecular weight >800. As is compared with that of
TTCn-TTF in Figure 1, the even-odd effect is not so obvious
for TTCn-TSeF.
The TTCn-TTF compounds with small n (¯7) were
characterized by the presence of the glassy state23 where the
glass temperatures very roughly follow the so called “2/3 law
(Tg/Tm µ 2/3).”39 The glassy state was also observed for
TSeCn-TTF with n ¯ 7, though Tg was not able to be defined
due to the gradual transition.7 On the other hand, the TYCn-
TTF (Y = T and Se) compounds with long alkyl chains
exhibited solid-solid transition near Tm (n ² 8 for Y = T,
n = 6 and ²9 for Y = Se)7,23 and, in general, low-temperature
phase (Phase I) exhibited higher conductivity than that of
the high-temperature phase (Phase II).7,9-11 For example,
Phase I of TTC8-TTF has lower RT resistivity (µRT) and higher
TOF mobility (®TOF) (µRT = 1.2 © 105 ³ cm, ®TOF = 6.4
cm2 V¹1 s¹1) in comparison with Phase II (µRT = 7.0 © 107
³ cm, ®TOF = 0.77 cm2 V¹1 s¹1).9,10 These two phases have
very similar intra-column overlap patterns (as depicted in
single crystals, the table includes the data on compressed pellet
samples. TTC5-TSeF was not measured since the compound
easily liquefied.
It is interesting to note that the conductivity of TTCn-TSeF
with large n (107-108 ³ cm on a single crystal for n = 7, 8, and
10) was considerably low in comparison with the TYCn-TTF
series; 105-107 ³ cm for TTCn-TTF, 106 ³ cm for TSeCn-TTF
and TTeCn-TTF.3,4,7
For the series of TYCn-TTF (Y = T and Se), the conduc-
tivity enhancement by taking the most resistive one as a
standard is a good indicator to estimate the extra intermolecular
interactions (right two columns in Table 2), though strictly
speaking the comparison should be done concerning the
anisotropic conducting behaviors measured on single crystals.
For TTCn-TTF, the conductivity enhancement for n ² 4 clearly
indicates the presence of the Fastener Effect. The most resistive
compound among TTCn-TSeF measured is TTC4-TSeF on the
compaction pellet (µRT = 1.0 © 1014 ³ cm). The most conduc-
tive one (TTC10-TSeF µRT = 1.5 © 107 ³ cm on single crystal)
reaches ca. 6.7 © 106 times the conductivity of n = 4. TTCn-
TSeF compounds with n = 7 and 8 on single crystals and
n = 9, 11, and 13 on compressed pellets also exhibit large
enhancement of 4.8 © 104-7.7 © 105 suggesting the Fastener
Effect is active for n ² 7. The significant decrease of activation
energy for n = 7, 8, and 10 compared with those for n = 1
and 3 is in accordance with the manifestation of the Fastener
Effect. These compounds are demonstrated by yellow shadow
in Table 2.
As for TTC1-TSeF, the large enhancement (7.7 © 104) is
ascribed not to the Fastener Effect but to a formation of
network of atomic contacts (Atomic-Wire Effect) in the crystal
(vide infra), like those of TSeC1-TTF (Phase I)11 and TTeC1-
TTF.4 Those are indicated by blue shadow in Table 2.
Molecular and Crystal Structures: Although the structure
assuming the space group P21/n had been reported for TTC1-
TSeF previously,28 the better quality of diffraction data
collected on a CCD diffractometer proved that the previous
structure was incorrect. The following subsection concerns the
correct structure with the space gorup P21/c. The crystal data
for n = 1 and 10 are summarized in Table 3 and Supporting
Information.
Figure 6c for TTC10-TSeF) but a slightly different intra-
¹3
column overlap integrals: S = ¹4.89 © 10
(I-Phase) and
¹3
¹3.66 © 10 (II-Phase). It is important to note that only a
1.3-fold increase in calculated overlap integrals corresponds
to the enhancement both in carrier mobility by one order of
magnitude and in electric conductivity by two orders of
magnitude.
Figure 3 shows the DSC chart of TTCn-TSeF (n = 1 and
10). In accordance with the thermal properties for TYCn-TTF
compounds,22,27 a glassy state was observed for TTC1-TSeF
(Tg = ¹15.6 °C) but not for TTC10-TSeF, while a solid-solid
transition was observed for TTC10-TSeF (Ts = 58.2 °C) but not
for TTC1-TSeF. The ratio Tg/Tm of TTC1-TSeF is nearly 2/3.
TTC1-TSeF also exhibited two crystallization transitions (Tc =
15.3 and 78 °C) similarly to those for TTCn-TTF (n ¯ 7).23
Resistivity: The RT resistivity and activation energy for
conduction (¾a) of TTCn-TSeF without heat treatment are
summarized in Table 2. Since not all TTCn-TSeF afforded

340
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Tetrakis(alkylthio)tetraselenafulvalene (TTCn-TSeF)
Table 2. Semiconductive Parameters and Conductivity Enhancement of TTCn-TSeF Compared with Those of TTCn-
TTF and TSeCn-TTF Compoundsa),b)
TTCn-TSeF
TTCn-TTF
TSeCn-TTF
n
µ
RT/³ cm
¾a/eV
µRT(n = 4)/µRT
7.7 © 104
µRT(n = 1)/µRT
µRT(n = 4)/µRT
2.2 © 105 (Phase I)
3.0 © 102 (Phase II)
6.7 © 10
1
1.3 © 109
0.60
1 (Phase I)
2
3
4
5
6
1.0 © 1012 d)
2.6 © 1013
1.0 © 1014 d)
®
3.6 © 1012 d)
®
0.86
®
1.0 © 102
2
4
1
®
3.0 © 10
3.3 © 102
4.7 © 103
1
d)
®
®
4.5 © 102
6.3 © 10
1.7 © 105
2.8 © 10
7.6 © 102
1.2 © 103 (Phase I)
7.6 © 102 (Phase II)
2.4 © 104 (Phase I)
4.1 © 102 (Phase II)
8.3 © 103 (Phase I)
5.8 © 102 (Phase II)
7.8 © 104
7
8
9
1.3 © 108
0.18
0.20
®
7.7 © 105
5.9 © 105
5.9 © 104
2.3 © 104
2.9 © 105
2.7 © 105 d)
1.7 © 108
1.7 © 109 d)
10
11
12c)
13
14
15
1.5 © 107
2.1 © 109 d)
5.9 © 1010 d)
1.7 © 109 d)
5.3 © 1010 d)
®
0.17
®
6.7 © 106
4.8 © 104
1.7 © 103
5.9 © 104
1.9 © 103
®
2.2 © 104 d)
2.6 © 104 d)
5.9 © 104 d)
3.9 © 104 d)
3.4 © 104 d)
6.7 © 104 d)
5.2 © 104
®
®
5.5 © 102 d)
1.3 © 102 d)
®
®
3.7 © 102 d)
1.0 © 104 d)
a) The yellow and blue shadows indicate the data on which Fastener Effect and Atomic-Wire Effect are regarded
effective, respectively. b) ®: Not measured. c) Data may be not intrinsic since the sample is impure. d) Compaction
pellet sample.
Table 3. Crystallographic Data of TTC1-TSeF and TTC10-
C5
C9
TSeF
Se3
Se1
S3
S1
TTC1-TSeF
TTC10-TSeF
C7
C8
C3
C4
Formula
Formula weight
Crystal system
Space group
Crystal size/mm3
a/¡
b/¡
c/¡
¡/°
¢/°
C10H12S4Se4
576.28
C46H84S4Se4
1081.25
C2
C1
Monoclinic
P21/c
0.58 © 0.50 © 0.06 0.48 © 0.29 © 0.21
9.1110(9)
8.0115(8)
24.092(2)
90
95.135(1)
90
1751.5(3)
4
2.185
Mo K¡
88.36
Triclinic
S2
S4
ꢀ
P1
Se4
Se2
C10
C6
7.9573(6)
33.411(3)
5.1050(4)
93.111(1)
102.373(1)
88.452(1)
1323.6(2)
1
£/°
V/¡3
24.2°
23.2°
Z
Figure 4. Molecular structure of TTC1-TSeF showing the
atom labeling scheme. Hydrogen atoms are omitted for
clarity.
¹3
dcalcd/g cm
1.356
Mo K¡
29.58
Radiation
®(Mo K¡)/cm
¹1
the ³-segment is deformed like a boat and four alkyl chains
stretch in the same side. The crystal structure of TTC1-TSeF is
isomorphous with Phase I of TTC1-TTF.40 The bending angles
of 23.2 and 24.2° are similar to those of TTC1-TTF (Phase I,
19.3 and 23.7°). One molecule is crystallographically unique.
The two molecules A and B arrange almost orthogonally
(Figure 5a) with the distance between the centers of them
5.33 ¡ (5.23 ¡ for TTC1-TTF). Se atoms in the TSeF skeleton
form short Se£Se atomic contacts less than the sum of the
van der Waals radii (3.72-3.79 ¡ vs. van der Waals sum of
3.80 ¡42) and a little longer Se£C atomic contacts (3.62-3.67 ¡
vs. 3.60 ¡) as represented by dotted lines in Figure 5b. Outer
sulfur atoms contribute to the formation of S£S atomic contacts
Independent obsd
reflections
Reflections with
I > 2·(I)
4329
3334
6341
5170
Refined parameters 168
247
wR2 (for all data)
Rgt (for I > 2·(I))
GOF
0.0874
0.0363
1.027
0.0804
0.0263
1.109
TTC1-TSeF; Similarly to the TYCn-TTF molecules with
small n (e.g., TTCn-TTF: n = 1 (Phase I),40 2,41 3;25 TSeC2-
TTF6), TTC1-TSeF forms a boat shape (Figure 4) in which

G. Saito et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
341
(a)
(c)
a
A
a
b
B'
A
p1
p2
p1
b ~ 0.5
b ~ 0
p1
p1
B
b
b
B
A'
p2
c
0
0
b
p2
p2
b
(b)
a
A
b ~ -0.5
b ~ 0
c
0
B
Figure 5. Crystal structures of TTC1-TSeF, in which methyl groups are omitted for clarity. (a) Viewed along the c axis with scheme
of the intermolecular overlap integrals. b = 1.8 © 10¹3, p1 = 16.0 © 10¹3, p2 = ¹0.66 © 10¹3. (b) Intermolecular short atomic
contacts between A and B molecules. Thick and thin dotted lines indicate the Se£Se and Se£C contacts, respectively. (c) Viewed
along the b axis, in which only molecules located at 0 < b < 0.5 (upper figure) and ¹0.5 < b < 0 (lower figure) are depicted. Gray
and black molecules are located at around b = ¹0.5 and 0.0 in the upper figure, and b = 0.0 and 0.5 in the lower figure,
respectively, and molecules A¤ and B¤ are related to molecules A and B, respectively, by an inversion center. Thick and thin dotted
lines indicate the S£S contacts with the lengths of <3.6 and <3.7 ¡, respectively. Intermolecular overlap integrals along the
¹3
molecular long axis are: SAA¤ = 2.0 © 10¹3, SAB¤ = ¹0.70 © 10¹3, SBA¤ = ¹0.24 © 10
.
(3.53-3.67 ¡ vs. 3.60 ¡) along the molecular long axis (dotted
lines in Figure 5c). Accordingly, as long as atomic contacts
concern, the TTC1-TSeF crystal has quasi-three-dimensional
character.
TTC10-TSeF; With large n for TYCn-TXF, the ³-segment
becomes flat and two alkyl chains on one side stretch
oppositely to those on the other, to form chair-like shape with
dihedral angle between ³-segment and alkyl chains nearly
perpendicular (chair I form: TTCn-TTF (n = 4-6), TTeC8-TTF)
or ca. 50° (chair II form: Scheme 1b, TTCn-TTF (n = 7-11)).43
The molecular structure of TTC10-TSeF (Figure 6a) exhibits
chair II form with dihedral angle between C6Se4S4 plane and
outer alkyl chains of 50°. TTC10-TSeF has very similar lattice
parameters to those of TTC10-TTF41 and they are isostructural
to each other. The ³-segments of TTC10-TSeF molecules show
face-to-face stacking along the c axis with interplanar distance
of 3.55 ¡, which is longer than that in TTC10-TTF by 0.06 ¡
(3.49 ¡) (Figure 6b). There are heteroatomic contacts not only
within the column (Se£Se 3.79 ¡) but also between columns
(Se£Se 3.67 ¡, Se£S 3.69 ¡) less than the sum of the van der
Waals radii, as seen in Figure 6c. In the case of TTCn-TTF
(n = 7-11) compounds, on the other hand, short S£S contact
(3.54-3.60 ¡) was only observed along the intra-column
direction suggesting strong one-dimensionality. Therefore,
from the structural viewpoint, TTC10-TSeF crystals have much
higher dimensionality than TTCn-TTF ones.
The enhanced electric conductivity of TTC1-TSeF (1.3 ©
109 ³ cm, ¾a = 0.60 eV) in Table 2 suggests the formation of a
network of the heteroatomic contacts as conduction paths in
the crystal, though the enhancement is not so obvious in
comparison with those for TTeC1-TTF (µRT = 6.9 © 104 ³ cm,
¾a = 0.25 eV)3,4 and TSeC1-TTF (Phase I, 1.0 © 106 ³ cm,
0.26 eV).7,8,11,28a In the case of TTeC1-TTF, the molecular
structure and packing pattern (Supporting Information S3) are
considerably different from those of TTC1-TSeF. Namely two
methyl groups residing in diagonal positions are directed up
and down from the flat plane consisting of central tetrathio-TTF
moiety and two residual methyl groups, and the flat planes are
arranged in parallel to form a ³-column with rather large
interplanar distance of 3.76 ¡.4 The most characteristic feature
is that the neighboring ³-columns are connected by robust and
three-dimensional Te£Te atomic contacts (3.64 ¡ vs. 4.12 ¡)
affording high conductivity and ®TOF (Atomic-Wire Effect).
In spite of the presence of a network of the short atomic
contacts in TTC1-TSeF, the conductivity enhancement is rather
small and activation energy for conduction is considerably
large. These features may be ascribed to both non-parallel
packing of the ³-moieties and not much shortened intermo-
lecular heteroatomic contacts due to the small outer chalcogen
atoms; sulfur.
Molecular Packing. The interchain separation between the
alkyl groups is a measure of the compactness of the molecular
packing. The alkyl chains in hexatriacontane crystal form close
packing in a trans zig-zag conformation with interchain C£C
distances of 4.14-4.20 ¡.44,45 There are many short C£C
distances close to or less than those in hexatriacontane within a

342
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Tetrakis(alkylthio)tetraselenafulvalene (TTCn-TSeF)
(a)
(c)
(d)
(b)
c
c
q
a
p
c
a
p
q
0
b
Figure 6. (a) Molecular structure and (b) crystal structure viewed along the a axis of TTC10-TSeF. (c) Overlap pattern and side-by-
¹3
side short Se£Se or Se£S contacts. (d) Intermolecular overlap integrals in a TTC10-TSeF layer. a = ¹3.4 © 10¹3, c = 1.6 © 10
p = ¹1.0 © 10¹3, q = 0.3 © 10¹3. In (c) and (d), alkyl chains are omitted for clarity.
,
S
SR
SR
RS
RS
S
S
S
S
S
S
S
S
R
R
S
Benzene-fused bis(TTF)
R = CnH2n+1; n = 4,6,8
2,7-Dialkyl[1]benzothieno-
[3,2-b]benzothiophene
(Cn-BTBT)
R = CnH2n+1; n = 5-14
Scheme 4. Main molecules in this section.
molecule (Table 4A, arrow (i) in Figure 7) and between
columns along the side-by-side direction (Table 4B, arrow
(ii) in Figure 7), to connect the alkyl chains along the (a + c)
direction which corresponds to the side-by-side direction of the
central C6X4Y4 segments. There are several intermolecular
C£C distances less than 4.40 ¡ within a column (Table 4C,
arrows (iv), (v), and (vi) in Figure 7) which correspond to the
van der Waals attractive ones depicted by blue arrows in
Scheme 1b and are effective to fasten the ³-segments. There
are no short alkyl chain contacts between columns along the
oblique direction (arrow (iii) in Figure 7). The short C£C
distances (4.02 and 4.24 ¡) were also found along the b-
direction. Therefore the alkyl chains of TTC10-TSeF form
pseudo-three-dimensional close packing in the crystal. The
structural analysis of TTC10-TSeF suggests that the strong
tendency of the alkyl chains to form close packing is one of the
main reasons for Fastener Molecules TYCn-TXF to make the
³-segments squeezed and self-assembled resulting in the
segregated columns of ³-segments with proximate contact in
an insulating media.
Perspectives of TTCn-TSeF as FET Channel Materials.
The Fastener Effect for TTCn-TTF enhances bulk carrier
¹1
mobility (®TOF, single crystal) up to 6-20 cm2 V¹1 s (n = 8
and 10).9 However, the field-effect mobility (®FET) of thin-film
FET was found to be 10¹5-10¹6 cm2 V¹1 s¹1 for n = 8, 14, and
18.46 The most significant difference between observed ®TOF
and ®FET is associated with both differences in the way of
carrier injection and sample crystallinity. In the form of thin-
films of TTCn-TTF, the carrier could be dissipated considerably
after injection since the one-dimensional conduction paths are
more or less deteriorated by the insulating paraffin moieties.
Such a disadvantage might have manifested the low ®FET of
¹1
10¹2-10¹4 cm2 V¹1 s
on the solution processed thin-film
FETs of benzene-fused bis(TTF) derivatives (Scheme 4) hav-
ing one-dimensional stacking columns.47 On the other hand,
the two-dimensional feature has improved ®FET for 2,7-
ditridecyl[1]benzothieno[3,2-b]benzothiophene (C13-BTBT) as
¹1 48
affording moderately high ®FET of 1.2-2.8 cm2 V¹1 s
.
The calculated overlap integrals for TTC1-TSeF and TTC10-
TSeF are listed in Figures 5a and 6d. The TTC1-TSeF crystal

G. Saito et al.
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
343
Table 4. C£C Atomic Distances of TTC10-TSeF
Distances/¡
C
B
(iii)
Distances/¡
(A) Intramolecular C£C distances shorter than 4.30 ¡
(arrow (i) in Figure 7)
(iv)
(v)
C6A-C14A
C7A-C14A
C7A-C15A
C8A-C15A
C8A-C16A
C9A-C16A
C9A-C17A
C10A-C17A
C10A-C18A
4.075(3)
4.153(3)
4.218(3)
4.191(3)
4.133(3)
4.212(3)
4.189(3)
4.236(3)
4.153(4)
C11A-C18A
C11A-C19A
C12A-C19A
C12A-C20A
C12A-C21A
C13A-C20A
C13A-C21A
C13A-C22A
4.247(3)
4.184(4)
4.259(4)
4.150(5)
4.268(5)
4.262(5)
4.178(5)
4.273(6)
(vi)
(ii)
(i)
A
c
(B) Inter-column C£C distances shorter than 4.30 ¡
(arrow (ii) in Figure 7)
a
0
Figure 7. Trans zig-zag conformation of alkyl chains in
TTC10-TSeF crystal, for which only half of the molecules
are depicted. For arrows, see text.
C4A-C14C
C5A-C14C
C5A-C15C
C6A-C15C
C6A-C16C
C7A-C16C
C7A-C17C
C8A-C17C
4.051(3)
4.149(3)
4.112(3)
4.118(3)
4.202(3)
4.168(3)
4.146(3)
4.168(3)
C9A-C18C
C9A-C19C
C10A-C19C
C11A-C20C
C11A-C21C
C12A-C21C
C13A-C22C
4.197(3)
4.197(4)
4.202(4)
4.216(4)
4.264(4)
4.249(5)
4.249(6)
Summary
A series of TTCn-TSeF (n = 1-15) were successfully
prepared by a one-step reaction between dialkyl disulfide and
tetralithiated TSeF. Redox potentials in 1,2-dichloroethane and
optical absorption in chloroform are independent of the length
of alkyl chains. TTCn-TSeF compounds are weak electron
donor molecules and characterized by small on-site Coulomb
repulsion. The melting points exhibited a rapid decrease at the
initial n stage, showing minimum of 22.9 °C (n = 5) then a
gradual increase at large n likely those of TYCn-TTF (Y = T,
Se, and Te) compounds. The small n compound, TTC1-TSeF
exhibited a glassy state and two crystallization temperatures
before melting similar to those of TTCn-TTF (n = 2, 4, 5,
and 7). For large n compound, TTC10-TSeF showed a solid-
solid transition just below melting like those of TYCn-TTF
(Y = T and Se) compounds with long alkyl chains. Electrical
conductivity exhibited peculiar enhancement for n = 1 and
7 ¯ n ¯ 14 owing to the presence of high-dimensional hetero-
atomic contacts among the ³-moieties by Atomic-Wire Effect
and Fastener Effect, respectively. TTC1-TSeF has a pseudo-
three-dimensional conduction network with RT resistivity of
1.3 © 109 ³ cm. The ³-moieties of TTC10-TSeF were fastened
to form ³-columns with interplanar distance of 3.55 ¡ and
there are a variety of short heteroatomic contacts resulting in
two-dimensional electronic structure showing resistivity of
1.5 © 107 ³ cm while the TYCn-TTF derivatives showed
only quasi-one-dimensional nature. The structural analysis of
TTC10-TSeF suggests that the strong tendency of the alkyl
chains to form close packing is one of the main reasons
for Fastener Molecules TYCn-TXF to make the ³-segments
squeezed and self-assembled resulting in the segregated
columns of the ³-segments with proximate contacts. These
compounds having Atomic-Wire Effect or Fastener Effect may
manifest high carrier mobility, and are good candidates based
on the advantageous features: low dark conductivity, low donor
ability, and on-site Coulomb repulsion energy, high-dimen-
sional ³-electron structure, and high solubility in organic
solvents.
(C) Intra-column C£C distances
(arrows (iv), (v), and (vi) in Figure 7)
Arrow (iv)
C5A-C6B
C7A-C8B
C9A-C10B
Arrow (vi)
4.274(3)
4.344(3)
4.400(4)
C16A-C17B
C18A-C19B
C20A-C21B
C22A-C23B
4.418(4)
4.413(4)
4.417(4)
4.384(7)
Arrow (v)
C7A-C15B
4.383(3)
has a pseudo-three-dimensional conduction network through
¹2
the overlap integrals of p1 = 1.6 © 10 (== b), SAA¤ = 2.0 ©
¹3
¹4
10 (bc plane), and p2 = ¹6.6 © 10 (== a), though the con-
duction path along the a axis is rather feeble. While the TTC10-
TSeF crystal has a two-dimensional conduction path within the
¹3
¹3
ac plane with c = 1.6 © 10 and a = ¹3.4 © 10 and the
conduction planes are separated by thick alkyl chains along the
b axis.
Summarizing above, TTCn-TSeF (7 ¯ n ¯ 14) showing
Fastener Effect is a better candidate for FET channel than
TTCn-TTF analogs, because of the higher electronic dimen-
sionality, lower on-site Coulomb repulsion which is a favorable
factor for carrier conduction, lower dark conductivity to realize
high off-to-on resistivity ratio, and lower donor ability to avoid
the formation of charge-transfer adduct with oxygen, than those
of the latter compounds, along with high solubility in conven-
tional organic solvents (hexane, benzene, ethanol, etc.). TTC1-
TSeF makes also it an attractive candidate for FET channel;
namely, low dark conductivity, low donor ability, and on-site
Coulomb repulsion energy, pseudo-three-dimensional network
of heteroatomic contacts, and high solubility in organic
solvents.

344
Bull. Chem. Soc. Jpn. Vol. 83, No. 4 (2010)
Tetrakis(alkylthio)tetraselenafulvalene (TTCn-TSeF)
Iwasawa, H. Yamochi, G. Saito, Mol. Cryst. Liq. Cryst. 1991, 196,
167.
Supporting Information
25 C. Nakano, T. Mori, K. Imaeda, N. Yasuoka, Y. Maruyama,
H. Inokuchi, N. Iwasawa, G. Saito, Bull. Chem. Soc. Jpn. 1992, 65,
1878.
26 Z. Shi, K. Imaeda, C. Nakano, H. Inokuchi, T. Enoki, G.
Saito, Mol. Cryst. Liq. Cryst. 1995, 268, 161.
Detailed characterizations of dialkyl disulfides, elemental
analysis, and NMR and UV-vis data of TTCn-TSeF, crystallo-
graphic data of TTC1-TSeF and TTC10-TSeF, and molecular and
crystal structures of TTeC1-TTF. This material is available free of
charge on the Web at: http://www.csj.jp/journals/bcsj/.
27 T. Tanaka, T. Atake, Z. Shi, C. Nakano, T. Enoki, G. Saito,
H. Inokuchi, J. Phys. Chem. Solids 1997, 58, 295.
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Y. Higuchi, N. Yasuoka, Synth. Met. 1988, 27, 463.
29 R. Friend, Nature 1987, 329, 14.
30 G. M. Sheldrick, SADABS, Program for Siemens Area
Detector Absorption Correction, University of Göttingen,
Germany, 1996.
31 G. M. Sheldrick, SHELXS-97, Program for the Solution of
Crystal Structures, University of Göttingen, Germany, 1997.
32 G. M. Sheldrick, SHELXL-97, Program for the Refinement
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33 R. Ramakumar, Y. Tanaka, K. Yamaji, Phys. Rev. B 1997,
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ꢀ
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