Conformation and packing of odd-numbered α-oligothiophenes in single crystals

Article abstract of DOI:10.1246/bcsj.76.1561

X-ray single crystal analyses revealed the molecular geometry and molecular packing of odd-numbered α-oligothiophenes (septithiophene, quinquethiophene and terthiophene) in single crystals prepared by sublimation. Septithiophene crystallizes into triclinic, which is in contrast to the monoclinic packing of even-numbered oligomers. The molecular arrangement of septithiophene in a single crystal resembles that reported for even-numbered oligomers, while the molecules take a more random conformation: only one of the two terminal thienyl rings exhibits disorder and significant torsion from the conjugated plane. The X-ray diffraction data of a quinquethiophene single crystal suggest that the molecule with one of the two different orientations randomly occupies each site.

Full text of DOI:10.1246/bcsj.76.1561

ꢀ 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1561–1567 (2003) 1561
Conformation and Packing of Odd-Numbered ꢀ-Oligothiophenes
in Single Crystals
ꢀ
Reiko Azumi, Midori Goto,y Kazumasa Honda,yy and Mutsuyoshi Matsumoto
Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba Central 5-2, Higashi 1-1-1, Tsukuba 305-8565
yResearch Facilities Department, Technical Service Center, National Institute of Advanced Industrial Science and
Technology (AIST), Tsukuba Central 5-2, Higashi 1-1-1, Tsukuba 305-8565
yyInstitute for Materials and Chemical Process, National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba Central 5-2, Higashi 1-1-1, Tsukuba 305-8565
(Received December 27, 2002)
X-ray single crystal analyses revealed the molecular geometry and molecular packing of odd-numbered ꢀ-oligo-
thiophenes (septithiophene, quinquethiophene and terthiophene) in single crystals prepared by sublimation. Septithio-
phene crystallizes into triclinic, which is in contrast to the monoclinic packing of even-numbered oligomers. The mo-
lecular arrangement of septithiophene in a single crystal resembles that reported for even-numbered oligomers, while the
molecules take a more random conformation: only one of the two terminal thienyl rings exhibits disorder and significant
torsion from the conjugated plane. The X-ray diffraction data of a quinquethiophene single crystal suggest that the mole-
cule with one of the two different orientations randomly occupies each site.
Organic semiconducting compounds consisting of conjugat-
ed oligomers and polymers have been studied as promising
materials for electronic and optoelectronic devices.1–4 Be-
cause they possess features different from those of inorganic
materials, they offer potential materials not only as replace-
ments of conventional inorganic materials, but also for com-
pletely different types of devices. A great deal of effort has
been made to improve the efficiencies and stabilities of these
materials.
Oligothiophenes and polythiophenes are good candidates
Scheme 1.
for applications because of their excellent electronic proper-
ties, stability under ambient conditions, and ease of chemical
modification.1 Recently, oligothiophenes with defined conju-
gation lengths have received much attention as model com-
pounds to obtain a better understanding of the structure-phys-
ical properties relationship.1,2,4 The molecular conformation
and molecular packing are indispensable information since
these materials are in most cases expected to be used in the sol-
id state.
Unsubstituted ꢀ-oligothiophenes, the simplest compounds
in the family, have been intensively studied since Horowitz
et al. demonstrated the high charge mobility of ꢀ-sexithio-
phene (ꢀ-6T).5 Although unsubstituted ꢀ-oligothiophenes
have poor solubility in organic solvents, which renders the ap-
plication of wet fabrication processes difficult, their thin films
are easily evaporated onto solid surfaces.
structure was reported only for powder samples using Riedveld
method.14 It is therefore indispensable to examine the molec-
ular packing of 5T and septithiophene (7T) in single crystals
(Scheme 1). Furthermore interest arises from the analogy of
‘‘even-odd effect’’ of crystal packing of paraffins. It has been
known that the molecular packing of n-alkanes, fatty acids, liq-
uid crystals and long-chain amphiphiles depends strongly on
the parity of the number of carbon atoms in the methylene
chains, which affects their physical properties, such as the
melting point.15–20 Since a thiophene ring is five-membered,
the direction of the bond between two thiophene rings has a fi-
nite angle with respect to the long axis of the oligothiophene
molecule. This feature, similar to that of methylene chains
of paraffins, will cause the dependence of the molecular pack-
ing of oligothiophenes on the parity of the number of thio-
phene rings. In this paper we show the molecular geometry
and molecular packing of odd-numbered oligothiophenes in
single crystals prepared by sublimation.
So far, the crystal structures of ꢀ-bithiophene (ꢀ-2T), ter-
thiophene (3T), quaterthiophene (4T), 6T and octithiophene
(8T) have been solved using single crystals.6–13 They display
quite anisotropic packing with all the long molecular axes par-
allel to one another. As for quinquethiophene (5T), the crystal
Published on the web August 15, 2003; DOI 10.1246/bcsj.76.1561

1562 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Structures of Odd-Numbered Oligothiophenes
outer tube was heated at 340–380 ꢁC under a reduced pressure
of nitrogen (ca. 7 hPa) for several hours.
Experimental
Materials.
1,3-Bis(diphenylphosphino)propane nickel(b)
ꢀ-5T crystals were obtained by heating at 240–250 ꢁC under
reduced pressure of nitrogen using a similar apparatus as in the
case of ꢀ-7T. Crystals of ꢀ-3T were prepared using an ordinary
sublimation apparatus by heating at ca. 95 ꢁC under reduced pres-
sure.
chloride (NiCl2(dppp)) was purchased from Tokyo Kasei Kogyo
Co., Ltd. and used as received. Other reagents and solvents were
purchased from Wako Chemicals Co. and used as received. 2-
Bromobithiophene, 2,500-dibromoterthiophene, 2,20:50,200-terthio-
phene (ꢀ-3T), 2,20:50,200:500,2000:5000,20000-quinquethiophene (ꢀ-5T),
were synthesized following the reported method.21–23
X-ray Crystal Structure Analyses. ꢀ-7T Crystal at 206 K:
Red plate, 0:33 ꢂ 0:20 ꢂ 0:03 mm. Enraf-Nonius CAD4 diffrac-
tometer, graphite-monochromated Cu Kꢀ radiation. ꢁ(Cu Kꢀ) =
2,20:50,200:500,2000:5000,20000:50000,200000:500000,2000000-Septithiophene
(ꢀ-7T): A solution of 2-bromobithiophene (3.0 g, 12.2 mmol) in
dried diethyl ether (10 mL) was added dropwise to magnesium
turnings (0.29 g, 12.2 mmol) in boiling diethyl ether (2 mL).
The resulting mixture was refluxed for 2 hrs, allowed to cool to
room temperature, and transferred with a syringe to the dropping
funnel of a second apparatus. The Grignard solution was added
dropwise to a solution of 2,500-dibromoterthiophene (2.3 g, 5.6
mmol) and NiCl2(dppp) (30.3 mg, 56 mmol) in a 1:1 mixture of
dried benzene and diethyl ether (20 mL). The resulting red disper-
sion was refluxed for 6 hrs, allowed to cool to room temperature,
and hydrolyzed with ice cold 1 M HCl. The precipitate was fil-
tered, washed repeatedly with a diluted HCl solution and water,
and dried in vacuo. After Soxhlet extraction with hexane, the re-
maining powder was repeatedly sublimed to obtain red crystals.
Yield: 0.32 g (9.9%). mp 344–346 ꢁC (Lit. mp 327–328 ꢁC24)
Anal. Found: C, 58.30; H, 2.33; S, 38.71%. Calcd. For C28H16S7:
C, 58.30; H, 2.79; S, 38.91%.
60.90 cmꢃ1
.
Reflections measured: 10534, unique: 9271, of
which 6297 had I > 2ꢂðIÞ. No decay correction. An empirical
absorption correction was applied. A structure determination
was done using the teXsan crystallographic software package26
with direct methods using SIR92 and refinements with full-matrix
least-squares on F2 for 631 variable parameters. All non-hydro-
gen atoms were refined anisotropically. Twenty five hydrogen
atoms out of 32 were found in the difference Fourier map and oth-
ers were attached at calculated positions. R1 ¼ 0:097 (I > 2ꢂðIÞ),
Rw2 ¼ 0:270 (I > 0ꢂðIÞ), residual electron density þ0:86=ꢃ0:79
27
ꢀ ꢃ3
eA . The graphics were performed using PLATON. Crystallo-
graphic data have been deposited at the Cambridge Crystallo-
graphic Data Centre as a supplementary publication no. CCDC-
192275.
ꢀ-7T Crystal at Room Temperature:
Red disc, 0:25 ꢂ
0:25 ꢂ 0:06 mm. Enraf-Nonius CAD4 diffractometer, graphite-
monochromated Cu Kꢀ radiation. ꢁ(Cu Kꢀ) = 60.28 cmꢃ1. Re-
flections measured: 9121, unique: 8935, of which 5862 had
I > 2ꢂðIÞ. No decay correction. An empirical absorption correc-
tion was applied. A structure determination was done using the
teXsan crystallographic software package with direct methods us-
ing SIR92 and refinements with full-matrix least-squares on F for
631 variable parameters. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms were attached at calculated
positions. R ¼ 0:102, Rw ¼ 0:156, residual electron density
Single crystals of ꢀ-7T were obtained by sublimation
with a slight modification of the method reported by others
(Fig. 1).9–11,13,25 A compound of 50–150 mg was placed at the
bottom of a glass tube of 15 mm in diameter. Nitrogen was intro-
duced through an inner glass tube whose edge was positioned ca.
10 mm above the bottom of the outer tube. The bottom of the
ꢀ ꢃ3
þ0:54=ꢃ0:51 eA . The crystal structure of ꢀ-7T at room tem-
perature is essentially the same as that obtained at 206 K, suggest-
ꢁ
ꢀ
ing no phase transition. Triclinic P1, a ¼ 5:988ð1Þ A, b ¼
ꢁ
ꢁ
ꢀ
ꢀ
7:823ð2Þ A, c ¼ 52:865ð9Þ A, ꢀ ¼ 91:16ð2Þ , ꢃ ¼ 91:50ð1Þ ,
ꢄ ¼ 89:94ð2Þꢁ, Z ¼ 4.
ꢀ-5T Crystal: Orange plate, 0:40 ꢂ 0:26 ꢂ 0:10 mm. Enraf-
Nonius CAD4 diffractometer, graphite-monochromated Cu Kꢀ
Reflections measured:
3010, unique: 1459, of which 488 had I > 4ꢂðIÞ. No decay
correction. An empirical absorption correction was applied.
radiation. ꢁ(Cu Kꢀ) = 58.70 cmꢃ1
.
A
structure determination was done using the teXsan crystallograph-
ic software package with direct methods using SIR92 and refine-
ments with full-matrix least-squares on F for 101 variable
parameters. All non-hydrogen atoms were refined isotropically.
Hydrogen atoms were not included. R ¼ 0:203, Rw ¼ 0:162, re-
ꢀ ꢃ3
sidual electron density þ0:43=ꢃ0:49 eA
.
ꢀ-3T Crystal: Yellow plate, 0:60 ꢂ 0:20 ꢂ 0:05 mm. RIGA-
KU AFC7R diffractometer at 203 K using graphite-monochromat-
ed Mo Kꢀ radiation. ꢁ(Mo Kꢀ) = 6.23 cmꢃ1. Reflections mea-
sured: 10336, unique: 5166, of which 3212 had I > 3ꢂðIÞ. No
decay correction. An empirical absorption correction was
applied. A structure determination was done using the teXsan
crystallographic software package with direct methods using
SIR92 and refinements with full-matrix least-squares on F for
271 variable parameters. All non-hydrogen atoms were refined
anisotropically. R ¼ 0:057, Rw ¼ 0:078, residual electron density
ꢀ ꢃ3
.
Fig. 1. Apparatus for sublimation.
þ0:15=ꢃ0:17 eA

R. Azumi et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1563
Table 1. Structure Determination Summary
5Ta)
C20H12S5
Results and Discussion
7T
C28H16S7
3Tb)
All three compounds (ꢀ-3T, 5T and 7T) formed crystals
large enough for X-ray analysis. The crystal structure of ꢀ-
3T in the crystal formed by sublimation was essentially the
same as that in the crystal fabricated by re-crystallization from
an ether solution.8 Because the packing manner of 3T is sig-
nificantly different from those of larger oligomers, probably
due to the lack of molecular length, 3T was not included in
the discussion.
Red, shell-like crystals with sizes up to 2 mm in diameter
and 0.1 mm in thickness were formed by sublimation of ꢀ-
7T. The X-ray diffraction was measured both at room temper-
ature and at low temperature (206 K). The molecular structure
of ꢀ-7T in a single crystal with atomic numbering scheme ob-
tained from the measurement at 206 K is shown in Fig. 2a.
Crystal data are collected in Table 1. There are two crystallo-
graphically independent molecules in an asymmetric unit
whose conformation is similar to each other. This is in con-
trast to the results for the oligomers with even thiophene rings,
such as ꢀ-4T (low-temperature polymorph),9 6T (low-temper-
ature polymorph)11 and 8T,13 where there is only one crystal-
lographically independent molecule. The molecules exhibit an
approximately flat conformation. The terminal thienyl rings at
Formula
C12H8S3
248.39
203
Formula weight 576.90
Temperature/K 206
412.65
296
Crystal system
Space group
triclinic
¯
P1
(monoclinic) monoclinic
(P21=a)
(6.014(1))
(7.766(1))
(19.611(3))
(90)
(97.70(1))
(90)
(907.7(2))
(2)
P21=c
15.349(1)
5.688(1)
25.80(1)
90
97.883(4)
90
2331.1(9)
8
1.479
ꢀ
a/A
5.953(1)
7.767(1)
53.02(1)
91.21(1)
91.89(1)
89.92(1)
2449.6(6)
4
ꢀ
b/A
ꢀ
c/A
ꢀ/ꢁ
ꢃ/ꢁ
ꢄ/ꢁ
ꢀ 3
V/A
Z
ꢅ
calcd/Mg mꢃ3
1.564(1.548c)) 1.510
a) ꢀ-5T has significant disorder in a crystal (see the text). Fur-
ther analyses were therefore not successful. b) The crystal
structure of ꢀ-3T was essentially same as that in the crystal
fabricated by re-crystallization from an ether solution.8 c) Cal-
culated density based on the measurements at room tempera-
ture.
Fig. 2. a) Molecular structure of ꢀ-7T with the atomic numbering scheme obtained by the measurements at 206 K. Displacement
ellipsoids are drawn at the 50% probability level. Torsion angles between adjacent thiophene rings: A–B 7.1(4)ꢁ, B–C 0.7(3)ꢁ, C–
D 0.6(3)ꢁ, D–E 0.5(3)ꢁ, E–F 0.6(3)ꢁ, F–G 1.9(3)ꢁ, H–I 6.6(4)ꢁ, I–J 0.5(3)ꢁ, J–K 0.2(3)ꢁ, K–L 0.6(3)ꢁ, L–M 0.6(3)ꢁ, M–N 1.1(3)ꢁ.
b) Molecular structure of ꢀ-7T obtained by the measurements at room temperature. Large disorder is observed only at rings A and
H, and not at rings G or N.

1564 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Structures of Odd-Numbered Oligothiophenes
one of the edges of the molecule, rings A and H in Fig. 2a,
however, twist significantly along the C4–C5 and C32–C33
bonds. The dihedral angle between rings A and B is 7.1(4)ꢁ,
the one between H and I is 6.6(4)ꢁ, and the others are less than
2.0ꢁ. Moreover, the p-conjugating plane of the molecules is
bent at rings A and H. Such a significant torsion and a bend
of the molecules have not been observed for even-numbered
oligothiophenes.9,11,13
morph),12 while this feature is not always mentioned explicitly
in the literature. What is intriguing is that the disorder takes
place only at one edge of the molecule in the present case,
i.e., at rings A and H, and not at ring G or N. Disorder at only
one edge of the molecule is not common in the crystals of oli-
gothiophene derivatives, but has been reported for a substitut-
ed quinquethiophene (5T) derivative.28 Thus, this feature
seems to be related to the parity of the number of thiophene
units.
The thiophene rings of 7T have essentially been revealed to
take an all-anti conformation. Disorder is suggested at rings A
and H by relatively large bond lengths at C(3)–C(4) (1.440(8)
ꢁ
ꢀ-7T was crystallized in triclinic, P1, which is in contrast to
the monoclinic packing of ꢀ-4T (low-temperature poly-
morph),9 6T (low-temperature polymorph)11 and 8T.13 This
may be related to the less symmetric shape of ꢀ-7T compared
with those of even-numbered oligomers. The angles ꢀ
(91.21(1)ꢁ) and ꢄ (89.92(1)ꢁ), however, deviate only slightly
from 90ꢁ. The deviation of the packing manner of ꢀ-7T from
the monoclinic one is thus small.
ꢀ
A) and C(31)–C(32) (1.422(8) A) compared with the other
ꢀ
ꢀ
C=C double bonds in the molecules (1.32–1.40 A, Table 2).
ꢀ
The bond lengths at S(1)–C(4) (1.702(7) A) and S(8)–C(32)
ꢀ
(1.699(7) A) also deviate from the normal value of the S–C
bond lengths. The X-ray data taken at room temperature show
greater disorder (Fig. 2b). The bond lengths and angles at
rings A and H deviate significantly from the normal values
for a thiophene ring, and the atoms have large temperature
factors. The feature should arise from the large mobility of
rings A and H. The contribution of a small fraction of sulfur
at positions C(3) and C(31) due to the random coexistence of
syn and anti conformations is also suspected. A similar elon-
gation of C=C double bonds at terminal thienyl rings,
although to a lesser extent, are seen for 2T,7 3T,8 4T (high-
temperature polymorph)9,10 and 6T (high-temperature poly-
Figure 3 shows packing diagrams of ꢀ-6T, 7T and 8T.29 ꢀ-
7T molecules are packed in a manner similar to ꢀ-6T and 8T.
ꢀ
The lengths of two shorter axes (a ¼ 5:953ð1Þ A, b ¼ 7:767ð1Þ
ꢀ
A) are nearly identical to those for even-numbered oligomers.
ꢀ
The length of the longest axis (c ¼ 53:02ð1Þ A) is between
those for ꢀ-6T (low-temperature polymorph) and 8T. 7T mole-
cules take herringbone-like arrangement. The angle between
the planes of neighboring molecules is ca. 63ꢁ, which is slight-
ly smaller than those of ꢀ-6T (low-temperature polymorph,
Table 2. Bond Lengths of ꢀ-7T Based on the Measurements at 206 K
ꢀ
C=C double bond (A)
ꢀ
C–C single bond (thiophene ring) (A)
ꢀ
S–C bond (A)
C(1)
C(3)
C(5)
C(7)
C(2)
C(4)
C(6)
C(8)
1.35(1)
C(2)
C(6)
C(3)
C(7)
1.386(9)
1.406(8)
1.415(8)
1.405(8)
1.410(8)
1.390(8)
1.407(8)
1.373(10)
1.404(8)
1.395(8)
1.420(8)
1.396(8)
1.415(8)
1.411(8)
S(1)
S(1)
S(2)
S(2)
S(3)
S(3)
S(4)
S(4)
S(5)
S(5)
S(6)
S(6)
S(7)
S(7)
S(8)
S(8)
C(1)
C(4)
C(5)
C(8)
1.692(9)
1.702(7)
1.736(6)
1.724(6)
1.730(6)
1.729(6)
1.727(6)
1.722(6)
1.728(6)
1.724(6)
1.722(6)
1.721(6)
1.722(6)
1.686(7)
1.692(10)
1.699(7)
1.717(7)
1.726(6)
1.744(6)
1.717(6)
1.725(6)
1.727(6)
1.738(6)
1.725(6)
1.723(6)
1.725(6)
1.723(6)
1.713(7)
1.440(8)
1.349(8)
1.383(8)
1.376(8)
1.380(8)
1.362(8)
1.395(8)
1.384(8)
1.392(8)
1.378(8)
1.389(8)
1.378(8)
1.369(9)
1.35(1)
1.422(8)
1.366(8)
1.399(8)
1.365(8)
1.383(8)
1.356(8)
1.394(8)
1.379(8)
1.383(8)
1.359(8)
1.382(8)
1.377(9)
1.331(9)
C(10)
C(14)
C(18)
C(22)
C(26)
C(30)
C(34)
C(38)
C(42)
C(46)
C(50)
C(54)
C(11)
C(15)
C(19)
C(23)
C(27)
C(31)
C(35)
C(39)
C(43)
C(47)
C(51)
C(55)
C(9)
C(10)
C(12)
C(14)
C(16)
C(18)
C(20)
C(22)
C(24)
C(26)
C(28)
C(30)
C(32)
C(34)
C(36)
C(38)
C(40)
C(42)
C(44)
C(46)
C(48)
C(50)
C(52)
C(54)
C(56)
C(9)
C(11)
C(13)
C(15)
C(17)
C(19)
C(21)
C(23)
C(25)
C(27)
C(29)
C(31)
C(33)
C(35)
C(37)
C(39)
C(41)
C(43)
C(45)
C(47)
C(49)
C(51)
C(53)
C(55)
C(12)
C(13)
C(16)
C(17)
C(20)
C(21)
C(24)
C(25)
C(28)
C(29)
C(32)
C(33)
C(36)
C(37)
C(40)
C(41)
C(44)
C(45)
C(48)
C(49)
C(52)
C(53)
C(56)
ꢀ
C–C single bond (inter-ring) (A)
S(9)
S(9)
C(4)
C(8)
C(5)
C(9)
1.456(8)
1.449(8)
1.450(8)
1.446(8)
1.444(8)
1.459(8)
1.478(8)
1.439(8)
1.466(7)
1.441(8)
1.459(8)
1.459(8)
S(10)
S(10)
S(11)
S(11)
S(12)
S(12)
S(13)
S(13)
S(14)
S(14)
C(12)
C(16)
C(20)
C(24)
C(32)
C(36)
C(40)
C(44)
C(48)
C(52)
C(13)
C(17)
C(21)
C(25)
C(33)
C(37)
C(41)
C(45)
C(49)
C(53)

R. Azumi et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1565
Fig. 3. Packing diagrams of ꢀ-6T, 7T and 8T. The diagrams of 6T and 8T are reproduced using the atomic coordination param-
eters reported in Refs. 11 and 13, respectively.
66ꢁ) and 8T (65ꢁ).13 The molecules exhibit layer-like packing
with their long molecular axis slightly tilted from the normal
of the ab plane. We assume the presence of ‘‘interfaces’’ be-
tween the molecular layers in the crystals.
ꢀ
Table 3. Distances Less than 4.0 A between Terminal Car-
bon Atoms at Two Different Interfaces of ꢀ-7T Crystal
ꢀ
ꢀ
At the ‘‘rough interface’’ (A) At the ‘‘smooth interface’’ (A)
(corresponding to Fig. 4a) (corresponding to Fig. 4b)
A difference is found in the contacting manner between the
nearest molecules at every two interfaces of the adjacent
layers. At every interface of 6T and 8T, and at every two in-
terfaces of 7T, only one of the C–H bonds of each terminal
thienyl ring is directed toward the interface (Fig. 4a). Owing
to the shape of the interface, the protruding C–H bonds of con-
tacting layers are interdigitated. At the interface of 7T where
the ‘‘disordered’’ terminal thienyl rings are located, two of the
C–H bonds face the interface (Fig. 4b). The position of the
molecules in the next layer is thus different from that in the
former case, which causes the deviation from the monoclinic
packing. Furthermore, the shape of the interface is smoother
than that in the former case, which could lead to the less-de-
fined manner of the conformation of the terminal thienyl rings
in the adjacent layer.
C(56) C(56)a)
C(27) C(55)
C(28) C(28)d)
C(27) C(56)
C(27) C(55)e)
C(28) C(56)f)
C(55) C(56)a)
C(28) C(55)e)
3.76(1) C(2)
C(2)b)
C(30)c)
C(30)e)
C(29)
3.69(2)
3.77(1) C(30)
3.80(1) C(1)
3.81(1) C(2)
3.86(1) C(2)
3.87(1)
3.72(2)
3.89(1)
3.93(1)
3.99(1)
C(30)
3.87(1)
3.90(1)
Symmetry code: a) ꢃ1 ꢃ x, 1 ꢃ y, 1 ꢃ z; b) 3 ꢃ x, ꢃy, ꢃz;
c) 2 ꢃ x, 1 ꢃ y, ꢃz; d) ꢃx, ꢃy, 1 ꢃ z; e) 1 + x, y, z; f) ꢃx, 1
ꢃ y, 1 ꢃ z.
reported for 6T (low-temperature polymorph, 1.553 g cmꢃ3
and 8T (1.578 g cmꢃ3).31
)
ꢀ
The distances of less than 4 A between the carbon atoms at
two different interfaces of 7T are listed in Table 3. Carbon
atoms at the ‘‘rough interface (corresponding to Fig. 4a)’’ ex-
hibit more close interactions than those at the ‘‘smooth inter-
face (corresponding to Fig. 4b).’’
The above results suggest that the interaction between ter-
minal rings of neighboring molecules is somewhat weaker
for ꢀ-7T than for 6T and 8T. This feature seems to be reflect-
ed in the density of the crystal. Figure 5 shows the densities of
ꢀ-oligothiophene crystals estimated from the lattice constants.
ꢀ-5T exhibits more disordered structures. Orange platelet
crystals were obtained by sublimation of ꢀ-5T. Many of the
crystals exhibit perfect extinction under crossed polarizers, in-
dicating that they are single crystals. X-ray diffraction data,
however, show that ꢀ-5T has large disorders in single
crystals. We measured the diffractions of several single crys-
tals, and found many different results for the lattice constants.
The value of the longest crystal axis was sometimes too large
considering the size of the molecule. The atomic coordination
parameters of ꢀ-5T obtained by powder diffraction reported by
Porzio et al.14 did not reproduce our diffraction data.
The calculated density of the ꢀ-7T crystal based on room tem-
30
)
perature measurements (1.548 g cmꢃ3
is smaller than those

1566 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Structures of Odd-Numbered Oligothiophenes
Fig. 4. a) Scheme of interface between molecular layers of
ꢀ-6T, 8T and every two layers of 7T. Hydrogen atoms are
omitted. The terminal thienyl rings of the molecules in the
upper layer are illustrated with van der Waals radii. b)
Scheme of interface between the molecular layers of 7T
where ‘‘disordered’’ thienyl rings are located.
Fig. 6. a) Molecular structure of ꢀ-5T in one of the single
crystals. Extinction rule and electron density map suggest
that the molecule has inversion symmetry, which is impos-
sible for ꢀ-5T. b) Packing diagram of ꢀ-5T in a single
crystal.
The most successful results, but not enough for complete X-
ray analysis, are shown below. The space group and the lattice
ꢀ
constants obtained were P21=a, a ¼ 6:014ð1Þ A, b ¼ 7:766ð1Þ
32
ꢁ
ꢀ
ꢀ
A, c ¼ 19:611ð3Þ A, ꢃ ¼ 97:70ð1Þ .
The electron density
map shows two overlapping quinquethiophene-like molecules
which can be transformed to each other by inversion around
the center of symmetry located in the middle of the molecule
(Fig. 6a). The results suggest that ꢀ-5T with one of the two
different orientations randomly occupies each site. An attempt
to determine the contributions of ꢀ-5T molecules with two dif-
ferent orientations based on the electron density map was not
successful. Figure 6b shows the molecular packing of ꢀ-5T in
a single crystal. The packing manner of ꢀ-5T in a single crys-
tal is similar to those of ꢀ-7T and even-numbered oligothio-
phenes, as can be seen by a comparison with Fig. 3.
Similar to the case of ꢀ-7T, the calculated density of ꢀ-5T
crystal (1.510 g cmꢃ3) is smaller than the value obtained by
the interpolation of the densities of even-numbered oligothio-
phenes, as can be seen in Fig. 5. This fact also suggests a loos-
er packing of the molecules, which may cause the disorder.
Fig. 5. Calculated densities of ꢀ-oligothiophene crystals.
The values for ꢀ-4T, 6T and 8T are those reported in
Refs. 9, 11 and 13, respectively.

R. Azumi et al.
Bull. Chem. Soc. Jpn., 76, No. 8 (2003) 1567
J. L. Fave, and F. Garnier, Chem. Mater., 7, 1337 (1995).
12 T. Siegrist, R. M. Fleming, R. C. Haddon, R. A. Laudise,
A. J. Lovinger, H. E. Katz, P. Bridenbaugh, and D. D. Davis, J.
Mater. Res., 10, 2170 (1995).
13 D. Fichou, B. Bachet, F. Demanze, I. Billy, G. Horowitz,
and F. Garnier, Adv. Mater., 8, 500 (1996).
Conclusions
The molecular geometry and molecular packing of odd-
numbered ꢀ-oligothiophenes (ꢀ-7T, 5T and 3T) in single crys-
tals prepared by sublimation were investigated by X-ray single
crystal analyses. The molecular arrangement of ꢀ-7T in a sin-
gle crystal resembles that reported for even-numbered oligo-
mers, while the molecules take a more random conformation:
only one of the two terminal thienyl rings exhibits disorder and
significant torsion from the conjugated plane. The triclinic
packing of ꢀ-7T is also in contrast to the monoclinic one of
even-numbered oligomers. The X-ray diffraction data of the
ꢀ-5T single crystal suggest that the molecule with one of the
two different orientations randomly occupies each site.
The disorder seems to be reflected in the relatively small
densities of the ꢀ-7T and 5T crystal compared with those of
even-numbered oligomers. The above results show that an
‘‘even-odd effect’’ works not only for methylene chains, but al-
so for five-membered aromatic compounds.
14 W. Porzio, S. Destri, M. Mascherpa, and S. Bruckner, Acta
Polym., 44, 266 (1993).
15 R. Boese, H.-C. Weiss, and D. Blaser, Angew. Chem., Int.
Ed., 38, 988 (1999).
¨
16 V. R. Thalladi, R. Boese, and H.-C. Weiss, Angew. Chem.,
Int. Ed., 39, 918 (2000).
17 K. Takamizawa, Y. Urabe, J. Fujimoto, H. Ogata, and Y.
Ogawa, Ethermochimica Acta, 267, 297 (1995).
18 M. Goto, Yukagaku, 36, 909 (1987).
19 M. Kuribayashi and K. Hori, Liq. Cryst., 26, 809 (1999).
20 T. Shimizu and M. Masuda, J. Am. Chem. Soc., 119, 2812
(1997).
21 K. Tamao, S. Kodama, I. Nakajima, and M. Kumada, Tet-
rahedron, 38, 3347 (1982).
22 C. van Pham, A. Burkhardt, R. Shabana, D. D.
Cunningham, H. B. Mark, Jr., and H. Zimmer, Phosphorus, Sul-
fur, and Silicon, 46, 153 (1989).
We thank Prof. Dr. Peter Bauerle and Dr. Gunther Gotz of
¨
Universitat Ulm for their helpful suggestions on crystal struc-
¨
tures of oligothiophenes.
¨
¨
23 P. Bauerle, F. Wurthner, G. Gotz, and F. Effenberger, Syn-
¨
thesis, 1993, 1099.
¨
¨
24 J. Kagan and S. K. Arora, J. Org. Chem., 48, 4317 (1983).
25 F. R. Lipsett, Can. J. Phys., 35, 284 (1957).
References
1
‘‘Handbook of Oligo- and Polythiophenes,’’ ed by D.
Fichou, Wiley-VCH, Weinheim (1998).
‘‘Electronic Materials: The Oligomer Approach,’’ ed by K.
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27 A. L. Spek, Acta Crystallogr., Sect. A, 46, C34 (1990).
2
28 U. Mitschke, Thesis, Universitat Ulm, 1999.
¨
¨
3
‘‘Handbook of Conducting Polymers,’’ ed by T. A.
29 The packing diagrams of ꢀ-6T (low-temperature poly-
morph) and 8T are reproduced using the atomic coordination pa-
rameters reported in Refs. 11 and 13, respectively.
Skotheim, R. L. Elsenbaumer and J. R. Reynolds, 2nd ed., Marcel
Dekker, New York (1998).
4
S. Hotta, ‘‘Handbook of Organic Conductive Molecules
30 As crystals shrink with decreasing the temperature, the val-
ue of calculated density for 7T obtained by the measurements at
room temperature was employed for the comparison with those
for the other oligomers.
31 Since estimated values of crystal densities depend on the
condition of X-ray measurements, precise comparison of the den-
sity values of the crystals measured with different diffractometers
is not appropriate. The smaller values of the calculated densities
of odd-numbered oligothiophenes reported here are nevertheless
significant even considering the above problem.
and Polymers,’’ ed by H. S. Nalwa, John Wiley & Sons, Chiches-
ter (1997), Vol. 2, Ch. 8.
5
Solid State Commun., 72, 381 (1989).
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6
7
D. Fichou, J. Mater. Chem., 10, 571 (2000).
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1942 (1994).
8
and E. G. J. Starring, Synth. Met., 30, 381 (1989).
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Haddon, Adv. Mater., 10, 379 (1998).
32 We also examined the set of lattice constants with duplicat-
ꢀ
ed value of c-axis (ca. 38 A). The trial, however, did not fit well
10 L. Antolini, G. Horowitz, F. Kouki, and F. Garnier, Adv.
Mater., 10, 382 (1998).
11 G. Horowitz, B. Bachet, A. Yassar, P. Lang, F. Demanze,
the observed diffraction: all the (00l) (l ¼ 2n þ 1) reflections are
null.