Synthesis, crystal structures, and properties of 6,12-diaryl-substituted indeno[1,2-b]fluorenes

Article abstract of DOI:10.1002/chem.201200591

Fused polycyclic indeno[1,2-b]fluorene derivatives with aryl substituents at the 6,12-positions have been prepared as a potential antiaromatic 20π electronic system. They showed strong absorptions in the visible region and amphoteric redox properties. The quinoid-type molecular structures were revealed by X-ray crystal-structure analysis, which indicated that the bond lengths of the quinoid unit depend on the aryl substituents. Whereas nucleus-independent chemical shift NICS(1) calculations indicate the antiaromatic nature of the s-indacene core, they have higher stability than substituted acene derivatives. The derivatives with difluorophenyl or anthryl groups were stable in solution. Vapor-deposited thin films showed ambipolar carrier transportation in the field-effect transistor devices.

Full text of DOI:10.1002/chem.201200591

FULL PAPER
DOI: 10.1002/chem.201200591
Synthesis, Crystal Structures, and Properties of 6,12-Diaryl-Substituted
IndenoACTHUNRTGNEUNG[1,2-b]fluorenes
Jun-ichi Nishida, Shingo Tsukaguchi, and Yoshiro Yamashita*[a]
Abstract: Fused polycyclic indeno
[1,2-
tal-structure analysis, which indicated
that the bond lengths of the quinoid
unit depend on the aryl substituents.
Whereas nucleus-independent chemical
shift NICS(1) calculations indicate the
antiaromatic nature of the s-indacene
core, they have higher stability than
substituted acene derivatives. The de-
rivatives with difluorophenyl or anthryl
groups were stable in solution. Vapor-
deposited thin films showed ambipolar
carrier transportation in the field-effect
transistor devices.
b]fluorene derivatives with aryl sub-
stituents at the 6,12-positions have
been prepared as a potential antiaro-
matic 20p electronic system. They
showed strong absorptions in the visi-
ble region and amphoteric redox prop-
erties. The quinoid-type molecular
structures were revealed by X-ray crys-
Keywords: antiaromaticity · molec-
ular electronics · polycycles · quino-
dimethanes · semiconductors
Introduction
Polycyclic fused p-conjugated compounds have attracted
much attention on account of their unique electronic proper-
ties.[1] They show redox-active properties that can be used
for organic electronics accompanied with electron transfer[2]
and nanotechnology.[3] The molecular design of new p-con-
jugated systems is important to control their physical prop-
erties. Acenes such as pentacene have been extensively stud-
ied and used as p-type semiconductors.[4] However, the in-
troduction of cyclopentadiene rings to polycyclic systems
drastically changes the physical and chemical properties as
seen in pentalenes[5] and s-indacenes[6–8] that possess antiaro-
matic 4np electronic structures. The fused polycyclic antiar-
omatic systems are considered to have high HOMO levels,
low LUMO levels, and narrow HOMO–LUMO gaps rela-
tive to linear acene-type aromatic compounds, which are fa-
vorable for carrier transportation and absorptions in the
visible region. Although antiaromatic systems are generally
unstable, the introduction of fused rings increases the stabili-
ty and allows them to be handled applicatively.[2a,9]
Among the polycyclic 4np systems, antiaromatic s-inda-
cene with a 12p-electron system is an important key com-
pound.[6] The introduction of fused benzene rings increases
the stablity of the s-indacene and also promotes the qui-
The quinoid structure is considered to have a biradical con-
tribution in the form of 1* that leads to high reactivity at
the 6,12-positions,[7a] in which positions the R substituent
seems to play an important role in determining the electron-
ic structures as well as the stability. Recently derivatives
with bulky triisopropylsilylethynyl (TIPSE) groups were iso-
lated by Haley et al.[8a,b] They are stable due to the steric
protection and p delocalization through the ethynyl groups,
and the bond lengths and the physical properties are consid-
ered to be strongly affected by the TIPSE groups. On the
other hand, the effects of aryl substituents on the electronic
properties and the molecular structures have not been inves-
noid-type bond alternation in indenoACTHNUTRGNEUNG[1,2-b]fluorene (IF) 1.
[a] Dr. J.-i. Nishida, S. Tsukaguchi, Prof. Dr. Y. Yamashita
Department of Electronic Chemistry
Interdisciplinary Graduate School of
Science and Engineering
Tokyo Institute of Technology
4259, Nagatsuta, Midori-ku, Yokohama 226-8502 (Japan)
Fax : (+81) 45-924-5489
E-mail: yoshiro@echem.titech.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200591.
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tigated, although the diphenyl derivative 2 was reported by
Scherf et al.[7b] We have now prepared IF derivatives 3–5
with 2,6-difluorophenyl, 9-anthryl, and thienyl groups, and
investigated the structures by X-ray analysis to reveal the
bond alternation. The electronic structures were investigated
with molecular orbital (MO) calculations and their carrier
transportation ability was studied by applying them to field-
effect transistors (FET).[10]
Results and Discussion
Synthesis: IF derivatives 3–5 were synthesized by a similar
procedure to that for 2,6-difluorophenyl or TIPSE-substitut-
ed pentacene-5,12-dione derivatives 7, which we have re-
Figure 1. UV/Vis spectra of a) IF derivatives 2–5 and b) 2,6-difluorophen-
yl-substituted IF 3 and pentacenedione 7a.
Table 1. UV-visible spectral data of 2–5 and 7a.[a]
ported.[11] Nucleophilic addition of aryl lithium reagents to
indenofluorenedione 8[12] followed by dehydroxylation with
tin(II) dichloride gave the target compounds as shown in
Scheme 1. Except for thienyl derivative 5, IF derivatives
labs [nm] (loge)
ledge [eV]
2
294, 323, 542 (4.60)
2.01
2.34
2.20
1.94
1.75
3
227, 316, 529 (4.53)
4
5
7a
255, 315, 347, 366, 386, 522 (4.28)
227, 308, 397, 607 (4.57)
302, 538, 578 (4.84)
[a] In CH2Cl2.
ure 1b).[11] Replacement of the phenyl substituents with
bulky 2,6-difluorophenyl and 9-anthryl groups brought
about blueshifts of the absorption maximum to l=529 and
522 nm, respectively. This result can be explained in terms
of the difference in conjugation of the substituents with the
indacene core since the dihedral angles between the sub-
stituents and indacene are larger in the difluorophenyl and
anthracene derivatives. On the other hand, the introduction
of thiophene rings afforded a redshift of the absorption
maximum to 607 nm. This can be attributed to the less hin-
dered structure as well as the electron-donating property of
the thiophene ring.
Scheme 1. Preparation of IF derivatives 2–5: a) ArLi (2 equiv) in THF,
b) SnCl2 in HCl.
could be finally purified by sublimation, for which the yields
after sublimation are shown. Thienyl derivative 5 was puri-
fied by silica gel column chromatography and gel-permea-
tion chromatography (GPC; eluent: chloroform). Except for
anthracene derivative 4, which showed poor solubility in or-
ganic solvents, NMR spectra could be measured in CDCl3.
X-ray crystallographic analysis: X-ray crystal-structure anal-
ysis of IFs 2–4 was carried out to investigate the quinoid
structure (Figure 2). The single crystals were obtained by
slow sublimation. In phenyl derivative 2, the IF unit has
a planar geometry with a center of symmetry, and the two
phenyl rings take on a twisted conformation to the planar
1
The H NMR spectra of 4 could be measured in deuterated
o-dichlorobenzene at 908C.
Optical properties: IF derivatives 2–5 with aryl substituents
exhibited intense absorptions in the visible region as depict-
ed in Figure 1a. The absorption maxima and molar extinc-
tion coefficients in dichloromethane are summarized in
Table 1. The absorption maximum of phenyl derivative 2 ap-
pears at l=542 nm with a large molar extinction coefficient.
The spectrum is similar to that of the substituted pentacene-
dione derivative 7a with a fused quinoid system (Fig-
À
indacene unit with a dihedral angle of 43.38. The C C bond
À
À
À
lengths of C1 C2 (1.390 ꢁ), C9 C10 (1.360 ꢁ), and C1 C9
(1.460 ꢁ) show the quinoid structure of the central benzene
unit. Derivatives 3 and 4 have a similar planar geometry and
quinoid structure to the indacene core. Aryl substituents at
the 6,12-positions are twisted, and their bond lengths and di-
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IndenoACHTUNGTRENNUNG[1,2-b]fluorenes
FULL PAPER
Figure 2. a–c) ORTEP drawing of 2–4, respectively, and d–f) crystal packing of 2–4, respectively (ellipsoids drawn at the 50% probability level).
hedral angles are summarized in Table 2. The dihedral
angles between the aryl groups and indacene core are de-
pendent on the aryl groups and become larger with an in-
crease in the bulkiness of the substituents. The anthracene
derivative 4 shows the largest dihedral angle of 76.58. In ad-
dition, the bond alternation of the quinoid unit seems to
the difference is not so large compared with the experimen-
À
À
tal errors, whereas the bond lengths of C1 C9 and C2 C11
are longer than those of 2. On the other hand, derivative
6[8a] with TIPSE groups shows longer bond lengths of C1
C2 (1.390 ꢁ) and C9 C10 (1.374 ꢁ) and shorter bond
lengths of C1 C9 (1.457 ꢁ) and C2 C11 (1.416(3) ꢁ) rela-
tive to the aryl-substituted derivatives. The shorter bond
À
À
À
À
À
relate to the dihedral angles. Thus, the bond lengths of C1
À
À
C2 and C9 C10 in 4 are shorter than those in 2, although
length of C2 C11 suggests p conjugation through the ethyn-
yl units. These facts indicate that the twisted aryl groups
strengthen the contribution of the quinoid structure.
Molecule 2 forms a p-stacking columnar structure in
a manner that avoids the interaction between the phenyl
substituents with an interplanar distance of 3.588 ꢁ between
the central benzene and the adjacent five-membered ring as
depicted in Figure 2d. The introduction of two 2,6-difluoro-
phenyl groups in 3 afforded a well-ordered p-stacking struc-
ture. A half-slipped-type stacking along the molecular long
axis is observed with a close interplanar distance of 3.326 ꢁ.
This structure seems favorable to carrier transportation. In
anthracene derivative 4, p stacking of the indacene unit is
not observed; instead, overlapping between the anthracene
groups (3.415 ꢁ) is observed (Figure 2f). This is attributed
to the bulkiness and p-conjugated system of the anthracene
group.
Table 2. Bond lengths [ꢁ] and dihedral angles [8] of aryl-substituted IF
derivatives 2–5 and TIPSE-substituted 6 in single crystals.
2
3
4
6[a]
À
C1 C2
À
C1 C9
1.3902(15)
1.4602(15)
1.3602(15)
1.4309(15)
1.4682(16)
1.4660(15)
43.3
1.387(3)
1.464(3)
1.360(3)
1.435(2)
1.467(3)
1.467(3)
56.6
1.376(3)
1.467(3)
1.358(3)
1.428(3)
1.470(3)
1.492(3)
76.5
1.390(3)
1.457(3)
1.374(3)
1.438(3)
1.470(3)
1.416(3)[b]
–
À
C9 C10
À
C1 C10*
À
C2 C3
À
C2 C11
dihedral angle
[a] In ref. [8a]. [b] Crystallographic data in CCDC-787154.
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Y. Yamashita et al.
Redox properties: IF derivatives 2–5 showed amphoteric
redox properties. The cyclic voltammograms were measured
in dichloromethane, and the redox potentials are summar-
ized in Table 3. Derivative 2 shows a reversible one-electron
oxidation wave at +0.97 V and a reduction wave at À1.00 V
versus SCE as shown in Figure 3a. Replacement of the
phenyl groups with electron-withdrawing 2,6-difluorophenyl
groups increased the electron-accepting property of inda-
cene 3. On the other hand, anthracene derivative 4 showed
a positive shift only in the oxidation potential. Introduction
of the thienyl groups in 5 greatly lowered the oxidation po-
tential to +0.66 V. This is attributed to the electron-donat-
ing thienyl groups. Interestingly, the reduction potential of 5
is positively shifted and the HOMO–LUMO gap is reduced.
This fact indicates that the aryl groups at the 6,12-positions
are important in determining the HOMO and LUMO
levels. As shown in Table 3, the differences between the oxi-
dation and reduction potentials (EoxÀEred) are related to the
dihedral angles in Table 2. However, TIPSE-substituted de-
rivative 6 shows an oxidation potential at +1.23 V and a re-
duction potential at À0.62 V (versus SCE),[8b] thereby result-
ing in a HOMO–LUMO gap of 1.85 V. The high oxidation
potential can be attributed to the electron-withdrawing eth-
ynyl group. The narrow HOMO–LUMO gap may be due to
the contribution of biradical structure 1*. The thienyl deriv-
ative 5 seems to have a similar contribution from 1* on ac-
count of the less hindered substituent, which leads to the
narrower HOMO–LUMO gap.
Table 3. Electrochemical data of 2–5.[a]
[b]
Eox
E1red
EoxÀEred
2
3
4
5
+0.97
+1.18
+1.07
+0.66
À1.00
1.97
2.06
2.12
1.55
À0.88[c]
À1.05
À0.89[c]
[a] nBu4NPF6 (0.1m) in CH2Cl2, Pt electrode, V versus SCE. Half-wave
potentials. [b] Ered =Epc +0.03 V. [c] Quasi-reversible or irreversible peak.
DFT and nucleus-independent chemical shift (NICS) calcu-
lations: Molecular orbital calculations of 2–5 were carried
out by using the Gaussian 03 program at the B3LYP/6-
31G(d) level of theory to investigate the substituent effects.
The optimized dihedral angles between the aryl groups and
the s-indacene core are 45.38 in 2, 51.68 in 3, 71.08 in 4, and
34.18 in 5. These dihedral angles of 2–4 are consistent with
those obtained from the X-ray analysis, and the dihedral
angle of 34.18 in 5 suggests that the p conjugation through
the thienyl groups is effective. The calculated bond lengths
of 5 show the smallest bond alternation (see Table S2 in the
Supporting Information). The calculations of the HOMO
and LUMO energies are depicted in Figure 4. The HOMO–
LUMO differences are dependent on the aryl substituents
and the thienyl derivative 5 shows the narrowest value of
1.90 eV. Introduction of the five-membered thiophene rings
weakens the quinoid character and promotes the p delocali-
zation that leads to the smaller HOMO–LUMO gap.
Figure 4. HOMO and LUMO energies [eV] of 2–5 calculated by using
Figure 3. Cyclic voltammograms of a) 2, b) 3, c) 4, and d) 5.
DFT at the B3LYP/6-31G(d) level of theory.
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IndenoACHTUNGTRENNUNG[1,2-b]fluorenes
FULL PAPER
By extension, to investigate the aromaticity of the aryl-
substituted IF derivatives,[13] we calculated the (NICS)(1)
values[9,14] at the RHF/6-31+G(d) level of theory by using
both the CIF files of 2–4 and the optimized molecular struc-
tures of 2–5 (Table 4). Although the calculated values are
considered to be strongly influenced by the aryl groups as
shown in Table S3 in the Supporting Information, the central
A and B rings exhibit antiaromatic positive values in all de-
rivatives.
ly. This result indicates that introduction of bulky aryl sub-
stituents is effective in enhancing the stability of the inda-
cene core. The higher stability of 3 compared with 4 can be
ascribed to the lower HOMO level.
Field-effect transistor (FET) characteristics: Although
redox-active IF derivatives were expected to show carrier
transportation properties in thin films, FET devices based
on them have not yet been reported. We have now succeed-
ed in measuring the FET characteristics on the basis of aryl
derivatives by using a vapor deposition method. Thin films
of IFs 2–4 were thermally deposited on silica/Si wafers with
interdigitated Au bottom electrodes in a high-vacuum cham-
ber (approximately 230–3508C: 10À5 Pa). Silica dielectric
surfaces were treated with hexamethyldisilazane (HMDS).
The measurements were carried out in situ, and the results
are summarized in Table 5. The film of 2 exhibited p-type
Table 4. Calculated NICS(1)[a] based on CIF files of 2–4 and optimized
structures of 2–5.[b]
A ring
B ring
C ring
2 (CIF)
3 (CIF)
4 (CIF)
2 (optimized)
3 (optimized)
4 (optimized)
5 (optimized)
1.1
1.8
1.6
1.2
1.8
2.0
0.7
1.5
2.0
2.2
1.2
1.9
2.4
1.1
À8.7
À8.7
À8.8
À9.3
À9.1
À8.8
À9.1
Table 5. FET characteristics with bottom contact geometries.[a]
Mobility [cm2 VÀ1 sÀ1
]
On/Off
Threshold [V]
2
3
3
4
4
p: 1.6ꢂ10À5
p: 1.9ꢂ10À5
n: 8.2ꢂ10À6
p: 1.1ꢂ10À5
n: 1.6ꢂ10À6
60
10
10
100
30
À2
À48
+36
À62
+65
[a] RHF/6-31+G(d) level of theory. [b] Structures optimized using DFT
at the B3LYP/6-31G(d) level of theory. Average values of B and B’ rings,
or C and C’ rings.
[a] Data calculated by using transfer plots at VDS = +/À100 V. Silica gate
dielectric: 300 nm thick. HMDS-treated surface. Tsub =208C. Interdigitat-
ed gold source and drain electrodes, L/W: 25 mm/294 mm.
Stability in solution: To investigate the stability in solution,
the solutions of IF derivatives 2–5 in dichloromethane
(10À5 m) were exposed to ambient light in air at 208C for
several weeks. UV-visible spectra were recorded at regular
and gradient intervals to obtain time-absorbance profiles.
The results are illustrated in Figure 5. The stability increased
semiconducting behavior with
a
mobility of 1.6ꢂ
10À5 cm2 VÀ1 sÀ1. Interestingly, the introduction of 2,6-difluor-
ophenyl groups in 3 imbued it with an electron-transporting
property (8.2ꢂ10À6 cm2 VÀ1 sÀ1) as well as a hole-transport-
ing one (1.9ꢂ10À5 cm2 VÀ1 sÀ1) as shown in Figure 6. The 9-
anthryl derivative 4 also showed ambipolar characteristics.
Figure 5. Absorbance–time profiles for IF derivatives 2–5.
relative to substituted pentacene derivatives.[4b,c] Indacenes 3
and 4 with bulky 2,6-difluorophenyl and 9-anthryl groups
showed significantly longer lifetimes than the phenyl- and
thienyl-substituted derivatives 2 and 5. Plots of lnA (A: ab-
sorbance at a given lmax) versus time [h] afforded the rate
constants (k) (see Figure S4 in the Supporting Information).
The obtained rate constants for 2–5 were 9.2ꢂ10À4, 3.5ꢂ
10À5, 1.5ꢂ10À4, and 9.0ꢂ10À4 hÀ1, respectively, and their
half-lives (t1/2) were 753, 19800, 4620, and 770 h, respective-
Figure 6. The a) p-type and b) n-type output characteristics of an FET
based on 3.
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Y. Yamashita et al.
(2C), 129.17 (4C), 128.85 (4C), 128.50 (2C), 127.70 (2C), 127.32 (2C),
122.31 (2C), 120.41 (2C), 119.53 ppm (2C); IR (KBr): n˜ =3054, 1563,
1557, 1488, 1367, 1346, 1332, 1170, 1028, 932, 892, 761, 697 cmÀ1; MS (EI)
(70 eV): m/z (%): 404 (100) [M+]; elemental analysis calcd (%) for
C32H20: C 95.02, H 4.98; found: C 94.89, H 4.65.
These results are consistent with the amphoteric redox prop-
erties of the IF core. The relatively low mobilities obtained
here may be ascribed to the less-ordered molecular arrange-
ments in the thin films, because no sharp reflection peak
was observed in the XRD diffractograms of vapor-deposited
thin films. Modification of the p-conjugated systems by in-
troducing substituents may improve the carrier-transporting
properties.
Synthesis of 6,12-bis(2,6-difluorophenyl)indenoACTHNUTRGNEUG[N 1,2-b]fluorene (3): n-Bu-
tyllithium (1.65m, 2.47 mL, 4.07 mmol) was added dropwise to a solution
of 1,3-difluorobenzene (464 mg, 4.07 mmol) in dry THF (40 mL) at
À788C under Ar. The mixture was kept for 1 h. A suspension of dione 8
(500 mg, 1.77 mmol) in THF (10 mL) was added to the solution, and the
reaction mixture was stirred at À788C for 2 h and warmed to RT. The re-
action mixture was heated at reflux for 8 h. A solution of tin(II) chloride
anhydride (0.77 g, 4.07 mmol) in concentrated HCl (10 mL) was added to
the mixture, and the mixture was heated at reflux for 24 h. After the sol-
vent was removed, the residue was neutralized with 10% aqueous NaOH
(200 mL). After extraction of the mixture with toluene, the organic layer
was washed with water and brine and dried over Na2SO4. After the sol-
vent was removed, the crude product was purified by silica column chro-
matography (CH2Cl2) followed by sublimation. Black crystals (193 mg,
Conclusion
In conclusion, we have succeeded in preparing fused poly-
cyclic IF derivatives with aryl substituents and investigated
the effect of aryl substituents. We have found here that the
molecular structures, the physical properties accompanied
by HOMO–LUMO energies, and the stability are signifi-
cantly dependent on the aryl substituents. Twisted bulky
substituents increase the contribution of the quinoid struc-
ture and enhance the stability. This fact could be supported
by X-ray single-crystal analysis along with DFT calculations.
Furthermore, we have demonstrated the ambipolar carrier
transportation of the IFs for the first time. Although the
mobilities of vapor deposition films are not so high on ac-
count of the amorphous film structures, the modification of
the structures would improve the FET performances. Con-
struction of further fused polycyclic systems is now under-
way in our group.
1
0.407 mmol) of 3 were obtained in 23% yield. M.p. 350–3518C; H NMR
(300 MHz, CDCl3, 218C): d=7.43 (brt, 2H), 7.34 (brd, 2H), 7.15–6.98
(m, 10H), 6.94–6.89 ppm (m, 2H); 13C NMR (75 MHz, CDCl3, 238C):
d=162.45 (dd,
JACHTUNGTRENNUNG
137.57 (2C), 136.42 (2C), 133.57 (2C), 130.39 (t, JAHCTUNGTRENNUNG
128.05 (2C), 127.57 (2C), 122.52 (2C), 120.48 (2C), 119.73 (2C), 112.2–
111.84 ppm (6C); IR (KBr): n˜ =3060, 1622, 1573, 1568, 1456, 1359, 1264,
1232, 1153, 999, 889, 860, 770, 760, 695, 549 cmÀ1; EI (MS) (70 eV): m/z
(%): 416 (100) [M+]; elemental analysis calcd (%) for C32H16F4: C 80.67,
H 3.38; found: C 80.90, H, 3.18.
Synthesis of 6,12-bis(anthracen-9-yl)indenoACTHNUTRGNE[NUG 1,2-b]fluorene (4): n-Butyl-
lithium (1.65m, 2.47 mL, 4.07 mmol) was added dropwise to a solution of
9-bromoanthracene (1.04 g, 4.07 mmol) in dry THF (40 mL) at À788C
under Ar. The suspension was kept for 1 h in THF (10 mL). A suspen-
sion of dione 8 (500 mg, 1.77 mmol) in THF (10 mL) was added to the
solution, and the reaction mixture was stirred at À788C for 2 h and
warmed to RT. The reaction mixture was heated at reflux for 8 h. A solu-
tion of tin(II) chloride anhydride (0.77 g, 4.07 mmol) in concentrated
HCl (10 mL) was added to the mixture, and the mixture was heated at
reflux for 24 h. The crude product was filtered by suction, washed with
water, methanol, and hexane, and dried under vacuum. Purification by
sublimation gave black crystals (0.150 mg, 0.248 mmol) of 4 in 14% yield.
M.p. >3508C; 1H NMR (400 MHz, [D4]o-dichlorobenzene, 908C): d=
8.53 (s, 2H), 8.11 (d, J=8.5 Hz, 4H), 8.06 (d, J=8.5 Hz, 4H), 7.45 (t, J=
8.5 Hz, 4H), 7.31 (t, J=8.5 Hz, 4H), 6.91 (d, J=1.1 Hz, 2H), 6.88 (d, J=
7.5 Hz, 2H), 6.81 (t, J=7.5 Hz, 2H), 6.73 (t, J=7.5 Hz, 2H), 6.42 ppm (d,
Experimental Section
General: Melting points were obtained using a Shimadzu DSC-60. 1H
and 13C NMR spectra were recorded using a Jeol-ECP 300 spectrometer.
An 1H NMR spectrum at high temperature was recorded using a Bruker
AVANCE-400 spectrometer. EI-MS and FAB-MS data were collected
using a JEOL JMS-700 mass spectrometer. IR spectra were recorded
using a JASCO FT/IR-4100 Fourier transform infrared spectrometer.
UV/Vis spectra were recorded using a JASCO V-650 spectrophotometer.
Cyclic voltammograms were recorded using a Hokuto-Denko HZ-5000.
Pt disk, Pt wire, and SCE were used as working, counter, and reference
electrodes. XRD measurements were carried out using a Rigaku RINT
with a CuKa source (l=1.541 ꢁ).
J=7.5 Hz, 2H); IRACTHUNTGRNEUNG(KBr): n˜ =3046, 2357, 1713, 1567, 1557, 1443, 1410,
1344, 1266, 890, 759, 737, 703, 514 cmÀ1; MS (EI) (70 eV): m/z (%): 604
(100) [M+]; elemental analysis calcd (%) for C48H28: C 95.33, H 4.67;
found: C 95.46, H 4.48.
Synthesis of 6,12-bis(5-hexylthiophen-2-yl)indenoACHTNUTRGNE[NUG 1,2-b]fluorene (5): n-
Synthesis of 6,12-diphenylindenoACTHNUTRGNE[UNG 1,2-b]fluorene (2): n-Butyllithium
Butyllithium (1.65m, 2.46 mL, 4.07 mmol) was added dropwise to a solu-
tion of 2-hexylthiophene (690 mg, 4.07 mmol) in dry THF (30 mL) at
À788C under Ar. The mixture was kept for 1 h. A suspension of dione 8
(500 mg, 1.77 mmol) in THF (20 mL) was added to the solution, and the
reaction mixture was stirred at À788C for 2 h and warmed to RT. The re-
action mixture was heated at reflux for 12 h. A solution of tin(II) chlo-
ride dihydrate (SnCl2/2H2O) (0.77 g, 4.07 mmol) in concentrated HCl
(10 mL) was added to the mixture, and the mixture was heated at reflux
for 2 h. After the solvent was removed, the residue was neutralized with
10% aqueous NaOH (200 mL). After extraction of the mixture with tolu-
ene, the organic layer was washed with water and brine, and dried over
Na2SO4. After solvent was removed, the crude product was purified by
silica column chromatography (CH2Cl2) and by GPC (CHCl3) to give
a blue solid (37 mg, 0.0633 mmol) of 5 in 4% yield. M.p. 120–1218C;
1H NMR (300 MHz, CDCl3, 258C): d=7.74 (s, 2H), 7.61 (brt, 2H), 7.51
(brt, 2H), 7.41 (d, J=3.3 Hz, 2H), 7.11 (brt, 4H), 6.94 (d, J=3.3 Hz,
2H), 2.96 (t, J=7.5 Hz, 4H), 1.81–1.70 (m, 4H), 1.51–1.26 (m, 12H),
1.00–0.92 ppm (m, 6H); 13C NMR (75 MHz, CDCl3, 238C): d=148.84
(1.65m, 2.47 mL, 4.07 mmol) was added dropwise to a solution of bromo-
benzene (634 mg, 4.07 mol) in dry THF (40 mL) at À788C under Ar. The
mixture was kept for 1 h in THF (10 mL). A suspension of 8 (500 mg,
1.77 mmol) in THF (10 mL) was added to the solution, and the reaction
mixture was stirred at À788C for 2 h and warmed to RT. The reaction
mixture was heated at reflux for 8 h. A solution of tin(II) chloride anhy-
dride (0.77 g, 4.07 mmol) in concentrated HCl (10 mL) was added to the
mixture, and the mixture was heated at reflux for 24 h. After the solvent
was removed, the residue was neutralized with 10% aqueous NaOH
(200 mL). After extraction of the mixture with toluene, the organic layer
was washed with water and brine and dried over Na2SO4. After the sol-
vent was removed, the crude product was purified by silica column chro-
matography (CH2Cl2) followed by sublimation. Black crystals (179 mg,
0.44 mmol) of compound 2 were obtained in 25% yield. M.p. 241–2428C;
1H NMR (300 MHz, CDCl3, 238C): d=7.63 (dd, J=7.8, 1.8 Hz, 4H), 7.56
(dd, J=7.8, 7.8 Hz, 4H), 7.48–7.39 (m, 4H), 7.37 (s, 2H), 7.28–7.27 (m,
2H), 7.09–7.02 ppm (m, 4H); 13C NMR (75 MHz, CDCl3, 258C): d=
144.28 (2C), 143.28 (2C), 139.56 (2C), 138.24 (2C), 134.21 (2C), 133.73
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IndenoACHTUNGTRENNUNG[1,2-b]fluorenes
FULL PAPER
(2C), 142.22 (2C), 139.12 (2C), 138.52 (2C), 135.78 (2C), 134.51 (2C),
132.62 (2C), 128.22 (2C), 127.47 (2C), 127.11 (2C), 125.39 (2C), 122.68
(2C), 120.13 (2C), 119.07 (2C), 31.57–31.58 (4C), 30.42 (2C), 28.89 (2C),
22.60 (2C), 14.10 ppm (2C); IR (KBr): n˜ =1727, 1549, 1509, 1451, 1342,
1134, 929, 889, 809, 760, 700 cmÀ1; MS (FAB): m/z: 584 [M+]; HRMS
(FAB): m/z calcd for C40H40S2: 584.2571 [M+]; found: 584.2568; elemen-
tal analysis calcd (%) for C40H40S2: C 82.14, H 6.89, S 10.96; found: C
80.19, H 7.86, S 8.88.
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X-ray crystal-structure analysis: The X-ray measurements of 2, 3, and 4
were carried out using a Rigaku R-AXIS RAPID imaging plate diffrac-
tometer with MoKa radiation (l=0.71075 ꢁ) at À1808C. The structures
were solved by direct methods (SIR2004) and refined by full-matrix
least-squares methods on F2 with anisotropic temperature factors for
non-hydrogen atoms. Hydrogen atoms were refined using the riding
model. Absorption correction was applied using an empirical procedure.
Crystal data for 2: C32H20; Mr =404.51; crystal dimensions 0.78ꢂ0.78ꢂ
0.75 mm; orthorhombic; space group Pbcn; a=26.8450(13), b=
10.3708(5),
c=7.3818(3) ꢁ;
V=2055.13(16) ꢁ3;
Z=4;
1calcd =
1.307 gcmÀ3; 18425 reflections collected, 2365 independent (Rint =0.045);
GoF=1.09, R1 =0.048, wR2 =0.140 for all reflections.
Crystal data for 3: C32H16F4; Mr =476.47; crystal dimensions 0.30ꢂ0.30ꢂ
0.25 mm; monoclinic; space group P21/c; a=8.4169(8), b=11.2467(10),
c=11.3554(11) ꢁ; b=90.082(3)8; V=1074.93(17) ꢁ3; Z=2; 1calcd
=
1.472 gcmÀ3; 10065 reflections collected, 2470 independent (Rint =0.063);
GoF=1.087, R1 =0.061, wR2 =0.182 for all reflections.
Crystal data for 4: C48H28; Mr =604.75; crystal dimensions 0.40ꢂ0.30ꢂ
0.30 mm; monoclinic; space group C2/c; a=20.6738(20), b=8.3161(8),
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c=17.5904(19) ꢁ; b=91.287(3)8; V=3023.5(5) ꢁ3; Z=4; 1calcd
=
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CCDC-866841 (2), -866842 (3), and -866843 (4) contain the supplementa-
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www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research (nos.
19350092 and 22550162) from the Ministry of Education and Culture,
Sports, Science and Technology, Japan, and by the Global COE program
“Education and Research Center for Emergence of New Molecular
Chemistry”. We thank Material Analysis Suzukake-dai Center, Technical
Department, Tokyo Institute of Technology, for elemental analysis, MS
measurements, and high-temperature NMR spectroscopic measurements.
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Received: February 23, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
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Y. Yamashita et al.
Substituent dependency: Fused poly-
cyclic indenoACHTNUGTRNEUNG[1,2-b]fluorene derivatives
Quinoid Compounds
with aryl substituents have been pre-
pared as a potential example of antiar-
omatic 20p electronic systems (see
scheme). X-ray analysis revealed qui-
noid-type molecular structures, which
indicated that the bond lengths of the
quinoid unit depend on the aryl sub-
stituents.
J.-i. Nishida, S. Tsukaguchi,
Y. Yamashita* ................. &&&& — &&&&
Synthesis, Crystal Structures, and
Properties of 6,12-Diaryl-Substituted
IndenoACHTUNGTRENNUNG[1,2-b]fluorenes
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These are not the final page numbers!