Synthesis, characterization, and photoluminescence of thiophene-containing spiro compounds

Article abstract of DOI:10.1055/s-2008-1078571

Spiro[fluorene-9,4′-[4H]indeno[3,2-b]thiophene] (spiro-FIT) and bis(spiro-FIT)arenes were synthesized. The UV/vis spectra, emission spectra, and cyclic voltammetry of these compounds are described. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1078571

1902
LETTER
Synthesis, Characterization, and Photoluminescence of Thiophene-Containing
Spiro Compounds
S
ynthesis and C
o
haracterizati
s
on of
T
hi
h
iy
uunds ki Kowada, Yoshio Matsuyama, Kouichi Ohe*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan
Fax +81(75)3832499; E-mail: ohe@scl.kyoto-u.ac.jp
Received 25 April 2008
temperature (Td), which are very important for the appli-
Abstract: Spiro[fluorene-9,4¢-[4H]indeno[3,2-b]thiophene]
cation of low-molecular-weight compounds to optoelec-
tronic devices. In addition, their solubility is higher than
(spiro-FIT) and bis(spiro-FIT)arenes were synthesized. The UV/
vis spectra, emission spectra, and cyclic voltammetry of these com-
that of the corresponding compounds without a spiro moi-
ety, because their perpendicular conformations based on
the spiro linkage efficiently suppress intermolecular inter-
actions between the p-systems. Thus, it is expected that
the solubility and FF in the solid state of thiophene-based
compounds would be improved by incorporation of a
spiro moiety into their framework. However, to the best of
our knowledge, there are few reports on spiro compounds
containing thiophene rings.5
pounds are described.
Key words: spiro compounds, Stille reaction, heterocycles, cross-
coupling, chromophores
Recently, p-conjugated compounds such as organic light-
emitting diodes (OLED), photovoltaic cell, and organic
field-effect transistors (OFET) have received consider-
able attention in the field of organic electronics. In partic-
ular, thiophene-based compounds such as poly- and
oligothiophenes are among the most studied organic ma-
terials because of their charge-transport properties.1
Thiophene/phenylene1c,2 and thiophene/fluorene1c,3 co-
oligomers have also been widely studied for applications
in OFET and OLED. These oligomers show better oxida-
tive stability than the all-thiophene analogues and are sta-
ble in air. However, these thiophene-based compounds
often face the problem of limited solubility. The incorpo-
ration of alkyl chains into the thiophene backbone results
in improved solubility. Their photoluminescence efficien-
cies (FF) are usually low because of increased nonradia-
tive decay, because the alkylated compounds tend to
interact with adjacent molecules in the solid state.1a The
interchain interaction is effective for applications in
OFET, but another type of method to increase the solubil-
ity of the materials for OLED is needed.
In this paper, we wish to report the synthesis and proper-
ties of the thiophene-containing spiro compounds,
spiro[fluorene-9,4¢-[4H]indeno[3,2-b]thiophene] (spiro-
FIT) and bis(spiro-FIT)arenes. The optical and electro-
chemical characteristics of bis(spiro-FIT)arenes are easily
tunable by changing the linking arenes. The Stille cou-
pling reaction can be used for their synthesis, and, thus,
desirable materials for practical applications to OLED can
be obtained.
Scheme 1 depicts the synthesis of spiro-FIT and its deriv-
atives.6a,b The reaction of 9-fluorenone with the Grignard
reagent derived from 1-bromo-2-thienylbenzene afforded
alcohol 1 in 58% yield. An acid-promoted intramolecular
alkylation furnished a thiophene-containing spiro com-
pound spiro-FIT in 96% yield. Bromination of spiro-FIT
with NBS or lithiation of spiro-FIT followed by reaction
with Bu3SnCl produced the bromo derivative Br-spiro-
FIT (76%) or Sn-spiro-FIT (70%), respectively.
9,9¢-Spirobifluorene derivatives are regarded as the most
promising candidates for construction of organic opto-
electronics.4 The rigidity of spiro compounds provides a
high glass-transition temperature (Tg) and decomposition
2,2¢-Bispiro[fluorene-9,4¢-[4H]indeno[3,2-b]thiophene]
(2) was synthesized by the Stille coupling reaction of Br-
S
S
S
X
S
a
b
c or d
OH
Br
1
58%
spiro-FIT
96%
(c) Br-spiro-FIT (X = Br) 76%
(d) Sn-spiro-FIT (X = SnBu3) 70%
Scheme 1 Synthesis of spiro-FIT, Br-spiro-FIT, and Sn-spiro-FIT. Reagents and conditions: (a) (i) Mg, THF, r.t., 1 h; (ii) 9-fluorenone,
THF, r.t. to reflux, 3 h; (b) HCl, AcOH, r.t., 1 h; (c) NBS, DMF, r.t., 14 h; (d) (i) t-BuLi, THF, –78 °C, 1 h; (ii) Bu3SnCl, –78 °C to r.t., 90 min.
SYNLETT 2008, No. 12, pp 1902–1906
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x
.x
x
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0
0
8
Advanced online publication: 02.07.2008
DOI: 10.1055/s-2008-1078571; Art ID: U04308ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis and Characterization of Thiophene-Containing Spiro Compounds
1903
Sn-spiro-FIT
+
Br-spiro-FIT
pling products 3d and 3h, respectively, although
prolonged reaction time was necessary (entries 4 and 8).
S
S
The thermal properties of prepared spiro compounds were
investigated by thermogravimetric analysis (TGA). They
showed high Td up to 442 °C (Table 2).
Pd(PPh3)4 (5 mol%)
toluene, 110 °C, 9 h
As shown in Figure 1, the cyclic voltammogram (CV) for
spiro-FIT in CH2Cl2 containing 0.10 M Bu4NPF6 showed
irreversible oxidation waves, while that of 2 showed re-
versible waves. Irreversible waves for spiro-FIT might
be due to in situ electrochemical oxidative coupling of its
generated radical cations. Oxidation waves of compounds
3a–f were reversible, while those of compounds 3g and 3h
were irreversible (Table 2). In comparison with com-
pound 2, the first oxidation potentials for 3a and 3b in-
crease with increasing length of the linkers. On the other
hand, the second oxidation potentials decrease. These data
suggest that the coulombic repulsion would decrease be-
cause of the long distance between both thiophene rings.7
Oxidation potentials are also affected by the electronic na-
2 77%
Scheme 2 Synthesis of 2
spiro-FIT with Sn-spiro-FIT (Scheme 2). The Stille
coupling reaction was also employed for the synthesis of
bis(spiro-FIT)arenes using several dibromoarenes and
two equivalents of Sn-spiro-FIT (Table 1).6c Several het-
eroaromatic rings (entries 5–8) as well as aromatic hydro-
carbons (entries 1–4) were successfully introduced.
Sterically hindered 9,10-dibromoanthracene and 6,6¢-di-
bromo-2,2¢-bipyridine reacted cleanly to produce the cou-
Table 1 Synthesis of Bis(spiro-FIT)arenes using Stille Couplinga
S
S
Ar
Br
Br
Ar
Pd(PPh3)4 (5 mol%)
toluene, 110 °C
Sn-spiro-FIT
3a–h
Yield (%)b
65
Ar
Entry
1
Time (h)
14
Product
3a
2
3
14
12
3b
3c
76
68
Me
Me
4
39
3d
77
5
6
10
12
3e
3f
74
82
S
O
7
8
13
40
3g
3h
83
85
N
N
N
a Sn-spiro-FIT (0.400 mmol) and dibromoarenes (0.200 mmol) in toluene (2.0 mL).
b Isolated yield.
Synlett 2008, No. 12, 1902–1906 © Thieme Stuttgart · New York

1904
T. Kowada et al.
LETTER
ture of the linkers. Incorporation of electron-rich het-
eroarenes, such as thiophene and furan, provides higher
HOMO levels (3e and 3f). In contrast, 3g and 3h involv-
ing pyridine and bipyridine lower their HOMO levels.
Similarly to the results of the CV, the electronic nature of
the linkers affects the absorption and emission maxima
(Figure 2). Both maxima of 3e were red shifted relative to
3a, while those of 3g were blue shifted. Compared with 2,
the absorption maxima of 3a–d with aromatic hydrocar-
bons as the linker were observed at almost the same wave-
length, although 3b exhibited a blue shift because of the
slightly twisted biphenyl ring (Table 2). However, for 2
and 3a,b, the values of FF are enhanced as the p-frame-
work is extended. Except for 3d, all bis(spiro-FIT)arenes
showed relatively high quantum yields.
Figure 1 The cyclic voltammograms of spiro-FIT and 2 in CH2Cl2
Figure 2 The UV/vis absorption and fluorescence spectra of 3a,b,e,g in THF
Table 2 Optical and Electrochemical Properties of spiro-FIT, 2, and 3a–h
abs lmax (nm)a e (× 104 L mol–1 cm–1) PL lmax (nm)b
c
FF
E1/2 oxd (V)d
0.96h
Td (°C)e
217
Spiro-FIT
300, 311
405
1.53
338, 348f
444, 471
441, 469
436, 462
440, 468
439, 466f
485, 519
465, 498
412, 433
411, 431
<0.01
0.07
0.48
0.71
0.60
0.02
0.32g
0.81g
0.76
0.53
i
2
3.54
0.50, 0.96
0.59, 0.84
0.68, 0.78
0.57, 0.74
0.58
–
3a
3b
3c
3d
3e
3f
403
5.49
438
i
389
6.65
–
i
404
6.69
–
i
403
1.63
–
434
4.41
0.41, 0.72
0.34, 0.69
0.82h
435
i
425
4.22
–
3g
352, 382
365, 379
3.83, 3.75
5.83, 6.00
442
i
3h
0.93h
–
a c = 1.00 × 10–5 mol L–1.
b c = 1.00 × 10–7 mol L–1; lex = 366 nm.
c Quinine sulfate in 0.1 M aq H2SO4 (366 nm, FF = 0.55) as a standard.
d In CH2Cl2 containing 0.10 M Bu4NPF6 vs. Fc/Fc+ at 100 mV s–1.
e Decomposition temperature obtained from TGA.
f c = 1.00 × 10–6 mol L–1.
g Fluorescein in 0.1 M aq NaOH (436 nm, FF = 0.90) as a standard.
h Irreversible.
i Not determined.
Synlett 2008, No. 12, 1902–1906 © Thieme Stuttgart · New York

LETTER
Synthesis and Characterization of Thiophene-Containing Spiro Compounds
1905
Some similar compounds without a spiro linkage have
been reported by other groups (Figure 3).2a,8
References and Notes
(1) (a) Perepichka, I. F.; Perepichka, D. F.; Meng, H.; Wudl, F.
Adv. Mater. 2005, 17, 2281. (b) Fichou, D. J. Mater. Chem.
2000, 10, 571. (c) Murphy, A. R.; Fréchet, J. M. J. Chem.
Rev. 2007, 107, 1066.
(2) (a) Mushrush, M.; Facchetti, A.; Lefenfeld, M.; Katz, H. E.;
Marks, T. J. J. Am. Chem. Soc. 2003, 125, 9414.
R
S
S
R
4a (R = H)
abs = 373 nm
(b) Dingemans, T. J.; Bacher, A.; Thelakkat, M.; Pedersen,
L. G.; Samulski, E. T.; Schmidt, H.-W. Synth. Met. 1999,
105, 171. (c) Hotta, S.; Ichino, Y.; Yoshida, Y.; Yoshida, M.
J. Phys. Chem. B 2000, 104, 10316. (d) Lee, S. A.; Hotta,
S.; Nakanishi, F. J. Phys. Chem. A 2000, 104, 1827.
(e) Ohsedo, Y.; Yamate, T.; Okumoto, K.; Shirota, Y.
J. Photopolym. Sci. Technol. 2001, 14, 297. (f) Kojima, T.;
Nishida, J.; Tokito, S.; Yamashita, Y. Chem. Lett. 2007, 36,
1198.
4b (R = n-C6H13
)
λ
λ
E
λ
λ
abs = 373 nm
em = 436, 460 nm
em = 431, 455 nm
1/2 oxd = 0.67, 1.18 V
S
S
S
R
R
5b (R = n-C6H13
)
5a (R = H)
(3) Aldred, M. P.; Vlachos, P.; Contoret, A. E. A.; Farrar, S. R.;
Chung-Tsoi, W.; Mansoor, B.; Woon, K. L.; Hudson, R.;
Kelly, S. M.; O’Neill, M. J. Mater. Chem. 2005, 15, 3208.
(4) (a) Saragi, T. P. I.; Spehr, T.; Siebert, A.; Fuhrmann-Lieker,
T.; Salbeck, J. Chem. Rev. 2007, 107, 1011. (b) Walzer, K.;
Maennig, B.; Pfeiffer, M.; Leo, K. Chem. Rev. 2007, 107,
1233. (c) Luo, J.; Zhou, Y.; Niu, Z.-Q.; Zhou, Q.-F.; Ma, Y.;
Pei, J. J. Am. Chem. Soc. 2007, 129, 11314. (d) Takagi, K.;
Momiyama, M.; Ohta, J.; Yuki, Y.; Matsuoka, S.; Suzuki,
M. Macromolecules 2007, 40, 8807.
(5) (a) Xie, L.-H.; Fu, T.; Hou, X.-Y.; Tang, C.; Hua, Y.-R.;
Wang, R.-J.; Fan, Q.-L.; Peng, B.; Wei, W.; Huang, W.
Tetrahedron Lett. 2006, 47, 6421. (b) Mitschke, U.;
Bäuerle, P. J. Chem. Soc., Perkin Trans. 1 2001, 740.
(c) Ong, T.-T.; Ng, S.-C.; Chan, H. S. O.; Vardhanan, R. V.;
Kumura, K.; Mazaki, Y.; Kobayashi, K. J. Mater. Chem.
2003, 13, 2185. (d) Xie, L.-H.; Hou, X.-Y.; Hua, Y.-R.;
Huang, Y.-Q.; Zhao, B.-M.; Liu, F.; Peng, B.; Wei, W.;
Huang, W. Org. Lett. 2007, 9, 1619.
E1/2 oxd = 0.49, 0.86 V
λabs = 408 nm
λ
em = 472, 503 nm
R
S
S
R
6 (R = n-C6H13
)
λ
abs = 378 nm
em = 432, 458 nm
λ
Figure 3 Optical and electrochemical properties of thiophene/phen-
ylene oligomers
Both in the absorption and emission spectra, the maxi-
mum wavelengths of spiro compounds 2 and 3a,e are
bathochromic shifted compared with those of similar
compounds without a spiro linkage. In addition, spiro
compounds have lower oxidation potentials than nonspiro
compounds. It is considered that these results can be at-
tributed to the increase in planarity of the p-conjugated
systems as a result of the spiro linkage.
(6) Representative Experimental Procedures
(a) Preparation of Spiro[fluorene-9,4¢-[4H]indeno[3,2-
b]thiophene] (spiro-FIT)
To an AcOH solution (30 mL) of 9-(2-thienylphenyl)-
fluoren-9-ol (1, 390 mg, 1.14 mmol) was added concentrated
HCl (1 mL) at r.t., and the mixture was stirred for 1 h. After
the addition of H2O (30 mL), precipitate was collected,
washed with H2O, and dissolved in CH2Cl2. The CH2Cl2
solution was washed with 5% aq NaHCO3 and brine. The
organic layer was dried over MgSO4 and filtered. The
solvents were evaporated, and the residue was purified with
column chromatography on SiO2 (EtOAc–hexane, 1:50) to
give spiro-FIT (352 mg, 96%) as a white solid; mp 167.0–
167.3 °C. 1H NMR (300 MHz, CDCl3): d = 6.47 (d, 1 H,
J = 4.7 Hz), 6.63 (d, 1 H, J = 7.3 Hz), 6.80 (d, 2 H, J = 7.3
Hz), 6.98 (dd, 1 H, J = 7.3, 7.7 Hz), 7.12 (dd, 2 H, J = 7.3,
7.7 Hz), 7.22 (d, 1 H, J = 4.8 Hz), 7.28 (dd, 1 H, J = 7.3, 7.7
Hz), 7.36 (dd, 2 H, J = 7.3, 7.3 Hz), 7.53 (d, 1 H, J = 7.3 Hz),
7.82 (d, 2 H, J = 7.7 Hz). 13C NMR (75.5 MHz, CDCl3):
d = 63.5, 118.9, 120.0, 121.4, 123.7, 123.8, 125.9, 127.6,
127.7, 127.8, 128.1, 138.6, 141.7, 143.5, 146.8, 151.8,
152.0. Anal. Calcd for C23H14S: C, 85.68; H, 4.38. Found: C,
85.61; H, 4.18.
In summary, a new thiophene-containing spiro compound
spiro-FIT has been synthesized. Stille coupling between
Sn-spiro-FIT and dibromoarenes provided p-extended
bis(spiro-FIT)arenes. Almost all of the coupling products,
except for 3d, showed efficient photoluminescence.
[4H]Indeno[3,2-b]thiophenes containing the spirofluo-
rene structure as a building block are expected to find ap-
plications to organic functional materials.
Acknowledgment
This research was supported by Scientific Research B (No.
19350093) from the Japan Society for the Promotion of Science.
T.K. gratefully acknowledges the financial support by the Global
COE Program ‘International Center for Integrated Research and
Advanced Education in Materials Science’ (No. B-09) of MEXT.
We wish to thank Dr. Saburo Hosokawa and Professor Masashi
Inoue for assistance with TG analysis.
(b) Preparation of 2-Bromospiro[fluorene-9,4¢-
[4H]indeno[3,2-b]thiophene] (Br-spiro-FIT)
To a DMF solution (10 mL) of spiro-FIT (352 mg, 1.09
mmol) was added a solution of NBS (236 mg, 1.31 mmol) in
DMF (10 mL) in the dark, and the mixture was stirred at r.t.
for 14 h. The reaction mixture was poured into brine,
extracted with EtOAc, and washed with brine. The organic
layer was dried over MgSO4 and filtered. The solvents were
evaporated, and the residue was purified with column
Synlett 2008, No. 12, 1902–1906 © Thieme Stuttgart · New York

1906
T. Kowada et al.
LETTER
chromatography on SiO2 (EtOAc–hexane, 1:50) to give Br-
spiro-FIT (333 mg, 76%) as a white solid; mp 183.2–183.7
°C. 1H NMR (300 MHz, CDCl3): d = 6.48 (s, 1 H), 6.63 (d,
1 H, J = 7.7 Hz), 6.80 (d, 2 H, J = 7.3 Hz), 6.99 (dd, 1 H,
J = 7.3, 7.7 Hz), 7.12 (dd, 2 H, J = 7.3, 7.3 Hz), 7.27 (dd, 1
H, J = 7.3, 7.7 Hz), 7.36 (dd, 2 H, J = 7.3, 7.7 Hz), 7.46 (d,
1 H, J = 7.3 Hz), 7.82 (d, 2 H, J = 7.7 Hz). 13C NMR (75.5
MHz, CDCl3): d = 64.1, 114.0, 118.9, 120.1, 123.7, 123.8,
124.5, 126.2, 127.8, 128.0, 138.3, 141.7, 143.6, 146.0,
150.5, 150.9 (one peak cannot be discriminated due to
overlap with another peak). Anal. Calcd for C23H13BrS: C,
68.83; H, 3.30. Found: C, 68.59; H, 3.27.
dissolved in THF, and filtered by Florisil. The solvents were
evaporated to give 3f (117 mg, 82%) as a yellow solid; mp
>300 °C. 1H NMR (300 MHz, CDCl3): d = 6.39 (s, 2 H),
6.61–6.63 (m, 4 H), 6.82 (d, 4 H, J = 7.7 Hz), 6.97 (dd, 2 H,
J = 6.6, 7.7 Hz), 7.12 (dd, 4 H, J = 6.6, 7.3 Hz), 7.28 (dd, 2
H, J = 6.6, 7.3 Hz), 7.37 (dd, 4 H, J = 6.6, 7.3 Hz), 7.48 (d,
2 H, J = 7.7 Hz), 7.83 (d, 4 H, J = 7.7 Hz). 13C NMR (75.5
MHz, CDCl3): d = 63.7, 107.2, 116.7, 118.8, 120.1, 123.6,
123.8, 126.1, 127.8, 127.9, 136.0, 138.4, 141.7, 142.2,
146.4, 148.5, 151.5, 152.6 (one peak cannot be discriminated
due to overlap with another peak). Anal. Calcd for
C50H28OS2: C, 84.72; H, 3.98. Found: C, 84.45; H, 3.88.
(7) (a) Turbiez, M.; Frère, P.; Roncali, J. J. Org. Chem. 2003,
68, 5357. (b) Takamiya, K.; Oharuda, A.; Aso, Y.; Ogura,
F.; Otsubo, T. Chem. Mater. 2000, 12, 2196.
(8) (a) Apperloo, J. J.; Groenendaal, L. B.; Verheyen, H.;
Jayakannan, M.; Janssen, R. A. J.; Dkhissi, A.; Beljonne, D.;
Lazzaroni, R.; Brédas, J.-L. Chem. Eur. J. 2002, 8, 2384.
(b) Yokooji, A.; Satoh, T.; Miura, M.; Nomura, M.
Tetrahedron 2004, 60, 6757.
(c) Preparation of 2,5-bis{spiro[fluorene-9,4¢-
[4H]indeno[3,2-b]thiophen-2-yl]}furan (3f)
Sn-spiro-FIT (245 mg, 0.400 mmol), 2,5-dibromofuran
(45.1 mg, 0.200 mmol), Pd(PPh3)4 (11.6 mg, 0.0100 mmol),
and toluene (2 mL) were added to a dry Schlenk flask under
N2. After the mixture was stirred at 110 °C for 12 h in the
dark, the reaction mixture was cooled, and yellow precipitate
was filtered. The precipitate was washed with Et2O,
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