Facile synthesis, structure, and properties of benzo[1,2-b:4,5-b′] dichalcogenophenes

Article abstract of DOI:10.1021/jo051812m

A general and convenient synthesis of benzo[1,2-b:4,5-b′]- dichalcogenophenes including the thiophene (BDT, 1), selenophene (BDS, 2), and tellurophene (BDTe, 3) homologues is developed. Thus synthesized heterocycles are structurally characterized by single-crystal X-ray analysis, and all three homologues are isostructural with one another. They all have completely planar molecular structures packed in a herringbone arrangement. Their physicochemical properties were also elucidated by means of cyclic voltammetry (CV) and UV-vis spectra.

Full text of DOI:10.1021/jo051812m

SCHEME 1. Synthesis of
Benzodichalcogenophenes 1-3
Facile Synthesis, Structure, and Properties
of Benzo[1,2-b:4,5-b′]dichalcogenophenes
Kazuo Takimiya,* Yasushi Konda, Hideaki Ebata,
Naoto Niihara, and Tetsuo Otsubo
Department of Applied Chemistry, Graduate School of
Engineering, Hiroshima University, Kagamiyama 1-4-1,
Higashi-Hiroshima 739-8527, Japan
ktakimi@hiroshima-u.ac.jp
Received August 28, 2005
ment of new electronic materials, because in general,
carrier transport in organic solids is governed by inter-
molecular overlap, which can be enhanced by intermo-
lecular chalcogen-chalcogen contacts. In this regard, it
is important to develop an effective synthetic method for
these heterocycles as a key molecular framework for
novel functional materials. We report here a general
synthetic route to the parent benzo[1,2-b:4,5-b′]dichal-
cogenophenes (1-3), the X-ray structures, and electro-
chemical and photochemical properties of the materials.
A general and convenient synthesis of benzo[1,2-b:4,5-b′]-
dichalcogenophenes including the thiophene (BDT, 1), se-
lenophene (BDS, 2), and tellurophene (BDTe, 3) homologues
is developed. Thus synthesized heterocycles are structurally
characterized by single-crystal X-ray analysis, and all three
homologues are isostructural with one another. They all
have completely planar molecular structures packed in a
herringbone arrangement. Their physicochemical properties
were also elucidated by means of cyclic voltammetry (CV)
and UV-vis spectra.
Synthesis. The reported syntheses of the sulfur com-
pound, BDT (1), by Kossmehl et al.8 or Katz et al.,5a
require thiophene derivatives as key starting materials.
Because of limited availability of selenophene and tel-
lurophene derivatives,9 we sought a different synthetic
strategy applicable to not only 1 but also BDS (2) and
BDTe (3). Thus, starting from the central benzene part
we examined an intramolecular cyclization reaction
between the acetylene substituents and the chalcogenate
anion intermediates (Scheme 1).10
Thiophene-containing fused-aromatic compounds rep-
resent an interesting class of electronic materials utilized
for organic conductors,1,2 narrow band gap polymers,3,4
and field-effect transistors.5 Benzo[1,2-b:4,5-b′]dithiophene
(BDT, 1) is one of such prototypical π-frameworks and
has been widely used.5a,6 The selenium and tellurium
homologues, benzo[1,2-b:4,5-b′]diselenophene (2) and ben-
zo[1,2-b:4,5-b′]diselenophene (3), are so far unknown,7 but
these heterocycles are very intriguing in view of develop-
(5) (a) Laquindanum, G. L.; Katz, H. E.; Lovinger, A. J.; Dodabal-
apur, A. Adv. Mater. 1997, 9, 36-39. (b) Li, X.-C.; Sirringhaus, H.;
Garnier, F.; Holmes, A. B.; Moratti, S. C.; Feeder, N.; Clegg, W.; Teat,
S. J.; Friend, R. H. J. Am. Chem. Soc. 1998, 120, 2206-2207. (c)
Sirringhaus, H.; Friend, R. H.; Wang, C.; Leuningerb, J.; Mu¨llen, K.
J. Mater. Chem. 1999, 9, 2095-2101. (d) Laquindanum, J. G.; Katz,
H. E.; Lovinger, A. J. J. Am. Chem. Soc. 1998, 120, 664-672. (e)
Kunugi, Y.; Takimiya, K.; Yamashita, K.; Aso, Y.; Otsubo, T. Chem.
Lett. 2002, 958-959. (f) Takimiya, K.; Kunugi, Y.; Toyoshima, Y.;
Otsubo, T. J. Am. Chem. Soc. 2005, 127, 3605-3612. (g) Nicolas, Y.;
Blanchard, P.; Roncali, J.; Allain, M.; Mercier, N.; Deman, A.-J.; Tardy,
J. Org. Lett. 2005,7, 3513-3516. (h) Xiao, K.; Liu, Y.; Qi, T.; Zhang,
W.; Wang, F.; Gao, J.; Qiu, W.; Ma, Y.; Cui, G.; Chen, S.; Zhan, X.; Yu,
G.; Qin, J.; Hu, W.; Zhu, D. J. Am. Chem. Soc. 2005, 127, 13281-
13286.
* To whom correspondence should be addressed. Tel: +81-82-424-
7734. Fax: +81-82-424-5494.
(1) For reviews on organic conductors based on sulfur-containing
aromatics, see: (a) Nakasuji, K. Pure Appl. Chem. 1990, 62, 477-482.
(b) Otsubo, T. Synlett 1997, 544-550.
(2) (a) Wudl, F.; Haddon, R. C.; Zellers, E. T.; Bramwell, F. B. J.
Org. Chem. 1979, 44, 2491-2493. (b) Kono, Y.; Miyamoto, H.; Aso, Y.;
Otsubo, T.; Ogura, F.; Tanaka, T.; Sawada, M. Angew. Chem., Int. Ed.,
Engl. 1989, 28, 1222-1123. (c) Otsubo, T.; Kono, Y.; Hozo, N.;
Miyamoto, H.; Aso, Y.; Ogura, F.; Tanaka, T.; Sawada, M. Bull. Chem
Soc. Jpn. 1993, 66, 2033-2041. (d) Takimiya, K.; Yashiki, F.; Aso, Y.;
Otsubo, T.; Ogura, F.; Chem. Lett. 1993, 365-367. (e) Takimiya, K.;
Otsubo, T.; Ogura, F. J. Chem. Soc., Chem. Commun. 1994, 1859-
1860. (f) Takimiya, K.; Kato, K.; Aso, Y.; Ogura, F.; Otsubo, T. Bull.
Chem Soc. Jpn. 2002, 75, 1795-1805.
(3) (a) Roncali, J. Chem. Rev. 1997, 97, 173-206. (b) Pomerantz,
M. in Handbook of Conducting Polymers, 2nd ed.; Skotheim, T. A.,
Elsenbaumer, R. L., Reynolds, J. R., Eds.; Marcel Dekker: New York,
1998; pp 277-309.
(4) (a) Wudl, F.; Kobayashi, M.; Heeger, A. J. J. Org. Chem. 1984,
49, 3382-3384. (b) Kobayashi, M.; Boysel, N.; Wudl, F.; Heeger, A. J.
J. Chem. Phys. 1985, 82, 5717-5723.
(6) (a) Kobayashi, K.; Gajurel, C. L. J. Chem. Soc., Chem. Commun.
1986, 1779-1980. (b) Yoshida, S.; Fujii, M.; Aso, Y.; Otsubo, T.; Ogura,
F. J. Org, Chem. 1994, 59, 3077-3081.
(7) Recently we have reported the synthesis of 2,6-diphenyl deriva-
tives of benzo[1,2-b:4,5-b′]dichalcogenophenes and their utilization for
organic field-effect transistors; Takimiya, K.; Kunugi, Y.; Konda, Y.;
Niihara, N.; Otsubo, T. J. Am. Chem. Soc. 2004, 126, 5084-5085.
(8) Beimling, P.; Kossmehl, G. Chem. Ber. 1986, 119, 3198-3203.
(9) Renson, M. In The Chemistry of Organic Selenium and Tellurium
Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley & Sons:
Chichester, 1986; Vol. 1, pp 406-444.
(10) (a) Sashida, H.; Sadamori, K.; Tsuchiya, T. Synth. Commun.
1998, 28, 713-727. (b) Neef, C. J.; Brotherston, I. D.; Ferraris, J. P.
Chem. Mater. 1999, 11, 1957-1958.
10.1021/jo051812m CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/15/2005
J. Org. Chem. 2005, 70, 10569-10571
10569

TABLE 1. Electrochemical and UV-vis Data of 1-3
Together with Their Estimated HOMO and LUMO Levels
Eoxa (V)
λmaxb (nm) HOMOc Eg
LUMO
(eV)
d
anodic/onset peak/edge
(eV)
(eV)
BDT (1)
BDS (2)
+0.95/+0.80
+0.89/+0.73
335/344
350/357
380/398
-5.6
-5.5
-5.1
3.6
3.5
3.1
-2.0
-2.0
-2.0
BDTe (3) +0.48/+0.29
a Versus Fc/Fc+. b Absorption spectra. c Estimated from the
onset of oxidation peak. d Determined from absorption edge.
FIGURE 1. Cyclic voltammograms of 1-3.
For the synthesis of 1, 1,4-dibromo-2,5-bis(2-trimeth-
ylsilylethynyl)benzene (4) prepared from 1,4-dibromo-2,5-
diiodobenzene and trimethylsilylacetylene by the palla-
dium-catalyzed Sonogashira coupling11 was treated
t
consequently with BuLi and elemental sulfur, and the
reaction was finally quenched by addition of alcohol. After
the usual workup and purification by column chroma-
tography, desired 2,6-bis(trimethylsilyl)benzo[1,2-b:4,5-
b′]dithiophene (1′) was isolated in 70% yield, which was
then easily desilylated by a treatment with tetrabutyl-
ammonium fluoride (TBAF) to give 1 in 96% yield. In a
similar manner, BDS (2) and BDTe (3) were synthesized
using selenium and tellurium powder, respectively, via
bis(trimethylsilyl)derivatives 2′ and 3′, respectively. Two
novel heterocycles 2 and 3 were fully characterized by
spectroscopic and combustion elemental analyses.
X-ray Structure Analysis. Single crystals of suitable
quality for X-ray analysis were obtained by sublimation12
for BDT (1) or recrystallization from chloroform for BDS
(2) and BDTe (3). Compounds 1-3 are isostructural to
one another with triclinic P-1 space group. The unit cells
consist of two crystallographically independent molecules,
both of which are located at the inversion center. All of
these benzodichalcogenophenes are completely planar as
shown in Figure S1 and crystallize in a typical her-
ringbone arrangement (see Supporting Information, Fig-
ures S1 and S2).
Electrochemical and Photochemical Properties.
Electrochemical studies were carried out by means of
cyclic voltammetry (CV). All of these heterocycles show
irreversible oxidation waves (Figure 1), and the oxidation
potentials (Table 1) defined by anodic peaks shift ca-
thodically from +0.95 V (vs Fc/Fc+) for BDT (1) to +0.48
V for BDTe (3), indicating that the HOMO level elevates
in the order of BDT (1) < BDS (2) , BDTe(3). From the
onset of the oxidation peaks listed in Table 1, the HOMO
FIGURE 2. UV-vis spectra of 1-3 in THF.
levels of these compounds are roughly estimated to be
-5.6 eV for 1, -5.5 eV for 2, and -5.1 eV for 3 under the
premise that the energy level of Fc/Fc+ is 4.8 eV below
the vacuum level.13
UV-vis spectra of the present benzodichalcogenophenes
(1-3) shown in Figure 2 are similar to one another in
shape, reflecting their similar electronic structures. They
consist of three bands, located at around ∼260, 300, and
330-400 nm. The first and the third bands shift batho-
chromically in the order of BDT (1), BDS (2), and BDTe
(3). Since the third band can be assigned as the π-π*
transition, HOMO-LUMO energy gap is estimated to be
3.1-3.6 eV from the absorption edges. Taking into
account the HOMO levels of 1-3 determined electro-
chemically, the LUMO levels of 1-3 are estimated to be
almost the same (Table 1). This means that the chalcogen
atoms in the present π-framework do not play an
important role in the LUMO, whereas they do in the
HOMO. This consideration is qualitatively supported by
MO calculations.14 The HOMO and LUMO of BDT (1)
are depicted in Figure 3 as representative of the benzo-
dichalcogenophene system. It should be noted that large
coefficients reside on the chalcogen atoms in the HOMO,
(13) (a) Bre´das, J.-L.; Silbey, R.; Boudreaux, D. S.; Chance, R. R. J.
Am. Chem. Soc. 1983, 105, 6555-6559. (b) Pommerehne, J.; Vestweber,
H.; Guss, W.; Mark, R. F.; Ba¨ssler, H.; Porsch, M.; Daub, J. Adv. Mater.
1995, 7, 551-554.
(14) MO calculations were carried out by DFT methods at the
B3LYP-6-31G(d) level using the PCGAMESS program. (a) Granovsky,
A. A. http://classic.chem.msu.su/gra/gamess/indx.html. (b) Schmidt, M.
W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.; Jensen,
J. J.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; Windus, T. L.;
Dupuis, M.; Montgomery, J. A. J. Comput. Chem. 1993, 14, 1347-
1363.
(11) Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. J. Am. Chem.
Soc. 1997, 119, 4578-4593.
(12) Laudise, R. A.; Kloc, C.; Simpkins, P. G.; Siegrist, T. J. Cryst.
Growth 1998, 187, 449-454.
10570 J. Org. Chem., Vol. 70, No. 25, 2005

was washed with water (20 mL × 3), dried over MgSO4
(anhydrous), and concentrated in vacuo. The residue was puri-
fied by column chromatography on silica gel eluted with hexane
(Rf ) 0.4) to give colorless microcrystals after recrystallization
1
from hexane (0.3 g, 65%): mp 181-184 °C; H NMR δ 0.38 (s,
18H), 7.71 (s, 2H), 8.31 (s, 2H); 13C NMR δ -0.1, 121.5, 133.6,
140.8, 141.6, 148.1; MS (EI) m/z 430 (M+). Anal. Calcd for C16H22-
Se2Si2: C, 44.85; H, 5.18. Found: C, 44.77; H, 5.03.
2,6-Bis(trimethylsilyl)benzo[1,2-b:4,5-b′]dithiophene (1′).
Compound 1′ was prepared from 4 by a similar reaction as
colorless microcrystals (hexane), 70% yield: mp 191-192 °C; 1H
NMR δ 0.39 (s, 18H), 7.45 (s, 2H), 8.26 (s, 2H); 13C NMR δ -0.4,
116.0, 129.8, 139.1, 140.7, 143.6; MS (EI) m/z 334 (M+). Anal.
Calcd for C16H22S2Si2: C, 57.42; H, 6.63. Found: C, 57.62; H,
6.83.
2,6-Bis(trimethylsilyl)benzo[1,2-b:4,5-b′]ditelluro-
phene (3′). Pale yellow plates from chloroform, 55% yield: mp
234-235 °C; 1H NMR δ 0.34 (s, 18H), 8.14 (s, 2H), 8.34 (s, 2H);
13C NMR δ 0.4, 130.7, 131.0, 141.4, 142.7, 147.9; MS (EI) m/z
530 (M+). Anal. Calcd for C16H22Si2Te2: C, 36.55; H, 4.22.
Found: C, 36.30; H, 4.25.
FIGURE 3. Optimized geometry and frontier orbitals of BDT
(1) at the B3LYP-6-31G(d) level: (a) HOMO and (b) LUMO.
and on the contrary the coefficients on the chalcogen
atoms in the LUMO are fairly small.
By employing 1,4-dibromo-2,5-bis(2-trimethylsilyleth-
ynyl)benzene (4) as a common intermediate, all of the
benzo[1,2-b:4,5-b′]dichalcogenophenes (1-3) are effec-
tively synthesized via double-heterocycle formation. The
resulting heteroarens 1-3 have a planar molecular
structure and assume a herringbone packing in their
crystal structures elucidated by X-ray crystallographic
analysis.
Studies on electrochemical properties and UV-vis
spectra of the benzodichalcogenophenes gave a rough
estimation of the levels of their frontier orbitals. Rather
lower oxidation potentials were recorded for the tellurium
homologue, BDTe (3), which has the highest HOMO level
among the three compounds. On the other hand, the
LUMO levels estimated from the HOMO-LUMO energy
gap determined by the absorption edge in UV-vis spectra
are almost the same. These experimental results can be
understood by the nature of the calculated frontier
molecular orbitals. Thus, benzo[1,2-b:4,5-b′]chalcogeno-
phenes with heavy chalcogen atoms, especially tellurium
atoms, are expected to be a suitable component for the
p-type (hole transporting) organic semiconductor rather
than the n-type (electron transporting).
Typical Procedure for the Synthesis of Benzo[1,2-b:4,5-
b′]dichalcogenophens (1-3). Benzo[1,2-b:4,5-b′]diseleno-
phene (2). To a solution of 2′ (0.23 g, 0.5 mmol) in THF (10
mL) was added a solution of tetrabutylammonium fluoride (1.0
M, 1.1 mL, 1.1 mmol), and the resulting solution was stirred at
room temperature for 3 h. Addition of water (20 mL) made a
precipitate, which was collected by filtration. The product was
successively washed with water (10 mL) and ethanol (10 mL)
and dried. Recrystallization from chloroform gave analytical
sample of 2 as colorless plates (0.13 g, 93%): mp 255-257 °C
(in a sealed tube); 1H NMR δ 7.58 (d, J ) 5.9, 2H), 7.98 (d, J )
5.9, 2H), 8.35 (s, 2H); 13C NMR δ 122.0, 126.8, 128.8, 137.8,
139.8; MS (EI) m/z 286 (M+). Anal. Calcd for C10H6Se2: C, 42.28;
H, 2.14. Found: C, 42.27; H, 2.16. UV-vis (in THF): λmax (ꢀ) )
256 (45328), 265 (53924), 291 (7746), 302 (6433), 318 (3267), 331
(9763), 346 (18774) nm. PL (in THF): λmax ) 367 nm (Φ ) 2.5
× 10-4).
Benzo[1,2-b:4,5-b′]dithiophene (1)8. Compound 1 was pre-
pared from 1′ by a similar reaction, 96% yield: mp 199-201 °C
(197.5-198.0)8; 1H NMR δ 7.35 (d, J ) 5.5 Hz, 2H), 7.46 (d, J )
5.5 Hz, 2H), 8.31 (s, 2H); 13C NMR δ 116.8, 122.9, 127.0, 137.1,
137.5; MS (EI) m/z 190 (M+). UV-vis (in THF): λmax (ꢀ) ) 258
(61848), 280 (4316), 292 (6571), 302 (7432), 322 (7980), 335
(12722) nm; PL (in THF): λmax ) 343 nm (Φ ) 0.078).
Benzo[1,2-b:4,5-b′]ditellurophene (3). Yield 89%; mp 283-
285 °C (melt with decomposition); 1H NMR δ 7.88 (d, J ) 7.1
Hz, 2H), 8.30 (s, 2H), 8.64 (d, J ) 7.1 Hz, 2H); 13C NMR δ 120.4,
129.1, 130.9, 135.4, 145.0; MS (EI) m/z 386 (M+). Anal. Calcd
for C10H6Te2: C, 31.49; H, 1.59. Found: C, 31.59; H, 1.39. UV-
vis (in THF): λmax (ꢀ) ) 2709 (42178), 277 (39851), 295 (9899),
339 (4610), 356 (10183), 376 (19740) nm.
Experimental Section
1,4-Dibromo-2,5-bis(2-trimethylsilylethynyl)benzene (4).11
Trimethylsilylacetylene (5.8 mL, 41 mmol), PdCl2(PPh3)2 (400
mg, 0.6 mmol), and CuI (235 mg, 1.2 mmol) were added
successively to a deaerated solution of 1,4-dibromo-2,5-diiodo-
benzene11,15 (10.0 g, 21 mmol) in diisopropylamine (60 mL) and
benzene (100 mL). The resulting mixture was stirred for 1 h at
room temperature, then diluted with water (150 mL), and
extracted with ether (60 mL × 2). The extract was washed with
water (60 mL × 2) and dried (MgSO4). Evaporation of the solvent
gave an oily residue, which was subjected to column chroma-
tographyonsilicagelelutedwithhexanetogive1,4-dibromo-2,5-bis(tri-
methylsilylethynyl)benzene as a colorless solid (8.4 g, 97%): mp
Acknowledgment. This work was partially sup-
ported by Industrial Technology Research Grant Pro-
gram in 2005 from the New Energy and an Industrial
Technology Development Organization (NEDO) of Ja-
pan and a Grant-in-Aid for Scientific Research on
Priority Areas of Molecular Conductors (no. 15073218)
and Scientific Research (no. 16750162) from the Min-
istry of Education, Science, Sports, and Culture, Japan.
K.T. is indebted for financial support from Electronic
Technology Research Foundation Chugoku.
1
167-170 °C; H NMR δ 0.27 (s, 18H), 7.67 (s, 2H); 13C NMR δ
-0.3, 101.4, 103.0, 123.7, 126.4, 136.4; MS (EI) m/z 428 (M+).
Typical Procedure for Synthesis of 2,6-Bis(trimethyl-
silyl)benzo[1,2-b:4,5-b′]dichalcogenophens (1′-3′). 2,6-Bis-
(trimethylsilyl)benzo[1,2-b:4,5-b′]diselenophene (2′). To a
solution of 4 (0.4 g, 1.0 mmol) in ether (15 mL) at -78 °C was
t
added a pentane solution of BuLi (1.4 M, 2.9 mL, 4.0 mmol).
The resulting mixture was stirred at the same temperature for
15 min and then gradually warmed to room temperature.
Selenium powder (0.16 g, 2.0 mmol) was then added in one
portion, and the resulting mixture was stirred for 15 min. After
addition of ethanol (30 mL), the mixture was further stirred for
1 h and then extracted with chloroform (20 mL × 3). The extract
Supporting Information Available: Crystallographic
Information Files (CIF) for 1-3, ORTEP drawings of molecular
structures of 1-3, crystal structure of 3, photo luminescence
(PL) spectra of 1 and 2, and details for molecular orbital (MO)
calculations. This material is available free of charge via the
Internet at http://pubs.acs.org.
(15) Hart, H.; Harada, K.; Du, C.-J. F. J. Org. Chem. 1985, 50,
3104-3110.
JO051812M
J. Org. Chem, Vol. 70, No. 25, 2005 10571