One-pot synthesis of symmetric octithiophenes from asymmetric β-alkylsulfanyl bithiophenes

Article abstract of DOI:10.1021/ma0614141

Starting from 4-(octylsulfanyl)-2,2′-bithiophene, 4-bromo-4′-(octylsulfanyl)-2,2′-bithiophene, 4-iodo4′- (octylsulfanyl)-2,2′-bithiophene, 4-bromo-4′-[(S)-2- methylbutylsulfanyl]-2,2′-bithiophene, and 4-iodo-4′-[(S)-2- methylbutylsulfanyl]-2,2′-bithiophene, a new series of symmetrically β-substituted octithiophenes were synthesized by one-pot oxidative coupling with FeCl₃. The octithiophenes obtained are soluble in common organic solvents and show different solvatochromic properties depending on the substitution type. In particular, the bromine atom exerts a positive influence on the supramolecular organization: the brominated octithiophenes display high filmability, solvatochromism, and CD induced by aggregation (when the chiral 2-methylbutylsulfanyl group is present), properties usually observed for polythiophenes. Density functional theory (DFT) calculations were carried out an a model bithiophene (4-substituted with a methylsulfanyl group) in order to understand the possible mechanism of the growth, the regiochemistry, and the reason for the polymerization leads to an octithiophene.

Full text of DOI:10.1021/ma0614141

Macromolecules 2006, 39, 8293-8302
8293
One-Pot Synthesis of Symmetric Octithiophenes from Asymmetric
â-Alkylsulfanyl Bithiophenes
Adele Mucci,* Francesca Parenti, Rita Cagnoli, Rois Benassi, Alessio Passalacqua,
Lisa Preti, and Luisa Schenetti
Dipartimento di Chimica, UniVersita` degli Studi di Modena e Reggio Emilia, Via G. Campi 183,
41100 Modena, Italy
ReceiVed June 23, 2006; ReVised Manuscript ReceiVed September 5, 2006
ABSTRACT: Starting from 4-(octylsulfanyl)-2,2′-bithiophene, 4-bromo-4′-(octylsulfanyl)-2,2′-bithiophene, 4-iodo-
4′-(octylsulfanyl)-2,2′-bithiophene, 4-bromo-4′-[(S)-2-methylbutylsulfanyl]-2,2′-bithiophene, and 4-iodo-4′-[(S)-
2-methylbutylsulfanyl]-2,2′-bithiophene, a new series of symmetrically â-substituted octithiophenes were
synthesized by one-pot oxidative coupling with FeCl3. The octithiophenes obtained are soluble in common organic
solvents and show different solvatochromic properties depending on the substitution type. In particular, the bromine
atom exerts a positive influence on the supramolecular organization: the brominated octithiophenes display high
filmability, solvatochromism, and CD induced by aggregation (when the chiral 2-methylbutylsulfanyl group is
present), properties usually observed for polythiophenes. Density functional theory (DFT) calculations were carried
out an a model bithiophene (4-substituted with a methylsulfanyl group) in order to understand the possible
mechanism of the growth, the regiochemistry, and the reason for the polymerization leads to an octithiophene.
Scheme 1
Introduction
Structurally well-defined oligothiophenes (OTs) have been
extensively investigated as model compounds to better under-
stand the properties of the related R-conjugated semiconducting
polymers. More recently, they have attracted increasing attention
as a low-cost alternative to silicon materials for electronic device
applications, such as field effect transistors (FET),1-3 organic
light-emitting diodes (OLED),4,5 photovoltaic cells,6,7 and sen-
sors.8,9 The good performances of R-conjugated oligomers are
strongly related to the fact that they are materials with a
rigorously defined chain and conjugation length, permitting a
better control on the supramolecular organization and thus well-
defined optical properties in the devices.10-12 Because, in most
applications, conjugated oligomers are used in the solid state,
the fact of being monodisperse materials, which often can be
crystallized and in many cases also sublimed, permits the
investigation of their solid-state properties in crystals or in vapor-
deposited thin films.13 On the other hand, the solubility of these
materials in organic solvents or water is a prerequisite for the
formation of films by spin-coating or casting techniques, and
in this respect, it is worthwhile stressing that oligomers are more
soluble than related polymers, and an improved solubility,
together with the possibility of a modulation of the chemical-
physical properties, can be achieved by adequate substitutions
in the â-position of the thiophene ring.
Our previous studies on alkylsulfanyl bithiophenes have
shown that oxidative polymerization with FeCl3 of 4,4′-bis-
(alkylsulfanyl)-2,2′-bithiophenes afforded high-molecular-weight
polymers with very interesting chemical physical properties,
such as a small band gap between ground and excited states
that allows for easy p- and n-electrochemical doping (thanks to
the electrodonating sulfur atom), a marked solvatochromism, a
high solubility in organic solvents, and a good filmability.14,15
The same reaction performed on 3,3′-bis(butylsulfanyl)-2,2′-
bithiophene16 and on 3-(butylsulfanyl)-2,2′-bithiophene17 af-
forded two hexamers in high yields.
We pursued these investigations with the aim of gaining a
further insight into the reactivity of â-alkylsulfanyl-substituted
bithiophenes, and in this paper, we report on the synthesis and
oxidative polymerization of bithiophenes 1-5 (Scheme 1).
Bithiophene 1 is formed by an octylsulfanyl â-substituted and
an unsubstituted thiophene ring, while bithiophenes 2-5 are
formed by two â-substituted thiophene rings, bearing a halogen
atom and an alkylsulfanyl group, with tail-to-tail (TT) regio-
chemistry.
Astonishingly, five symmetric octithiophenes OT1-OT5
with the same regiochemistry were obtained in high percentage
from bithiophenes 1-5 through oxidative polymerization with
FeCl3. All synthesized oligomers are soluble in common organic
solvents (CHCl3, THF, DMF, DMSO) and thus easily process-
able and characterizable. The two bromo-functionalized octi-
thiophenes form free-standing films and show a remarkable
solvatochromism, properties very similar to those observed for
alkylsulfanyl polythiophenes.14,15
A computational study carried out at the DFT level on
4-(methylsulfanyl)-2,2′-bithiophene, aimed at establishing the
possible sequences of the coupling reactions leading to the
formation of an octithiophene with the experimental regiochem-
istry, suggests a head-to-tail (HT)/head-to-head (HH) two-step
mechanism.
Experimental Section
General Techniques. All air- or moisture-sensitive reactions
* Corresponding author. E-mail: mucci.adele@unimo.it.
were performed under prepurified nitrogen or argon with dry
10.1021/ma0614141 CCC: $33.50 © 2006 American Chemical Society
Published on Web 10/26/2006

8294 Mucci et al.
Macromolecules, Vol. 39, No. 24, 2006
glassware. Tetrahydrofuran (THF) and diethyl ether were distilled
from sodium and benzophenone prior to use. Pyridine, toluene,
chloroform, and nitromethane were dried by standard procedures.
Anhydrous iron(III) chloride was purchased from Fluka.
1H and 13C NMR spectra were recorded with Bruker Avance400
spectrometer operating at 400.13 and 100.61 MHz, respectively,
and with a Bruker DPX-200 spectrometer operating at 200.13 MHz.
UV-Vis spectra were recorded using a Perkin-Elmer Lambda Bio
20 UV-visible spectrophotometer. CD spectra were recorded with
a JASCO J-710 spectropolarimeter. Mass spectra were recorded
using a Finnigan MAT SSQ 710 A mass spectrometer equipped
with a direct inlet probe (DIP). IR spectra were recorded using a
Perkin-Elmer I-series FT-IR microscope equipped with a diamond
cell.
[(S)-2-methylbutylsulfanyl]thiophene; bp 87 °C at 2 mmHg;
[R]20D ) +26 (c ) 1.0, CHCl3). 1H NMR (400 MHz, CDCl3, TMS
δ): 7.31 (dd, J ) 5.0, 3.0 Hz, 1H, H-5), 7.09 (dd, J ) 3.0, 1.3 Hz,
1H, H-2), 7.02 (dd, J ) 5.0, 1.3 Hz, 1H, H-4), 2.88 (dd, J ) 12.5,
5.8 Hz, 1H, H-R), 2.69 (dd, J ) 12.5, 7.5 Hz, 1H, H-R′), 1.63 (m,
1H, H-â), 1.52 (m, 1H, H-γ), 1.25 (m, 1H, H-γ′), 1.01 (d, J ) 6.5
Hz, 3H, γ-CH3), 0.89 (t, J ) 7.4 Hz, 3H, δ-CH3). (b) As above,
starting from (+)-3-[(S)-2-methylbutylsulfanyl]thiophene (10.2 g,
54 mmol), 11.2 g (77%) of 2-bromo-3-[(S)-2-methylbutylsulfanyl]-
thiophene were obtained as a brown oil; bp 77 °C/0.01 mmHg.
1H NMR (200 MHz, CDCl3, TMS δ): 7.25 (d, J ) 5.7 Hz, 1H,
H-5), 6.92 (d, J ) 5.7 Hz, 1H, H-4), 2.87 (dd, J ) 12.5, 5.6 Hz,
1H, H-R), 2.68 (dd, J ) 12.5, 7.3 Hz, 1H, H-R′), 1.53 (m, 2H, H-â
and H-γ), 1.25 (m, 1H, H-γ′), 1.01 (d, J ) 6.6 Hz, 3H, γ-CH3),
0.89 (t, J ) 7.4 Hz, 3H, δ-CH3). (c) As above, starting from
2-bromo-3-[(S)-2-methylbutylsulfanyl]thiophene (7.07 g, 26.6 mmol),
3.61 g (52%) of pale-yellow oil were obtained; [R]D20 ) +26 (c )
Synthesis of 5-Bromo-3-(octylsulfanyl)-2-(trimethylsilyl)thio-
phene.18 (a) To a solution of 3-methoxythiophene (2.00 g, 17.4
mmol) in toluene (20 mL), toluene-4-sulfonic acid (0.14 g, 0.8
mmol) and octanthiol (2.56 g, 17.4 mmol) were added. The reaction
mixture was stirred for 20 h at 80 °C, then it was allowed to cool
to room temperature and diluted with diethyl ether. The organic
layer was washed with water dried over MgSO4, filtered, and
vacuum evaporated, obtaining 3.72 g (93%) of 3-(octylsulfanyl)-
1
1.0, CHCl3). H NMR (400 MHz, CDCl3, TMS δ): 7.07 (s, 1H,
H-4), 2.82 (dd, J ) 12.4, 5.7 Hz, 1H, H-R), 2.65 (dd, J ) 12.4, 7.4
Hz, 1H, H-R′), 1.53 (m, 2H, H-â and H-γ), 1.25 (m, 1H, H-γ′),
0.99 (d, J ) 6.6 Hz, 3H, γ-CH3), 0.89 (t, J ) 7.4 Hz, 3H, δ-CH3),
0.42 (s, JCH3,Si ) 6.9 Hz, 9H, 5-SiMe3). Elemental analysis C12H21-
BrS2Si Calcd: C, 42.72; H, 6.27; S, 19.01. Found: C, 42.54; H,
6.35; S, 18.89.
1
thiophene, as a pale-yellow oil; bp 111 °C/0.5 mmHg. H NMR
(200 MHz, CDCl3, TMS δ): 7.33 (dd, J ) 5.0, 3.0 Hz, 1H, H-5),
7.13 (dd, J ) 1.3, 3.0 Hz, 1H, H-2), 7.04 (dd, J ) 1.3, 5.0 Hz, 1H,
H-4), 2.86 (t, J ) 7.2 Hz, 2H, R-CH2), 1.64 (m, 2H, â-CH2), 1.41
(m, 2H, γ-CH2), 1.29 (m, 8H, 4 CH2), 0.90 (t, J ) 6.9 Hz, 3H,
CH3). (b) To a solution of 3-(octylsulfanyl)thiophene (2.64 g, 11.6
mmol) in glacial acetic acid (8 mL), N-bromosuccinimide (2.06 g,
11.6 mmol) was added in small portions, maintaining the temper-
ature between 15 and 17 °C. After stirring for 2 h at 25 °C, the
mixture was poured in iced water and extracted with diethyl ether.
The organic layers were washed with a saturated solution of
NaHCO3 with water and dried over MgSO4. After removal of the
solvent, the residue was distilled under reduced pressure to give
3.45 g (97%) of 2-bromo-3-(octylsulfanyl)thiophene as brown oil;
Synthesis of 2-(Trimethylsilyl)-5-(trimethylstannyl)thiophene.
A solution of 5-bromo-2-(trimethylsilyl)thiophene20 (4.20 g, 16.5
mmol) in THF (60 mL) was cooled to -80 °C; butyllithium in
n-hexane (1.6 M, 10.3 mL, 16.5 mmol) was slowly added, keeping
the temperature below -70 °C. The mixture was stirred at -80 °C
for 30 min, then a solution of trimethyltin chloride in THF (1 M,
16.5 mL, 16.5 mmol) was dropwise added, and the stirring was
continued for 30 min at -80 °C. The mixture was warmed to room
temperature, poured in iced water, and then extracted with diethyl
ether. After removal of the solvent and vacuum distillation, a white
1
solid 1.70 g (30%) was obtained; bp 66 °C/0.1 mmHg. H NMR
(400 MHz, CDCl3, TMS δ): 7.40 (d, J ) 3.1 Hz, JH-3,Sn ) 3.8
1
Hz, 1H, H-3), 7.30 (d, J ) 3.1 Hz, JH-4,Sn ) 24.0 Hz, 1H, H-4),
bp 142-145 °C/0.3 mmHg). H NMR (400 MHz, CDCl3, TMS
119
117
0.37 (s, JCH3, Sn ) 57.7 Hz, JCH3, Sn ) 55.1 Hz, 9H, 5-SnMe3),
0.33 (s, JCH3,Si ) 6.6 Hz, 9H, 2-SiMe3). Elemental analysis C10H20-
SSiSn Calcd: C, 37.64; H, 6.32; S, 10.05. Found: C, 37.49; H,
6.44; S, 9.85.
δ): 7.27 (d, J ) 5.4 Hz, 1H, H-5), 6.94 (d, J ) 5.4 Hz, 1H, H-4),
2.86 (t, J ) 7.2 Hz, 2H, R-CH2), 1.60 (m, 2H, â-CH2), 1.41 (m,
2H, γ-CH2), 1.29 (m, 8H, 4 CH2), 0.89 (t, J ) 6.9 Hz, 3H, CH3).
(c) To a cooled solution (-70 °C) of butyllithium in n-hexane (1.6
M, 3.5 mL, 5.6 mmol), a solution of diisopropylamine (0.61 g, 6
mmol) in dry THF (6 mL) was added. The temperature was kept
at -30 °C for 1 h and then lowered to -80 °C. A solution of
2-bromo-3-(octylsulfanyl)thiophene (1.43 g, 4.6 mmol) in dry THF
(8 mL) was quickly added, and stirring was continued for 30 min
at the same temperature. A solution of chlorotrimethylsilane (0.51
g, 4.6 mmol) in dry THF (4 mL) was slowly added, and the stirring
was continued for 30 min at -80 °C. The mixture was then poured
in 1 M HCl extracted with diethyl ether, washed with water, and
then dried (MgSO4). After removal of the solvent, the residue was
purified by column chromatography on silica gel (petroleum ether
bp 40-60 °C) giving 1.19 g (67%) of 5-bromo-3-(octylsulfanyl)-
2-(trimethylsilyl)thiophene as pale-yellow oil; 1H NMR (400 MHz,
CDCl3, TMS δ): 7.09 (s, 1H, H-4), 2.80 (t, J ) 7.2 Hz, 2H, R-CH2),
1.62 (m, 2H, â-CH2), 1.39 (m, 2H, γ-CH2), 1.29 (m, 8H, 4 CH2),
0.90 (t, J ) 6.9 Hz, 3H, CH3), 0.38 (s, JCH3,Si ) 6.9 Hz, 9H, Si-
(CH3)3). Elemental analysis C15H27BrS2Si Calcd: C, 47.47; H, 7.17;
S, 16.90. Found: C, 47.52; H, 7.20; S, 16.41.
Synthesis of 3-Bromo-2-(trimethylsilyl)-5-(trimethylstannyl)-
thiophene. (a) According to ref 21, to a solution of butyllithium
in n-hexane (1.6 M, 27.5 mL, 44 mmol) in dry THF (20 mL) at
-70 °C, a solution of diisopropylamine (4.82 g, 48 mmol) in dry
THF (7 mL) was added. The temperature was raised to -30 °C,
and stirring was continued at this temperature for 1 h. To the
reaction mixture cooled to -80 °C, a solution of 2,3-dibromo-
thiophene (8.90 g, 37 mmol) in dry THF (7 mL) was quickly added,
and the stirring was continued for 30 min at the same temperature.
The intermediate thus formed was trapped by slow addition of a
solution of chlorotrimethylsilane (4.01 g, 37 mmol) in dry THF (4
mL), and stirring was continued for 30 min at -80 °C. The mixture
was then poured into 1 M HCl extracted with diethyl ether. The
organic layers were washed with water and dried over MgSO4. The
solvent was removed, and the residue was distilled under reduced
pressure to give 10.41 g (90%) of 3,5-dibromo-2-(trimethylsilyl)-
1
thiophene as a pale- yellow oil; bp 95-97 °C/2 mmHg. H NMR
(200 MHz, CDCl3, TMS) δ): 7.02 (s, 1H, H-4), 0.38 (s, JCH3,Si
)
Synthesis of (+)-5-Bromo-3-[(S)-2-methylbutylsulfanyl]-2-
(trimethylsilyl)thiophene. (a) A solution of potassium tert-butylate
(37.25 g, 0.33 mol) in dry ethanol (110 mL) was cooled to 0 °C,
then a solution of 3-mercaptothiophene19 (27.00 g, 0.23 mol) in
dry ethanol (5 mL) was slowly added, keeping the temperature
below 10 °C. A solution of 1-bromo-2-methylbutane [R]D20 ) +4
(c ) 1.1, CHCl3) (35.15 g, 0.23 mol) in dry ethanol (20 mL) was
dropped, maintaining the temperature between 0 and 10 °C. The
reaction mixture was refluxed for 1 h and 30 min, cooled, and then
poured in an ice-water bath and extracted with diethyl ether. The
organic layer was washed with water and dried over MgSO4,
filtered, and fractionally distilled to give 12.71 g (68%) of (+)-3-
6.9 Hz, 9H, SiMe3). (b) According to ref 22, to a solution of 3,5-
dibromo-2-(trimethylsilyl)thiophene (3.02 g, 7.5 mmol) in dry THF
(40 mL) at -80 °C, a solution of butyllithium in n-hexane (1.6 M,
6 mL, 9.6 mmol) was dropwise added under stirring, and stirring
was continued at this temperature for 40 min. A solution of
trimethyltin chloride in dry THF (1 M, 10.5 mL, 10.5 mmol) was
then dropwise added, and the reaction mixture was allowed to reach
room temperature, poured in an ice-water bath, and extracted with
diethyl ether. The organic layers were washed with water, dried
over MgSO4, the solvent evaporated, and the crude product was
fractionally distilled obtaining 1.84 g (48%) of a pale-yellow oil;
1
bp 93-95 °C/0.2 mmHg. H NMR (200 MHz, CDCl3, TMS) δ):

Macromolecules, Vol. 39, No. 24, 2006
One-Pot Synthesis of Symmetric Octithiophenes 8295
7.15 (s, 1H, H-4), 0.39 (s, JCH3,Si ) 6.9 Hz, 9H, SiMe3), 0.37 (s,
Calcd: C, 44.03; H, 4.85; S, 22.04. Found: C, 43.89; H, 4.91; S,
21.93.
119
117
JCH3, Sn ) 57.7 Hz, JCH3, Sn ) 55.3 Hz, 9H, SnMe3). Elemental
analysis C10H19BrSSiSn Calcd: C, 30.18; H, 4.81; S, 8.06. Found:
C, 30.25; H, 4.71; S, 7.92.
Synthesis of 4-Bromo-4′-[(S)-2-methylbutylsulfanyl]-2,2′-
bithiophene (4). (a) From 1.07 g (3.2 mmol) of 5-bromo-3-[(S)-
2-methylbutylsulfanyl]-2-(trimethylsilyl)thiophene and 1.26 g (3.2
mmol) of 3-bromo-2-(trimethylsilyl)-5-(trimethylstannyl)thiophene,
1.35 g of 4-bromo-4′-[(S)-2-methylbutylsulfanyl]-5,5′-bis(trimeth-
ylsilyl)-2,2′-bithiophene as crude product (brown oil) were obtained.
(b) A solution of crude substrate (1.35 g, 2.7 mmol) in THF (60
mL) and water (1.7 mL) was cooled to -5 °C. A solution of
tetrabutylammonium fluoride (1 M in THF, 14.2 mL, 14.2 mmol)
was slowly added to the reaction mixture. After stirring for 4 h at
-5 °C, sodium bicarbonate (5% aq, 50 mL) was added, then the
mixture was extracted with diethyl ether and washed with water.
The organic layers were dried over MgSO4 then filtered and evap-
orated, and the crude product was purified by column chromatog-
raphy on silica gel (petroleum ether bp 40-60 °C), giving 0.34 g
(36%) of 4 a pale-yellow viscous oil. 1H NMR (400 MHz, CDCl3,
TMS δ): 7.12 (d, J ) 1.5 Hz, 1H, H-5), 7.07 (d, J ) 1.4 Hz, 1H,
H-3′), 7.06 (d, J ) 1.5 Hz, 1H, H-3), 6.98 (d, J ) 1.4 Hz, 1H,
H-5′), 2.89 (dd, J ) 12.5, 5.9 Hz, 1H, H-R), 2.70 (dd, J ) 12.5,
7.5 Hz, 1H, H-R′), 1.65 (m, 1H, H-â), 1.55 (m, 1H, H-γ), 1.25 (m,
1H, H-γ′), 1.03 (d, J ) 6.6 Hz, 3H, γ-CH3), 0.89 (t, J ) 7.4 Hz,
3H, δ-CH3). 13C NMR (100.61 MHz, CDCl3, TMS δ): 138.0 (C-
2), 136.4 (C-2′), 134.1 (C-4′), 126.4 (C-3′), 126.3 (C-3), 121.8 (C-
5′), 121.7 (C-5), 110.3 (C-4), 42.2 (C-R), 34.6 (C-â), 28.6 (C-γ),
18.8 (C-γ′), 11.2 (C-δ). Elemental analysis C13H15BrS3 Calcd: C,
44.95; H, 4.35; S, 27.69. Found: C, 45.01; H, 4.32; S, 27.45.
Synthesis of 4-Iodo-4′-[(S)-2-methylbutylsulfanyl]-2,2′-bithio-
phene (5). As described for 3, from 4-bromo-4′-[(S)-2-methylbu-
tylsulfanyl]-5,5′-bis(trimethylsilyl)-2,2′-bithiophene 2.59 g (5.4
mmol) in benzene (80 mL) and 2.9 mL (22.0 mmol) of hydriodic
acid (57%), in 64 h, 1.17 g (55%) of 5, as a pale-yellow solid,
were obtained; mp 34 °C; [R]20D ) +13.7 (c ) 1.0 in CHCl3). 1H
NMR (400 MHz, CDCl3, TMS δ): 7.28 (d, J ) 1.4 Hz, 1H, H-5),
7.13 (d, J ) 1.4 Hz, 1H, H-3), 7.06 (d, J ) 1.5 Hz, 1H, H-3′), 6.98
(d, J ) 1.4 Hz, 1H, H-5′), 2.89 (dd, J ) 12.5, 5.9 Hz, 1H, H-R),
2.70 (dd, J ) 12.5, 7.5 Hz, 1H, H-R′), 1.66 (m, 1H, H-â), 1.53 (m,
1H, H-γ), 1.25 (m, 1H, H-γ′), 1.02 (d, J ) 6.6 Hz, 3H, γ-CH3),
0.89 (t, J ) 7.4 Hz, 3H, δ-CH3). 13C NMR (100.61 MHz, CDCl3,
TMS δ): 138.6 (C-2), 135.8 (C-2′), 133.8 (C-4′), 130.9 (C-3), 127.6
(C-5), 126.4 (C-3′), 121.6 (C-5′), 77.6 (C-4), 42.5 (C-R), 34.6 (C-
â), 28.5 (C-γ), 18.9 (C-γ′), 11.1 (C-δ). Elemental analysis C13H15-
IS3 Calcd: C, 39.59; H, 3.83; S, 24.39. Found: C, 39.48; H, 3.87;
S, 24.22.
General Procedure for the Oxidative Coupling with FeCl3.
Bithiophenes 1-5 were dissolved in chloroform, then a suspension
of FeCl3 (4:1 molar ratio) in nitromethane was slowly added (1 h).
The mixture was stirred at room temperature for 20 h, and after
evaporation of the solvent, the residue was stirred (1 h) with a
solution of methanol and HCl 1 N. After removal of the solvent,
the dark product formed was Soxhlet-extracted with methanol (24
h), n-pentane (24 h), and chloroform (24 h). The octamers were
recovered from the chloroform phases.
Synthesis of OT1. Bithiophene 1 (0.20 g, 0.6 mmol) in
chloroform (10 mL) and FeCl3 (0.38 g, 2.4 mmol) in nitromethane
(10 mL) gave 0.15 g (75%) of octithiophene. HPLC: 90%. MIC-
IR (neat): 3104 (w), 3072 (w), 3062 (w), 2955 (m), 2922 (m),
2869 (w), 2851 (m), 1487 (m), 1468 (m), 1455 (m), 1417 (w), 1377
(w), 1278 (w), 1220 (w), 925 (w), 852 (w), 825 (m), 809 (m), 784
(m), 721 (m). MS (EI) m/z: 1234 (100, M+•), 146 (39, C8H18S),
36 (62, C6H11), 70 (50, C5H10), 56 (54, C4H8). Elemental analysis
C64H82S12 Calcd: C, 62.19; H, 6.69; S, 31.13. Found: C, 62.26;
H, 6.72; S, 30.95.
Synthesis of 4-(Octylsulfanyl)-2,2′-bithiophene (1). (a) A
solution of 5-bromo-3-(octylsulfanyl)-2-(trimethylsilyl)thiophene
(1.37 g, 3.6 mmol) in dry toluene (14 mL) was dropwise added to
a stirred solution of 2-(trimethylsilyl)-5-(trimethylstannyl)thiophene
(1.15 g, 3.6 mmol) and tetrakis(triphenylphosphine)palladium(0)
(0.33 g, 0.29 mmol) in dry toluene (8 mL) at 105 °C. The reaction
mixture was stirred for 3 days at this temperature. After cooling, it
was transferred into a separatory funnel, diluted with diethyl ether,
and washed with saturated NaHCO3 and water. The organic phase
was dried over MgSO4 and evaporated, obtaining 1.54 g of
4-(octylsulfanyl)-5,5′-bis(trimethylsilyl)-2,2′-bithiophene that was
directly used without further purification in the subsequent desi-
lylation step. (b) In analogy to ref 20, to a solution of 4-(octylsul-
fanyl)-5,5′-bis(trimethylsilyl)-2,2′-bithiophene (1.54 g, 3.4 mmol)
in benzene (4 mL), hydriodic acid (13.6 mmol, 1.7 mL, 57%) was
dropwise added. The mixture was stirred at room temperature for
2 h before being poured into water. The aqueous phase was
extracted with diethyl ether, and the organic extracts were washed
with 1 M NaOH and brine and dried over MgSO4. The solvent
was removed by reduced pressure to provide a brown oil that was
purified by column chromatography on silica gel (petroleum ether
bp 40-60 °C), giving 0.42 g (40%) of 1 as a white solid after
removal of the residual eluant; mp 26-27 °C. 1H NMR (400 MHz,
CDCl3, TMS δ): 7.23 (dd, J ) 5.0, 1.2 Hz, 1H, H-5′), 7.16
(dd, J ) 3.6, 1.2 Hz, 1H, H-3′), 7.07 (d, J ) 1.4 Hz, 1H, H-3),
7.01 (dd, J ) 5.0, 3.6 Hz, 1H, H-4′), 6.97 (d, J ) 1.4 Hz, 1H,
H-5), 2.86 (t, J ) 7.2 Hz, 2H, R-CH2), 1.65 (m, 2H, â-CH2), 1.41
(m, 2H, γ-CH2), 1.28 (m, 8H, 4 CH2), 0.88 (t, J ) 6.9 Hz, 3H,
CH3). 13C NMR (100.61 MHz, CDCl3, TMS δ): 137.9 (C-2), 136.8
(C-2′), 133.1 (C-4), 127.8 (C-4′), 125.9 (C-3), 124.7 (C-5′), 123.9
(C-3′), 121.6 (C-5), 35.1 (C-R), 31.7 (C-ú), 29.3 (C-â), 29.1 (C-δ,
C-ꢀ), 28.6 (C-γ), 22.6 (C-η), 14.0 (C-θ). Elemental analysis
C16H22S3 Calcd: C, 61.88; H, 7.14; S, 30.98. Found: C, 61.74; H,
7.13; S, 30.66.
Synthesis of 4-Bromo-4′-(octylsulfanyl)-2,2′-bithiophene (2).
(a) From 1.25 g (3.1 mmol) of 5-bromo-3-(octylsulfanyl)-2-
(trimethylsilyl)thiophene and 1.19 g (3.1 mmol) of 3-bromo-2-
(trimethylsilyl)-5-(trimethylstannyl)thiophene, 1.34 g of 4-bromo-
4′-(octylsulfanyl)-5,5′-bis(trimethylsilyl)-2,2′-bithiophene (brown
oil) were obtained. (b) From 1.34 g (2.5 mmol) of 4-bromo-4′-
(octylsulfanyl)-5,5′-bis(trimethylsilyl)-2,2′-bithiophene in benzene
(50 mL) and 0.9 mL (5.1 mmol) of hydriodic acid (48%), in 16 h,
0.34 g (35%) of 2 as a pale-yellow solid were obtained; mp 36
1
°C.; H NMR (400 MHz, CDCl3, TMS δ): 7.12 (d, J ) 1.4 Hz,
1H, H-5), 7.072 (d, J ) 1.4 Hz, 1H, H-3′), 7.068 (1H, d, J ) 1.4
Hz, H-3), 7.01 (d, J ) 1.4 Hz, 1H, H-5′), 2.86 (t, J ) 7.2 Hz, 2H,
R-CH2), 1.65 (m, 2H, â-CH2), 1.41 (m, 2H, γ-CH2), 1.27 (m, 8H,
4 CH2), 0.88 (t, J ) 6.9 Hz, 3H, CH3). 13C NMR (100.61 MHz,
CDCl3, TMS δ): 138.0 (C-2), 136.4 (C-2′), 133.5 (C-4′), 126.5
(C-3′), 126.3 (C-3), 122.3 (C-5′), 121.7 (C-5), 110.4 (C-4), 35.2
(C-R), 31.8 (C-ú), 29.3 (C-â), 29.1 (C-δ, C-ꢀ), 28.7 (C-γ), 22.6
(C-η), 14.1 (C-θ). Elemental analysis C16H21BrS3 Calcd: C, 49.35;
H, 5.44; S, 24.70. Found: C, 49.45; H, 5.37; S, 24.32.
Synthesis of 4-Iodo-4′-(octylsulfanyl)-2,2′-bithiophene (3). As
described in the above procedure (b), from 2.01 g (3.8 mmol) of
4-bromo-4′-(octylsulfanyl)-5,5′-bis(trimethylsilyl)-2,2′-bithio-
phene in benzene (95 mL) and 2.0 mL (15.4 mmol) of hydriodic
acid (57%), in 64 h, 0.72 g (42%) of 3 as a pale-yellow viscous oil
were obtained. 1H NMR (400 MHz, CDCl3, TMS δ): 7.28 (d, J )
1.4 Hz, 1H, H-5), 7.12 (d, J ) 1.4 Hz, 1H, H-3), 7.07 (1H, d, J )
1.4 Hz, 1H, H-3′), 7.01 (d, J ) 1.4 Hz, 1H, H-5′), 2.86 (t, J ) 7.2
Hz, 2H, R-CH2), 1.65 (m, 2H, â-CH2), 1.41 (m, 2H, γ-CH2), 1.27
(m, 8H, 4 CH2), 0.88 (t, J ) 6.9 Hz, 3H, CH3). 13C NMR (100.61
MHz, CDCl3, TMS δ): 138.8 (C-2), 136.1 (C-2′), 133.6 (C-4′),
131.0 (C-3), 127.7 (C-5), 126.6 (C-3′), 122.4 (C-5′), 77.6 (C-4),
35.2 (C-R), 31.8 (Cú), 29.6 (C-â), 29.2 (C-δ), 29.1 (C-ꢀ), 28.7
(C-γ), 22.7 (C-η), 14.1 (C-θ). Elemental analysis C16H21IS3
Synthesis of OT2. Bithiophene 2 (0.40 g, 1 mmol) in chloroform
(17 mL) and FeCl3 (0.66 g, 4 mmol) in nitromethane (17 mL) gave
0.36 g (55%) of octithiophene. HPLC: 60%. MIC-IR (neat): 3111
(w), 3072 (w), 3055 (w), 2954 (m), 2924 (m), 2868 (w), 2851 (m),
1476 (m), 1467 (sh), 1441 (sh), 1377 (w), 1262 (w), 930 (w), 869
(w), 819 (m), 796 (sh), 720 (w). MS (EI) m/z: 1552 (<1, M +
6+•), 146 (55, C8H18S), 80/82 (62, HBr), 69 (71, C5H9), 55 (100,

8296 Mucci et al.
Macromolecules, Vol. 39, No. 24, 2006
Scheme 2
C4H7). Elemental analysis C64H78Br4S12 Calcd: C, 49.54; H, 5.07;
S, 24.80. Found: C, 49.63; H, 5.03; S, 24.55.
at the same level of theory and plotted using Gaussview.27
Molecular electrostatic potential maps are reported onto 0.0004
e/bohr3 isosurface of electrodensity, and representations of SOMO
orbital isodensity refer to an isovalue of 0.025.
Synthesis of OT3. Bithiophene 3 (1.20 g, 3 mmol) in chloroform
(50 mL) and FeCl3 (1.9 g, 12 mmol) in nitromethane (50 mL).
Yield: 0.97 g, 83%. HPLC: 75%. MIC-IR (neat): 3103 (w), 3076
(sh), 2954 (m), 2931 (m), 2856 (m), 1477 (m), 1466 (m), 1459
(sh), 1376 (w), 927 (w), 865 (w), 820 (m), 793 (w), 728 (w). MS
(EI) m/z: 1486 (<1, M+• - 2I + 2H), 254 (20, I2), 146 (56,
C8H18S), 128 (81, HI), 71 (87, C5H11), 57 (100, C4H9). Elemental
analysis C64H78I4S12 Calcd: C, 44.18; H, 4.52; S, 22.12. Found:
C, 44.15; H, 4.57; S, 21.88.
Synthesis of OT4. Bithiophene 4 (0.20 g, 0.6 mmol) in
chloroform (10 mL) and FeCl3 (0.38 g, 2.4 mmol) in nitromethane
(10 mL) gave 0.10 g (53%) of octithiophene. HPLC: 85%. MIC-
IR (neat): 3107 (w), 3080 (w), 3059 (w), 2961 (m), 2925 (m),
2871 (m), 2854 (m), 1546 (w), 1480 (m), 1460 (m), 1378 (m), 929
(m), 872 (m), 840 (m), 821 (m), 811 (sh), 730 (w). MS (EI) m/z:
1384 (<1, M + 6+•), 104 (8, C5H11S), 79/81 (40, Br), 70 (47,
C5H10), 55 (100, C4H7). Elemental analysis C52H54Br4S12 Calcd:
C, 45.15; H, 3.93; S, 27.81. Found: C, 45.11; H, 3.98; S, 27.67.
Synthesis of OT5. Bithiophene 5 (0.30 g, 0.8 mmol) in
chloroform (13 mL) and FeCl3 (0.5 g, 3.2 mmol) in nitromethane
(13 mL) gave 0.23 g (70%) of octithiophene. HPLC: 85%. MIC-
IR (neat): 3098 (w), 3078 (w), 3058 (w), 2964 (m), 2928 (m),
2871 (m), 2857 (m), 1478 (m), 1459 (m), 1378 (m), 930 (m), 867
(m), 838 (sh), 825 (m), 793 (m), 736 (w). MS (EI) m/z: 1570 (<1,
M+•), 254 (85, I2), 127 (58, I), 104 (39, C5H12S), 70 (100, C5H10),
55 (98, C4H7). Elemental analysis C52H54I4S12 Calcd: C, 39.75; H,
3.46; S, 24.49. Found: C, 39.81; H, 3.49; S, 24.15.
Results
Synthesis. R,R′-Bithiophenes are the most simple oligomers
and can be used as starting materials for the synthesis of longer
macromolecules. The Stille-type coupling between a tin and a
haloderivative was the procedure followed to generate bithio-
phenes13 1-5 (Scheme 2).
Bithiophenes 1-5 were prepared from 4-X-4′-(alkylsulfanyl)-
5,5′-bis(trimethylsilyl)-2,2′-bithiophenes (X ) Br, H) through
desilylation. When HI 58% was used as the desilylating agent,
the bromine derivatives were simultaneously desilylated and
iodinated. 4-X-4′-(alkylsulfanyl)-5,5′-bis(trimethylsilyl)-2,2′-
bithiophenes (X ) Br, H) were in turn obtained by coupling
3-(alkylsulfanyl)-5-bromo-2-(trimethylsilyl)thiophene and 2-(tri-
methylsilyl)-5-(trimethylstannyl)thiophene or 3-bromo-2-(tri-
methylsilyl)-5-(trimethylstannyl)thiophene in the presence of a
palladium(0) catalyst.
Octithiophenes OT1-OT5 were synthesized from the cor-
responding bithiophenes 1-5 by oxidative polymerization with
FeCl3 in CH3NO2/CHCl3 (Scheme 1) in 50-80% yield of
separated product. Octithiophenes OT2 and OT4 give red-green
free-standing films easily detachable from the glassware, while
OT1, OT3 and OT5 are red-orange scaly solids.
Computational Methods. All calculations were performed with
the Gaussian0323 program package. Becke’s three-parameter func-
tional with nonlocal correlation provided by the Perdew/Wang
expression (B3PW91)24 combined with the economical but well
balanced MIDI!25 basis set was used. The hybrid spin unrestricted
DFT wave functions were employed for open shell systems.
Geometry optimizations were carried out on all reactants, products,
and transition states, and then harmonic frequency confirmed the
identity of stationary states.
NMR and MS Characterization. The regiochemistry of
octithiophenes OT1-OT5 and the complete assignment of 1H
and 13C resonances were determined through NMR 1H,13C
inverse-detection techniques, which have already been success-
fully used in the interpretation of the regiochemistry of OTs
and PTs.28
1
The H NMR spectrum of OT1 reported in Figure 1, as an
The molecular electrostatic potential maps (MEP)26 of the
optimized geometry structures of oligothiophenes were calculated
example, displays a pair of doublets at 7.30 and 7.15 ppm,
characterized by a â,â′-coupling constant J ) 3.8 Hz, three

Macromolecules, Vol. 39, No. 24, 2006
One-Pot Synthesis of Symmetric Octithiophenes 8297
The analysis of the complex correlation pattern permits the
unambiguous assignment of all proton and carbon signals, as
reported in Tables 1 and 2, and the reconstruction of an
octithiophene skeleton which corresponds to structure a in Chart
1. For this assignment is particularly diagnostic the presence
of an interring correlation between proton H-3′′ and carbon C-5′.
The 1H NMR spectra of OT2-OT5 display, in the aromatic
region, a pair of doublets characterized by a coupling constant
J ) 1.4 Hz, and three singlets indicating the presence of a 2,4-
disubstituted and of three trisubstituted rings in the oligomeric
backbone. Signals from two different alkyl chains are found in
the aliphatic region.
The HMQC and HMBC experiments enable the contextual
detection and assignment of aromatic carbon signals of each
thiophene ring to be made, and they permit establishing that
the first ring bears a halogen in the 4-position and to assign the
alkylsulfanyl chain bonded to C-4′. Unfortunately, the correla-
tion between H-3′ and C-2′′ (or between H-4′′ and C-5′) was
not detected, and we could not establish if the third ring bears
a halogen or an alkylsulfanyl group in 3′′ position. The problem
was overcome through a halogen-hydrogen exchange by
treatment of OT2-OT5 with butyllithium. The 1H NMR spectra
of the octithiophenes thus dehalogenated correspond to that of
OT1, indicating that their regiochemistry is that depicted by
structure c in Chart 1, i.e., the third thiophene ring is that bearing
the halogen atom.
Figure 1. 1H NMR spectrum of octithiophene OT1.
Chart 1
Mass spectra, acquired under electron impact conditions after
direct insertion of solid samples and heat induced vaporization,
confirm that our oligomers are octithiophenes as deduced by
NMR measurements. All mass spectra show the peak of the
molecular ion along with the correct isotopic cluster; only for
OT3, the peak at higher m/z values corresponds to a partially
deiodinated species.
double doublets of an AMX system at 7.26, 7.19 and 7.04 ppm,
characterized by three coupling constants J ) 1.0, 5.2, and
3.7 Hz, respectively, two singlets at 7.11 and 7.19 ppm, two
overlapped triplets at 2.91 (2H) and 2.88 ppm (2H), a multiplet
at 1.65 ppm (4H), two broad signals at 1.41 (4H) and 1.28 ppm
(16H), and a triplet at 0.88 ppm (6H).
UV-Vis and CD Spectroscopy. UV-Vis spectroscopy is
a highly responsive technique for the investigation of confor-
mational changes and intermolecular interactions of conjugated
systems in solution and in the solid state. Solutions of octithio-
phenes OT1-OT5 in chloroform (good solvent) show a broad
and unstructured absorption band with λmax values (Table 3)
very similar to that reported for a HT regioregular octadecyl
octithiophene-5-carboxylic acid benzyl ester (λmax 427 nm),31
50-20 nm blue-shifted with respect to regioregular HH-TT
poly(alkylsulfanyl)thiophenes14,15 and 80-50 nm blue-shifted
with respect to a regioregular HT poly(butylsulfanyl)thiophene.32
These absorptions are attributable to the π-π* transitions
and reflect the conformational freedom of the thienyl backbones.
It is observed that the λmax of iodinated octithiophenes OT3
and OT5 is lower than that of the brominated ones OT2 and
OT4, which in turn is lower than that of nonhalogenated OT1.
This trend parallels that of the higher steric hindrance of the
iodine and bromine atoms with respect to hydrogen that induce
The coupling pattern of the aromatic protons indicates that a
2,5-disubstituted, two trisubstituted, and one 2-monosubstituted
thiophene rings are present, and the two triplets around 2.9 ppm
1
point to the presence of two different octylsulfanyl chains. H
NMR spectrum of OT1 is compatible with two possible
structures, a and b, corresponding to symmetric octithiophenes
(Chart 1).
The HMQC29 spectrum of the aromatic region allows us to
identify all directly bonded H,C pairs to confirm that all protons,
except H-5 at 7.26 ppm, are â-protons (1J(H,C) ≈ 170 Hz) and
to rule out the formation of R,â-coupling between thiophene
units.
The identification of the quaternary carbons coupled to
protons through intraring long-range coupling constants around
10 Hz or less was made by running two HMBC30 experiments
with evolution delays of 50 and 100 ms.
Table 1. 1H NMR Data (δ, ppm) for Octithiophenes OT1-OT5
compound H-3 H-4 H-5 H-3′ H-3′′ H-4′′ H-3′′′ chain CH2(R) CH2(â) CH2(γ) CH2(δ) CH2(ꢀ) CH2(ú) CH2(η) CH3(θ)
OT1
OT2
OT3
7.19 7.04 7.26 7.11 7.30 7.15
7.19 4′-
4′′′-
2.91
2.88
2.85
2.86
2.83
2.86
1.65
1.65
1.60
1.60
1.59
1.61
1.41
1.41
1.37
1.37
1.38
1.36
1.28
1.28
1.25
1.25
1.25
1.25
1.28
1.28
1.25
1.25
1.25
1.25
1.28
1.28
1.25
1.25
1.25
1.25
1.28
1.28
1.25
1.25
1.25
1.25
0.88
0.88
0.87
0.87
0.86
0.86
7.13
7.19
7.17 7.16
7.33 7.16
7.17
7.25
7.19 4′-
4′′′-
7.18 4′-
4′′′-
chain CH2(R)
CH(â) CH2(γ)
CH3(γ′) CH3(δ)
OT4
OT5
7.13
7.19
7.17 7.16
7.33 7.16
7.17
7.25
7.19 4′-
2.88/2.70
1.62
1.62
1.62
1.62
1.50/1.24
1.50/1.24
1.50/1.25
1.50/1.25
1.00
1.01
0.97
1.00
0.89
0.895
0.88
0.89
4′′′- 2.90/2.72
7.17 4′-
2.87/2.68
4′′′- 2.89/2.71

8298 Mucci et al.
Macromolecules, Vol. 39, No. 24, 2006
Table 2. 13C NMR Data (δ, ppm) for Octithiophenes OT1-OT5a
C-5 C-2′ C-3′ C-4′ C-5′ C-2′′ C-3′′ C-4′′
compound
C-2
C-3
C-4
C-5′′
C-2′′′ C-3′′′ C-4′′′ C-5′′′
OT1
OT2
OT3
OT4
OT5
136.4 124.1 128.0 125.0 134.6 128.3 128.8 134.4 134.9 126.7 123.9 136.8 136.9 127.1 132.6 131.6
137.3 126.6 110.6 122.1 136.0 127.6 133.8 130.5 128.7 112.1 127.0 137.4 135.2 127.8 132.8 132.3
138.1 131.4
77.8 128.2 136.3 127.4 134.3 131.6 133.0
84.3 132.2 139.6 135.1 127.9 132.8 132.4
137.2 126.5 110.4 122.1 135.8 127.5 133.9 130.0 128.4 112.0 127.0 137.7 135.0 127.7 132.8 132.0
138.0 131.4
chain
77.8 128.1 136.1 127.4 134.7 131.2 132.8
84.4 132.2 139.8 134.8 127.8 132.9 132.2
CH2(R)
CH2(â)
CH2(γ)
CH2(δ)
CH2(ꢀ)
CH2(ú)
CH2(η)
CH3(θ)
OT1
OT2
OT3
4′-
36.37
36.33
36.17
36.44
35.95
36.44
29.65
29.65
29.48
29.48
29.50*
29.55*
28.75
28.75
28.68
28.74
28.67#
28.75#
29.2
29.2
29.2
29.2
29.2
29.2
31.75
31.75
31.80
31.80
31.81
31.81
22.63
22.63
22.65
22.65
22.66
22.66
14.15
14.15
14.11
14.11
14.11
14.11
4′′′-
4′-
4′′′-
4′-
4′′′-
29.2
29.2
29.18$
29.21$
29.11§
29.14§
chain
CH2(R)
CH (â)
CH 2(γ)
CH 3(γ′)
CH3(δ)
OT4
OT5
4′-
43.6
43.3
43.0
43.6
34.7
34.7
34.9
34.9
28.4
28.4
28.6
28.7
18.6
18.6
18.8
18.8
10.8
10.8
11.2
11.2
4′′′-
4′-
4′′′-
a The directly acquired 13C NMR spectra display only aliphatic signals; the aromatic carbon chemical shifts derive from inverse-detection experiments
(lower resolution). *, #, § Denote interchangeable assignments.
Table 3. Relevant UV Data for Octithiophenes OT1-OT5 and
are only 20-30 nm blue-shifted with respect to those observed
for poly(alkylsulfanyl)thiophenes.14,15,32 Evidently, the bromine
atoms permit a more planar conformation to be achieved by
the octithiophenes OT2 and OT4 in the presence of high
amounts of nonsolvent, while the small hydrogen and the bulky
iodine atoms do not. We suppose that the peculiar difference
between the absorption properties of our OTs in the absence
and in the presence of a poor solvent derives from a compromise
between steric interactions and packing forces, related to the
different polarizability of hydrogen, bromine, and iodine atoms.
Probably only in the case of bromine, the packing forces are
strong enough to overcome the steric distortions and induce
planarity through stacking interactions.
Circular dichroism (CD) measurements made on films of
OT4, slowly cast from chloroform or THF, and on chloroform
solutions of OT4 in the presence of a high percentage of
methanol, show the presence of a bisignate Cotton effect (Figure
3), as has been previously observed for polythiophenes34,38,39
and OTs carrying chiral side chains.36,40 Interestingly, OT5 does
not develop any CD signal neither in solution nor in the solid
state.
Related Poly(alkylsulfanyl)Thiophenes
λmax
(CHCl3, nm)
ꢀ
λmax
compound
(mol-1 L cm-1
)
(CHCl3/CH3OH, nm)
OT1
OT2
OT3
OT4
OT5
a
456
435
419
430
419
502
470-466
469
1.1 × 107
6.2 × 107
4.2 × 107
5.0 × 107
3.5 × 107
468, 500, 540, 584
458, 502, 542, 590
515, 555, 600
520, 560, 610
530, 565, 623
b
c
a Regioregular HT poly(butylsulfanyl)thiophene.32 b Regioregular HH-
TT poly(alkylsulfanyl)thiophenes.14 c Chiral regioregular HH-TT poly-
(alkylsulfanyl)thiophene.15
a distortion in the planarity of the backbone, which translates
into a decrease in effective conjugation length and into a blue-
shift of the optical absorption.
To gain a deeper insight into the conformational and
aggregation properties of OTs, UV-Vis spectra were recorded
in CHCl3/CH3OH mixtures (Figure 2).
A marked difference in the solvatochromic behavior of the
brominated OT2 and OT4 (spectrum not shown, but similar to
that of OT2) with respect to the nonhalogenated OT1, and the
iodinated OT3 and OT5 (spectrum not shown, but very similar
to that of OT3) is found. A significant red-shift, accompanied
by the formation of a fine vibronic structure in the absorption
curves, occurs in the case of OT2 and OT4 by increasing the
methanol-to-chloroform ratio, or in thin films, whereas OT1,
OT3 and OT5 show a lower solvatochromism. In the case of
OT1 and OT4 spectra are also affected by the formation of a
precipitate at high methanol percentages.
CD has been observed on chiral OTs and polythiophenes in
the presence of aggregates,15,34,36,38,39,41,42 and only a few cases
of CD at the single molecule level are reported for chiral
polythiophenes.39 An interchain mechanism, based on the
formation of chiral superstructures,42 is almost certainly involved
in optical activity of OTs, nevertheless the development of CD
induced by aggregation only in OTs longer than five-six
thiophenic units36,40 does not permit excluding an interplay
between intrachain and interchain factors.
DFT Calculations on the Oligomer Growth. The compu-
tational study was carried out at the B3PW91/MIDI! level on
4-(methylsulfanyl)-2,2′-bithiophene, with the aim to establish
the possible sequence of the coupling reactions, leading to the
formation of the octithiophene with the experimental regio-
chemistry. Unsymmetrical substrates can react, leading to the
formation of regioisomers, which differ by the relative position
of the substituents. The experimental regiochemistry of the final
octithiophene, one inner HH and two lateral HT junctions, which
depends on the mode of coupling of the monomers, give relevant
information on the mechanism of the oligomerization.
The theoretical approach was focused on the calculation of
the Gibbs free energy of activation of competitive coupling
The red-shift and the appearance of the vibronic structure
after addition of a nonsolvent is typical of regioregular HT
polyalkylthiophenes33.34 and of regioregular (HT and HH-TT)
poly(alkylsulfanyl)thiophenes,14,15,32 and it is often attributed
to a planarization of the backbone and then to an aggregation
process, which give rise to the new vibronic bands. This
behavior has been observed only in few cases when OTs are
concerned,35 whereas a blue-shift has been reported for some
sexithiophenes.36 The positions of the vibronic bands of OT2
and OT4 are very similar to those reported for a thermochromic
undecathiophene R,ω-disubstituted with dendritic wedges37 and

Macromolecules, Vol. 39, No. 24, 2006
One-Pot Synthesis of Symmetric Octithiophenes 8299
Figure 2. UV-Vis spectra in CHCl3/CH3OH mixtures of (a) OT1, (b) OT2, (c) OT3, and (d) OT2 in thin film.
transition state energies corresponding to different RC-RC
coupling reaction pathways, is based on recent conclusions
reported for five-ring heterocyclic oligomers,46,47 which have
demonstrated that these reactions involve the coupling between
two radical cations, and that the subsequent deprotonation
processes are fast.47
Scheme 3 displays a representation of the RC-RC mecha-
nism applied to a selected reaction pathway, the HT one, and
the following considerations are valid for all the reaction
pathways considered in our analysis (i.e., also the HH and the
TT ones). To simplify the discussion, we labeled the two rings
of the starting monomer as A for the ring without substituent
(tail) and B for the ring with substituent (head). The most stable
conformation calculated for the radical cation of the starting
monomer AB (AB+•) is the fully coplanar one, with the two
rings trans to each other and the methylsulfanyl groups in the
same plane of the thiophene rings. The structure of the HT
transition state is characterized by the two monomers parallel
but not on the same plane and by the distortion of the CR
hydrogens from the planar geometry. This orientation facilitates
the overlap between the two 2pz orbitals of the interacting CR,
that is the initial stage of the σ-type orbital formation. The
distance between the two reactive carbons becomes shorter, and
their hybridization moves to sp3 during the formation of the
dimeric dication intermediate. The final step is represented by
the loss of the two protons, which restores the aromaticity of
the two rings.
Figure 3. CD spectra of OT4 films, cast under slow evaporation
conditions (1) from THF, (2) from chloroform, and cast under fast
evaporation conditions (3) from chloroform, (4) from THF. (5) CD
solution spectrum in chloroform/methanol 1:9 mixture.
reactions to compare the relative probabilities of the different
reaction pathways, as has been already carried out in the case
of oligopyrroles and oligothiophenes.43 It has been shown44,45
that the calculated unpaired-electron spin-density distribution,
orbital analysis, and charge distribution in the radical cations
involved in the oxidative coupling provide important information
that can be used to predict the reaction sites of the polymeri-
zation process. Thus, molecular electrostatic potential maps26
and semioccupied molecular orbitals (SOMO) were calculated
for selected oligomers in order to rationalize the evolution of
the electronic structure with the chain growth. This approach
offers an insight into the effect of the substituents on the reactive
sites (CR) and an indication of the driving forces for bond
formation.
The various reaction pathways, which could be involved in
the formation of octithiophenes, are shown in Scheme 4, together
with the calculated free energy barriers ∆G† for each transition
state. The number of the coupling steps leading to octithiophenes
can be two or three, depending on the substrates involved in
the second step. For each step, we compare the activation energy
of all the possible regioisomeric attacks, but only the substrates
Two mechanisms have been proposed for the oxidative
coupling of heteroaromatic rings, i.e., the coupling between two
radical cations (RC-RC) or the attack of one radical cation on
the neutral substrate. Our approach, which compares the

8300 Mucci et al.
Macromolecules, Vol. 39, No. 24, 2006
Scheme 3. Multistep RC-RC Mechanism for the HT Coupling
Scheme 4. Free Activation Energies ∆G† (Numbers over the Arrows, in kcal/mol) Calculated for Selected Coupling Reactions Involving
the Monomer AB in Various Reaction Pathways and Leading to Octithiophenes (See the Text for Further Details)a
a The two octithiophenes deriving from the two competitive routes are squared.
deriving from the transition states with the lower activation
barrier are considered as reactive in the successive step.
Three isomeric quaterthiophenes characterized by different
inner junctions, AB-AB, AB-BA, and BA-AB, can be
formed in the first step. The free activation energy for the HT
coupling (AB-AB) is 6 and 3 kcal/mol lower than those
calculated for the HH and TT couplings, respectively. Hence,
the quaterthiophene ABAB is that most probably formed in the
first step. Its radical cation (ABAB+•) can react with another
ABAB+• unit or with a AB+• unit in the second step. For each
of these reactions, all isomeric couplings were considered.
In the first case, the dimerization process leads directly to
the formation of octithiophenes. The free activation energy for
the HH coupling (ABAB-BABA) is 6 and 15 kcal/mol lower
than those calculated for the HT and TT couplings, respectively.
A similar result is obtained in the second case, which can be
viewed as a chain growth process: three hexamers can form
(two out of four pathways lead to the equivalent ABAB-AB
and AB-ABAB sexithiophenes) and the free activation energy
for the HH coupling (ABAB-BA) is 4, 6, and 10 kcal/mol
lower than those calculated for the two HT and TT couplings,
respectively. A further step is necessary to obtain an octithio-
phene, i.e., the coupling of the radical cation of the asymmetric
hexamer, ABABBA (ABABBA+•) with one AB+• unit. Four
different isomers can be generated, and in this case, the
calculated activation energies for the two HT couplings are
5-10 kcal/mol lower than those for the TT ones. The ∆G† of
the two HT couplings differ by 3 kcal/mol, and the route with
the lower activation energy (generating the ABABABBA
octithiophene) does not lead to the isomer experimentally
observed (ABABBABA), which is obtained through the other
HT coupling.
Our approach, based on transition state calculations of
successive coupling reactions, predicts that the HT is the favorite
coupling in the first step, whereas the HH is favorite in the
second one. In the third possible step (i.e., coupling between a
sexithiophene and a bithiophene), the HT attacks are favorite
compared to the TT ones. Regarding the dimerization (two steps)
and the chain-propagation (three steps) mechanism, we found
that they seem to have nearly the same energy barriers at the
second step, suggesting a possible competition between them.
Nevertheless, the last route leads to the formation of an
octithiophene with a regiochemistry that is not that experimen-
tally observed, and this supports the dimerization process.
The change predicted for the regioselectivity of the coupling
steps (i.e., HT for the first and HH for the second one) could
be explained as a consequence of the evolution of two electronic
effects with the oligomer length. These effects are related to

Macromolecules, Vol. 39, No. 24, 2006
One-Pot Synthesis of Symmetric Octithiophenes 8301
The last point concerns the reason the reaction does not
proceed effectively toward the formation of a polymer. In our
opinion, this behavior should be explained by considering the
reduced reactivity of the external CR due to the low localization
of SOMO on these atoms in the radical cation of the octithio-
phene ABABBABA, as depicted in Figure 5. A similar behavior,
observed also for the oxidative coupling of 3,3′-bis(butylsul-
fanyl)-2,2′-bithiophene and of 3-(butylsulfanyl)-2,2′-bithio-
phene (which form hexamers)16,17 but not for that of 4,4′-bis-
(alkylsulfanyl)-2,2′-bithiophenes (which readily polymerize),14,15
suggests that the low SOMO localization at the outer CR is
directly linked to the lack of alkylsulfanyl groups close to them
in the intermediate oligomeric radical cations. Further work
aimed at deriving a theoretical rationalization of the whole of
these experimental results is needed.
Conclusions
In this paper, we present the study of the oxidative polym-
erization with FeCl3 of 4-(octylsulfanyl)-2,2′-bithiophene and
of four TT bithiophenes bearing alkylsulfanyl chains and
halogens as substituents in â-position. Exploiting the ability of
the alkylsulfanyl group in driving the regiochemistry of the
coupling, we were able to synthesize five octithiophenes with
the same regiochemistry. When the substituents are the octyl-
sulfanyl or the 2-methylbutylsulfanyl group and the bromine
atom, the octithiophenes possess a pronounced solvatochromism,
Figure 4. Molecular electrostatic potential maps (a and c) and SOMO
(b and d) isosurfaces for AB+• and ABAB+•
.
the SOMO density and to the charge distribution in the reacting
radical cations and act on the value of the energy barrier, as
has already been discussed by Lacroix et al. for the study of
polypyrrole growth.44 Figure 4 shows the SOMO orbital and
the molecular electrostatic potential maps for AB+• and
ABAB+•, which provide an insight into the results obtained.
Concerning AB+•, a higher (blue) and a lower (green) positive
electrostatic potential for the B and the A ring, respectively,
are shown in the molecular electrostatic potential plot (Figure
4a), whereas SOMO, delineating the areas where the unpaired
electron is most localized, involves more the π system of the B
ring than that of A (Figure 4b). The charge and the unpaired
electron distributions, related to the electrostatic potential (Figure
4c) and to the SOMO (Figure 4d), respectively, become
appreciably diffused on the whole substrate in the case of
ABAB+•. It is to be noted that the electrostatic potential values,
as well as the shape of the SOMO, on the terminal CR of the
outer B ring are significantly smaller if compared with those
of the corresponding to the CR in AB+•.
On the basis of the above considerations, in the first coupling
step (between two AB+• units), the HH coupling is favored by
the frontier orbital interaction, but the strong electrostatic
repulsion between the outer CR of the B rings turns out to be
directing the reaction toward the HT coupling. The decreasing
of the electrostatic potential of ABAB+•, and in particular close
to the CR of the outer B ring, with respect to AB+•, reduces
the repulsion between the two reactive centers in the second
coupling step. Therefore, the frontier orbital interaction, which
still favors the HH coupling, has a greater influence than the
electrostatic repulsion on the energy barrier.
λ
max, close to that observed for long alkylsulfanyl poly-
thiophenes, circular dichroism induced by aggregation (in the
case of the chiral substituent), and they appear as free-standing
films, that is quite unusual for oligomeric materials. Both the
less and the more steric demanding hydrogen and iodine atoms
alter the properties of the synthesized molecules, which result
in less solvatochromic properties and display lower filmability.
DFT calculations on the model molecule 4-(methylsulfanyl)-
2,2′-bithiophene helped us in establishing that the oligomeric
growth is the result of a HT coupling step followed by a HH
one and in deriving which electronic effect drives the regiose-
lectivity in each step. The orbital and the electrostatic interac-
tions contribute in determining the height of the activation
energy barrier, and their relative weights evolve with the
elongation of the backbone in the oligomerization process.
The experimental regiochemistry of OT2-OT5, indicates that
the behavior toward oxidative coupling of halogenated alkyl-
sulfanyl bithiophenes 2-5 is also clearly dominated by the
directing ability of the alkylsulfanyl sulfur atom, and the halogen
atom seems to influence the percentage of the ABABBABA
octithiophene obtained.
The oxidative polymerization is revealed to be a good method
for generating symmetric octithiophenes from asymmetric TT
alkylsulfanyl bithiophenes, which can be further functionalized,
for the bromine and iodine atoms are replaceable by other
nucleophiles.
Figure 5. SOMO isosurface for the octithiophene ABABBABA+•
.

8302 Mucci et al.
Macromolecules, Vol. 39, No. 24, 2006
(24) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5652; Perdew, J. P.;
Wang, Y. Phys. ReV. B 1992, 45, 13244-13248.
(25) Easton, R. E.; Giesen, D. J.; Welch, A.; Cramer, C. J.; Truhlar, D. G.
Theor. Chim. Acta 1996, 93, 281-301.
(26) Murray, J. S., Sen, K. D., Eds. Molecular Electrostatic Potentials:
Concepts and Applications; Theoretical and Computational Chemistry
Book Series, Vol. 3; Elsevier: Amsterdam, 1996.
(27) GaussView, version 3.0, Dennington, R., II; Keith, T.; Millam, J.;
Eppinnett, K.; Hovell, W. L.; Gilliland, R.; Semichem, Inc.: Shawnee
Mission, KS, 2003.
(28) Schenetti, L.; Mucci A. In New AdVances in Analytical Chemistry;
Atta-ur-Rahman, Ed.; Taylor & Francis Inc.: New York, 2002; Vol.
3, p 1.
(29) Bax, A.; Griffey, R. H.; Hawkins, B. L. J. Magn. Reson. 1983, 55,
301-315.
(30) Bax, A.; Summers, M. F. J. Am. Chem. Soc. 1986, 108, 2093-2094.
(31) Kirschbaum, T.; Azumi, R.; Mena-Osteritz, E.; Ba¨uerle, P. New. J.
Chem. 1999, 23, 241-250.
(32) Goldoni, F.; Iarossi, D.; Mucci, A.; Schenetti, L.; Zambianchi, M. J.
Mater. Chem. 1997, 7, 593-596.
(33) Kiriy, N.; Ja¨hne, E.; Adler, H.-J.; Schneider, M.; Kiriy, A.; Gorodyska,
G.; Minko, S.; Jehnichen, D.; Simon, P.; Fokin, A. A.; Stamm, M.
Nano Lett. 2003, 3, 707-712; Sandstedt, C. A.; Rieke, R. D.; Eckhardt,
C. J. Chem. Mater. 1995, 7, 1057-1059.
(34) Langeveld-Voss, B. M. W.; Janssen, R. A. J.; Meijer, E. W. J. Mol.
Struct. 2000, 512, 285-301.
(35) Kiriy, N.; Kiriy, A.; Bocharova, V.; Stamm, M.; Richter, S.; Plo¨tner,
M.; Fischer, W.-J.; Krebs, F. C.; Senkovska, I.; Adler, H.-J. Chem.
Mater. 2004, 16, 4757-4764; Kiriy, N.; Bocharova, V.; Kiriy, A.;
Stamm, M.; Krebs, F. C.; Adler, H.-J. Chem. Mater. 2004, 16, 4765-
4771.
(36) Lecle`re, P.; Surin, M.; Viville, P.; Lazzaroni, R.; Kilbinger, A. F. M.;
Henze, O.; Feast, W. J.; Cavallini, M.; Biscarini, F.; Schenning, A. P.
H. J.; Meijer, E. W. Chem. Mater. 2004, 16, 4452-4466 and references
herein.
(37) Apperloo, J. J.; Janssen, R. A. J.; Malenfant, P. R. L.; Frechet, J. M.
J. Macromolecules 2000, 33, 7038-7043.
(38) Goto, H.; Yashima, E. J. Am. Chem. Soc. 2002, 124, 7943-7949;
Goto, H.; Okamoto, Y.; Yashima, E. Macromolecules 2002, 35, 4590-
4601; Brustolin, F.; Goldoni, F.; Meijer, E. W.; Sommerdijk, N. A. J.
M. Macromolecules 2002, 35, 1054-1059.
(39) Zhang, Z.-B.; Fujiki, M.; Motonaga, M.; Nakashima, H.; Torimitsu,
K.; Tang, H.-Z. Macromolecules 2002, 35, 941-944; Nilsson, K. P.
R.; Johan, J. D. M.; Konradsson, P.; Ingana¨s, O. Macromolecules 2004,
37, 6316-6321.
(40) Sakurai, S.; Goto, H.; Yashima, E. Org. Lett. 2001, 3, 2379-2382.
(41) Langeveld-Voss, B. M. W.; Beljonne, D.; Shuai, Z.; Janssen, R. A.
J.; Meskers; S. C. J.; Meijer, E. W.; Bredas, J.-L. AdV. Mater. 1998,
10, 1343-1348.
Acknowledgment. We thank the Centro Interdipartimentale
Grandi Strumenti of the University of Modena and Reggio
Emilia for the use of the Bruker DPX-200 and Avance 400
spectrometers, the Perkin-Elmer i-series FT-IR microscope, and
the Finnigan MAT SSQ 710 A mass spectrometer, and Prof.
A. Forni for the CD measurements.
Supporting Information Available: Coupled HMQC spectrum
of OT1. Long range 1H,13C inverse-detection NMR spectra of OT1.
This material is available free of charge via the Internet at http://
pubs.acs.org
References and Notes
(1) Katz, H. E.; Bao, Z. J. Phys. Chem. B 2000, 104, 671-678.
(2) Horowitz, G. AdV. Mater. 1998, 10, 365-377.
(3) Hotta, S.; Waragai, K. AdV. Mater. 1993, 5, 896-908.
(4) Kovac, J.; Peternai, L.; Lengyel, O. Thin Solid Films 2003, 433, 22-
26.
(5) Furuta, P.; Brooks, J.; Thompson, M. E.; Frechet, J. M. J. J. Am. Chem.
Soc. 2003, 125, 13165-13172.
(6) Huynh, W. U.; Dittmer, J. J.; Janke, J.; Libby, W. C.; Whiting, G. L.;
Alivisatos, A. P. AdV. Funct. Mater. 2003, 13, 73-79.
(7) Liu, J.; Tanaka, T.; Sivula, K.; Alivisatos, A. P.; Frechet, J. M. J. J.
Am. Chem. Soc. 2004, 126, 6550-6551.
(8) Crone, B.; Dodabalapur, A.; Gelperin, A.; Torsi, L.; Katz, H. E.;
Lovinger, A. J.; Bao, Z. Appl. Phys. Lett. 2001, 78, 2229-2231.
(9) Someya, T.; Katz, H. E.; Gelperin, A.; Lovinger, A. J.; Dodabalapur,
A. Appl. Phys. Lett. 2002, 81, 3079-3081.
(10) Kohler, A.; Wilson, J. S.; Friend, R. H. AdV. Mater. 2002, 14, 701-
707.
(11) Destri, S.; Pasini, M.; Botta, C.; Porzio, W.; Bertini, F.; Marchio`, L.
J. Mater. Chem. 2002, 12, 924-933.
(12) Tonzola, C. J.; Maksudul, M. A.; Kaminsky, W.; Jenekhe, S. A. J.
Am. Chem. Soc. 2003, 125, 13548-13558.
(13) Ba¨uerle, P. In Handbook of Oligo- and Polythiophenes; Fichou, D.,
Ed.; Wiley-VCH: Weinheim, 1999; p 89.
(14) Iarossi, D.; Mucci, A.; Schenetti, L.; Seeber, R.; Goldoni, F.; Affronte,
M.; Nava, F. Macromolecules 1999, 32, 1390-1397.
(15) Iarossi, D.; Mucci, A.; Parenti, F.; Schenetti, L.; Seeber, R.; Zanardi,
C.; Forni, A.; Tonelli, M. Chem.sEur. J. 2001, 7, 676-685.
(16) Mucci, A.; Parenti, F.; Schenetti, L.; Zanardi, C. Trends Heterocycl.
Chem. 2001, 7, 55-64.
(17) Iarossi, D.; Mucci, A.; Schenetti, L.; Sodini, V. J. Heterocycl. Chem.
1999, 36, 241-247.
(18) Goldoni, F.; Langeveld-Voss, B. M. W.; Meijer, E. W. Synth. Commun.
1998, 28, 2237-2244.
(19) Cagnoli, R.; Lanzi, M.; Mucci, A.; Parenti, F.; Schenetti, L. Synthesis
2005, 267-271.
(42) Beljonne, D.; Langeveld-Voss, B. M. W.; Shuai, Z.; Janssen, R. A.
J.; Meskers, S. C. J.; Meijer, E. W.; Bredas, J.-L. Synth. Met. 1999,
912-913.
(43) Lacroix, J.-C.; Maurel, F.; Lacaze, P.-C. J. Am. Chem. Soc. 2001,
123, 1989-1996; Lacroix, J.-C.; Maurel, F.; Lacaze, P.-C. Synth. Met.
1999, 101, 675-676; Yurtsever, M.; Yurtsever, E. Polymer 2004, 45,
9039-9045.
(20) Tour, J. M.; Wu, R. Macromolecules 1992, 25, 1901-1907.
(21) Frohlich, H.; Kalt, W. J. Org. Chem. 1990, 55, 2993-2995.
(22) Baumgartner, T.; Bergmans, W.; Ka´rpa´ti, T.; Neumann, T.; Nieger,
M.; Nyula´szi, L. Chem.sEur. J. 2005, 11, 4687-4699.
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, revision B.04; Gaussian, Inc.: Wallingford, CT, 2004.
(44) Lacroix, J.-C.; Valente, R.-J.; Maurel, F.; Lacaze, P.-C. Chem.sEur.
J. 1998, 4, 1667-1677.
(45) Smith, J. R.; Cox, P. A.; Campbell, S. A.; Ratcliffe, N. M. J. Chem.
Soc., Faraday Trans. 1995, 91, 2331-2338; Ando, S.; Ueda, M. Synth.
Met. 2002, 129, 207-213; Fre´chette, M.; Belleteˆte, M.; Bergeron, J.-
Y.; Durocher, G.; Leclerc, M. Synth. Met. 1997, 84, 223-224.
(46) Andrieux, C. P.; Audebert, P.; Hapiot, P.; Save´ant, J.-M. J. Phys. Chem.
1991, 95, 10158-10164; Guyard, L.; Hapiot, P.; Neta, P. J. Phys.
Chem. 1997, 101, 5698-5706; Tschuncky, P.; Heinze, J.; Smie, A.;
Engelmann, G.; Kossmehl, G. J. Electroanal. Chem. 1997, 433, 223-
226.
(47) Audebert, P.; Cate, J.-M.; Le Coustumer, G.; Duchenet, V.; Hapiot,
P. J. Phys. Chem. 1995, 99, 11923-11929.
MA0614141