Thiophene-fused phospholo[3,2-b]phospholes and their dichalcogenides: Synthesis and structure-photophysical properties relationships

Article abstract of DOI:10.1016/j.crci.2010.04.021

The PCl₃-promoted intramolecular cascade cyclization produced a series of thiophene-fused phospholo[3,2-b]phosphole derivatives, including non-oxidized 2, dioxides 3, and disulfides 4. These derivatives exhibit significantly red-shifted absorpt

Full text of DOI:10.1016/j.crci.2010.04.021

C. R. Chimie 13 (2010) 1082–1090
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Full paper/Memoire
Thiophene-fused phospholo[3,2-b]phospholes and their
dichalcogenides: Synthesis and structure–photophysical
properties relationships
*
Aiko Fukazawa, Taka-aki Murai, Liangchun Li, Youming Chen, Shigehiro Yamaguchi
Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
A R T I C L E I N F O
A B S T R A C T
Article history:
The PCl3-promoted intramolecular cascade cyclization produced a series of thiophene-
fused phospholo[3,2-b]phosphole derivatives, including non-oxidized 2, dioxides 3, and
disulfides 4. These derivatives exhibit significantly red-shifted absorptions and
fluorescences compared with their benzene-fused analogues. Among the thiophene-
fused series, the non-oxidized 2 has the highest fluorescence quantum yield of 0.95. This
trend is in contrast to that observed for the benzene analogues, in which a dioxide
derivative shows the most intense fluorescence.
Received 3 February 2010
Accepted after revision 23 April 2010
Available online 11 June 2010
Keywords:
Phosphorus
Fused-ring systems
Cyclization
´
ß 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Conjugation
Chromophores
Fluorescence
1. Introduction
different from pyrrole in terms of the geometry, electronic
structure, and thus properties, and thereby serves as a
The incorporation of main group elements into the
conjugated framework is a powerful strategy for the design
of new -electron materials with unusual electronic
p
-
unique building unit [3]. Various types of phosphole-
containing -conjugated compounds have been investi-
gated to date, including 2,5-difunctionalized phospholes
[4,5], phosphole-based polymers [6], phosphole-contain-
ing macrocycles [7], phosphole-cored dendrimers [8], and
p
p
structures [1]. Among various main group elements, the
group 15 phosphorus is particularly interesting, because
phosphanyl groups can be readily modified by oxidation to
phosphine oxides or sulfides, formation of phosphonium
salts, and complexation with Lewis acids or transition
metals. This diversity in the chemical modification enables
us to tune the electronic and structural properties over a
wide range, and thus, has attracted many researchers to
fused phosphole
p systems, such as dibenzophospholes
[9,10], dithienophospholes [11], and benzophospholes
[12–15].
As a new entity for the fused phosphole derivatives, we
have recently succeeded in the synthesis of dibenzo-fused
phospholo[3,2-b]phosphole dioxides 1 (R = Ph). The most
striking feature of this skeleton is the incorporation of two
phosphorus atoms into the skeleton and thereby the
accumulative effect of the two phosphoryl groups (> P O)
develop a variety of phosphorus-containing
materials [2].
p
-electron
Among the various phosphorus-containing
p
-conju-
gated skeletons, phosphole, a phosphorus analogue of
pyrrole, is of particular interest, because it is largely
makes the skeleton highly electron-accepting. As a
consequence, 1 demonstrated unusual fluorescence prop-
erties totally different from the already known bridged
stilbenes [16] (Fig. 1).
To elaborate this highly electron-accepting phos-
pholo[3,2-b]phosphole dioxide skeleton, we now replace
* Corresponding author.
E-mail address: yamaguchi.shigehiro@b.mbox.nagoya-u.ac.jp
(S. Yamaguchi).
the stilbene skeleton with
a more electron-donating
1631-0748/$ – see front matter ß 2010 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2010.04.021

A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
1083
Fig. 1. Phospholo[3,2-b]phosphole derivatives.
dithienylvinylene skeleton. We envisioned that this struc-
tural modification would lead to a narrower HOMO–LUMO
gap, and thus, more interesting properties such as absorp-
tion and fluorescence at longer wavelengths. Facile func-
tionalization of the thiophene rings would also increase the
of cis and trans isomers. These isomers could be separated
by silica gel column chromatography and were obtained in
18 and 42% yields for cis-3 and trans-3, respectively.
Similarly, the corresponding phospholophosphole disul-
fide 4 was synthesized by using S8 as an oxidant instead of
mCPBA and obtained in 31 and 42% yields for cis-4 and
trans-4, respectively. Their structures were verified by
NMR spectroscopy and mass spectrometry and finally by
X-ray crystallographic analyses (Fig. 2). A noteworthy fact
in the reaction is that the cyclization requires a heating
condition at high temperature (101 8C), while the cycliza-
potential utility of this skeleton as a core for extended
p-
conjugated materials. This article discloses the syntheses
and photophysical properties of a series of thiophene-fused
phospholo[3,2-b]phosphole derivatives, including non-oxi-
dized 2, dioxides 3, and disulfides 4. In particular, the effects
of the fused rings as well as the oxidation states of the
phosphorus atoms on the fluorescence properties are
discussed.
tion for the synthesis of the benzene analogue
1
spontaneously proceeds even at room temperature [16].
This difference may be ascribed to a more severe ring strain
in the fused system consisting only of the five-membered
rings and/or the electronic effect of the thiophene rings on
the nucleophilicity and electrophilicity of the phosphorus
centers (Figs. 3 and 4).
2. Results and discussion
2.1. Synthesis
Although we tried to isolate the non-oxidized phos-
pholophosphole 2 directly from the reaction mixture after
the cyclization, all attempts failed due to the contamina-
tion of a small amount of the dioxides 3. Therefore, we
conducted the reduction of the isolated pure trans-3 with
HSiCl3, as shown in Scheme 2, and finally succeeded in
obtaining 2 in 54% yield in a pure form. The 1H NMR
measurement revealed that this was a mixture of cis and
trans isomers in a cis/trans ratio of 1/1.7, despite starting
from the pure trans-3. The obtained compound was used
for comparisons in the photophyscial properties with
compounds 3 and 4, without further separation of the cis
and trans isomers.
The thiophene-fused phospholophospholes were pre-
pared by a modified procedure of our recently reported
PCl3-promoted nucleophilic cascade cyclization, as shown
in Scheme 1 [16]. Thus, starting from bis(3-bromo-2-
thienyl)acetylene 5, dilithiation using t-BuLi in THF
followed by the reaction with PhP(NEt2)Cl produced the
corresponding aminophosphanyl intermediate 6 in situ.
After replacement of the solvent THF by dioxane, the
reaction mixture was treated with an excess amount of
PCl3 and refluxed for 18 h in order to accomplish the
cyclization. Finally, the produced thiophene-fused phos-
pholophosphole 2 was oxidized with mCPBA to give the
corresponding phospholophosphole dioxide 3 as a mixture
Scheme 1. Synthesis of dithiophene-fused phospholo[3,2-b]phosphole derivatives.

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A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
Fig. 2. ORTEP drawings of (a) cis-3, (b) trans-3, and (c) cis-4 (50% probability for thermal ellipsoids). Hydrogen atoms and solvent molecules are omitted for
clarity.
Scheme 2. HSiCl3 reduction of phospholo[3,2-b]phosphole dioxide.
2.2. Photophysical properties
the other hand, by oxidizing the phosphorus atoms to the
dioxides trans-3, the labs and lem are shifted to longer
wavelengths by 72–73 nm (3500 cmꢀ1) and 94–95 nm
(3000 cmꢀ1), respectively, and thus compounds 3 show a
red fluorescence. Similar trends were observed upon
oxidation to phosphine sulfides 4, where the labs and
Photophysical properties of the thiophene-fused phos-
pholophosphole derivatives 2–4 were investigated, and
these data were compared with those of the dibenzo-fused
phospholophosphole 7 (1/1.1 cis/trans mixture), its oxides
1, and sulfides 8. Their data are summarized in Table 1.
Whereas all the derivatives have cis and trans isomers,
their photophysical properties in solutions are essentially
comparable. A thiophene-fused phospholophosphole 2 (1/
l
em are shifted to longer wavelengths by 65–68 nm (3200–
3300 cmꢀ1) and 71–76 nm (2400–2500 cmꢀ1), respective-
ly. Whereas the red-shifts upon oxidation of the phospho-
rus center were also observed for other known
1.7 cis/trans mixture) has an absorption maximum (labs
)
phosphorus-containing p-electron systems, the extent of
at 420 nm and exhibits an intense yellowish green
fluorescence with the maximum (l
em) at 516 nm.1 On
the red-shifts observed for the dithieno-fused phospholo-
phospholes are much larger than those for compounds
consisting of a mono-phosphole ring like 2,5-dithienyl-
phospholes [4] and dithienophospholes [11].
The effect of the fused rings on the photophysical
properties was investigated next. All the thiophene-fused
phospholophosphole derivatives 2, 3, and 4 exhibited longer
absorption and fluorescence maxima compared with their
dibenzo-fused counterparts 7, 1, and 8, respectively,
1
TD-DFT calculations for compounds 2, 3, and 4 demonstrated that the
transition energies for the lowest-energy excited states are nearly
identical to each other between the cis and trans isomers. Such an identity
between geometrical isomers were experimentally and theoretically also
confirmed in the benzene-fused phospholo[3,2-b]phospholes [16].

A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
1085
Fig. 4. Fluorescence Spectra of 2 (solid line, in CHCl3), trans-3 (broken
dotted line, in CH2Cl2) and trans-4 (dotted line, in CH2Cl2).
Fig. 3. UV-vis absorption spectra of 2 (solid line, in CHCl3), trans-3
(broken dotted line, in CH2Cl2) and trans-4 (dotted line, in CH2Cl2).
Table 1
Photophysical data for a series of phospholo[3,2-b]phosphole derivatives.
Compound
Absorption
abs/nma
Fluorescence
em/nmb
l
e
/104
M
ꢀ1 cmꢀ1
l
FFL
t
s/nsd
kr/sꢀ1
knr/sꢀ1
c
2e,g
420
492
493
488
485
1.67
1.13
1.12
1.07
1.11
516
610
611
592
587
0.95
0.04
0.04
0.21
0.33
7.5
1.0
1.0
5.2
6.5
1.3 ꢁ 108
4.0 ꢁ 107
4.0 ꢁ 107
4.0 ꢁ 107
5.1 ꢁ 107
6.7 ꢁ 106
9.6 ꢁ 108
9.6 ꢁ 108
1.5 ꢁ 108
1.0 ꢁ 108
cis-3f
trans-3f
cis-4f
trans-4f
7f,h
trans-1f
trans-8f
351
1.27
0.69
0.51
415
480
0.07
0.98
1.4
5.0 ꢁ 107
6.6 ꢁ 108
395
15.7
6.2 ꢁ 107
1.3 ꢁ 106
i
i
i
i
i
395(sh)
–
–
–
–
–
a
Only the longest absorption maxima are shown.
b
c
d
e
f
Emission maxima upon excitation at the absorption maximum wavelengths.
Absolute fluorescence quantum yields determined by a calibrated integrating sphere system within ꢂ 3% errors.
Fluorescence lifetimes within ꢂ 0.5 ns errors.
In CHCl3.
In CH2Cl2.
g
h
i
A mixture of 1/1.7 cis/trans isomers.
A mixture of 1/1.1 cis/trans isomers.
No fluorescence was observed.
.
reflecting the narrower HOMO–LUMO energy gap in the
thiophene-fused system. The mostnoteworthy fact isthat in
the thiophene series, the non-oxidized compound 2 shows a
very high quantum yield of 0.95, although their oxidized
derivatives show only faint fluorescence with a FF of 0.04
and 0.21–0.33 for 3 and 4, respectively. This trend is totally
opposite to that for the benzene-fused analogues as well as
fluorescence quantum yields significantly increase upon
oxidation [17]. To the best of our knowledge, the only
exceptions are Baumgartner’s dithienophosphole deriva-
tives, which exhibit intense fluorescence regardless of the
oxidation states of the phosphorus atoms [11].
To obtain deeper insights into the origin of these
differences in FF between the thiophene series and the
benzene series, we investigated the excited-state dynam-
other phosphorus-containing
p-conjugated compounds. In
general, while trivalent phosphanes are weakly fluorescent
due to the quenching effect by lone-pair electrons, their
ics. According to the equations
F
F = kr ꢁ ts and
kr þ knr
¼
tꢀs 1, the radiative (kr) and nonradiative (knr
)

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A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
decay rate constants were determined (Table 1). In both of
the series, the oxidation of the phosphorus atoms to the
phosphine oxides or sulfides results in a decrease in the kr
value. This is consistent with the fact that the oxidized
compounds have longer absorption wavelengths and
tions on model compounds trans-20, trans-30, and trans-
40, where trimethylsilyl groups are used in place of
triisopropylsilyl, at the B3LYP/6-31G(d) level of theory.
The calculations of the benzene-fused trans-1 were
also conducted for a comparison. As shown in Fig. 5,
the oxidation of the thiophene-fused phospholophosp-
hole 20 to the phosphine oxide 30 results in a significant
decrease in the LUMO level (trans-20: ꢀ1.73 eV, trans-30:
ꢀ2.55 eV), which is much greater than the decrease in
the HOMO level (trans-20: ꢀ5.01 eV, trans-30: ꢀ5.48 eV).
The oxidation to the phosphine sulfide 40 also leads to a
decrease in the LUMO level (ꢀ2.59 eV for trans-40), the
extent of which is almost comparable to that for the
phosphine oxide. In a comparison between the thio-
phene-fused trans-30 and the benzene-fused trans-1, the
thiophene derivative has a much higher HOMO level as
smaller molar absorption coefficients
non-oxidized derivatives 2 and 7. This different tendency is
e compared to the
that, in the thiophene-fused series, the non-oxidized
phosphine
2 has a significantly small knr value of
6.7 ꢁ 106 sꢀ1, while the phosphine oxide 1 has a small
knr value in the benzene series. Obviously, these retarded
nonradiative decay processes for 2 and 1 are responsible
for their high fluorescence quantum yields. These facts
demonstrate that the fluorescence efficiency highly
depends not on the oxidation state of the phosphorus
atom but on the
series of compounds have rigid and flat
p
-conjugated skeleton. Because both
-conjugated
p
well as a slightly lower LUMO level. This result
skeletons, their rate constants for the internal conversion
may not be significantly different. Instead, the rate
constant of the intersystem crossing process may be
demonstrates that the high electron-donating character
of the dithienylvinylene skeleton compared to the
stilbene skeleton is mainly responsible for the lower
transition energies for the thiophene derivatives. In
dependent on the
p-conjugated skeletons.
addition, the thiophene derivative 30 has
oscillator strength compared to that of
0.1508, trans-30: 0.3121). The thiophene derivative 30
may have more significant intramolecular charge
transfer character in the excited state that leads to the
stronger oscillator strength.
a
larger
2.3. Theoretical calculations
1 (trans-1:
To elucidate the effect of the fused rings and the
oxidation states of the phosphorus atoms on the
electronic structures, we performed the TD-DFT calcula-
a
Fig. 5. Energy diagrams and pictorial representations of the frontier MOs for thiophene-fused phospholo[3,2-b]phospholes trans-20, trans-30, and trans-40,
together with those of benzene-fused phospholo[3,2-b]phosphole dioxide trans-1, calculated at the B3LYP/6-31G(d) level. Their lowest-energy transitions
were estimated by TD-DFT calculations at the same level.

A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
1087
3. Conclusion
dissolved in anhydrous dioxane (12.0 mL). PCl3 (0.40 mL,
628 mg, 4.57 mmol) was added to the mixture in one
portion at room temperature, and the reaction mixture
was stirred at reflux temperature for 18 h. After concen-
tration of the reaction mixture under reduced pressure,
degassed anhydrous toluene (72 mL) was added. The
resulting precipitate was removed by filtration under an
argon atmosphere and the filtrate was concentrated under
reduced pressure to give 765 mg of crude 2 as brown waxy
solids. Without further purification, this crude 2 was
dissolved in CHCl3 (12.0 mL), and mCPBA (341 mg,
1.52 mmol) was added at room temperature, resulting in
an immediate color change of the reaction mixture from
dark brown to bright red. After stirring for 1 h, the mixture
was washed with 10% Na2SO3 aq., and the aqueous layer
was extracted with CHCl3 for three times. The combined
organic layer was washed with brine, dried over Na2SO4,
and filtered. After concentration of the filtrate under
reduced pressure, the resulting crude products were
subjected to a silica gel column chromatography (CHCl3
as eluent) to give almost pure trans-3 (Rf = 0.40) and cis-3
(Rf = 0.06) both as red solids. These products were
We have synthesized
a series of thiophene-fused
phospholo[3,2-b]phosphole derivatives as new fused
phosphole derivatives on the basis of the PCl3-induced
intramolecular cascade cyclization. The obtained thio-
phene-fused phospholophosphole derivatives exhibit sig-
nificantly red-shifted absorptions and fluorescences
compared with their benzene-fused analogues, mainly
due to the highly electron-donating character of the
dithienylvinylene skeleton. The study on the structure–
photophysical properties relationship demonstrated sig-
nificantly different trends between the thiophene series
and the benzene series. Although the thiophene-fused
phospholophosphole dioxide 3 and disulfide 4 show only
faint fluorescences, the non-oxidized derivative 2 exhibits
an intense fluorescence. This is in contrast to the fact that a
dioxidized derivative shows the highest quantum yield
among the benzene-fused derivatives. These facts demon-
strate that the relationship between the fluorescence
efficiency and the oxidation states of the phosphorus
atoms is highly influenced by the character of the
conjugated skeletons.
p-
thoroughly purified by
a preparative GPC to afford
spectroscopically pure trans-3 (240 mg, 0.32 mmol, 42%
yield) and cis-3 (106 mg, 0.14 mmol, 18% yield) both as red
solids.
4. Experimental
General. Melting points (mp) were determined with a
Yanaco MP-S3 or a Stanford Research System OptiMelt
MPA100 instrument (MPA100). 1H and 13C NMR spectra
were recorded with a JEOL AL-400 spectrometer (400 MHz
for 1H and 100 MHz for 13C) in CDCl3 and chemical shifts
cis-3. mp: 208.0–209.0 8C. 1H NMR (400 MHz, CDCl3)
d
1.06 (d, J = 6.8 Hz, 36H), 1.29 (sept, J = 6.8 Hz, 6H), 7.34 (t,
J = 1.5 Hz, 2H), 7.45 (t, J = 7.3 Hz, 4H), 7.58 (t, J = 7.3 Hz, 2H),
7.80 (dd, J = 7.3, 1.5 Hz, 4H). 13C {1H} NMR (100 MHz,
CDCl3) d 11.8 (s), 18.6 (s), 128.5 (dd, JCP = 105, 6.6 Hz), 129.4
are reported in
d
ppm using CHCl3 for 1H (7.26 ppm) and
(t, JCP = 6.6 Hz), 130.8 (t, JCP = 5.8 Hz), 133.2 (t, J = 7.8 Hz),
137.3 (dd, JCP = 122, 2.5 Hz), 143.7 (d, JCP = 5.7 Hz), 144.4 (d,
JCP = 119 Hz), 151.2 (pseudo t, JCP = 20 Hz). 31P {1H} NMR
13C (77.16 ppm) for CDCl3 as an internal standard. 31P NMR
spectra were recorded with a JEOL AL-400 spectrometer
(162 MHz) using H3PO4 (0.0 ppm) as an external standard.
Mass spectra were measured with a JEOL JMS 700 (FAB) or
Bruker micrOTOF Focus (APCI). Thin layer chromatography
(TLC) was performed on plates coated with a 0.25-nm
thickness of Silica Gel 60 F254 (Merck). Column chroma-
tography was performed using silica gel PSQ100B (Fuji
Silysia Chemical). Recycle preparative gel permeation
chromatography (GPC) was performed using LC-918 with
polystyrene gel columns (JAIGEL 1H and 2H, Japan
Analytical Industry) with chloroform as an eluent. Anhy-
drous Et2O, THF, and toluene were purchased from Kanto
Chemicals. PhP(NEt2)Cl [18] and bis(3-bromo-5-triisopro-
(162 MHz, CDCl3)
40H55O2P2S2Si2: 749.2657. Found: 749.2659 ([M + H]+).
trans-3. mp > 300 8C. 1H NMR (CDCl3)
1.05 (dd,
d 22.1. HRMS (FAB) m/z Calcd. for
C
d
J = 7.6 Hz, 36H), 1.29 (sept, J = 7.2 Hz, 6H), 7.33 (t, J = 1.4 Hz,
2H), 7.50 (t, J = 6.8 Hz, 4H), 7.61 (t, J = 7.2 Hz, 2H), 7.80 (dd,
J = 6.8, 1.4 Hz, 4H). 13C {1H} NMR (CDCl3)
d 11.6 (s), 18.6 (s),
127.7 (dd, JCP = 113, 6.6 Hz), 129.5 (t, JCP = 6.2 Hz), 131.1 (t,
JCP = 5.7 Hz), 133.5 (s), 137.2 (dd, JCP = 122, 1.7 Hz), 143.7 (t,
JCP = 5.8 Hz), 144.1 (dd, JCP = 107, 1.7 Hz), 151.2 (pseudo t,
JCP = 20 Hz). 31P {1H} NMR (CDCl3)
d 23.2. HRMS (FAB) m/z
Calcd. for C40H55O2P2S2Si2: 749.2657. Found: 749.2674
([M + H]+).
pylsilyl-2-thienyl)acetylene
5
[19] were synthesized
Thiophene-fused phospholo[3,2-b]phosphole disul-
fide 4. To a solution of bis(3-bromo-5-triisopropylsilyl-2-
thienyl)acetylene 5 (200 mg, 0.30 mmol) in anhydrous THF
(5.0 mL) was added t-BuLi in n-pentane (1.59 M, 0.80 mL,
1.25 mmol) dropwise over 10 min at –78 8C, and the
mixture was stirred for 2.5 h. PhP(NEt2)Cl (0.12 mL,
139 mg, 0.645 mmol) was then added to the mixture
dropwise over 5 min at the same temperature. After
stirring for 10 min, the reaction mixture was allowed to
warm to room temperature and stirred for 1.5 h. All
volatiles were removed under reduced pressure, and the
residual mixture was dissolved in anhydrous dioxane
(5 mL). PCl3 (0.27 mL, 416 mg, 3.03 mmol) was then added
in one portion at room temperature, and the resulting
reaction mixture was stirred at reflux temperature for 18 h.
according to the literature method. All reactions were
performed under an argon atmosphere, unless stated
otherwise.
Thiophene-fused phospholo[3,2-b]phosphole diox-
ide 3. To a solution of bis(3-bromo-5-triisopropylsilyl-2-
thienyl)acetylene 5 (0.50 g, 0.76 mmol) in anhydrous THF
(12.0 mL) was added t-BuLi in n-pentane (1.57 M, 2.00 mL,
3.14 mmol) dropwise over 10 min at ꢀ78 8C, and the
mixture was stirred for 1 h. PhP(NEt2)Cl (0.29 mL, 326 mg,
3.14 mmol) was added to the mixture dropwise over 5 min
at the same temperature. After stirring for 10 min, the
reaction mixture was allowed to warm to room tempera-
ture and stirred for 1 h. All volatiles were then removed
under reduced pressure, and the residual mixture was

1088
A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
After concentration of the reaction mixture under reduced
pressure, degassed anhydrous THF (20 mL) and S8 (933 mg,
3.64 mmol) were added. After stirring at reflux tempera-
ture for 1.5 h, the reaction mixture was allowed to cool to
room temperature. The resulting precipitates were re-
moved by filtration, the filtrate was washed with water,
and the aqueous layer was then extracted with CHCl3 three
times. The combined organic layer was washed with brine,
dried over Na2SO4, and filtered. After concentration of the
filtrate under reduced pressure, the resulting crude
products were subjected to a silica gel column chroma-
tography (2/1 hexane/CHCl3) to give 99 mg (0.13 mmol,
43% yield) of trans-4 (Rf = 0.58) and 73 mg (0.093 mmol,
31% yield) of cis-4 (Rf = 0.38) as orange solids, respectively.
mixture was thoroughly purified by recrystallization from a
hexane/CHCl3 mixed solvent to give pure trans-8 as yellow
crystals (93 mg, 0.20 mmol, 28% yield): mp > 300 8C. 1H
NMR (CDCl3)
J = 7.6 Hz, 2H), 7.58 (d, J = 8.0 Hz, 2H), 7.66 (dd, J = 12, 7.6 Hz,
2H), 7.87–7.92 (m, 4H). 13C{1H} NMR (CDCl3)
124.5 (t,
d7.37–7.42(m, 2H), 7.44–7.48 (m, 6H), 7.54(d,
d
JCP = 4.5 Hz,CH), 125.2(d, JCP = 92 Hz,C), 127.2(d, JCP = 12 Hz,
CH), 127.9 (d, JCP = 40 Hz, CH), 129.4 (d, JCP = 13, 6.2 Hz, CH),
130.2 (t, JCP = 6.6 Hz, CH), 131.0 (t, JCP = 6.2 Hz, CH), 133.0 (s,
CH), 136.9 (t, JCP = 16 Hz, C), 139.9 (dd, JCP = 106, 4.5 Hz, C),
149.2 (d, JCP = 87 Hz, C). 31P{1H} NMR (CDCl3)
d
37.6. HRMS
(APCI) m/z Calcd. for
457.0407 ([M + H]+).
C26H19P2S2: 457.0398. Found:
X-ray crystallographic analysis of cis-3. Single crystals
of cis-3 suitable for X-ray crystallographic analysis were
obtained by slow diffusion of hexane into a solution of cis-
cis-4. mp 126.8–127.7 8C. 1H NMR (CDCl3)
d 1.08 (dd,
J = 7.6, 2.0 Hz, 36H), 1.31 (sept, J = 7.6 Hz, 6H), 7.32 (t,
J = 2.0 Hz, 2H), 7.42 (pseudo t, J = 6.8 Hz, 4H), 7.54 (t,
3 in chloroform. Intensity data were collected at 123 K
J = 7.2 Hz, 2H), 7.69–7.74 (m, 4H). 13C{1H} NMR (CDCl3)
d
with Mo K
monochromator.
measured at a maximum 2
a
radiation (
l
= 0.71070 A) and a graphite
˚
11.9 (s, CH), 18.7 (s, CH3), 128.8 (dd, JCP = 89, 6.6 Hz, C),
129.3 (pseudo t, JCP = 6.6 Hz, CH), 130.7 (pseudo t,
JCP = 6.2 Hz, CH), 132.8 (s, CH), 133.3 (pseudo t, JCP = 7.9 Hz,
CH), 141.1 (d, JCP = 102 Hz, C), 144.1 (pseudo t, JCP = 5.8 Hz,
C), 145.3 (d, JCP = 88 Hz, C), 149.5 (pseudo t, JCP = 19 Hz, C).
A
total of 15,120 reflections was
angle of 50.08, of which
u
7713 were independent reflections (Rint = 0.0513). The
structure was solved by a direct method (SIR97) [20] and
refined by the full-matrix least squares on F2 (SHELXL-97)
[21]. All non-hydrogen atoms were refined anisotropical-
ly, and all hydrogen atoms were placed using AFIX
instructions. The crystal data are as follows: Formula
31P{1H} NMR (CDCl3)
40H55P2S4Si2: 781.2195. Found: 781.2224 ([M + H]+).
trans-4. mp 254.3–254.8 8C. 1H NMR (CDCl3)
1.06 (d,
d 29.3. HRMS (APCI) m/z Calcd. for
C
d
J = 7.6 Hz, 18H), 1.09 (d, J = 7.6 Hz, 18H), 1.31 (sept,
J = 7.6 Hz, 6H), 7.32 (t, J = 2.0 Hz, 2H), 7.47 (pseudo t,
J = 6.4 Hz, 4H), 7.55 (t, J = 6.4 Hz, 2H), 7.81–7.87 (m, 4H).
C
41H55Cl3O2P2S2Si2, FW = 868.50, crystal size 0.16 mm ꢁ
˚
0.16 mm ꢁ 0.02 mm, triclinic, P-1 (#2), a = 8.512(3) A,
˚
˚
b = 16.002(6) A, c = 16.865(6) A,
79.632(11)8,
Dcalcd = 1.288 g cmꢀ3
(I > 2
a
= 83.469(12)8,
b
=
3
13C{1H} NMR (CDCl3)
d
11.9 (s, CH), 18.66 (s, CH3), 18.70 (s,
g
= 84.845(12)8, V = 2239.4(14) A , Z = 2,
˚
CH3), 127.9 (dd, JCP = 100, 8.7 Hz, C), 129.4 (pseudo t,
JCP = 6.6 Hz, CH), 131.0 (pseudo t, JCP = 6.2 Hz, CH), 133.0 (s,
CH), 133.2 (pseudo t, JCP = 7.8 Hz, CH), 141.2 (d,
JCP = 101 Hz, C), 144.1 (pseudo t, JCP = 5.4 Hz, C), 145.1 (d,
JCP = 88 Hz, C), 149.4 (pseudo t, JCP = 19 Hz, C). 31P{1H} NMR
,
m
= 0.456 mmꢀ1
,
R1 = 0.0728
s
(I)), wR2 ¼ 0:1483 (all data), GOF = 1.141.
X-ray crystallographic analysis of trans-3. Single
crystals of trans-3 suitable for X-ray crystallographic
analysis were obtained by slow diffusion of hexane into
(CDCl3)
d
29.9. HRMS (APCI) m/z Calcd. for C40H55P2S4Si2:
a solution of trans-3 in chloroform. Intensity data were
781.2195. Found: 781.2217 ([M + H]+).
collected at 123 K with Mo K
a
radiation (
l
= 0.71070 A)
˚
Thiophene-fused phospholo[3,2-b]phosphole 2. To a
solution of trans-3 (30.8 mg, 0.041 mmol) in degassed
and graphite monochromator. A total of 13,745 reflections
was measured at a maximum 2 angle of 50.08, of which
u
anhydrous toluene (6.0 mL) was added HSiCl3 (41
m
L,
3763 were independent reflections (Rint = 0.0593). The
structure was solved by a direct method (SIR97) [20] and
refined by the full-matrix least squares on F2 (SHELXL-97)
[21]. All non-hydrogen atoms were refined anisotropically,
and all hydrogen atoms were placed using AFIX instruc-
tions. The crystal data are as follows: Formula
55 mg, 0.406 mmol) in one portion at room temperature,
and the mixture was stirred for 5 min, resulting in an
immediate color change from red to yellow green. After
removal of volatiles under reduced pressure, 26 mg of crude
2 was obtained as yellow solids. After reprecipitation using
degassed hexane at 4 8C, 15.8 mg (0.022 mmol) of 2 was
obtained in 54% yield as yellow solids. According to the
integral ratio of the signals in 31P NMR measurement, the
ratioofthecisandtransisomerswasdeterminedtobe1:1.7:
C
40H54O2P2S2Si2, FW = 749.07, crystal size 0.20 mm ꢁ
0.10 mm ꢁ 0.05 mm, monoclinic, P21/a (#14), a =
˚
˚
˚
b
16.26(5) A, b = 8.03(2) A, c = 16.33(9) A,
= 91.44(4)8, V =
= 0.287 mmꢀ1
(all data),
2132(14) A , Z = 2, Dcalcd = 1.167 g cmꢀ3
,
m
,
3
˚
mp261–262 8C. 1H NMR (CDCl3)
1.37 (m, 6H), 7.30–7.31 (m, 8H), 7.43–7.47 (m, 4H). 31P{1H}
NMR (CDCl3) –18.5, –16.2. HRMS (APCI) m/z Calcd. for
40H55P2S2Si2: 717.2753. Found: 717.2772 ([M + H]+).
Benzene-fused phospholo[3,2-b]phosphole disulfide
d
1.08–1.33(m, 36H), 1.27–
R1 = 0.0784
GOF = 1.178.
(I > 2s(I)),
wR2 ¼ 0:1684
d
X-ray crystallographic analysis of cis-4. Single crystals
of cis-4 suitable for X-ray crystallographic analysis were
obtained by slow diffusion of hexane into a solution of cis-4
C
8. A solution of trans-1 (306 mg, 0.72 mmol) and Lawesson
reagent (295 mg, 0.73 mmol) in anhydrous toluene (14 mL)
was stirred at reflux temperature for 4 h. All volatiles were
removed under reduced pressure, and the residual mixture
was subjected to silica gel column chromatography (1/2
hexane/CH2Cl2, Rf = 0.55) to give 332 mg of crude mixture of
trans-8 containinga considerableamount ofimpurities. This
in dichloromethane. Intensity data were collected at 123 K
˚
Ka radiation (l = 0.71070 A) and graphite
with Mo
monochromator. A total of 18,960 reflections was mea-
sured at a maximum 2 angle of 55.08, of which 5498 were
u
independent reflections (Rint = 0.0518). The structure was
solved by a direct method (SIR97) [20] and refined by
the full-matrix least squares on F2 (SHELXL-97) [21]. All

A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
1089
[4] (a) F. Mathey, F. Mercier, F. Nief, J. Fischer, A. Mitschler, J. Am. Chem.
Soc. 104 (1982) 2077;
non-hydrogen atoms were refined anisotropically, and all
hydrogen atoms were placed using AFIX instructions. The
crystal data are as follows: Formula C42H58Cl4P2S4Si2,
FW = 951.04, crystal size 0.14 mm ꢁ 0.07 mm ꢁ 0.02 mm,
(b) M.-O. Bevierre, F. Mercier, L. Ricard, F. Mathey, Angew. Chem. Int.
Ed. Engl. 29 (1990) 655;
(c) E. Deschamps, L. Ricard, F. Mathey, Angew. Chem. Int. Ed. Engl. 33
(1994) 1158.
˚
˚
monoclinic, C2/c (#15), a = 29.333(5) A, b = 8.9161(14) A,
´
[5] (a) C. Hay, D.L. Vilain, V. Deborde, L. Toupet, R. Reau, Chem. Commun.
3
˚
˚
c = 18.380(3) A,
b
= 91.6565(8)8, V = 4805.1(14) A , Z = 4,
(1999) 345;
Dcalcd = 1.315 g
cmꢀ3 = 0.566 mmꢀ1
,
m
,
R1 = 0.0616
´
(b) C. Hay, C. Fischmeister, M. Hissler, L. Toupet, R. Reau, Angew. Chem.
Int. Ed. 39 (2000) 1812;
(c) C. Hay, M. Hissler, C. Fischmeister, J. Rault-Berthelot, L. Toupet, L.
(I > 2s(I)), wR2 ¼ 0:1395 (all data), GOF = 1.108.
Photophysical Properties Measurements. UV/Vis ab-
sorption spectra were recorded on a Shimadzu UV-3510
spectrometer with a resolution of 0.5 nm. Emission spectra
of 1–3 were measured with a Hitachi F-4500 spectrometer
with a resolution of 1 nm. Dilute solutions in degassed
spectral grade solvents in a 1-cm square quartz cell were
used for the absorption and fluorescence measurements.
Absolute fluorescence quantum yields were determined
with a calibrated integrating sphere system C9920-02
(Hamamatsu Photonics). Fluorescence lifetimes were
measured on a Picosecond Fluorescence Lifetime Mea-
surement System C4780 (Hamamatsu Photonics)
equipped with a PLP laser (377 nm for cis- and trans-4,
and 405 nm for 2) or a dye laser (coumarin 307 in ethanol,
for cis- and trans-2). All solvents (purchased from Nakarai
Tesque) were degassed by Ar bubbling for 30 min before
preparation of the sample solution.
Computational Method. The geometry optimizations
of model compounds 1, trans-20, trans-30, and trans-40 were
performed using the Gaussian 03 program [22] at the
B3LYP/6-31G(d) level of theory. The lowest energy
transitions of 1, trans-20, trans-30, and trans-40 were
estimated by TD-DFT calculations at the B3LYP/6-
31G(d)//B3LYP/6-31G(d) level of theory.
´
´
Nyulaszi, R. Reau, Chem. Eur. J. 7 (2001) 4222;
(d) C. Fave, T.-Y. Cho, M. Hissler, C.-W. Chen, T.-Y. Luh, C.-C. Wu, R.
´
Reau, J. Am. Chem. Soc. 125 (2003) 9254;
(e) C. Hay, C. Fave, M. Hissler, J. Rault-Berthelot, R. Re´au, Org. Lett. 5
(2003) 3467;
(f) C. Fave, M. Hissler, T. Ka´rpa´ti, J. Rault-Berthelot, V. Deborde, L.
Toupet, L. Nyula´szi, R. Re´au, J. Am. Chem. Soc. 126 (2004) 6058;
(g) H.-C. Su, O. Fadhel, C.-J. Yang, T.-Y. Cho, C. Fave, M. Hissler, C.-C. Wu,
R. Re´au, J. Am. Chem. Soc. 128 (2006) 983;
´
(h) M. Sebastian, M. Hissler, C. Fave, J. Rault-Berthelot, C. Odin, R. Reau,
Angew. Chem. Int. Ed. 45 (2006) 6152.
[6] (a) S.S.H. Mao, T.D. Tilley, Macromolecules 30 (1997) 5566;
(b) Y. Morisaki, Y. Aiki, Y. Chujo, Macromolecules 36 (2003) 2594.
[7] (a) Y. Matano, T. Nakabuchi, T. Miyajima, H. Imahori, H. Nakano, Org.
Lett. 8 (2006) 5713;
(b) Y. Matano, T. Miyajima, T. Nakabuchi, H. Imahori, N. Ochi, S. Sakaki,
J. Am. Chem. Soc. 128 (2006) 11760;
(c) Y. Matano, T. Miyajima, N. Ochi, T. Nakabuchi, M. Shiro, Y. Nakao, S.
Sakaki, H. Imahori, J. Am. Chem. Soc. 130 (2008) 130, 990;
(d) Y. Matano, M. Nakashima, T. Nakabuchi, H. Imahori, S. Fujishige, H.
Nakano, Org. Lett. 10 (2008) 553;
(e) Y. Matano, T. Nakabuchi, S. Fujishige, H. Nakano, H. Imahori, J. Am.
Chem. Soc. 130 (2008) 16446.
[8] T. Sanji, K. Shiraishi, M. Tanaka, Org. Lett. 9 (2007) 3611.
[9] Y. Makioka, T. Hayashi, M. Tanaka, Chem. Lett. 33 (2004) 44.
[10] R.-F. Chen, R. Zhu, Q.-L. Fan, W. Huang, Org. Lett. 10 (2008) 2913.
[11] (a) T. Baumgartner, T. Neumann, B. Wirges, Angew. Chem. Int. Ed. 43
(2004) 6197;
(b) T. Baumgartner, W. Bergmans, T. Ka´rpa´ti, T. Neumann, M. Nieger, L.
Nyula´ski, Chem. Eur. J. 11 (2005) 4867;
(c) T. Neumann, Y. Dienes, T. Baumgartner, Org. Lett. 8 (2006) 495;
(d) S. Durben, Y. Dienes, T. Baumgartner, Org. Lett. 8 (2006) 5893;
(e) Y. Dienes, S. Durben, T. Ka´rpa´ti, T. Neumann, U. Englert, L. Nyula´ski,
T. Baumgartner, Chem. Eur. J. 13 (2007) 7487;
Acknowledgements
(f) Y. Dienes, U. Englert, T. Baumgartner, Z. Anorg. Alleg. Chem. 635
(2009) 238;
This work was partially supported by Grant-in-Aid
(Nos. 17069011, 19675001, and 20750029) from the
Ministry of Education, Culture, Sports, Science, and
Technology, Japan.
(g) Y. Ren, Y. Dienes, S. Hettel, M. Parvez, B. Hoge, T. Baumgartner,
Organometallics 28 (2009) 734.
[12] (a) H. Tsuji, K. Sato, L. Ilies, Y. Itoh, Y. Sato, E. Nakamura, Org. Lett. 10
(2008) 2263;
(b) H. Tsuji, K. Sato, Y. Sato, E. Nakamura, J. Mater. Chem. 19 (2009)
3364.
[13] T. Sanji, K. Shiraishi, M. Tanaka, Org. Lett. 10 (2008) 2689.
[14] A. Fukazawa, Y. Ichihashi, Y. Kosaka, S. Yamaguchi, Chem. Asian J. 4
(2009) 1729.
Appendix A. Supplementary data
[15] (a) T. Miyajima, Y. Matano, H. Imahori, Eur. J. Org. Chem. (2008) 255;
(b) Y. Matano, T. Miyajima, T. Fukushima, H. Kaji, Y. Kimura, H.
Imahori, Chem. Eur. J. 14 (2008) 8102;
(c) A. Saito, T. Miyajima, T. Nakashima, T. Fukushima, H. Kaji, Y.
Matano, H. Imahori, Chem. Eur. J. 15 (2009) 10000.
[16] A. Fukazawa, M. Hara, T. Okamoto, E.-C. Son, C. Xu, K. Tamao, S.
Yamaguchi, Org. Lett. 10 (2008) 913.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.crci.2010.04.021.
References
[17] (a) R.C. Smith, J.D. Protasiewicz, Dalton Trans. (2003) 4738;
(b) S. Yamaguchi, S. Akiyama, K. Tamao, J. Organomet. Chem. 646
(2002) 277;
[1] (a) S. Yamaguchi, K. Tamao, Chem. Lett. 34 (2005) 2;
´
(b) M. Hissler, P. Dyer, R. Reau, Coord. Chem. Rev. 244 (2003) 1;
(c) K. Akasaka, T. Suzuki, H. Ohrui, H. Meguro, Anal. Lett. 20 (1987) 731;
(d) J. Bourson, L. Oliveros, Phosphorus Sulfur 26 (1986) 75;
(e) N.A. Rozenal’skaya, A.I. Bakanov, B.M. Uzhinov, B.I. Stepanov, J. Gen.
Chem. USSR 45 (1975) 263.
(c) A. Fukazawa, S. Yamaguchi, Chem. Asian J. 4 (2009) 1386.
[2] Recent reviews on phosphorus-containing p-conjugated materials:
´
(a) T. Baumgartner, R. Reau, Chem. Rev. 106 (2006) 4681;
(b) F. Mathey, Angew. Chem. Int. Ed. 42 (2003) 1578.
[3] Representative reviews on phospholes:
(a) A.N. Hughes, C. Srivanavit, J. Heterocycl, F. Mathey, Chem. 7 (1970)
1;
[18] M. Pan˜kowski, W. Chodkiewicz, M.-P. Simonnin, Inorg. Chem. 24 (1985)
533.
[19] A. Fukazawa, H. Yamada, S. Yamaguchi, Angew. Chem. Int. Ed. 47 (2008)
5582.
[20] A. Altomare, G. Cascarano, C. Giacovazzo, A. Gualiardi, A. G. G. Moliterni,
M. C. Burla, G. Polidori, M. Camalli, R. Spagna, SIR 97, 1997.
[21] G.M. Sheldrick, SHELX-97, Program for the Refinement of Crystal
Structures, University of Gottingen, Gottingen, Germany, 1997.
[22] Gaussian 03 (Revision C.02), M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E.
Scuseria, M.A. Robb, J.R. Cheeseman, J.A. Montgomery, Jr., T. Vreven,
(b) F. Mathey, Chem. Rev. 88 (1988) 429;
(c) L.D. Quin, A.N. Huges, in: The Chemistry of Organophosphorus
Compounds, ed. F.R. Hartley, Wiley, Chichester, 1990, vol. 1,
pp. 295–384
´
(d) L. Nyulaszi, Chem. Rev. 101 (2001) 1229;
(e) M. Hissler, C. Lescop, R. Re´au, Pure Appl. Chem. 79 (2007) 201;
(f) Y. Matano, H. Imahori, Org. Biomol. Chem. 7 (2009) 1258.

1090
A. Fukazawa et al. / C. R. Chimie 13 (2010) 1082–1090
K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B.
Zakrzewski, S. Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K.
Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui,
A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-Laham,
C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson, W.
Chen, M.W. Wong, C. Gonzalez, J.A. Pople, Gaussian, Inc., Pittsburgh, PA
(2004).
Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji,
M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P.
Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Strat-
mann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y.
Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G.