Synthesis and photochromic properties of thiophenophan-1-enes containing a polyether bridge

Article abstract of DOI:10.1039/b823492b

[2.n]Thiophenophan-1-ene derivatives containing a polyether bridge have been synthesized by the coupling reaction of bis(iodomethyl)dithienylethene with polyethylene glycols under high dilution conditions. All prepared [2.n]thiophenophan-1-enes were photo

Full text of DOI:10.1039/b823492b

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Synthesis and photochromic properties of thiophenophan-1-enes
containing a polyether bridge
Michinori Takeshita,* Chinatsu Tanaka, Takashi Miyazaki, Yukari Fukushima
and Miki Nagai
Received (in Montpellier, France) 5th January 2009, Accepted 8th April 2009
First published as an Advance Article on the web 22nd April 2009
DOI: 10.1039/b823492b
[2.n]Thiophenophan-1-ene derivatives containing a polyether bridge have been synthesized by the
coupling reaction of bis(iodomethyl)dithienylethene with polyethylene glycols under high dilution
conditions. All prepared [2.n]thiophenophan-1-enes were photochromic, as photocyclization of the
open forms took place by UV irradiation to give a yellow solution of the closed form and their
ring opening reactions occurred upon visible irradiation. There were significant differences in the
quantum yields for the photocyclization reactions and the photo ring-opening reactions due to the
difference in their structures since their electric properties are similar. The kinetic parameters of
the thermal ring opening reaction of the closed forms of thiophenophan-1-enes were estimated
and they were also dependent on their bridges.
suppressed due to the steric hindrance between the inner
Introduction
substituents and the opposite aromatic rings. However, the
reported closed forms of [2.n]metacyclophan-1-enes composed
of benzene rings are not thermally stable.6 This is due to the
high aromatic stabilization energy of the benzene rings.8 The
difference in the energy of formation between the open form
and the closed form of [2.n]metacyclophan-1-ene is large,
since the former is aromatic (6p system) and the latter is
anti-aromatic (12p system). These facts encouraged us to
develop thermally stable photochromic cyclophan-1-enes for
materials utilized in molecular photomemory. In this paper,
we describe the syntheses and photochromic properties of
[2.n]thiophenophan-1-enes containing flexible polyether
bridges. The structure of the resulting thiophenophan-1-enes
could be more flexible than [2.2]metacyclophan-1-enes and less
flexible than diarylethenes. Moreover, since the aromatic rings
of the cyclophan-1-enes are substituted by thiophene rings,
which have a lower aromatic stabilization energy, one might
expect a high thermal stability of both photoisomers, as for
dithienylethenes.
Photochromic compounds have been widely studied, since
there have been possibilities for utilizing them as optical
materials and materials for photomemory.1 Among the
photochromic compounds, dithienylethenes are the most
promising compounds for several reasons; (1) both photo-
isomers are thermally stable and can be stored in the dark for
extended times, (2) the fatigue resistance is quite high and the
photochromic reaction can be repeated many times, (3) photo-
reaction is very rapid, the reaction takes place in several
picoseconds etc.2 Therefore, dithienylethenes have been studied
vigorously as materials for organic molecular photomemory.
On the other hand, there are two conformations in the open
form of diarylethenes, the parallel and the anti-parallel.2,3
In solution, these conformations exchange slowly and the
photocyclization reaction proceeds only from the anti-parallel
conformation.3 Therefore, the quantum yield, namely the
photon efficiency, for photocyclization reaction is dependent
on the conformational ratio. Thus there are many efforts to
overcome this problem, for example, to introduce bulky
substituents at their inner positions to increase the ratio of
the photoactive conformation,3 utilizing host–guest chemistry4
to carry out the photochromic reaction in the crystalline state,5
and so on. Recently, we have reported that the photochromic
reaction of [2.n]metacyclophan-1-enes takes place in high
efficiency since there is no photoinactive conformation in
[2.n]metacyclophan-1-enes.6 The photochromic reaction
proceeds not only in solution but also in a polymer matrix
due to the conformational rigidity of the [2.n]metacyclophan-
1-enes.7 The conformation of the [2.n]metacyclophan-1-ene is
‘‘pre-structured’’ for the photocyclization reaction and this
extends even to polymer matrices. The conformation is hardly
effected by the medium since the conformational exchange is
Results and discussion
Syntheses of [2.n]thiophenophan-1-enes are shown in
Scheme 1. Although the intramolecular cyclization reaction
of bis(chloromethyl)dithienylethene 2a was carried out, no
desired thia[2.3]phane 3a was obtained and a polymeric
mixture was afforded instead. Thus the closed form 2b was
prepared by the irradiation of 2a with UV light, then the
coupling reaction with Na2S was carried out under high
dilution conditions. The two chloromethyl groups of 2b are
fixed and their separation is short relative to those of 2a.
Indeed, the intramolecular coupling reaction of 2b afforded
the closed form 3b. The open form of thia[2.3]phane 3a was
obtained by the irradiation of 3b with visible light.9 The
other thiophenophan-1-enes were prepared by the coupling
reactions of bis(iodomethyl)dithienylethene 4 and the ethylene
Department of Chemistry and Applied Chemistry, Faculty of Science
and Engineering, Saga University, Honjo 1, Saga 840-8502, Japan
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Scheme 1
glycols or bis(mercaptomethyl)dithienylethenes 8 and ethylene
glycol ditosylates under high dilution conditions as shown in
Scheme 1. The dithienylethene having two methoxymethyl
groups 12 was also prepared as a reference for comparing
photochromic properties with thiophenophan-1-enes.
and the color of the closed form returned to the initial state
upon visible light (4420 nm) irradiation, indicating 5 is
photochromic. All prepared thiophenophan-1-enes (3, 5–7
and 9–11) and the dithienylethene 12 showed similar phenomena
as described for 5, and their photochromic reactions are shown
in Scheme 1.
The absorption spectral change of a solution of thiopheno-
phan-1-ene 5 in CH2Cl2 upon irradiation with 330 nm light
is shown in Fig. 1 as example. Upon UV irradiation, the
colorless solution of 5a turned yellow and the absorption
maximum at 454 nm, which is attributed to the absorption
of the closed form, gradually increased. The absorption spectrum
The absorption maxima and the molar extinction coefficients
of the closed forms of thiophenophan-1-enes and the
reference 12b in CH2Cl2 in the visible region are summarized
in Table 1. The absorption maxima of the closed form of the
thiophenophan-1-enes were dependent on the chain length.
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distances of the reactive carbon atoms of the most stable
conformations of the open forms of thiophenophan-1-enes
were estimated with AM1-MOPAC9711 and the results are
also summarized in Table 2. The energy minimized structures
of 3a and 7a calculated on AM1 in MOPAC97 are shown in
Fig. 2. The quantum yields of the small thiophenophan-1-enes
such as 3a (0.67) and 5a (0.70) were higher than that of the
reference 12a (0.45). The distances between their reactive
carbon atoms were estimated as 3.0 and 3.6 A for 3a and 5a,
respectively. Moreover, their conformations were fixed to
anti-parallel, which is photoreactive. Then it seems that
the quantum yields were dependent on their distances in
such thiophenophan-1-enes with rigid structures. On the
other hand, the quantum yields for photocyclization of
thiophenophan-1-enes having flexible long chains such as 6a
and 9–11a were similar to that of the reference 12a and their
values were below 0.50. The distances between the reactive
carbon atoms of their most stable conformations were
estimated as 4.3–5.0 A which appears too long to undergo
the photocyclization reaction efficiently.5 However, since
these large thiophenophan-1-enes are more flexible than small
thiophenophan-1-enes such as 3a and 5a, it becomes easy for
the reactive carbon atoms to access each other in solution.
Moreover, the electronic circumstances of these thiophenophan-
1-enes and the dithienylethene are similar. Thus their photo-
cyclization reactions took place similarly to dithienylethene. In
the case of 7a, the distance is only 3.6 A due to its structure
and the reactive carbon atoms approach together. Thus, the
quantum yield of 7a is higher than those of the other flexible
thiophenophan-1-enes. It seems that there are three groups in
the quantum yields for the photo ring-opening (photobleaching,
cycloreversion) reactions of the closed forms. Those of 3b, 9b,
and 12b were similar and the values were low at around 0.09.
In contrast, the most reactive set contains 5b, 7b and 10b, with
values in the range 0.29–0.36. The observed differences are due
to different potential energy surfaces,12 however, we could not
find any correlation between the quantum yields and the
structures.
Fig. 1 Absorption spectral change of a solution of 3 in CH2Cl2 upon
irradiation with 330 nm light.
Table 1 Absorption maxima (lmax/nm) and molar extinction coeffi-
cients (emax/MÀ1 cmÀ1) of the closed forms of thiophenophan-1-enes
in CH2Cl2
3b
5b
6b
7b
9b
10b 11b 12b
l
e
max/nm
449 454 452 456 454 477 456 448
max/MÀ1 cmÀ1 5400 3300 5300 4900 7000 6400 4800 5700
Those of 7b and 10b were longest among their groups (without
or with sulfur atoms on their bridges). Since there are four
heteroatoms on the chains of 7b and 10b and the chains
become more flexible and can avoid steric hindrance, these
lengths could be suitable for good p conjugation in the closed
forms. The molar extinction coefficients of the closed forms
were estimated from the absorption spectra and HPLC
analyses of the same solutions to obtain the concentrations
of the closed forms. The molar extinction coefficient of 5b was
the smallest and that of 9b was the largest.
Table 2 shows the quantum yields for the photocyclization
reactions of the open forms of thiophenophan-1-enes in
CH2Cl2 and those for the ring opening reactions of the closed
forms in CHCl3.10 In contrast with dithienylethenes, the
conformational exchange of thiophenophan-1-enes is suppressed
by the steric hindrance between the inner substituents and the
opposite thiophene rings. Hence the photoinactive parallel
conformation can be excluded during purification. It is
reported that the quantum yields for photocyclization
reactions of the open forms of dithienylethenes in the
crystalline state are dependent on the distance between the
two reactive carbon atoms.5 When the distance is longer than
4 A, the photocyclization scarcely occurred.5 Then the
In the case of [2.n]metacyclophan-1-enes, the thermal
stability of the closed forms were dependent on the chain
length (n).6 When the chain length of the metacyclophan-1-ene
is small as in [2.2]metacyclophan-1-ene, the thermal ring
opening reaction of the closed form is slower than for longer
Table 2 Quantum yields for the photocyclization reactions of the
open forms (at 313 nm, in CH2Cl2), the reactive C–C distances of the
open forms, and quantum yields for photo ring-opening reactions of
the closed forms (at 517 nm in CHCl3)
Thiophenophan-1-ene
3
5
6
7
9
10
11
12
Photocyclization
C–C distancea/A
Photo ring-opening
0.67 0.70 0.42 0.66 0.49 0.47 0.42 0.45
3.0 3.6 4.3 3.6 4.7 4.5 5.0 —
0.09 0.36 0.24 0.29 0.08 0.34 0.20 0.09
Fig. 2 Energy minimized structure of (a) 3a and (b) 7a. The reactive
a
Calculated on AM1-MOPAC97.
carbon atoms are circled.
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Table 3 Kinetic parameters for the thermal ring opening reaction of the closed form of thiophenophan-1-enes
Closed form
3b
5b
6b
7b
9b
10b
11b
12b
A/sÀ1
5.1 Â 103
3.0 Â 106
2.9 Â 102
4.7 Â 104
3.4 Â 1014
1.3 Â 1010
1.9 Â 1010
1.5 Â 109
4.8 Â 108
9.8 Â 108
3.7 Â 107
2.6 Â 107
2.0 Â 1010
5.4 Â 107
5.8 Â 107
7.3 Â 108
Ea/kJ molÀ1
Half-life at 293 K/s
58
41
140
110
100
85
102
93
chains. This is due to the steric energies of the metacyclo-
phan-1-enes. Since the small metacyclophan-1-enes, the open
form, have large steric energy due to the steric repulsion of
the inner substituents and the opposite benzene rings, the
difference in the energy of formation between the aromatic
open form and the non-aromatic closed form is small, and
according to the Horiuti–Polanyi–Evans rule,13 the activation
energy becomes larger. The thermal stability of the closed
forms of the synthesized thiophenophan-1-enes have been
estimated, with results summarized in Table 3, while rates
for the thermal ring-opening reaction were measured in
toluene or decalin at various temperatures. It was found that
the decay curves followed first-order kinetics. An Arrhenius
plot of the thermal ring-opening reaction of 6b is shown in
Fig. 3 as example. Some dithienylethenes are known as
thermally irreversible photochromic compounds.2 In the
thiophenophan-1-ene family, the thermal stability of compound
3b having the shortest chain was quite low and the activation
Conclusion
Thiophenophan-1-enes having various chain lengths have
been synthesized and their photochromic properties were
investigated. The absorption maxima, the quantum yields for
photocyclization reactions and photo ring-opening reactions,
and the thermal stability of the closed forms were dependent
on their chain length. These phenomena were due to the
difference in their steric circumstances. Generally the smaller
thiophenophan-1-enes such as 3 and 5 have different photo-
chromic features from those of dithienylethenes, showing high
quantum yields for photocyclization and low thermal stability
of the closed forms, since they have rigid structures. In
contrast, the larger thiophenophan-1-enes have similar
features to those of dithienylethenes, with high thermal stability
of the closed forms. The photochromic properties can thus be
tuned by changing the bridge length of thiophenophan-1-enes.
Among them, the closed form of a thiophenophan-1-ene
having three oxygen atoms on its bridge 6b was extraordinarily
stable so as to allow us to utilize the material for photo-
memory applications.
energy for the ring-opening reaction was only 58 kJ molÀ1
.
Also the closed form of the small thiophenophan-1-ene 5b
was thermally unstable with small activation energy. The
pre-exponential factors of these thermal reactions were small
and the temperature dependences for thermal reactions were
low. The half-lives of these closed forms were 35 days and 13 h
at 293 K, respectively. On the other hand, the closed form of
thiophenophan-1-ene having three oxygen atoms on its bridge
(6b) was extraordinarily stable and its activation energy was
largest and the half-life was 422 years at 293 K. These values
are better than those of the dithienylethene 12b. Since the
electronic circumstances of these closed forms are similar,
these differences in thermal stabilities are owing to the
difference in their steric circumstances. Different from the
metacyclophan-1-enes composed of benzene rings, the closed
forms of the small thiophenophan-1-enes were less thermally
stable than those of the large thiophenophan-1-enes.
Experimental
General remarks
All melting points were uncorrected. Absorption spectra were
measured with an absorption spectrophotometer (Hitachi,
U-3310). 1H NMR spectra were recorded on a FT-NMR,
JEOL-AL300, spectrometer at 300 MHz. All chemical shifts
are given in ppm relative to TMS and coupling constants in
Hz. Mass spectra were taken JEOL JMS-GCMATE II (EI,
70 eV). Photoirradiation was carried out by using a 500 W
super high-pressure mercury lamp and monochromic light was
obtained by passing it through a monochromator (JOBIN
YVON). The quantum yields were determined by a similar
manner to that described in the literature.8 The samples were
not degassed. Nomenclatures of thiophenophan-1-enes were
referred to the IUPAC Phane Nomenclature.14
Syntheses
23,23,24,24,25,25-Hexafluoro-13,15,33,35-tetramethyl-5-thia-2(1,2)-
cyclopentena-1,3(2,4)dithiophenacyclohexaphane (3a). A solution
of 0.20 g of bis(chloromethyl)dithienylethene 2a6 (0.40 mmol) in
200 ml of ethanol was irradiated with UV light to afford a
solution of the closed form 2b. To a refluxing solution of 120 mg
of Na2SÁ9H2O (0.50 mmol) in 1000 ml of EtOH, the solution of
2b was added dropwise for 12 h. The solvent was evaporated
in vacuo and CH2Cl2 and brine were added to the residue. The
organic phase was washed with brine and dried over MgSO4.
The solvent was evaporated in vacuo and the residue
was subjected to silica-gel column chromatography. The
Fig. 3 Arrhenius plot for thermal ring opening reaction of 6b.
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hexane–chloroform (10 : 1) eluate was evaporated in vacuo and
recrystallization of the residue from MeOH afforded 45 mg of 3a
in 25% yield; pale yellow plates; mp 163.0 1C. dH(300 MHz;
CDCl3; TMS) 1.36 (6H, s), 2.45 (6H, s), 3.50 (2H, d, J = 15 Hz),
3.98 (2H, d, J = 15 Hz). HRMS (EI): m/z = 454.0318 (M+).
Calc. for C19H16F6S3: 454.0316. Found: C, 50.00; H, 3.50. Calc.
for C19H16F6S3: C, 50.21; H, 3.55%.
m/z = 570 (M+). Found: C, 52.56; H, 4.92. Calc. for
C25H28F6O4S2: C, 52.61; H, 4.95%.
5,11-Dithia-23,23,24,24,25,25-hexafluoro-8-oxa-13,15,33,35-
tetramethyl-2(1,2)-cyclopentena-1,3(2,4)dithiophenacyclodode-
caphane (9a). To a refluxing solution of 0.42 g of KOH
(7.5 mmol) and 0.14 g of NaBH4 in 250 ml of EtOH was
added a solution of 0.73 g of 86 (1.5 mmol) and 0.62 g of
diethylene glycol ditosylate (1.5 mmol) in 50 ml of THF for 5 h
and additionally the solution was refluxed for 24 h. The
solvent was evaporated in vacuo and CH2Cl2 and brine were
added to the residue. The organic phase was washed with brine
and was dried over MgSO4. The solvent was evaporated and
the residue was subjected to the silica-gel column chromato-
graphy. Recrystallization of the CHCl3–MeOH eluate from
MeOH afforded 60 mg of 9a in 7.1% yield; yellow prisms
(MeOH); mp 126.0 1C. dH(300 MHz; CDCl3; TMS) 1.86
(6H, s), 2.44 (6H, s), 2.56 (4H, t, J = 13.5 Hz), 3.40 (4H, t,
J = 13.5 Hz), 3.60 (4H, s). MS (EI): m/z = 558 (M+). Found:
C, 49.15; H, 4.23. Calc. for C23H24F6OS4: C, 49.45; H, 4.33%.
5-(3,3,4,4,5,5-Hexafluoro-2-(4-(iodomethyl)-3,5-dimethyl-
(2-thienyl))cyclopent-1-enyl)-3-iodomethyl-2,4-dimethylthio-
phene (4). To a solution of 1.0 g of 2a6 (2.03 mmol) in 50 ml of
acetone was added 1.52 g of NaI (10.2 mmol) and the solution
was refluxed for 3 h. The solvent was evaporated in vacuo and
50 ml of chloroform was added to the residue. The precipitate
was filtered off and the solvent was evaporated in vacuo.
Recrystallization of the residue from hexane–chloroform
afforded 1.0 g of 4 (1.14 mmol) in 70% yield; pale yellow
plates; mp 168.0 1C. dH(300 MHz; CDCl3; TMS) 1.69 (6H, s),
2.49 (6H, s), 4.19 (4H, s). HRMS (EI): m/z = 675.8717 (M+).
Calc. for C19H16I2F6S2: 675.8688.
8,11-Dioxa-5,14-dithia-23,23,24,24,25,25-hexafluoro-13,15,33,35-
tetramethyl-2(1,2)-cyclopentena-1,3(2,4)dithiophenacyclopenta-
decaphane (10a). Compound 10a was obtained from 8 and
triethylene glycol ditosylate by a similar manner to that
described for the synthesis of 9a. The yield was 18%; yellow
prisms (MeOH); mp 124.0 1C. dH(300 MHz; CDCl3; TMS)
1.60 (6H, s), 2.45 (6H, s), 2.63 (4H, t, J = 12 Hz), 3.57 (4H, s),
3.69 (4H, t, J = 12 Hz), 3.70 (4H, s). MS (EI): m/z = 602
(M+). Found: C, 49.83; H, 4.72. Calc. for C25H28F6O2S4: C,
49.82; H, 4.68%.
5,8-Dioxa-23,23,24,24,25,25-hexafluoro-13,15,33,35-tetramethyl-
tetramethyl-2(1,2)-cyclopentena-1,3(2,4)dithiophenacyclonona-
phane (5a). To a refluxing mixture of 144 mg of NaH
(6.0 mmol) in 40 ml of dried THF, a solution of 680 mg of
4 (1.0 mmol) and 62 mg of ethylene glycol (1.0 mmol) in 50 ml
of THF was added dropwise for 5 h. The solution was
refluxed overnight and the solvent was evaporated in vacuo.
The residue was poured into brine and AcOEt was added. The
organic phase was washed with brine and was dried over
MgSO4. The solvent was evaporated in vacuo and the residue
was subjected to
a silica-gel column chromatography.
5,17-Dithia-23,23,24,24,25,25-hexafluoro-13,15,33,35-tetramethyl-
8,11,14-trioxa-2(1,2)-cyclopentena-1,3(2,4)dithiophenacyclo-
octadecaphane (11a). Compound 11a was obtained from 8 and
tetraethylene glycol ditosylate by a similar manner to that
described for the synthesis of 9a. The yield was 9.9%; yellow
prisms (MeOH–H2O); mp 106.0 1C. dH(300 MHz; CDCl3;
TMS) 1.65 (6H, s), 2.46 (6 H, s), 2.59 (4 H, t, J = 13 Hz),
3.57–3.70 (16 H, m). MS (EI): m/z = 646 (M+). Found: C,
50.51; H, 4.95. Calc. for C27H32F6O3S4: C, 50.14; H, 4.99%.
Recrystallization of the CHCl3 eluate from MeOH afforded
40 mg of 5a (0.084 mmol) in 8.4% yield; yellow prisms
(MeOH); mp 135.1 1C. dH(300 MHz; CDCl3; TMS) 1.54
(6H, s), 2.44 (6H, s), 3.13–3.20 (2H, m), 3.36–3.44 (2H, m),
4.28 (2H, d, J = 13 Hz), 4.44 (2H, d, J = 13 Hz), MS (EI):
m/z = 482 (M+). Found: C, 52.71; H, 4.36. Calc. for
C21H20F6O2S2: C, 52.27; H, 4.18%.
23,23,24,24,25,25-Hexafluoro-13,15,33,35-tetramethyl-5,8,11-
trioxa-2(1,2)-cyclopentena-1,3(2,4)dithiophenacyclododeca-
phane (6a). Compound 6a was obtained from 4 and diethylene
glycol by a similar manner to that described for the synthesis
of 5a. The yield was 15%; pale yellow plates (MeOH–CHCl3);
mp 215.0 1C. dH(300 MHz; CDCl3; TMS) 1.61 (6H, s), 2.47
(6H, s), 3.42 (4H, t, J = 8.4 Hz), 3.54 (4H, t, J = 8.4 Hz), 4.34
(4H, s). HRMS (EI): m/z = 526.1078 (M+). Calc. for
C23H24F6O3S2: 526.1071. Found: C, 52.48; H, 4.58. Calc. for
C23H24F6O3S2: C, 52.46; H, 4.59%.
5-(3,3,4,4,5,5-Hexafluoro-2-(4-(methoxymethyl)-3,5-dimethyl-
(2-thienyl))cyclopent-1-enyl)-2,4-dimethyl(3-thienyl))methoxy-
methane (12a). To a solution of sodium methoxide (8.8 mmol)
in 30 ml of methanol, 2 (200 mg, 0.43 mmol) was added and
the solution was stirred for 3 h at room temperature. The
mixture was poured into brine and extracted with diethyl
ether. The solution was dried over MgSO4 and the solvent
was evaporated in vacuo. The residue was subjected silica gel
column chromatography and recrystallization of the chloro-
form eluate from hexane afforded 26 mg of 12a in 12% yield;
brown prisms (hexane); mp 94.5 1C. dH(300 MHz; CDCl3;
TMS) 1.70 (6H, s), 2.46 (6H, s), 3.24 (6H, s), 4.23 (4H, s). MS
(EI): m/z = 484 (M+). Found: C, 52.23; H, 4.66. Calc. for
C21H22O2F6S2: C, 52.06; H, 4.58%.
23,23,24,24,25,25-Hexafluoro-13,15,33,35-tetramethyl-5,8,11,14-
tetraoxa-2(1,2)-cyclopentena-1,3(2,4)dithiophenacyclopentade-
caphane (7a). Compound 7a was obtained from 4 and
triethylene glycol by a similar manner to that described for
the synthesis of 5a. The yield was 6.3%; pale orange needles
(MeOH–CHCl3); mp 168.0 1C. dH(300 MHz; CDCl3; TMS)
1.67 (6H, s), 2.46 (6H, s), 3.50 (4H, t, J = 10.2 Hz), 3.62
(4H, s), 3.63 (4H, t, J = 10.2 Hz), 4.36 (4H, s). MS (EI):
Kinetic measurements. The activation energies and the
pre-exponential factors for the thermal ring-opening reactions
were estimated by the Arrhenius plots of the rate constants of
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Acknowledgements
The authors thank the GDRI PHOENIX, CNRS for partial
financial support and also are grateful to Zeon Co. Ltd. for
providing perfluorocylopentene.
9 M. Takeshita, M. Nagai and T. Yamato, Chem. Commun., 2003,
1496–1497.
10 The quantum yields of the photocyclization reaction of thiopheno-
phan-1-enes were obtained by comparing the initial rates for the
photocyclizations of thiophenophan-1-enes with that of bis(2-
methyl-1-benzothien-3-yl)hexafluorocyclopentene: K. Uchida,
E. Tsuchida, Y. Aoi, S. Nakamura and M. Irie, Chem. Lett.,
1999, 63–64. The quantum yields for photo ring-opening reactions
of the closed forms were also estimated in a similar manner.
11 AM1 calculations were performed using MOPAC97, Fujitsu Ltd,
Tokyo, 1997.
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