Toward multi-addressable molecular systems: Efficient synthesis and photochromic performance of unsymmetrical bisthienylethenes

Article abstract of DOI:10.1016/j.dyepig.2010.03.018

Various synthetic routes have been compared to access to unsymmetrical 1,2-bisthienylperfluorocyclopentenes having one electro-withdrawing formyl group. The strategy based on key monosusbtituted cyclopentenes appears to be the most reliable and versatile

Full text of DOI:10.1016/j.dyepig.2010.03.018

Dyes and Pigments 89 (2011) 246e253
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Toward multi-addressable molecular systems: Efficient synthesis and
photochromic performance of unsymmetrical bisthienylethenes
*
Guillaume Sevez, Jean-Luc Pozzo
Université de Bordeaux, Institut des Sciences Moléculaires, UMR CNRS, 5255 Talence, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Various synthetic routes have been compared to access to unsymmetrical 1,2-bisthienylper-
fluorocyclopentenes having one electro-withdrawing formyl group. The strategy based on key mono-
susbtituted cyclopentenes appears to be the most reliable and versatile synthetic approach. Applying this
controlled sequential synthesis to appropriate thiophenic building blocks leads to the preparation of
Received 20 February 2010
Received in revised form
5 March 2010
Accepted 16 March 2010
Available online 8 April 2010
p
-conjugated extended pushepull system where photochromic performance were characterised.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Photochromism
Diarylethene
Unsymmetrical
Performance
1. Introduction
photochromic performance of four unsymmetrical bisthienyle-
thenes 1e4 (Scheme 1) bearing a formyl group on position 5 as
Multi-addressable organic materials stimulated by light is
currently a very active research topic and such systems are
expected to be of great importance for optical computing as logic
gates, field-effect transistors and high density data storage systems.
[1e5] The design and synthesis for functional molecules that could
serve as molecular devices for sensing, switching, and signal
transduction from optical inputs are areas of intense activity and
tremendous potential significance. The goal is a miniaturization of
functional elements down to the molecular level, which could
result in a markedly increased performance as a consequence of
ultra-high density of the functional elements compared to current
devices and in that regard organic photochromic compounds are
targeted candidates because of the light-induced reversible isom-
erization between two isomers having different absorption spectra
acting as a binary system. Several attempts to prepare multi-
photochromic switches have been reported recently. [6e10] In the
course of our programme to prepare photoinduced NLO-phores
[11e13] we demonstrated that 1,2-bisthienylethenes [14] hereafter
named BTE for convenience bearing an electronically withdrawing
group are key intermediates to the route for covalently linked BTE
to indolinoxazolidines which exhibit promising tunable hyper-
polarisabilities. In this article, we describe the synthesis along the
a strong electro-withdrawing group that can be used as interme-
diates for the preparation of multi-addressable systems based on
bisthienyletheneeindolinooxazolidine hybrid [15] or azacrown and
bisthienylethene. [16]
2. Discussion
2.1. Synthesis
As a synthetic route to prepare an unsymmetrical substituted
BTE containing one aldehyde function from
a symmetrical
compound has been reported to proceed efficiently [17], we tried to
synthesize the targeted unsymmetrical BTE starting from the
diiodinated dithienylethene 5. This latter compound was selected
as a common intermediate since iodine is a suitable prerequisite for
either a carbonecarbon coupling reaction, following Sonogashira or
Suzuki procedures, or a formylation using n-butyllithium and DMF
as reagents. A symmetrical compound presents the advantage of
using the same intermediate for all the desired target molecules.
Compound 5 was prepared in 87% yield by double lithiation of the
well-known dichlorinated dithienylethene 6 [14] using n-butyl-
lithium subsequently followed by a substitution on iodine as
depicted on Scheme 2.
The reaction has repeated several times and we found that this
approach is unsuccessful either for the formylation as well as the
carbonecarbon coupling reaction. Indeed, the reaction of 5 with 1
* Corresponding author. Tel.: þ33 54000 2752.
E-mail address: jl.pozzo@ism.u-bordeaux1.fr (J.-L. Pozzo).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.03.018

G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
247
hydrolysis of the compound 17 which results from the reaction of
the monosubstituted perfluorocyclopentene 18 [21] with the acetal
19 [17] as shown in Scheme 7. The electron-withdrawing formyl
group of thiophene 20 was protected with 2,2-dimethylpropane-
1,3-diol [22] to give the acetal 19 in 89% yield.
Despite the strong acidic conditions (trifluoroacetic acid in
a mixture of THF and water), the acetal 19 could not be deprotected
at room temperature, this protecting group is known to be a robust
one. This result was already observed during the deprotection of
diacetal-substituted dithienylethene 21 to give the symmetrical
diformyl-substituted one 22. [17] We found that the deprotection
of diacetal 1 was almost quantitative when the reaction was carried
out with aqueous hydrochloric acid in refluxing methanol
(Scheme 8).
Scheme 1. Targeted unsymmetrical BTE 1e4.
equivalent of n-butyllithium followed by an addition of DMF
afforded an interesting mixture of the diformylated compound and
the starting material in a 1:1 ratio (Scheme 3) where no significant
amount of desired unsymmetrical BTE was obtained. As a confir-
mation of the lack of selectivity, the Sonogashira coupling with 1
equivalent of phenylacetylene gave a mixture of three compounds
which were difficult to purify due to their similar polarities and
which were identified as the starting material, the mono-
substituted and disubstituted compounds.
An other synthetic route involving a monosubstituted per-
fluorocyclopentene has to be considered: the unsymmetrization is
performed from the beginning and the molecule is built step-
by-step starting from thiophene building blocks. The synthetic
strategy relies on the reaction of the halogenated key synthon 10
with different conveniently substituted thiophenes to first obtain
chlorinated BTEs which were subsequently exchanged with lithium
using n-butyllithium and reacted with DMF to afford the targets
possessing a formyl group Scheme 4.
The synthesis of 10 was performed as previously described [18]
and thiophenes 11 and 13 were synthesized through a palladium-
catalyzed Sonogashira coupling reaction in the presence of copper
iodide starting from the diiodiated compound 14 and phenyl-
acetylene derivatives in good yield. A copper-free method [19]
could also be used to prepare thiophene 11 in 64% yield (Scheme 5).
The diiodination of 2-methylthiophene gave a mixture of two
regioisomers, i.e. 2,4-diiodo-5-methylthiophene 14 and 2,3-diiodo-
5-methylthiophene in 84% and 12% yield respectively. These two
isomers could not be separated neither by chromatography on silica
gel nor by distillation under vacuum. The purification was realized
during the next step as the reaction of the undesired and minor
isomer was not observed during the Sonogashira coupling reaction
using phenylacetylene. Suzuki coupling of the boronic acid 15 [20]
with 4-iodothioanisole 16 afforded thiophene 12 in 72% yield. The
compound 16 was prepared in 88% yield by a lithiation of 1,4-
diiodobenzene to afford the lithium thiophenolate which reacted
on methyl iodide as depicted on Scheme 6.
2.2. Experimental section
2.2.1. 1,2-bis(5-chloro-2-methyl-3-thienyl)perfluorocyclopentene 6
To a stirred solution of 3-bromo-5-chloro-2-methylthiophene
(13.79 g, 65.21 mmol) in anhydrous diethyl ether (140 mL) was
added dropwise n-butyllithium (42.8 mL, 1.6 M in hexanes,
68.48 mmol) at ꢀ80 ꢁC under nitrogen atmosphere and the solu-
tion was stirred for 15 min. Perfluorocyclopentene (4.4 mL,
32.61 mmol) was added and the mixture was stirred for 4 h at
ꢀ80 ꢁC. The mixture was diluted with diethyl ether (100 mL) and
the reaction was quenched with an aqueous solution of hydro-
chloric acid (1% v/v, 200 mL). The aqueous layer was extracted with
diethyl ether (3 ꢂ 70 mL) and the organic layers were washed with
an aqueous solution of NaHCO3 (75 mL), water (2 ꢂ 70 mL), brine
(70 mL), dried over Na2SO4, filtered and the solvent was evapo-
rated. The crude product was washed with methanol to afford 7.0 g
of compound 6 as a white solid in 49% yield. 1H NMR (300 MHz,
CDCl3):
(75.5 MHz, CDCl3):
d
(ppm) ¼ 6.89 (s, 2H, ArH), 1.89 (s, 6H, CH3). 13C NMR
d
(ppm) ¼ 140.7; 128.2; 125.6; 124.2; 91.7; 14.5.
LRMS (EI), m/z (%): 438 (M þ 2, 74), 436 (Mþ, 100), 403 (23), 401
(53), 386 (75), 366 (60), 343 (26), 332 (44), 78 (18), 61 (28), 59 (30),
45 (19).
2.2.2. 1,2-bis(5-iodo-2-methyl-3-thienyl)perfluorocyclopentene 5
To a stirred solution of 1,2-bis(5-chloro-2-methyl-3-thienyl)
perfluorocyclopentene 6 (2.91 g, 6.66 mmol) in anhydrous diethyl
ether (150 mL) was added dropwise n-butyllithium (10.4 mL, 1.6 M
in hexanes, 16.64 mmol) the solution was stirred for 1 h at room
temperature under nitrogen atmosphere. Iodine (5.08 g,
19.97 mmol) was added and the mixture was stirred 2 h at room
temperature. The solution was diluted with diethyl ether (100 mL)
and the organic layer was washed with an aqueous solution of
Na2S2O3 (10% w/v, 100 mL), water (2 ꢂ 50 mL), dried over MgSO4,
filtered and the solvent was evaporated. The crude product was
flash chromatographed on silica gel (pentane) to afford 3.6 g of
compound 5 as a slightly pink solid in 87% yield. 1H NMR (300 MHz,
The chlorinated dithienylethenes 7e9 result from the lithiation
of the thiophenes 11e13 with n-butyllithium which react on the key
synthon 10 in moderate to good yield. Finally, the dithienylethenes
2e4 were obtained from the formylation with n-butyllithium/DMF
of the chlorinated compounds 7e9. BTE 1 was prepared by acid
CDCl3):
(75.5 MHz, CDCl3):
d
(ppm) ¼ 7.19 (s, 2H, ArH), 1.89 (s, 6H, CH3). 13C NMR
d
(ppm) ¼ 147.8; 136.1; 126.7; 70.9; 14.5.
Scheme 2. Synthetic pathway for diiodinated BTE 5.

248
G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
2.2.3. (5-chloro-2-methyl-3-thienyl)perfluorocyclopentene 10
To a stirred solution of 3-bromo-5-chloro-2-methylthiophene
(8.0 g, 37.82 mmol) in anhydrous diethyl ether (120 mL) was added
dropwise n-butyllithium (26.0 mL,1.6 M in hexanes, 41.61 mmol) at
ꢀ80 ꢁC under nitrogen atmosphere and the solution was stirred for
15 min. Perfluorocyclopentene (10.2 mL, 75.65 mmol) was added
and the mixture was stirred for 4 h at ꢀ80 ꢁC. The reaction was
quenched with an aqueous solution of hydrochloric acid (1% v/v,
150 mL) and the aqueous layer was extracted with diethyl ether
(4 ꢂ 40 mL). The organic layers were washed with an aqueous
solution of NaHCO3 (5% w/v, 50 mL), water (2 ꢂ 50 mL), brine
(50 mL), dried over Na2SO4, filtered and the solvent was evapo-
rated. The crude product was flash chromatographed on silica gel
(pentane) to afford 10.0 g of compound 10 as a yellow liquid in 81%
yield. 1H NMR (300 MHz, CDCl3):
d
(ppm) ¼ 6.92 (bs, 1H, ArH), 2.40
(d, J ¼ 3.4 Hz, 3H, CH3). 13C NMR (75.5 MHz, CDCl3):
(ppm) ¼ 153.5
d
Scheme 3. Attempt to prepare unsymmetrical BTE from dihalogenated BTE.
(m, CF); 149.5 (m, CF2); 142.5 (s); 128.5 (s); 125.7 (s); 119.2 (s); 118.4
(m), 114.3 (m, CF2); 110.8 (m, CF2); 107.1 (m); 14.6 (s, CH3). LRMS
Scheme 4. General route.

G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
249
Scheme 5. Synthesis of thiophenes 11 and 13 via a Sonogashira coupling reaction.
(EI), m/z (%): 326 (M þ 2, 47), 324 (Mþ, 100), 305 (14), 289 (97), 269
sonicated. The beige precipitate was filtered and washed with
diethyl ether. The organic layer was evaporated and the crude
product was flash chromatographed on silica gel (pentane) to
afford 4.1 g of compound 11 as a white solid in 84% yield.
(19), 219 (23), 189 (21), 170 (13), 145 (13), 131 (22), 69 (21), 45 (16).
2.2.4. 2,4-diiodo-5-methylthiophene 14
2-methylthiophene (20.0 g, 0.204 mol), iodine (49.12 g,
0.194 mol), iodic acid (16.13 g, 0.092 mol) were dissolved in
a mixture of water (50 mL), chloroform (150 mL) and acetic acid
(150 mL) and the mixture was refluxed for 24 h. After cooling down
to room temperature, the solvent was evaporated and the residue
was dissolved in chloroform (200 mL). The organic layer was
washed with an aqueous solution of Na2S2O3 (10% w/v, 150 mL),
a solution of NaHCO3 (5% w/v, 2 ꢂ 50 mL), brine (50 mL), dried over
Na2SO4, filtered and the solvent was evaporated. The crude product
was dissolved with pentane and passed through a silica gel column
to afford a mixture composed of 60.0 g of compound 14 in 84% yield
and 9.0 g of 2,3-diiodo-5-methylthiophene in 12% yield as a orange
2.2.5.1. Free-copper method. 2,4-diiodo-5-methylthiophene 14 (8.7 g,
24.86 mmol), bis(triphenylphosphine)palladium(II) chloride (0.698 g,
0.944 mmol) and phenylacetylene (2.81 mL, 26.11 mmol) were
dissolved in piperidine (7.4 mL) and the solution was stirred for 3 h
at 70 ꢁC. After cooling down to room temperature, the mixture was
diluted with diethyl ether (50 mL) and water (50 mL), and the
aqueous layer was extracted with diethyl ether (4 ꢂ 50 mL). The
organic layers were washed with an aqueous solution of hydro-
chloric acid (1% v/v, 2 ꢂ 50 mL), water (3 ꢂ 50 mL), brine (50 mL),
dried over MgSO4, filtered and the solvent was evaporated. The
crude product was flash chromatographed on silica gel (pentane)
and washed with methanol to afford 5.1 g of compound 11 as
liquid.1H NMR (300 MHz, CDCl3):
d
(ppm) ¼ 7.07 (s,1H, ArH), 2.42 (s,
3H, CH3). 13C NMR (75.5 MHz, CDCl3):
d
(ppm) ¼ 145.1; 143.2; 80.4;
a
white solid in 64% yield. 1H NMR (250 MHz, CDCl3):
70.8; 18.1. LRMS (EI), m/z (%): 350 (Mþ), 223 (52), 96 (76), 67 (18).
d
(ppm) ¼ 7.53e7.48 (m, 2H, ArH), 7.38e7.34 (m, 3H, ArH), 7.15
(s, 1H, ArH), 2.43 (s, 3H, CH3). 13C NMR (75.5 MHz, CDCl3):
2.2.5. 3-iodo-2-methyl-5-(phenylethynyl)thiophene 11
d
(ppm) ¼ 140.8 (CeCH3); 139.1 (CH thiophene); 131.5 (CH phenyl);
To a degassed solution of 2,4-diiodo-5-methylthiophene 14
(5.22 g, 14.92 mmol), copper(I) iodide (0.293 g, 1.543 mmol), bis
(triphenylphosphine)palladium(II) chloride (0.184 g, 0.257 mmol)
in a mixture of anhydrous diethyl ether (20 mL) and diisopropyl-
amine (25 mL) was added phenylacetylene (1.9 mL, 17.15 mmol).
The mixture was stirred for 19 h at room temperature under
nitrogen atmosphere. Then, the solvent was evaporated, the
residue was dissolved with diethyl ether and the solution was
128.7 (CH phenyl); 128.5 (CH phenyl); 122.7 (Cq phenyl); 122.6 (Cq
thiophene); 93.9 (Cq); 81.7 (Cq); 80.2 (CeI); 18.2 (CH3). LRMS (EI),
m/z (%): 324 (Mþ), 197 (M-I, 40), 152 (24), 145 (18), 98 (21).
2.2.6. 4-[(4-iodo-5-methylthiophen-2-yl)ethynyl]-N,N-
dimethylaniline 13
To a degassed solution of 2,4-diiodo-5-methylthiophene 14
(6.10 g, 17.43 mmol), copper(I) iodide (0.344 g, 1.804 mmol), bis
Scheme 6. Synthesis of thiophene 12.

250
G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
Scheme 7. Synthesis of targeted BTE 1.
(triphenylphosphine)palladium(II) chloride (0.211 g, 0.301 mmol)
in a mixture of anhydrous diethyl ether (25 mL) and diisopropyl-
amine (30 mL) was added 4-ethynyl-N,N-dimethylaniline (2.91 g,
20.04 mmol) and the solution was stirred for 20 h at room
temperature under nitrogen atmosphere. Then, the solvent was
evaporated, the residue was dissolved in diethyl ether (100 mL) and
sonicated. The brown precipitate was filtered, washed with diethyl
ether. The organic layers were washed with an acidulated aqueous
solution (100 mL), water (2 ꢂ 100 mL), dried over MgSO4, filtered
and the solvent was evaporated. The crude product was chroma-
tographed on silica gel (petroleum ether/dichloromethane: 1/1) to
afford 4.94 g of compound 13 as a yellow solid in 77% yield. 1H NMR
layers were extracted with diethyl ether (2 ꢂ 100 mL). The organic
layers were washed with water (3 ꢂ 150 mL), brine (150 mL), dried
over MgSO4, filtered and the solvent was evaporated to afford 13.1 g
of compound 16 as a slightly yellow solid in 88% yield. 1H NMR
(250 MHz, CDCl3):
d
(ppm) ¼ 7.56 (d, J ¼ 8.4 Hz, 2H, ArH), 6.96 (d,
J ¼ 8.4 Hz, 2H, ArH), 2.44 (s, 3H, CH3). 13C NMR (62.9 MHz, CDCl3):
d
(ppm) ¼ 138.6; 137.6; 128.2; 89.3; 15.7. LRMS (EI), m/z (%): 250
(Mþ, 100), 235 (M-CH3, 55), 123 (M-I, 22), 108 (58), 77 (24), 45 (35).
2.2.8. 3-bromo-2-methyl-5-[4-(methylsulfanyl)phenyl]
thiophene 12
3-bromo-2-methyl-5-thienylboronic acid 15 (4.87 g, 22.05 mmol),
4-iodothioanisole 16 (5.51 g, 22.05 mmol), tetrakis(triphenyl-
phosphine)palladium (0.637 g, 0.551 mmol) and sodium carbonate
(8.88 g, 83.79 mmol) were dissolved in THF (200 mL) and water
(20 mL), and the solution was stirred 17 h at 80 ꢁC under nitrogen
atmosphere. After cooling down to room temperature, the solvent
was evaporated and the residue was dissolved in dichloromethane
(50 mL) and water (50 mL). The aqueous layer was extracted with
dichloromethane (2 ꢂ 50 mL) and the organic layers were washed
with water (4 ꢂ 100 mL), brine (50 mL), dried over MgSO4, filtered
and the solvent was evaporated. The crude product was flash
chromatographed on silica gel (pentane/dichloromethane: 80/20)
to afford 4.7 g of compound 12 as a white solid in71% yield. 1H
(250 MHz, CDCl3):
(s, 1H, ArH), 6.65 (d, J ¼ 8.8 Hz, 2H, ArH), 2.99 (s, 6H, CH3), 2.42
(s, 3H, CH3). 13C NMR (62.9 MHz, CDCl3):
d
(ppm) ¼ 7.38 (d, J ¼ 8.8 Hz, 2H, ArH), 7.08
d
(ppm) ¼ 150.3; 139.6;
137.8 (CH); 132.7 (CH); 123.7; 111.8 (CH); 109.2; 95.3; 80.0; 79.6;
40.2 (CH3); 18.2 (CH3). LRMS (EI), m/z (%): 367 (Mþ, 100), 240 (M-I,
6), 196 (25), 120 (25). HRMS (ESI), (M þ Hþ) calcd for C15H15NSI:
367.9964, found: 367.9965.
2.2.7. 4-iodothioanisole 16
To a stirred solution of 1,4-diiodobenzene (19.62 g, 59.50 mmol)
in anhydrous diethyl ether (500 mL) was added dropwise
n-butyllithium (39.0 mL, 1.6 M in hexanes, 62.40 mmol) at ꢀ80 ꢁC
under nitrogen atmosphere and the solution was stirred for 20 min.
Sulfur (2.10 g, 65.40 mmol) was added and the mixture was stirred
until the disappearance of the precipitate. Then, methyl iodide was
added (7.40 mL, 118.90 mmol), the cooling bath was removed and
the solution was stirred for 17 h at room temperature under
nitrogen atmosphere. The reaction was quenched with an aqueous
solution of ammonium chloride (10% w/v, 300 mL) ant the aqueous
NMR (250 MHz, CDCl3):
7.23 (d, J ¼ 8.5 Hz, 2H, ArH), 7.07 (s, 1H, ArH), 2.50 (s, 3H, CH3),
2.41 (s, 3H, CH3). 13C NMR (62.9 MHz, CDCl3):
d
(ppm) ¼ 7.41 (d, J ¼ 8.5 Hz, 2H, ArH),
d
(ppm) ¼ 140.7;
138.4; 133.4; 130.4; 126.9; 125.7; 125.2; 109.9; 15.8; 15.0. LRMS
(EI), m/z (%): 300 (M þ 2, 96), 298 (Mþ, 100), 283 (M-CH3, 70), 285
(68), 219 (M-Br, 14), 204 (16), 203 (18), 172 (13), 171 (35), 109 (16),
108 (8).
Scheme 8. Synthesis of BTE 22.

G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
251
2.2.9. 4-bromo-5-methylthiophene-2-carbaldehyde 20
m/z: 496 (Mþ); HRMS (FAB-LSIMS), (Mþ) calcd for C22H22O2F6S2:
To a stirred solution of 5-methyl-2-thiophenecarboxaldehyde
(39.2 g, 0.311 mol) in acetic acid (320 mL) was added dropwise
a solution of bromine (19.2 mL, 0.373 mol) in acetic acid (150 mL)
over 1 h in the absence of light and at room temperature. The
reaction mixture was stirred vigorously in the dark for 16 h at room
temperature and then the reaction was quenched adding carefully
and slowly a saturated solution of NaHCO3 (3 L). The mixture was
extracted with diethyl ether (2 ꢂ 500 mL) and the organic layers
were washed with a solution of NaHCO3 (5% w/v, 5 ꢂ150 mL), water
(2 ꢂ 150 mL), brine (150 mL), dried over Na2SO4, filtered and the
solvent was evaporated. The brown crude product was recrystal-
lized from hexane to afford 43 g of compound 20 as a yellow solid in
496.0965, found: 496.0985.
2.2.12. 1-(2,5-dimethyl-3-thienyl)-2-(5-formyl-2-
methyl-3-thienyl)perfluorocyclopentene 1
To a solution of 1-(2,5-dimethyl-3-thienyl)-2-(5-(5,5-dimethyl-
1,3-dioxacyclohex-2-yl)-2-methyl-3-thienyl)perfluorocyclopentene
17 (1.9 g, 3.83 mmol) in THF (300 mL) and water (75 mL) was added
trifluoroacetic acid (35 mL) and the mixture was stirred for 24 h at
room temperature. Then the reaction was quenched with a satu-
rated aqueous solution of NaHCO3 (350 mL) and the mixture was
extracted with diethyl ether (3 ꢂ 100 mL). The organic layers were
washed with an aqueous solution of NaHCO3 (2% w/v, 2 ꢂ 150 mL),
water (3 ꢂ 150 mL), dried over Na2SO4, filtered and the solvent was
evaporated. The crude product was washed with cold methanol
and recrystallized from hexane to afford 1.0 g of the compound 1 as
a slightly yellow solid in 64% yield. mp ¼ 117e118 ꢁC; 1H NMR
67% yield. mp ¼ 56.5 ꢁC; 1H NMR (300 MHz, CDCl3):
(ppm) ¼ 9.74
d
(s, 1H, CHO), 7.56 (s, 1H, ArH), 2.45 (s, 3H, CH3). 13C NMR (75.5 MHz,
CDCl3):
d
(ppm) ¼ 181.6; 145.8; 140.1; 138.7; 111.2; 15.9. LRMS (EI),
m/z (%): 206 (M þ 2, 83), 205 (Mþ1, 100), 204 (Mþ,82), 175 (M-CHO,
18), 125 (M-Br, 26), 96 (43), 69 (17).
(300 MHz, CDCl3):
6.70 (s, 1H, ArH), 2.42 (s, 3H, CH3), 2.00 (s, 3H, CH3), 1.83 (s, 3H,
CH3). 13C NMR (75.5 MHz, CDCl3):
d
(ppm) ¼ 9.84 (s, 1H, CHO), 7.74 (s, 1H, ArH),
2.2.10. 2-(4-Bromo-5-methylthiophen-2-yl)-5,5-
dimethyl-1,3-dioxane 19
d
(ppm) ¼ 182.2; 151.9; 141.8;
140.0; 138.6; 136.5; 126.9; 124.5; 124.1; 15.5; 15.2; 14.4. LRMS
(FAB-LSIMS), m/z: 409 (MeHþ); HRMS (FAB-LSIMS), (MeHþ) calcd
for C17H11OF6S2: 409.0156, found: 409.0146.
4-bromo-5-methylthiophene-2-carbaldehyde 20 (20.0 g,
0.098 mol), 2,2-dimethylpropane-1,3-diol (15.3 g, 0.146 mol) and
para-toluenesulfonic acid monohydrate (3.08 g, 0.015 mol) were
dissolved in benzene (150 mL) and the mixture was refluxed for 9 h.
After cooling down to room temperature, the reaction mixture was
diluted with dichloromethane (150 mL) and washed with a solution
of NaHCO3 (5% w/v, 150 mL), water (2 ꢂ 150 mL), brine (150 mL),
dried over MgSO4, filtered and the solvent was evaporated. The
crude product was recrystallized form hexane to afford 25.3 g of the
compound 19 as a beige solid in 89% yield. mp ¼ 72.1e72.8 ꢁC; 1H
2.2.13. 1-(5-chloro-2-methyl-3-thienyl)-2-(2-methyl-5-
phenylethynyl-3-thienyl)perfluorocyclopentene 7
To a solution of 3-iodo-2-methyl-5-(phenylethynyl)thiophene
11 (4.29 g, 13.245 mmol) in anhydrous THF (130 mL) was added
dropwise n-butyllithium (10.0 mL, 1.6 M in hexane, 15.894 mmol)
and the solution was stirred for 1 h at ꢀ80 ꢁC under nitrogen
atmosphere. (5-chloro-2-methyl-3-thienyl)perfluorocyclopentene
10 (3.35 g, 10.331 mmol) dissolved in anhydrous THF (15 mL) was
added and the mixture was stirred for 2 h at ꢀ80 ꢁC. The cooling
bath was removed and the solution was stirred for 15 h at room
temperature. An aqueous solution of hydrochloric acid (1% v/v,
100 mL) was added and the aqueous layer was extracted with
diethyl ether (2 ꢂ 50 mL). The organic layers were washed with an
aqueous solution of NaHCO3 (5% w/v, 50 mL), water (2 ꢂ 50 mL),
brine (70 mL), dried over MgSO4, filtered and the solvent was
evaporated. The crude product was flash chromatographed on silica
gel (petroleum ether) and washed with methanol to afford 2.7 g of
the compound 7 as a white solid in 51% yield. 1H NMR (300 MHz,
NMR (250 MHz, CDCl3):
d
(ppm) ¼ 6.94 (s, 1H, ArH), 5.52 (s, 1H, CH),
3.73 (d, J ¼ 11.0 Hz, 2H, CH2), 3.60 (d, J ¼ 10.7 Hz, 2H, CH2), 2.37 (s,
3H, CH3), 1.25 (s, 3H, CH3 acetal), 0.78 (s, 3H, CH3 acetal). 13C NMR
(75,5 MHz, CDCl3):
d
(ppm) ¼ 138.6 (s, CeCH); 134.9 (s, CeCH3);
128.1 (s, CH); 108.7 (s, CeBr); 97.9 (s, CH acetal); 72.2 (s, CH2eO);
30.5 (s, Cq acetal); 23.3 (s, CH3); 22.1 (s, CH3); 15.1 (s, CH3). LRMS
(FAB-LSIMS), m/z: 291 (M þ Hþ); HRMS (FAB-LSIMS), (M þ Hþ)
calcd for C11H16BrO2S: 291.00543, found: 291.00535.
2.2.11. 1-(2,5-dimethyl-3-thienyl)-2-(5-(5,5-dimethyl-1,3-
dioxacyclohex-2-yl)-2-methyl-3-thienyl)perfluorocyclopentene 17
To
a
solution of 2-(4-bromo-5-methylthiophen-2-yl)-5,5-
CDCl3):
7.25 (s, 1H, ArH), 6.91 (s, 1H, ArH), 1.95 (s, 3H, CH3), 1.88 (s, 3H, CH3).
13C NMR (75.5 MHz, CDCl3):
128.9; 128.6; 128.1; 125.7; 124.9; 124.3; 122.5; 122.1; 119.4 (CF2);
116.0 (CF2); 94.2; 81.5; 14.6. LRMS (EI), m/z (%): 504 (M þ 2, 44), 502
(Mþ, 100), 467 (M-Cl, 42), 452 (41), 419 (20), 243 (25), 226 (68), 145
(60), 121 (24), 59 (20).
d
(ppm) ¼ 7.53e7.50 (m, 2H, ArH), 7.38e7.34 (m, 3H, ArH),
dimethyl-1,3-dioxane 19 (4.51 g, 15.49 mmol) in anhydrous THF
(90 mL) was added dropwise n-butyllithium (11.62 mL, 1.6 M in
hexane, 18.59 mmol) at ꢀ80 ꢁC under nitrogen atmosphere and
the mixture was stirred for 45 min. The resulting solution was
added dropwise over 10 min to a solution of (2,5-dimethyl-3-
thienyl)perfluorocyclopentene 18 (4.72 g, 15.49 mmol) in anhy-
drous THF (50 mL) and the mixture was stirred for 2 h at ꢀ80 ꢁC.
The cooling bath was removed and the stirring was carried on for
14 h at room temperature. Then an aqueous solution of hydro-
chloric acid (0.5% v/v, 200 mL) was added and the mixture was
extracted with diethyl ether (4 ꢂ 75 mL). The organic layers were
neutralized with water (6 ꢂ 100 mL), dried over MgSO4, filtered
and the solvent was evaporated. The yellow brown syrup was
chromatographed on silica gel (heptane then dichloromethane/
heptane: 1/1) to afford 5.28 g of the compound 17 as a slightly
orange solid in 69% yield. mp ¼ 102e103 ꢁC; 1H NMR (300 MHz,
d
(ppm) ¼ 143.4; 140.7; 131.6; 131.4;
2.2.14. 1-(5-formyl-2-methyl-3-thienyl)-2-(2-methyl-5-
phenylethynyl-3-thienyl)perfluorocyclopentene 2
To a solution of 1-(5-chloro-2-methyl-3-thienyl)-2-(2-methyl-
5-phenylethynyl-3-thienyl)perfluorocyclopentene 7 (2.0 g, 3.97 mmol)
in anhydrous diethyl ether was added dropwise n-butyllithium
(3.22 mL, 1.6 M in hexane, 5.16 mmol) and the solution was stirred
for 1 h at room temperature under nitrogen atmosphere. Anhy-
drous DMF (0.92 mL, 11.90 mmol) was added and the mixture was
stirred for 0.5 h at room temperature. The reaction was quenched
with an aqueous solution of hydrochloric acid 1 M (50 mL) and the
mixture was extracted with diethyl ether (3 ꢂ 50 mL). The organic
layers were washed with an aqueous solution of NaHCO3 (5% w/v,
70 mL), water (3 ꢂ 70 mL), brine (70 mL), dried over MgSO4, filtered
and the solvent was evaporated. The crude product was flash
chromatographed on silica gel (pentane then dichloromethane) to
CDCl3):
d
(ppm) ¼ 7.10 (s, 1H, ArH), 6.70 (s, 1H, ArH), 5.56 (s, 1H,
CH acetal), 3.76e3.72 (m, 2H, CH2eO), 3.63e3.60 (m, 2H, CH2eO),
2.41 (s, 3H, CH3), 1.86 (s, 3H, CH3), 1.81 (s, 3H, CH3), 1.26 (s, 3H,
CH3 acetal), 0.79 (s, 3H, CH3 acetal). 13C NMR (75.5 MHz, CDCl3):
d
(ppm) ¼ 142.4; 139.9; 139.5; 137.9; 125.1; 124.7; 124.6; 124.4;
116.3; 98.0; 77.6; 30.3; 23.1; 21.9; 15.2; 14.5. LRMS (FAB-LSIMS),

252
G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
afford 0.93 g of the compound 2 as a yellow solid in 47% yield. 1H
NMR (300 MHz, CDCl3):
3 as a green solid in 69% yield. 1H NMR (250 MHz, CDCl3):
d
(ppm) ¼ 9.85 (s, 1H, CHO), 7.75 (s, 1H,
d
(ppm) ¼ 9.85 (s, 1H, CHO), 7.78 (s, 1H, ArH), 7.44 (d, J ¼ 8.3 Hz, 2H,
ArH), 7.52e7.48 (m, 2H, ArH), 7.38e7.34 (m, 3H, ArH), 7.24 (s, 1H,
ArH), 7.24 (d, J ¼ 8.3 Hz, 2H, ArH), 7.20 (s, 1H, ArH), 2.50 (s, 3H, CH3),
ArH), 2.06 (s, 3H, CH3), 1.91 (s, 3H, CH3). 13C NMR (75.5 MHz, CDCl3):
2.04 (s, 3H, CH3), 1.92 (s, 3H, CH3). 13C NMR (62.9 MHz, CDCl3):
d
(ppm) ¼ 182.2 (CH); 152.0 (Cq); 143.3 (Cq); 142.0 (Cq); 136.2 (CH);
d
(ppm) ¼ 182.2 (CHO); 152.0; 142.6; 141.9 (CH); 141.1; 139.0; 137.7
131.6 (CH); 131.1 (CH); 129.0 (CH); 128.6 (CH); 126.4 (Cq); 124.6
(Cq); 122.5 (Cq); 122.4 (Cq); 94.4 (Cq); 81.3 (Cq); 15.7 (CH3); 14.6
(CH3). LRMS (EI), m/z (%): 496 (Mþ,100), 481 (37), 452 (12), 419 (15),
226 (36), 145 (45), 121 (17), 59 (17).
(m); 136.4 (CH); 134.7 (m, CF2); 129.8; 128.9 (CH); 126.8 (CH);
126.6; 126.0 (CH); 125.3; 116.1 (m, CF2); 111.1 (m); 15.7 (CH3); 15.6
(CH3); 14.6 (CH3). HRMS (ESI), (M þ Hþ) calcd for C23H17OF6S3:
519.0340, found: 519.0359.
2.2.15. 1-(5-chloro-2-methyl-3-thienyl)-2-(2-methyl-5-[4-
(methylsulfanyl)phenyl]-3-thienyl)perfluorocyclopentene 8
2.2.17. 1-(5-chloro-2-methyl-3-thienyl)-2-(2-methyl-5-[4-ethenyl-
N,N-dimethylaniline]-3-thienyl)perfluorocyclopentene 9
To
a
solution of 3-bromo-2-methyl-5-[4-(methylsulfanyl)
To a solution of 4-[(4-iodo-5-methylthiophen-2-yl)ethynyl]-
N,N-dimethylaniline 13 (3.60 g, 9.803 mmol) in anhydrous diethyl
ether (150 mL) was added dropwise n-butyllithium (7.4 mL,1.6 M in
hexane, 11.763 mmol) and the solution was stirred for 1 h at ꢀ80 ꢁC
under nitrogen atmosphere. (5-chloro-2-methyl-3-thienyl)per-
fluorocyclopentene 10 (2.88 g, 8.874 mmol) dissolved in anhydrous
diethyl ether (15 mL) was added and the mixture was stirred 1 h at
ꢀ80 ꢁC then 16 h at room temperature. An aqueous solution of
hydrochloric acid (1% v/v, 100 mL) was added and the aqueous layer
was extracted with diethyl ether (2 ꢂ 70 mL). The organic layers
were washed with a solution of NaHCO3 (5% w/v, 100 mL), water
(2 ꢂ 100 mL), brine (100 mL), dried over MgSO4, filtered and the
solvent was evaporated. The crude product was chromatographed
on silica gel (petroleum ether/dichloromethane : 70/30) then
recrystallized from methanol to afford 2.12 g of the compound 9 as
slightly green solid in 44% yield. 1H NMR (300 MHz, CDCl3):
phenyl]thiophene 12 (4.47 g, 14.92 mmol) in anhydrous THF
(300 mL) was added dropwise n-butyllithium (10.3 mL, 1.6 M in
hexane, 16.42 mmol) and the solution was stirred for 1 h at ꢀ80 ꢁC
under nitrogen atmosphere. (5-chloro-2-methyl-3-thienyl)per-
fluorocyclopentene 10 (5.12 g, 15.77 mmol) dissolved in anhydrous
THF (15 mL) was added and the mixture was stirred 2 h at ꢀ80 ꢁC
then 15 h at room temperature. The solvent was evaporated and the
residue was dissolved in a mixture of diethyl ether (200 mL) and an
aqueous solution of hydrochloric acid (1% v/v, 100 mL). The aqueous
layer was extracted with diethyl ether (2 ꢂ 70 mL) and the organic
layers were washed with an aqueous solution of NaHCO3 (5% w/v,
70 mL), water (2 ꢂ 70 mL), brine (70 mL), dried over MgSO4, filtered
and the solvent was evaporated. The crude product was flash
chromatographed on silica gel (pentane/dichloromethane: 80/20)
to afford 5.7 g of compound 8 as a slightly purple solid in 73% yield.
1H NMR (250 MHz, CDCl3):
d
(ppm) ¼ 7.46 (d, J ¼ 8.4 Hz, 2H, ArH),
d
(ppm) ¼ 7.38 (d, J ¼ 9.0 Hz, 2H, ArH), 7.17 (s, 1H, ArH), 6.92 (s, 1H,
ArH), 6.65 (d, J ¼ 9.0 Hz, 2H, ArH), 3.00 (s, 6H, CH3), 1.93 (s, 3H, CH3),
1.88 (s, 3H, CH3). 13C NMR (75.5 MHz, CDCl3):
7.26 (d, J ¼ 8.4 Hz, 2H, ArH), 7.22 (s, 1H, ArH), 6.95 (s, 1H, ArH), 2.51
(s, 3H, CH3), 1.97 (s, 3H, CH3), 1.88 (s, 3H, CH3).
d
(ppm) ¼ 150.5;
142.3; 140.7; 132.8 (CH); 130.1 (CH); 128.0; 125.7 (CH); 124.7;
124.3; 123.2; 111.9 (CH); 108.9; 95.6; 79.5; 40.2 (CH3); 14.6 (CH3).
LRMS (EI), m/z (%): 547 (M þ 2, 45), 545 (Mþ, 100), 265 (13), 247
(34), 188 (28). HRMS (ESI), (M þ Hþ) calcd for C25H19NF6S2Cl:
546.0546, found: 546.0554.
2.2.16. 1-(5-formyl-2-methyl-3-thienyl)-2-(2-methyl-5-[4-
(methylsulfanyl)phenyl]-3-thienyl)perfluorocyclopentene 3
To a solution of 1-(5-chloro-2-methyl-3-thienyl)-2-(2-methyl-
5-[4-(methylsulfanyl)phenyl]-3-thienyl)perfluorocyclopentene
8
(3.88 g, 7.39 mmol) in anhydrous diethyl ether (200 mL) was added
dropwise n-butyllithium (5.54 mL,1.6 M in hexane, 8.87 mmol) and
the solution was stirred for 1 h at 0 ꢁC under nitrogen atmosphere.
Anhydrous DMF (1.43 mL, 18.48 mmol) was added and the solution
was stirred 1 h at room temperature. The reaction was quenched
with an aqueous solution of hydrochloric acid 1 M (50 mL) and the
aqueous layer was extracted with diethyl ether (50 mL). The
organic layers were washed with an aqueous solution of NaHCO3
(5% w/v, 70 mL), water (3 ꢂ 70 mL), brine (70 mL), dried over
MgSO4, filtered and the solvent was evaporated. The crude product
was flash chromatographed on silica gel (pentane/dichloro-
methane: 30/70 then dichloromethane) to afford 2.63 g of compound
2.2.18. 1-(5-formyl-2-methyl-3-thienyl)-2-(2-methyl-5-[4-ethenyl-
N,N-dimethylaniline]-3-thienyl)perfluorocyclopentene 4
To a solution of 1-(5-chloro-2-methyl-3-thienyl)-2-(2-methyl-5-[4-
ethenyl-N,N-dimethylaniline]-3-thienyl)perfluorocyclopentene
(1.70 g, 3.109 mmol) in anhydrous diethyl ether (70 mL) was added
dropwise n-butyllithium (2.53 mL, 1.6 M in hexane, 4.042 mmol)
and the solution was stirred for 1 h at 0 ꢁC under nitrogen atmo-
sphere. Anhydrous DMF (0.61 mL, 7.773 mmol) was added and the
mixture was stirred for 1 h at room temperature. The reaction
mixture was diluted with diethyl ether (50 mL) and a solution of
hydrochloric acid 1 M (50 mL) was added. The aqueous layer was
9
Fig. 1. Absorption spectra of dithienylethenes 1e4 in acetonitrile, C ¼ 5 ꢂ 10ꢀ5 mol Lꢀ1; Open forms (Left) and photostationnary state after irradiation with 254 nm light (Right).

G. Sevez, J.-L. Pozzo / Dyes and Pigments 89 (2011) 246e253
253
Table 1
dithienylethenes 1e4 are summarized in Table 1. This behaviour
has been observed even after numerous UV/Vis. irradiation cycles.
UVeVisible spectroscopic data of the open and closed (PSS) forms of the compounds
1e4.
Compound
R1
Concentration
(mol Lꢀ1
lmax open
form (nm)
lmax PSS (nm)
3. Conclusion
)
1
2
3
4
Me
C2Ph
PhSMe
C2PhN(Me)2
5.10 ꢂ 10ꢀ5
6.04 ꢂ 10ꢀ5
3.03 ꢂ 10ꢀ5
4.08 ꢂ 10ꢀ5
250
267, 303
255, 308
261, 340
374, 580
361, 612
397, 623
Unsymmetrical 1,2-bisthienylperfluorocyclopentenes bearing
a formyl group as an electro-withdrawing group on one side and
various p-conjugated extended susbtituents on the other side were
411, 472, 649
prepared using a sequential synthetic strategy. This versatile
approach would allow the design of photocontrolled push-pull
NLO-phores. The photochromic performance has been investigated
extracted with diethyl ether (2 ꢂ 50 mL) and the organic layers
were washed with a solution of NaHCO3 (5% w/v, 70 mL), water
(3 ꢂ 50 mL), brine (50 mL), dried over MgSO4, filtered ant the
solvent was evaporated. The crude product was chromatographed
on silica gel (petroleum ether/dichloromethane : 1/1) to afford
1.35 g of the compound 4 as a green solid in 80% yield. 1H NMR
and it has been demonstrated that the
p-conjugated susbtituents
deeply modify the absorption spectra of the both isomeric forms
whereas keeping the excellent P-type properties. The bath-
ochromic shift for the open-ring isomers has been determined to as
high as 90 nm.
(250 MHz, CDCl3):
7.37 (d, J ¼ 8.9 Hz, 2H, ArH), 7.16 (s, 1H, ArH), 6.64 (d, J ¼ 8.9 Hz, 2H,
d
(ppm) ¼ 9.84 (s, 1H, CHO), 7.75 (s, 1H, ArH),
ArH), 3.00 (s, 6H, CH3), 2.05 (s, 3H, CH3), 1.89 (s, 3H, CH3). 13C NMR
References
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d
(ppm) ¼ 182.2 (CHO); 152.0; 150.5; 142.2;
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Absorption spectra were recorded in non degassed acetonitrile
solutions at room temperature. Upon irradiation with 254 nm light,
the colourless open form of the dithienylethenes 1e4 was converted
to the closed form, this photochromic reaction was characterised by
a colour change of the solutions from sky blue to purple due to an
extension of the conjugation on the whole molecule. The ring-
closing of the dithienylethenes was accompanied by a decreasing of
the absorption bands in UV range and the appearance of new broad
bands in the visible region which are ascribed to closed-ring isomer.
The effect of the substituents R1 bearing by the dithienylethenes
1e4 on their electronic properties was investigated. More the
substituent extend the conjugation and more the absorption band
of the closed forms is red-shifted. On another aspect, the effect of
the substituents R1 is more pronounced for the open-ring forms in
which the maximum absorption band varies from 250 nm
(1, R1 ¼ Me) to 340 nm (4, R1 ¼4-ethynyl-N,N-dimethylaniline) than
for the closed-ring forms for which we observed an bathochromic
shift of 69 nm, the maximum absorption band being centred at 580
and 649 nm for respectively for 1 and 4 (Fig. 1).
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previously described BTE, i.e. 0.3 <
f < 0.4. On the contrary the ring
closure electrocyclisation efficiency is strongly affected for
compound 4 for which the quantum yield has been found to be as
low as 0.07. This huge difference can be explained by the strong
electron-donating character of the 4-ethynyl-N,N-dimethylaniline
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temperature and they do not come back to the open forms when
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spectra were recovered in all cases. The UVeVisible spectroscopic
data of the open and closed (photostationnary state) forms of the
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