Synthesis and photochromic properties of functional diarylethene with a 2,5-dihydrothiophene bridging unit

Article abstract of DOI:10.1021/ol034166r

(Matrix presented) A novel synthetic route to symmetric and nonsymmetric dithienylethene derivatives with a 2,5-dihydrothiophene bridging unit was described. A class of new functional photochromic compounds was prepared and showed photochromic properties similar to those of known diarylethenes.

Full text of DOI:10.1021/ol034166r

ORGANIC
LETTERS
2003
Vol. 5, No. 9
1435-1437
Synthesis and Photochromic Properties
of Functional Diarylethene with a
2,5-Dihydrothiophene Bridging Unit
Yi Chen,* De X. Zeng, and Mei G. Fan
Technical Institute of Physics and Chemistry, The Chinese Academy of Sciences,
Beijing, 100101, P. R. China
yichencas@yahoo.com.cn
Received January 30, 2003
ABSTRACT
A novel synthetic route to symmetric and nonsymmetric dithienylethene derivatives with a 2,5-dihydrothiophene bridging unit was described.
A class of new functional photochromic compounds was prepared and showed photochromic properties similar to those of known diarylethenes.
Diarylethenes, notably the bis(thien-3-yl) system, display
excellent photochromic properties1 and are the most promis-
ing photochromic compounds among various photochromic
compounds for photoelectronic applications such as optical
memony media2 and photoswitching devices3 because of their
fatigue resistant4 and thermally irreversible properties.5 There
are several 1,2-bis(thien-3-yl) systems containing maleic
anhydride,6 maleimide,7 perfluorocyclopentene,8 and cyclo-
pentene9 units that have been employed so far. Each unit
has its advantages and disadvantages. Diarylethenes with a
perfluorocyclopentene bridging unit, for instance, exhibit
excellent photochromic properties. However, the expensive
and rather volatile starting material octafluorocyclopentene
is a major disadvantage. Both diarylmaleic anhydrides and
diarylmaleimides are readily accessible but are sensitive to
acidic conditions.
We report herein a new class of diarylethenes with a 2,5-
dihydrothiphene unit10 and a novel synthetic route to prepar-
ing symmetric and nonsymmetric functional dithienylethene
derivatives. We also present the photochromic properties of
(1) (a) Irie, M. Jpn. J. Appl. Phys. 1989, 28, Suppl. 28-3, 215. (b)
Uchida, K.; Nakayama, Y.; Irie, M. Bull. Chem. Soc. Jpn. 1990, 63, 1311.
(c) Nakayama, Y.; Hayashi, M.; Irie, M. Bull. Chem. Soc. Jpn. 1991, 64,
789. (d) Iwata, S.; Ishihara, Y.; Qian, C.-P.; Tanaka, K. J. Org. Chem.
1992, 57, 3726. (e) Saika, T.; Irie, M.; Shimidzu, T. J. Chem. Soc., Chem.
Commum. 1994, 2123.
(2) (a) Tsujioka, T.; Tatezono, F.; Harada, T.; Kuroki, K.; Irie, M. Jpn.
J. Appl. Phys. 1994, 33, 5788. (b) Tatezono, F.; Harada, T.; Kuroki, K.;
Irie, M. Jpn. J. Appl. Phys. 1993, 32, 3987. (c) Tsivgoulis, G. M.; Lehn,
J.-M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1119. (d) Tsivgoulis, G. M.;
Lehn, J.-M. Chem. Eur. J. 1996, 2, 1399. (e) Seibold, H.; Port, H. Chem.
Phys. Lett. 1996, 252, 135. (f) Stallaacci, F.; Bertarelli, C.; Toscano, F.;
Gallazzi, M. C.; Zerbi, G. Chem. Phys. Lett. 1999, 302, 563.
(3) (a) Irie, M. Chem. ReV. 2000, 100, 1685. (b) Kim, E.; Choi, K.; Rhee,
S. B. Macromolecules 1998, 31, 5726. (c) Kawai, T.; Koshido, T.; Yoshino,
K. Appl. Phys. Lett. 1995, 67, 795. (d) Lucas, L. N.; Esch, J. V.; Kellogg,
R. M.; Feringa, B. L. Chem. Commun. 2001, 759. (e) Murguly, E.; Norsten,
T. B.; Branda, N. R. Angew. Chem., Int. Ed. 2001, 40, 1752. (f) Mulder,
A.; Jukovie, A.; Lucas, L. N.; Esch, J. V.; Feringa, B. L.; Huskens, J.;
Reinhoudt, D. N. Chem. Commum. 2002, 2734.
(4) Irie, M. In Organic Photochromic and Thermochromic Compounds;
Crano, J. C., Guglielmetti, R., Eds.; Plenum Press: New York, 1999; Vol.
1, p 207.
(5) (a) Irie, M.; Sakemura, K.; Okinaka, M.; Uchida, K. J. Org. Chem.
1995, 60, 8305. (b) Gilat, S. L.; Kawai, S. H.; Lehn, J.-M. Chem. Eur. J.
1995, 1, 275. (c) Uchida, K.; Kido, Y.; Yamaguchi, T.; Irie, M. Bull. Chem.
Soc. Jpn. 1998, 71, 1101.
(6) Irie, M.; Mohri, M. J. Org. Chem. 1988, 53, 803.
(7) Yamaguchi, T.; Uchida, K.; Irie, M. J. Am. Chem. Soc. 1997, 119,
6066.
(8) Hanazawa, R.; Sumiya, R.; Horikawa, Y.; Irie, M. J. Chem. Soc.,
Chem. Commun. 1992, 206.
(9) Lucas, L. N.; Esch, J. V.; Kellogg, R. M.; Feringa, B. L. Chem.
Commun. 1998, 2313.
(10) Huang, Z. N.; Xu, B. A.; Jin, S.; Fan, M. G. Synthesis 1998, 1092.
10.1021/ol034166r CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/29/2003

these new compounds. Compared with reported synthetic
methods and properties of diarylethenes, the merits of this
paper are based on (1) a class of new diarylethenes with
symmetric and nonsymmetric molecular structures, (2) cheap
starting materials, and (3) readily accessible dithienylethene
derivatives. The synthesis can be performed on a large scale
from cheap starting materials (Scheme 1). Compound 1a was
yield; when the ratio of 1a and BunLi and DMF was 1:5.0:
1.5 (mole), compound 3a as the major product was obtained
in 53% yield, and compounds 2a and 4a as the minor product
were obtained in 15% and 8% yield, respectively. The yields
in the coupling step were very good (total yields were about
80%) and the regioselectivity of the aldehydelyzation of
compound 1a was reasonable. The conversion of 5a and 6a
was performed by reduction of 2a and 3a with NaBH4 in
EtOH at room temperature, respectively. Schiff base 7a and
8a were obtained by treatment of 2a and 3a with 2-ami-
nophenol in EtOH under reflux, respectively. This new route
provides ready access to a variety of symmetric or nonsym-
metric diarylethenes with a 2,5-dihydrothiophene unit.
The photochromic behavior was illustrated by Figures 1
and 2. Figures 1 and 2 represent the changes of absorption
Scheme 1. Synthetic Route of Functional Diarylethene with a
2,5-Dihydrothiophene Bridging Unit
Figure 1. Absorption changes of 2a in acetonitrile upon irradiation
at 254 nm (2 × 10-5 M).
of 2a and 3a in acetonitrile upon irradiation at 254 nm. In
general, the absorption of the ring-open form appears at a
shorter wavelength, while the absorption of the ring-closed
obtained starting from 2-methylthiophene, which was chlo-
rinated at the 5-position with NCS in AcOH, followed by
acylation and bromination with CH3COCl in dichoromethane
(DCM) and Br2 in chloroform, respectively. 1,1′-Bis[3-(5-
chloro-2-methyl)-acetylthiophene]-dimethyl sulfide, which
was obtained from 3-(5-chloro-2-methyl)-1′-bromine-acetyl-
thiophene with Na2S in EtOH, was used in the McMurry
coupling reaction11 with TiCl4 and Zn in THF to afford 1a.
Monoaldehyde 2a and dialdehyde 3a were synthesized by
lithiation of 1a under different conditions followed by
quenching with DMF. It is worth noting that when the ratio
of 1a and BunLi and DMF was 1:2.5:1.5 (mole), compound
2a as the major product was obtained in 60% yield, and
compound 3a as the minor product was obtained in 20%
Figure 2. Absorption changes of 3a in acetonitrile upon irradiation
at 254 nm (2 × 10-5M).
form takes place at a longer wavelength since π-electrons
delocalize throughout the two condensed thiphene rings and
further extend to the substituents in the ring-closed form.
When 2a was irradiated, two new absorption bands appeared
at 348 and 526 nm, respectively, corresponding to closed
form 2b. A similar result was obtained from Figure 2 when
3a was irradiated at 254 nm, and the two new absorption
(11) Furstner, A.; Hupperts, A.; Ptock, A.; Janssen, E. J. Org. Chem.
1994, 59, 5215.
1436
Org. Lett., Vol. 5, No. 9, 2003

bands appeared at 389 and 582 nm, respectively, which were
ascribed to the closed form isomer 3b. Both figures showed
the typical absorption spectral changes of diarylethene
derivatives in solvents.12 From the figures it could also be
seen clearly that an isobestic point appeared in both absorp-
tion spectra. That indicated only two isomers existed when
the compound underwent the photoisomerization reaction.
The UV-Vis data of other compounds for the open and
closed forms are listed in Table 1. Compared to the known
maxima of the ring-open isomer and the ring-closed isomer
were obviously different. The absorption maximum of 3 was
red shifted as much as 34 nm for ring-open isomer and 56
nm for ring-closed isomer in comparison with the absorption
maximum of 2 in acetonitrile. More differences in absorption
maximum of both isomers were obtained by comparison of
7 and 8.
The photochromic bleaching was performed with com-
pound 3 and illustrated in Figure 3. It showed 3b (closed
Table 1. UV-Vis Data of Compounds in Acetonitrile
compd
λ
max/nm (open)
λ
max/nm (closed)
1
2
3
4
5
6
7
8
234
448, 305
526, 345
582, 384
512, 375
452, 301
454, 301
497, 371
608
232a
266a
243a
224
232
296, 246
362, 260
a Shoulder.
Figure 3. Photochromic bleaching of 3b in acetonitrile upon
irradiation at g450 nm.
diarylethene derivatives, the absorption maximum of 1, 3,
and 8 in the closed form was almost the same as was
reported.6 Compounds 2, 4, 5, 6, and 7 also showed the
typical absorption spectral changes of photochromic di-
arylethene derivatives upon irradiation in solvent. From the
viewpoint of application to optical memory media, it is
desired to develop photochromic compounds that have
sensitivity in the wavelength region 530-650 nm (DVD).
The effect of substituents on the absorption maximum in
actonitrile was examined. When chloro or hydroxy groups
were substituted at the 5- and 5′-position of the thiophene
rings, the absorption maximum of the ring-closed form (1b,
5b, 6b) was about 450 nm in acetonitrile. When an electron-
withdrawing substituent was introduced into the 5- and 5′-
position of the thiophene ring, the absorption maximum of
the ring-closed form 3b was shifted to 582 nm in acetonitrile.
However, when an electorn-donating substituent was intro-
duced into the 5- and 5′-position of the thiophene ring, the
absorption maxium of the ring-closed form 8b was further
shifted to 608 nm in acetonitrile.
It is interesting to compare the absorption maximum of
the ring-open isomer and ring-closed isomer of symmetric
and nonsymmetric compounds such as 2 and 3, 5 and 6, and
7 and 8. When the substituent attached at the 5- and
5′-position was neither strongly electron-donating nor strongly
electron-withdrawing, the absorption maximum of both ring-
opened isomer and ring-closed isomer was just a little bit
different for symmetric and nonsymmetric compounds (5 at
452 nm and 6 at 454 nm, in acetonitrile). However, when
the substituents at the 5- and 5′-position were strong electron-
donating or electron-withdrawing groups, the absorption
form) could be easily reversed back to open form 3a upon
irradiation (g450 nm) in solution. There was also an obvious
isobestic point at 324 nm, and it indicated the equilibrium
of two isomers (open form and closed form) existed in
isomerization upon irradiation. This result corresponded with
the above. The fatigue resistance experiments also showed
that compound 8 performed very well: after eight cycles no
degradation was detected by UV-Vis absorption but there
was about 10% decrease in absorption (optical density) for
compounds 2 and 3 after one cycle. In addition, preliminary
investigations showed that all compounds were thermally
stable at ambient temperature.
In conclusion, a facile synthetic route to the preparation
of functional dithienylethene derivatives with a 2,5-dihy-
drothiophene bridging unit has been developed. It can been
achieved by obtaining symmetric and nonsymmetric dithi-
enylethene derivatives with a 2,5-dihydrothiophene unit by
controlling the ratio of starting material and reagent. All
dithienylethene derivatives with a 2,5-dihydrothiophene unit
show photochromic behavior and further study of photo-
chromic properties and applications of compounds is in
progress.
Acknowledgment. This work was supported by the
National Science Foundation of China (NO 60277001) and
the National Principal Research Project “973” (G 1999033005).
Supporting Information Available: Experimental pro-
cedures and characterization relating to the syntheses of 1a-
8a. This material is available free of charge via the Internet
at http://pubs.acs.org.
(12) (a) Irie, M.; Sayo, K. J. Phys. Chem. 1992, 96, 767. (b) Nakayama,
Y.; Hayashi, K.; Irie, M. Bull. Chem. Soc. Jpn. 1991, 64, 789.
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