Gated photochromism of 1,2-diarylethenes

Article abstract of DOI:10.1021/ol070487h

A dithienylethene derivative containing a cyclobutene-1,2-dione skeleton does not exhibit photochromic properties. However, when both ketone functions are protected with cyclic acetal groups, photochromic behavior is observed.

Full text of DOI:10.1021/ol070487h

ORGANIC
LETTERS
2007
Vol. 9, No. 10
1915-1918
Gated Photochromism of
1,2-Diarylethenes
Joe1l Ku1hni and Peter Belser*
Department of Chemistry, UniVersity of Fribourg, Chemin du Muse´e 9,
1700 Fribourg, Switzerland
peter.belser@unifr.ch
Received February 26, 2007
ABSTRACT
A dithienylethene derivative containing a cyclobutene-1,2-dione skeleton does not exhibit photochromic properties. However, when both ketone
functions are protected with cyclic acetal groups, photochromic behavior is observed.
The properties of organic switches have been widely detailed
in the literature.1 One of the main challenges in employing
these photochromic compounds for applications in optical
memory media is to establish nondestructive readout capabil-
ity. One of the ways to induce this property is to introduce
gated photochromic reactivity into the system.
A compound is said to possess the property of gated
reactivity if it converts from a photoinert state at a particular
wavelength to a photoactive state by the application of
external stimuli such as reactive chemicals,2-6 heat,7,8 or
multiphoton absorption.9
[4 + 2] cycloaddition reactions,3 acid/base reactions,4 redox
processes,6 and hydrogen bondings6,8 have been employed
to manipulate the photochromic reactivity. Previously, a
derivative similar to 1a, wherein methyl groups were present
in lieu of phenyl substituents, was found to be photoinert.10
The absence of any photochromic reaction was attributed to
the apparent rigidity of the structure.10 In contrast, cyclo-
butene-1,2-dione derivatives can perform a photochemical
(4) Kawai, S. H.; Gilat, S. L.; Lehn, J.-M. Eur. J. Org. Chem. 1999,
2359-2366.
(5) (a) Huck, N. P. M.; Feringa, B. L. J. Chem. Soc., Chem. Commun.
1995, 1095-1096. (b) Matsui, F.; Taniguchi, H.; Yokoyama, Y.; Sugiyama,
K.; Kurita, Y. Chem. Lett. 1994, 1869-1872. (c) Yokoyama, Y.; Yamane,
T.; Kurita, Y. J. Chem. Soc., Chem. Commun. 1991, 1722-1724.
(6) Irie, M.; Miyatake, O.; Uchida, K.; Eriguchi, T. J. Am. Chem. Soc.
1994, 116, 9894-9900.
Several gated diarylethene photochromic systems have
been reported. Strategies such as esterification reactions,2
(1) (a) Bouas-Laurent, H.; Durr, H. Pure Appl. Chem. 2001, 73, 639-
665. (b) Bamfield, P. Chromic Phenomena-Technological Applications of
Colour Chemistry; The Royal Society of Chemistry: Cambridge, 2001. (c)
Du¨rr, H.; Bouas-Laurent, H. Photochromism: Molecules and Systems;
Elsevier: Amsterdam, 1990. (d) Brown, G. H. Photochromism; Wiley-
Interscience: New York, 1971. (e) Tian, H.; Yang, S. Chem. Soc. ReV.
2004, 33, 85-97. (f) Irie, M. Chem. ReV. 2000, 100, 1685-1716.
(2) Ohsumi, M.; Fukaminato, T.; Irie, M. Chem. Commun. 2005, 3921-
3923.
(7) Irie, M.; Eriguchi, T.; Takada, T.; Uchida, K. Tetrahedron 1997, 53,
12263-12271.
(8) Irie, M.; Miyatake, O.; Uchida, K. J. Am. Chem. Soc. 1992, 114,
8715-8716.
(9) (a) Murakami, M.; Miyasaka, H.; Okada, T.; Kobatake, S.; Irie, M.
J. Am. Chem. Soc. 2004, 126, 14764-14772. (b) Miyasaka, H.; Murakami,
M.; Itaya, A.; Guillaumont, D.; Nakamura, S.; Irie, M. J. Am. Chem. Soc.
2001, 123, 753-754. (c) Uchida, M.; Irie, M. J. Am. Chem. Soc. 1993,
115, 6442-6443.
(3) Lemieux, V.; Branda, N. R. Org. Lett. 2005, 7, 2969-2972.
10.1021/ol070487h CCC: $37.00
© 2007 American Chemical Society
Published on Web 04/19/2007

ring opening reaction yielding 1,2-bisketenes (see 4 in
Scheme 2).11 At room temperature a fast thermal back
reaction takes place and the photochemical transformation
to 1b is not observed. 1,2-Bisketenes are not directly
observed but rather proposed as reactive intermediates from
trapping experiments.12
did not undergo any photochromic reaction during irradiation
at 365 nm. The excited state of 1a was efficiently quenched
by the ring-opening reaction yielding 4 (Scheme 2). In the
Scheme 2. Trapping Reaction of 1,2-Bisketenes 4 by
The aim of this work is to activate the photochromic
property of 1a by protecting the ketone functionality, which
actually causes the suppression of the photochemically
induced opening reaction of cyclobutene-1,2-dione. We have
designed and synthesized a chemically gated diarylethene
derivative containing a cyclobutene-1,2-dione skeleton (Scheme
1). Compound 1a was prepared from diethyl squarate, and
Methanol
absence of a trapping agent, thermal back reaction occurs
very fast and 4 cannot be observed at room temperature.
Nevertheless, the highly reactive intermediate 4 can be
trapped with methanol, forming the moiety 5.13 This obser-
vation does not exclude the possibility of the absence of
photochromism due to rigidity of the system. Compound 2a
with only one ketone functionality does not display any
photochromic behavior.
Scheme 1. Protection Reactions of 1a, Deprotection Reactions
of 3a and 3b, and Photochromism of 3a
Compound 3a was obtained by protecting both ketone
functionalities of 1a. Upon irradiation at 313 nm, the
colorless solution of 3a in acetonitrile became increasingly
violet, indicative of its closing process. Opening reaction
takes place upon irradiation with visible light at 550 nm.
UV-vis spectra of this typical photochromic behavior are
shown in Figure 1 (part I). Compound 3a has a broad
absorption band at 275 nm. After closing the switching
molecule, two new absorption bands appear at 361 and 565
nm, attributable to 3b.
the diethoxy groups were substituted by thiophene moieties;
compounds 2a and 3a were synthesized by a typical
protecting reaction of ketones.13 The absorption spectrum
of 1a was measured in acetonitrile at room temperature; 1a
(10) (a) Krayushkin, M. M.; Shirinian, V. Z.; Belen’kii, L. I.; Shadronov,
A. Y.; Martynkin, A. Y.; Uzhinov, B. M. MendeleeV Commun. 2002, 141-
143. (b) Shirinyan, V. Z. Krayushkin, M. M.; Belen’kii, L. I.; Vorontsova,
L. G.; Starikova, Z. A.; Martynkin, A. Y.; Ivanov, V. L.; Uzhinov, B. M.
Chem. Heterocycl. Compd. 2001, 37, 77-84.
(11) (a) Allen, A. D.; Colomvakos, J. D.; Diederich, F.; Egle, I.; Hao,
X.; Liu, R.; Lusztyk, J.; Ma, J.; McAllister, M. A.; Rubin, Y.; Sung, K. T.;
Tidwell, T.; Wagner, B. D. J. Am. Chem. Soc. 1997, 119, 12125-12130.
(c) Liu, R.; Tidwell, T. T. J. Chem. Soc., Perkin Trans. 2 1996, 2757-
2762. (d) Allen, A. D.; Colomvakos, J. D.; Egle, I.; Lusztyk, J.; McAllister,
M. A.; Tidwell, T. T. B.; Wagner, D.; Zhao, D.-c. J. Am. Chem. Soc. 1995,
117, 7552-7553.
Figure 1. (I) Absorption spectra of 3 in acetonitrile solution: (s)
open-ring isomer (3a), (- - -) closed-ring isomer (3b) obtained after
irradiation of a solution of 3a in acetonitrile at 313 nm. (II)
Absorption spectra of closed forms in the visible region in
acetonitrile. Closed isomers of 3b (s), 2b (- - -) and 1b (‚ ‚ ‚ ‚).
(12) (a) Chapman, O. L.; McIntosh, C. L.; Barber, L. L. J. Chem. Soc.
D 1971, 1162-1163. (b) Obata, N.; Takizawa, T. J. Chem. Soc. D 1971,
587-588. (c) Blomquist, A. T.; LaLancette, E. A. J. Am. Chem. Soc. 1961,
83, 1387-1391. (d) Mallory, F. B.; Roberts, J. D. J. Am. Chem. Soc. 1961,
83, 393-397.
(13) See Supporting Information for details.
1916
Org. Lett., Vol. 9, No. 10, 2007

The deprotection of 3b occurs easily under acidic condi-
tions, forming 2b. Moreover, the first deprotection is much
faster than the second one. Therefore, by adding a base, it is
possible to arrest the reaction after the first deprotection in
order to obtain 2b. Compound 3a shows the same behavior
as 3b. Only the closed forms (1b, 2b, and 3b) have
absorption bands above 400 nm (Table 1). The deprotection
Table 1. Wavelength Maxima and Absorption Coefficients of
Open and Closed Isomers of Diarylethenes
a
compd
λmax/nm (ꢀmax × 104 M-1 cm-1
)
1a
1b
2a
2b
3a
3b
267 (3.7), 290 (4.1), 365 (0.9)
292 (2.5), 436 (0.3), 548 (0.1), 800 (0.2)
259 (2.7), 289 (4.1), 346b (0.6)
294 (2.3), 400 (0.5), 666 (0.4)
275 (4.2)
275 (2.7), 293 (2.6), 361 (0.8), 565 (1.2)
a MeCN at 293 K. Solution concentration: 3 × 10-5 M. b Shoulder.
reaction14 of 3b can be followed by spectroscopic measure-
ments in the visible region (Figure 1, part II). During the
first deprotection, the band at 565 nm disappears while a
new band is seen at 666 nm, attributable to 2b. The second
deprotection leads to a decrease in the band intensity at 666
nm with the appearance of a new band at 800 nm, attributable
to 1b. As mentioned earlier, deprotection processes of the
closed forms (2b and 3b) are accompanied by a strong red
shift. The results of UV-vis spectra have been summarized
in Table 1.
1
Figure 2. (I) H NMR spectra of 3a in chloroform solution after
Photocycloreversion occurs by irradiation at 800 nm for
1b and 650 nm for 2b. Consequently, deprotection of cyclic
acetal does not suppress ring-opening reactions. Moreover,
1b also undergoes a spontaneous back reaction in the dark
at room temperature. The reaction rate was determined by
applying a first-order reaction model. The rate constant and
the half-life were 0.025 h-1 and 28 h, respectively.13 The
rate constant for the back reaction increases drastically under
acidic conditions.
irradiation with light at 313 nm. (II) After the addition of
methanesulfonic acid, one of the protecting groups of 3a and 3b is
eliminated, and (III) both protecting groups of 3b are eliminated.
to that of 2a, the spectrum shows the presence of 2a, 1a,
and 1b (Figure 2, part III). After 4 days, only the singlet of
1a at 2.65 ppm was observed.
Closing and opening reactions of 3 were performed several
times. After only 10 irradiation cylces, there is a ca. 25%
loss of photochromic activity,13 indicating that the system
is not very robust for any kind of recording/storage applica-
tion. Side products were detected after the closing reaction
1
However, this process can also be studied by H NMR
measurements wherein the peaks corresponding to the methyl
groups of the thiophene moieties are prominent (Figure 2).
Methyl groups of 3a appear at 2.21 ppm. Upon irradiation
at 313 nm, 57% of 3a was converted into 3b and a new
peak appeared at 2.18 ppm, assignable to the methyl groups
of 3b (Figure 2, part I). Under acidic conditions,15 the peak
at 2.18 ppm (2.21 ppm) was replaced by two peaks appearing
at 2.24 and 2.31 ppm (2.37 and 2.44 ppm) indicating the
formation of 2b (2a) (Figure 2, part II). Because of the faster
reaction rate for the deprotection reaction of 2b compared
1
of 3a by H NMR spectroscopy, and this could possibly
explain the decreasing effect. Protection and deprotection
reactions, however, did not show any undesired side reac-
tions.
In summary, we have developed a new chemically gated
dithienylethene switch whose photochromic reactions can be
manipulated by the addition of an acid.
(14) A solution of 3a (2.5 cm3, 3 × 10-5 M) in acetonitrile was irradiated
at 313 nm for 1 min. Methanesulfonic acid (10 µL) was added, and the
deprotection processes was followed by UV-vis spectra.
Acknowledgment. We thank the Swiss National Science
Foundation for financial support.
(15) Forty solutions of 3a (2.5 cm3, 3 × 10-5 M) in acetonitrile
were irradiated at 313 nm for 1 min. Solvent was removed in the dark.
The residue was dissolved in deuterated chloroform. Methanesulfonic acid
Supporting Information Available: Synthetic details and
characterizations for compounds, including CIF file. This
material is available free of charge via the Internet at
1
(10 µL) was added and deprotecting processes was followed by H NMR
spectra.
Org. Lett., Vol. 9, No. 10, 2007
1917

3http://pubs.acs.org. Crystal structure data for compound
1a (CCDC 626864) can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, by email to
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB2 1EZ, UK; fax +44 1223 336033.
OL070487H
1918
Org. Lett., Vol. 9, No. 10, 2007