A. J. VAZQUEZ AND N. S. NUDELMAN
of methyl signals of different area can be observed, and likewise
two signals for the methoxy protons. This fact can be interpreted
as due to the presence of the so-called parallel (p) and antiparallel
presence of two ring-opened conformational isomers and the
sensitivity of the photocromism to the solvent effects which
allows a fine tuning of the whole photochemical cycle make
these novel diarylethenes very useful compounds as potential
optical materials.
(
ap) isomers. In base to the integration area of methyl protons
for each compound (area /areaap), it is possible to estimate the
p
percentage of each conformer in the ring-opened isomer;
those are around: 33% p (1o), 36% p (2o) and 42% p, (3o),
respectively. A recent study on photocromic C2-symmetric
chiral diarylethene report the observation of four separate
Acknowledgement
AJV is a grateful recipient of a post-doctoral fellowship of the
National Research Council (CONICET). Authors are indebted to
the University of Buenos Aires and the Agencia Nacional de
Promoción Científica y Tecnológica (ANPCYT) for financial support.
1
doublets of the secondary methyl groups in the H NMR
[
28]
5
00 MHz spectrum of the conformational isomers.
An alternative explanation for the exponential kinetics
observed for the photoinduced cyclization was provided by
one of the reviewers of the present study. ‘Since the reagent
absorbs in the UV, as the product forms, it competes for the light,
decreasing the amount of light deposited in the reagent. Thus,
the reaction starts out faster and then slows down as the product
competes until eventually reaching a photostationary state’. In
REFERENCES
[
[
1] S. Pu, C. Fan, W. Miao, G. Liu, Dyes Pigments 2010, 84, 25.
2] T. Yamaguchi, K. Ushida, M. Irie, J. Am. Chem. Soc. 1997, 119, 6066.
[3] L. Giordano, T. M. Jovin, M. Irie, E. A. Jares-Erijman, J. Am. Chem. Soc.
002, 124, 7481.
4] E. A. Jares-Erijman, T. M. Jovin, Nat. Biotechnol. 2003, 21,1387.
5] Y. Garcia, V. Ksenofontov, R. Lapouyade, A. D. Naik, F. Robert,
P. Gütlich, Opt. Mater. 2011, 33, 942.
2
fact, if k
c
is the rate constant for the open state cyclization and
[
[
k
r
the rate constant for the closed state cycloreversion, and
considering that both states absorb UV light, a complex expo-
nential kinetic law could be derived as well. Nevertheless, the
other two findings described in the present study, namely: the
double signals in the NMR spectra and the solvent effects
observed for the nitro-substituted compound could not be
explained by the alternative explanation, whereas they are fully
consistent with the presence of the two isomers for the open
compound. Therefore, although the influence of the decreasing
amount of light in the kinetic law could not be ruled out, the
proposal of the conformational equilibrium accounts for all the
observed facts. Further evidence on the existence of both con-
formers in this type of photocromic dibenzothiophenylethene
derivatives was recently afforded by the observation that one
compound crystallizes with an antiparallel conformation which
exhibit good photocromism, whereas other crystallizes with a
[6] J. J. D. Jong, L. N. Lucas, R. Hania, A. Pugzlys, R. M. Kellogg, B. L. Feringa,
K. Duppen, J. H. van Esch, Eur. J. Org. Chem. 2003, 1887.
[
[
[
7] R. M. Kellogg, M. B. Groen, H. Wynberg, J. Org. Chem. 1967, 32, 3093.
8] W. Liu, D. Jiang, S. Pu, S. A. Cui, J. Phys. Conf. 2011, 276, 1.
9] M. Irie, Proc. Jpn. Acad., Ser. B 2010, 86, 472.
10] Z. Li, Y. Lin, J. L. Xia, H. Zhang, F. Fan, Q. Zeng, D. Feng, J. Yin, S. H.
Liu, Dyes Pigments 2011, 90, 245, and references therein.
11] M. Irie, Chem. Rev. 2000, 100, 1685.
[
[
[
[
12] T. Yamaguchi, M. Irie, Chem. Lett. 2004, 33,1398.
13] S. Z. Pu, F. S. Zhang, J. K. Xu, L. Shen, Q. Xiao, B. Chen, Mater. Lett.
2
006, 60, 485.
[14] S. Z. Pu, T. S. Yang, J. K. Xu, L. Shen, G. Z. Li, Q. Xiao, et al. Tetrahedron
2005, 61, 6623.
15] C. B. Fan, S. Z. Pu, G. Liu, T. S. Yang, J. Photochem. Photobiol. A Chem.
008, 194, 333.
16] C. B. Fan, S. Z. Pu, G. Liu, T. S. Yang, J. Photochem. Photobiol. A Chem.
008, 197, 415.
[17] H. H. Liu, Y. Chen, J. Phys. Org. Chem. 2011, 24, 517.
[
2
[
2
[
27]
parallel conformation which exhibit no photocromism.
[
[
18] M. Irie, K. Sayo, J. Phys. Chem. 1992, 96, 7671.
19] E. J. Shin, H. S. Jung, J. Photochem. Photobiol. A Chem. 2005, 173,
The above results indicate that the novel diarylethenes
exhibit remarkable properties, their solvent and kinetic behav-
ior are appropriate for their applications in optical materials,
the cyclization/ring opening cycles could be repeated 50 times
in the four solvents and the presence of parallel and antiparallel
conformers could be a useful phenomenum for their use in
1
95.
[
20] S. Kobatake, Y. Terakawa, H. Imagawa, Tetrahedron 2009, 65, 6104.
[21] Compounds 1–3 were synthesized in the laboratory of Elizabeth A.
Jares-Erijman.
[
22] S. A. Díaz, G. O. Menéndez, M. H. Etchehon, L. Giordano, T. M. Jovin,
E. A. Jares-Erijman, ACS Nano 2011, 5, 2795.
23] L. Giordano, R. J. Vermeij, E. A. Jares-Erijman, Arkivoc 2005, 2005, 268.
24] K. Moritmisu, K. Shibata, S. Kobatake, M. Irie, J. Org. Chem. 2002,
‘gated’ photocromism.
[
[
6
7, 4574.
25] M. Irie, K. Sakemura, M. Okinaka, K. Uchida, J. Org. Chem. 1995,
0, 8305.
CONCLUSIONS
[
6
The examined photochromic diarylethenes 1–3 undergo a
photoinduced ring closure upon exposure to UV light, showing
two maxima in the visible region, one near 420 nm and the other
near 520 nm. The cyclization process can be completely reverted
by exposure to visible (nearly green) light. The maxima are little
sensitive to the substitution pattern, showing, however, the
appearance of another peak at ca. 325 nm, when a nitro group
is introduced. On other hand, the UV spectra of the three
compounds are little sensitive to the solvent influence. The
cycloreversion for the three compounds shows first-order
kinetics, whereas the cyclization kinetics shows a complex order,
being the plot well fitted by an exponential function. This
complex kinetic behavior could be justified on the basis of the
proposal of the presence of two conformers for the open-ring
structure, the parallel and the antiparallel conformers. The unusual
[26] P. Atkins, R. Friedman, Molecular Quantum Mechanics, 4th ed, Oxford
University Press, Oxford, U.K., 2005.
[
27] S. Pu, R. Wang, G. Liu,W. Liu, S. Cui, P. Yan, Dyes Pigments 2012,
4, 195–206.
28] S. Delbaere J. Berthet, T. Shiozawa, Y. Yokoyama, J. Org. Chem. 2012,
7, 1853–1859.
9
[
7
rd
[29] L. Wang, C. Zhang, S. Pu, G. Liu, 3 Int. Congress on Image and Signal
Processing, 2010, 2857.
30] W. Liu, S. Pu, T. Yang, G. Liu, S. Cui, Pacific Area Conference on
Circuits, Communications and System, 2009, 465.
31] O. I. Kobeleva, T. M. Valova, V. A. Barachevskii, M. M. Krayushkin,
B. V. Lichitskii, A. A. Dudinov, O. Y. Kuznetsova, G. E. Adamov,
E. P. Grebennikov, Optic. Spectros. 2010, 109, 101.
[
[
[32] H. H. Liu, Y. Chen, J. Phys. Org. Chem. 2012, 25, 142–146.
[33] A. J. Vazquez, N. S. Nudelman, Int. J. Chem. Kinet. 2012, in press.
[34] G. Favaro, F. Ortica, A. Romani, P. Smimmo, J. Photochem. Photobiol.
A Chem. 2008, 196, 190.
[35] M. Irie, O. Miyatake, K. Uchida, J. Am. Chem. Soc. 1992, 114, 8715.
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