Photochromic films prepared by oxidation polymerization of a diarylethene having phenol moieties

Article abstract of DOI:10.1246/cl.2002.476

Photochromic films containing diarylethene chromophores were prepared by oxidation polymerization of a diarylethene having phenol moieties. Upon alternate irradiation with UV and visible light, the polymer films exhibited coloration/decoloration cycles. The films were amorphous and kept the state after one year storage at room temperature.

Full text of DOI:10.1246/cl.2002.476

476
Chemistry Letters 2002
Photochromic Films Prepared by Oxidation Polymerization of a Diarylethene
Having Phenol Moieties
Kingo Uchida,ꢀ Atsushi Takata, Shinichiro Nakamura,y and Masahiro Irieyy
Department of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, Seta, Otsu 520-2194
yMCC-Group Science and Technology Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida, Yokohama 227-8502
yyDepartment of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University and
CREST, Japan Science and Technology Corporation (JST), 6-10-1 Hakozaki, Fukuoka 812-8581
(Received January 24, 2002; CL-020083)
Photochromic films containing diarylethene chromophores
were prepared by oxidation polymerization of a diarylethene
having phenol moieties. Upon alternate irradiation with UV and
visible light, the polymer films exhibited coloration/decoloration
cycles. The films were amorphous and kept the state after one year
storage at room temperature.
the hexane solution of 1a (3:8 Â 10À5 mol/l). Upon UV light
(280nm) irradiation, the solution turned to blue and absorption
bands appeared at 545 (": 1:1 Â 104 dm3 molÀ1 cmÀ1) and
347 nm (": 1:1 Â 104 dm3 molÀ1 cmÀ1) attributable to 1b, and
the peak of 1a at 254 nm (": 2:1 Â 104 dm3 molÀ1 cmÀ1) was
suppressed. Upon visible light (ꢀ > 500 nm) irradiation, the blue
color was bleached and regenerated the open-ring isomer 1a. The
quantum yields of cyclization and cycloreversion of 1 were 0.19
(measured by 280 nm light irradiation) and 0.03 (measured by
492 nm light irradiation), respectively.
Photochromic molecules attract much attention from both
fundamental as well as practical points of view because of their
potential for applications to optical devices such as optical
memories and switches.1 Among the photochromic compounds,
diarylethenes are regarded as the best candidate, because of the
thermal stability of their both isomers and the fatigue resistant
property.2 For the fabrication of thin photochromic films for the
applications, various methods have been employed; for example,
the dispersion of the dyes into polymer matrices,3 LB films of
diarylethenes having long alkyl chain,4 and preparation of
crystal5 or amorphous films of diarylethenes having bulky
substituents.6
Dispersing the photochromic molecules into polymer
matrices is the most convenient method to prepare the photo-
chromic films.3 Although increment of the dye concentration is
strongly desired to enhance the photochromic efficiency,
preparation of films containing high concentration of the dyes is
not easy because segregation takes place to some extent after long
term storage. Bulk amorphous and crystalline photochromic films
have been extensively studied for the purpose. We now propose a
new method to form thin films by oxidation polymerization.
Scheme 1. Synthetic route of 1a.
The diarylethene 1a was polymerized according to Hay’s
method.9 To the o-dichlorobenzene solution (10ml) containing
0.8 mg of N,N,N0,N0-tetramethylethylenediamine and 10mg of
copper (I) bromide, oxygen gas (300 ml/min) was introduced at
85 ꢁC. Diarylethene 1a (2.5 g, 4:3 Â 10À3 mol) in 10ml of o-
dichlorobenzene was slowly added to the mixture and stirred for
1.5 h at the temperature. The reaction mixture was poured into a
methanol solution (2.5 l) containing 25 ml of hydrochloric acid
and 25 ml of phosphinic acid. The precipitate was isolated by
centrifuge (3500 rpm, 5 min) and dissolved into a small amount of
chloroform. The pre-polymer solution was casted on a quartz
plate. After the solvent was evaporated at room temperature a thin
film was prepared. The film was insoluble to any solvents. The
A diarylethene derivative 1,2-bis[2,4-dimethyl-5-(o-hydro-
xyphenyl)-3-thienyl]hexafluorocyclopentene (1a)7 was synthe-
sized from 2,4-dibromo-3,5-dimethylthiophene 28 as shown in
Scheme 1. Figure 1 illustrates the absorption spectral changes of
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
477
Figure 3. Absorption spectral changes of the amorphous
Figure 1. Absorption spectra of hexane solutions of 1a
(3:8 Â 10À5 mol/l, solid line), 1b (broken line), and photo-
stationary state (dotted line) under irradiation with 280nm
light.
film (3 ꢁm thickness) prepared by oxidation polymerization
of 1a; solid line: before UV irradiation, broken line: after UV
irradiation.
Ministry of Education, Science, Sports, and Culture, and by
CREST and ACT of Japan Science and Technology Cooperation
(JST).
References and Notes
1
H. Duerr and H. Bouas-Laurent, ‘‘Photochromism: Molecules
and Systems,’’ Elsevir, Amsterdam (1990).
2
M. Irie, Chem. Rev., 100, 1685 (2000); M. Irie and M. Mohri,
J. Org. Chem., 53, 803 (1988); M. Irie and K. Uchida, Bull.
Chem. Soc. Jpn., 73, 985 (1998); S. H. Kawai, S. L. Gilat, and
J.-M. Lehn, Chem. Eur. J., 1, 285 (1995); G. M. Tsivgoulis
and J.-M. Lehn, Chem. Eur. J., 2, 1399 (1996).
3
N. Tanio and M. Irie, Jpn. J. Appl. Phys., 33, 1914 (1994); T.
Tsujioka, F. Tatezono, T. Harada, K. Kuroki, and M. Irie, Jpn.
J. Appl. Phys., 33, 5788 (1994).
4
5
S. Abe, K. Uchida, I. Yamazaki, and M. Irie, Langmuir, 13,
5504 (1997).
S. Kobatake, K. Shibata, K. Uchida, and M. Irie, J. Am. Chem.
Soc., 122, 12135 (2000); M. Irie, T. Lifka, S. Kobatake, and N.
Kato, J. Am. Chem. Soc., 122, 4871 (2000); T. Yamada, S.
Kobatake, K. Muto, and M. Irie, J. Am. Chem. Soc., 122, 1589
(2000); M. Irie, K. Uchida, T. Eriguchi, and H. Tsuzuki,
Chem. Lett., 1995, 899.
Figure 2. IR spectral changes of the
diarylethene 1a before (solid line) and
after polymerization (broken line).
absorption band attributable OH group disappeared in the FT IR
spectrum of the polymer film as shown in Figure 2.
6
7
T. Kawai, N. Fukuda, D. Groeschl, S. Kobatake, and M. Irie,
Jpn. J. Appl. Phys., 38, L1194 (1999); H. Utsumi, D.
Nagahama, H. Nakano, and Y. Shirota, J. Mater. Chem., 10,
2436 (2000).
1a: colorless needles; mp 93.5–94.9 ꢁC; 1H-NMR (400 MHz,
CDCl3) ¼ 1:82 (s, 3H, ap 2-Me), 1.88 (s, 3H, p 2-Me), 2.36 (s,
3H, ap 4-Me), 2.42 (s, 3H, p 4-Me), 6.93–7.00 ppm (m, 8H,
aromatic protons); (the ratio of ap: p isomers ¼ 1 : 1).
M. Irie, K. Sakemura, M. Okinaka, and K. Uchida, J. Org.
Chem., 60, 8305 (1995).
The polymer film p(1a) showed a reversible photochromic
reaction by alternate irradiation with UV and visible light. The
spectral change of the film is shown in Figure 3. X-ray diffraction
measurement showed no peaks even after 1 year storage at room
temperature. This indicates that the polymer film is in the
amorphous phase. The new amorphous photochromic film will be
applicable for wave-guide and novel recording media.
8
9
This work was supported by Sumitomo Foundation, a Grant-
in-Aid for Scientific Research (C) No. 12640567 from the
A. S. Hay, Polym. Eng. Sci., 16, 1 (1976).