Physiochemical stable novel yellow developing photochromic compounds having a thiazole group

Article abstract of DOI:10.1080/15421400590947144

Diarylethene derivatives having a thiazole ring as the aryl group 1a, 2a, and 3a have been synthesized in an attempt to obtain photochromic compounds which change the color from colorless to yellow, and have low photocycloreversion quantum yields and high

Full text of DOI:10.1080/15421400590947144

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Photochemically Stable
Novel Yellow Developing
Photochromic Compounds
Having a Thiazole Group
Shizuka Takami a & Masahiro Irie a
a Department of Chemistry and Biochemistry ,
Graduate School of Engineering, Kyushu University,
and “Nanotechnology Support Project” of the
Ministry of Education, Culture, Sports, Science and
Technology (MEXT), Japan , Hakozaki, Higashi-ku,
Fukuoka, Japan
Published online: 31 Aug 2006.
To cite this article: Shizuka Takami & Masahiro Irie (2005) Photochemically
Stable Novel Yellow Developing Photochromic Compounds Having a Thiazole
Group, Molecular Crystals and Liquid Crystals, 431:1, 467-471, DOI:
10.1080/15421400590947144
To link to this article: http://dx.doi.org/10.1080/15421400590947144
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Mol. Cryst. Liq. Cryst., Vol. 431, pp. 167=[467]–171=[471], 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590947144
Photochemically Stable Novel Yellow Developing
Photochromic Compounds Having a Thiazole Group
Shizuka Takami
Masahiro Irie
Department of Chemistry and Biochemistry, Graduate School of
Engineering, Kyushu University, and ‘‘Nanotechnology Support Project’’
of the Ministry of Education, Culture, Sports, Science and Technology
(MEXT), Japan, Hakozaki, Higashi-ku, Fukuoka, Japan
Diarylethene derivatives having a thiazole ring as the aryl group 1a, 2a, and 3a
have been synthesized in an attempt to obtain photochromic compounds which
change the color from colorless to yellow, and have low photocycloreversion quan-
tum yields and high absorption coefficients of the colored isomers. Compounds
1 and 3 exhibited reversible photochromic reactions in hexane solution. The
closed-ring isomers 1b and 3b showed orange and yellow colors, respectively.
The e value of 3b at the absorption maximum is 18400 Mꢀ1cmꢀ1, which is much
larger than those of 1b (e ¼ 10000 Mꢀ1cmꢀ1) and 2b (e ¼ 11400 Mꢀ1cm ꢀ1). The
photocyclization=cycloreversion quantum yields of 3 were determined to be 0.19
and 0.0014, respectively. The yellow color was sufficiently photochemically stable
under room light.
Keywords: absorption coefficient; diarylethene; photochromism; photocycloreversion
quantum yield; yellow photochromic dye
INTRODUCTION
Photochromic compounds have attracted much attention because
of their potential ability for optical memory media, photo-optical
This work was partly supported by ‘‘Nanotechnology Support Project’’ of the Ministry
of Education, Culture, Sports, Science, and Technology (MEXT), Japan and a Grant-in-
Aid for Scientific Research(S) (No. 15105006) from the Ministry of Education, Culture,
Sports, Science, and Technology (MEXT), Japan.
Address correspondence to Masahiro Irie, Department of Chemistry and Biochemistry,
Graduate School of Engineering, Kyushu University, and ‘‘Nanotechnology Support Pro-
ject’’ of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan. E-mail: irie@cstf.kyushu-u.ac.jp
167=[467]

168=[468]
S. Takami and M. Irie
switching and display devices [1]. Among them diarylethenes with
heterocyclic aryl groups, such as thiophene or benzothiophene groups,
are the most promising candidates for the applications [2] because of
their fatigue resistant and thermally irreversible photochromic per-
formance [3]. For the application to a full color display it is indispens-
able to prepare red and yellow developing diarylethene derivatives [4].
When the thiophene rings of 1,2-bis(2-methyl-5-phenyl-3-thienyl)
perfluorocyclopentenes [4] are replaced with thiazole rings, the
absorption maximum of the closed-ring isomer shifts from 575 nm
(blue) to 525 nm (red) [5]. Another approach to further shift the
absorption band to shorter wavelength (yellow) is to attach the thio-
phene rings to the ethene moiety at the 2-position [6]. Very recently,
oxazolylfulgides and 2,3-bis(2,3,5-trimethyl-3-thienyl)maleic imidine
have been reported as yellow photochromic dyes [7]. However, These
colored isomers are photochemically unstable and the photocyclorever-
sion quantum yields are rather high. For a full color display it is
strongly desired to develop yellow photochromic compounds which
have low photocycloreversion quantum yields and thermal stability
at room temperature. In previous papers we showed that introduction
of alkoxy groups at the reactive carbons of diarylethene derivatives
remarkably suppresses the photocycloreversion quantum yields [8].
Here we examined the photochromism of 1-thiazolyl-2-thienylcyclo-
pentene derivative 1a, a 1-thiazolyl-2-stryl cyclopentene derivative
2a, and a 1-thiazolyl-2-vinylcyclopentene derivative 3a having meth-
oxy substituents to obtain yellow photochromic compounds having
a low photocycloreversion quantum yield.
EXPERIMENTAL
Compound 1a [9] and 2a [10] were synthesized by the reaction of
4-bromo-5-methyl-2-phenylthiazole [5] with 4 and 5 by bromine-lithium
exchange followed by nucleophilic displacement of fluoride, respectively.
Compound 3a [11] was synthesized by the coupling reaction of 6 and
2-bromo-3-methyl-2-butene [9]. The structures of all compounds were
confirmed by 1H NMR, mass spectroscopy, and elemental analysis.

Photochemically Stable Novel Yellow
169=[469]
SCHEME 1 Syntheses of compounds 1a, 2a, and 3a.
RESULTS AND DISCUSSIONS
4-Thiazolyl [5] and 2-thienyl [6] chromophores were chosen as the aryl
groups of diarylethenes to shift the absorption maximum of the closed-
ring isomers to shorter wavelengths. Upon irradiation with 313 nm
light, the colorless solution of 1a turned orange, in which a visible
absorption band was observed at 483 nm. The orange color is due to
the closed-ring isomer 1. When the orange solution was irradiated
with visible light (k > 440 nm), the spectrum readily returned back
to the original one. The conversion from 1a to 1b in the photostation-
ary state under irradiation with 313 nm light was 66%. The batho-
chromic shifts of 1b are not large enough to exhibit yellow color.
Therefore, the 2-thienyl group [6] was replaced with a stryl and an
ethylene units to further shift the absorption band of the closed-ring
isomer to shorter wavelengths.
First, we investigated the photochromic reaction of compound 2a
with stryl and thiazole groups. Upon irradiation with 313 nm light,
the colorless solution turned yellow, in which a visible absorption band
was observed at 426 nm. The yellow color is due to the closed-ring

170=[470]
S. Takami and M. Irie
isomer 2b. However, when the yellow solution was irradiated with vis-
ible light (k > 440 nm), the spectrum did not return back to the orig-
inal one. Although 2b showed yellow color, the photo side-product
was formed in the photochromic reaction.
Next, we designed a derivative 3a, which has methoxy substituents
at the para-position of the phenyl ring and 5-position of the thiazole
ring. When the stryl unit of compound 2a is replaced with a ethylene
unit, the absorption maximum of the closed-ring isomer is expected to
shift to a wavelength much shorter absorption maximum of 2b
(424 nm). In order to obtain yellow colored closed-ring isomer, it is
required to introduce substituents [11]. Both methoxy substituents
are effective to induce bathochromic shift. The methoxy group at the
5-position is also known to decrease the photocycloreversion quantum
yield. Upon irradiation with 313 nm light the colorless hexane solution
of 3a slowly turned yellow, showing an absorption maxima at 410 nm.
The photostationary spectrum is almost the same as the colored
isomer, indicating a high conversion from the colorless to the colored
isomers by irradiation with 313 nm light. The yellow colored solution
slowly returned back to the initial colorless solution upon prolonged
irradiation with visible light.
Figure 1 shows the absorption spectra of these closed-ring isomers
1b, 2b, and 3b in hexane. The absorption maximum of 3b shows
yellow color, which is a hypsochromic shift as much as 80 nm in com-
parison with that of 1b. The e value of 3b at the absorption maximum
is 18400 Mꢀ1cmꢀ1
, which is much larger than those of 1b
(e ¼ 10000 Mꢀ1cmꢀ1) and 2b (e ¼ 11400 Mꢀ1cmꢀ1).
FIGURE 1 Absorption spectra of the closed-ring isomers 1b (dotted line), 2b
(solid line), and 3b (bold solid line) in hexane.

Photochemically Stable Novel Yellow
171=[471]
The photocyclization=cycloreversion quantum yields of 1 were 0.36
and 0.16, respectively. The cyclization quantum yield of 3a was 0.19.
On the other hand, the photocycloreversion quantum yield of 3b was
remarkably suppressed to 0.0014. The yellow colored isomer 3b was
found to be sufficiently photochemically stable under room light. The
absorption coefficient of 3b was obtained to be 18400 Mꢀ1cmꢀ1, which
is much larger than that of the closed-ring isomers of yellow develop-
ing diarylethenes. The large absorption coefficient of 3b is due to the
methoxy group at the para-position of the phenyl ring [12]. Compound
3 is a useful candidate as a yellow photochromic dye.
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[9] Data for compound 1a: 1a (14%) as a colorless solid after elution from silica gel with
10% ethyl acetate in hexane, m.p. ¼ 107–108ꢁC. 1H NMR (CDCl3, 200 MHz):
d ¼ 1.80 (s, 3H), 1.98 (s, 3H), 6.86 (d, J ¼ 5.0 Hz, 1H), 7.44 (m, 4H), 7.88 (m, 2H).
MS (m=z) 445 (Mþ), Anal. Found: C, 53.96; H, 2.85; N, 3.00%. Calcd for
C20H13F6NS2: C, 53.93; H, 2.94; N, 3.14%.
[10] Data for compound 2a: 2a (11%) as a colorless solid after elution from silica gel with
10% ethyl acetate in hexane, 1H NMR (CDCl3, 200 MHz): d ¼ 1.67 (s, 3H), 1.75
(s, 3H), 2.39 (s, 3H), 7.34–7.16 (m, 5H), 7.42–7.34 (m, 3H), 7.85–7.76 (m, 2H). MS
(m=z) 479 (Mþ), Anal. Found: C, 62.62; H, 3.99; N, 2.92%. Calcd for C25H19F6NS:
C, 62.64; H, 4.02; N, 2.96%.
[11] Data for compound 3a: 3a (5%) as a colorless oil after elution from silica gel with
30% ethyl acetate in hexane, m.p. ¼ 93–94ꢁC. 1H NMR (200 MHz, CDCl3):
d ¼ 1.49 (s, 3H), 1.75 (s, 3H), 1.93 (s, 3H), 3.86 (s, 3H), 4.01 (s, 3H), 6.93 (d,
J ¼ 9.0 Hz, 2H), 7.71 (d, J ¼ 9.0 Hz, 2H). MS (m=z) 463 (Mþ). Anal. Found:
C, 54.30; H, 4.20; N, 3.18%. Calcd for C21H19F6NO2S2: C, 54.42; H, 4.13; N, 3.02%.
[12] Irie, M., Sakemura, K., Okinaka, M., & Uchida, K. (1995). J. Org. Chem., 60, 8305.