Coumarinyl(thienyl)thiazoles: Novel photochromes with modulated fluorescence

Article abstract of DOI:10.1021/ol800223g

Novel photochromic 5-(3'-coumarinyl)-4-(3 -thienyl)thiazoles have been synthesized. These compounds display intensive fluorescence emission in the open form A, which is modulated by light. Fluorescence intensity decreases significantly upon irradiation of A with UV-light (λ< 400 nm) due to formation of the cyclic form B. Irradiation of B with visible light (λ > 470 nm) promotes its opening and the recovering of fluorescence Novel dihetarylethenes undergo photochromic modulation of fluorescence both in solution and in polymeric matrices.

Full text of DOI:10.1021/ol800223g

ORGANIC
LETTERS
2008
Vol. 10, No. 6
1319-1322
Coumarinyl(thienyl)thiazoles: Novel
Photochromes with Modulated
Fluorescence
Valery F. Traven,*,† Andrei Y. Bochkov,† Mikhail M. Krayushkin,‡
Vladimir N. Yarovenko,‡ Boris V. Nabatov,‡ Sergei M. Dolotov,†
|
Valery A. Barachevsky,§ and Irina P. Beletskaya
MendeleeV UniVersity of Chemical Technology, Moscow 125047, Miusskaya sq., 9,
Russian Federation, Zelinsky Institute of Organic Chemistry, Russian Academy of
Sciences, Moscow 119991, Leninsky aVenue, 47, Russian Federation, Photochemistry
Center, Russian Academy of Sciences, Moscow 119421, NoVatoroV str., 7a, Russian
Federation, and Frumkin Institute of Physical Chemistry, Russian Academy of
Sciences, Moscow 119071, Leninsky aVenue, 31, Russian Federation
traVen@muctr.ru
Received January 31, 2008
ABSTRACT
Novel photochromic 5-(3
in the open form A, which is modulated by light. Fluorescence intensity decreases significantly upon irradiation of A with UV-light (
nm) due to formation of the cyclic form B. Irradiation of B with visible light ( > 470 nm) promotes its opening and the recovering of fluorescence.
Novel dihetarylethenes undergo photochromic modulation of fluorescence both in solution and in polymeric matrices.
′
-coumarinyl)-4-(3′′-thienyl)thiazoles have been synthesized. These compounds display intensive fluorescence emission
λ
< 400
λ
Efficient photochromes with modulated fluorescence are
compounds of potential interest for molecular electronics and
optical memory device industries.1-4 Complex systems
integrating both photochromic and fluorescent functions into
a single molecule have been reported.5-8 Fluorescence
quenching operates in these systems via the mechanism of
energy transfer from emitting moiety to the cyclic form of
photochrome. Mixtures of photochromic and fluorescent
compounds have also been proposed to provide fluorescence
modulation.9-11 Intermolecular mechanism of energy transfer
is responsible for fluorescence modulation in such two-
molecule fluorescent photochromes. Coumarin derivatives
have also been used in the systems of that kind.9
(6) Fukaminato, T.; Sasaki, T.; Kawai, T.; Tamai, N.; Irie, M. J. Am.
Chem. Soc. 2004, 126, 14843.
(7) Golovkova, T. A.; Kozlov, D. V.; Neckers, D. C. J. Org. Chem. 2005,
70, 5545.
(8) Xiao, S.; Xi, T.; Li, F.; Huang, C. Tetrahedron Lett. 2005, 46, 9009.
(9) Sheng, X.; Peng, A.; Fu, H.; Yao, J.; Liu, Y.; Wang, Y. J. Mater.
Res. 2007, 22, 1558.
(10) Corredor, C. C.; Huang, Z.-L.; Belfield, K. D. AdV. Mater. 2006,
18, 2910.
(11) Corredor, C. C.; Huang, Z.-L.; Belfield, K. D.; Morales, A. R.;
Bondar, M. V. Chem. Mater. 2007, 19, 5165.
† Mendeleev University.
‡ Zelinsky Institute of Organic Chemistry.
§ Photochemistry Center.
| Frumkin Institute of Physical Chemistry.
(1) Irie, M. Chem. ReV. 2000, 100, 1685.
(2) Raymo, F. M. AdV. Mater. 2002, 14, 401.
(3) Gilat, S. L.; Kawai, S. H.; Lehn, J.-M. Chem.-Eur. J. 1995, 1, 275.
(4) Rudzinski, C. M.; Nocera, D. G. In Optical Sensors and Switches;
Schaze, K. S., Ed.; Marcel Dekker: New York, 2001; pp 1-93.
(5) Kawai, T.; Sasaki, T.; Irie, M. Chem. Commun. 2001, 711.
10.1021/ol800223g CCC: $40.75
© 2008 American Chemical Society
Published on Web 02/28/2008

We have earlier designed and prepared novel photo-
chromes with modulated fluorescencescoumarin spiropyr-
anes derivatives.12 Their fluorescence was modulated by
photochromic transformation of spiropyran moiety. The rates
of the photoinduced spectral changes were depended both
on spiropyran structure and on media.
Scheme 2. Synthetic Route to Coumarinyl(thienyl)thiazoles
Herein we report design and synthesis of novel di-
hetarylethenes that include conjugated double bonds respon-
sible for both photochromism and fluorescence in a single
molecule. Numerous studies have been devoted to the
photochromic dihetarylethene derivatives.1 Thienylethenes
are among the most promising photochromic compounds
owing to efficient photoisomerization reaction, the thermal
stability of both isomers, and excellent fatigue resistance.
The best structures include an ethene double bond into a
cycle, prohibiting cis-trans photoisomerization of the open
form, and providing better yields of photoinduced cyclization.
Earlier we have synthesized compounds that contain thiazole
ringasacyclicethenefragmentofphotochromicdithienylethenes.13-14
Dithienylthiazoles similar to 1 have been synthesized, and
their photochromism has studied (Scheme 1). Some other
dichloromethane solution of 4 with bromine at room tem-
perature gave corresponding R-bromoketone 5 in high yield
(92%). Thiazoles 2a-e were synthesized by refluxing a
methanol solution of R-bromoketone and thioamides XC-
(S)NH2. Thioamides of acetic (a), benzoic (b), 4-methoxy-
benzoic acids (c), thiourea (d), and phenylthiourea (e) were
used. Yields of thiazoles 2a-e were 61-89%. Coumarinyl-
Scheme 1. Photochromic Dithienylthiazole13
1
(thienyl)thiazoles 2a-e were characterized by H and 13C
NMR-spectra, mass-spectra, and elemental analysis.
One can suggest a new method for fluorescence photo-
modulation of dihetarylethene system in 2: 3-4 double bond
of the coumarin moiety is responsible both for photochromic
and fluorescent properties of the molecule (Scheme 3).
photochromic dithienylthiazoles15 and 4,5-bis(thiazol-4-yl)-
thiazoles16 were also reported.
Although many derivatized dithienylethenes exhibit good
reversibility of fluorescence intensity, most of the reported
examples have relatively small quantum yields of fluores-
cence. Fluorescence data have not been reported for com-
pounds 1 as well.
Scheme 3. Photoisomerisation of Coumarinyl(thienyl)thiazoles
In search for novel structures with photomodulated
fluorescence, we have synthesized coumarinyl(thienyl)-
thiazoles 2 (Scheme 2). Many coumarin derivatives are well-
known for their excellent fluorescent properties.17,18
A synthetic pathway to 2 started from Friedel-Crafts
acylation of 2,5-dimethylthiophene with a 3-coumarinylacetyl
chloride 3, affording ethanone 4 in 71% yield. Treatment of
(12) Traven, V. F.; Miroshnikov, V. S.; Chibisova, T. A.; Barachevsky,
V. A.; Venediktova, O. V.; Strokach, Yu. P. Russ. Chem. Bull. 2005, 54,
2417.
(13) Krayushkin, M. M.; Ivanov, S. N.; Martynkin, A. Yu.; Lichitsky,
B. V.; Dudinov, A. A.; Uzhinov, B. M. Russ. Chem. Bull. 2001, 50, 116.
(14) Krayushkin, M. M.; Lichitsky, B. V.; Mikhalev, A. P.; Nabatov, B.
V.; Dudinov, A. A.; Ivanov, S. N. Russ. J. Org. Chem. 2006, 42, 860.
(15) Nakashima, T.; Atsumi, K.; Kawai, S.; Nakagawa, T.; Hasegawa,
Y.; Kawai, T. Eur. J. Org. Chem. 2007, 3212.
Besides, coumarin derivatives can undergo thermally ir-
reversible photochemical 2π + 2π dimerization upon pho-
toirradiation, thus providing another method to modulate
fluorescence.19,20
Spectral and photochemical properties of coumarinyl-
(thienyl)thiazoles 2 have been studied using acetonitrile as
a solvent (Table 1). These compounds have two intersected
(16) Kawai, S.; Nakashima, T.; Atsumi, K.; Sakai, T.; Harigai, M.;
Imamoto, Y.; Kamikubo, H.; Kataoka, M.; Kawai, T. Chem. Mater. 2007,
19, 3479.
(17) Brackman, U. Laser Dyes, Lamadachrome, Data Sheets, 2nd ed.;
Gottingen: Germany, 1997; p 268.
(18) Haugland, R. P. Handbook of Fluorescent Probes and Research
Chemicals; Spence, M. T. Z., Ed.; Molecular Probes, Inc.: Eugene, 1996.
(19) Mal, N. K.; Fujiwara, M.; Tanaka, Y. Nature 2003, 421, 350.
(20) Trenor, S. R.; Shultz, A. R.; Love, B. J.; Long, T. E. Chem. ReV.
2004, 104, 3059.
1320
Org. Lett., Vol. 10, No. 6, 2008

We have found the decrease of fluorescence intensity to
not follow the first-order kinetics model. One can suggest
that at least two processes are responsible for the decrease
of fluorescence: (1) concentration of fluorescent open form
A decreases due to photocyclization reaction, and (2)
fluorescence photoquenching operates in this system via
intermolecular mechanism of energy transfer in photosta-
tionary state from fluorescent open form A to cyclic form
B, since emission band of A and absorption band of B are
located in the same spectral region.
Table 1. Spectral Data for Open A and Cyclic B Forms of
3-(4-Thienylthiazole-5-yl)coumarins 2
entry
λAmax, nm
ꢀ
λflmax, (IA
)
fl.
λBmax, nm
2a
2b
2c
2d
2e
350
374
382
398
410
7300
14100
16300
7400
504 (125)
501 (295)
510 (280)
543 (7)
500
517
515
496
500
13400
551 (50)
Upon visible light irradiation (>470 nm) of cyclic forms
of 2, reverse spectral transformations, shown in Figure 2,
bands at 300-410 nm in electron absorption spectra and
emission bands at 500-550 nm in fluorescence spectra. A
bathochromic shift of absorption and emission maxima in
spectra of compounds 2a-e is observed due to increase of
electron donation of substituent X. However, amino-functions
at position 2 of thiazole ring (2d, 2e) provide significant
decrease of fluorescence intensity if compared with com-
pounds, bearing aryl- and alkyl groups at that position
(2a-c).
Photochemical transformations of coumarinyl(thienyl)-
thiazoles 2 have been induced by irradiation of their solutions
in acetonitrile with filtered light of Hg-Xe lamp. Thus, each
of the compounds 2 has been irradiated by light at its longest
wavelength absorption maximum.
Absorption and emission spectra of compounds 2 are
changed upon UV irradiation. Figure 1 shows UV/visible
Figure 2. Absorption spectra of 2b (4 × 10-5 M, CH3CN, 25 °C)
after UV-irradiation (365 nm) (line 1) and after irradiation with
visible light (>470 nm) for 1, 2, 4, 8, 12, 16, 24 s (lines 2-8).
(Inset) Fluorescence spectra of the same solution.
are displayed: both absorption and emission are gradually
reverted to the initial spectra, specific to open forms of 2.
In contrast to dark irreversibility of cyclic forms of
dihetarylethenes where heteroaryl fragments are bound to
cyclopentene or perfluorocyclopentene ring,1 cyclic forms
of dihetarylthiazoles undergo ring-opening reactions in the
dark.13-16 The rate of this transformation is much dependent
on the substituents at positions 2 and 5 of the thiazole ring.
Compounds 1 show the lowest dark stability and undergo
50% transformation for several hours.13 Cyclic forms of
coumarinyl(thienyl)thiazoles 2 are much more stable: half-
life of cyclic form of 2b in the dark is about 3 days and the
best thermal stability shows 2esits cyclic form concentration
decreases only for 27% after being stored for 8 days in the
dark. Apparently, electron donating substituents (for example,
phenylamino-group) at position 2 of thiazole ring provide
the highest stabilization effect for cyclic forms B.
Figure 1. Absorption spectra of 2b (4 × 10-5 M, CH3CN, 25 °C)
before (line 1) and after irradiation with UV light (365 nm) for 1,
2, 4, 8, 12 s (lines 2-6). (Inset) Fluorescence spectra of the same
solution.
absorption spectra of 2b, irradiated by 365 nm light for
different times. A new absorption band, corresponding to
cyclic form of 2b, appears at 400-500 nm region. Its
intensity increases gradually upon irradiation while absorp-
tion intensity at 350-400 nm decreases (Figure 1, lines 2-6).
Similar changes are observed in the emission spectra,
shown as an inset in Figure 1. Fluorescence intensity of 2
decreases significantly with no change of the emission
maxima position. It is obvious that only open form A of 2
is responsible for fluorescence of the photochromic system.
We have recently shown,21,22 that stability of photoinduced
forms is definitely increased in the polymeric matrices. For
(21) Barachevsky, V. A.; Karpov, R. E.; Venediktova, O. V.; Valova,
T. M.; Strokach, Yu. P.; Miroshnikov, V. S.; Chibisova, T. A.; Traven, V.
F. Russ. Chem. Bull. 2005, 54, 2425.
Org. Lett., Vol. 10, No. 6, 2008
1321

reaction, accompanied with photomodulated fluorescence.
The photoinduced changes of its spectra are shown in
Figure 3.
It follows from the comparison of the obtained spectral
data that the position of the absorption band maximum of
the photoinduced cyclic form has not been changed when
compared with that of coumarinyl(thienyl)thiazole 2b in CH3-
CN solution. Besides, the photoinduced cyclic form in
PMMA becomes rather more stable (half-life is 14 days).
In conclusion, the effects of the introduction of coumarin
moiety in dihetarylthiazoles include: coumarinyl(thienyl)-
thiazoles possess prominent fluorescence in the open form
and much better thermal stability of their cyclic forms.
Insertion of methyl group in the position 4 of coumarin
moiety might provide further increase of thermal stability
of these novel photomodulated fluorophores. The structural
modification of coumarinyl(thienyl)thiazoles and study of
their behavior in polymeric matrices are in progress now.
Figure 3. Absorption spectra of 2b (PMMA-film, 25 °C) before
(line 1) and after irradiation with UV light (365 nm) for 20, 40,
60, 90, 150, 250 s (lines 2-7). (Inset) Fluorescence spectra of the
same sample.
Acknowledgment. Authors thank the Russian Foundation
for Basic Research for financial support (Grant # 07-03-
00936).
example, introduction of indoline spiropyrans of coumarin
series into polymethylmetacrylate (PMMA) film significantly
increases thermostability of photoinduced form if compared
with that in solution. We have found coumarinyl(thienyl)-
thiazole 2b in the PMMA film to undergo photochromic
Supporting Information Available: Experimental de-
1
tails, H and 13C NMR-spectra, mass spectra, elemental
analysis, UV/vis absorption and fluorescence spectra, irradi-
ated by UV and visible light for different times. This material
is available free of charge via the Internet at http://pubs.acs.org.
(22) Dolotov, S. M.; Miroshnikov, V. S.; Chibisova, T. A.; Sin, S.-L.;
Venediktova, O. V.; Valova, T. M.; Dunaev, A. A.; Strokach, Yu. P.;
Barachevsky, V. A.; Traven, V. F. Russ. Chem. Bull. 2007, 56, 116.
OL800223G
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Org. Lett., Vol. 10, No. 6, 2008