Coumarinyl(thienyl)thiazoles as new fluorescent molecular photoswitches

Article abstract of DOI:10.1007/s11172-009-0025-3

A number of new photochromic 3-(4-phenylthiazol-5-yl)-and 3-(4-hetarylthiazol-5-yl)- coumarins has been synthesized. These compounds possess properties of molecular photo- switches providing a reversible change of the fluorescence intensity in the visible

Full text of DOI:10.1007/s11172-009-0025-3

Russian Chemical Bulletin, International Edition, Vol. 58, No. 1, pp. 162—169, January, 2009
162
Coumarinyl(thienyl)thiazoles as new fluorescent molecular
photoswitches*
A. Yu. Bochkov,a V. N. Yarovenko,b V. A. Barachevskii,c B. V. Nabatov,b
M. M. Krayushkin,b S. M. Dolotov,a V. F. Traven´,a and I. P. Beletskayad
aD. I. Mendeleev University of Chemical Technology of Russia,
9 Miusskaya pl., 125047 Moscow, Russian Federation.
Eꢀmail: traven@muctr.ru
bN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
cPhotochemistry Center of the Russian Academy of Sciences,
7a ul. Novatorov, 119421 Moscow, Russian Federation
dA. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
31 Leninsky prosp., 119071 Moscow, Russian Federation
A number of new photochromic 3ꢀ(4ꢀphenylthiazolꢀ5ꢀyl)ꢀ and 3ꢀ(4ꢀhetarylthiazolꢀ5ꢀyl)ꢀ
coumarins has been synthesized. These compounds possess properties of molecular photoꢀ
switches providing a reversible change of the fluorescence intensity in the visible region of the
spectrum upon alternating irradiation of their solutions with the visible and UV light. Irradiation
with the UV light (λ < 400 nm) leads to their electrocyclization and loss of fluorescence,
whereas irradiation of the cyclic form with the visible light (λ > 400 nm) returns the system to
the state with the original absorption and fluorescence spectra. Switching of fluorescence is
also observed in polymer matrices.
Key words: photochromism, dihetarylethenes, 3ꢀhetarylcoumarins, 4,5ꢀdihetarylthiazoles,
molecular switches, photomodulation of fluorescence.
Scheme 1
The interest to dihetarylethenes prone to photoinduced
electrocyclic reactions (Scheme 1) is caused by the possiꢀ
bility of their use as materials for optoelectronics, in parꢀ
ticular, for the development of lightꢀsensitive recording
media with the ultrahigh informational capacity for the
threeꢀdimensional optical memory.1,2 Introduction of a
bridged double bond into a cycle fixes its cisꢀconfiguraꢀ
tion, that increases the quantum yields of the photoꢀ
cyclization reaction. The dihetarylethenes containing
fragments of cyclopentene and perfluorocyclopentene
as the ethene bridge are the most studied.1 In addition,
examples of dihetarylethenes in which the hetaryl fragments
are bonded by a hetarene ''bridge'',3 in particular, the
thiazole one4—7 are also known. Among dihetarylethenes,
derivatives containing at least one thiophene fragment
conjugated with the C=C double bond possess especially
valuable photochromic characteristics.
In the recent years, structures of photochromic comꢀ
pounds able to function as molecular photoswitches,
which upon the action of light reversibly change not only
color, but also other properties, for example, fluorescence,
are under intensive study.8 Such systems can be used, in
particular, for the development of photochromic recordꢀ
ing media with nonꢀdestructive readout of recorded inꢀ
formation.9—15
* Dedicated to Academician A. I. Konovalov on his 75th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 162—169, January, 2009.
1066ꢀ5285/09/5801ꢀ0162 © 2009 Springer Science+Business Media, Inc.

Novel coumarinꢀbased fluorescent switches
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
163
During study of coumarin derivatives capable to the
photoinduced change of fluorescence,16—18 we obtained a
number of new unsymmetrical dihetarylethenes posꢀ
sessing properties of fluorescent photoswitches. These
dihetarylethenes contain a coumarin fragment at position
5 of the thiazole ''bridge'' and the thiophene or benzothioꢀ
phene fragment at position 4 (see Scheme 1). Such comꢀ
pounds possess an intensive fluorescence which reversibly
changes under the action of the visible and UV light.
Earlier,4 we have described the synthesis of dithienylꢀ
thiazoles (Scheme 2). The Friedel—Crafts reaction of
thienylglyoxal 1 with 2,5ꢀdimethylthiophene afforded
acyloin 2, which further was converted into αꢀchloroꢀ
ketone 3 by the standard method. The subsequent reflux
Scheme 2
Scheme 3
6a, 7a, 8a—e: Y = HC=CH; R1 = R2 = R3 = H
6b, 7b, 9a—e: Y = S; R1 = R2 = Me, R3 = H
6c, 7c, 10a—e: Y = S; R1 = H, R2, R3 = —HC=CH—CH=CH—
8—10: X = Me (a), Ph (b), 4ꢀOMeC6H4 (c), NH2 (d), NHPh (e)

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Bochkov et al.
Table 1. Spectral characteristics of the starting and photoꢀ
induced forms of 3ꢀ(4ꢀarylthiazolꢀ5ꢀyl)coumarins 8—10
of a methanol solution of 3 and thiourea led to 2ꢀaminoꢀ
4,5ꢀdithienylthiazole 4. Later, we have shown5 that acyloin
2 can be converted into thiazole 4 in one step by the
reaction with thiourea in trifluoroacetic acid.
abs
fl
photo
Comꢀ
pound
λ
ε
λ
max/nm
λ
Aphoto
max
max
max
/nm
(Ifl (rel. units)) /nm
The realization of Scheme 2 for the coumarin derivaꢀ
tives turned out to be somewhat difficult. The oxidation
of 3ꢀacetylcoumarin upon treatment with SeO2 did not lead
to 3ꢀcoumarinylglyoxal, the coumarin analog of compound
1. Therefore, we have chosen an alternative approach to
the synthesis of 3ꢀ(thienylthiazolyl)coumarins (Scheme 3).
Ethanones 6 turned out to be available by the Friedel—
Crafts acylation of benzene, 2,5ꢀdimethylthiophene, and
2ꢀmethylbenzothiophene with 3ꢀcoumarinylacetyl chloꢀ
ride (5). Earlier,19 an approach to the preparation of the
acyl chloride from 3ꢀcoumarinylacetic acid by the proꢀ
longed reflux of the acid in excess thionyl chloride has
been described. However, this method is inconvenient
since a significant resinification of the reaction mixture
was observed in the course of the reaction. We applied
more mild conditions: a solution of 3ꢀcoumarinylacetic
acid in dichloromethane was kept with excess thionyl
chloride for 12 h at room temperature. After the solvent
was evaporated, a crystalline acyl chloride was obtained,
which was used in the acylation reaction. The acylation of
benzene with acyl chloride 5 in the presence of AlCl3 at
50 °C for 3 h leads to ketone 6a in 75% yield. The reaction
of the acyl chloride with 2,5ꢀdimethylthiophene and
2ꢀmethylbenzothiophene was carried out at reduced
temperatures (–5—10 °C). Ethanones 6b and 6c were
obtained in 71 and 61% yields, respectively. The strucꢀ
tures of compounds 6a—c were confirmed by elemental
analysis, 1H NMR spectroscopic, and mass spectrometric
data. It should be noted that to successfully carry out the
acylation reaction with participation of acyl chloride 5,
the use of a large amount of aluminum chloride turned
out to be necessary, in contrast to the analogous reactions
with participation of aliphatic and aromatic acyl chloꢀ
rides. When 1.1 mole of AlCl3 per 1 mole of acyl chloride
5 was used, we failed to isolate the desired acylation prodꢀ
ucts 6a—c. It was found that the formation of these products
begins only when more than 2 moles of AlCl3 per 1 mole
of acyl chloride 5 are present in the reaction mixture.
Obviously, this can be explained by the fact that the first
mole of AlCl3 is consumed in the complex formation with
the lactone fragment of coumarin, whereas the second, in
the activation of the acyl chloride function in accordance
with the standard scheme of the Friedel—Crafts acylaꢀ
tion. It is known20 that coumarins form complexes with
Lewis acids, in particular, with AlCl3.
8a
8b
8c
8d
8e
9a
9b
9c
338
362
390
392
402
350
374
382
398
410
365
376
378
406
390
7400
9360
7440
6880
8780
7300
14100
16300
7400
13400
3200
5450
5400
6450
8530
426 (230)
445 (80)
458 (410)
474 (165)
552 (360)
504 (125)
501 (295)
510 (280)
543 (7)
551 (50)
466 (125)
468 (75)
473 (260)
505 (220)
490 (215)
—
—
—
—
—
500
517
515
496
500
481
502
502
480
495
—
—
—
—
—
0.22
0.22
0.30
0.28
0.25
0.06
0.04
0.04
0.21
0.10
9d
9e
10a
10b
10c
10d
10e
abs
fl
Note. λ max and λ max are the absorption and fluorescence band
maxima, respectively; ε/L cm–1 mol–1 is the coefficient of
photo
molar extinction; λ
is the wavelength of the absorption
max
maximum of the photoinduced form; Aphoto
is the value of
max
optical density in the absorption band maximum of the photoꢀ
induced form in the photostationary state.
4ꢀmethoxybenzoic acids, as well as thiourea and pheꢀ
nylthiourea. The yields of thiazoles 8—10 were 54—94%.
3ꢀ(4ꢀPhenylthiazolꢀ5ꢀyl)coumarins 8 and 3ꢀ(4ꢀhetarylꢀ
thiazolꢀ5ꢀyl)coumarins 9 and 10 synthesized were charꢀ
acterized by elemental analysis, H NMR spectroscopy,
and mass spectrometry data.
Spectral properties of the compounds synthesized were
studied in acetonitrile. The results of spectral and kinetic
studies of thiazoles 8—10 are given in Table 1.
In the absorption spectra of each thiazole 8a—e, two
partially overlapping absorption bands are recorded in the
region 300—410 nm (Fig. 1, curve 1). In the sequence of comꢀ
1
A
I (rel. units)
0.6
0.4
0.2
0
600
400
200
2
1
The reaction of ethanones 6a—c with bromine in
dichloromethane at room temperature afforded αꢀbromoꢀ
ketones 7a—c in 83—92% yield. Thiazoles 8—10 were
obtained by reflux of methanol solutions of αꢀbromoꢀ
ketones 7a—c with compounds containing thioamide
fragment. We used thioamides of acetic, benzoic, and
0
300
400
500
600
λ/nm
Fig. 1. Absorption (1) and emission spectra (2) of compound 8e.

Novel coumarinꢀbased fluorescent switches
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
165
pounds 8a (X = Me), 8b (X = Ph), 8c (X = 4ꢀMeOC6H4),
8d (X = NH2), 8e (X = NHPh), a bathochromic shift of
the longꢀwave absorption band maximum is observed,
which is caused, apparently, by the enhancement of donor
properties of substituents in this sequence. 3ꢀ(4ꢀPhenylꢀ
thiazolꢀ5ꢀyl)coumarins 8 fluoresce in the visible region
of the spectrum, the emission maxima are in the region
420—550 nm (see Fig. 1, curve 2) and they are also bathoꢀ
chromiccally shifted in the sequence 8a—e (see Table 1).
Absorption and fluorescence spectra of compounds 9
before irradiation are analogous in its form to the absorpꢀ
tion spectra of compounds 8. In the sequence of comꢀ
pounds 9a—e, a bathochromic shift of the absorption and
fluorescence band maxima is also observed. However, in
contrast to compounds 8, the presence of the amino group
at position 2 of the thiazole ring (compounds 9d,e) leads
to a significant decrease in the intensity of fluorescence in
comparison with 2ꢀarylꢀ and 2ꢀalkylthiazoles 9a—c.
In the absorption spectra of compounds 10, two overꢀ
lapping absorption bands in the region 280—400 nm
(Fig. 2, curve 1) can be also highlighted. In the spectra of
2ꢀphenylꢀsubstituted thiazoles 10b,c, the overlapping is
especially pronounced in comparison with analogous
compounds 8b,c and 9b,c (Fig. 3, curve 1), that leads to
the appearance of a shoulder in the absorption spectrum.
The absorption and emission bands in the spectra of comꢀ
pounds 10a—e are additionally bathochromically shifted
in comparison with compounds 8 and 9.
Photochemical transformatons of compounds 8—10
were studied by irradiation of their acetonitrile solutions
with the filtered light of mercuryꢀxenon lamp. The irraꢀ
diation with the wavelength corresponding to the longꢀ
wave absorption band maximum of the starting forms of
compounds 8—10 was separated using composite glass
light filters.
Irradiation of solutions of 3ꢀ(4ꢀphenylthiazolꢀ
5ꢀyl)coumarins 8 with the UV light did not cause any
changes in the spectra, that suggests the absence of the
electroꢀcyclization reaction (see Scheme 1). Conversely,
compounds 9 and 10 turned out to be capable of photoꢀ
induced changes in both the absorption and the fluoreꢀ
scence spectra. The irradiation of solutions of the open
forms of compounds 9 with the filtered UV light leads to a
decrease in intensity of the absorption band in the region
350—400 nm and to the appearance of the absorption
band in the visible region of the spectrum (496—517 nm),
the intensity of which grows with time (see Fig. 3, curves
2—6). The intensity of fluorescence on photoirradiation
of compounds 9a—e decreases by 3—6 times (Fig. 4) with
the positions of the fluorescence band maxima remaining
unchanged (see Table 1). The retention of the fluoresꢀ
cence maxima positions suggests that only the initial form
of these compounds causes their fluorescence.
A
I (rel. units)
0.6
0.4
0.2
0
0.6
0.4
0.2
2
1
3
0
300
400
500
600
λ/nm
Fig. 2. Absorption (1) and emission spectra (2) of the initial
form and absorption spectrum of the photoinduced form (3) of
compound 10c.
The irradiation of the photoinduced cyclic forms of
compounds 9 with light of the wavelength corresponding
Ifl (rel. units)
A
1
0.6
0.4
300
200
6
0.2
6
100
1
0
400
500
600
λ/nm
300
400
500
600
λ/nm
Fig. 3. Absorption spectra of compound 9b in solution before (1)
and after irradiation with light of 365 nm in wavelength for 1 (2),
2 (3), 4 (4), 8 (5), and 12 s (6).
Fig. 4. Fluorescence spectra of compound 9b in solution before
(1) and after irradiation with light of 365 nm in wavelength for
1 (2), 2 (3), 4 (4), 8 (5), and 12 s (6).

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Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
Bochkov et al.
Scheme 4
A
0.4
0.2
0
2
4
6
8
10
N
Fig. 6. Fatigue resistance of phototransformations (optical
density at 516 nm) of compound 9b in solution (acetonitrile);
here and on Fig. 7 N means the cycle number.
Compounds 9 are able to undergo repeated mutually
reversible phototransformations depicted by Scheme 4.
However, already after 10—12 cycles of phototransformaꢀ
tions, the optical density in the absorption maximum of
the colored form is lower 50% of the initial value (Fig. 6).
The photocyclization reactions of compounds 9 turned
out to be thermally reversible. After irradiation of solutions
with the UV light until the photostationary state is reached,
a slow decrease in the value of optical density in the
absorption band maximum of the photoinduced cyclic
form was observed on keeping the solutions in the dark.
The rate of spontaneous bleaching in the dark depends on
the nature of substituent in the thiazole ring. Compound
9b having the phenyl substituent completely decolorizes
for 8 days, whereas other compound decolorize only partꢀ
ially for this time. Probably, the donor substituents (methyl,
pꢀmethoxyphenyl, and phenylamino groups) stabilize the
closed form of compounds 9. The effect mentioned is the
strongest in the case of phenylamino group 9e: the optical
density in the absorption band maximum of the closed
form of compound 9e decreases by only 27% for 8 days.
This agrees with the fact that the closed forms of dithienylꢀ
ethenes connected by the azole bridges are thermally unꢀ
stable.4—7 The time of 50% conversion of the closed form 4
into the open one is only several hours. From the data
obtained it follows that the introduction of the coumarin
fragment into the conjugated system of thienylthiazole signiꢀ
ficantly increases the thermal stability of the closed form.
On the prolonged irradiation of solutions of comꢀ
pounds 9 with the nonfiltered light of a mercuryꢀxenon
lamp, a photodecomposition is observed. The photoꢀ
decomposition rate depends on the nature of substituent
at position 2 of the thiazole ring. Compounds containing
methyl and pꢀmethoxymethyl substituents turned out to
be the least lightꢀresistant. The complete decomposition
was observed after irradiation for 80—120 s.
to their absorption maximum in the visible region leads to
the reverse phototransformatons of the closed form into
the open one with virtually complete recovery of the
absorption and fluorescence spectra of the compound
initial form. The photochromic transformations of comꢀ
pounds 9 observed are explained by the photoinduced
electrocyclic reaction (Scheme 4), rather than, for
example, by the [2+2]ꢀcyclodimerization of compounds
9 at the 3—4 double bond of the coumarin fragment.
The explanation suggested confirms the fact of the
appearance of a longꢀwave absorption in the EAS, that
corresponds to an increase in the chain of conjugation on
passing from the open form to the closed. In addition, the
growth of the absorption intensity in the region 500 nm
on irradiation of the starting forms follows the first order
kinetics, rather than the second order, which would have
been the case for the photoinduced reaction of a [2+2]ꢀ
cycloaddition (Fig. 5).
ln(1 – A/Amax
)
0
–1
–2
–3
0
2
4
6
8
t/s
Fig. 5. Optical density changes on coloring of compound 9b in
solution in coordinates of the first order reaction.

Novel coumarinꢀbased fluorescent switches
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
167
A
tion. In addition, it turned out to be possible to increase
the stability in the dark of the closed form up to several
days instead of several hours, which was reported earlier,
by the variation of the substituent at position 2 of the
thiazole ring in the coumarin derivatives.4 Additional
increase in the thermal stability of the closed forms
of 3ꢀ(4ꢀarylthiazolꢀ5ꢀyl)coumarins can be successfully
achieved by their incorporation into the poly(methyl
methacrylate) film.
0.2
0.1
Experimental
1H NMR spectra were recorded on a Bruker ACꢀ200
spectrometer in CDCl3 and (CD3)2SO. Melting points were
measured on a Boetius heating block. Mass spectra (EI) were
recorded on a Kratos MSꢀ30 instrument (70 eV) with the
direct injection of a substance into the ion source. Thinꢀlayer
chromatography was performed on Merck 60 F254 plates.
A singleꢀbeam CARY UV 50 spectrophotometer (Varian)
was used for the recording of absorption spectra of solutions.
Fluorescence spectra of solutions were recorded on a CARY
ECLIPSE spectrofluorimeter (Varian). Absorption and fluoreꢀ
scence spectra were recorded in 1ꢀcm thick cuvettes. Acetonitrile
(HPLC grade, Acros) was used as the solvent. Concentration of
solutions for the absorption and fluorescence spectra recording
0
10
N
Fig. 7. Fatigue resistance of phototransformations (optical
density at 516 nm) of compound 9b in the PMMA film.
In the case of 2ꢀmethylbenzothiophene derivatives 10,
the irradiation with the UV light leads also to the appearꢀ
ance of a new absorption band in the visible region (see
Fig. 2, curve 2). However, its intensity is considerably
lower than that for the colored closed forms of compounds
9. Irradiation of the colored forms of compounds 10 with
the visible light leads to the disappearance of the absorption
band in the visible region, however, the absorption specꢀ
trum of the initial open form is not completely recovered,
that can suggest the more efficient photodecomposition
of these compounds in comparison with compounds 9.
Earlier,17,21 we have shown that the introduction of
spiropyrans of the coumarin series into the poly(methyl
methacryate) significantly increases stability of the
photoinduced form in comparison with the solution. We
studied also the phototransformatons of compounds 9 in
the poly(methyl methacrylate) film. The spectral changes
observed on irradiation of the film with the visible and
UV light are similar to the changes in solution. The posiꢀ
tions of the absorption and fluorescence bands are virtuꢀ
ally unchanged relatively to the solution in acetonitrile.
However, the introduction of 3ꢀ(4ꢀhetarylthiazolꢀ
5ꢀyl)coumarins into the polymer matrix allowed us to
increase the fatigue resistance of phototransformations: a
50% decrease in optical density in the absorption maxiꢀ
mum of the cyclic form was observed after 18 cycles of
phototransformatons (Fig. 7). In addition, the stability in
the dark of the cyclic forms in the polymer is significantly
higher than in solution: the optical density in the absorpꢀ
tion maximum of the closed form of the film, irradiated
with the UV light until the photostationary state, decreases
by 50% for 30 days (compound 9b).
was 4•10–5 mol L–1
.
For the photochemical studies of solutions, the visible and
UV filtered irradiation of a Hamamatsu LCꢀ4 gasꢀdischarge
mercuryꢀxenon lamp, separated using composite glass light filters
from the standard set of colored glasses, was used.
The synthesis of compounds 6a—c was described by us
earlier.22
Bromination of 3ꢀ(2ꢀarylꢀ2ꢀoxoethyl)coumarins (general
procedure). Bromine (1 mmol) was added to a solution of ketone
6a—c (1 mmol) in dichloromethane (15 mL) and the mixture
was kept for ~14 h. The next day, the solvent was evaporated,
the residue was chromatographed on a short column with silica
gel (eluent, dichloromethane).
3ꢀ(1ꢀBromoꢀ2ꢀoxoꢀ2ꢀphenylethyl)ꢀ2Hꢀchromenꢀ2ꢀone (7a).
The yield was 89%, white crystals, m.p. 143—144 °C. Found
(%): C, 59.34; H, 3.32. C17H11BrO3. Calculated (%): C, 59.50;
H, 3.23. 1H NMR (CDCl3), δ: 6.66 (s, 1 H, CHBr); 7.35—8.13
(m, 9 H arom.); 8.26 (s, 1 H, H(4) coumarin). MS, m/z
(Irel (%)): 344 [M]+ (5), 263 [M – Br]+ (3), 235 (7), 218 (3), 207
(12), 191 (22), 178 (18), 130 (33), 114 (12), 108 (100), 89 (8), 78
(98), 63 (28), 51 (97), 38 (37).
3ꢀ[1ꢀBromoꢀ2ꢀ(2,5ꢀdimethylꢀ3ꢀthienyl)ꢀ2ꢀoxoethyl]ꢀ
2Hꢀchromenꢀ2ꢀone (7b). The yield was 92%, white crystals,
m.p. 122—123 °C. Found (%): C, 54.29; H, 3.58; S, 8.31.
C17H13BrO3S. Calculated (%): C, 54.12; H, 3.47; S, 8.50.
1H NMR (CDCl3), δ: 2.44 (s, 3 H, Me(5) thiophene); 2.70 (s,
3 H, Me(2) thiophene); 6.33 (s, 1 H, CHBr); 7.17 (s, 1 H,
H(4) thiophene); 7.33—7.38 (m, 2 H, H(5)—H(8) coumarin);
7.54—7.61 (m, 2 H, H(6)—H(7) coumarin); 8.23 (s, 1 H, H(4)
coumarin). MS, m/z (Irel (%)): 377 [M]+ (1), 298 [M – Br]+
(6), 269 (7), 217 (25), 139 (100), 111 (27).
In conclusion, a number of differences between 3ꢀ(4ꢀarylꢀ
thiazolꢀ5ꢀyl)coumarins studied in this work and dithienylꢀ
thiazoles described earlier4,5 should be highlighted. Inꢀ
troduction of the coumarin fragment gave to the new thiazoles
pronounced fluorescent properties, changing on irradiaꢀ
3ꢀ[1ꢀBromoꢀ2ꢀ(2ꢀmethylbenzo[b]thiophenꢀ3ꢀyl)ꢀ2ꢀoxoethyl]ꢀ
2Hꢀchromenꢀ2ꢀone (7c). The yield was 83%, white crystals,
m.p. 147—149 °C. Found (%): C, 58.25; H, 3.28; S, 7.63.

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Bochkov et al.
C20H13BrO3S. Calculated (%): C, 58.12; H, 3.17; S, 7.76.
1H NMR (CDCl3), δ: 2.88 (s, 3 H, Me); 6.48 (s, 1 H, CHBr);
7.33—8.52 (m, 9 H arom.). MS, m/z (Irel (%)): 413 [M]+ (4),
255 (100), 227 (30), 175 (76), 149 (49).
Preparation of thiazoles 8—10 (general procedure). A solution
of bromoketone 7 (0.25 mmol) and the corresponding thioamide
(0.3 mmol) in methanol (25 mL) was refluxed for 3 h, cooled,
and poured in aqueous K2CO3 (2 g in water (150 mL)). The
crystals formed were filtered off.
coumarin); 7.33—7.65 (m, 4 H, H(5)—H(8) coumarin). MS,
m/z (Irel (%)): 415 [M]+ (100).
3ꢀ[4ꢀ(2,5ꢀDimethylꢀ3ꢀthienyl)ꢀ2ꢀ(4ꢀmethoxyphenyl)ꢀ
1,3ꢀthiazolꢀ5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (9c). The yield was 61%,
yellow crystals, m.p. 142—143 °C. Found (%): C, 67.53;
H, 4.44; N, 3.02; S, 14.23. C25H19NO3S2. Calculated (%):
C, 67.39; H, 4.30; N, 3.14; S, 14.39. 1H NMR (CDCl3), δ: 2.33
(s, 3 H, Me(5) thiophene); 2.47 (s, 3 H, Me(2) thiophene); 3.90
(s, 3 H, OMe); 6.78 (s, 1 H, H(4) thiophene); 7.02 (d, 2 H,
J = 8.4 Hz); 7.28—7.60 (m, 5 H, H(4)—H(8) coumarin); 8.22
(d, 2 H, J = 8.4 Hz). MS, m/z (Irel (%)): 445 [M]+ (100).
3ꢀ[2ꢀAminoꢀ4ꢀ(2,5ꢀdimethylꢀ3ꢀthienyl)ꢀ1,3ꢀthiazolꢀ5ꢀyl]ꢀ
2Hꢀchromenꢀ2ꢀone (9d). The yield was 80%, yellow crystals,
m.p. 160—165 °C (decomp.). Found (%): C, 60.88; H, 3.81;
N, 7.97; S, 18.01. C18H14N2O2S2. Calculated (%): C, 61.00;
3ꢀ(2ꢀMethylꢀ4ꢀphenylꢀ1,3ꢀthiazolꢀ5ꢀyl)ꢀ2Hꢀchromenꢀ2ꢀone
(8a). The yield was 70%, white crystals, m.p. 167—168 °C.
Found (%): C, 71.53; H, 4.20; N, 4.29; S, 10.15. C19H13NO2S.
1
Calculated (%): C, 71.45; H, 4.10; N, 4.39; S, 10.04. H NMR
(DMSOꢀd6), δ: 3.45 (s, 3 H, Me); 7.34—7.68 (m, 9 H arom.);
7.98 (s, 1 H, H(4) coumarin). MS, m/z (Irel (%)): 319 [M]+
(100), 304, [M – Me]+ (24), 291 (31), 277 (20), 250 (21), 221
(35), 205 (13), 189 (24).
1
H, 3.98; N, 7.90; S, 18.09. H NMR (CDCl3), δ: 2.21 (s, 3 H,
Me(5) thiophene); 2.43 (s, 3 H, Me(2) thiophene); 5.16 (br.s,
2 H, NH2); 6.68 (s, 1 H, H(4) thiophene); 7.22—7.52 (m, 5 H,
H(4)—H(8) coumarin). MS, m/z (Irel (%)): 354 [M]+ (100).
3ꢀ[4ꢀ(2,5ꢀDimethylꢀ3ꢀthienyl)ꢀ2ꢀ(phenylamino)ꢀ1,3ꢀthiazolꢀ
5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (9e). The yield was 89%, yellow
crystals, m.p. 172 °C (decomp.). Found (%): C, 67.03; H, 4.30;
N, 6.38; S, 14.74. C24H18N2O2S2. Calculated (%): C, 66.95;
3ꢀ(2,4ꢀDiphenylꢀ1,3ꢀthiazolꢀ5ꢀyl)ꢀ2Hꢀchromenꢀ2ꢀone (8b).
The yield was 96%, yellow crystals, m.p. 157—158 °C.
Found (%): C, 75.71; H, 3.84; N, 3.57; S, 8.36. C24H15NO2S.
1
Calculated (%): C, 75.57; H, 3.96; N, 3.67; S, 8.41. H NMR
(CDCl3), δ: 7.19—8.34 (m, 15 H arom.). MS, m/z (Irel (%)):
381 [M]+ (100), 353 (25), 277 (27), 250 (22), 221 (52), 205 (21),
189 (42), 176 (16).
1
H, 4.21; N, 6.51; S, 14.89. H NMR (CDCl3), δ: 2.26 (s, 3 H,
3ꢀ[2ꢀ(4ꢀMethoxyphenyl)ꢀ4ꢀphenylꢀ1,3ꢀthiazolꢀ5ꢀyl]ꢀ
2Hꢀchromenꢀ2ꢀone (8c). The yield was 90%, yellow crystals,
m.p. 196—197 °C. Found (%): C, 72.77; H, 4.30; N, 3.35;
S, 7.91. C25H17NO3S. Calculated (%): C, 72.97; H, 4.16; N, 3.40;
Me(5) thiophene); 2.40 (s, 3 H, Me(2) thiophene); 6.69 (s, 1 H,
H(4) thiophene); 7.05—7.53 (m, 10 H arom.); 8.50 (br.s, 1 H,
NH). MS, m/z (Irel (%)): 430 [M]+ (100).
3ꢀ[2ꢀMethylꢀ4ꢀ(2ꢀmethylbenzo[b]thiophenꢀ3ꢀyl)ꢀ1,3ꢀthiazolꢀ
5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (10a). The yield was 68%, white
crystals, m.p. 135—136 °C. Found (%): C, 67.68; H, 3.98;
N, 3.49; S, 16.60. C22H15NO2S2. Calculated (%): C, 67.84;
H, 3.88; N, 3.60; S, 16.46. 1H NMR (CDCl3), δ: 2.56, 2.82
(both s, 3 H each, Me); 6.80—7.80 (m, 9 H arom.). MS, m/z
(Irel (%)): 389 [M]+ (100), 374 [M – Me]+ (35).
1
S, 7.79. H NMR (CDCl3), δ: 3.88 (s, 3 H, OMe); 6.96—8.01
(m, 14 H arom.). MS, m/z (Irel (%)): 411 [M]+ (100), 278 (34),
250 (23), 221 (27), 205 (9), 189 (14).
3ꢀ(2ꢀAminoꢀ4ꢀphenylꢀ1,3ꢀthiazolꢀ5ꢀyl)ꢀ2Hꢀchromenꢀ2ꢀone
(8d). The yield was 68%, yellow crystals, m.p. 193 °C (decomp.).
Found (%): C, 67.52; H, 3.85; N, 8.59; S, 10.18. C18H12N2O2S.
1
Calculated (%): C, 67.48; H, 3.78; N, 8.74; S, 10.01. H NMR
3ꢀ[4ꢀ(2ꢀMethylbenzo[b]thiophenꢀ3ꢀyl)ꢀ2ꢀphenylꢀ1,3ꢀthiazolꢀ
5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (10b). The yield was 54%, yellow
crystals, m.p. 139—140 °C. Found (%): C, 72.01; H, 3.89;
N, 3.01; S, 14.33. C27H17NO2S2. Calculated (%): C, 71.82;
(CDCl3), δ: 5.19 (br.s, 2 H, NH2); 7.15—7.59 (m, 10 H arom.).
MS, m/z (Irel (%)): 320 [M]+ (100), 305 (6), 292 (14), 278 (10),
205 (10), 221 (13), 189 (13).
1
3ꢀ(4ꢀPhenylꢀ2ꢀphenylaminoꢀ1,3ꢀthiazolꢀ5ꢀyl)ꢀ2Hꢀchromenꢀ
2ꢀone (8e). The yield was 94%, orange crystals, m.p. 205—206 °C.
Found (%): C, 72.62; H, 4.13; N, 7.01; S, 7.99. C24H16N2O2S.
H, 3.79; N, 3.10; S, 14.20. H NMR (CDCl3), δ: 2.59 (s, 3 H,
Me); 7.23—7.69 (m, 14 H arom.). MS, m/z (Irel (%)): 451 [M]+
(100).
1
Calculated (%): C, 72.71; H, 4.07; N, 7.07; S, 8.09. H NMR
2ꢀ(4ꢀMethoxyphenyl)ꢀ3ꢀ[4ꢀ(2ꢀmethylbenzo[b]thiophenꢀ
3ꢀyl)ꢀ1,3ꢀthiazolꢀ5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (10c). The yield was
73%, yellow crystals, m.p. 158—159 °C. Found (%): C, 69.73;
H, 3.87; N, 2.99; S, 13.30. C28H19NO3S2. Calculated (%):
C, 69.83; H, 3.98; N, 2.91; S, 13.32. 1H NMR (CDCl3), δ: 2.58,
3.89 (both s, 3 H each, OMe); 6.98—8.20 (m, 13 H arom.). MS,
m/z (Irel (%)): 481 [M]+ (100), 454 (12), 348 (11), 315 (11), 287
(10), 258 (11), 253 (37).
3ꢀ[2ꢀAminoꢀ4ꢀ(2ꢀmethylbenzo[b]thiophenꢀ3ꢀyl)ꢀ1,3ꢀthiazolꢀ
5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (10d). The yield was 65%, yellow
crystals, m.p. 172—176 °C (decomp.). Found (%): C, 64.63;
H, 3.65; N, 7.07; S, 16.48. C21H14N2O2S2. Calculated (%):
C, 64.59; H, 3.61; N, 7.17; S, 16.42. 1H NMR (CDCl3), δ: 2.56
(s, 3 H, Me); 5.28 (br.s, 2 H, NH2); 6.98—7.82 (m, 8 H arom.);
8.03 (s, 1 H, H(4) coumarin). MS, m/z (Irel (%)): 390 [M]+
(100), 375 (17), 362 (14), 348 (20), 332 (26).
(CDCl3), δ: 7.07—7.63 (m, 15 H arom.); 7.77 (br.s, 1 H, NH).
MS, m/z (Irel (%)): 396 [M]+ (100), 293 (12), 278 (9), 265 (8),
251 (9), 237 (9), 221 (10).
3ꢀ[4ꢀ(2,5ꢀDimethylꢀ3ꢀthienyl)ꢀ2ꢀmethylꢀ1,3ꢀthiazolꢀ5ꢀyl]ꢀ
2Hꢀchromenꢀ2ꢀone (9a). The yield was 64%, white crystals,
m.p. 150—151 °C. Found (%): C, 64.63; H, 4.11; N, 4.02;
S, 9.21. C19H15NO2S2. Calculated (%): C, 64.56; H, 4.28;
N, 3.96; S, 9.05. 1H NMR (CDCl3), δ: 2.35 (s, 3 H, Me(5)
thiophene); 2.53 (s, 3 H, Me(2) thiophene); 3.27 (s, 3 H, Me(2)
thiazole); 6.81 (s, 1 H, H(4) thiophene); 7.33—7.66 (m, 5 H,
H(4)—H(8) coumarin). MS, m/z (Irel (%)): 353 [M]+ (100), 338
[M – Me]+ (21), 325 (12), 311 (7), 294 (6), 279 (18), 251 (14),
219 (39), 208 (13), 189 (7), 139 (48).
3ꢀ[4ꢀ(2,5ꢀDimethylꢀ3ꢀthienyl)ꢀ2ꢀphenylꢀ1,3ꢀthiazolꢀ5ꢀyl]ꢀ
2Hꢀchromenꢀ2ꢀone (9b). The yield was 76%, yellow crystals,
m.p. 170—171 °C. Found (%): C, 69.46; H, 4.00; N, 3.45;
S, 15.32. C24H17NO2S2. Calculated (%): C, 69.37; H, 4.12;
3ꢀ[4ꢀ(2ꢀMethylbenzo[b]thiophenꢀ3ꢀyl)ꢀ2ꢀ(phenylamino)ꢀ
1,3ꢀthiazolꢀ5ꢀyl]ꢀ2Hꢀchromenꢀ2ꢀone (10e). The yield was 82%,
yellow crystals, m.p. 185 °C (decomp.). Found (%): C, 69.42;
H, 3.80; N, 6.07; S, 13.83. C27H18N2O2S2. Calculated (%):
1
N, 3.37; S, 15.43. H NMR (CDCl3), δ: 2.34 (s, 3 H, Me(5)
thiophene); 2.48 (s, 3 H, Me(2) thiophene); 6.78 (s, 1 H, H(4)

Novel coumarinꢀbased fluorescent switches
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 1, January, 2009
169
C, 69.51; H, 3.89; N, 6.00; S, 13.74. 1H NMR (CDCl3), δ: 2.44
(s, 3 H, Me); 6.92—7.80 (m, 14 H arom.); 8.29 (br.s, 1 H, NH).
MS, m/z (Irel (%)): 466 [M]+ (100), 451 (11), 438 (10), 348 (9),
331 (27).
14. T. B. Norsten, N. R. Branda, J. Am. Chem. Soc., 2001, 123,
1784.
15. A. S. Dvornikov, Y. Liang, C. S. Cruse, P. M. Rentzepis,
J. Phys. Chem. B, 2004, 108, 8652.
16. V. F. Traven, V. S. Miroshnikov, T. A. Chibisova, V. A.
Barachevskii, O. V. Venediktova, Yu. P. Strokach, Izv. Akad.
Nauk, Ser. Khim., 2005, 2342 [Russ. Chem. Bull., Int. Ed.,
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This work was financially supported by the Russian
Foundation for Basic Research (Project No. 07ꢀ03ꢀ00932).
17. V. A. Barachevskii, R. E. Karpov, O. V. Venediktova, T. M.
Valova, Yu. P. Strokach, V. S. Miroshnikov, T. A. Chibisova,
V. F. Traven, Izv. Akad. Nauk, Ser. Khim., 2005, 2350 [Russ.
Chem. Bull., Int. Ed., 2005, 54, 2425].
18. V. F. Traven, A. Y. Bochkov, M. M. Krayushkin, V. N.
Yarovenko, B. V. Nabatov, S. M. Dolotov, V. A. Barachevsky,
I. P. Beletskaya, Org. Lett., 2008, 10, 1319.
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Received February 29, 2008;
in revised form September 18, 2008