Synthesis of new fluorescent 1-(thien-2-yl)-9H-thieno[3,4-b]-chroman-9-ones and their fluorescent photomodulation by photochromic dihetarylethenes

Article abstract of DOI:10.1016/j.tetlet.2015.01.101

New fluorescent derivatives of 1-(thien-2-yl)-3-methyl-9H-thieno[3,4-b]-chroman-9-one are synthesized and their spectral properties studied. The prepared fluorescent compounds are combined with several photochromic benzothienyl dihetarylethenes to provide

Full text of DOI:10.1016/j.tetlet.2015.01.101

Accepted Manuscript
Synthesis of new fluorescent 1-(thien-2-yl)-9H-thieno[3,4-b]-chroman-9-ones
and their fluorescent photomodulation by photochromic dihetarylethenes
K.S. Levchenko, V.A. Barachevski, O.I. Kobeleva, O.V. Venidiktova, T.M.
Valova, A.M. Bogacheva, K.A. Chudov, E.P. Grebennikov, P.S. Shmelin, N.O.
Poroshin, G.E. Adamov, V.N. Yarovenko, M.M. Krayushkin
PII:
S0040-4039(15)00128-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.01.101
TETL 45771
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
23 October 2014
17 December 2014
16 January 2015
Please cite this article as: Levchenko, K.S., Barachevski, V.A., Kobeleva, O.I., Venidiktova, O.V., Valova, T.M.,
Bogacheva, A.M., Chudov, K.A., Grebennikov, E.P., Shmelin, P.S., Poroshin, N.O., Adamov, G.E., Yarovenko,
V.N., Krayushkin, M.M., Synthesis of new fluorescent 1-(thien-2-yl)-9H-thieno[3,4-b]-chroman-9-ones and their
fluorescent photomodulation by photochromic dihetarylethenes, Tetrahedron Letters (2015), doi: http://dx.doi.org/
10.1016/j.tetlet.2015.01.101
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Graphical Abstract
Synthesis of new fluorescent 1-(thien-2-yl)-
9H-thieno[3,4-b]-chroman-9-ones and their
fluorescent photomodulation by
Leave this area blank for abstract info.
photochromic dihetarylethenes
K.S. Levchenko∗ , V.A. Barachevski, O. I. Kobeleva, O.V. Venidiktova, T.M. Valova, A.M. Bogacheva, K.A.
Chudov, E. P. Grebennikov, P. S. Shmelin, N.O. Poroshin, G.E. Adamov, V. N. Yarovenko, M. M. Krayushkin

1
Tetrahedron Letters
journal homepage: www.els evier.com
Synthesis of new fluorescent 1-(thien-2-yl)-9H-thieno[3,4-b]-chroman-9-ones and
their fluorescent photomodulation by photochromic dihetarylethenes
K.S.Levchenkoa∗ , V.A.Barachevskib, O. I. Kobelevab, O.V.Venidiktovab, T.M. Valovab, A.M. Bogachevac,
K.A. Chudov d, E. P. Grebennikova, P. S. Shmelina, N.O. Poroshina, G.E. Adamova, V. N. Yarovenkod, M.
M. Krayushkind
a Central Science Research Institute of Technology “Technomash”, 4 Ivana Franko St., Moscow 121108, Russia
b Photochemistry Center of RAS, 7a, bld. 1, Novatorov, Moscow 119421, Russia
c I.Ya. Postovsky Institute of Organic Synthesis, Russian Academy of Sciences, 20 S. Kovalevskoy, Yekaterinburg 620990, Russia;
d N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky Pr., Moscow 119991, Russia;
ARTICLE INFO
ABSTRACT
Article history:
Received
New fluorescent derivatives of 1-(thien-2-yl)-3-methyl-9H-thieno[3,4-b]-chroman-9-one are
synthesized and their spectral properties studied. The prepared fluorescent compounds are
combined with several photochromic benzothienyl dihetarylethenes to provide mixed systems
exhibiting reversible photo-induced fluorescence modulation in solution. The obtained results
are promising for the development of polymeric photochromic recording media with a non-
destructive fluorescence readout of optical information for RAM with extra large information
capacity
Received in revised form
Accepted
Available online
Keywords:
9H-thieno[3,4-b]-chroman-9-one
Electrophilic substitution
Photochromic diarylethene
Synthesis
2009 Elsevier Ltd. All rights reserved.
Photochromism
Fluorescence
Studies towards the development and improvement of multi-
layer recording media for two-photon, three-dimensional (3D)
optical memory with ultra high information capacity (recording
density 1011-1012 bit/cm3) have been carried out.1,2,3 One
important area of research is the creation of photochromic
is often low in FRET-systems. In this case, switching of the
photochromic component contributes to only partial fluorescence
quenching. Thirdly, to ensure non-destructive readout of
information the wavelength of the fluorescence excitation light
should not overlap the absorption bands of both forms of the
photochromic compound. One promising alternative is the use of
composite mixtures based on fluorescent and photochromic
molecules. This approach is used in much recent work and has
many advantages.6,7 For example, Shouzhi Pu et al. designed
fluorescence switch based on a photochromic diarylethene and a
rhodamine B dye.6 This photoswitchable system displayed a high
fluorescence quenching efficiency (>90%) and remarkable
fatigue resistance in both solution and a solid medium. In this
case, short distances between photoactive components or their
covalent bonding is not required. Moreover the efficiency of
fluorescence quenching by photoswitching can be adjusted by
variation of the concentration of components.
polymeric recording media with
a non-destructive optical
fluorescent readout of information that could provide 3D
information storage. The development of such recording media is
possible by using the phenomenon of inductive energy transfer
(Forster or fluorescence resonance energy transfer) between the
components, termed FRET effect.4,5 This effect occurs, for
example, in photochromic films or solutions if a mixture of
compounds or hybrid materials comprising an organic or
inorganic fluorophore and photochromic diarylethene are used.
In this case irradiation of the photochromic compound in open
form results in formation of a colored isomer, which absorbs the
excitation energy of the fluorophore and hence results in
quenching of fluorescence. Modulation of fluorescence intensity
is provided by reversible photochromic transformations of
dihetarylethenes. The implementation of such an effect is
possible under several conditions. Firstly, photochromic and
fluorescent molecules should be located at short enough distances
to make transfer of excitation energy possible. This is possible by
direct crosslinking of photoactive compounds. Secondly, the
absorption bands of the photochrome and the emission bands of
2,8,9
In continuation of our previous studies,
we herein present
the synthesis of new fluorescent 1-(thien-2-yl)-9H-thieno[3,4-b]-
chroman-9-ones and investigations of their spectral properties.
The obtained fluorophores were used with previously reported
dihetarylethenes10,11 in the development of photochromic systems
with reversible photo-induced modulation of the fluorescence.
The spectral characteristics of the fluorophores were adapted for
spectral characteristics of photochromes through a series of
modifications.
t—he—flu—orophore should overlap. The efficiency of energy transfer
∗ Corresponding author. Tel.: +8-985-188-6215; fax: +7-499-144-8514; e-mail: k.s.levchenko@gmail.com

2
Tetrahedron Letters
Previously, we have shown that 9H-thieno[3,4-b]-chroman-
proposed that introduction of a methyl group at position 3 (as
electron-donating group) would improve the fluorescence
intensity of the molecule and allow the selective introduction of
substituents at the 5-position of the thiophene moiety for tuning
of the location of the spectral bands.
9-ones are excellent fluorophores with well-separated absorption
and fluorescence bands, and exhibit high fluorescence intensity.
Moreover, the fluorescence can be enhanced by the introduction
of a thienyl group at position 1 of the 9H-thieno[3,4-b]-chroman-
9-one and an electron-donating group at position 3.10 In this
regard, 1-(thien-2-yl)-3-methyl-9H-thieno[3,4-b]-chroman-9-one
6 (see Schemes 1 and 2) was selected as the fluorophore. We
The synthesis of the new fluorescent 1-thienyl-9H-thieno[3,4-
b]-chromone-9-one 6 was carried out according to Schemes 110
and 2:
o
o
Scheme 1. Reagents and conditions: i Thiophene-2-carbonyl chloride, pyridine, 0-15 C, 1 h; ii, t-BuOK, DMF, -10 to 10 C; iii,
(C2H5CO)2O, C2H5COONa, 70-80 оС, 30 min; iv, Br2, CCl4, 50-60 оС, 1 h; v, CH3C(S)NH2, DMF, 70-80 оС, 2 h.
O
Br
NO2
O
S
S
S
S
O
O
O
S
S
S
S
O
7
O
9
O
8
i
ii
O
O
iv
O
O
Cl
S
S
S
O
O
O
O
ix
v
iii
S
S
O
14
O
6
10
NH2
S
vii
viii
vi
O
O
N
S
S
O
O
S
O
S
S
S
O
O
O
11
13
12
Scheme 2. Reagents and conditions: i NBS, CCl4, reflux, 1 h; ii, Cu(NO3)2·3H2O, (CH3CO)2O, 0-5 °С, 12 h; iii, ClCH2C(O)Cl, AlCl3,
CH2Cl2, 0-25 °С, 1.5 h; iv, CH3C(O)SH, K2CO3, DMF, 20 °С; v, CH3OCHCl2, AlCl3, CH2Cl2, 0-25 °С, 1.5 h; vi, CH3C(O)Cl, AlCl3, CH2Cl2,
0-25 °С, 1.5 h; vii HS(CH2)4SH, K2CO3, DMF, 20 °С; viii, NH2C(S)NH2, EtOH, reflux, 20 h; ix, ClC(O)C(O)Et, AlCl3, CH2Cl2, 0-25 °С, 1.5 h;
Compounds 1-3 were prepared according to established
procedures.10 It should be noted that this synthetic route (Scheme
1) is relatively simple. (i) Acylation, (ii) Baker–Venkataraman
rearrangement and (iii) cyclization proceed smoothly with yields
ranging from good to high. It is noteworthy that bromination of
chromophoric groups were introduced at the thiophene 5-position
via electrophilic substitution reactions (Scheme 2). In our opinion
introduction of an electron-withdrawing group at position 5 of
the thiophene ring should improve the fluorescent properties of
the products and cause bathochromic shifts of the absorption and
fluorescent bands due to the electron push-pull effect.
Chloroacetyl (10), formyl (11), acetyl (12) and ethyloxalyl (14)
substituents were introduced using standard Friedel-Crafts
conditions and AlCl3 as the catalyst affording the desired
products in 50-65% yields. The best method for the selective
synthesis of the nitro derivative 8 involved the use of copper
nitrate in acetic anhydride as a nitrating agent. Also, it was
decided to synthesize a substance based on compound 10 with a
thiazole moiety and sulfur-containing substituents. It should be
2-ethylchromone
4 is carried out more selectively than
bromination of earlier synthesized 2-methylchromones (which
gives 3-acyl-2-bromomethyl- and 2-dibromomethyl-chromen-4-
ones) 10 and leads to mono brominated adduct 5 only. Compound
6 was prepared in 74% yield by heating 5 with thioacetamide in
DMF solution. We prepared a series of fluorophore derivatives
from 6 to improve its optical properties and to expand the
possibilities of its application in a variety of photochromic
composite systems. In particular, several electron-withdrawing

3
noted that unlike mercaptoacetic acid, 1,4-butandithiol did not
give any products of nucleophilic substitution. Acetyl derivative
12 was isolated instead of disubstituted 1,4-butanedithiol
(obviously due to the two step process of nucleophilic
substitution and intermolecular reduction ).
compounds 6-14 to dihetarylethene in the closed form
B (Table 2).
The absorption and fluorescence spectral data of the synthesized
products 6-14 are summarized in Table 1 and show that all
compounds have similar properties: fluorescence characterized
by a large Stokes shift. Figure 1 shows the absorption and
fluorescence spectra of compound 6 in toluene as an example.
Scheme 3. Photoinduced isomerization of compounds 15-17
Table 1. Spectral characteristics of compounds 6-14.a
Photochromic compounds for the realization of photo-induced
fluorescence modulation were selected with the maximum of
overlap of the absorption bands of the cyclic isomer B and the
fluorescence of fluorophores 6-14. The properties of the
photochromic compounds used are shown in Table 2.
λabs
(nm)
422
ε
λem
(nm)
497
SS
(nm)
75
λex
(nm)
422
Ifl
max
Compound
-1
(M-1.cm )
(a.u.)
150
6
10925
7
423
444
432
430
430
429
455
442
~17750
14938
21875
22375
11500
12750
10625
23625
505
514
498
494
492
492
533
510
82
70
66
64
62
63
78
68
432
460
432
431
432
428
460
448
95
Table 2. Spectral characteristics of compounds 15-17.a
8
245
375
90
Compound R1
R2
ε
∆Dphot
/DA
abs
abs
9
λА
λВ
(M-1.cm-1)
(nm)
(nm)
10
11
12
13
14
205
235
120
285
15
16
H
H
332
12500
12500
490
0.8
1.0
a λabs, λex, and λem are the wavelengths of the maxima of the absorption bands,
the fluorescence excitation and fluorescence spectra of compounds 6-14,
respectively; ε - molar extinction coefficient; SS - Stokes shift; Ifl -
fluorescence intensity at the maximum of the fluorescence band of
360
341
523
565
max
compounds 6-14.
17
F
40800
0.2
λAabs, λBabs, are the wavelengths of the maxima of the absorption bands of
open (A) and cyclic (B) forms of the dihetarylethenes, respectively; DA
a
−
value of absorbance at the maximum of the absorption band of the form A;
∆Dphot - photoinduced change in the optical density at the maximum of the
absorption band of the cyclic form B.
Table 2 shows that the selected dihetarylethenes 15, 16 have
different spectral characteristics to the cyclic form and have almost
the same sensitivity to UV radiation (sensitivity is estimated as the
ratio of light-induced optical density at the wavelength of the
maximum absorption band of isomer B to the optical density at the
maximum absorption band of the open form of dihetarylethene A).
Figure 1. Absorption (1) and fluorescence emission (2, λex=422
nm) and excitation (3, λem=497nm) spectra of 6 in toluene.
As expected, derivatives 7-14 were characterized by long- Compound 17 has a significantly higher extinction due to the
wavelength shifted absorption bands compared to the absorption intensely absorbing chromophoric moiety R1. In this case,
band of the compound 6. The value of the bathochromic shift of however, the compound is characterized by a significant reduction
the absorption band depends on the electron-withdrawing
properties of the substituent on the thienyl moiety (Table 1). The
strongest bathochromic shifts of the absorption and fluorescence
spectra were observed for nitro-substituted 8, and the compounds
with ethyl oxalate 14 and aminothiazole 13 moieties. Most of the
compounds are characterized by comparable fluorescence
intensities (Table 1). However, the fluorescence intensities of
compounds 6,7,10 and 13 were 2-3 times lower than for the
compound 9.
of the photoinduced optical density at the wavelength of maximum
absorption of the cyclic form B. As an example, Figure 2 shows the
absorption spectra of the open and cyclic isomers of photochromic
compound 16 in toluene and the high reversibility of the
photochromic
transformations
of
selected
compounds.
Figure 3 shows the results of a study of the photoinduced
modulation of the fluorescence in the composite of photochromic
compound 15 and the fluorophore 9 (molar ratio 4:1) in toluene.
The decrease of the fluorescence intensity after irradiation with UV
light observed is due to the appearance of the absorption band of
the cyclic isomer B overlapping the emission band of compound 9.
This results in the inductive energy transfer from excited
fluorophore to the cyclic form B of the dihetarylethene. Subsequent
irradiation of the solution with visible light leads to a complete
recovery of the absorption spectrum of the original open-isomer
and the initial fluorescence intensity of the fluorophore.
Several thermally irreversible photochromic dihetarylethenes
were selected for the preparation of composite systems with
reversible photo-induced modulation of the fluorescence.
Photochromic transformations of these compounds result from
the reversible photoinduced isomerization between open
colorless form A and the cyclic form B (Scheme 3).12
Photochromic molecules were chosen from previously
synthesized compounds12,13 with characteristics that contribute to
the inductive transfer of excitation energy from the fluorescent

4
Tetrahedron
In conclusion, we have developed efficient methods for the
synthesis and modification of new fluorescent 1-(thien-2-yl)-3-
methyl-9H-thieno[3,4-b]-chroman-9-one derivatives. The
synthesized fluorescent compounds were used with photochromic
benzothienyl dihetarylethenes to provide systems with reversible
photo-induced modulation of fluorescence in solution. The
obtained results are promising for the development of
photochromic polymeric recording media with non-destructive
fluorescence readout of optical information for RAM with extra
large information capacity.
Acknowledgments
Figure 2. Absorption spectra of 16 in toluene (c = 2×10-4 M) before
(1) and after irradiation with UV light (λ=300-360 nm) (2) and
subsequent irradiation with visible light (λ>500 nm) (3).
This work was supported by RFBR (project number № 14-07-
00733 A, № 14-03-90022, № 13-03-00964a,), and the Presidium
of the Russian Academy of Sciences. The authors thank Dr. A.
Y. Bochkov for helpful suggestions.
Supplementary Material
Supplementary data (experimental
procedures and
characterization data of synthesized compounds) associated with
this article can be found, in the online version.
References and notes
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Valova, T.M.; Krayushkin, M.M.; Yarovenko, V.N.; Levchenko,
K.S.; Kiyko, V.V.; Vasilyuk, G.T. Optical Materials 2013, 35,
1805–1809.
Figure 3. The absorption (1-3) and fluorescence (4-6, λex =430 nm)
spectra of a mixture of photochrome 15 (c = 4×10-5 M) and the
fluorophore 9 (c = 1×10-5 M) in a molar ratio of 4:1 in toluene before
(1,4) and after irradiation with UV light (λ=300-360 nm) (2,5) and
subsequent irradiation with visible light(λ>500 nm) (3,6).
3. Kurbangaleev, V.; Poroshin, N.O.; Malyshev, P.P.; Shmelin, P.S.
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Figure 4. Photoinduced change in the fluorescence intensity of the
fluorophore 8 in a mixture with diarylethene 17 (molar ratio 1:36) in
chlorobenzene after irradiation with UV light (λ=300-360 nm) (A)
and subsequent irradiation with visible light (λ>500 nm) (B).
Similar photoinduced modulation of the fluorescence was
observed for the solution containing dihetarylethene 16 (4×10-5
M) and fluorophore 14 (1×10-5 M). For photochromic
dihetarylethene 17, fluorophores 8 and 13 were most appropriate
for its spectral properties (see data in Tables 1 and 2). Exposure
of a chlorobenzene solution of 17 and 13 (molar ratio of 9:1) to
UV light results in a reduction of the fluorescence intensity by 10
times. However, irradiation with visible light did not lead to
complete recovery of the fluorescence intensity due to
photodegradation of the fluorophore 13. Obviously, the
insufficient stability can be attributed to the introduction of an
aminothiazole fragment.
12. Irie. M. Chem. Rev. 2000, 100, 1685-1716.
13. Krayushkin, M.M.; Bogacheva, A.M.; Komogortsev, A.N.;
Lichitsky, B. V.; Dudinov, A. A.; Levchenko, K. S.; Kobeleva, O.
I.; Valova, T. M.; Barachevsky, V. A.; Charushin, V. N. J. Sulfur
Chem. 2013, 34, 580-587.
A practically acceptable result was obtained when using a
mixture of photochromic compounds 17 and the nitro derivative
8 with excellent stability in chlorobenzene solution. Efficient
fluorescence quenching was achieved by using a ratio of
fluorescent and photochromic compounds of 1:36 (Figure 4).