Photoinduced formation of the laser dye coumarin 6 from its dihydro derivatives

Article abstract of DOI:10.1016/j.dyepig.2017.07.001

The dihydro form of the laser dye Coumarin 6 and its acylated derivatives undergo photoinduced transformations with Coumarin 6 formation. The reactions go easily both in organic solvents and in polymer films with a high increase of fluorescence. Irreversibility of the reaction provides potential use of the new photosensitive media for optical information recording and sensing technologies.

Full text of DOI:10.1016/j.dyepig.2017.07.001

Accepted Manuscript
Photoinduced formation of the laser dye coumarin 6 from its dihydro derivatives
Valerii F. Traven, Dmitrii A. Cheptsov, Natalya P. Solovjova, Tatjana A. Chibisova,
Ilya I. Voronov, Sergei M. Dolotov, Ivan V. Ivanov
PII:
S0143-7208(17)31095-1
10.1016/j.dyepig.2017.07.001
DYPI 6090
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 6 June 2017
Revised Date: 29 June 2017
Accepted Date: 2 July 2017
Please cite this article as: Traven VF, Cheptsov DA, Solovjova NP, Chibisova TA, Voronov II, Dolotov
SM, Ivanov IV, Photoinduced formation of the laser dye coumarin 6 from its dihydro derivatives, Dyes
and Pigments (2017), doi: 10.1016/j.dyepig.2017.07.001.
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Dyes and Pigments
Volume XXX, Date, Page XX–XX
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Photoinduced Formation of the Laser Dye Coumarin 6 From
Its Dihydro Derivatives
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Valerii F. Traven ,
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Dmitrii A. Cheptsov ,
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Natalya P. Solovjova ,
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Tatjana A. Chibisova ,
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Ilya I. Voronov ,
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Sergei M. Dolotov ,
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Ivan V. Ivanov
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a
D.I. Mendeleev University of Chemical Technology of Russia, Miusskaya Sq., 9, Moscow, Russian
Federation
b
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow
region, Russian Federation
DOI:
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Highlights
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Photodehydrogention of dihydrohetarenes;
Photoinduced formation of Coumarin 6;
Photoinduced fluorescence;
Optical information recording;
Sensing technologies
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Abstract
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The dihydro form of the laser dye Coumarin 6 and its acylated derivatives undergo photoinduced
transformations with Coumarin 6 formation. The reactions go easily both in organic solvents and in
polymer films with a high increase of fluorescence. Irreversibility of the reaction provides potential use
of the new photosensitive media for optical information recording and sensing technologies.
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Graphical abstract

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R
N
O
N
S
S
hv
Coumarin 6
N
O
N
O
O
1
a-c
2
R = H (1a), C(O)H (1b), C(O)CH (1c)
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Formation of Coumarin 6
upon irradiation 1a-c
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Keywords
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Coumarin 6;
Phototransformation;
Laser dyes;
Fluorescence;
Optical memory
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1. Introduction
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Materials possessing functionality that can be activated by irradiation are of great importance
because of their potential use in various applications such as optical data storage, printing, drug delivery
systems (DDS), biological function imaging and sensing elements. Among the types of functionality,
fluorescence switching is one of the most important functions for volumetric optical data storage [1].

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The access of the stored data is achieved by measuring the fluorescence emitted by the fluorescing
photoproduct [2-5]. Therefore light-sensitive organic recording media based on photochemical
transformations of organic compounds appear to be the most promising in the design of the WORM
(Write Once Read Many) recording media for 3D bitwise archive optical memory. These media have, in
principle, a higher resolution than the currently used temperature-sensitive materials.
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One of the types of WORM material recording media is composed of two components: an
photogenerator of acidity (PGA) and a dye precursor (DP). The DP molecules are colorless and stable in
neutral media. They become strongly colored and fluorescing in the presence of an acid produced by the
light-sensitive PGA molecules when they are exposed to light. For example, lactone forms of some dyes
have no fluorescence in neutral media, but easily transform into strong fluorescent open forms in the
presence of acid [6-10].
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Chemically modified fluorophores, in which fluorescence is blocked by the presence of a
photocleavable protecting group is another type of WORM material recording media that was firstly
introduced by Ware and co-workers [11]. Their fluorescence activation does not need acid
photogenerators. Many photosensitive organic compounds as potential fluorophores have then been
synthesized for various sensor applications. N-Acetyl or N-benzoyl oxazine derivatives shown below,
which are known as leuco dyes, are used in many kinds of applications including pressure-sensitive
carbonless copy paper [12], thermographic and photothermographic imaging [13]. Rentzepis and
coworkers have used these photosensitive derivatives to provide fluorescence activation under
illumination with the formation of fluorescent oxazine dye [5]. Among various photocleavable
protecting groups reported, the 6-nitroveratroyloxycarbonyl (NVOC) group has gained much attention
due to efficient removal upon UV irradiation [14]. Kitani et al. have prepared novel photolabile
protecting groups, thiochromone S,S-dioxide for various alcohols, amines and carboxylic acids [15]. The

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photodeprotection proceeded smoothly to release alcohols, amines or carboxylic acids almost
quantitatively under 313 nm light. As the reaction proceeded, the absorption at near 365 nm increased,
and a new fluorescent emission at 440 nm was observed due to the tetracyclic compound formation that
has 100 times stronger fluorescent intensity than the starting thiochromone S,S-dioxide. Series of
photoactive chromone derivatives have been synthesized by Krayushkin et al. [16]. Derivatives of 2-
furyl-3-acetylchromones were of interest as photosensitive organic systems designed for use in various
photocontrolled photonic devices. 2-Furyl-3-acetylchromones undergo irreversible changes under UV
irradiation to form fluorescent products providing optical information reading.
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Looking for new chemically modified fluorophores possessing strong photoactivated
fluorescence we turned our attention on the dihydro form of the laser dye Coumarin 6. Its structure
contains a thiazoline ring that is easily oxidized via dehydrogenation by different oxidizing reagents [17-
21]. Coumarin 6 dihydro form has been found as an appropriate probe to detect peroxides [17]. It has
shown both good water compatibility and cell permeability, and then fluorescence turn-on property in
living cells. The fluorescence of Coumarin 6 dihydro form was turned on by the addition of H O and
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reached the fluorescence intensity of commercially available Coumarin 6 within 1 h. Li et al., have
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described a fluorescence turn-on chemodosimeter for Cu based on the ion promoted oxidation of
Coumarin 6 dihydro form [18] and found this method as highly selective and sensitive one. Ezeh and
Harrop have used Coumarin 6 dihydro form as the first selective (25-fold) and sensitive (low-ppb)
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fluorescence turn-ON response sensor for As cations in organic media and under ambient conditions
[19]. This method is advantageous over common As-sensing strategies, which are far less sensitive (high
ppb) and require the use and generation of toxic chemicals. Different benzthiazoline derivatives and
their analogs demonstrate their reducing abilities in reactions with unsaturated nitriles and ketones as
well [20, 21].

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To the best of our knowledge, photoinduced Coumarin 6 formation along UV irradiation of
Coumarin 6 dihydro form derivatives has not been reported to the present time. In this paper we report
on the photochemical transformation of Coumarin 6 dihydro form and its N-acylated forms. As we have
found, Coumarin 6 dihydro form and its N-acylated derivatives 1a-c are photosensitive substrates that
transform into highly fluorescent laser dye Coumarin 6 under irradiation thus providing their use as new
potential media for optical information recording.
R
N
S
N
O
O
1a-c
R = H (1a); R = C(O)H (1b); R = C(O)CH (1c)
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2. Experimental
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2.1. Materials
The deuterated solvents (CDCl , DMSO-d ) for NMR spectroscopy were obtained from Merck.
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The lactone form of Rhodamine B was used as precursor of fluorescent laser dye (high purity grade,
Aldrich). Hexachloroethane was used as a halogen-containing additive (high purity grade, Aldrich). The
other chemicals and solvents were Aldrich HPLC or spectral grade and were used without further
purification.
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2.2. General equipment
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H and C NMR spectra were recorded on «Bruker Avance» (500 МHz) with 0.05% Me Si as
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the internal standard. Structural determinations of obtained compounds, spatial configurations including
were made with the aid of HSQC and ROESY spectra Mass-spectra were recorded on "Thermo
.
Scientific" (ISQ LT Single Quadrupole Mass Spectrometer, ionizing energy equal to 70 eV. Analysis of
the reaction mixtures was performed using liquid chromatograph "Shimadzu SPD-20A" (column
"Phenomenex C18", the wavelength detector 438 nm). Chromato-mass spectra obtained using liquid
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chromatography-mass spectrometer "Shimadzu LCMS-2020" (column "Phenomenex SiO ", the
2
wavelength detector 438 nm). Analysis of the reaction mixtures by liquid chromatograph (HPLC) was
performed using eluent consisting of acetonitrile and water in volume ratio 4:1 respectively and at a flow
rate of 1 mL/min. Analysis of the reaction mixtures by liquid chromatography-mass spectrometer
(HPLC/MS) was performed using eluent composed of petroleum ether and ethyl acetate in the volume
ratio 7:3 respectively, and at a flow rate of 1 mL/min.
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Electronic absorption spectra were recorded on an APELPD_303UV spectrophotometer and
fluorescent spectra – on Cary Eclipse (Varian) spectrofluorimeter. Photo-irradiation was carried out
using an L 5283 xenon lamp (HAMAMATZU lamp) through a light filter to select light in UV region at
360 nm and in the visible region at 420 nm with corresponding glass filters. Analytical thin layer
chromatography was performed on silica gel plates (Merck, Kieselgel 60, 0.25 thickness) with F254
indicator. Relative rates of photodehydrogenation reactions of the Coumarin 6 dihydro form and its N-

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acylated derivatives have been measured by intensity of absorption band of the Coumarin 6 dihydro
form at 450 nm in solvents at the 0.2-0.8 range of optical density. Rate constants of the first order
reactions have been calculated, based on the measured data for 5 runs. Concentrations of the
components have been used as follows: compounds 1a-c - 50-60 µM, and С С1 - 80-85 mM.
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6
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Polymethylmetacrylate films (60-90 µm) with moleculary dispersed compound 1b (or 1c) and
C Cl were prepared by casting the corresponding solution onto a glass surface from mixture of ethyl
2
6
o
acetate and toluene (3:1) and drying then at 100 C. Concentrations of the compounds 1b, c were 4,5-5
mM, and С С1 - 260-280 mM.
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3. Synthesis
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Reactions of 3-formyl- and 3-carboxycoumarin derivatives with binucleophiles are common in
the synthesis of 3-heterylcoumarins [17, 18]. We have used the reaction of 3-formyl-7-
diethylaminocoumarin with 2-aminothiophenol for obtaining of laser dye Coumarin 6 dihydroform
(compound 1a). Synthesis of 1a has been carried out in absolute ethanol under a stream of argon for 6
hours with excess of 2-aminothiophenol (Scheme 1). Coumarin 6 dihydro form 1a has been identified
with a yield of 76% without prior purification and used then in the N-acylation reactions. Mixed
anhydride of formic and acetic acids has been used in the N-formylation of compound 1a [22], thus
obtaining compound 1b with a yield of 77%. We have used several procedures for the N-acetylation
reaction of compound 1a. In the first unsuccessful procedure, the reaction between 3-formyl-7-
diethylaminocoumarin and 2-aminothiophenol was carried out at room temperature, then heated to 80°C
in acetic anhydride as a solvent. In the second procedure, acetic anhydride has been added to Coumarin
6 dihydro form reaction mixture without isolation dihydro form 1a. Only the third attempt turned to be
successful for the synthesis of compound 1c. The acetylation reaction has been carried out with

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previously synthesized Coumarin 6 dihydro form 1a. It has been heated in acetic anhydride, first at room
temperature (stirring for 3 hours), then at 80°C for 3 hours (Scheme 1). As a result, the product of this
reaction was chromatographically pure N-acetylated Coumarin 6 dihydro form (compound 1c).
O
N
O
O
2
NH2
SH
EtOH,
rt,
under Ar
O
(excess)
-
H O
2
N
HCOOAc
S
rt,
N
O
O
HN
O
under Ar
1b
S
O
N
O
N
O
Ac O
2
S
1
a
0
2
0-80 C,
N
O
under Ar
1
c
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Scheme 1. Synthesis of Coumarin 6 dihydro form (1a) and its N-acylated derivatives 1b and 1c
4. Structural aspects
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The N-Acylated derivatives of Coumarin 6 dihydro form possess amide-isomerism due to hindered
rotation around N(15)‒C(16) bond. The mixture of the amide s-cis- (79%) and s-trans- (21%) isomers
1
are observed in H NMR spectrum (DMSO-d ) of compound 1b. The signals of protons H(4), H(5),
6
1
1
H(9), H(14) and CHO are doubled. Using two-dimensional HH-spectrum recorded in "ROESY", the
configuration of the predominant isomer has been identified: s-cis-configuration, which corresponds to

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s-cis-orientation of the C(16)=O group of the aldehyde fragment and the coumarin nucleus around the
N(15)-C(16) bond.
H
14
O
14
1
3
13
12
1
6
16
1
4a
14a
O
H
1
2
N
N
15
5
4
15
3
5
4
4a
4a
1
0a 11
6
10a 11
6
S
9
S
9
3
10
10
N
7
8a
O
1
2
O
N
7
8a
O
1
2
O
8
8
1
b, s-cis-isomer
1b, s-trans-isomer
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H, H-ROESY spectrum of compound 1b (500 MHz, DMSO-d ) is shown in Fig. 1.
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Fig. 1. H, H-ROESY of compound 1b (500 MHz, DMSO-d )
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The signals of the protons C(4)-H, C(9)-H, C(14)-H and NCOCH of the compound 1c in the H
3
NMR spectrum, recorded at room temperature are noticeably broadened. A distinct narrowing of the
signals is observed with increasing temperature. The marked dependence of the shape of the signals
from the temperature is caused by the s-cis- / s-trans- isomerism of NCOCH -fragment in the compound
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1c, similar to that of compound 1b.
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5. Photooxidation of compounds 1a-c in organic solvents
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The photophysical parameters (positions of absorption bands λabs, molar extinction coefficients ε,
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positions of fluorescence bands λfl, fluorescence quantum yields φfl, Stokes shifts) of the compounds 1a,
1b, 1c, 2 and Coumarin 6 are listed in Table 1.
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Table 1. Photophysical parameters of the compounds 1a, 1b, 1c, 2 and Coumarin 6
Compound
λabs,nm
ε
, L/mol*cm
λfl,nm
Stokes shift, nm
φfl
1
1
1
2
a
b
c
385
390
390
437
450
24460
27230
27480
44270
54000
-
-
-
-
-
-
-
-
-
460
490
0.41*
0.8**
23
40
Coumarin 6
* [23]
1
1
3
4
** [24]
1
1
5
6
All of the compounds 1a-c turned to be photosensitive substrates during their irradiation in organic
solvents. The changes in the electronic absorption spectra of the toluene solution of compound 1a as a

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function of time after irradiation with UV light are shown in Fig. 2 (left). Two isobestic points at 342
and 410 nm were observed in the absorption spectra after UV irradiation. The intensity of the absorption
band at 395 nm was found to decrease as a function of time after light irradiation, whereas the
absorption intensity at 450 nm increased. Changes in electronic absorption spectra are accompanied by
changes in the fluorescent spectra, where a significant increase of the fluorescence intensity at 510 nm
has been recorded (Fig. 2, right).
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One can see in Fig. 2, the measured electronic absorption and emission spectra of the final reaction
mixture of compound 1a photodehydrogenation in toluene are very close to those of the laser dye
Coumarin 6, that apparently formed as a product of photodehydrogenation of its dihydro form.
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1
1
1
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Fig. 2. Electronic absorption (left) and fluorescence (right) spectra of the compound 1a in toluene before
(1) after (to 9) irradiation at 250-400 nm; curves 10 - electronic absorption and fluorescence spectra of
Coumarin 6
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Another confirmation of photodehydrogenation of the compound 1a to Coumarin 6 has been
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obtined by NMR spectroscopy: the H NMR spectrum of the reaction mixture obtained as a result of

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dihydro form irradiation contains clear signals of Coumarin 6. It has also been found in the reaction
mixture by high-pressure liquid chromatography. Coumarin 6 is not the only product of dihydro form 1a
phototransformation. 3-Formyl-7-diethylaminocoumarin (2) has been detected as a minor by-product of
the irradiation of the Coumarin 6 dihydro form 1a as well.
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Hydrogen generated through the photodehydrogenation of Coumarin 6 dihydro form 1a has been
identified in the experiment when the dihydro form 1a was irradiated in toluene in the presence of
benzoquinone – an active acceptor of hydrogen. Hydroquinone has been detected among the reaction
products. The results of the reaction mixture analysis by HPLC-method are given in the Supplementary
data.
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How does photodehydrogenation of Coumarin 6 dihydro form undergo? Several schemes of
photodehydrogenation of dihydrohetarenes have earlier been discussed. If the reaction is carried out in
the presence
СCl or C Cl , it is accompanied by an increase of acidity of the reaction medium. This
4 2 6
direction of the reaction has been reported, in particular, for photodehydrogenation of dihydropyridines
and pyrazolines [8-10]. For example, the increase in acidity has been observed while conducting the
reaction with pyrazolines in carbon tetrachloride in the presence of acid indicator Thymol Blue [9b].
Irradiation experiments in toluene in the presence of C Cl and lactone of Rhodamine dye provided
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another test for the acid formation through the photodehydrogenation of pyrazolines [10]. The lactone
ring opening of Rhodamine dyes undergoes very easily in the presence of acid with an intense increase
of fluorescence due to the formation of Rhodamine dye. Photogeneration of acidity in these experiments
is consistent with a previously proposed scheme of pyrazolines photodehydrogenation (Scheme 2).

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*
+
R1
R1
R1
N
H
N
H
hv
N
H
N
H
CCl4
N
H
N
H
.
-
H
R2
H
R2
H
R2
+
CCl4
R
R
R
-
+
-Cl
-H
R, R1, R2 = Aryl, Hetaryl, t-Bu
R1
R1
N N
H
N
H
N
H
.
.
+
CCl3
-
CHCl3
R2
R2
R
R
1
2
Scheme 2. The presumed mechanism of photooxidation of aryl(hetaryl)pyrazolines
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It turned out, however, that irradiation of compound 1a in the presence of the lactone of
Rhodamine B does not lead to the opening of its lactone ring, since absorption of the open form of
Rhodamine B at 560 nm has not been detected. This fact indicates that Scheme 2 which describes
pyrazolines photodehydrogenation is not suitable to rationalise the process of photodehydrogenation of
compound 1a. This conclusion is in agreement with the observation that the addition of
hexachloroethane does not cause a notable increase in rate of photodehydrogenation of Coumarin 6
dihydro form (Table 2).
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Table 2. Effect of hexachloroethane on the rate of photodehydrogenation of Coumarin 6 dihydro form.
-
1
Photodehydrogenation experiment
Rate constant, s
0,0086±0,0004
,0092±0,0004
Coumarin 6 dihydro form 1a
Coumarin 6 dihydro form 1a +
0
hexachloroethane
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1
1
2
The lack of ionic intermediates in phototransformation of Coumarin 6 dihydro form is also in
accordance with comparison of the rates of this reaction in various solvents. It turned out that the

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reaction proceeds even at a much lower rate in more polar solvents (ethanol, acetonitrile) than in
nonpolar toluene (Table 3).
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Table 3. Rates of photodehydrogenation of Coumarin 6 dihydro form in different solvents.
Dielectric
-1
Solvent
Rate constant, s
0,0211±0,0009
constant
2,0
ε
toluene
acetone
20,7
0,0224±0,0009
0,0049±0,0002
0,0055±0,0002
ethanol
24,3
acetonitrile
37,5
4
5
6
Almost the same rate constants in toluene and acetone as well as lack of effect of hexachloroethane
indicate that the reaction of photodehydrogenation of Coumarin 6 dihydro form 1a does not involve the
proton generation and ionic intermediates under irradiation. It seems to operate via radical intermediates.
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Compounds 1b and 1c possess photosensitivity as well. Irradiation of their solutions is
accompanied by changes in electronic absorption and emission spectra. Fig. 3 shows electronic
absorption and emission spectra recorded during irradiation of solutions of compound 1b in toluene.
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Fig. 3. Electronic absorption (left) and fluorescence (right) spectra of compound 1b in toluene before (1)
and after (to 10) irradiation at 250-400 nm
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4
Similar changes in electronic absorption and emission spectra are detected during irradiation of
compound 1c in toluene solution (Fig. 4).
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6
7
Fig. 4. Electronic absorption (left) and fluorescence (right) spectra of compound 1c in toluene before (1)
and after (to 8) irradiation at 250-400 nm
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The composition of the products formed during the irradiation of compounds 1b and 1c are
presented in the Fig. 5. As one can see, N-formyl- and N-acetylderivatives of Coumarin 6 dihydro form
upon irradiation are also converted into Coumarin 6 and 3-formyl-7-diethylaminocoumarin 2.
1

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Fig. 5. HPLC-Analysis of the reaction mixtures formed during the irradiation of N-formylderivative 1b
(top) and N-acetylderivative 1c (bottom) in toluene: m/z=350 corresponds to Coumarin 6, m/z=245
corresponds to 3-formyl-7-diethylaminocoumarin
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6
The results of the analysis of the respective reaction mixtures are presented in Table 4 (see the
Supplementary data for more detail).
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Table 4. Ratios of Coumarin 6 / 3-formyl-7-diethylaminocoumarin obtained after irradiation 1a-1c.
Compound
Solvent
Composition of the products (in mol. %)

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-Formyl-7-
Coumarin 6
79
diethylaminocoumarin
toluene*
21
1
a
toluene ****
ethanol
88
83
66
81
61
91
92
30
89
12
17
34
19
39
9
toluene*
toluene**
toluene***
toluene ****
ethanol
1
b
8
toluene*
70
11
1
c
ethanol
1
2
3
4
5
* Toluene from Aldrich
** Toluene from Aldrich + water (1%)
*** Toluene from Aldrich, dried over sodium
**** Toluene from Aldrich, under stream of argon
6. Photooxidation of compounds 1a-c in polymer films
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Unfortunately, compound 1a undergoes dehydrogenation reaction during the preparation of
polymer films. In contrast the N-acylated derivatives of Coumarin 6 dihydro form 1b and 1c were quite
stable and showed the required thermal stability for fabrication of polymethylmethacrylate films with
their participation. Irradiation of polymer films containing compounds 1b and 1c in PMMA causes the
changes in absorption and emission spectra similar to those in solutions. The isobestic point at 410 nm
1

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2
3
4
5
6
7
was observed in the absorption spectra after UV irradiation of 1c in the PMMA film. The intensity of the
absorption maximum at 394 nm was decreased and absorption maxima at 450 and 520 nm have
appeared. Changes in the absorption spectra are accompanied by the appearance of maxima of the
fluorescence at 475 and 550 nm (Fig. 6). The spectral characteristics of the irradiated polymer films
show that N-acylated derivatives of Coumarin 6 dihydro form 1b and 1c in the polymer film by
irradiation undergo mainly in Coumarin 6 in accordance with the restricted access of oxygen to the zone
of phototransformation.
8
9
0
Fig. 6. Absorption (left) and fluorescence (right) spectra of compound 1c in PMMA film before (1) and
1
after (to 6) irradiation at 250-400 nm
1
1
1
2
It should be noted, that all discussed phototransformations of N-acylated derivatives of Coumarin
6 dihydro form 1b and 1c support the suitability of these substrates for optical information recording.
1
3
7. Discussion
1
1
4
5
Two reactions occur during irradiation of the compounds 1a-c in organic solvents: formation of
the laser dye Coumarin 6 and formation of 3-formyl-7-diethylaminocoumarin 2. Most likely, these

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2
3
4
5
6
reactions undergo as parallel processes, since the irradiation of the Coumarin 6 in our experimental
conditions does not lead to any transformations. Both reactions seem to be associated with a relative
easy homolysis of N-H- and N-C-bonds during irradiation of compounds 1a-c. The resulting radical pair
3 can be stabilized then with release of H atom and formation of Coumarin 6 (Scheme 3). This
transformation is rather obvious and does not need additional comments. The radical pair, similar to pair
3 was proposed as a key intermediate in the study of phototransformation of N-acetyloxazine [1].
7
8
9
0
1
2
3
4
5
6
7
8
Formation of 3-formyl-derivative 2 can be understood as product of rearrangement inside the
radical pair 3 during compound 1b irradiation. However, presence of compound 2 among products of
irradiation of compounds 1a and 1c demands discussion of other paths of 3-formyl-7-
1
1
1
1
1
1
1
1
1
diethylaminocoumarin formation. Hydrolysis of compounds 1a-c or O -participation in the
2
transformation of radical pair 3 can be suggested as possible paths. While discussing 3-formyl-7-
diethylaminocoumarin 2 formation, we conducted a series of experiments with compounds 1a and 1b
under different conditions, since phototransformation of these compounds is accompanied by minimal
amounts of minor by-products. Ratios of Coumarin 6 / compound 2 are shown in the Table 3. As one
can see, water does not participate in the transformation of compound 1b to 3-formyl-7-
diethylaminocoumarin. So, retro-thiazoline-ring formation does not take place during the reaction.
Moreover, use of 95%-ethanol (solvent much more fitted for hydrolysis reactions) leads to significantly
lower content of 3-formyl-7-diethylaminocoumarin among irradiation products.
1
2
2
2
2
9
0
1
2
3
Several schemes of the photooxidation of dihydrohetarenes with the participation of atmospheric
oxygen were discussed in literature. By one of the schemes, a dye molecule can serve as a
photosensitizer in those photooxidations [25]. Excited by irradiation or directly the dye molecule reacts
with the dihydrohetarene molecule, providing thus its reaction further with oxygen. An alternative
direction involves the transmission of excitation from the sensitizer (as a sensitizer can operate a

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2
3
dihydrohetarene as well) to the oxygen molecule, which reacts then with a substrate. Both directions
involve the active participation of oxygen in the process of photodehydrogenation and predominantly
radical nature of the oxidation process as a whole.
4
5
6
7
8
9
We have conducted several experiments in toluene under stream of argon. Сomposition of the
products of the compounds 1a and 1b irradiation is given in the Table 3. Amount of compound 2
decreases notably when the reactions have been carried out under stream of argon. One can assume that
the formation of 3-formyl-7-diethylaminocoumarin is caused by the reaction of radical pair 3 with an
excited oxygen molecule – reaction that competes with elimination of a hydrogen atom as shown in
scheme 3.
.. N
R
N
hv
*
1a-c
S
S
1
a-c
-
RH
N
O
O
N
O
O
3
*
O
2
O
N
O
O
2
1
1
0
1
Scheme 3. The presumed paths of phototransformation of derivatives of Coumarin 6 dihydro form.
1
1
2
3
It is noteworthy that absorption and emission bands of Coumarin 6 and 3-formyl-7-
diethylaminocoumarin 2 are located very close in the spectra as shown in Fig. 7.

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2
3
Fig. 7. Absorption (left) and fluorescence (right) spectra of the 3-formyl-7-diethylaminocoumarin (1, 3)
and Coumarin 6 (2, 4) in toluene
4
5
6
One can assume that the minor side reaction, formation of 3-formyl-7-diethylaminocoumarin would not
provide much inconvenience along sensing applications of compounds 1a-c phototransformations,
especially in polymer film that would hinder access of atmospheric oxygen to sensing media.
7
8
8. Synthetic procedures
8.1. The synthesis of the Coumarin 6 dihydro form 1a
9
0
1
2
2-Aminothiophenol (0.3 ml, 2.71 mmol) was added dropwise to solution of 3-formyl-7-
diethylaminocoumarin (0.36 g, 1.47 mmol) in anhydrous ethanol (15 mL) under a stream of argon. The
resultant mixture was stirred during 6 hrs. at room temperature. Upon completion of the reaction, the
precipitate was filtered off and dried in a vacuum desiccator over calcium chloride.
1
1
1
1
1
1
3
4
7-Diethylamino-3-(2,3-dihydro-1,3-benzothiazol-2-yl)coumarin 1a: Yield 76%, m.p. 195-200°C. H
3
NMR (500
М
Hz, (CD ) SO,
δ
(ppm.), J (Hz)): 1.10 (t, 6H, N(CH CH )
J
CH
2
CH
3
=7.0); 3.41 (q, 4H,
3
2
2
3 2,

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3
3
4
1
2
3
4
5
6
7
N(CH CH ) , JCH
2
CH
3
=7.0); 6.18 (d, 1H, H(9), J
=3.0); 6.54 (d, 1H, H(8), J =2.3); 6.59-6.62 (m,
2
3 2
9,NH
6,8
3
4
3
1H, H(13)); 6.66 (dd, 1H, H(6), J =8.9, J =2.3); 6.73 (d, 1H, H(11), J11,12=7.7); 6.84 (d, 1H, NH,
5,6
6,8
3
3
3
J9,NH=3.0); 6.88-6.91 (m, 1H, H(12)); 6.99 (d, 1H, H(14), J13,14=7.6); 7.45 (d, 1H, H(5), J =8.9); 7.75
5,6
1
3
(s, 1H, H(4));
С NMR (126 МHz, (CD ) SO, δ (ppm.)): 12.8 (N(CH CH ) ); 44.6 (N(CH CH ) ); 63.9
3 2 2 3 2 2 3 2
(C); 96.9 ( ); 107.8 (C); 109.7 (C); 110.1 (C); 119.6 (C); 121.9 (C); 122.3 (C); 125.7 (C); 125.8 ( );
С
С
1
13
130.1 ( ); 138.0 (С); 147.7 (С); 151.0 (С); 155.8 (С); 161.2 (С). H and C NMR spectra are identical
С
to those given in [17] (see Suppl. Data). MS, m/z: 352 ([M], 70).
8.2. The synthesis of compound 1b
8
9
0
1
2
Compound 1a (0.70 g, 1.99 mmol) has been dissolved in the solution of acetic anhydride (17.0 mL,
1
1
1
180,33 mmol) and concentrated formic acid (7.82 mL, 207.37 mmol). The reaction mixture was stirred
then for 12 hrs. at room temperature under Ar . The formed precipitate was filtered off, washed with
2
toluene, dried in a vacuum desiccator over calcium chloride and paraffin.
1
1
1
1
1
1
1
2
2
2
2
3
4
5
6
7
8
9
0
1
2
3
7-Diethylamino-3-(3-formyl-2,3-dihydro-1,3-benzothiazol-2-yl)coumarin, s-cis- and s-trans-isomers
1
1b: Yield 77%, m.p. 230 - 231,5 °C. NMR spectra of s-cis-isomer – H (500
М
Hz, (CD ) SO,
δ
(ppm.),
=7.0); 6.56 (s, 1H,
H(8)); 6.64 (s, 0,79H, H(9)); 6.68 (d, 1H, H(6), J =8.9); 7.09-7.31 (m, 3H, H(11,12,13)); 7.39 (d,
3
2
3
3
J (Hz)): 1.10 (t, 6H, N(CH CH ) , JCH
2
CH
3
=7.0); 3.41 (q, 4H, N(CH CH ) , JCH
2 3
CH
2
3 2
2
3 2
3
5,6
3
3
0,79H, H(5), J =8.9); 7.59 (s, 0,79H, H(4)); 7.63 (d, 0,79H, H(14), J13,14=7.9); 9.10 (s, 0,79H, CHO);
5,6
1
3
С
(126 МHz, (CD ) SO, δ (ppm.)): 12.2 (N(CH CH ) ); 44.0 (N(CH CH ) ); 60.5 (C); 96.3 (C); 106.9
3 2 2 3 2 2 3 2
(C); 109.3 (C); 112.9 (C); 118.2 (C); 122.8 (C); 125.3 (C); 125.6 (C); 128.5 (C); 129.6 (C); 136.5 (C);
1
136.9 (C); 150.7 (C); 155.4 (C); 160.0 (CHO); 161.6 (C). NMR spectra of s-trans-isomer – H (500
3
М
Hz, (CD ) SO,
δ
(ppm.), J (Hz)): 1.10 (t, 6H, N(CH CH ) , JCH
2
CH
3
=7.0); 3.41 (q, 4H, N(CH CH ) ,
2 3 2
3
2
2
3 2
3
3
J
CH
2
CH
3
=7.0); 6.56 (s, 1H, H(8)); 6.68 (d, 1H, H(6), J =8.9); 6.83 (s, 0,21H, H(9)); 7.09-7.31 (m, 3H,
5,6
3
3
H(11,12,13)); 7.47 (d, 0,21H, H(5), J =8.9); 7.52 (s, 0,21H, H(4)); 8.02 (d, 0,21H, H(14), J13,14=7.9);
5,6

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1
2
3
4
8.59 (s, 0,21H, CHO); С (126 МHz, (CD ) SO, δ (ppm.)): 12.2 (N(CH CH ) ); 44.0 (N(CH CH ) );
3 2 2 3 2 2 3 2
62.5 (C); 96.3 (C); 106.9 (C); 109.3 (C); 117.4 (C); 119.6 (C); 123.1 (C); 125.3 (C); 125.8 (C); 129.2
(C); 129.9 (C); 136.5 (C); 136.9 (C); 150.7 (C); 155.4 (C); 160.3 (CHO); 161.6 (C). MS, m/z: 380 ([M],
+
+
13). Found [M+H] = 381.1259, C H N O S requires [M+H] = 381.1267.
21
20
2
3
5
8.3. The synthesis of compound 1c
6
7
8
Compound 1a (0.29 g, 0.82 mmol) was suspended in acetic anhydride (10 mL). The resultant mixture
was stirred for 3 hrs. at room temperature and heated then at 80°C for 3 hrs. The formed precipitate was
filtered off, washed with toluene, dried in a vacuum desiccator over calcium chloride and paraffin.
9
0
1
2
3
4
5
6
7-Diethylamino-3-(3-acetyl-2,3-dihydro-1,3-benzothiazol-2-yl)coumarin 1c: Yield 72%, m.p. 244-
1
3
1
1
1
1
1
1
1
245°C. H NMR (500
МHz, CDCl3,
δ
(ppm.), J (Hz)): 1.23 (t, 6H, N(CH CH ) , JCH
2
CH
3
=7.0); 2.34 (bs,
2
3 2
3
3
3H, COCH ); 3.43 (q, 4H, N(CH CH ) , JCH
2
CH
3
=7.0); 6.53 (s, 1H, H(8)); 6.58 (d, 1H, H(6), J =8.8);
3
2
3 2
5,6
1
3
6.70 (bs, 1H, H(9)); 7.07-7.21 (m, 4H, H(11,12,13,14)); 7.29 (bd, 1H, H(5)); 8.18 (bs, 1H, H(4)); C
NMR (126 Hz, CDCl3, (ppm.)): 11.8 (N(CH CH ) ); 23.0 (COCH ); 44.4 (N(CH CH ) ); 62.6 (C);
М
δ
2
3 2
3
2
3 2
97.0 (C); 107.5 (C); 108.8 (C); 118.5 (C); 119.2 (C); 122.5 (C); 124.8 (C); 124.9 (C); 128.4 (C); 128.8
(C); 135.5 (C); 137.9 (C); 150.3 (C); 155.5 (C); 160.3 (C); 168.4 (COCH ). MS, m/z: 394 ([M], 7).
3
+
+
Found [M+H] = 395.1431, C H N O S requires [M+H] = 395.1424.
22
22
2
3
1
7
9. Conclusions
1
1
2
2
8
9
0
1
Dihydro form of Coumarin 6 and its acylated derivatives undergo photoinduced transformation to laser
dye Coumarin 6. The reactions go easily both in organic solvents and in polymer films. High increase of
fluorescence is irreversible thus providing potential use of the phototransformations for optical
information recording and sensing technologies.

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Acknowledgment
This work was funded by the Russian Foundation for Basic Research (RFBR), grant no. 14-03-00564.
References
4
5
[1] Akiba M, Dvornikov AS, Rentzepis PM. Formation of oxazine dye by photochemical reaction of N-
acyl oxazine derivatives. J Photochem Photobiol A Chem 2007; 190: 69-76.
6
7
[2] Dvornikov AS, Rentzepis PM. Novel organic ROM materials for optical 3D memory devices. Opt
Commun 1997; 136: 1-6.
8
9
[3] Liang YC, Dvornikov AS, Rentzepis PM. Fluorescent photochromic fulgides. Res Chem Intermed
1998; 24: 905-914.
1
1
1
0
1
2
[4] Pudavar HE, Joshi MP, Prasad PN, Reinhardt BA. High-density three-dimensional optical data
storage in a stacked compact disk format with two-photon writing and single photon readout. Appl Phys
Lett 1999; 74: 1338-1340.
1
1
3
4
[5] Liang Y, Dvornikov AS, Rentzepis PM. Synthesis and photochemistry of photochromicfluorescing
indol-2-ylfulgimides. J Mater Chem 2000; 10: 2477-2482.
1
1
1
5
6
7
[6] Rentzepis PM, Dvornikov AS. Dye precursor molecules chemically reactive with the light-altered
form of light-sensitive molecules to form stable fluorescent dye, particularly for optical memories
including two-photon threedimensional optical memories. US Patent 2002; 6,432,610 B1.
1
1
2
8
9
0
[7] Rentzepis PM, Dvornikov AS. Dye precursor molecules chemically reactive with the lightaltered
form of light-sensitive molecules to form stable fluorescent dye, particularly for optical memories
including two-photon three-dimensional optical memories. US Patent 2003; 2003/0073031 A1.

ACCEPTED MANUSCRIPT
1
2
3
[8] Belfield KD, Schafer KJ. A New Photosensitive Polymeric Material for WORM Optical Data
Storage Using Multichannel Two-Photon Fluorescence Readout. Chemistry of Materials, 2002; 14:
3656-3662.
4
5
6
7
[9] a) Jin M-Z, Yang L, Wu L-M, Liu Y-C, Liu Z-L. Novel photoinduced aromatization of Hantzsch
1,4-dihydropyridines. Chem Commun 1998; 22: 2451-2452.
b) Traven VF, Ivanov IV. New reaction of photoaromatization of aryl- and hetarylpyrazolines. Russ
Chem Bull Int Ed 2008; 57: 1063-1069.
8
9
0
[10] Traven VF, Ivanov IV, Dolotov SM, Kobeleva OI, Barachevsky VA. Aryl(hetaryl)pyrazolines as
new photoacid generators for optical information recording. J Photochem Photobiol A Chem 2014; 295:
34-39.
1
1
1
1
1
2
3
[11] Ware BR, Brvenik LJ, Cummings RT, Furukawa RH, Krafft GA. Fluorescence photoactivation and
dissipation (FPD). In: Taylor DL, Waggoner AS, Murphy RF, Lanni F, Birge RR (Eds.) Applications of
Fluorescence in the Biomedical Sciences 1986: 141-157, Alan R. Liss, New York.
1
1
1
4
5
6
[12] Potts HA, Wood AH, Cook CC. The decomposition of N-benzoylleucomethylene blue during the
pressure-sensitive copying process. I. Identification of reaction products. J Appl Chem Biotechnol 1972;
22: 651-657.
1
1
7
8
[13] Thien TV. Thiazine, Oxazine, and Phenazine Leuco Dyes. In: Muthyala, R. (Eds.) Chemistry and
Application of Leuco Dyes 1997, 67-95, Plenum Press, New York.
1
2
9
0
[14] Min S-J, Ahn K-D, Kim J-M. Patterned Fluorescence Images Using a Photocleavable NVOC-
Protected Quinizarin. Bull. Korean Chem Soc 2005; 26: 1437-1439.

ACCEPTED MANUSCRIPT
1
2
[15] Kitani S, Sugawara K, Tsutsumi K, Morimoto T, Kakiuchi K. Synthesis and characterization of
thiochromone S,S-dioxides as new photolabile protecting groups. Chem Commun 2008; 18: 2103-2105.
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
[16] a) Krayushkin MM, Levchenko KS, Yarovenko VN, Zavarzin IV, Barachevsky VA, Puankov YuA,
Valova TM, Kobeleva OI. Synthesis and study of photosensitive chromone derivatives for recording
media of archival three-dimensional optical memory. ARKIVOC 2009; 9: 269-283.
b) Barachevsky VA, Kobeleva OI, Valova TM, Ait AO, Dunaev AA, Gorelik AM, Krayushkin MM,
Levchenko KS, Yarovenko VN, Kiyko VV, Grebennikov EP. Photochromic and irreversible
photofluorescent organic materials for 3D bitwise optical memory. Opt Memory and Neural Networks
2010; 19: 187-195.
1
1
1
1
1
1
1
1
1
c) Barachevsky VA, Strokach YuP, Puankov YuA, Kobeleva O I, Valova TM, Levchenko KS,
Yarovenko VN, Krayushkin MM. Light-sensitive heterocyclic compounds for information
nanotechnologies ARKIVOC 2009; 9: 70-95.
d) Krayushkin MM, Levchenko KS, Yarovenko VN, Christoforova LV, Barachevsky VA, Puankov
YuA, Valova TM, Kobeleva OI, Lyssenko KA. Synthesis and reactivity of 1-aryl-9H-thieno[3,4-
b]chromon-9-ones. New J Chem 2009; 33: 2267-2277.
e) Barachevsky VA, Kobeleva OI, Ait AO, Gorelik AM, Valova TM, Krayushkin MM, Levchenko KS,
Yarovenko VN, Kiyko VV, Vasilyuk GT. Optical polymer materials with photocontrolled fluorescence.
Opt Mater 2013; 35: 1805-1809.
1
2
2
9
0
1
[17] Lee D-N, Kim DY, Ghil SH, Kim H-J. Coumarin-Benzothiazoline Conjugate as a Fluorescence
Turn-On Probe for Reactive Oxygen Species and its Cellular Expression. Bull Korean Chem Soc 2011;
32: 3109-3112.
2
+
2
2
2
3
[18] Li J, Zeng Y, Hu Q, Yu X, Guo J, Pan Z. A fluorescence “turn-on” chemodosimeter for Cu in
aqueous solution based on the ion promoted oxidation. Dalton Trans 2012; 41: 3623-3626.

ACCEPTED MANUSCRIPT
1
2
[19] Ezeh VC, Harrop TC. A Sensitive and Selective Fluorescence Sensor for the Detection of
Arsenic(III) in Organic Media. Inorg Chem 2012; 51: 1213−1215.
3
4
[20] Chikashita H, Nishida S, Miyazaki M, Itoh K. 2-Phenylbenzimidazoline as a Reducing Agent in the
Preparation of Malononitriles from α,β-Unsaturated Dinitriles. Synth Commun 1983; 13: 1033-1039.
5
6
7
[21] Chikashita H, Miyazaki M, Itoh K. Lewis acid-promoted conjugate reduction of α,β-unsaturated
carbonyl compounds by 2-phenylbenzothiazoline (2-phenyl-2,3-dihydrobenzothiazole). J Chem Soc,
Perkin Trans 1 1987: 699-706.
8
9
[22] Breuer H, Schulze E. 2-Phenyl-3-acylbenzothiazolines and their oxides. US Patent 1973; 3,720,683
A.
1
1
1
0
1
2
[23] Bai H, Qian J, Tian H, Pan W, Zhang L, Zhang W. Fluorescent polarity probes for identifying
bovine serum albumin: Amplification effect of para-substituted benzene. Dyes and Pigments 2014;
103:1–8.
1
1
3
4
[24] Drexhage KH. Fluorescence efficiency of laser dyes. J Res Natl Bur Stand Sect A Phys Chem
1976; 80A: 421.
1
1
5
6
[25] Evans NA, Leaver IH. Dye sensitized photooxidation of 1,3-Diphenyl-2-pyrazoline. Aust J Chem
1974; 27: 1797-1803.
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Appendix A. Supplementary data
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Supporting Information
Photoinduced Formation of the Laser Dye Coumarin 6 From Its
Dihydroform Derivatives
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a*
a
а
a
2
3
Valerii F. Traven , Dmitrii A. Cheptsov , Natalya P. Solovjova , Tatjana A. Chibisova ,
b
a
a
Ilya I. Voronov , Sergei M. Dolotov , Ivan V. Ivanov
4
a
5
6
7
8
D.I. Mendeleev University of Chemical Technology of Russia, Miusskaya Sq., 9, Moscow, Russian
Federation. E-mail: valerii.traven@gmail.com
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow region,
b
Russian Federation
9
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1
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Table of Contents
1. General conditions
S2
S3
2. NMR spectra of compounds
3. Results of chromatography-mass spectrometric assays and HPLC
S12