Photochemical activities of polymers with aurone fragment

Article abstract of DOI:10.1080/15421406.2018.1542102

In this work we report preliminary results obtained for methacrylic polymers incorporating aurone side-group as photochemical active molecule. The aurone polymers were obtained by a three-step synthetic approach: (2Z)-6-hydroxy-2-(4-R-benzyliden)-1-benzofuran-3(2H)-ones were synthesized by using condensation reation of 6-hydroxybenzofuran-3-one with benzaldehydes; then methacrylate monomers were synthesized by reaction the alcohols with methacryloyl chloride; and the polymers were synthesized by free radical polymerization. Polymers were characterized by ¹HNMR spectroscopy and DSC techniques. Their physicochemical properties are determined by absorption, fluorescence excitation and emission spectroscopies.

Full text of DOI:10.1080/15421406.2018.1542102

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Photochemical activities of polymers with aurone
fragment
Vitaliy Smokal, Oksana Kharchenko, Yuriy Karabets, Nataliia Iukhymenko,
Andrii Kysil, Oksana Krupka & Aleksiy Kolendo
To cite this article: Vitaliy Smokal, Oksana Kharchenko, Yuriy Karabets, Nataliia Iukhymenko,
Andrii Kysil, Oksana Krupka & Aleksiy Kolendo (2018) Photochemical activities of
polymers with aurone fragment, Molecular Crystals and Liquid Crystals, 672:1, 11-17, DOI:
10.1080/15421406.2018.1542102
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
2018, VOL. 672, NO. 1, 11–17
https://doi.org/10.1080/15421406.2018.1542102
Photochemical activities of polymers with aurone fragment
Vitaliy Smokal, Oksana Kharchenko, Yuriy Karabets, Nataliia Iukhymenko, Andrii
Kysil, Oksana Krupka, and Aleksiy Kolendo
Kyiv Taras Shevchenko National University, Volodymyrska 60, 01033 Kyiv, Ukraine
KEYWORDS
ABSTRACT
Radical polymerization;
aryl(meth)acrylates; lumines-
cent properties;
photochemical properties;
aurone containing polymers
In this work we report preliminary results obtained for methacrylic
polymers incorporating aurone side-group as photochemical active
molecule. The aurone polymers were obtained by a three-step syn-
thetic
approach:
(2Z)-6-hydroxy-2-(4-R-benzyliden)-1-benzofuran-
3(2H)-ones were synthesized by using condensation reation of 6-
hydroxybenzofuran-3-one with benzaldehydes; then methacrylate
monomers were synthesized by reaction the alcohols with methacry-
loyl chloride; and the polymers were synthesized by free radical poly-
1
merization. Polymers were characterized by HNMR spectroscopy and
DSC techniques. Their physicochemical properties are determined by
absorption, fluorescence excitation and emission spectroscopies.
1. Introduction
Aurones are well known group of natural dyes that are contained in vegetables, espe-
cially fruits, and flowers [1]. Aurones contained in the sunflower family, or asteraceae,
were the first to be discovered in the early 1940s [2]. It’s belonging to the flavonoid
class of natural products [3]. Recent investigations have shown that these compounds
have good biological activities and much better than flavones and chalcones [4].
Investigations in vitro have established that natural aurones and their synthetic analo-
gies exhibit antibacterial, antiviral, antiparasitic, antioxydant, anticancer activity [5–7].
4-Hydroxy aurones have been developed as receptors, which allow for 00naked-eye00
detection of cyanide anions with high selectivity and sensitivity. These compounds
exhibit remarkable response to cyanide anions. The addition of CNꢀ to acetonitrile sol-
utions induced obvious colour, UV–vis and fluorescence change [8].
A number of naturally occurring aurones which possess various hydroxylation pat-
terns have numerous biological activities [4]. Therefore, formidable efforts have been
made on the synthesis of (Z)-aurone and its derivatives.
In particular, researches have reported that synthetic derivatives of aurone exsist in
thermodynamically more stable Z-isomer. They are able to photoinduced Z-E-isomeriza-
tion and in some cases to reversible photoisomerization [9]. Photochromism attract
attention of researcher as striking phenomena in photochemistry, which involves light
induced reversible transformation of a molecule between two states with different
absorption spectra [10–15]. In this respect, aurones show unique photochemical and
CONTACT Vitaliy Smokal
vitaliismokal@gmail.com; Nataliia Iukhymenko
yukhimenko.n@gmail.com
Kyiv Taras
Shevchenko National University, Volodymyrska 60, 01033, Kyiv, Ukraine
ß 2018 Taylor & Francis Group, LLC

12
V. SMOKAL ET AL.
photophysical properties as fluorescent photochromic materials, which could be useful
in a variety of applications such as fluorescent labels and probes in biology and medi-
cine, as photoswitches in opticts in optical memory applications because the stored
information is accessed from written form by fluorescence property [16, 17].
The present work deals with the photochemical properties of functionalized methacrylic
polymers with aurone fragments. It has been shown that irradiation of aurone derivatives
in various solutions gives a rise to a product the trans isomerisation. The changes in the
absorption under UV irradiation of these compounds were investigated in solution.
2. Experimental
Methods
1H NMR (400 MHz) spectra were recorded on a Mercury (Varian) 400 spectrometer.
Chemical shift are in ppm from the internal standard tetramethylsilane.
UV-VIS spectra were recorded on a Shimadzu UV-1800 spectrometer (Shimadzu,
Kyoto, Japan) at room temperature in solution in a quartz liquid cell.
Infrared spectra were recorded on Perkin Elmer BX with KBr. EL-TEMP melting
point apparatus was used for melting points measurements.
Differential Scanning Calorimetry (DSC): A Q20 model DSC (TA Instruments) with
a continuous N2 purge was used to determine the glass and phase transition tempera-
tures (Tg) of all polymers. Two scans were run at a heating rate of 10 ꢁC/min up to
200 ꢁC, followed by a cooling to 20 ꢁC, giving the values of Tg.
The absorption and steady-state fluorescence spectra were recorded on a Shimadzu
UV-1800 spectrophotometer and Shimadzu RF-6000 spectrofluorometer, respectively.
The emission spectra were measured by adjusting the excitation wavelengths to the
wavelength maximum in the absorption spectra, while fluorescence excitation spectra
were recorded at wavelengths corresponding to the maximum in the emission spectra.
An intensity scale of fluorescence excitation and fluorescence spectra is given in arbi-
trary units. Spectral grade tetrahydrofuran (THF) and ethanol from Fluka were used as
solvents in all spectroscopic measurements.
Materials
Standard distillation procedures were performed for triethylamine and THF just prior to
use. All other reagents and solvents were commercially available and used as received.
General procedure for synthesis of 6-hydroxyaurones. Aromatic aldehyde (10 mmol)
and 50% aqueous potassium hydroxide solution (2.3 ml) were added to the solution of
6-hydroxybenzofuran-3-on (1.5 g, 10 mmol) in the mixture of ethanol (10 ml) and dime-
thylformamide (DMF) (10 ml) the mixture was stirred 4-6 hours (monitoring by TLC).
Reaction mixture was precipitated in 50 ml hot water with stirring and was neutralized
by concentrated hydrochloric acid to getting pH 6-7. The precipitate was formed, and
then it was filtered and washed with water. After crystallization from methanol/DMF
the yellow or red crystalline 6-hydroxyaurones were obtained.
(2Z)-2-Benzylidene-6-hydroxy-1-benzofuran-3(2H)-one. The yellow crystals were
obtained, m.p. 259-260 ꢁC, yield: 83%.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
13
Figure 1. Z-E-isomerization of the aurone fragment.
Figure 2. Synthesis of aurones methacrylate monomers and copolymers.
1H NMR (400 MHz, DMSO-d6), d, ppm: 6.61-6.68 (3H, m, –C ¼ CH, 2a, 7-H), 7.44
3
3
(3H, m, 3ꢀ, 4ꢀ, 5ꢀ-H), 7.55 (1H, d, J ¼ 8.4 Hz, 4-H), 7.89 (2H, d, J ¼ 7.5 Hz, 2ꢀ, 6ꢀ-H),
10.98 (1H, s, 6-OH).
(2Z)-2-[4-(Dimethylamino)benzylidene]-6-hydroxy-1-benzofuran-3(2H)-one. The red
crystals were obtained, m.p. 242-244ꢁ‘, yield: 84%.
1H NMR (400 MHz, DMSO-d6), d, ppm: 3.20 (6H, s, NMe2), 6.61 (1H, s, –C ¼ CH),
6.61 (1H, d, J ¼ 2.0 Hz, H-7), 6.65 (1H, dd, J ¼ 8.4, 2.0 Hz, H-5), 6.72 (2H, d,
3
3
3J ¼ 8.5 Hz, H-30, 50), 7.50 (1H, d, J ¼ 8.5 Hz, H-4), 7.73 (2H, d, J ¼ 8.5 Hz, H-20, 60),
10.74 (1H, s, 6-OH).
IR (KBr, cmꢀ1): 3072, 2960, 1674, 1644, 1580, 1455, 1376, 1315, 1285, 1249, 1207,
1154, 1131, 1109, 770, 684.
(2Z)-6-Hydroxy-2-(4-nitrobenzylidene)-1-benzofuran-3(2H)-one. The yellow crystals
were obtained, m.p. 249-251ꢁ‘, yield: 80%.
1H NMR (400 MHz, DMSO-d6), d, ppm: 6.695 (1H, dd, J ¼ 8.4, 2.0 Hz, H-5), 6.725
(1H, d, J ¼ 2.0 Hz, H-7), 6.82 (1H, s, –C ¼ CH), 7.57 (1H, d, J ¼ 8.4 Hz, H-4), 8.14 (2H,
d, J ¼ 8.9 Hz, H-20, 60), 8.26 (2H, d, J ¼ 8.9 Hz, H-30, 50), 11.15 (1H, s, 6-OH).
General procedure for synthesis of 6-methacryloxyaurones. (2Z)-6-Hydroxyaurone
(1 mol) was dissolved in 10 ml DMF and triethylamine (1 mol) was added to the solu-
tion. The reaction mixture was kept in an ice-water bath at 0ꢁ‘ with stirring.
Methacryloyl chloride (1.5 mol) was added drop wise. The reaction mixture was stirred
for 4 h at 0ꢁ‘. After stirring the reaction mixture was precipitated in ice. Precipitate
was filtered, washed with water and dried. Solid precipitate was crystallized from mix-
ture toluene:hexane (1:2). Yellow-orange solid of 6-methacryloxyaurones were obtained
with yields 60-80%.

14
V. SMOKAL ET AL.
Figure 3. Changes in the absorption spectra of P2 in THF before (1) and after 1 s period (2) after 3 s
(3), 4 s (4), 5 s (5), 5 s (6), 5 s (7) upon irradiation at k¼ 366nm revealing the trans-cis isomerization.
(2Z)-2-Benzylidene-6-methacryloxy-1-benzofuran-3(2H)-one (A2). The light yellow
crystals were obtained, m.p. 129ꢁ‘, yield: 60%.
1H NMR (400 MHz, DMSO-d6), d, ppm: 2.07 (3H, s, CH3), 5,90 (s, -C ¼ CH (cis)),
6.36 (s, -C ¼ CH (trans)), 7.07 (1H, dd, J ¼ 8.5, 2.0 Hz, H-5), 6.87 (1H, d, J ¼ 2.0 Hz, H-
7), 7.33 (1H, s, -C ¼ CH), 7.83 (1H, d, J ¼ 8.5 Hz, H-4), 7.39-7.48 (2H, m, H-20, 60), 7.94
(2H, d, J ¼ 8.8 Hz, H-30, 50).
IR (KBr, cmꢀ1): 3072, 3041, 2960, 1734, 1714, 1660, 1606, 1452, 1436, 1316,1272,
1250, 1188, 1144, 1127, 1098, 966, 942, 770, 684.
(2Z)-2-[4-(Dimethylamino)benzylidene]-6-methacryloxy-1-benzofuran-3(2H)-one
(A1). The orange crystalline compound was obtained, m.p. 153ꢁ‘, yield: 68%.
1H NMR (400 MHz, DMSO-d6), d, ppm: 2.06 (3H, s, CH3), 3.05 (6H, s, NMe2), 5,88
(s, -C ¼ CH (cis)), 6.35 (s, -C ¼ CH (trans)), 7.05 (1H, dd, J ¼ 8, 2.0 Hz, H-5), 7.00 (1H,
d, J ¼ 2.0 Hz, H-7), 7.38 (1H, s, -C ¼ CH), 7.85 (1H, d, J ¼ 8 Hz, H-4), 8.18 (2H, d,
J ¼ 8.9 Hz, H-20, 60), 8.28 (2H, d, J ¼ 8.9 Hz, H-30, 50).
(2Z)-6-Methacryloxy-2-(4-nitrobenzylidene)-1-benzofuran-3(2H)-one (A3). The yel-
low crystalline compound was obtained, m.p. 220ꢁ‘, yield: 82%.
1H NMR (400 MHz, DMSO-d6), d, ppm: 2.07 (3H, s, CH3), 5,91 (s, -C ¼ CH (cis)),
5,91(s, -C ¼ CH2 (trans)), 7.05 (1H, dd, J ¼ 8, 2.0 Hz, H-5), 7.00 (1H, d, J ¼ 2.0 Hz, H-
7), 7.38 (1H, s, -C ¼ CH), 7.85 (1H, d, J ¼ 8 Hz, H-4), 8.18 (2H, d, J ¼ 8.9 Hz, H-20, 60),
8.28 (2H, d, J ¼ 8.9 Hz, H-30, 50).
Polymerization
The aurone polymers were synthesized by free-radical polymerization. The polymeriza-
tion was carried out in 10 wt% DMF solution of monomers and was conducted using
azobis(isobutyronitrile) (AIBN) as a free-radical initiator (1 wt% of monomer) at 80ꢁ‘
24 h in argon atmosphere. The reaction mixture was precipitate in absolute methanol,

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
15
Figure 4. Changes in the absorption spectra of P3 in THF before (1) and after 2 s period (2) after 4 s
(3), 4 s (4), 4 s (5), 4 s (6), 10 s (7), 20 s (8) upon irradiation at k¼ 366nm revealing the trans-cis
isomerization.
and then the polymer was redissolved in THF, and then precipitated in methanol. This
procedure was repeated several times to ensure removal of unreacted methacrylic mono-
mer and finally the copolymer was dried under reduced pressure at 60ꢁ‘ for constant
weight. The synthesis of copolymers based on aurones methacrylic monomers and
methylmethacrylate (MMA) was as a typical polymerization procedure [18,19,20].
3. Results and discussion
The 6-hydroxyaurone derivatives with different substituents have been obtained by the
condensation of 6-hydroxybenzofuran-3-ones with benzaldehydes in solution of ethanol
and DMF. The aurone methacrylate monomers were synthesized by reacting the aurone
alcohols with methacryloyl chloride in the presence of triethylamine as nucleophilic
catalyst and hydrochloric acid acceptor. The polymers were synthesized by free radical
polymerization using AIBN as radical initiator.
Polar substituents in aurone compounds such as –N(CH3)2 and –NO2 can act as
retarding agents of free radical polymerization reaction. Therefore, long reaction time is
needed to synthesize polymers with high yield. The structures of obtained polymers
were confirmed by 1H NMR spectra. The compositions of the copolymers were well-
controlled as the initial ratio of the aurone monomers and MMA (n:m ¼ 1:3). The Tg
are 106ꢁ‘, 95ꢁ‘, 106ꢁ‘ for P1, P2, P3 . As expected, the glass transition temperatures
(Tg) are typical for methacrylate copolymers without conformationally flexible alkyl
chains and rigid moieties. Also the introduction of polar substituents in aurone com-
pounds such as –N(CH3)2 and –NO2 in the methacrylate monomers tend to slightly
increase Tg (P1 and P3 vs P2).
Investigation of photochemical properties of aurones were conducted taking into
account the spectral characteristic which we can study after measurement absorption

16
V. SMOKAL ET AL.
Figure 5. The absorption -1, emission (kex¼366:375-700 nm) -2, fluorescence of excitation (220-
515:515, k ¼ 420 nm) -3 of A3 in ethanol at room temperature.
and fluorescence emission spectra. Absorption and fluorescence emission spectra of
aurones were measured in quartz cells, which were filled with THF or ethanol .
The absorption spectra compounds P2 and P3 during UV irradiation are represented
in Fig.3, 4.
In the spectrum of absorption the THF solutions of P2 (Fig. 3) and P3 (Fig. 4) have
three bands with vibrational structure, i.e. the intensive long-wave bands with approxi-
mate maximum of 370 nm and 316 nm for P2, of 380 nm and 317 nm for P3 and a
medium-intensity absorption band with its maximum about 250 nm for both P2 and
P3 copolymers.
During the P2 and P3 solutions irradiation process the decolouration is observed
accompanied with a drop of the long-wave maximum intensity, as well as an decrease
of absorption intensity at 370 nm with isosbestic point at 346, 396 nm for P2 and the
decrease of the absorption intensity at 380 nm with isosbestic point at 345, 396 nm for
P3. The presence of isosbestics points at 396 can be also prompting the running proc-
esses of photo-Fries rearrangement typical of j- oxyketones structures.
The stable state of the aurone molecule is the cis isomeric configuration [9]. The
absorption in the visible range of a photon induces the transition to the trans isomer.
This state is metastable with the reverse transition to the cis- state taking place through
photo activation. Therefore, a molecule absorbing of a photon undergoes a complete
cis-trans-isomerization. From the trans form, molecules come back to the cis form by
two mechanisms – spontaneous thermal reactions and trans-cis photoisomerization. The
normalised absorption, fluorescence of excitation and fluorescence spectra of A3 in
ethanol are shown in Fig.5.
The emission was observed between 400 and 650 nm with kF at 514 nm for A3 and
corresponding to S1!S0 transition. The methacrylic polymers based on aurone deriva-
tives offer great promise for practical device applications due to their photochemical
properties particularly for the optical data storage.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
17
4. Conclusion
The present work reflects the experimental investigations of the photochemical proper-
ties of the aurone derivatives. The idea of the photo-Fries reaction possibility by UV-
irradiation has been obtained. The total understanding of the relationship between the
structure and photochemical properties of aurone derivatives reveals the possibility for
their potential applications in the field of photonics and optoelectronics. Polymers based
on them are very promising for optical data storage as well as the orientation of photo-
chromic polymers, the photoalignment of liquid crystals and all-optical processing.
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