Synthesis and study of photochromic properties of copolymers based on functionalized chromenes

Article abstract of DOI:10.1007/s11172-011-0219-3

Chromenes functionalized with methacryl groups were synthesized and involved into the radical polymerization to obtain copolymers with ethyl acrylate. Comparison of spectral kinetic characteristics of poly(methyl methacrylate) glasses containing chromenes and photochromic copolymers as additives led to a conclusion that incorporation of a photochromic compound as a part of a copolymer into the polymeric glass increases efficiency of photocoloration of photochromic compounds in the polymeric layer.

Full text of DOI:10.1007/s11172-011-0219-3

Russian Chemical Bulletin, International Edition, Vol. 60, No. 7, pp. 1469—1475, July, 2011
1469
Synthesis and study of photochromic properties of copolymers
based on functionalized chromenes
V. P. Grachev,a G. M. Bakova,a L. I. Makhonina,a E. A. Yurieva,a S. M. Aldoshin,a
A. M. Gorelik,b and V. A. Barachevskiib
aInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
1 prosp. Akad. Semenova, 142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (496) 522 3507. Eꢀmail: grachov@icp.ac.ru
bCenter of Photochemistry, Russian Academy of Sciences,
7a, korp. 1 ul. Novatorov, 119421 Moscow, Russian Federation
Chromenes functionalized with methacryl groups were synthesized and involved into the
radical polymerization to obtain copolymers with ethyl acrylate. Comparison of spectral kinetic
characteristics of poly(methyl methacrylate) glasses containing chromenes and photochromic
copolymers as additives led to a conclusion that incorporation of a photochromic compound as
a part of a copolymer into the polymeric glass increases efficiency of photocoloration of photoꢀ
chromic compounds in the polymeric layer.
Key words: chromenes, photochromic copolymers, photochromic glasses, radical polymerꢀ
ization, spectral kinetic characteristics.
Development of photochromic materials for different
designations in most cases is based on the use of polymeric
binders, which makes it necessary to optimize their comꢀ
ponent composition to provide high light sensitivity and
acceptable rate of thermal relaxation.1 This can be reached,
for example, by the use of combꢀlike polymers as the polyꢀ
meric binders, since they are characterized by the large
free molecular volume.2 The efficiency of photochromic
transformations of spiro compounds in polymeric matriꢀ
ces based on methyl methacrylate (MMA) can be increased
by its copolymerization with alkyl methacrylates having
bulky substituents.3 The free molecular volume in a polyꢀ
mer increases if branched or hyperbranched polymers are
incorporated into the polymeric matrix of macromoleꢀ
cules.4 In fact, it was found that the rate of photochromic
transformations in the matrices of branched, as well as
linear polyacrylates, existing at room temperature in the
highly elastic state, is by 5—10 times higher than in polyꢀ
mers based on methacrylates.5,6
photochemical reactions in the polymers under considerꢀ
ation can significantly increase. This can result from the
covalent binding of a spiro compound with the molecule
of elastomer, which is separated in the PMMA matrix as a
microphase.
The purpose of the present work is to study possibilities
for the synthesis of photochromic PMMA glasses conꢀ
taining sites with increased molecular lability in the form
of the elastomer microphase, in which all the molecules of
photochromic compound are localized.
To solve this problem, we synthesized a lowꢀmolecuꢀ
larꢀweight PEA by radical polymerization in the presence
of photochromic 8ꢀallylꢀ6ꢀformylꢀ1´,3´,3´ꢀtrimethylꢀ
spiro[2Hꢀ1ꢀbenzopyranꢀ2,2´ꢀindoline] (Photꢀ1) containꢀ
ing an allyl group, which can be involved into copolymerꢀ
ization with ethyl acrylate (EA) in order for the photoꢀ
chromic fragments to be fixed on the polymeric chain.
Later it was shown7 that the efficiency of photochemiꢀ
cal reactions of molecules of photochromic 8ꢀallylꢀ6ꢀ
formylꢀ1´,3´,3´ꢀtrimethylspiro[2Hꢀ1ꢀbenzopyranꢀ2,2´ꢀ
indoline] increases in the glasses of poly(methyl methꢀ
acrylate) (PMMA) modified with linear and branched
poly(ethyl acrylates) (PEA). The maximum effect occurs
in the presence of the linear PEA additives, which form
sites with increased molecular lability. A suggestion was
made that it is reasonable to localize all the molecules of a
photochromic compound in such sites; the efficiency of
The process was performed in ethanol (70 wt.%). Howꢀ
ever, attempted synthesis of the photochromic elastomer
failed. Kinetic studies showed that when the ratio of reꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1446—1452, July, 2011.
1066ꢀ5285/11/6007ꢀ1469 © 2011 Springer Science+Business Media, Inc.

1470
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Grachev et al.
Scheme 1
agents EA : Photꢀ1 = 5 : 1, Photꢀ1 strongly inhibits the
process of polymerization of EA and decreases its highest
conversion to 23%. Moreover, the copolymer synthesized
did not exhibit photochromic properties. The negative reꢀ
sult that obtained can be explained, from the one hand, by
low stability of spiropyrans to radical reactions, and form
the other hand, by high activity of the acrylate radical. In
this connection, in this work we synthesized spiro comꢀ
pounds from the chromene class functionalized with the
reactive methacryl group. Such compounds differ from
spiropyrans by higher stability to irreversible phototransꢀ
formations. We also obtained copolymers on their basis
and studied their photochromic properties in solutions,
films, and PMMA glasses.
Results and Discussion
and the photochromic part of the molecules, the absoluteꢀ
ly identical photochroms are attached to the polymeric
chain at different distances.
Synthesis of functionalized chromenes. Photochromic
naphthopyrans Photꢀ2, Photꢀ3, and Photꢀ4 were syntheꢀ
sized by the reaction of hydroxynaphthopyrans 1 and 2
with methacryloylamino acids 3 and 4. Amino acids 3 and
4 were obtained by the reaction of methacryloyl chloride
with aminohexanoic and aminoacetic acids, respectively
(Scheme 1).
Synthesis of copolymers of ethyl acrylate with photoꢀ
chromic compounds. Copolymers of EA with photochromic
compounds Photꢀ2 (linear Polꢀ1 and branched PolBꢀ1),
Photꢀ3 (linear Polꢀ2), and Photꢀ4 (linear Polꢀ3) were
synthesized by radical copolymerization according to the
procedures developed earlier.7
Since chromenes Photꢀ3 and Photꢀ4 differ only in the
size of their alkyl fragments between the methacryl group

Photochromic copolymers with chromenes
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1471
Table 1. Molecular mass characteristics of photoꢀ
chromic copolymers*
the PMMA glasses obtained with the additives of chromene
Photꢀ2 and derived from it copolymers are given in Table 2
and in Figs 1—3.
Figure 1 shows the photoinduced changes in the abꢀ
sorption spectra of compound Photꢀ2 in solution and polyꢀ
meric films.
In the PMMA film, unlike in solutions, a somewhat
growth in the τ1/2, is observed in addition to some changes
in the absorption spectra, and, as it was expected, the
efficiency of photocoloration falls by 2.5 times (see Table 2).
Introduction of the PEA additives to the composition unꢀ
der consideration does not lead to the expected improveꢀ
ment in kinetic characteristics. Conversely, degree of the
photocoloration becomes somewhat smaller. If the rate
constants k1 and k2 remain unchanged values of the conꢀ
tent of the polymer described by the slow constant k2 inꢀ
creases (proportion of the preexponents A1/A2 decreases).
Polymer
Mn•10–3
Mw•10–4 Mw/Mn
Polꢀ1
PolBꢀ1
Polꢀ2
Polꢀ3
24.0
2.9
20.0
22.0
4.9
2.6
5.5
5.3
2.1
9.0
2.8
2.4
* Mn and Mw are the number average and weight
average molecular masses, respectively.
The molecular mass characteristics of the synthesized
copolymers are given in Table 1.
The procedure7 was used for the synthesis of PMMA
glasses containing additives of the synthesized copolyꢀ
mers, as well as chromenes and linear lowꢀmolecularꢀ
weight PEA.
Spectral kinetic studies. It is known1 that chromenes
undergo reversible phototransformations of the starting
colorless cyclic form A to the photoinduced colored form
B upon irradiation with the UV light absorbed by the startꢀ
ing form (Scheme 2).
A
1.0
Scheme 2
4
0.5
3
5
6
1
2
0
300
400
500
600
λ/nm
Fig. 1. Absorption spectra of the starting (1—3) and photoinduced
(4—6) forms of compound Photꢀ2 in acetone (1, 4), in PMMA
(2, 5), and in PMMA with 2% PEA additive (3, 6).
A
1.5
1.0
5
4
6
1
0.5
3
2
Spontaneous bleaching of the photoinduced form B
can be accelerated upon the action of visible irradiation
absorbed by this form or upon heating.
300
400
500
600
λ/nm
The research results on spectral kinetic characteristics
of photochromic compound Photꢀ2, its copolymers Polꢀ1,
PolBꢀ1 in solutions and in films, as well as the samples of
Fig. 2. Absorption spectra of starting (1—3) and photoinduced
(4—6) forms of copolymer Polꢀ1 in acetone (1, 4), in film (2, 5),
and in PMMA (3, 6).

1472
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Grachev et al.
A
highly elastic state at the temperature of experiment (amꢀ
bient), and in their solutions, the difference in lability of
the photochromic part of the molecule can be due to the
uneven distribution of the photochromic fragments in the
macromolecular chain. Where the density of the chain
units with photochromic fragments is larger, their lability
can be restricted due to the interaction with each other.
This can also be the reason for the smaller contribution of
the slow constant k2 in the linear copolymer Polꢀ1 as comꢀ
pared to the branched PolBꢀ1. Judging from the proporꢀ
tion of the preexponential factors (see Table 2), the fast
component prevails in all the cases. The unexpected presꢀ
ence of two constants in the description of kinetics of the
bleaching of the starting Photꢀ2 in the solvent is apparentꢀ
ly due to the position and the nature of the substituent in
the pyran fragment.
The synthesized chromene Photꢀ2 is characterized by
the high rate of relaxation of the photoinduced form. In
this case, its covalent binding to the elastomer polymeric
chain does not decrease the indicated value. The time of
halfꢀconversion during the dark bleaching in the PMMA
glass is just by 1.5—2 times longer than in the solvent, i.e.
even a glassꢀlike matrix affects weakly the dark bleaching
of the photoinduced form of chromene Photꢀ2. Therefore,
the τ1/2 value in the case of PMMA film apparently is
virtually the same for the starting chromene in the absence
and in the presence of the elastomer additives and for the
chromene covalently bound to the elastomer. This result
differs from that obtained in the experiments with the
formylꢀsubstituted spiropyran, where both the rate of the
reaction and efficiency of photocoloration of the photoꢀ
chrom in the glassꢀlike matrices changed significantly in
the presence of the elastomer additives.7 Apparently, such
a behavior of the chromene is due to the fact that the rate
constants of its dark relaxation is by the order of magniꢀ
tude higher as compared to the formylꢀsubstituted spiroꢀ
pyran and the open merocyanine form is characterized by
low thermodynamic stability. The weak effect of the
PMMA matrix on the rate of photochemical transformaꢀ
tions can be also due to the low level of intermolecular
interaction of the phenyl fragments of the spiropyran ring
with the PMMA macromolecules.
0.4
0.2
0
4
3
2
1
300
400
500
600
λ/nm
Fig. 3. Absorption spectra of the starting (1, 2) and photoinducꢀ
ed (3, 4) forms of chromenes Photꢀ3 (1, 3) and Photꢀ4 (2, 4) in
acetone.
Copolymerization of compound Photꢀ2 with EA virꢀ
tually does not change the rate of bleaching in acetone
(the τ1/2 values are close). Copolymers Polꢀ1 (see Fig. 2)
and PolBꢀ1 have similar spectral characteristics. However,
the efficiency of photocoloration for the linear copolymer
Polꢀ1 in all the compositions under study is lower than for
the branched copolymer PolBꢀ1. The content of photoꢀ
chromic fragments in the sites with reduced molecular
lability characterized by the slow constant is by 3—4 times
lower for Polꢀ1 than for PolBꢀ1 in all the compositions.
Apparently, in the branched polymer PolBꢀ1, the branchꢀ
ing nodes considerably restrict the segmental lability of
the chain units around the photochromic fragment, that
affects characteristics of its photochromic transformations.
Going from solutions to the copolymer films and PMMA
glasses, the efficiency of photocoloration of both copolyꢀ
mers falls, but, like in solutions, it is ∼2 times higher for
the branched copolymer PolBꢀ1 than for Polꢀ1. Kinetics
of the dark bleaching in films remains the same as in
solution, whereas in glasses the rate decreases and the
τ
1/2 values in both samples increase twofold.
Analysis of the results of spectral kinetic studies of
photochromic transformations of compound Photꢀ2 and
copolymers Polꢀ1 and PolBꢀ1 allows us to draw the folꢀ
lowing conclusions. Kinetic curves of the dark bleaching
of compound Photꢀ2 and its photochromic copolymers
are not described by one exponential dependence neither
in solutions, nor in polymeric films and glasses. The curves
are approximated corresponding to the biexponential equaꢀ
tion D(t) = A1exp(–k1t) + A2exp(–k2t), whose constants
reflect molecular lability in the sites where the photoꢀ
chrom is localized. The difference in the constants indiꢀ
cates the presence of structural heterogeneity in the polyꢀ
meric glasses, that is not unexpected, and a relatively even
distribution of photochromic fragments in the glassꢀlike
matrix. In photochromic copolymers, which are in the
To sum up, it should be noted that copolymers Polꢀ1
and PolBꢀ1 are inferior in the efficiency of the photocolorꢀ
ation process in both films and PMMA glasses to the
PMMA glasses based on chromene Photꢀ2 (see Table 1).
In this connection, we studied behavior of the syntheꢀ
sized chromenes Photꢀ3 and Photꢀ4 with methoxy subꢀ
stituents in the phenyl fragments, which were incorporatꢀ
ed in order to intensify intermolecular interactions with
the matrix and increase the activation volume, as well as
with the methacryl substituents as R2.
The results of the studies of the obtained photochrom
samples, as well as copolymers Photꢀ2 and Photꢀ3 on their
basis are given in Table 2 and in Fig. 3.

Photochromic copolymers with chromenes
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1473
Table 2. Spectroscopic kinetic characteristics of chromenes and their copolymers*
Object
under study
λ
max/nm
(DA)
ε•10–3
λ
max/nm
ΔDBPhot/DA
kBA/s–1
(k1/k2)
A1/A2
τ1/2/s
B
Phot
/L mol–1 cm–1
(ΔDB
)
Photꢀ2 in acetone
(c = 7.0•10–5 mol L–1
PolBꢀ1 in acetone
353 (0.22)
353 (0.43)
353 (0.62)
344 (0.3)
345 (1.2)
342 (0.3)
342 (0.3)
345 (0.3)
345 (0.5)
352 (0.26)
3.1
2.9
3.5
—
424 (0.5)
422 (0.5)
424 (0.4)
431 (0.2)
428 (0.5)
424 (0.3)
423 (0.2)
425 (0.2)
425 (0.2)
487 (0.2)
2.5
1.2
0.7
0.7
0.4
1.0
0.7
0.7
0.4
0.8
(0.160/
0.050)
(0.192/
0.005)
(0.225/
0.003)
(0.297/
0.007)
(0.208/
0.013)
(0.125/
0.009)
(0.123/
0.011)
(0.213/
0.027)
(0.130/
0.013)
0.211
1.43
1.92
8.33
2.04
7.14
3.03
2.22
0.92
2.70
—
6.0
5.0
5.0
5.0
4.0
8.0
9.0
9.0
8.0
4.0
)
Polꢀ1 in acetone
Film PolBꢀ1
Film Polꢀ1
—
Photꢀ2 (0.05 wt.%)
in PMMA
Photꢀ2 (0.05 wt.%)
in PMMA + 2% PEA
PolBꢀ1 (2%) in PMMA
—
—
—
Polꢀ1 (2%) in PMMA
—
Photꢀ3 in acetone
(c = 7.0•10–5 mol L–1
Polꢀ2 in acetone
Film Polꢀ2
Photꢀ3 (0.1%)
in PMMA
3.7
3.9
—
)
)
351 (0.28)
355 (2.1)
342 (1.0)
488 (0.3)
498 (>2.5)
490 (0.2)
1.0
>1.2
0.2
0.210
0.110
8.20
—
0.91
4.0
8.0
81.0
(0.021/
0.0023)
(0.160/
0.0094)
0.172
Polꢀ2 (2%)
in PMMA
340 (1.7)
—
491 (0.6)
490 (0.3)
0.4
1.0
4.60
—
7.0
Photꢀ4 in acetone
(c = 7.0•10–5 mol L–1
Polꢀ3 in acetone
Film Polꢀ3
Photꢀ4 (0.1%)
in PMMA
352 (0.29)
4.2
4.5
351 (0.22)
341 (1.4)
342 (1.0)
4.0
—
—
491 (0.3)
501 (0.9)
493 (0.2)
1.5
0.6
0.2
0.133
0.070
(0.018/
0.0023)
(0.090/
0.0062)
12.7
—
0.81
6.0
12.0
93.0
Polꢀ3 (2%)
in PMMA
340 (1.9)
—
493 (0.7)
0.2
2.7
11.0
* λ max and λ max are the wavelengths of the absorption band maxima of the starting (A) and photoinduced (B) forms; DA is the optical
A
B
Phot
density in the absorption band maximum of the starting form; ΔDB
is the photoinduced change in the optical density in the
absorption band maximum of the photoinduced form B in the photoequilibrium state; k1 and k2 are the rate constants of the dark
bleaching; A1/A2 is the ratio of preexponential factors of the dark bleaching reaction; τ1/2 is the time of spontaneous twofold decrease in
the photoinduced optical density in the photostationary state.
Comparison of the data (see Table 2, Figs 1 and 3)
shows that chromenes Photꢀ3 and Photꢀ4 (methoxy deꢀ
rivatives of chromene Photꢀ2) are characterized by the
same absorption spectra of the cyclic form A as those of
chromene Photꢀ2, whereas the absorption bands of the
photoinduced form B in acetone are shifted by ∼65 nm to
the longꢀwave region of the spectrum.
An increase in the spacer length in the case of chromene
Photꢀ3 as compared to compound Photꢀ4 leads to the
insignificant hypsochromic shift of the absorption bands
of the photoinduced form B, that, probably, is due to the
steric effects of the spacers on the conformation of the
merocyanine form of the molecule.
Unlike for chromene Photꢀ2, the process of dark reꢀ
laxation of the photoinduced form in acetone is described
by the first order kinetics, whereas the rate constants of
the dark relaxation insignificantly depend on the spacer
length.
Similar properties are also observed in the case of soluꢀ
tions of copolymers in acetone, however, the efficiency of
the photocoloration process either increases, as in the case
of copolymer Polꢀ3, or is not changed, as in the case of
copolymer Polꢀ2. The degree of photocoloration of the
solution of photochromic copolymer with a short spacer
Polꢀ3 is even higher than for compound Polꢀ3 in acetone,
that is apparently due to the reduced rate of the dark

1474
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
Grachev et al.
A
a solution of 2,7ꢀdihydroxynaphthalene (5.0 g, 0.03 mol) and
1,1ꢀdiphenylꢀ2ꢀpropynꢀ1ꢀol (6.5 g, 0.03 mol) in diethyl ether
(50 mL). The reaction mixture was stirred for 4 h at ∼20 °C and
filtered, diethyl ether was evaporated off from the filtrate, and
the residue was extracted with toluene. The solvent was evapoꢀ
rated in vacuo, the product that obtained was subjected to
chromatography on silica gel using the benzene—ethyl acetate
(10 : 1) mixture as an eluent. Evaporation of the solvents gave
chromene 1 (2.5 g). Crystallization from toluene yielded a light
yellow powder (2.1 g), m.p. 152 °C.
3
2
1
4
5ꢀHydroxyꢀ3,3ꢀdiphenylꢀ3Hꢀnaphtho[2,1ꢀb]pyran (2). A caꢀ
talytic amount of pꢀtoluenesulfonic acid was added to a solution
of 2,3ꢀdihydroxynaphthalene (1.14 g, 7.5 mmol) and 1,1ꢀdiꢀ
(4ꢀmethoxyphenyl)ꢀ2ꢀpropynꢀ1ꢀol (2.0 g, 7.5 mmol) in anꢀ
hydrous benzene (60 mL). The reaction mixture was stirred for
2 h at 50 °C and filtered, the solvent was evaporated in vacuo.
The oil that obtained was subjected to chromatography on silica
gel (eluent: benzene—ethyl acetate (10 : 1)) and recrystallized
from the benzene—hexane (1 : 2) mixture to yield a light pink
powder (2 g, 65%), m.p. 116—118 °C.
NꢀMethacryloylꢀεꢀaminohexanoic acid (3). A solution of
6ꢀaminohexanoic acid (7.51 g, 0.10 mol) and hydroquinone
(60 mg) in 2 M aq. NaOH (50 mL) was cooled with stirring in an ice
bath, followed by addition in portions of 2 M aq. NaOH (50 mL)
and methacryloyl chloride (10.45 g, 0.10 mol L–1) so that the pH
of the reaction mixture corresponded to 9—10. A colored soluꢀ
tion was stirred for 3 h at ∼20 °C, followed by addition of conꢀ
centrated HCl to pH 1—3, saturation with sodium chloride, and
extraction with ethyl acetate (2×100 mL). The extract was washed
with water to neutrality, the organic layer was separated, dried
with magnesium sulfate, and concentrated in vacuo. The comꢀ
pound thus obtained was subjected to chromatography on a colꢀ
umn with silica gel using ethyl acetate as an eluent. The yield
was 8.0 g (40%), light yellow oil. 1H NMR, δ: 1.10—1.60 (m, 6 H,
CH2(CH2)3CH2); 1.82 (s, 3 H, Me); 2.21 (t, 2 H, CH2CO); 3.12
(m, 2 H, CH2N); 5.30 (s, 1 H, C=CH2); 5.63 (s, 1 H, C=CH2);
7.80 (t, 1 H, NH); 11.90 (s, 1 H, COOH).
2
1
300
400
500
600
λ/nm
Fig. 4. Absorption spectra of the starting (1, 2) and photoinduced
(3, 4) forms of copolymers Polꢀ2 (1, 3) and Polꢀ3 (2, 4) in film.
bleaching. Conversely, for the thin films and PMMA glassꢀ
es the efficiency of photocoloration becomes higher for
the copolymers derived from chromene Polꢀ3 with the
long spacer. In the case of films of copolymers, it considꢀ
erably exceeds this parameter for compounds Photꢀ3 and
Photꢀ4 in PMMA.
The rate constants of the dark bleaching for copolymer
Polꢀ2 with the chromene having a long alkyl fragment is
higher than that for copolymer Polꢀ3 with a short spacer,
whereas the τ1/2 time is shorter by 1.5 times.
The photoinduced changes in the absorption spectra
of the Polꢀ2 and Polꢀ3 copolymer films are shown in Fig. 4.
Copolymers behave similarly in the PMMA glasses.
The glassꢀlike matrix does not significantly affect the rate
of the dark relaxation in the photochrom (τ1/2 remains
virtually the same), however, the kinetic curves are deꢀ
scribed by the biexponential equation. The efficiency of
the photocoloration processes also sharply drops.
Unlike copolymers, the individual chromenes Photꢀ3
and Photꢀ4 in the PMMA glasses are characterized by
a sharp decrease in the rate constant of the dark bleaching
and a fall in the photocoloration efficiency. In this case,
the highest efficiency of photocoloration was obtained in
the PMMA glasses containing copolymer Polꢀ2.
NꢀMethacryloylaminoacetic acid (4). A solution of glycine
(7.51 g, 0.10 mol) and hydroquinone (60 mg) in 2 M aq. NaOH
(50 mL) was cooled to –10 °C with mechanical stirring. The
thus obtained solution was diluted with 2 M aq. NaOH (50 mL)
and methacryloyl chloride (10.5 g, 0.10 mol). The reaction mixꢀ
ture was stirred for 2 h, keeping the pH within 9—10. A solution
that obtained was treated with conc. hydrochloric acid to pH 1—3,
saturated with NaCl, and extracted with THF. The extract was
washed with water, dried with magnesium sulfate, the solvent
was evaporated in vacuo. The solid product thus obtained was
recrystallized from the acetone—diethyl ether (10 : 1) mixture,
In conclusion, the results of the present studies suggest
a possibility to control efficiency of photocoloration of
chromenes upon the action of a UV irradiation and the
rate of their dark relaxation through the use of copolymers
with spacers of different lengths.
1
m.p. 104—105 °C. The yield was 6.1 g (43%). H NMR, δ: 1.86
(s, 3 H, Me); 3.76 (d, 2 H, CH2N); 5.38 (s, 1 H, C=CH2); 5.71
(s, 1 H, C=CH2); 8.21 (t, 1 H, NH); 12.44 (t, 1 H, COOH).
9ꢀ(NꢀMethacryloylꢀεꢀaminohexanoyloxy)ꢀ3,3ꢀdiphenylꢀ3Hꢀ
naphtho[2,1ꢀb]pyran (Photꢀ2). A solution of 9ꢀhydroxyꢀ3,3ꢀpheꢀ
nylꢀ3Hꢀnaphtho[2,1ꢀb]pyran (1) (0.53 g, 1.5 mmol), Nꢀmethaꢀ
cryloylꢀεꢀaminohexanoic acid (0.30 g, 1.5 mmol), N,Nꢀdicycloꢀ
hexylcarbodiimide (0.30 g, 1.5 mmol), and 4ꢀpyrrolidinopyriꢀ
dine (0.023 g, 0.15 mmol) in anhydrous dichloromethane (40 mL)
was stirred at ∼20 °C for 16 h. The N,Nꢀdicyclohexylurea that
formed was filtered off, the filtrate was washed with water
(3×50 mL), 5% aq. acetic acid, and again with water (3×50 mL).
The organic layer was separated and dried with magnesium sulꢀ
Experimental
1
H NMR spectra were recorded on a Bruker AM300 SF
spectrometer (300.13 MHz) in DMSOꢀd6 using Me4Si as an
internal standard; TLC was performed on DCꢀAlufolien Kieselꢀ
gel 60 F254 plates (Merck).
9ꢀHydroxyꢀ3,3ꢀdiphenylꢀ3Hꢀnaphtho[2,1ꢀb]pyran (1). A caꢀ
talytic amount of pꢀtoluenesulfonic acid (0.01 g) was added to

Photochromic copolymers with chromenes
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 7, July, 2011
1475
fate, the solvent was evaporated in vacuo. A benzene—ethyl aceꢀ
tate (2 : 1) (10 mL) mixture was added to the product obtained,
which was stirred and filtered. The filtrate was subjected to chroꢀ
matography on silica gel eluting with the benzene—ethyl acetate
(2 : 1) mixture. The yield was 0.21 g (29%), light red oil.
1H NMR, δ: 1.91 (s, 3 H, Me); 4.28 (d, 2 H, CH2); 5.47 (s, 1 H,
7´ꢀCH2); 5.81 (s, 1 H, 7´ꢀCH2); 6.59 (d, 1 H, 2ꢀH); 6.86 (m, 4 H,
Ar); 7.40 (m, 5 H, Ar); 7.50 (m, 2 H, Ar); 7.59 (s, 1 H, Ar); 7.81
(d, 1 H, 6ꢀH); 8.09 (d, 1 H, 1ꢀH); 8.63 (t, 1 H, NH).
with an UFSꢀ2 light filter, which transmitted the UV irradiaꢀ
tion in the region 280—380 nm. The intensity of photolyzing
irradiation was 2.4•10–4 Einstein s–1, the measurements were
performed by chemical actinometer based on potassium ferriꢀ
oxalate.
Efficiency of photocoloration (degree of photocoloration) of
photochromic systems was evaluated based on the value of the
photoinduced optical density in the absorption band maximum
of the photoinduced merocyanine form B in the state of photoꢀ
equilibrium, normalized on the value of optical density in the
absorption band maximum of the starting spiropyran form A
(ΔDBPhot/DA). This parameter totalizes effects of all the photo
and thermal transformations of photochromic molecules in the
state of photoequilibrium (ΔDBPhot) with allowance for the abꢀ
sorption of light by the photochromic systems with different conꢀ
centration of photochromic molecules in the layer (DA) and alꢀ
lows us to evaluate the real efficiency of photocoloration of
photochromic systems as a whole. To exclude significant errors
in the evaluation of the photocoloration efficiency, the comparꢀ
ative spectroscopic kinetic studies were performed under the
same experimental conditions.
5ꢀ(NꢀMethacryloylaminoacetoxy)ꢀ3,3ꢀdi(4ꢀmethoxyphenyl)ꢀ
3Hꢀnaphtho[2,1ꢀb]pyran (Photꢀ4). A solution of compound 2
(0.60 g, 1.5 mmol), Nꢀmethacryloylaminoacetic acid (0.21 g,
1.5 mmol), N,Nꢀdicyclohexylcarbodiimide (0.30 g, 1.5 mmol),
and 4ꢀpyrrolidinopyridine (0.023 g, 0.15 mmol) in anhydrous
dichloromethane (40 mL) was stirred at ∼20 °C for 16 h. N,NꢀDiꢀ
cyclohexylurea was filtered off, the filtrate was washed with waꢀ
ter (3×50 mL), 5% aq. acetic acid (3×50 mL), water (3×50 mL),
and dried with MgSO4. The organic solvent was evaporated
in vacuo. The final product (5 mL) was stirred in the benzꢀ
ene—ethyl acetate (2 : 1) mixture, filtered, and the filtrate was
subjected to chromatography on silica gel using benzene—ethyl
acetate (2 : 1) as an eluent. The yield was 0.46 g (59%), a light
pink powder; m.p. 138—140 °C. 1H NMR, δ: 1.91 (s, 3 H, Me);
3.69 (s, 6 H, (OMe)2); 4.28 (d, 2 H, CH2); 5.47 (s, 1 H,
CO—CH2); 5.81 (s, 1 H, CO—CH2); 6.59 (d, 1 H, 2ꢀH); 6.86
(m, 4 H, Ar); 7.40 (m, 5 H, Ar); 7.50 (m, 2 H, Ar); 7.59 (s, 1 H,
Ar); 7.81 (d, 1 H, 6ꢀH); 8.09 (d, 1 H, 1ꢀH); 8.63 (t, 1 H, NH).
5ꢀ(NꢀMethacryloylꢀεꢀaminohexanoyloxy)ꢀ3,3ꢀdi(4ꢀmethꢀ
oxyphenyl)ꢀ3Hꢀnaphtho[2,1ꢀb]pyran (Photꢀ3). Photochrom
Photꢀ3 was obtained according to the procedure for compound
Photꢀ4 using Nꢀmethacryloylꢀεꢀaminohexanoic acid as an acyꢀ
lating agent. The yield was 0.26 g (62%), a white powder; m.p.
The authors are grateful to S. V. Kurmaz for the synꢀ
thesis of the branched photochromic copolymer PolBꢀ1.
References
1. V. A. Barachevskii, G. I. Lashkov, V. A. Tsekhomskii, Foꢀ
tokhromizm i ego primenenie [Photochromism and its Applicaꢀ
tion], Khimiya, Moscow, 1977, 279 pp. (in Russian).
2. N. A. Plate, V. P. Shibaev, Grebneobraznye polimery i zhidkie
kristally [Combꢀlike Polymers and Liquid Crystals], Khimiya,
Moscow, 1980, 303 pp. (in Russian).
3. O. V. Kameneva, L. A. Smirnova, K. V. Kir´yanov, A. H.
Maslov, V. A. Barachevckii, A. P. Alekcandrov, H. M. Biꢀ
tyurin, Vysokomolekulyar. Soedin., Ser. A, 2003, 45, 1508
[Polym. Sci., Ser. A (Engl. Transl.), 2003, 45].
1
127—129 °C. H NMR, δ: 1.38 (m, 2 H, CH2); 1.45 (m, 2 H,
CH2); 1.71 (m, 2 H, CH2); 1.84 (s, 3 H, Me); 2.67 (t, 2 H, CH2);
3.07 (m, 2 H, CH2); 3.70 (s, 6 H, OMe); 5.29 (s, 1 H, =CH2);
5.63 (s, 1 H, =CH2); 6.51 (d, 1 H, Ar); 6.88 (d, 4 H, 3ꢀAr); 7.30
(d, 4 H, 3ꢀAr); 7.38—7.52 (m, 3 H, Ar); 7.60 (s, 1 H, 6ꢀH); 7.79
(d, 1 H, Ar); 7.86 (t, 1 H, NH); 8.11 (d, 1 H, Ar).
4. G. V. Korolev, M. L. Bubnova, Vysokomolekulyar. Soedin.,
Ser. C, 2007, 49, 1357 [Polym. Sci., Ser. with (Engl. Transl.),
2007, 49].
5. S. V. Kurmaz, I. S. Kochneva, E. O. Perepelitsina, G. V.
Korolev, V. P. Grachev, S. M. Aldoshin, Izv. Akad. Nauk,
Ser. Khim., 2007, 191 [Russ. Chem. Bull., Int. Ed., 2007,
56, 197].
6. S. V. Kurmaz, I. S. Kochneva, V. V. Ozhiganov, V. P.
Grachev, S. M. Aldoshin, Dokl. Akad. Nauk, 2007, 417, 646
[Dokl. Chem. (Engl. Transl.), 2007].
7. V. P. Grachev, G. M. Bakova, S. V. Kurmaz, L. I. Makhonꢀ
ina, E. A. Yur´eva, S. M. Aldoshin, Vysokomolekulyar. Soeꢀ
din., Ser. A, 2011, 53, № 9 [Polym. Sci., Ser. A (Engl. Transl.),
2011, 53, No. 9].
Synthesis of photochromic copolymers. Linear copolymers of
EA (Polꢀ1, Polꢀ2, and Polꢀ3) were obtained by radical copolyꢀ
merization in ethanol (70 wt.%) in the presence of azobisꢀ
(isobutyronitrile) (AIBN) as initiator (1•10–2 mol L–1). The poꢀ
lymerization was performed in the evacuated tubes at 60 °C until
the reaction reached completion (120 h). The branched copolyꢀ
mer of EA (PolBꢀ1) was synthesized by the threeꢀdimensional
radical copolymerization with butanediol diacrylate (BDDA),
which was controlled by the agent of the chain transfer, i.e.,
1ꢀdecanethiol, according to the method described earlier.8 The
content of the branching agent, BDDA and 1ꢀdecanethiol, was
12 mol.% with respect to EA. Conditions for the synthesis of
PolBꢀ1: T = 80 °C, the reaction time was 5.5 h, AIBN was the
initiator (0.02 mol L–1). The content of the reaction mixture in
toluene was 80 wt.%. The polymers that obtained were dried
in vacuo at ∼20 °C until the weight was constant.
8. S. V. Kurmaz, I. S. Kochneva, V. V. Ozhiganov, A. A. Batuꢀ
rina, G. A. Estrina, Zh. Prikl. Khim., 2008, 81, 1710 [Russ. J.
Appl. Chem. (Engl. Transl.), 2008, 81].
Photochemical studies. Absorption spectra of the samples
were recorded on an Ocean Optics HR 2000 spectrometer in the
automatic scanning mode through the given periods of time and
then processed as massifs of data using the software based on the
Igor Pro 4.0. Irradiation was produced by a DRShꢀ1000 UV lamp
Received March 4, 2011;
in revised form May 11, 2011