Synthesis and study of photochromic asymmetric bis-spiropyran

Article abstract of DOI:10.1134/S0012500816120090

Asymmetric indoline-benzoxazine bis-spiropyran showing improved photochromic properties due to the electron-donating methoxy group has been prepared by multistage synthesis. The molecular structure of 8-methoxy-3-methyl-4-oxo-2H-1,3-benzoxazine-2-spiro-2′

Full text of DOI:10.1134/S0012500816120090

ISSN 0012-5008, Doklady Chemistry, 2016, Vol. 471, Part 2, pp. 378–383. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © I.V. Ozhogin, V.V. Tkachev, B.S. Luk’yanov, E.L. Mukhanov, A.V. Chernyshev, O.A. Komissarova, V.I. Minkin, S.M. Aldoshin, 2016, published in
Doklady Akademii Nauk, 2016, Vol. 471, No. 6, pp. 676–681.
CHEMISTRY
Synthesis and Study of Photochromic Asymmetric Bis-spiropyran
I. V. Ozhogina,*, V. V. Tkachevb, B. S. Luk’yanova, E. L. Mukhanova, A. V. Chernysheva,
O. A. Komissarovaa, Academician V. I. Minkina, and Academician S. M. Aldoshinb
Received August 15, 2016
Abstract—Asymmetric indoline-benzoxazine bis-spiropyran showing improved photochromic properties
due to the electron-donating methoxy group has been prepared by multistage synthesis. The molecular struc-
ture of 8-methoxy-3-methyl-4-oxo-2H-1,3-benzoxazine-2-spiro-2'H,8'H-pyrano-[2,3-f]chromene-8′-
spiro-2''-1'',3'',3''-trimethylindoline has been studied by X-ray diffraction. After exposure to UV light, the
absorption spectra display several long-wavelength maxima, which can correspond to different merocyanine
isomers of the bis-spiro compound.
DOI: 10.1134/S0012500816120090
Asymmetric bis-spiropyrans, whose photoactive sponding acid (3) with thionyl chloride and gaseous
centers are connected through an electron π-system, methylamine;
are of particular interest in a series of organic photo-
(2) cyclization of N-methylamide 2 under the action
chromic compounds because their photoinduced iso-
of concentrated perchloric acid in acetic anhydride to
mers are clearly distinguishable in spectra and can con-
siderably differ in photokinetic characteristics [1–4].
form 1,3-benzoxazin-4-onium perchlorate 4;
(3) condensation of benzoxazinonium perchlorate 4
with 2,4-dihydroxyisophthalic aldehyde 5 in glacial
acetic acid;
(4) cyclization of intermediate styryl salt 6 under
the action of triethylamine in diethyl ether into spiro-
pyran of 1,3-benzoxazin-4-one series 7.
The use of the latter compound as an analogue of
salicylic aldehyde upon heating with 1,2,3,3-
tetramethyl-3H-indolium perchlorate in the presence
of an equimolar amount of piperidine in isopropanol
resulted in the preparation of asymmetric bis-spiropy-
ran 1 containing methoxy group in one of hetarene
fragments of molecule.
Previously, the possibility of photoactivated opening
of two pyran rings was theoretically substantiated for
the first time by the example of asymmetric benzox-
azine-indoline bis-spiropyrans, whose nonequivalent
hetarene portions are linked via the common pyrano-
chromene moiety [3, 4]. The introduction of the elec-
tron-donating methoxy substituent into the benzox-
azine moiety of a new bis-spiro compound allowed
one to increase the stability of its merocyanine isomers
and potentially extend the range of performance char-
acteristics, which provides an opportunity to consider
such compounds as promising prototypes of multipo-
sition molecular switches for molecular electronics
and sub-diffraction microscopy [5, 6].
The structure of the obtained compound was
proved by the data of elemental analysis, IR spectro-
scopy, and 1H and 13C NMR. The IR spectrum of bis-
spiropyran 1 shows a typical absorption band of the
carbonyl group of benzoxazine moiety (1681 cm–1)
and the bands corresponding to the stretching vibra-
tions of Cspiro–O bond (925, 941 cm–1). The 1H NMR
spectrum displays the signals of diastereotopic gem-
dimethyl groups of the indoline moiety as two singlets,
which confirms the adjacency of the C(CH3)2 group
with the asymmetric carbon atom. The signals of pro-
tons of the methyl groups at the nitrogen atoms of the
indoline and oxazine moieties appear at 2.6 and
3.1 ppm, respectively. The characteristic signals of 3'-
and 9'-protons of the pyranochromene moiety appear
at about 5.8 and 5.5 ppm, which form the AB system
with the protons in the 4'- and 10'-positions. J-Con-
In this work, we performed a multistage synthesis
of 8-methoxy-3-methyl-4-oxo-2H-1,3-benzoxazine-
2-spiro-2'H,8'H-pyrano-[2,3-f]chromene-8′-spiro-
2''-1'',3'',3''-trimethylindoline (1) shown in Scheme 1.
The synthesis procedure included the following:
(1) preparation of N-methyl-3-methoxysalicyl-
amide (2) by the sequential treatment of the corre-
a Institute of Physical and Organic Chemistry, Southern
Federal University, pr. Stachki 194/2, Rostov-on-Don,
344090 Russia
b Institute of Problems in Chemical Physics, Russian Academy
of Sciences, pr. Akademika Semenova 1, Chernogolovka,
Moscow oblast, 142432 Russia
* e-mail: lab811@ipoc.sfedu.ru, ilyuh@ya.ru
378

SYNTHESIS AND STUDY OF PHOTOCHROMIC ASYMMETRIC BIS-SPIROPYRAN
379
O
O
O
CH3
CH3
OH
NHCH3
OH
N
ClO4−
1) SOCl2
Ac2O
+
2) CH3NH2
HClO4
OH
O
OMe
OMe
OMe
4
3
2
CHO
O
OH
(5)
CH3
AcOH,HClO4
N
+
CHO
OH
O
OH
CHO
OH
ClO−4
OMe
6
Et2O
Et3N
CH3
N
O
CH3
O
H3C
CH3
CH3
ClO4−
+
N
CH3
N
O
O
O
CH3
N
O
O
i-PrOH,
OMe
OMe
N
H
H3C
H3C
OHC
OH
7
1
Scheme 1.
stants of 9.8 and 10.5 Hz indicate the cis configuration ring at the dimethyl-substituted analogue С(8'2) has a
of the corresponding vinyl moieties and confirm the
existence of the bis-spiropyran as a spirocyclic form.
bend along the line С(9')⋅⋅⋅O(7') = 40.0°. At the same
time, the molecule of the bis-spiro compound has
bends along the O(1')⋅⋅⋅C(3') and O(7')⋅⋅⋅C(9') lines of
21.9° and 12.1°, which indicates the considerable
change in molecule geometry upon transition from
sp2- and sp3-hybridized carbon atoms to spiro config-
uration.
To study the possibility of photoizomerization
transformations of compound 1 in solid state, we have
grown its single crystals and investigated their molec-
ular structure by X-ray diffraction analysis. Figure 1
exhibits the structure of molecule of the prepared bis-
spiropyran. In single crystal, the compound exists as a
bis-spirocyclic isomeric form containing three struc-
tural fragments: benzoxazine, pyranochromene, and
indoline (left, central, and right in designations in
Fig. 1). Each fragment has nonplanar structure, there
are characteristic inflection lines: O(1)⋅⋅⋅N(3),
O(1')⋅⋅⋅C(3'), O(7')⋅⋅⋅C(9'), and C(3')⋅⋅⋅N(1').
We compared the geometric parameters of com-
pound (1) and previously studied 7'-hydroxy-3-
methyl-8'-formyl-4-oxo-3,4-dihydro-2H-spiro(1,3-
benzoxazine-2,2'-[2H]-chromene) [8] and 1',3',3'-
trimethyl-7-methoxy-spiro(indoline-2,2'-[2H]-chro-
mene) [9], which can be considered as the prototypes
of the left and right moieties of the prepared bis-spiro-
pyran, respectively. The analysis of obtained data
showed that the previously studied spiropyran of ben-
zoxazine series contains bends along O(1')⋅⋅⋅C(3') and
O(1)⋅⋅⋅N(3) lines of 33.1° and 32.1°, whereas the
angles of similar bends in the new bis-spiropyran are of
21.9° and 33.7°, respectively. The bending angles at
the spiro atom of the right portion of molecule 1 and
in the model spiropyran of indoline series [9] also dif-
fer: the bending angles in the moiety of the compound
The central pyranochromene moiety (between the
С(2'2) and С(8'2) atoms) is encountered in the Cam-
bridge Structural Database (version 1.18) only once as
8,8-dimethylpyrano[2,3-h]coumarin [7]. The mole-
cule of this compound contains two methyl groups at
the analogue of spiro atom С(8'2) and the carbonyl
oxygen at the analogue of С(2'2) atom. The analysis of
the geometry parameters of the previously studied
compound [7] reveals that the carbon atom at the car-
bonyl oxygen atom lies in the plane of the С(3')–
C(14'), O(1'), and O(7) atoms within 0.05 Å, while the studied in this work along the O(7')⋅⋅⋅C(9') and
DOKLADY CHEMISTRY Vol. 471 Part 2 2016

380
OZHOGIN et al.
С(5')
С(6')
С(4')
С(13')
С(3)
N(3)
С(3')
С(11'')
N(1'')
O(7')
С(11')
C(7'')
C(4'')
С(14')
С(12')
С(2'2)
O(1')
C(8'')
C(9'')
C(6'')
C(5'')
С(4)
O(3)
C(8'2)
С(10')
O(1)
С(9)
С(8)
С(9')
С(10)
С(5)
C(3'')
C(3A'')
C(3B'')
O(8)
С(6)
C(8A)
C(7)
Fig. 1. Molecular structure of compound 1 according to X-ray diffraction data.
values measured to date for the known indolino-ben-
zoxazine bis-spiropyrans. Previously, the longest life-
time (66 s) was detected for the compound containing
hydroxyethyl substituent at the nitrogen atom of the
indoline moiety, however, containing no substituents
in the benzoxazine moiety [4]. On the basis of
obtained data, one can draw a conclusion that the
introduction of electron-donating groups into ben-
zene ring of benzoxazine portion of unsymmetrical
bis-spiropyrans is efficient way to modify molecule to
increase stability of its merocyanine isomers.
C(3'')⋅⋅⋅N(1'') lines are 12.1° and 27.2°, respectively
(16.7° and 33.3°, respectively, for monospiropyran [9]).
Such a considerable difference in bending angles in
the closest environment of the spiro atoms of bis-
spiropyran 1 molecule as compared with its mono-
spiro analogues indicates the difference in no–σ*
c–o
interaction in the spiro nodes in a wide range and,
hence, the possibility to extend the range of activating
effect on the electronic states of molecule.
Under the action of UV light, both separate and
combined opening of two pyrane rings of bis-spiro
compound 1 is possible theoretically to give three
merocyanine isomers (Scheme 2)
Thus, we have synthesized unsymmetrical
indoline-benzoxazine
bis-spiropyran
showing
improved photochromic characteristics due to the
presence of electron-donating methoxy group. Photo-
chemical studies showed the presence of several long-
wavelength maxima in absorption spectra, which can
correspond to different merocyanine isomers of bis-
spiro compound At present, we study the detailed
mechanism of photochromic transformations of these
bis-spiro compounds with the aim to establish the
possibility of photoactivated opening of the pyran
rings, both one and the others.
The absorption spectra of initial (before irradia-
tion) solutions of bis-spiropyran 1 in acetonitrile show
the lack of absorption bands in the visible spectral
region, which indicates the complete shift of thermo-
dynamic equilibrium toward bis-spirocyclic form 1a.
The strongest absorption bands of this isomer are
observed at 206 and 249 nm with molar extinction
coefficients ε = 78 400 and 45 300 L mol–1 cm–1,
respectively. When bis-spiropyran solution was
exposed to UV light (313 nm) at 288 K, absorption
bands with maxima at 420 and 600 nm, supposedly
corresponding to merocyanine isomers 1b and 1c,
appeared in spectrum in the visible region (Fig. 2).
EXPERIMENTAL
1H and 13C NMR spectra were recorded in the
pulsed Fourier transform mode on a Bruker DPX-250
spectrometer operating at 250 MHz at the Scientific
and Educational Laboratory of Resonance Spectros-
copy, Department of Natural and High Molecular
Compounds Chemistry of Southern Federal Univer-
sity. Chemical shifts were measured on the δ scale
using the residual proton signals of the deuterated sol-
After the termination of irradiation, the long-wave-
length maxima extinct, this indicates the occurrence
of thermal recyclization of merocyanine forms into
initial spirocyclic compound. The calculated lifetime
τ20
1/2 of merocyanine at 293 K showing absorption band
20
at 600 nm is 106 s, which is maximal among the
τ1/2
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SYNTHESIS AND STUDY OF PHOTOCHROMIC ASYMMETRIC BIS-SPIROPYRAN
CH3
381
O
N
H3C
O−
N
O
hν12
O
O
O
CH3
N
O
hν21, Δ
O
CH3
+N
OCH3
H3C
H3C
H3C
OCH3
H3C
1a
1b
hν13
hν24
hν31, Δ
hν42, Δ
O
O
CH3
N
CH3
N
O−
+
hν34
+
CH3
−O
O
O
hν43, Δ
O
CH3
N
−O
+N
H3C
H3C
OCH3
OCH3
H3C
CH3
1d
1c
Scheme 2.
vent CDCl3 (δ = 7.26 ppm) as a reference. The IR solutions of the compounds before and after irradia-
tion were recorded on an Agilent 8453 spectropho-
tometer using a DRSh-250 mercury lamp as a source
spectra of compounds were recorded on a Varian
Excalibrum 3100 FT-I instrument by attenuated total
reflection method. Electronic absorption spectra of of photoactive UV light and a light filter to isolate the
0.3
0.2
0.1
0
350
400
450
500
550
600
650
700
750
λ, nm
Fig. 2. Changes in electronic absorption spectra of compound 1 in acetonitrile upon exposure to light with wavelength 313 nm.
–4
Interval between spectra corresponds to 10 s, T = 288 K, C = 1.13 × 10 M.
DOKLADY CHEMISTRY Vol. 471 Part 2 2016

382
OZHOGIN et al.
line of the mercury spectrum at 313 nm. Elemental indolium perchlorate were dissolved in 10 mL of iso-
analysis was carried out by the classical microanalysis propanol. Piperidine (0.1 mL, 1.1 mmol) was added to
method [10]. Melting points were determined on a the resultant mixture on heating. The mixture was
Fisher Scientific Fisher–Jones device.
heated under reflux about 10 min and allowed to stand
overnight in a dark place. The resultant precipitate was
separated by filtration and washed with a minimal
amount of hexane. The matter was chromatographed
on silica gel using chloroform as an eluent. Yield 36%,
mp 150°C. IR (ν, cm–1): 1681 (С=О); 1605 (С=С);
7'-Hydroxy-8'-formyl-8-methoxy-3-methyl-4-oxo-
spiro(1,3-benzoxazin-2-2'-[2H]-chromene) (7). (1) 3-
Methoxysalicylic acid 3 (16.8 g, 0.1 mol), 200 mL of
toluene, and 14.6 mL of thionyl chloride were placed
into a round-bottomed flask and the reaction mixture
was heated under reflux about 5 h. About one third of
the solvent was removed by distillation, the solution
was transferred into a flat-bottomed flask and a flow
of dry methylamine was passed through the solution.
The resultant suspension was filtered, the mother
liquor was collected and dried with anhydrous sodium
sulfate for several hours. The major portion of toluene
was distilled off, the residual concentrate was cooled,
and the precipitated product was separated and recrys-
1
941, 925 (Сspiro–О). H NMR (CDCl3, δ, ppm,
J, Hz): 1.07 (d, 3Н, 3''-СН3), 1.22 (s, 3Н, 3''-СН3),
2.64 (s, 3Н, 1''-СН3), 3.15 (s, 3Н, 3-СН3), 3.74 (s,
3Н, 8-ОСН3), 5.51 (dd, 1Н, J = 10.5, 9'-Н), 5.88 (d,
1Н, J = 9.8, 3'-Н), 6.38 (d, 1Н, J = 8.4, 6′-Н), 6.48 (d,
1Н, J = 7.7, 7''-Н), 6.70 (dd, 1Н, J = 10.5, 10'-Н),
6.81 (t, 1Н, J1 = 7.4, J2 = 7.3, 5''-Н), 6.90 (1Н, J = 9.8,
4'-Н), 6.95 (1Н, J = 8.4, 5'-Н), 7.02 (d, 1Н, J = 7.4,
4''-Н), 7.07–7.17 (m, 3Н, 7-Н, 6-Н, 6''-Н), 7.91 (d,
1Н, 5-Н). 13C NMR ((CDCl3, δ, ppm) ): 162.0, 156.6,
148.5, 147.2, 142.8, 137.0, 130.5, 128.4, 128.0, 122.9,
121.9, 119.6, 119.4, 119.0, 117.7, 117.4, 115.4, 111.2,
109.6, 107.9, 107.4, 107.2, 105.3, 104.9, 56.9, 52.3,
52.0, 30.3, 29.2, 26.2, 20.4.
1
tallized from ethyl alcohol. Yield 64%. H NMR
(CDCl3, δ, ppm, J, Hz): 2.99 (d, 3H, J = 4.9, N–
СН3), 3.87 (s, 3H, O–СН3), 6.61 (s, 1H, NH), 6.77 (t,
1H, J = 8.0, 5-H), 6.94 (dd, 1H, J = 8.0, 1.3, 4-H),
7.03 (dd, 1H, J = 8.1, 1.4, 6-H), 11.89 (s, 1H, OH).
(2) Acetyc anhydride (6 mL) was added to 1.81 g
(0.01 mol) of N-methyl-3-methoxysalicyloylamide 2,
next 1 mL of perchloric acid was added on cooling.
After 24 h, the white precipitate was separated by fil-
tration and washed with diethyl ether. Yield 90%. The
compound was used without additional purification
and identification.
For C31H28N2O5 anal. calcd. (%): C, 73.2; H, 5.5;
N, 5.5. Found (%): C, 73.3; H, 5.6; N, 5.4.
X-ray diffraction study. Unit cell parameters and
three-dimensional set of intensities were obtained at
150 K on an Xcalibur Eos diffractometer (MoKα radi-
ation, graphite monochromator). Red single crystals
C31H28N2O5 are monoclinic: a = 7.4405(8) Å, b =
24.088(3) Å, с = 14.5180(14) Å, β = 97.659(9)°, V =
2578.8(5) Å3, FW = 508.55, Z = 4, ρ(calcd) =
1.310 g/cm3, μ(МоКα) = 0.089 mm–1, space group P21.
Intensities of 11 583 reflections were measured in the
angle range (2θ ≤ 52.14°) by ω scan from a single crys-
tal 0.20 × 0.06 × 0.05 mm in size. Absorption correc-
tions were applied using the Multiscan procedure.
After rejection of systematic absences and merging of
equivalents, the working array of measured F2(hkl)
and σ(F2) comprised 7475 unique reflections, 2819 of
which were with F2 > 2σ(F2). The structure was solved
by direct methods and refined by full-matrix least
squares on F2 with the SHELXTL program in the
anisotropic approximation for non-hydrogen atoms.
The hydrogen atoms in crystal structure 1 were located
from a difference Fourier map; then, the coordinates
and isotropic thermal parameters of all H atoms were
calculated by the least squares procedure using the rid-
ing model [11], the absolute shifts of all 694 variable
structure parameters in the last cycle of full-matrix
refinement were less than 0.003 σ; the final value R1 =
0.068.
(3) 2,3-Dimethyl-8-methoxy-1,3-benzoxazin-4-
onium perchlorate 4 (3.06 g, 0.01 mol) was added to a
hot solution of 1.66 g (0.01 mol) of 2,4-dihydroxy-
isophthalic aldehyde 5 in 10 mL of acetic acid. The
reaction mixture was heated under reflux about 7 min,
next sealed and allowed to stand overnight. The resul-
tant bright orange precipitate of styryl salt 6 was sepa-
rated by filtration and washed with diethyl ether (3 ×
15 mL). The salt was placed into anhydrous diethyl
ether (50 mL) and equimolar amount of triethylamine
was added dropwise. One day later, the ether was
decanted, the solvent was removed, and the residue
was chromatographed on silica gel using chloroform as
an eluent. Yield 22%, mp 158°C. IR (ν, cm–1): 1679
1
(С=О); 1641, 1594 (С=С); 946, 921 (Сspiro–О). H
NMR (CDCl3, δ, ppm, J, Hz): 3.14 (s, 3Н, N–СН3),
3.74 (s, 3Н, 8-OСН3), 5.97 (d, 1Н, J = 9.8, 3'-Н),
6.59 (d, 1Н, J = 8.6, 6'-Н), 6.94 (d, 1Н, J = 9.8, 4'-Н),
7.03–7.13 (m, 2Н, 6-Н, 7-H), 7.36 (d, 1Н, J = 8.6, 5′-
Н), 7.63 (d, 1Н, 5-Н), 9.85 (s, 1Н, 8'-СНО), 11.69 (s,
1Н, 7'-ОН).
For C19H15NO6 anal. calcd. (%): C, 64.6; H, 4.3;
N, 4.0. Found (%): C, 64.6; H, 4.5; N, 3.9.
8-Methoxy-3-methyl-4-oxo-2H-1,3-benzoxazin-
2-spiro-2'H,8'H-pyrano-[2,3-f]chromene-8'-spiro-
2''-1'',3'',3''-trimethylindoline (1). Spiropyran 7
ACKNOWLEDGMENTS
This work was supported the Ministry of Education
(0.353 g, 1 mmol) and 0.275 g (1 mmol) of 3-H- and Science of the Russian Federation in the frame-
DOKLADY CHEMISTRY
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SYNTHESIS AND STUDY OF PHOTOCHROMIC ASYMMETRIC BIS-SPIROPYRAN
383
6. Minkin, V.I., in Molecular Switches, London: Wiley,
work of the State Assignment for Research, project
no. 4.1979.2014/K.
2011, vol. 1, p. 37.
7. Bauri, A.K., Foro, S., Lindner, H.-J., and Nayak, S.K.,
Acta Crystallogr. Sect. E: Struct. Rep. Online, 2006,
vol. 62, no. 7, pp. o290–o2901.
REFERENCES
8. Alekseenko, Yu.S., Luk’yanov, B.S., Utenyshev, A.N.,
Mukhanov, E.L., Kletsky, M.E., Tkachev, V.V., Krav-
chenko, N.N., Minkin, V.I., and Aldoshin, S.M.,
Chem. Heterocycl. Comp., 2006, no. 6, pp. 803–812.
1. Nourmohammadian, F. and Abdi, A.A., Spectrochim.
Acta A: Mol. Biomol. Spectrosc., 2016, no. 153, pp. 53–
62.
2. Malkin, Y.N., Kuz’min, V.A., and Mikhailenko, F.A.,
9. Aldoshin, S.M., Atovmyan, L.O., and Kozina, O.A.,
Russ. Chem. Bull., 1977, vol. 26, no. 1, pp. 70–74.
Russ. Chem. Bull., 1987, vol. 36, no. 1, pp. 169–171.
3. Mukhanov, E.L., Alekseenko, Y.S., Luk’yanov, B.S.,
Dorogan, I.V., and Bezuglyi, S.O., High Energy Chem.,
2010, no. 3, pp. 220–223.
4. Mukhanov, E.L., Dorogan, I.V., Chernyshev, A.V.,
Bezuglyi, S.O., Ozhogin, I.V., Lukyanova, M.B., and
Lukyanov, B.S., Int. J. Photoenergy, 2013, no. 2013,
pp. 1–8.
10. Gel'man, N.E., Terent’eva, E.A., Shanina, T.M., and
Kiparenko, L.M., Metody kolichestvennogo organi-
cheskogo elementnogo analiza (Quantitative Elemental
Analysis), Moscow: Khimiya, 1987.
11. Sheldrick, G.M., SHELXTL, Bruker, AXS, Madison
(WI), 2000.
Translated by I. Kudryavtsev
5. Minkin, V.I., Chem. Rev., 2004, no. 5, pp. 2751–2776.
DOKLADY CHEMISTRY Vol. 471 Part 2 2016