New Photochromic Salt Spiropyran with Benzyl Substituent

Article abstract of DOI:10.1134/S0012500818100026

A new salt spiropyran of indoline series containing benzyl substituent in the 8'-position of the [2H]-chromene moiety of the molecule has been synthesized and studied. The structure of the obtained compound has been confirmed by methods ¹H NMR and IR spectroscopy. The study of spectral characteristics and photochromic behavior of the target compound has shown that growing of its single crystal resulted in destruction on account of hydrolysis in acetonitrile. The ¹H NMR spectra of the initial salt spiropyran and product of hydrolysis have been compared.

Full text of DOI:10.1134/S0012500818100026

ISSN 0012-5008, Doklady Chemistry, 2018, Vol. 482, Part 2, pp. 220–224. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © M.B. Luk’yanova, A.D. Pugachev, V.V. Tkachev, B.S. Luk’yanov, G.V. Shilov, A.S. Kozlenko, I.A. Rostovtseva, V.I. Minkin, S.M. Aldoshin, 2018, published
in Doklady Akademii Nauk, 2018, Vol. 482, No. 4.
CHEMISTRY
New Photochromic Salt Spiropyran
with Benzyl Substituent
M. B. Luk’yanovaa, A. D. Pugacheva,*, V. V. Tkachevb, B. S. Luk’yanova,c,**, G. V. Shilovb,
A. S. Kozlenkoa, I. A. Rostovtsevaa, Academician V. I. Minkina, and Academician S. M. Aldoshinb
Received May 10, 2018
Abstract—A new salt spiropyran of indoline series containing benzyl substituent in the 8'-position of the
[2H]-chromene moiety of the molecule has been synthesized and studied. The structure of the obtained com-
pound has been confirmed by methods 1H NMR and IR spectroscopy. The study of spectral characteristics
and photochromic behavior of the target compound has shown that growing of its single crystal resulted in
destruction on account of hydrolysis in acetonitrile. The 1H NMR spectra of the initial salt spiropyran and
product of hydrolysis have been compared.
DOI: 10.1134/S0012500818100026
Spiropyrans are representatives of organic photo-
The structure of the obtained compound 3 was
1
chromic compounds [1]. Due to photochromic prop- proved by the data of elemental analysis, IR and H
NMR spectroscopy.
The IR spectrum of salt spiropyran 3 has typical
absorption bands corresponding to the stretching
erties they can be used to create smart materials as
photosensitive switches of various properties [2]. Non-
volatile memory cells were designed on the basis of
photochromic spiropyran salts [3]. Two factors are
necessary to use spiropyrans in optical memory
devices: the long lifetime of photoinduced isomer and
the maximal proximity of long-wavelength absorption
maximum to the IR range. It is known that bulky sub-
stituents in the 2H-chromene moiety of molecule and
at the nitrogen atom of the hetarene fragment provide
a possibility to increase lifetime of photoinduced iso-
mer for the spiropyrans of indoline series [4].
−
vibrations of Cspiro–O bond (923 cm–1),
group
ClO4
(1095 cm–1), the C=C bond of the 2H-pyrane ring
(1607 cm–1), and the C=C bond of the vinyl fragment
(1302 cm–1).
The 1H NMR spectrum of compound 3 has a char-
acteristic signal of proton in the 3'-position at
5.93 ppm as a doublet with spin-spin coupling con-
stant 10.3 Hz, which indicates the cis configuration of
the vinyl fragment C(3')=C(4'). The proton signals of
CH2 group appear as a two-proton doublet of doublets
at 3.62 ppm. The signals of trans vinyl protons of the
salt fragment as two one-proton doublets are observed
at 7.53 and 8.36 ppm with spin-spin coupling constant
16.2 Hz. Three-proton singlet signal at 4.12 ppm cor-
responds to the N+–CH3 fragment of cationic substit-
uent.
Single crystals of compound 3 were grown from
acetonitrile solution to study details of molecular
structure. X-ray diffraction study revealed that the
obtained crystals are those of spiropyran of indoline
series 4 with formyl group in the 6'-position of the 2H-
chromene portion of molecule.
For the previously synthesized spiropyrans with a
cationic substituent [5, 6] the merocyanine isomer has an
absorption band in the near-IR region (λmax = 728 nm).
In this work, with the aim to combine two these fac-
tors in one molecule, we synthesized 1,3,3-trimethyl-6'-
[(E)-2-(1'',3'',3''-trimethylindolium-2''-yl)vinyl]-8'-ben-
zyl-spiro[indolino-2,2'-2H-chromene] perchlorate (3)
according to Scheme 1.
aResearch Institute of Physical and Organic Chemistry,
Southern Federal University, Rostov-on-Don, 344090 Russia
bInstitute of Problems in Chemical Physics, Russian Academy
of Sciences, Chernogolovka, Moscow oblast, 142432 Russia
Figure 1 displays the molecular structure of spiro-
pyran 4 containing formyl substituent in the 6'-posi-
tion and benzyl group in the 8'-position.
Atoms N(1), C(3)–C(9) occupy the same plane
with deviation not larger 0.15 Å, producing angle 24.9°
with the plane of N(1), C(3), and C(2'2) atoms, the
cDon State Technical University, Rostov-on-Don,
344007 Russia
*e-mail: lab811@ipoc.sfedu.ru
**e-mail: bluk@ipoc.sfedu.ru
220

NEW PHOTOCHROMIC SALT SPIROPYRAN
221
OH
O
CH3
CH3
O
CH3
H3C
H3C
H3C
i-PrOH, Et3N
2
+
CH3
ClO4
CH3
+
N
+
N
N
CH3
CH3
ClO4
O
1
2
3
Scheme 1.
sum of the angles at the nitrogen atom is 345.6°. The the hydrogen atoms of gem dimethyl group of other
molecule.
right fragment relative to the C(2'2) spiro atom (atoms
O(1'), O(2'), C(3')–C(12')) is out of “its own” plane
by not more than 0.024 Å, producing angle 15.3° with
the plane of atoms O(1'), C(2'2), and C(3'). The con-
sideration of C(11') atom environment using Newman
projection along the C(11')–C(8') bond displays that
the right-hand portion of spiropyran lays in the plane
close to the plane of atoms C(11'), C(8'), and H(11b).
Phenyl ring C(13')–C(18') is oriented similarly relative
to the plane of atoms C(11'), C(8'), and H(11a). Mol-
ecules are packed in single crystal in such a manner
that intermolecular contacts of 2.57 and 2.69 Å are
This took place most likely because of hydrolysis of
the cationic spiropyran in acetonitrile during crystal
growing followed by formation of 1,3,3-trimethyl-6'-
formyl-8'-benzylspiro[indolino-2,2'-2H-chromene] 4
and tetramethylindolium perchlorate 1 by Scheme 2.
We studied the spectral and photochemical proper-
ties of compound 3 in acetonitrile solution. The
obtained compound was in equilibrium between spi-
rocyclic and merocyanine forms. The UV spectrum of
cyclic isomer showed two bands with maxima at 249
and 303 nm. It is important to note that, in compari-
realized between the O(2') atom of one molecule and son with the majority of previously studied spirocyclic
C(19)
C(4)
C(23)
C(13)
C(5)
C(12)
C(8)
C(2)
C(11)
C(25)
C(7)
O(17)
O(1)
C(20)
N(3)
C(16)
C(9)
C(14)
C(18)
C(10)
C(22)
C(6)
C(21)
C(15)
C(24)
C(31)
C(26)
C(34)
C(33)
C(32)
Fig. 1. Molecular structure of compound 4 according to X-ray diffraction study.
DOKLADY CHEMISTRY Vol. 482 Part 2 2018

222
LUK’YANOVA et al.
CH3
O
CH3
CH3
H3C
CH3
CH3
ClO4
H3C
H3C
H3C
H2O
O
+
+
N
CH3
+
N
N
N
O
CH3
CH3
CH3
ClO4
3
4
1
Scheme 2.
compounds, the closed form of salt spiropyrans also
Thus, we synthesized new salt spiropyran. Its
exhibited a wide strong absorption band in the visible structure was confirmed by IR and 1H NMR spectros-
copy. The compound showed photochromic proper-
ties in acetonitrile. The colored photoinduced from
was characterized by long-wavelength absorption band
with maximum at 648 nm and long lifetime of 264.5 s.
We established by X-ray diffraction study that the tar-
get spiropyran undergoes hydrolysis upon crystal
growth in acetonitrile solution.
region with maximum at 457 nm, which is explained
by the length of conjugation chain. The maximum of
absorption band for photoinduced isomer was 648 nm.
Exposure to UV light with wavelength 365 nm led to
increase in the intensity of absorption band at 648 nm.
Figure 2 represents the changes in the absorption
spectra upon irradiation in acetonitrile.
After termination of irradiation, we observed spec-
trum restoration. Compound 3 had relatively long life-
time of the photoinduced isomer (264.5 s). This is
explained by the presence of the benzyl substituent in
the 8' position of the 2H-chromene fragment, which
causes steric hindrances for recyclization reaction.
EXPERIMENTAL
1H NMR spectra in DMSO and deuteriochloro-
form solutions were recorded on a Bruker DPX-250
spectrometer operating at 250 MHz in the Training
and Research Laboratory of Resonance Spectroscopy,
Absorption, arb. units
2.0
1.5
1.0
0.5
0
0.12
0.09
0.06
0.03
0
550
600
650
700
750
200
300
400
500
600
700
λ, nm
Fig. 2. Changes in the absorption spectra of compound 3 upon exposure to UV light (λ = 365 nm, irradiation time 10 s) in ace-
irr
tonitrile, T = 293 K. Inset shows change in absorption spectra in the region corresponding to the photoinduced isomer.
DOKLADY CHEMISTRY
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2018

NEW PHOTOCHROMIC SALT SPIROPYRAN
223
Chair of Natural and Macromolecular Compounds, trile. The precipitate (orange crystals) was separated
Chemistry Department, Southern Federal University. by filtration and washed with cold ethanol. Mp =
1
Signal position was determined in the δ scale, assign-
ments were made relative to the signals of residual pro-
tons of the deuterated solvent CDCl3 (δ = 7.26 ppm)
and DMSO-d6 (δ = 2.50 ppm).
265°C (from acetonitrile). Yield 26.8%. H NMR
(250 MHz, DMSO-d6, δ, ppm, J, Hz): 1.06 (3H, s,
gem-C(CH3)2), 1.10 (3H, s, gem-C(CH3)2), 1.76 (6H,
s, gem-C(CH3)2), 2.41 (3H, s, N–CH3), 3.62 (2H, dd,
IR spectra were recorded on a Varian Excalibur J = 13.5, 46.1 Hz,), 4.12 (3H, s, N+–CH3), 5.93 (1H,
3100 FT-iR spectrometer by attenuated total reflec-
tion. Electronic absorption spectra before and after
irradiation in acetonitrile solutions were obtained on
an Agilent 8453 spectrophotometer equipped with an
adapter for sample thermostating.
Solution photolysis was performed with the use of
a Newport system equipped with a 200-W mercury
lamp with a set of interference light filters.
Elemental analysis was carried out by classical
microanalysis method [7]. Melting points were deter-
mined on a ThermoFisher Scientific Fisher-Johns
melting point apparatus.
X-ray diffraction analysis. Unit cell parameters of
crystal and 3D set of intensities were obtained at 150 K
on an Agilent Technologies Excalibur Eos automated
diffractometer (MoKα radiation, graphite monochro-
mator). Single crystals of C27H25NO2 are monoclinic:
a = 28.544(3) Å, b = 9.5450(6) Å, c = 16.011(1) Å, β =
105.503(8) Å, V = 4203.6(6) Å3, M = 395.48, Z = 8,
ρ(calcd.) = 1.250 g/cm3, μ(MoKα) = 0.078 mm–1,
space group C2/c. Intensities of 23136 reflections were
measured in the range (2θ ≤ 58.10°) by ω-scanning of
a single crystal with dimensions 0.30 × 0.27 ×
0.26 mm. An empirical absorption correction was
made by using Multiscan procedure. After exclusion of
systematic absences and averaging of equivalent
reflection intensities, working array of measured
F2(hkl) and σ(F2) included 5549 independent reflec-
tions, 3945 of which were with F2 > 2σ(F2). The struc-
ture was solved by direct methods and refined in full-
matrix least squares on F2 by SHELXTL software in
anisotropic approximation for non-hydrogen atoms.
The majority of H atoms in the crystal structure were
located in difference Fourier synthesis. Next, coordi-
nates and isotropic thermal parameters of all hydrogen
atoms were refined by least squares procedure with an
idealized riding model [8]. The absolute shifts of all
282 variables in the last cycle of full-matrix refinement
were less 0.001 σ, final value R1 = 0.074.
1,3,3-Trimethyl-6'-[(E)-2-(1'',3'',3''-trimethylin-
dolium-2''-yl)vinyl]-8'-benzyl-spiro[indolino-2,2'-2H-
chromene] perchlorate (3). 2-Hydroxy-3-benxyl-5-
formylbenzaldehyde 2 (0.48 g, 2 mmol) was dissolved
on heating in 15 mL of isopropanol. Next, a solution
of 1.094 g (4 mmol) of 1,2,3,3-tetramethyl-3H-
indolium perchlorate 1 was added and 0.28 mL of (one
molar equivalent) of triethylamine was added drop- Program for Young Scientists (grant no. MK-439.2017.3
wise with stirring. The mixture was refluxed with stir- (M.B. Luk’yanova and A.D. Pugachev)) and the State
ring for about 60 min. The resultant precipitate was Contract no. 01201361863 (V.V. Tkachev, G.V. Shilov,
separated by filtration and recrystallized from acetoni- and S.M. Aldoshin).
d, J = 10.3 Hz, H-3'), 6.63 (1H, d, J = 7.6 Hz, H-7),
6.76 (2H, m, arom. protons), 6.90 (1H, t, J = 7.3 Hz,
H-5), 7.08 (4H, m, arom. protons), 7.14 (1H, m,
arom. proton), 7.23 (1H, t, J = 7.5 Hz, arom. proton),
7.53 (1H, d, J = 16.2 Hz, trans-vinyl proton), 7.62
(2H, m, arom. protons), 7.86 (2H, m, arom. protons),
7.99 (1H, s, arom. proton), 8.20 (1H, s, arom. proton),
8.36 (1H, d, J = 16.2 Hz, trans-vinyl proton). IR (ν,
cm–1): 923 ν(Cspiro–O), 1095 ν (
−), 1607 ν(C=C
ClO4
2H-pyran ring), 1302 ν(C=C vinyl fragment).
For C39H40N2O5Cl anal. calcd. (%): C, 71.82; H,
6.18; N, 4.30; Cl, 5.44.
Found (%): C, 71.86; H, 6.15; N, 4.34; Cl 5.42.
1,3,3-Trimethyl-6'-formyl-8'-benzyl-spiro[indoli-
no-2,2'-2H-chromene] (4). 2-Hydroxy-3-benzyl-5-
formylbenzaldehyde 2 (0.48 g, 2 mmol) was dissolved
on heating in 15 mL of isopropanol. Next, a solution
of 0.547 g (2 mmol) of 1,2,3,3-tetramethyl-3H-
indolium perchlorate 1 was added and 0.28 mL of (one
molar equivalent) triethylamine was added dropwise
with stirring. The mixture was refluxed with stirring
for about 30 min. The resultant precipitate was filtered
off and recrystallized from ethanol. The precipitate
(white crystals) was separated by filtration and washed
with cold ethanol. Mp = 98°C (from ethanol). Yield
1
61.4%. H NMR (250 MHz, CDCl3, δ, ppm, J, Hz):
1.11 (3H, s, gem-C(CH3)2), 1.16 (3H, s, gem-
C(CH3)2), 2.42 (3H, s, N–CH3), 3.60 (2H, dd, J = 14.1,
29.7 Hz,–CH2–), 5.75 (1H, d, J = 10.3 Hz, H-3'), 6.49
(1H, d, J = 7.7 Hz, H-7), 6.77 (2H, m, arom. pro-
tons), 6.91 (2H, m, arom. protons), 7.08 (4H, m,
arom. protons), 7.23 (1H, m, arom. proton), 7.51 (1H, s,
arom. proton), 7.64 (1H, s, arom. proton), 9.83 (1H, s,
–CHO). IR (ν, cm–1): 926 ν(Cspiro–O), 1593 ν(C=C
2H-pyran ring), 1687 ν(C=O formyl group).
For C27H25NO2 anal. calcd. (%): C, 82.00; H, 6.37;
N, 3.54.
Found (%): C, 82.03; H, 6.36; N, 3.51.
ACKNOWLEDGMENTS
This work was supported by the Presidential Grant
DOKLADY CHEMISTRY Vol. 482 Part 2 2018

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LUK’YANOVA et al.
5. Luk’yanova, M.B., Tkachev, V.V., Luk’yanov, B.S.,
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Translated by I. Kudryavtsev
DOKLADY CHEMISTRY
Vol. 482
Part 2
2018