Kinetics of photochemical reactions of a new biphotochromic compound upon photolysis with light of different wavelengths

Article abstract of DOI:10.1134/S001814391604010X

Using the method of microsecond flash photolysis with UV and visible light, the spectral and kinetic characteristics of intermediate products of photolysis in toluene and methanol solutions of a new biphotochromic compound have been studied, in which two photochromic moieties, spironaphthoxazine and azomethine, are linked to each other in such a way that there is conjugation between π-electronic systems of the moieties in the ground state of the molecule. Two intermediate products have detected, whose relative efficiency of formation substantially depends on the solvent and the wavelength of excitation light.

Full text of DOI:10.1134/S001814391604010X

ISSN 0018ꢀ1439, High Energy Chemistry, 2016, Vol. 50, No. 4, pp. 259–265. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © P.P. Levin, N.L. Zaichenko, A.S. Tatikolov, A.I. Shienok, L.S. Kol’tsova, I.M. Shcherbakova, O.Yu. Os’kina, I.R. Mardaleishvili, A.O. Ait, A.A. Berlin,
2016, published in Khimiya Vysokikh Energii, 2016, Vol. 50, No. 4, pp. 270–276.
PHOTOCHEMISTRY
Kinetics of Photochemical Reactions of a New Biphotochromic
Compound upon Photolysis with Light of Different Wavelengths
P. P. Levina, N. L. Zaichenkob, A. S. Tatikolova, A. I. Shienokb, L. S. Kol’tsovab, I. M. Shcherbakovab,
O. Yu. Os’kinab, I. R. Mardaleishvilib, A. O. Aitc, and A. A. Berlinb
aEmanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119334 Russia
eꢀmail: levinp@sky.chph.ras.ru
bSemenov Institute of Chemical Physics, Russian Academy of Sciences,
ul. Kosygina 4, Moscow, 119991 Russia
eꢀmail: zaina@polymer.chph.ras.ru
cPhotochemistry Center, Russian Academy of Sciences,
ul. Novatorov 7a, Moscow, 119421 Russia
eꢀmail: ait@photonics.ru
Received June 26, 2015; in final form, December 24, 2015
Abstract—Using the method of microsecond flash photolysis with UV and visible light, the spectral and
kinetic characteristics of intermediate products of photolysis in toluene and methanol solutions of a new
biphotochromic compound have been studied, in which two photochromic moieties, spironaphthoxazine
and azomethine, are linked to each other in such a way that there is conjugation between ꢀelectronic systems
π
of the moieties in the ground state of the molecule. Two intermediate products have detected, whose relative
efficiency of formation substantially depends on the solvent and the wavelength of excitation light.
Keywords: bichromophoric compound, spironaphthoxazine, azomethine, photochromism, merocyanine,
photoinduced proton transfer, cis–trans isomerization, flash photolysis
DOI: 10.1134/S001814391604010X
The design of photocontrollable multiphotochroꢀ formation of 10'ꢀformyl derivative. Then condensaꢀ
mic systems, whose photochemical and photophysical
behavior can be controlled by changing the wavelength
of excitation light, and study of their properties are an
active area of current research [1–7]. Such comꢀ
pounds are promising to create on their basis of a new
generation of materials for molecular electronics:
photocontrollable molecular switches, logic gates,
molecular devices, etc.
tion of 10'ꢀformyl derivative with pꢀmethoxyaniline
was performed, whereby a compound was obtained in
which two photochromic moieties, spironaphthoxꢀ
azine and azomethine, were linked to each other
in such a way that there was conjugation between the
π
ꢀelectronic systems of the spironaphthoxazine and
hydroxyazomethine moieties in the ground state of the
molecule, with the “phenolic” part of the hydroxyaꢀ
zomethine moiety being incorporated in the
spironaphthoxazine moiety, unlike all compounds
studied by us earlier [8–11].
In continuation of our works on the search for
compounds with switchable properties [8–11],
we synthesized and studied a new biphotochromic
compound—1,3ꢀdihydroꢀ9'ꢀhydroxyꢀ10'ꢀ(4ꢀmethꢀ
oxyphenyliminomethyl)ꢀ1,3,3ꢀtrimethylspiro[2
indoleꢀ2,3'ꢀ[3 ]naphtho[2,1ꢀb][1,4]oxazine]
Hꢀ
In spironaphthoxazine II, as a part of the BPCꢀI
molecule, a photochromic process occurs under the
action of light, involving photodissociation of the
C–O spiro bond in the closed form IIA (having an
absorption band with λmax ~ 337 nm, which practiꢀ
cally does not absorb in the region of 400–500 nm)
and cis–trans isomerization to form the colored
merocyanine form IIB with an absorption maxiꢀ
H
(BPCꢀI), whose molecule combines two moieties of
different nature, photochromic processes in which
lead to spectrally distinguished products. In the synꢀ
thesis of compound I, we used the developed by us earꢀ
lier method of regioselective orthoꢀformylation of 9'ꢀ
hydroxysubstituted spironaphthoxazine with the use
of paraformaldehyde and the complex of magnesium
dichloride with triethylamine [12], which led to the mum at 600 nm [11].
259

260
LEVIN et al.
Me
O
Me
O
Me
Me
OHC
N
OH
OH
N
(CH O)
2
n
MgCl , Et N
2
3
N
N
Me
Me
MeO
N
NH2
OMe
Me
Me
O
OH
N
N
Me
BPCꢀI
Me
Me
OH
N
N
N
O
Me
OMeM
II
III
Me
Me
O
Me
Me
N
N
N
Me
N
O
Me
II B
II
A
In pꢀmethoxyanil of 2ꢀhydroxyꢀ1ꢀnaphthaldehyde photolysis apparatus with registration of electronic
III, which models the second photochromic moiety of absorption [9]. Combinations of standard light filters
the BPCꢀI molecule, under the action of light, transiꢀ for photolytic flash lamps permeable to UV light in the
tion from the cisꢀenol form to the transꢀketo form can range of 300 ≤ λ ≤ 370 nm or visible light in the range
occur as a result of intramolecular proton transfer in of 440 ≤ λ ≤ 520 nm were used. The data of the
the electronically excited state (excited state intramoꢀ work represent the average values obtained by the
lecular proton transfer, ESIPT), followed by cis–trans treatment for at least ten kinetic curves under these
isomerization [13–16]. Hence, for BPCꢀI, we may conditions [9].
expect occurring the photoprocesses of different
nature, which were described above, leading to the forꢀ
mation of spectrally distinguished photoproducts.
All measurements were carried out at room temꢀ
perature. 1H NMR spectra were recorded on a Bruker
WMꢀ400 spectrometer at 25°C in CDCl3.
Calculation and optimization of the structures of
molecules in the ground state were performed by the
DFT method with the B3LYP functional in the 6ꢀ
EXPERIMENTAL
To prepare solutions, methanol and toluene of UV
spectroscopic grade were used. Absorption spectra in
the UV and visible regions were measured on a Multiꢀ
Specꢀ1501 spectrophotometer.
31G(d, p) basis.
Synthesis of BPCꢀI
1,3ꢀDihydroꢀ9'ꢀhydroxyꢀ10'ꢀformylꢀ1,3,3ꢀtrimethylꢀ
ꢀindoleꢀ2,3'ꢀ[3 ]naphto[2,1ꢀb][1,4]oxazine]
ꢀmethoxyaniline (21 mg,
The absorption spectra and the kinetics of formaꢀ
tion and decay of intermediate products were meaꢀ spiro[2
H
H
sured in the time range
≥
10
μ
s on a microsecond flash (43 mg, 0.115 mmol) and p
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KINETICS OF PHOTOCHEMICAL REACTIONS
261
0.17 mmol) were dissolved in toluene (5 ml) in a roundꢀ 8.7); 7.43 (d, 1H, H(6’), J5', 6' = 8.5); 7.59 (d, 1H,
bottom flask equipped with a reflux water condenser and
refluxed for 1.5 h. The reaction was monitored by TLC in
the system benzene–acetone 19 : 1. Then the cooled
reaction mixture was evaporated. The product was isoꢀ
lated by preparative TLC in the system benzene–acetone
9 : 1. The photochromic fraction with Rf = 63 was colꢀ
lected. It was desorbed from silica gel by the system benꢀ
zene–acetone 5 : 1. 50 mg (0.104 mmol) of beige powder
H(7’), J7', 8' = 9.0); 7.76 (s, 1H, H(2')); 10.72 (s, 1H,
OH). Found, %: C, 73.42; H, 5.85; N, 8.18. Calcuꢀ
lated, %: C, 75.45; H, 5.70; N, 8.80. C30H27N3O3
.
RESULTS AND DISCUSSION
Absorption Spectra of BPCꢀI
with mp 222–224
°
C
was obtained with the yield of 91%.
1H NMR (400 MHz, CDCl3,
J
/Hz), /ppm: 1.37
δ
The absorption spectrum of BPCꢀI in a toluene
solution (Fig. 1) indicates its presence mainly in the
form of АЕ with a small amount of АКс, because a
(s, 3H, C(CH3)); 1.38 (s, 3H, C(CH3)); 2.79 (c, 3H,
NCH3); 3.85 (s, 3H, O(CH3)); 6.59 (d, 1H, H(7),
shoulder at about 470 nm characteristic of the cis
ꢀ
J
6,7 = 7.8); 6.75 (d, 1H, H(5'), J5', 6' = 8.5); 6.85 (d, 1H,
H(8’), J7', 8 ' = 9.0); 6.90 (t, 1H, H(5), 4, 5 = 7.1, J5, 6
7.4); 7.00 (d, 2H, H(2’’), J2'', 3'' = 8.7); 7.09 (d, 1H,
ketone is observed [17]. The presence of the intense
absorption band at about 470 nm in the absorption
spectrum of BPCꢀI in methanol indicates the predomꢀ
inance of the form АКс in this solvent.
J
=
H(4), J4, 5 = 7.1); 7.23 (t, 1H, H(6),
7.8); 7.26 (c, 1H, CHN); 7.35 (d, 2H, H(3''), J2'', 3''
J
5, 6 = 7.4, J6, 7
=
=
MeO
MeO
r
= 1.57
Å
N
N
Me
Me
O
O
Me
Me
O
OH
N
N
N
N
Me
Me
АЕ
АKc
Photolysis of Model Compound III
Model azomethine III in a MeOH solution is
mainly present in the form of cisꢀketone Кс λmax = 440
and 460 nm) and in toluene in the form of cisꢀenol Ес
λmax = 390 nm) with a high content of Кс [11]. In the
wavelength region 430 nm, mostly Кс form absorbs,
tation with light of 430 or 470 nm. Flash photoexcitaꢀ
tion of III in toluene and methanol solutions with UV
and visible light at the absorption bands of the Ес and
Кс tautomers leads to the formation of one intermediꢀ
ate product, Kt, with maximums in the absorption
spectra at 450 and 480 nm in toluene and methanol,
(
(
≥
which provides a possibility of its selective photoexciꢀ respectively [11, 18]:
O
OH
O
OMe
N
OMe
NH
h
ν
h
ν
KT
NH
OMe
KT
Kt
Ес
Kc
The decay kinetics of Kt obeys the oneꢀexponential
Photolysis of I in Methanol
BPCꢀI in a methanol solution occurs mainly in the
cisꢀketo form AKc
law with the rate constants of 7.1
×
102 and 2.0 2.0
×
104 s–1 in toluene and methanol, respectively.
.
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262
LEVIN et al.
Upon flash photoexcitation of AKc with visible data for the model azomethine II, they were assigned
light, the formation of two intermediate products with to the forms AKt and ВКс, respectively. Upon photolysis
absorption maximums at 470 and 600 nm is observed, of I in methanol with visible light, photoexcitation
the ratio of their intensities = 5.5 : 1, and the rate conꢀ occurs predominantly of AKc, which leads to cis–trans
stants of their oneꢀexponential decay
≈
5.0
×
104 and isomerization in the hydroxyazomethine moiety and
0.86 s–1, respectively (Fig. 2). By analogy with the the formation of AKt without breaking the spiro bond
hybrid compounds studied by us earlier [9–11] and the C–O:
OMe
MeO
r
= 1.62 Å
r
= 1.7 Å
N H
H N
N
Me
Me
Me
O
Me
O
O
N
h
ν
N
N
O
Me
Me
AKc
AKt
But since the two photochromic moieties in the moleꢀ form, likely ВKc, appears as a result of successive cis–
cule are in conjugation, breaking of the spiro bond also trans isomerizations:
occurs with a relatively low yield, and a merocyanine
r
= 1.61 Å
MeO
Me
H O
N
MeO
N H
Me
O
Me
Me
N
N
h
ν
N
O
N
O
Me
Me
BKc
AKc
Upon excitation of I with UV light, the same two
A
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1
2
intermediate products are observed, but their ratio
dramatically changes toward increasing the portion of
the merocyanine form (the ratio of their intensities =
1.33 : 1).
3
4
This behavior of BPCꢀI differs very much from that
of BPCꢀIV studied by us earlier [9], in which
spironaphthoxazine and azomethine moieties were
also combined with conjugation between them, but
these moieties were differently combined into a moleꢀ
cule (the spironaphthoxazine moiety was the “amine”
part of the hydroxyazomethine fragment).
300
350
400
450
, nm
500
550
600
λ
Fig. 1. Absorption spectra of BPCꢀI in (
1
) toluene and
) methanol.
(2) methanol and model II in ( ) toluene and (4
3
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KINETICS OF PHOTOCHEMICAL REACTIONS
263
A
0.02
A
0.020
0.015
0.010
1
1
0
0.005
2
400
500
600
700
, nm
2
λ
0
–0.005
–0.010
400
500
600
700
, nm
λ
–0.02
Fig. 2. Absorption spectra of intermediate products arising
Fig. 3. Absorption spectra of intermediate products arising
upon photolysis with visible light of I in methanol, meaꢀ
upon photolysis with visible light of I in toluene, measured
sured (1) immediately and (2) in 50
µ
s after the flash.
(1) immediately and (2) in 30 ms after the flash.
photolysis products on the wavelength of exciting light
was not observed at all.
Me
Me
N
HO
R1
N
N
O
Photolysis of I in Toluene
Me
BPCꢀIV
R2
Molecules of I in a toluene solution exist mainly in
the AЕc form, but the portion of the ketoꢀform AKc
remains noticeable, in contrast to BPCꢀIV, for which
it was not observed in toluene [9].
In a series of BPCꢀIV with different substituents
R1 = R2 = H; R1 = R2 = Cl; R1 = H, R2 = Br; R1 = H,
(
R2 = NO2
laser photolysis, the formation of three isomeric forms
was observed: AKt
; R1 = R2 = NO2), under the conditions of
Flash photoexcitation of I in toluene solutions with
,
ВЕ, and ВКс, characterized by difꢀ visible light results in the formation of two isomers: AKt
ferent absorption spectra and decay constants: for and a product with the open form
В in the ratio of 7.6 :
AKt
λmax
620 nm,
–
λmax
≈
500 nm,
k
= 1
×
104–1
×
105 s–1; for ВЕ
λmax
–
≈
1, which were characterized by the absorption maxiꢀ
mums at 470 and 590 nm (Fig. 3). The decay kinetics
≈
600 nm,
k
= 0.5–1.6 s–1; for ВКс
–
k
= 14–17 s–1. A strong dependence of the of these isomers obeys the first order law with the rate
ratio of these intermediates on the nature of the solꢀ constants of 1.0
×
102 and 23 s–1, respectively. We
vent and the substituents in the azomethine moiety believe that in this case the merocyanine form ВКс is
was observed, whereas a dependence of the ratio of the also formed:
MeO
O
MeO
NH
Me
NH
Me
Me
Me
O
O
N
N
h
ν
N
N
O
Me
Me
AKc
BKc
This conclusion is confirmed by calculations and 0.1562 eV, which is almost 7 times higher than the
optimization of the isomeric forms of the molecules in energy kT at . Hence, it follows from thermodyꢀ
0°C
the ground state, performed by the DFT method, namic considerations that in successive cis–trans
which showed that in this case the difference of the isomerizations, the only form BKc will be observed.
energies of the ground states of the structures BKc and Note that the source of ВКс can be not only the closed
BKt is 0.443 eV, which is almost 20 times higher than form АКс present in toluene in a small amount, which
the energy kT at
0°C
, and the difference of the enerꢀ can be converted into ВКс upon absorption of a quanꢀ
gies of the ground states of the structures BE and BKc is tum of light. The relatively high quantum yield of ВКс
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264
LEVIN et al.
A
0.05
0.04
0.03
0.02
0.01
0
1
2
400
500
600
700
, nm
λ
–0.01
Fig. 5. Absorption spectra of intermediate products arising
upon photolysis with UV light of I in toluene, measured (
immediately and ( ) in 30 ms after the flash.
1
)
2
This stabilizing effect is not observed in methanol
because of the interaction of molecules of I with the
solvent.
The same two isomeric products are observed upon
photolysis of I with UV light, but with the ratio of their
signals of 2.13 : 1 (Fig. 5). The kinetic parameters of
these processes coincide with the analogous values
obtained upon photolysis with visible light.
Kt
Fig. 4. Projection of the structure of
A optimized by the
DFT method for compound I.
apparently indicates that ВКс appears also upon photoꢀ
excitation of the enol form АЕ of compound I. We may
assume that ВКс is formed as a result of prototropic
processes being a kind of thermodynamic relaxation of
In summary, the photolysis of I in both toluene and
methanol leads to the formation of two intermediate
products differing in absorption as a result of competꢀ
itive photochromic processes: opening of the spiro
a common precursor of the forms В.
cycle, ESIPT, and conversion of cisꢀketone to trans
ꢀ
ketone. The ratio of these products strongly depends
on the nature of the solvent and the wavelength of
exciting light. In particular, the portion of the merocyꢀ
anine form increases about four times upon photolysis
with UV light compared with that upon photolysis
with visible light in toluene solution. The formation of
the merocyanine form upon excitation with visible
light is likely due to existence of conjugation between
the photochromic moieties. The intramolecular
hydrogen bond between the oxazine N atom and the
proton of the NH group of the azomethine moiety
leads to a very strong increase in the lifetime of the
form AKt in toluene.
It is noteworthy that unlike the case of model comꢀ
pound III and BPCꢀIV studied earlier (the rate conꢀ
stant of about
4
×
103 s–1) [9], the AKt form of I has a
very long lifetime (about 15 ms). The most likely reaꢀ
son for this fact is the stabilizing effect of the intramoꢀ
lecular hydrogen bond between the oxazine nitrogen
atom and hydrogen of the NH group of the azomeꢀ
thine moiety (Fig. 4). The distance between covalently
unbound H and N atoms in
value is close to analogous distances in sixꢀmembered
cycles in AKc (1.62 and AЕ (1.57
, in which a
hydrogen bond is known to exist, in contrast to the
structure , in which, according to the data
Kt (1.95
A
Kt = 1.70 Å, which in its
Å
)
Å)
B
Å)
on optimization of the structure of the molecule, there
is no hydrogen bond due to a constrained nonꢀplanar
structure.
ACKNOWLEDGMENTS
This work was supported by the Russian Academy
of Sciences under Presidium program no. 8 and by the
Russian Foundation for Basic Research, project
no. 13ꢀ03ꢀ00396a.
Me
N Me
OMe
Me
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Translated by A. Tatikolov
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