Photochromic and cation-binding properties of new crowned spiropyrans

Article abstract of DOI:10.1080/15421400590947289

Spectral properties of new crowned spiropyrans and their cationic complexes are described.

Full text of DOI:10.1080/15421400590947289

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Photochromic and Cation-
Binding Properties of New
Crowned Spiropyrans
a
a
a
A. A. Khodonov , A. Yu. Lukin , A. V. Laptev
,
a
b
c
V. I. Shvets , O. V. Demina , S. P. Gromov , A. I.
c
c
c
Vedernikov , Yu. P. Strokach , O. V. Venidiktova
,
c
c
c
T. M. Valova , M. V. Alfimov & V. A. Barachevsky
a
M. V. Lomonosov State Academy of Fine Chemical
Technology , Moscow, Russia
b
N. M. Emanuel Institute for Biochemical Physics ,
RAS, Moscow, Russia
c
Photochemistry Center of RAS , Moscow, Russia
Published online: 31 Aug 2006.
To cite this article: A. A. Khodonov , A. Yu. Lukin , A. V. Laptev , V. I. Shvets , O. V.
Demina , S. P. Gromov , A. I. Vedernikov , Yu. P. Strokach , O. V. Venidiktova , T. M.
Valova , M. V. Alfimov & V. A. Barachevsky (2005) Photochromic and Cation-Binding
Properties of New Crowned Spiropyrans, Molecular Crystals and Liquid Crystals, 431:1,
15-521
5
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Mol. Cryst. Liq. Cryst., Vol. 431, pp. 215=[515]–221=[521], 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590947289
Photochromic and Cation-Binding Properties of New
Crowned Spiropyrans
A. A. Khodonov
A. Yu. Lukin
A. V. Laptev
V. I. Shvets
M. V. Lomonosov State Academy of Fine Chemical Technology, Moscow,
Russia
O. V. Demina
N. M. Emanuel Institute for Biochemical Physics, RAS, Moscow, Russia
S. P. Gromov
A. I. Vedernikov
Yu. P. Strokach
O. V. Venidiktova
T. M. Valova
M. V. Alfimov
V. A. Barachevsky
Photochemistry Center of RAS, Moscow, Russia
Spectral properties of new crowned spiropyrans and their cationic complexes are
described.
Keywords: benzocrown ethers; crowned spiropyrans; ionophore; spectral data
INTRODUCTION
The photochromic properties of spiropyrans (SPs) have been exten-
sively studied due to their potential applications in high-density
This work was partly supported by the RFBR (Projects No. 04-03-32746, No. 02-03-
3
2320); INTAS 2001-0267; ISTC No#2117; The Ministry of Science and Education RF
(No. 203.02.05.004) and Government of Moscow grants.
Address correspondence to A. A. Khodonov, M. V. Lomonosov State Academy of Fine
Chemical Technology, pr. Vernadskogo 86, Moscow, 117571 Russia. E-mail: khodretinal@
mtu-net.ru
215=[515]

2
16=[516]
A. A. Khodonov et al.
optical data storage and non-linear optical devices [1] as well as photo-
switchable molecular receptors [1,2]. Most of the previous studies have
been focused on the derivatives having a strong electron-withdrawing
0
substituent, such as nitro group at the 6 -position of SP, so as to
increase the life-time of the photoinduced coloured merocyanine
(
MC) form, whereas much less attention has been paid to SP deriva-
tives, which lack a strong electron withdrawing substituent in the
benzopyran ring [2,3]. Our research is devoted to the investigation
of photochromic properties of the SP molecules, which possess the
ionophoric moiety for effective cation binding.
In this paper, we describe the synthesis and properties of a series of
new crowned SPs with different macroheterocycle size (CSP-1 and
CSP-2, where R ¼ CH , R ¼ H and R is an ionophore residue).
1
3
2
3
The molecules contained either of two crown-ether ionophores (mono-
benzo-5(6)-crown-15(18)), which was bound via a C=C-spacer to the
0
6
-position of the pyran moiety instead of the nitro group.
EXPERIMENTAL
The spectral - kinetic study of CSPs was conducted in acetonitrile
ꢀ4
solutions (C 2 10 M). The electronic spectra of samples were
measured on a Cary-50 spectrophotometer (Varian), and the kinetic
curves of photoinduced and spontaneous change of solution optical
density were recorded on the special kinetic set-up. The photochemi-
cal transformations were carried out under filtered radiation of the
SVD-120 or DRSH-250 mercury lamps using the standard glass light
filters.
RESULTS AND DISCUSSION
Synthesis
Thus far, most studies have been focused on the design of
approaches for introducing an ionophore fragment, either at the

Photochromic and Cation-Binding Properties
217=[517]
0
6
-position, or at the N atom of the indoline cycle, or at the 8 -
position of the benzopyrane ring of CSPs containing monoazacrown
ether or 15-crown-5 ether moieties [2]. In our case, the ionophoric
0
group was attached to the 6 -position of the pyran moiety via
C=C-spacer. We proposed a new effective approach to ionophore
introduction into the SP molecule involving the Wittig olefination
0
of 4 -formyl-crowns (4 a,b) with the ylide, generated from phos-
phonium salt (8) under phase transfer catalysis conditions (see
Scheme 1). The starting compounds (4 a,b) were obtained by Duff
formylation of benzo-15-crown-5 or benzo-18-crown-6, as described
previously [4]. Phosphonium salt (8) was prepared with 80% yield
by condensation of Fischer’s base (7) with correspondent salicyl-
aldehyde derivative (6) [5].
The key reaction used to prepare CSP-1, CSP-2 consists in the
0
Wittig olefination of 4 -formyl-crowns (4 a,b) with the ylide, generated
from triphenylphosphonium salt (8) under phase-transfer catalysis
conditions (CH Cl , K CO , 18-crown-6, 3–5 days), which were
2
2
2
3
developed in our earlier study [6]. It was found that the Wittig olefina-
tion follows preferably E-selectivity for the newly formed bond and
gives moderate yields of products. The pure E-isomers were obtained
by column chromatography and recrystallization. The structure of
1
all compounds was confirmed unambiguously by IR; UV; H NMR-
spectroscopy and mass-spectrometry.
SCHEME 1

2
18=[518]
A. A. Khodonov et al.
Photochromic Properties
Earlier, it was shown using pulse irradiation that SPs without elec-
tron-withdrawing substituents undergo photochromic transforma-
tions between initial colorless spiroform (A, SP) and photoinduced
coloured merocyanine forms (B, MC) due to fast relaxation of the
ꢀ1
photoinduced MC form at room temperature (k ¼ 11,5 s in cyclohex-
ane [3]). A spectral - kinetic study of CSPs has shown that they display
photochromic properties in contrast to the unsubstituted derivatives
(
Fig. 1).
It can be seen from Figure 1 that the initial CSP-1 acetonitrile sol-
ution is already coloured as a result of partial shift of the equilibrium
toward the MC form taking place in the dark. Successive exposure of
solution to the UV- and visible filtered light of a SVD-120 mercury
lamp induces interconversion of the two forms (SP $ MC) of the photo-
chromic compound. The k
value for the absorption band of the
max
photoinduced MC form equals 470 nm. The thermal bleaching pro-
ceeds extremely slowly (Fig. 2), in contrast to that in unsubstituted
SPs. This can be explained by the effect of the electronic and steric
factors of the crown macroheterocycle.
The similar properties are detected for the CSP-2 compound. The
þ3
related spectral changes are observed upon the introduction of La
ions into a solution (Fig. 3). They are enhanced during storage of the
sample solution in the dark. These observabled spectral changes are
caused by the gradual shift of equilibrium toward the MC form. As
ꢀ4
FIGURE 1 Absorption spectra of CSP-1 in acetonitrile (C 2 10 M): before
1), and under UV- (2) and visible light (3).
(

Photochromic and Cation-Binding Properties
219=[519]
FIGURE 2 Kinetic curve of the photoinduced changes in the optical density
of CSP-1 in acetonitrile under UV-light of a DRSH-250 lamp and after
switching-off illumination.
soon as the formation of the cation-ionophore complex has completed,
the obtained solution no longer exhibit the photochromic properties.
It can be explained by the strong electrostatic interaction between
ꢀ
4
FIGURE 3 Absorption spectra of CSP-1 in acetonitrile (C 2 10 M) mea-
sured: before (1), and within 5 (2), 20 (3), and 60 min (4), and 25 h 15 min (5)
þ3
after the introduction of the La salt, respectively. The concentration ratio
þ3
C
=CLa ¼ 1:100.
CSPꢀ1

2
20=[520]
A. A. Khodonov et al.
þ3
phenoxide ion of the MC form and La =ionophore complex. The
þ3
solution of the complex with low La concentration partly retains
its photochromic properties, due to the residual concentration of
photochromic molecules not involved in complexation.
A comparative study of the complexation efficiency for CSP-1
molecule with two metal ions has shown that this is somewhat higher
þ3
þ2
for La than for Mg . CSP-2 is slightly more effective than CSP-1
þ3
as regards complexation with La ions. This is due to the good match
between the sizes of the interacting species. It was found that their
stability against irreversible phototransformations increases after
þ2
introduction of Mg ions into solution about the concentration ratio
CCSP-1=C
¼ 1:10 (Fig. 4.). Probably, it is a sequent of high light
Mgþ2
resistance of coloured non-photochromic complexes.
CONCLUSIONS
An effective synthetic approach to CSPs containing an ionophoric
0
group linked to the 6 -position of pyran moiety via a C=C-spacer was
proposed.
Photochromic properties of the SP molecules with the ionophoric
fragment at the C6
0
ꢀ position of the pyran ring were detected at room
temperature, being due to retardation of thermal relaxation rate of the
MC form.
It was shown for the CSPs, that after completion of the cation-
ionophore complex formation, the resulting samples do not exhibit
FIGURE 4 Kinetic curves of optical density changes of photocoloration and
photodegradation processes of CSP-1 in acetonitrile: without (1) and in the
þ 2
presence of a Mg
salt (2). Concentration ratio: CCSP-1=CMgþ2 ¼ 1:10.

Photochromic and Cation-Binding Properties
221=[521]
photochromic properties. The absorption spectra of these non-photo-
chromic species were almost identical to those of photoinduced MC
form solutions without addition of metal salts. Also, solutions of these
species were found to exhibite higher stability against irreversible
photochemical transformations. It was found that at low metal ion
concentrations, the photochromic properties are partly retained due
to the residual concentration of photochromic molecules not involved
in the complexation process.
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