Crown-containing spironaphthoxazines and spiropyrans 3. Synthesis and investigation of the merocyanine form of crown-containing spirobenzothiazolinonaphthoxazine

Article abstract of DOI:10.1023/A:1020950620582

A method for the synthesis of the spirobenzothiazolinonaphthoxazine, stable in the merocyanine form and containing a crown-ether fragment was developed. The complexing properties of the prepared merocyanine compound and the spectroscopic and photochromic characteristics of its complexes with alkaline earth metal cations were studied by NMR and UV spectroscopy. The results were analyzed using quantum-chemical calculations. The addition of alkaline earth metal perchlorates to a solution of a crown ether-containing merocyanine dye in MeCN results in the coordination of metal cations to two binding centers, namely, the crown-ether fragment and the merocyanine oxygen atom. This gives rise to two types of complexes, which differ substantially in their structurally. The complexation induces changes in the UV spectra and influences on the photochromic behavior of the prepared compound.

Full text of DOI:10.1023/A:1020950620582

Russian Chemical Bulletin, International Edition, Vol. 51, No. 8, pp. 1441—1450, August, 2002
1441
Crownꢀcontaining spironaphthoxazines and spiropyrans
3.* Synthesis and investigation of the merocyanine form of crownꢀcontaining
spirobenzothiazolinonaphthoxazine
a
a
a
b
b
O. A. Fedorova,a A. V. Koshkin, S. P. Gromov, V. G. Avakyan, V. B. Nazarov, S. B. Brichkin,
ꢀ
T. G. Vershinnikova,b T. M. Nikolaeva,b L. A. Chernych,b and M. V. Alfimova
aPhotochemistry Center of Joint N. N. Semenov Institute of Chemical Physics
of the Russian Academy of Sciences,
7A ul. Novatorov, 117421 Moscow, Russian Federation.
Fax: +7 (095) 936 1255. Eꢀmail: fedorova@photonics.ru
bInstitute of the Problems of Chemical Physics, Russian Academy of Sciences,
142432 Chernogolovka, Moscow Region, Russian Federation
A method for the synthesis of the spirobenzothiazolinonaphthoxazine, stable in the
merocyanine form and containing a crownꢀether fragment was developed. The complexing
properties of the prepared merocyanine compound and the spectroscopic and photochromic
characteristics of its complexes with alkaline earth metal cations were studied by NMR and
UV spectroscopy. The results were analyzed using quantumꢀchemical calculations. The addiꢀ
tion of alkaline earth metal perchlorates to a solution of a crown etherꢀcontaining merocyanine
dye in MeCN results in the coordination of metal cations to two binding centers, namely, the
crownꢀether fragment and the merocyanine oxygen atom. This gives rise to two types of
complexes, which differ substantially in their structurally. The complexation induces changes
in the UV spectra and influences on the photochromic behavior of the prepared compound.
Key words: crown ether, spirobenzothiazolinonaphthoxazine, 1ꢀ[(3ꢀmethylꢀ
6,7,9,10,12,13,15,16ꢀoctahydro[1,4,7,10,13]pentaoxacyclopentadecyno[2,3ꢀf ][1,3]benzoꢀ
thiazolꢀ2(3H)ꢀyliden)methylimino]naphthalenꢀ2ꢀone, alkaline earth metals, complex forꢀ
1
mation; UV spectroscopy, Н NMR spectroscopy, photochromic behavior, oxidation.
It is known that spiropyrans and spironaphthoxazines
can exist in the ground state as two forms, namely, colꢀ
orless (closed) or colored (merocyanine) forms. The staꢀ
bility of a particular spiro compound form is determined
by two key factors, namely, the nature of the heterocyꢀ
clic nucleus and the electronic and steric properties of
substituents. For instance, indoline spiropyrans and
spironaphthoxazines exist predominantly as closed (i.e.,
colorless) forms, while both open (merocyanine) and
closed forms may be stable for spiropyrans of the
benzothiazolium series. In the case of spiropyrans conꢀ
taining a benzimidazolium nucleus, only the mercoꢀ
cyanine form is known.2
The variation of steric and electronic properties of
substituents in spiro compounds of the benzothiazolium
series is widely used to stabilize the open or closed form.
The heterocyclic residue containing no substituents or
containing electronꢀdonating substituents (electronic facꢀ
tor) is favorable for stable merocyanine form. The introꢀ
duction of substituents into 2ꢀposition of the oxazine
nucleus (steric factor) markedly stabilizes the closed form
with respect to the open form.2 Study of the structures of
the open and closed forms of a spiro compound contribꢀ
utes to the understanding of the photoisomerization beꢀ
havior, which, in turn, helps to find ways for controlling
phototransformation. This research is important regardꢀ
ing both the fundamental science and the manufacture
of new promising photosensitive materials for optical
lenses,3 or the development of optical systems for inforꢀ
mation recording4 and photosensitive biomaterials.5
Of special interest is the introduction of a crownꢀ
ether fragment into a spiro compound. Crown ethers are
known to form stable complexes with various metal catꢀ
ions. The complex formation involving crownꢀcontainꢀ
ing spiro compounds allows one to affect substantially
the spectroscopic and photochromic characteristics of
compounds.
In this study, we synthesized stable merocyanine forms
of dyes (MD) that belong to the spirobenzothiazolinoꢀ
naphthoxazine series, namely, MD 1а, serving as the
model compound, and MD 1b, containing a conjugated
crownꢀether fragment. The formation of complexes by
* For Part 2, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1330—1338, August, 2002.
1066ꢀ5285/02/5108ꢀ1441 $27.00 © 2002 Plenum Publishing Corporation

1442
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Fedorova et al.
Scheme 1
these compounds with alkaline earth metals and the efꢀ
fect of complexation on the capacity for photoisoꢀ
merization to the spiro form were studied.
Results and Discussion
Synthesis and structure of MD 1a,b. Dyes 1а,b were
synthesized starting from substituted 2ꢀmethylbenzoꢀ
thiazolium salts 2а,b, which were prepared from the corꢀ
responding benzothiazoles. Several methods have been
proposed in the literature for benzothiazole synthesis.6—8
We chose a fourꢀstep synthesis;7,8 the large number of
synthetic steps is well counterbalanced by the relatively
high yield in each step and the easy accessibility of the
starting compounds (Scheme 1).
The structure of MD 1а,b was proved on the basis of
the data of 1H NMR spectroscopy and COSY and NOESY
techniques. The compounds 1а,b synthesized can exist
as four isomers.
The COSY spectra of MD 1а,b were found to exꢀ
hibit crossꢀpeaks, which allow exact assignment of the

Crownꢀcontaining spironaphthoxazines
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
1443
βꢀH, β´ꢀH
H(4), H(5´), H(7´)
NMe
γꢀH, γ´ꢀH, δꢀH, δ´ꢀH
H(9´)
H(7)
α´ꢀH
αꢀH
H(6´)
H(2´)
H(10´)
H(8´)
δ
H(2´)—NMe
4
H(4)—NMe
α´ꢀH—H(7)
αꢀH—H(4)
5
6
7
8
9
10
10
9
8
7
6
5
4
δ
1
Fig. 1. NOESY H NMR spectrum of MD 1b.
1H NMR signals (see Experimental). The NOESY specꢀ
tra (Fig. 1) showed crossꢀpeaks attesting to spatial proxꢀ
imity of the NMeꢀgroup protons, the H(4) proton of the
benzothiazolium residue, and the H(2´) proton of the
azomethine group, and in the case of 1b, the αꢀН, H(4)
and α´ꢀH, H(7) protons. Among the possible isomeric
structures, this situation can occur only in the ttcꢀisomer.
The compound can exist as the ctcꢀisomer only if it is
mixed with the ttcꢀisomer. Since in the ctcꢀisomer, the
NMe group is close in space to the H(4) proton and is
remote from the H(2´) proton of the azomethine group,
the spectroscopic data thus suggest that MD 1а,b exist as
mixtures of ttcꢀ and ctcꢀisomers. In both isomers, the
H(2´) proton is located closely to the merocyanine oxyꢀ
gen atom, i.e., it can fall within the deshielding region of
the carbonyl oxygen, which is confirmed by the lowꢀ
field position of this signal (δ 10.3). The use of protic
solvents capable of hydrogen bonding to oxygen of the
merocyanine form may decrease the influence of the
anisotropic effect of the carbonyl group on the azomethine
proton and, hence, induce an upfield shift of the H(2´)
signal. Indeed, this is the case on passing from DMSOꢀd6
to CD3OH; in CD3CN, the chemical shift of the
azomethine proton virtually coincides with that found in
DMSOꢀd6.
H(2´), δ
1a
DMSOꢀd6
10.30
CD3CN
10.35
CD3OH
09.90
1b
10.30
10.30
10.00
In order to determine the relative stabilities of the
rotational isomers of the merocyanine spironaphthoxaziꢀ
nes, the heats of formation (∆Hf) and the relative enerꢀ
gies (∆E) of rotational isomers were determined for MD
1а as an example by semiempirical PM3 quantumꢀchemiꢀ
cal calculations with a standard set of parameters9
(Table 1). The calculations included full geometry optiꢀ
mization for all structures; the vibration frequencies for
the compounds were also calculated in the harmonic
approximation. The absence of negative values among
the resulting frequencies confirms that each compound
is matched by a local minimum on the potential energy
surface.
The calculation of the isomer proportions at room
temperature using the Boltzmann formula showed that
in the gas phase, MD 1а is an isomer mixture comprising
predominantly of the ctc (37%) and ttc (33%) isomers

1444
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Fedorova et al.
Table 1. Heats of formation (∆Hf) and
relative energies (∆E) of the rotational
isomers of MD 1a and their proportions
in the mixture in the gas phase accordꢀ
ing to quantumꢀchemical calculations
The absorption spectra of MD 1a,b are identical in
the longꢀwavelength region (the chromophore systems
are the same) and contain an intense peak at λ = 636 nm
(Fig. 2), which also confirms the existence of the stable
merocyanine form for MD 1a,b. The extinction coeffiꢀ
cients at the longꢀwavelength maximum (λ = 636 nm)
were 48800 and 38800 mol–1 cm–1 for MD 1a and 1b,
respectively.
Isomer
∆Hf
∆E
Content
kcal mol–1
Study of complexation by 1H NMR spectroscopy. The
addition of alkaline earth metal perchlorates to solutions
of compounds 1a,b in MeCN entails pronounced changes
ctt
ttt
ctc
ttc
12.45
12.17
9.93
2.52
2.24
0
0.124
0.152
0.374
0.331
1
in the H NMR spectra (Fig. 3), caused by complex
10.45
0.52
formation. The crownꢀcontaining MD 1b molecule conꢀ
tains two sites able to coordinate metal cations, viz., the
crownꢀether fragment and the merocyanine oxygen;
therefore, generally, the complexation can be represented
by Scheme 2. Compound 1а can form only type B comꢀ
plexes.
Note. The relative energy of the ctcꢀisoꢀ
mer was taken to be zero.
(see Table 1). The C=O bond length in the naphthalene
fragment in both isomers proved to be 1.22 Å, which
validates the merocyanine structure of the compound.
The addition of metal salts to solutions of compounds
1
1a,b induces changes in the positions of the H NMR
A
signals of aromatic protons, and in the case of 1b, it also
induces a downfield shift of the signals due to the crownꢀ
ether methylene protons (see Fig. 3).
a
1a
0.8
Ba2+
Ca2+
0.6
Mg2+
∆δ
0.4
0.2
a
Sr2+
600
Ca2+
0.5
1
0
300
300
400
500
500
λ/nm
0.4
1b
0.8
0.6
0.4
0.2
Mg2+
Ba2+
Sr2+
0.3
2
0.2
3
0.1
400
600
λ/nm
αꢀH
βꢀH
γꢀH
δꢀH
A
1
b
∆δ
1.5
1.0
0.5
2
3
b
0.6
0.4
4
1
0.2
2
3
0
4
5
6
–0.2
–0.4
–0.6
7
8
400
500
600
λ/nm
H(2´) H(5´) H(6´) H(7´) H(8´) H(9´) H(10´)
Fig. 2. Absorption spectra (MeCN, 25 °C, CMD
=
Fig. 3. Changes in the positions of the 1H NMR signals (in
CD3CN) of the crownꢀether moiety of MD 1b (a) and
the naphthalene fragment of MD 1а,b (b) in the presence
of Mg2+ (1, 4), Ca2+ (2), and Ba2+ (3) cations (MD 1b,
curves 1—3; MD 1a, curve 4).
4•10–5 mol L–1) of (a) MD 1a,b and their complexes with
various metal cations ([M2+] : [1a,b] = 100 : 1); (b) MD 1b (1)
and its complexes with Mg2+ cations ([Mg2+] : [1b] = 1 : 24 (2),
1 : 12 (3), 1 : 6 (4), 1 : 3 (5), 1 : 2 (6), 1 : 1 (7), and 2 : 1 (8)).

Crownꢀcontaining spironaphthoxazines
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
1445
Scheme 2
In the case of MD 1b, the downfield shift of the
proton signals corresponding to the methylene groups of
the ionophoric fragment indicates that the complexation
involves the crownꢀether, which has been shown in our
previous study for crownꢀcontaining spironaphthoxazines
of different structures10,11 (see Fig. 3, а, Scheme 2,
complex А).
have an influence on the signal of the Me group at the
benzothiazole N atom. In the betaine structure, the N
atom is positively charged and the signals of the Me
group (δ 4.30) are shifted downfield compared to the
signals of the Me group in the initial merocyanine
form (δ 3.90).
1
Thus, the data of the H NMR spectra of compound
The signal of the azomethine H(2´) proton in MD
1a,b undergoes a substantial upfield shift, while the proꢀ
ton signals of the naphthalene residues shift downfield,
the most appreciable effect being observed for the H(5´)
proton (see Fig. 3, b). This is probably due to complexꢀ
ation at the merocyanine oxygen atom. Indeed, the coꢀ
ordination of the metal cation to the O atom is expected
to displace the equilibrium toward the betaine form (see
Scheme 2, complex B). In complex B, the proton of the
azomethine fragment does not fall any longer in the
deshielding area of the carbonyl O atom; this leads to an
upfield shift of the H(2´) signal (see Fig. 3, b). The
formation of the oxygen—metal bond has a most proꢀ
nounced influence on the H(5´) proton of the naphthaꢀ
lene residue, located in the orthoꢀposition relative to the
merocyanine O atom. Indeed, the signal of this proton
undergoes the largest downfield shift (see Fig. 3, b).
Finally, the betaine structure of the molecule should
1b recorded after the addition of various metal cations
confirm that complexation involves both sites capable of
being coordinated by metal cations. Since the studies
were carried out at an equimolar ligand : metal cation
ratio, one can conclude that the solution contains an
equilibrium mixture of two types of complexes, A and B
(see Scheme 2). The presence of an equilibrium mixture
1
is confirmed by some signal broadening in the H NMR
spectra of the complexes formed by 1b. The influence of
the three metal cations studied (Mg2+, Ca2+, and Ba2+
)
is qualitatively the same; however, it gradually decreases
in this series, which may be due to the decrease in the
charge density;12 in the case of the crownꢀetherꢀconꢀ
taining complex, one more reason is the better fit of the
Mg2+ cation size to the 15ꢀcrownꢀ5 ether cavity.13
Optical absorption spectra and quantumꢀchemical calꢀ
culation for MD 1a,b. The complexation of MD 1a,b
with Mg2+, Ca2+, and Ba2+ cations in MeCN inꢀ

1446
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Fedorova et al.
A636
merocyanine oxygen. Figure 2, a shows the absorption
spectra of free compounds 1а,b and those in the presꢀ
ence of a 100ꢀfold excess of alkaline earth metal cations.
The addition of more metal cations causes virtually no
further spectral changes. It can be seen from the Figure
that each of the complexes MD 1а,b formed has its own
peculiar spectroscopic characteristics. A common feaꢀ
ture is that the addition of Mg2+ cations gives rise to the
most intense peak at λ = 500 nm, and Ba2+ and Sr2+
cations induce a less pronounced decrease in the absorpꢀ
tion at λ = 636 nm.
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
1
2
Unfortunately, we could not measure the complexꢀ
ation constants, because the changes in the optical denꢀ
sity observed during the titration of solutions of MD
1a,b with metal cations are accompanied by uncontrolꢀ
lable protonation, oxidation, and degradation processes
occurring in air (see below). Processing of the measureꢀ
ments results leads to relatively large discrepancies in the
calculated stability constants of complexes.
In order to study the influence of complexation on
the structural and electronic parameters of MD 1a,b, to
identify the energetically most favorable coordination
site, and to interpret the observed shifts of the absorpꢀ
tion bands, we carried out the РM3 calculations for the
rotational isomers of 1а,b and their complexes with Mg2+
in which the metal atoms are coordinated to either
0
0.2
0.4
0.6
0.8 [Mg2+] : [1a,b]
Fig. 4. Optical density of solutions of MD 1a (1) and 1b (2) in
MeCN at λ = 636 nm in the presence of the Mg2+ cation at
various [Mg2+] : [1a,b] molar ratios.
duces substantial changes in the absorption spectra (see
Fig. 2, a), which are manifested, first of all, as a decrease
in the absorption at λ = 636 nm and the appearance of a
typical broad band at about λ = 500 nm, these changes
appearing faster for MD 1b than for MD 1a (Fig. 4).
Apparently, this is due to the more efficient complex
formation owing to the simultaneous participation of
two complexation sites, the crownꢀether moiety and the
Table 2. Heats of formation (∆Hf), relative energies (∆E), bond lengths (d), and charges on the atoms (Q) of the
rotational isomers of spironaphthoxazines 1a,b and their complexes with Mg2+
Isomer
∆Hf (∆E)
/kcal mol–1
d/Å
Q/e
OC=O
C=O C(2)—C(2´) C(2´)—N
N—C(3´)
N
O(7)
O(8)
1a
ctc
9.93 (0)
368.3 (0)
1.22
1.36
1.36
1.47
1.40
1.29
1.30
1.42
0.14
0.52
–0.32
–0.33
–0.17
—
–0.20
—
ctc•Mg2+
(B)
ctc•Mg2+
(A)
396.3 (28)
1.22
1.35
1.40
1.30
0.30
–0.335
—
—
ttc
10.45 (0.52)
369 (0.7)
1.22
1.36
1.36
1.47
1.40
1.29
1.30
1.43
0.17
0.565
–0.313 –0.22
–0.20
—
ttc•Mg2+
(B)
–0.355
—
ttc•Mg2+
(A)
396 (27.7)
1.23
1.35
1.40
1.30
0.334
–0.29
—
—
1b
ctc
103.20 (0)
258.8 (0)
1.22
1.36
1.36
1.47
1.40
1.29
1.30
1.43
0.14
0.51
–0.32
–0.33
–0.17
—
–0.20
—
ctc•Mg2+
(B)
ctc•Mg2+
(A)
314.9 (56.1)
1.22
1.35
1.40
1.30
0.23
–0.335
—
—
ttc
103.1 (0.52)
257.4 (0.7)
1.22
1.36
1.36
1.47
1.40
1.29
1.30
1.42
0.17
0.565
–0.31
–0.313
–0.22
—
–0.20
—
ttc•Mg2+
(B)
ttc•Mg2+
(A)
258.9 (27.7)
1.23
1.35
1.40
1.30
0.288
–0.295
—
—
Note. The relative energy of the ctcꢀisomer and its complex with Mg2+ was taken to be zero; A and B are types of
complex (see Scheme 2).

Crownꢀcontaining spironaphthoxazines
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
1447
∆ν/cm–1
methoxyꢀgroup O atoms and the crownꢀether (А) or the
merocyanine O atom (В) (Table 2).
5000
According to the results, complexes B in which the
Mg2+ cations are coordinated to the merocyanine O atom
are thermodynamically more stable than complexes A in
which the Mg2+ cation resides in the crownꢀether cavity.
After coordination, complex B acquires a betaine
structure, which shows itself as an increase in the posiꢀ
tive charge in the benzothiazole fragment (by 0.16 e) and
elongation of the C=O bond (1.22 Å) in the naphthalene
fragment nearly to reach the C–O σꢀbond length (1.36 Å).
Finally, the lengths of the C(2)—C(2´), C(2´)—N, and
N—C(3´) bonds, forming the chromophore system,
change in such a way that the C(2)—C(2´) bond beꢀ
comes longer and more similar to a single bond, the
C(2´)—N bond is shortened to reach the length of a
double bond, and the N—C(3´) bond is elongated to
reach the single bond length. Since the initial meroꢀ
cyanine form is characterized by a more clearꢀcut averꢀ
aging of the bond lengths in the conjugated system, this
implies that the coordination of the metal cation to the
merocyanine O atom results in a more pronounced alꢀ
ternation of bond lengths and, hence, in a decrease in
the degree of conjugation. These changes in the strucꢀ
tural and electronic parameters suggest that the metal
coordination to the merocyanine O atom would induce a
hypsochromic shift of the absorption band of the comꢀ
plex with respect to the band in the spectrum of the
initial MD. Meanwhile, binding of the Mg2+ cation to
the O atoms of the crownꢀether moiety (complex А)
entails no significant changes in the electron density
distribution or in the bond lengths in the molecule; thus,
the complexation with Mg2+ cations is not expected to
cause any significant changes in the absorption spectrum.
Comparison of the absorption spectra of MD 1a,b
and their complexes with various metal cations (see
Fig. 2, а) shows that the longꢀwavelength absorpꢀ
tion bands actually undergo a hypsochromic shift ∆ν
Mg2+
4000
3000
2000
1000
0
Ca2+
Sr2+
Ba2+
0.9
1.0
1.1
1.2
1.3
χ
Fig. 5. Shift of the absorption band (∆ν) of MD 1b vs. Pauling
electronegativity of the metal (χ) (∆ν = ν
tion coefficient 0.997).
– ν1b, correlaꢀ
complex
structure. The concomitant changes in the absorption
spectra are similar to those induced by complexation
with alkaline earth metal cations. A maximum appears at
about λ = 500 nm, while the absorption at λ = 636 nm
decreases; however, upon subsequent addition of a soluꢀ
tion of alkali (KOH), the maximum at λ = 500 nm
disappears and the absorption at λ = 636 nm returns to
the state existing before the above manipulations (with
allowance for dilution). Analogous results were obtained
by using acetic or perchloric acid or by passing CO2
through solutions of MD 1a,b.
The fact that MD 1a,b are protonated on acidifying
the solution was confirmed by isolation and characterꢀ
ization of compound 3 (Scheme 3).
Scheme 3
(∆ν = ν
– νMD), which increases in the sequence
complex
Ba2+ < Sr2+ < Ca2+ < Mg2+, being linearly correlated
with the metal electronegativity (χ) with a good correlaꢀ
tion coefficient (Fig. 5). Since the χ value characterizes
the electronꢀwithdrawing capacity of the element, the
increase in ∆ν following an increase in χ implies that the
MD transition into the betaine form upon coordination
by the metal ion becomes more facile along the sequence
Ba2+ < Sr2+ < Ca2+ < Mg2+. Thus, these data confirm
the fact that the metal cation coordination to MD 1a,b
involves predominantly the merocyanine O atom, which
is manifested as a hypsochromic shift of the absorption
band of the complex, whose magnitude depends on the
electronic nature of the metal cation.
Oxidation and degradation of MD 1a,b. When soluꢀ
tions of MD 1a,b are stored for several days at ∼20 °C,
an absorption band appears in the region of 430—470 nm,
which corresponds to a new compound with intense fluoꢀ
rescence. The formation of the luminophore is irreversꢀ
Protonated MD 1a,b. In the presence of acids, the
merocyanine form of the dye existing in solutions of MD
1a,b is efficiently converted into the protonated betaine

1448
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Fedorova et al.
Scheme 5
ible and can be retarded by lowering the temperature or
by removing oxygen from the solution.
Published data14 lead to the suggestion that the arisꢀ
ing fluorescing product is an oxazole derivative resulting
from the oxidation of MD by atmospheric oxygen
(Scheme 4). The oxidation product 4 was isolated in
8% yield after a 300ꢀh storage of a solution of MD 1а in
MeCN and its structure was proved by a set of physicoꢀ
chemical methods (see Experimental).
Scheme 4
The oxidation is accompanied by intensive formation
of side products whose structure was not studied. The
possible mechanisms of the formation of the oxidation
and degradation products from the benzothiazole MD
have been described in detail previously.14,15
Photochromic properties of MD 1a,b. It is known that
the photoinduced merocyanine form of spiropyrans and
spironaphthoxazines can be converted into the cyclic
form not only in the dark but also upon irradiation within
the absorption band of the open form. The photochemiꢀ
cal formation of the MD spiro form is depicted in
Scheme 5.
the cisꢀisomer and cyclization to give the spiro form.
The formation of the coordination bond between the
merocyanine O atom and the metal cation can influence
the photochromic process in the following way. First,
coordination of the metal cation to the merocyanine O
atom shifts the equilibrium between the merocyanine
and betaine forms toward the latter. Since the first step
of the photochromic reaction, that is, trans—cisꢀisomerꢀ
ization involves rotation around the C—N bond, an inꢀ
t/s
Merocyanine dyes 1a,b can pass to the closed form
only on exposure to light. However, irradiation of soluꢀ
tions of these compounds by a flash of a 235ꢀJ xenon lamp
with an OS14 filter (transmission of light with λ > 580 nm)
does not change the absorption at λ = 636 nm, pointing
to a very low quantum yield of the photoinduced discolꢀ
oration. Only irradiation with a DKSShꢀ200 xenon lamp
with an OS14 or KS11 filter (transmission of light with
λ > 610 nm) for 60 s or with a DRShꢀ1000 mercury
lamp with a OS12ꢀ5 filter (transmission of light with
λ > 550 nm) for 30 s does allow one to obtain the closed
forms of these compounds and to study the regularities
of the photochromic process (Fig. 6).
140
120
100
80
1
1´
2´
60
2
3
3´
40
20
0
0.2
0.4
0.6
0.8 [M2+] : [1a,b]
Fig. 6. Lifetime of the closed form (t) of MD 1a (1—3) and
1b (1´—3´) in MeCN vs. the [M2+] : [1a,b] ratio (M2+
Ba2+ (1, 1´), Ca2+ (2, 2´), and Mg2+ (3, 3´)).
The discoloration of MD includes two successive
stages: isomerization of the transꢀmerocyanine to give
=

Crownꢀcontaining spironaphthoxazines
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
1449
crease in the contribution of the betaine form hampers
isomerization. Second, the coordination of oxygen to
the metal prevents oxygen from participating in the cyꢀ
clization giving the spiro ring. Indeed, as can be seen
from Fig. 6, an increase in the metal cation concentraꢀ
tion in a solution of MD 1а reduces the lifetime of the
closed form.
When complexation involves the crownꢀether moiꢀ
ety, the merocyanine structure of the molecule is reꢀ
tained. As can be seen from the data given in Table 2, in
type А complex, the ttcꢀisomer predominates in the mixꢀ
ture because, according to calculations, this isomer is
more stable than the ctcꢀisomer. Both these facts should
facilitate cyclization to give the spiro form.
When a metal cation is added to a solution of MD 1b
in MeCN, the metal cation is coordinated to both comꢀ
plexation sites. These two processes exert opposite efꢀ
fects on the photochromic transformation. Therefore,
despite the fact that an increase in the salt concentration
in a solution of MD 1b in MeCN does reduce the lifeꢀ
time of the closed form, this process is much slower than
that in the case of MD 1а (see Fig. 6).
The influence of the metal cations on the equilibꢀ
rium between the closed and the open forms of MD (see
Fig. 6) depends on characteristics of the cation and the
resulting complex. The interaction between the meroꢀ
cyanine oxygen and the metal cation is determined by
the charge density on the metal, i.e., the complex strength
decreases in the order Ba2+ < Ca2+ < Mg2+. The effect
of the cation on the lifetime of the closed form (see
Fig. 6) found in our photochemical experiments decreases
along the same sequence. In the complexes involving the
crownꢀether moiety, the correspondence of the metal
cation size to the crownꢀether cavity is important, in
addition to the charge density. In this case, both factors
act in the same direction; hence, the strength of the
complexes decreases in the sequence Ba2+ < Ca2+ < Mg2+
(see Fig. 6).
Experimental
1
H NMR spectra were recorded on Bruker АMXꢀ400 and
Bruker DRXꢀ500 spectrometers. Mass spectra were run on a
Varian MАТ 311А instrument (70 eV) with direct sample injecꢀ
tion into the ionization area.
The optical absorption spectra were measured on a Specord
M40 spectrophotometer and the lifetimes were determined usꢀ
ing a modernized experimental setup16 connected to an IBM
PC AT computer.
For the synthesis of spironaphthoxazines, commercial reꢀ
agents and solvents (Fluka, Merck, and Aldrich) were used as
received.
The reactions were monitored by TLC on DCꢀAlufolien
Kieselgel 60 F254 and DCꢀFertigplatten RPꢀ18 F254
s
plates. Column chromatography was performed using
Siliсa gel 60 (0.063—0.200 mm) and Siliсa gel 60 RPꢀ18
(0.040—0.063 mm).
1 ꢀ [ ( 3 ꢀ M e t h y l ꢀ 6 , 7 , 9 , 1 0 , 1 2 , 1 3 , 1 5 , 1 6 ꢀ o c t a h y d ꢀ
ro[1,4,7,10,13]pentaoxacyclopentadecyno[2,3ꢀf ][1,3]benzoꢀ
thiazolꢀ2(3H )ꢀylidene)methylimino]naphthalenꢀ2ꢀone (1b). A
mixture of benzothiazolium iodide 2b (0.247 g, 0.5 mmol),
1ꢀnitrosoꢀ2ꢀnaphthol (0.086 g, 0.5 mmol), EtOH (3 mL), and
Et3N (0.1 mL, 0.7 mmol) was refluxed for 2 h under argon.
The reaction mixture was cooled and concentrated. Chromatoꢀ
graphic separation gave 0.043 g (17%) of compound 1b, m.p.
122—124 °C (decomp.). Found (%): C, 57.62; H, 5.94; N, 4.70.
C
27H28N2O6S•3 H2O. Calculated (%): C, 57.64; H, 6.09;
N, 4.97. 1H NMR (DMSOꢀd6), δ: 3.64 (m, 8 H, 4 OCH2); 3.83
(m, 4 H, 2 OCH2); 4.00 (s, 3 H, NMe); 4.12 (m, 2 H, OCH2);
4.22 (m, 2 H, OCH2); 6.53 (d, 1 H, H(6´), J = 9.4 Hz); 7.15
(m, 1 H, H(8´)); 7.38 (m, 1 H, H(9´)); 7.50 (m, 3 H, H(4),
H(7´), H(5´)); 7.68 (s, 1 H, H(7)); 8.32 (d, 1 H, H(10´), J =
8.2 Hz); 10.31 (s, 1 H, H(2)). MS, m/z (Irel (%)): 493 [M]+ (7),
492 (22), 360 (16), 169 (15), 114 (14), 58 (23), 45 (26), 44 (12),
43 (100), 42 (13), 39 (14).
1ꢀ[(3ꢀMethylꢀ1,3ꢀbenzothiazolꢀ2(3H )ꢀylidene)methylꢀ
imino]naphthalenꢀ2ꢀone (1a) was prepared similarly to 1b from
salt 2а and 1ꢀnitrosoꢀ2ꢀnaphthol. Yield 44%, m.p. 188—190 °C
(decomp.). Found (%): C, 62.38; H, 5.93; N, 6.84.
C21H18N2O3S•1.5 H2O. Calculated (%): C, 62.20; H, 5.22;
1
N, 6.90. H NMR (DMSOꢀd6), δ: 3.91 (s, 3 H, OMe); 3.98 (s,
3 H, OMe); 4.32 (s, 3 H, NMe); 7.13 (d, 1 H, H(6´), J =
8.9 Hz); 7.36 (m, 1 H, H(8´)); 7.54 (m, 1 H, H(9´)); 7.72 (s,
1 H, H(4)); 7.75 (d, 1 H, H(7´), J = 7.1 Hz); 7.81 (d, 1 H,
H(5´), J = 8.9 Hz); 7.90 (s, 1 H, H(7)); 8.44 (d, 1 H, H(10´),
J = 7.7 Hz); 10.03 (s, 1 H, H(2)). MS, m/z (Irel (%)): 378 [M]+
(35), 209 (65), 170 (36), 169 (100), 142 (68), 141 (72), 114
(83), 113 (52), 63 (32), 58 (56), 43 (81).
2ꢀ[(2ꢀHydroxyꢀ1ꢀnaphthyl)imino]methylꢀ3ꢀmethylꢀ5,6ꢀdiꢀ
methoxyꢀ1,3ꢀbenzothiazolium perchlorate (3). Perchloric acid
(0.05 mL) was added to a solution of MD 1а (0.05 g, 0.13 mmol)
in 20 mL of MeCN. After keeping the reaction mixture for
0.5 h at ∼20 °C, the solvent and excess acid were removed in
vacuo and the residue was dried. Yield 0.06 g (quantitative),
m.p. 233—237 °C. Found (%): C, 50.38; H, 3.93; N, 5.84.
Thus, the data of the NMR and UV spectroscopy and
the results of quantumꢀchemical calculations indicate that
the addition of alkaline earth metal perchlorates to soluꢀ
tions of MD 1b in MeCN results in binding of the metal
cation to two complexation sites of the molecule, namely,
the crownꢀether moiety and the merocyanine carbonyl O
atom. The complexation at the crownꢀether fragment
entails a decrease in the longꢀwavelength absorption inꢀ
tensity and a slight hypsochromic shift of the band; durꢀ
ing the photochromic reaction, this process promotes the
formation of the closed form. Complexation at the
merocyanine O atom induces a substantial hypsochromic
shift of the longꢀwavelength absorption band and conꢀ
tributes to further stabilization of the open merocyanine
form. This study demonstrates the possibility of varying
the spectroscopic and photochromic characteristics of
spironaphthoxazines by means of complexation.
C
21H19ClN2O7S•H2O. Calculated (%): C, 50.76; H, 4.26;
N, 5.64. 1H NMR (CD3OD), δ: 3.95 (s, 3 H, OMe); 4.02 (s,
3 H, OMe); 4.07 (s, 3 H, NMe); 7.35 (d, 1 H, H(5´), J =
9.0 Hz); 7.50 (m, 1 H, H(8´)); 7.52 (s, 1 H, H(4)); 7.66 (m,
1 H, H(9´)); 7.70 (s, 1 H, H(7)); 7.79 (d, 1 H, H(6´), J =

1450
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 8, August, 2002
Fedorova et al.
8.7 Hz); 7.92 (d, 1 H, H(7´), J = 4.2 Hz); 7.96 (d, 1 H, H(10´),
J = 4.3 Hz).
5. I. Willer, Acc. Chem. Res., 1997, 30, 347.
6. Hsu and Q. Lin, Huaxue Xuebao, 1982, 40, 952.
7. S. P. Gromov, D. E. Levin, K. Ya. Burshtein, V. A.
Krasnovskii, S. N. Dmitrieva, A. A. Golosov, and M. V.
Alfimov, Izv. Akad. Nauk, Ser. Khim., 1997, 999 [Russ.
Chem. Bull., 1997, 46, 959 (Engl. Transl.)].
8. Yu. P. Kovtun, N. P. Shandura, and A. I. Tolmachev,
Khim. Geterotsikl. Soedin., 1996, 992 [Chem. Heterocycl.
Compd., 1996, 32 (Engl. Transl.)].
9. J. J. P. Stewart, J. Comput. Chem., 1989, 10, 209.
10. O. A. Fedorova, S. P. Gromov, Yu. P. Strokach, Yu. V.
Pershina, S. A. Sergeev, V. A. Barachevsky, G. Pepe,
A. Samat, R. Guglielmetti, and M. V. Alfimov, J. Chem.
Soc., Perkin Trans. 2, 1999, 1950.
11. O. A. Fedorova, S. P. Gromov, Yu. P. Strokach, Yu. V.
Pershina, S. A. Sergeev, V. A. Barachevskii, Zh. Pepe,
A. Samat, R. Guglielmetti, and M. V. Alfimov, Izv. Akad.
Nauk, Ser. Khim., 1999, 1974 [Russ. Chem. Bull., 1999, 48,
1950 (Engl. Transl.)].
12. Handbook of Chemistry and Physics, Ed. R. C. Weast,
66th ed., CRC Press, Boca Raton, 1985, Fꢀ164.
13. Hostꢀguest Complexes Chemistry, Eds. F. Fogtle and
E. Weber, Springer Verlag, Berlin—Heidelberg—New York—
Tokyo, 1985.
14. Organic Photochromic and Thermochromic Compounds,
Eds. J. C. Crano and R. Guglielmetti, Plenum Press, New
York, 1999, 2, 65.
15. D. Guade, R. Guatrin, R. Guglielmetti, and J. C. Duffy,
Bull. Soc. Chim. Fr., 1981, 1f, 14.
16. V. B. Nazarov, V. A. Soldatenkova, M. V. Alfimov,
P. Larezhini, A. Samat, and R. Guglielmetti, Izv. Akad.
Nauk, Ser. Khim., 1996, 2220 [Russ. Chem. Bull., 1996, 45,
2105 (Engl. Transl.)].
2ꢀ(1,3ꢀBenzoxazolꢀ2ꢀyl)ꢀ3ꢀmethylꢀ5,6ꢀdimethoxyꢀ1,3ꢀ
benzothiazolium perchlorate (4). A solution of MD 1а (0.05 g,
0.13 mmol) in 20 mL of MeCN was kept in a flask in the light
for 300 h. Perchloric acid (0.01 mL) was added to the reacꢀ
tion mixture, the solvent was evaporated, and the residue
was chromatographed on a column with SiO2 (elution with
MeCN—MeOH, 1 : 1) to give 5 mg (7%) of compound 4,
m.p. 133—135 °C. Found (%): C, 52.68; H, 3.93; N, 5.64.
C21H17ClN2O7S. Calculated (%): C, 52.90; H, 3.56; N, 5.87.
1H NMR (DMSOꢀd6), δ: 3.99 (s, 3 H, OMe); 4.08 (s, 3 H,
OMe); 4.90 (s, 3 H, NMe); 7.53 (s, 1 H, H(2´)); 7.79 (m, 1 H,
H(8´)); 7.89 (m, 1 H, H(9´)); 7.98 (s, 1 H, H(4)); 8.12 (s, 1 H,
H(7)); 8.21 (d, 1 H, H(6´), J = 9.0 Hz); 8.25 (d, 1 H, H(7´),
J = 8.1 Hz); 8.34 (d, 1 H, H(5´), J = 9.1 Hz); 8.63 (d, 1 H,
H(10´), J = 8.1 Hz).
This work was financially supported by the Russian
Foundation for Basic Research (Projects No. 99ꢀ03ꢀ33064
and No. 00ꢀ15ꢀ97433), PICS (Grant 705) and the INTAS
(Grant 97ꢀ31193).
References
1. Yu. P. Strokach, O. A. Fedorova, S. P. Gromov, A. V.
Koshkin, T. M. Valova, V. A. Barachevskii, M. V. Alfimov,
V. A. Lokshin, A. Samat, and R. Guglielmetti, Izv. Akad.
Nauk, Ser. Khim., 2002, 56 [Russ. Chem. Bull., Int. Ed.,
2002, 51, 58 (Engl. Transl.)].
2. Photochromism: Molecules and Systems, Eds. H. Durr and
H. BouasꢀLaurent, Elsevier, Amsterdam, 1990, 337.
3. Organic Photochromic and Thermochromic Compounds,
Eds. J. C. Crano and R. Guglielmetti, Plenum Press, New
York, 1999, 1, 85.
4. B. L. Feringa, W. F. Janger, and B. Lange, Tetrahedron,
1993, 37, 8267.
Received January 21, 2002;
in revised form April 24, 2002