Synthesis and complexation properties of photochromic benzochromenes containing aza- and diaza- 18-crown-6-ether fragments

Article abstract of DOI:10.1007/s11172-006-0250-y

Complex formation of Mg²⁺, Ba²⁺, and Pb²⁺ perchlorates with 3,3-diphenyl-3H-benzo[f]chromenes containing aza-and diaza-18-crown-6-ether or morpholine fragments was studied. The strong influence of the metal cations on the

Full text of DOI:10.1007/s11172-006-0250-y

Russian Chemical Bulletin, International Edition, Vol. 55, No. 2, pp. 287—294, February, 2006
287
Synthesis and complexation properties of photochromic benzochromenes
containing azaꢀ and diazaꢀ18ꢀcrownꢀ6ꢀether fragments
O. A. Fedorova,aꢀ Yu. P. Strokach,a A. V. Chebun´kova,a T. M. Valova,a
S. P. Gromov,a M. V. Alfimov,a V. Lokshin,b and A. Samatb
aPhotochemistry Center, Russian Academy of Sciences,
7a ul. Novatorov, 119421 Moscow, Russian Federation.
Fax: +7 (495) 936 1255. Eꢀmail: fedorova@photonics.ru
bDepartment of Natural Sciences, Mediterranean University,
UMR 6114 CNRS, Luminy, 13288 Marseille, France*
Complex formation of Mg2+, Ba2+, and Pb2+ perchlorates with 3,3ꢀdiphenylꢀ3Hꢀ
benzo[ f ]chromenes containing azaꢀ and diazaꢀ18ꢀcrownꢀ6ꢀether or morpholine fragments
was studied. The strong influence of the metal cations on the spectral characteristics of these
organic ligands and on the kinetic of photochromic transformations was found. The results
obtained were explained by the formation of carbonylꢀ"capped" complexes of various strucꢀ
tures.
Key words: azaꢀ18ꢀcrownꢀ6 ethers, 3,3ꢀdiphenylꢀ3Hꢀbenzo[ f ]chromenes, complex forꢀ
mation, photoinduced transformations, carbonylꢀ"capped" complex, magnesium complexes,
barium complexes, lead complexes.
Photochromic compounds attract attention due to a
possibility of using them as photochromic coatings, lenses,
films, optical memory elements, and photoswitches.1—5
To improve their characteristics, chemical modification
is used through introduction of diverse substituents differꢀ
ing in nature into the molecule skeleton.6—8 An alternaꢀ
tive method for changing the photochromic properties of
the compounds is the introduction of ionophoric fragꢀ
ments capable of binding to metal cations. Complex forꢀ
mation often affects substantially the characteristics of
photochromic compounds.9—15 However, the synthesis
and properties of benzochromenes containing ionophoric
fragments are poorly studied: only several crownꢀconꢀ
taining benzochromenes were described.16—18 The synꢀ
thesis of benzochromenes with ionophoric fragments is
not only of theoretical interest but can induce the prepaꢀ
ration of new optical sensors for metal cations, photoꢀ
switchable extracting complexones, and metal cation carꢀ
riers through membranes.
ing in nature, it seemed reasonable to analyze the types of
complexes formed from metal cations with ligands 1а—c
and the influence of complex formation on the photoꢀ
chemical and spectral properties of the latter.
Complex formation of the closed form of benzochroꢀ
menes 1а—c. Compounds 1a—c in acetonitrile have simiꢀ
lar UV spectra. The addition of metal cations (Li+, Na+,
Mg2+, Sr2+, Ba2+, Ag+, Cd2+, Pb2+) to solutions of
benzochromenes induce slight shifts (to 5 nm) of the
absorption band (Table 1). Since the crownꢀether fragꢀ
ment is not conjugated with the chromophoric moiety of
the molecule, metal cation binding with the ionophoric
fragment induces only slight shifts in the position of the
longꢀwavelength absorption band for the closed form.
The changes in the position of signals for protons in
1
the H NMR spectra of benzochromenes 1а—c upon the
addition of perchloric acid or Cа2+, Ba2+, and Pb2+ perꢀ
chlorates are shown in Table 2. In the presence of the
alkalineꢀearth metal cations, the NMR spectrum of comꢀ
pound 1a exhibits insignificant changes. When lead perꢀ
chlorate is added to a solution of ligand 1а, almost all
signals for protons undergo downfield shift similarly to
the shift occurred upon the addition of perchloric acid to
a solution of ligand 1b. The nitrogen atom of the crownꢀ
ether fragment of 1b is protonated under acidic condiꢀ
tions; the quaternized N atom becomes a withdrawing
substituent. Lead cations are capable, most likely, of coꢀ
ordinating at the nitrogen atom of the morpholine resiꢀ
due, which shifts signals for protons in the spectrum. The
In the present work, we synthesized benzochromenes
1a,b containing morpholine and azaꢀ18ꢀcrownꢀ6ꢀether
fragments as substituents and diazaꢀ18ꢀcrownꢀ6 ether 1c
with two benzochromene substituents. A known proceꢀ
dure of threeꢀstep synthesis18,19 (Scheme 1) was used to
synthesize these compounds. Since azaꢀ and diazacrown
ethers can bind with a wide range of metal cations differꢀ
* Faculte des Sciences de Luminy, Universite de la Mediterranee,
UMR 6114 CNRS, 13288 Marseille, France.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 280—287, February, 2006.
1066ꢀ5285/06/5502ꢀ0287 © 2006 Springer Science+Business Media, Inc.

288
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Fedorova et al.
Scheme 1
addition of the metal salts to crownꢀcontaining benzoꢀ
chromenes 1b,c induces metal cation binding to the
crownꢀether fragment (Scheme 2), which reflects in the
with the oxygen atoms and, hence, the greatest shifts were
observed for the Hδ, Hω, and Hσ protons. The size of the
Ba2+ cations corresponds to the cavity of the 18ꢀcrownꢀ
6ꢀether fragment, which allows them to coordinate with
all heteroatoms. Coordination of the lead cations with the
oxygen atoms of the crownꢀether ring is weaker than that
of the alkalineꢀearth metal cations.
Interestingly, the signal of the H(6) proton of the naphꢀ
thalene fragment of crownꢀcontaining benzochromenes
1b,c (δ 7.89) exhibits a downfield shift compared to a
similar signal for the proton of morpholine derivative 1a
(δ 7.75). Since the electronic effects of the morpholine
and azacrownꢀether substituents should be close, the difꢀ
ferences observed in the 1H NMR spectra are caused,
most likely, by other factors. Another unusual fact found
for this proton is related to the upfield shift of the signal
from the H(6) proton (see Table 2) induced by the addiꢀ
tion of the metal cations to crownꢀcontaining compounds
1b,c, while the signals for other protons of the naphthaꢀ
lene ring undergo downfield shifts. Perhaps, this effect is
due to the conformational rearrangement of the comꢀ
pound, which occurs during complex formation at the
crownꢀether fragment.
1
shape of the H NMR spectrum. However, the character
of the changes observed differs substantially from that
found for benzochromene 1а, as well as for benzoꢀ
chromene 1b in the presence of perchloric acid in the
solution (see Table 2).
Scheme 2
Mz+ = Li+, Na+, Mg2+, Sr2+, Ba2+, Ag+, Cd2+, Pb2+
The shift of the signal for the H(8) proton of the
naphthalene ring for the complexes under study is always
slightly greater than those for other naphthalene protons.
The fact observed agrees with the known data19 that the
donor and acceptor effects of substituents are especially
pronounced when the substituents occupy position 8 of
the naphthalene ring.
Substantial shifts of signals for the protons of the meꢀ
thylene groups in the crownꢀether fragment were revealed.
Their analysis suggests the structures of the complexes.
For example, the Cа2+ cations are relatively small for the
cavity of the 18ꢀcrownꢀ6ꢀether fragment. The character
of shifts of the signals shows the strongest coordination

Photochromic benzochromenes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
289
Table 1. Spectral parameters (λmax) of the initial forms of
chromenes 1а—c, photoinduced merocyanine forms 2a—c, and
their complexes with different metal cations; absorption of the
merocyanine form (A2max) in the photostationary state and the
residues are rather rigidly bonded through the crownꢀ
ether fragment resulting in steric hindrance on going from
the compact closed form to the longer open form of
benzochromene. The longꢀwavelength absorption bands
of merocyanine colored forms 2а,b lie at 420 nm, while
for 2c these bands are observed at 405 nm.
rate constants of thermal relaxation of the colored form (k2—1
(CL/CM = 1 : 100, MeCN, 25 °C)
)
Under the dark conditions, forms 2a—c of the chroꢀ
menes under study return rather slowly to their initial
states 1a—c, being the lowest in energy, which is caused
by the presence of the morpholine or crownꢀether fragꢀ
ments in their structures. The rate of this process is much
slower for chromene 1c than for 1b (see Table 1).
The introduction of the alkaline metal salts into soluꢀ
tions of chromene 1а exerts virtually no effect on the
position of the longꢀwavelength absorption band of the
merocyanine form of this compound (see Table 1). In the
case of crownꢀcontaining chromenes 1b,c, the presence
of lithium in solutions of perchlorates shifts this band to
the longꢀwavelength region by 30 and 20 nm, respecꢀ
tively, and the conversion to the merocyanine colored
form for these compounds reaches nearly 100%. A similar
behavior is observed when the Na+ salts are introduced
into the solutions, but the observed shifts of the longꢀ
wavelength absorption bands of the complexes of the
merocyanine form of crownꢀcontaining chromenes are
smaller than those in the case when the Li+ cations are
introduced.
In the case of the alkalineꢀearth metals, the complex
formation of merocyanine form 2а, as follows from an
analysis of the absorption spectra (see Table 1), is proꢀ
nounced only for the Mg2+ cations (λmax shifts to 40 nm)
at rather high concentrations of the salts introduced into
the solutions. This compound forms virtually no comꢀ
plexes with the Sr2+ and Ba2+ cations, whereas the spectra
of forms 2b,c in the presence of these ions exhibit considꢀ
erable shifts (more pronounced for the Sr2+ cations as
compared to the Ba2+ cations and greater for compound 2b
than for 2c) (Fig. 1; see also Table 1).
max
Initial
chromene
Cation
λ
λ
A2
k2—1
1
2
/s–1
nm
1а
1b
1с
—
Li+
355
355
355
360
355
355
365
360
365
355
360
360
365
360
360
365
365
360
360
360
360
360
360
360
355
360
360
422
430
430
460
420
420
462
467
465
420
450
440
470
470
460
460
495
500
405
440
430
470
465
450
460
490
490
0.52
0.50
0.17
0.13
0.024
0.16
0.15
0.39
0.30
0.67
0.38
0.33
0.22
0.34
0.36
0.82
0.72
0.21
0.42
0.63
0.65
0.34
0.70
0.68
0.48
0.68
0.70
0.31
0.42
0.55
0.45
0.43
0.53
0.20
0.53
0.58
Na+
Mg2+
Sr2+
Ba2+
Ag+
Cd2+
Pb2+
—
0.09
Li+
0.008
0.013
0.16
0.002
0.006
0.26
0.004
0.011
0.08
0.042
0.015
0.13
0.004
0.005
0.13
—
0.006
Na+
Mg2+
Sr2+
Ba2+
Ag+
Cd2+
Pb2+
—
Li+
Na+
Mg2+
Sr2+
Ba2+
Ag+
Cd2+
Pb2+
Complex formation of the open form of benzochromenes
1а—c. When chromenes 1a,b are irradiated with the light
at the 365ꢀnm wavelength, the conversion to the correꢀ
sponding merocyanine forms 2a,b in the photostationary
state is rather high (>80%) (Scheme 3). Under the same
photoexcitation conditions, the conversion of chromene
1c to merocyanine form 2c does not exceed 50%. It is
most likely that in the molecule of 1c two chromene
The introduction of the alkaline and alkalineꢀearth
metal salts into the solutions decreases the rate constant
of thermal relaxation of merocyanine form 2а, which is
more substantial for the Mg2+ cation. This agrees with
a considerable influence of this cation on the spectral
characteristics of merocyanine form 2а for complex forꢀ
mation.
Scheme 3
The rate constant of thermal relaxation for meroꢀ
cyanine forms 2b,c of crownꢀcontaining chromenes 1b,c
(k2—1), unlike the constant for chromene 1a, are characꢀ
terized by a more pronounced dependence of the nature
of the metal involved in complex formation. As follows
from the results presented in Table 1, the most stable
complexes are formed with the Sr2+ cations, somewhat
less stable complexes are characteristic of the Ba2+ catꢀ
ions, and the least stable complexes are formed with the
Mg2+ cations.

290
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Fedorova et al.

Photochromic benzochromenes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
291
A
Scheme 4
2.5
2.0
1.5
1.0
3
4
2
1
0.5
M+ = Li+, Na+
300
400
500
600 λ/nm
Fig. 1. Absorption spectra of the initial chromene 1b (1) and
chromene 1b in the presence of Mg(ClO4)2 (2), Ba(ClO4)2 (3),
and Pb(ClO4)2 (4) in solution irradiated with the light at the
365ꢀnm wavelength (CL = 2•10–4 mol L–1, MeCN).
ring closure, which is observed as the stabilization effect
of the open merocyanine form (see Table 1).
The presence of the Sr2+, Ba2+, Ag+, Cd2+, and Pb2+
cations in the photochromic transformations of chromene
1а exerts a weak effect on the stabilization of the open
form. Probably, the effect observed can be explained by
the low charge density on the alkalineꢀearth metal cations
and the low affinity of other cations to the carbonyl oxyꢀ
gen atom (see Table 1).
The presence of salts of transition (Ag+, Cd2+) and
heavy (Pb2+) metals in solutions of the compounds under
study results in the efficient formation of complexes of
the merocyanine form with cations of these metals, which
follows from the character of the spectra. However, for
solutions of these compounds, in the presence of the Ag+
ions, the positions of the absorption bands of the comꢀ
plexes virtually coincide, whereas in the presence of the
Cd2+ and Pb2+ cations the observed spectral shifts for
crownꢀcontaining forms 2b,c are much greater than those
for form 2а containing the morpholine residue.
According to the rate constants of thermal relaxation
of the merocyanine form (see Table 1), the Cd2+ and
Pb2+ salts are characterized by a high degree of stabilizaꢀ
tion of the complexes of crowned chromenes, whereas the
introduction of silver perchlorate destabilizes merocyanine
colored forms 2b,c.
It should be taken into account for an analysis of the
observed spectral effects that the complex formation of
merocyanine forms 2b,c can involve two coordination
centers, namely, the crownꢀether fragment and the carꢀ
bonyl oxygen atom. The shifts of the absorption bands for
compound 2а during complex formation depend mainly
on the efficiency of interaction between the metal cation
and the oxygen atom of the merocyanine form.
The Li+ and Na+ ions are much smaller than the cavꢀ
ity of azaꢀ18ꢀcrownꢀ6 ether and, hence, complexes of
these cations with the ionophoric fragment are, most
likely, very unstable. Therefore, for compounds 2а—c the
main contribution to complex formation with the Li+ and
Na+ ions is made by metal cation binding at the carbonyl
oxygen atom (Scheme 4).
For merocyanine forms 2b,c, one can propose the
coordination of the metal cations (Mg2+, Sr2+, Ba2+, Ag+,
Cd2+, Pb2+) primarily at the crownꢀether fragment to
form complexes of different structures. For instance, note
a considerable stabilization effect of the merocyanine form
for the Sr2+, Ba2+, Cd2+, and Pb2+ ions, which increases
its lifetime by thousands times (see Table 1). It is clear
that this effect can be due to the incorporation of the
metal cation into the cavity of the crownꢀether fragment.
The crownꢀether fragment is bonded to the chromene
molecule through the methylene spacer, which is not a
part of the chromophoric system of benzochromene and
cannot significantly change the electron density distribuꢀ
tion in the system of conjugated bonds and the ability to
the closure reaction. This can occur only if the oxygen
atom of the merocyanine form is involved in complex
formation, i.e., when a carbonylꢀ"capped" complex is
formed (Scheme 5). The participation of the oxygen atom
in the coordination of the metal cation bonded to the
macrocycle substantially stabilizes the open form. This
has been observed previously20 for spironaphthooxazines
containing the azacrownꢀether fragment as a substituent.
Since the Ag+ cation has a low charge density and a
low oxygen affinity and the diameter of the Mg2+ cation is
much smaller than the cavity of azaꢀ18ꢀcrownꢀ6 ether,
the participation of these cations in the formation of carꢀ
bonylꢀ"capped" complexes seems less probable. It can be
assumed that the addition of silver and magnesium perꢀ
chlorates induces the formation of a complex involving
the macrocycle (see Scheme 5). In such a complex, probꢀ
ably, the electron density will be withdrawn to the metal
cation, which would result in some decrease in the elecꢀ
tron density on the carbonyl oxygen atom. As a result, the
As a result of this complex formation, the absorption
spectra are shifted to the longꢀwavelength region, because
the carbonyl oxygen atom is a part of the chromophoric
system of the molecule. In addition, the formation of the
oxygen—metal coordination bond prevents, most likely,

292
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
Fedorova et al.
Scheme 5
which are similar to the carbonylꢀ"capped" complex
formed by merocyanine form 2b. The second fragment of
benzochromene is not involved in the formation of the
carbonylꢀ"capped" complex.
Scheme 6
inverse transformation into the closed form of benzoꢀ
chromene would be accelerated. In fact, in the presence
of the silver and magnesium cations, the rate constant of
relaxation of merocyanine forms 2b,c increases (see
Table 1).
An interesting difference was observed for the influꢀ
ence of the Ba2+, Cd2+, and Pb2+ cations on the stabilizaꢀ
tion of the open form of chromene 2c (Table 3). Experiꢀ
ments showed that equimolar additives of Cd2+ and Pb2+
to a solution of chromenes 2b,c give similar values for the
decrease in the rate constant of dark relaxation. In the
presence of the Ba2+ cations, the decrease in k2—1 for
bischromene 2c is an order of magnitude higher than
similar value for monochromene 2b.
We believe that the aboveꢀdescribed experimental facts
are caused by the formation of carbonylꢀ"capped" comꢀ
plexes differing in structure, which appear in the presence
of the Ba2+, Cd2+, and Pb2+ cations (Scheme 6). Close
k2—1 values obtained for the complexes of crownꢀconꢀ
taining forms 2b,c with the Cd2+ and Pb2+ cations indiꢀ
cate, probably, that the structures of the formed carboꢀ
nylꢀ"capped" complexes are similar. It is most likely that
compound 2c with the Cd2+ and Pb2+ cations forms comꢀ
plexes involving the crownꢀether fragment and the oxyꢀ
gen atom of one of merocyanines of benzochromene,
The substantial decrease in the k2—1 value for complex
2c with the Ba2+ cation can be explained by the participaꢀ
tion of the oxygen atom of the second merocyanine
benzochromene in the formation of the carbonylꢀ"capped"
complex. The additional coordination bond just leads to
the further stabilization of a complex of the open form of
bis(benzochromene) 2c.
Thus, it is shown in the present work for crownꢀconꢀ
taining benzochromene 1b, bis(benzochromene) 1c, and
model chromene 1а having the morpholine residue inꢀ
stead of the crownꢀether fragment how metal cations difꢀ
fering in nature and size affect the spectral and kinetic
characteristics of the crownꢀcontaining photochromic
compounds. Coordination of the metal cations can occur
at the oxygen atom of the merocyanine form, which stabiꢀ
lizes the open form and shifts absorption maxima to the
longꢀwavelength region. However, the strength of this
coordination bond is low.17 Complex formation at the
crownꢀether fragment does not exert a substantial influꢀ
ence on the spectral and kinetic characteristics of the
molecule, because this fragment is not conjugated with
Table 3. Rate constants of thermal relaxation of colored forms
2a—c of benzochromenes 1a—c (k2—1/s–1) and their complexes
with the Ba2+, Pb2+, and Cd2+ cations (CL/CM = 1 : 1,
MeCN, 25 °C)
Comꢀ
pound
Cation
—
Ba2+
Pb2+
Сd2+
2a
2b
2c
0.11
0.11
0.15
0.18
0.0016
0.00034
0.12
0.00035
0.00054
0.36
0.0042
0.006

Photochromic benzochromenes
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 2, February, 2006
293
fied on Al2O3 (CH2Cl2—MeOH (9 : 1) mixture as eluent). The
yield was 43 mg (35%).
the skeleton of the photochromic molecule. The strongest
binding of the metal cation and the most pronounced
influence on the spectral and kinetic characteristics were
observed for the carbonylꢀ"capped" complexes, whose forꢀ
mation simultaneously involved two coordination cenꢀ
ters, namely, the crownꢀether fragment and the oxygen
atom of the merocyanine form. It is shown that carbonylꢀ
"capped" complexes involving one or two benzochromene
molecules can be formed in the case of bis(benzoꢀ
chromenes). Therefore, the barium, strontium, lead, and
cadmium cations are most promising for binding the azaꢀ
and diazacrown compounds containing one or two chroꢀ
mene residues. Cations of this type can provide efficient
photocontrol of complex formation due to high distincꢀ
tions in the spectral characteristics of the free and
complexed ligands and substantial differences in stability
of the complexes in the closed and open forms.
7,16ꢀBis[(3,3ꢀdiphenylꢀ3Hꢀbenzo[ f ]chromenꢀ5ꢀyl)methyl]ꢀ
1,4,10,13ꢀtetraoxaꢀ7,16ꢀdiazacyclooctadecane (1c) was purified
on Al2O3 (CH2Cl2—MeOH (9 : 1) mixture as eluent). The yield
was 69 mg (30%), m.p. 178—182 °C (from hexane). Found (%):
C, 77.48; H, 6.55; N, 2.69. C64H62N2O6•2H2O. Calculated (%):
1
C, 77.55; H, 6.71; N, 2.83. H NMR (CDCl3), δ: 2.95 (t, 8 H,
NCH2, J = 5.8 Hz); 3.58 (s, 8 H, OCH2); 3.67 (t, 8 H, OCH2,
J = 5.8 Hz); 3.98 (s, 4 H, PhCH2); 6.25 (d, 2 H, H(2), J =
10.1 Hz); 7.25 (m, 4 H, H(4´), H(4″)); 7.31—7.37 (m, 12 H,
H(8), H(3´), H(3″), H(1)); 7.44 (m, 2 H, H(9)); 7.55 (m, 8 H,
H(2´), H(2″)); 7.74 (d, 2 H, H(7), J = 7.8 Hz); 7.85 (br.s, 2 H,
H(6)); 7.95 (d, 2 H, H(10), J = 8.4 Hz).
Study of complex formation by NMR spectroscopy. Comꢀ
plexes of 1a—c with the Ca2+, Ba2+, and Pb2+ cations were
prepared as follows. Calcium, barium, and lead perchlorates
(1.5•10–5 mol; for complexes 1b•Pb2+ and 1c•Pb2+ 3•10–5 mol)
and ligands 1a—c (3•10–6 mol) were dissolved in CD3CN
(0.6 mL). The complex of 1b with HClO4 was synthesized acꢀ
cording to the following procedure: compound 1b and HClO4
(4.92•10–6 mol) were dissolved in 0.6 mL of CD3CN. The corꢀ
responding spectra are presented in Table 2.
Experimental
1
H NMR spectra were recorded on a Bruker DRXꢀ500 specꢀ
Spectrophotometric and kinetic measurements. Spectrophoꢀ
tometric measurements were carried out in solutions of acetoniꢀ
trile (Aldrich, water content 0.005%). Magnesium, barium, and
lead perchlorates (reagent grade) were used for complex formaꢀ
tion. The ratio of concentrations of the metal salts and ligands
trometer (500.13 MHz, 25 °C) using Me4Si as the internal stanꢀ
dard. Chemical shifts and spinꢀspin coupling constants were
determined with an accuracy of 0.01 ppm and 0.1 Hz, respecꢀ
tively. Mass spectra were obtained on a Varian MAT 311A inꢀ
strument (ionization energy 70 eV). The course of the reactions
was monitored by TLC on 25 DCꢀAlufolien Kieselgel 60 F254
and DCꢀAlufolien Aluminiumoxid 60 F254 neutral (type E)
plates (Merck). Silica gel 60 (0.063—0.200 mm) and aluminium
oxide 150 (basic, type T, Merck) were used for column chromatoꢀ
graphy. 5ꢀBromomethylꢀ3,3ꢀdiphenylꢀ3Hꢀbenzo[ f ]chromene
was synthesized according to a described procedure.21,22 Azaꢀ
crown ethers, morpholine, and other reagents (Aldrich) were
used as received.
Synthesis of chromenes 1a—c (general procedure). Azacrown
ether or morpholine (0.2 mmol), 5ꢀbromomethylꢀ3,3ꢀdiphenylꢀ
3Hꢀbenzo[ f ]chromene (80 mg, 0.2 mmol; for diazacrown ether
160 mg, 0.4 mmol), triethylamine (60 mg, 0.6 mmol; for
diazacrown ether 120 mg, 1.2 mmol), and anhydrous THF
(25 mL) were placed in a threeꢀnecked flask under a nitrogen
atmosphere. The reaction mixture was refluxed for 6 h. The
solvent was evaporated, and the product was purified by column
chromatography.
5ꢀMorpholinomethylꢀ3,3ꢀdiphenylꢀ3Hꢀbenzo[ f ]chromene
(1a) was purified on SiO2 (benzene—MeOH (10 : 1) mixture as
eluent). The yield was 52 mg (57%), m.p. 150—152 °C (from
hexane). Found (%): C, 83.18; H, 6.32; N, 3.19. C30H27NO2.
Calculated (%): C, 83.11; H, 6.28; N, 3.23. 1H NMR
(DMSOꢀd6), δ: 3.30 (m, 4 H, NCH2); 3.62 (m, 4 H, OCH2);
3.74 (s, 2 H, PhCH2); 6.61 (d, 1 H, H(2), J = 9.7 Hz); 7.24 (m,
2 H, H(4´), H(4″)); 7.34 (m, 5 H, H(8), 2 H(3´), 2 H(3″)); 7.47
(m, 2 H, H(1), H(9)); 7.60 (m, 4 H, 2 H(2´), 2 H(2″)); 7.75
(br.s, 1 H, H(6)); 7.80 (d, 1 H, H(7), J = 8.0 Hz); 8.06 (d, 1 H,
H(10), J = 8.5 Hz). Mass spectrum, m/z (Irel %)): 433 [M+]
(22), 348 (37), 266 (100), 191 (33), 165 (23), 115 (22), 103 (26),
87 (65), 69 (51), 55 (67).
(CM/CL) was varied from 0.1 to 100 at CL = 2•10–4 mol L–1
.
Electronic absorption spectra of solutions were measured on a
Cary 50 spectrophotometer in cells with the 0.2ꢀcm optical path
length at 25 °C. Photostationary absorption spectra were meaꢀ
sured on a USB2000 fiberꢀoptical spectrometer (Ocean Optics)
with a continuous irradiation of the solutions with the light at
the 365ꢀnm wavelength from a DRShꢀ250 gasꢀdischarge merꢀ
cury lamp. Kinetic experiments were carried out using a laboraꢀ
tory setup providing measurements of the kinetics of photoꢀ
processes in the time interval from 1 ms.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos 05ꢀ03ꢀ32268
and 03ꢀ03ꢀ332888) and the Ministry of Education and
Science of the Russian Federation (Program "Developꢀ
ment of Scientific Potential of the Higher School").
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Received October 26, 2005