IR luminescence of neodymium(III) and ytterbium(III) complexes with acylpyrazolones in solutions

Article abstract of DOI:10.1134/S0036023611060179

Acylpyrazolones (L1-L5) have been synthesized and the conditions of their complexation with neodymium(III) and ytterbium(III) ions in aqueous solutions have been elucidated. The component ratio in the synthesized complexes is Nd(Yb) : L = 1 : 1. The conditions of excitation and luminescence of the ligands and complexes have been studied. The formation of mixed-ligand complexes upon the introduction of trio-ctyl- or triphenylphosphine oxide leads to a considerable rise of neodymium and ytterbium. In the presence of 1,10-phenanthroline and bathophenanthroline, competing complexation leads to a 20-70% decrease in luminescence intensity. The introduction of water-miscible organic solvents (30 vol %) decreases the Nd(III) and Yb(III) luminescence intensity by a factor of 9-20. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611060179

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 6, pp. 899–905. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © S.B. Meshkova, V.S. Matiichuk, M.A. Potopnyk, Z.M. Topilova, V.P. Gorodnyuk, K.N. Olenich, I.V. Bol’bot, 2011, published in Zhurnal Neorganicheskoi
Khimii, 2011, Vol. 56, No. 6, pp. 957–963.
COORDINATION
COMPOUNDS
IR Luminescence of Neodymium(III) and Ytterbium(III) Complexes
with Acylpyrazolones in Solutions
S. B. Meshkovaa, V. S. Matiichukb, M. A. Potopnykb, Z. M. Topilovaa,
V. P. Gorodnyuka, K. N. Olenicha, and I. V. Bol’bota
a Bogatskii Physicochemical Institute, National Academy of Sciences of Ukraine,
Lyustdorfskaya doroga 86, Odessa, 65080 Ukraine
b Franko National University, Universitetskaya ul. 1, Lviv, 79000 Ukraine
Received October 15, 2009
Abstract—Acylpyrazolones (L1–L5) have been synthesized and the conditions of their complexation with
neodymium(III) and ytterbium(III) ions in aqueous solutions have been elucidated. The component ratio in
the synthesized complexes is Nd(Yb) : L = 1 : 1. The conditions of excitation and luminescence of the ligands
and complexes have been studied. The formation of mixedꢀligand complexes upon the introduction of trioꢀ
ctylꢀ or triphenylphosphine oxide leads to a considerable rise of neodymium and ytterbium. In the presence
of 1,10ꢀphenanthroline and bathophenanthroline, competing complexation leads to a 20–70% decrease in
luminescence intensity. The introduction of waterꢀmiscible organic solvents (30 vol %) decreases the Nd(III)
and Yb(III) luminescence intensity by a factor of 9–20.
DOI: 10.1134/S0036023611060179
Unique spectroscopic properties of lanthanide ditions of formation and luminescence spectral propꢀ
(Ln) ions with an unfilled 4f shell in both simple salts erties of the Nd(III) and Yb(III) complexes with
and complexes with different organic reagents account acylpyrazolones.
for their use in scientific research and engineering, as
luminescent labels in biology and medicine, etc. The
narrowꢀband luminescence of these ions makes it posꢀ
sible to obtain pure red, green, and blue light emission
EXPERIMENTAL
In the work, we used 4ꢀarylꢀ5ꢀmethylꢀ2,4,dihydroꢀ
Hꢀpyrazolꢀ3ꢀones (L1–L5), which were synthesized
owing to energy transfer from the ligand in the excited
state to the Ln(III) ion. To this end, the triplet level of
the ligand must be higher than the emitting level of the
3
by the reaction of 3ꢀmethylꢀ1Hꢀ1ꢀphenylꢀ5ꢀpyraꢀ
zolone with corresponding carboxylic acid chlorides.
The purity of the synthesized acylpyrazolones was
checked by 1H NMR, IR spectroscopy, and elemental
analysis. The ligands used in the work were listed in
lanthanide; therefore, Eu(III) and Tb(III)
nates, binary and mixedꢀligand, have long been used.
The ligands in these compounds are ꢀdiketones, such
β
ꢀdiketoꢀ
β
as acetylꢀ, thienylꢀ, and benzoylacetones and their
analogues, including fluorinated ones. In addition to
Table 1. Initial (1 ×
10–2 M) ethanol solutions of
Nd(III) and Yb(III) chlorides were prepared by disꢀ
solving the oxides (99.99%) in HCl; then an HCl
excess was removed by evaporation to wet salts, which
were dissolved in twiceꢀdistilled water, and the soluꢀ
tions were made up to the required volume in a voluꢀ
metric flask. The exact concentration of lanthanides
was determined by titration of the chloride solutions
with an EDTA solution in the presence of Arsenazo I.
1,10ꢀPhenanthroline (Phen), bathophenanthroline
(bathoPhen), trioctylphosphine oxide (TOPO), and
triphenylphosphine oxide (TPPO) were used as secꢀ
βꢀdiketones, pyrazolones have also been used for
observation of luminescence of the Tb(III) and
Dy(III) ions [1]. The use of acylpyrazolones for
observing strong Tb(III) luminescence has only been
recently reported [2, 3].
The properties of lanthanide and other metal comꢀ
plexes with acylpyrazolones have been extensively
studied in the past decade in the context of their use as
the lightꢀemitting layers in electroluminescent
devices, which are being increasingly widely applied to
create multiꢀcolor flatꢀpanel displays and efficient
light sources [4–7].
ond ligands. Their 1 ×
10–1 M solutions in ethanol were
prepared from accurately weighed samples. Working
solutions of the ligands and lanthanides were prepared
by diluting the initial solutions.
However, almost no information is available on the
IR luminescence of Nd(III) and Yb(III) in complexes
with acylpyrazolones [6–8], which can be of interest
Binary and mixedꢀligand complexes were obtained
for designing fiber amplifiers in broadband telecomꢀ by mixing solutions of Nd (Yb) chlorides and the
munication devices. In this work, we studied the conꢀ ligand(s) at an optimal complexation pH. To achieve
899

900
MESHKOVA et al.
molecular
Table 1. List of the acylpyrazolones
Formula
L
Name
FW, g/mol
structural
O
H3C
N
4ꢀBenzoylꢀ5ꢀmethylꢀ2ꢀphenylꢀ2,4ꢀ
dihydroꢀ3 ꢀpyrazolonꢀ3ꢀone
O
N
L1
C17H14N2O2
C17H16N2O3
C17H13N3O4
278.31
H
O
CH3
O
H3C
5ꢀMethylꢀ4ꢀ(4ꢀmethoxybenzoyl)ꢀ
2ꢀphenylꢀ2,4ꢀdihydroꢀ3 ꢀpyrazoꢀ
lonꢀ3ꢀone
N
O
L2
H
308.33
N
O
O
H3C
N
N+
O
5ꢀMethylꢀ4ꢀ(4ꢀnitrobenzoyl)ꢀ2ꢀ
phenylꢀ2,4ꢀdihydroꢀ3 ꢀpyrazolonꢀ
3ꢀone
O
L3
H
323.30
N
CH3
O
O
H3C
4ꢀ(2,5ꢀDimethylꢀ3ꢀfuroyl)ꢀ5ꢀmethꢀ
ylꢀ2ꢀphenylꢀ2,4ꢀdihydroꢀ3 ꢀpyraꢀ
zolꢀ3ꢀone
N
CH3
L4
C17H16N2O3
H
298.32
O
N
CH3
O
CH3
CH3
O
O
O
4ꢀ(3,4,5ꢀMethoxybenzoyl)ꢀ3ꢀmethꢀ
ylꢀ1ꢀphenylpyrazolone
L5
C20H20N2O5
368.39
H3C
O
N N
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

IR LUMINESCENCE OF NEODYMIUM(III) AND YTTERBIUM(III) COMPLEXES
901
Ilum
,
arb. units
(а)
(b)
100
80
60
40
20
100
5
2
80
60
40
20
3
1
4
1
3
0
2
4
6
pH
0
2
4
6
Fig. 1 Luminescence intensity vs. pH of solutions of the (a) Nd(III) and (b) Yb(III) complexes with ligands (1) L1, (2) L2, (3)
–5
–4
L3, (
4) L4, and (5) L5 (
c
= 2
×
10 М;
c
= 2
×
10 M).
Nd,Yb
(L1–L5)
the necessary pH values, sodium acetate buffer soluꢀ acylpyrazolones under consideration showed that they
tions (pH 3–8) were used in which 0.5 M HClO4 and
1 M CH3COOH were added to pH 1 and 2, respectively.
The pH was monitored with an OPꢀ211 pHꢀmeter
(Hungary) equipped with an ESLꢀ43ꢀ07 glass elecꢀ
trode.
formed in an acidic medium (Fig. 1). This is consistent
with the protolytic properties of the ligands and the
dominance of their enol forms at pH 2–4 [9]. The
optimal pH values for Nd(III) and Yb(III) complex forꢀ
mation (pHopt) with the same ligands differ by 1–2 units.
In all cases, the strongest luminescence is observed in
the presence of a 5–10ꢀfold ligand excess, and the
luminescence maximum is achieved within 30 min
after the preparation of solutions of the complexes and
remains unchanged for an hour. Different methods
The lifetimes of the ligands (77 K) were measured
and the luminescence excitation spectra of the ligands
and their neodymium and ytterbium complexes were
recorded on a HoribaꢀJobin Yvon Fluorolog FL 3ꢀ22
spectrofluorimeter (ozoneꢀfree Xe lamp, 450 W)
equipped with an ElectroꢀOptical systems, Inc. DSSꢀ
IGA020L InGaAs detector cooled with liquid nitroꢀ
gen for IRꢀdomain measurements. The emission
intensity was the number of photons per second. The
luminescence spectra of all complexes were recorded
on an LOMO SDLꢀ1 spectrometer with a DRShꢀ250
mercury lamp and UFSꢀ2 light cutoff filter for separaꢀ
tion of the strongest lines at 313 and 365 nm (the lumiꢀ
nescence intensity was the height at the band maxiꢀ
mum in arbitrary units). The energies of the singlet
I
,
arb. units
337
335
273
60
50
40
30
20
10
2
1
(ES1) and triplet (ЕТ1) levels of the ligands were deterꢀ
mined from the luminescence spectra of their Gd(III)
complexes at 300 and 77 K, respectively.
3
The Nd(III) and Yb(IIII) complexes with
acylpyrazolones as suspensions in a water–ethanol
solution (water : ethanol = 9.5 : 0.5) [1] were studied
by measuring the luminescence inherent in these ions:
for neodymium, the luminescence was measured in
the range 850–1090 nm for the peaks at 877, 898, and
1060 nm; for ytterbium, measurements were taken in
the range 950–1000 nm (λmax = 980 nm). The lumiꢀ
nescence of solutions of the complexes was recorded
in a quartz cell (l = 1 cm).
250
300
350
400
, nm
450
500
550
λ
RESULTS AND DISCUSSION
Fig. 2. Excitation spectra of (
and its ( ) Nd(III) (
980 nm) complexes at 23°C.
1
) ligand L1 (
λ
= 416 nm)
lum
λ
Studying the effect of solution pH on the luminesꢀ
cence of the Nd(III) and Yb(III) complexes with the
2
λ
= 1060 nm)and (
3) Yb(III) (
=
lum
lum
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

902
MESHKOVA et al.
T1) levels and lifetimes (
, cm–1
, ms
Table 2. Energies of the singlet (
E
S1) and triplet (
E
τ
) of ligands L1–L5 in the excited state
*
(
ET1 – E
Ln ), cm–1
Ligand
E
S1, cm–1
E
T1, cm–1
Δ
E
τ
Nd(III)
Yb(III)
L1
L2
L3
L4
28980
24038
28985
25126
24810
22730
24810
22730
20080
4170
1308
4175
2396
3958
259.5 27.9
67.9 1.9
13310
11230
13310
11230
8580
14610
12500
14610
12500
9880
1099.0 25.0
45.9 0.9
L5
24053
79.7 2.1
4
–1
2
–1
*
E
( F ) = 11500 cm
;
E
( F ) = 10 200 cm
.
Nd
3/2
Yb
5/2
Table 3. Luminescence intensity (I) of the Nd(III) and Yb(III) complexes with acylpyrazolones (under identical luminesꢀ
cence recording conditions)
I
, arb. units, at
Nd(III)
4I9/2
λ
, nm
Yb(III)
2F5/2 2F7/2
Ligand
transition 4F3/2
877 nm
4F3/2
4I11/2
898 nm
1060 nm
980 nm
L1
L2
L3
L4
L5
15
28
23
13
39
14
25
22
17
35
12
13
15
10
17
53
46
22
12
85
–5
–4
Note:
c
= 2
×
10 M ;
c
= 1 × 10 M.
Nd, Yb
(L1– L5)
showed that the lanthanide : acylpyrazolone ratio in intramolecular energy transfer from them to the
the complexes is 1 : 1.
Nd(III) and Yb(III) ions, the emitting level energies of
which are considerably lower: 11500 cm–1 4F3/2
and
10200 cm–1 2F5/2
, respectively. The large gaps
between the Т1 level of the ligand and the emitting level
of the lanthanide (ЕТ1 ЕLn) are the source of lumiꢀ
nescence losses of the complexꢀforming ion. For
Yb(III), the gap is larger but it has one ground level;
for Nd(III), the gaps are smaller but additional losses
on the groundꢀstate sublevels are possible.
(
)
Inasmuch as the luminescence arisen from energy
transfer from the organic part of the complex molecule
to the lanthanide ion is mainly determined by the
absorptivity of the ligand, we studied the excitation
spectra of the ligands and their Nd(III) and Yb(III)
complexes. Figure 2 shows the excitation spectra of
ligand L1 and its Nd(III) and Yb(III) complexes. The
Nd(III) and Yb(III)excitation band maxima for the
complexes with L1 are observed at 335 and 337,
(
)
–
The considerable difference in
τ
values of the
respectively; this is evidence that the strong mercury ligands is caused by the electronic effect of substituꢀ
lines at 313 and 365 nm separated by a UFSꢀ2 light filꢀ ents. For the unsubstituted benzoyl moieties (L1)
ter can be used for Nd(III) and Yb(III) luminescence τ ≈ 260 ms. The introduction of electronꢀdonating
excitation.
substituents—4ꢀmethoxybenzoyl (L2) and 3,4,5ꢀtriꢀ
methoxybenzoyl (L5)—reduces the lifetime by a facꢀ
tor of 3.8 and 3.2, respectively. The introduction of the
As is known, intramolecular energy transfer from
the ligand in the excited state to the lanthanide ion is
possible if the triplet level energy ЕТ1 of the ligand is
higher than the energy of the emitting level of the lanꢀ
thanide. It follows from the triplet and singlet level
energies of the ligands in the excited state (Table 2)
and the gap between them (1308–4175 cm–1) that, in
furoyl substituent (L4) leads to a decrease in
tor of 5.6. The introduction of the electronꢀaccepting
substituent into the benzoyl moiety (L3) leads to a
sharp increase in , by 2.4 times, as compared with L1.
τ
by a facꢀ
τ
τ
The longꢀlived luminescence of the ligands observed at
77 K can be assigned to emission from the triplet state.
the case of ligands L1 and L3, S1
–Т1 energy transfer
can be accompanied by larger energy losses as comꢀ
Figure 3 shows, as an example, the luminescence
pared with the other ligands. However, the high ЕТ1 spectra of Nd(III) and Yb(III) complexes with some
and
τ
values of the ligands point to the possibility of other ligands under consideration. The luminescence
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

IR LUMINESCENCE OF NEODYMIUM(III) AND YTTERBIUM(III) COMPLEXES
903
898
877
980
4
2
877
898
980
1060
3
1
1060
860
920
1100 860
920 1100 940 1000 960 1000
, nm
λ
Fig. 3. Luminescence spectra of the (1, 2) Nd(III) and (3, 4) Yb(III) complexes with ligands (
1
,
3
) L1 and (
2
,
4
) L5 (
c
=
Nd,Yb
–5
–4
2
×
10 М;
c
= 1
×
10 M).
L1,L5
spectrum of the Nd(III) ion shows two bands with with L5 for which the luminescence remains
4
unchanged after the first 5 min of irradiation.
maxima at 877, 898 nm (the F3/2
and 1060 nm (the 4F3/2 4I11/2 transition). As distinct
from neodymium, ytterbium is characterized by one
emitting level (2F5/2) and one groundꢀstate level (2F7/2
4I9/2 transition)
Owing to their large coordination capacity, the lanꢀ
thanide ions in the complexes with different organic
ligands are coordinated to then largest possible numꢀ
ber of water molecules (“OH oscillators”), strong
luminescence quenchers. To mitigate (rule out) the
)
and a luminescence band at 980 nm. Table 3 presents
the luminescence intensities for the Nd(III) and
Yb(III) complexes with the acylpyrazolones under
consideration.
I
lum, arb. units
Comparison of data in Table 3 shows that the
Yb(III) ions in the complexes with the same ligands
exhibit considerably stronger luminescence than the
Nd(III) ions, for which energy loss on the groundꢀ
state sublevels is typical. Among the complexes with
the acylpyrazolones under consideration, those with
the ligands containing the methoxyꢀ or trimethoxyꢀ
benzoyl substituent (L2 and L5, respectively) are charꢀ
acterized by the strongest Nd(III) and Er(III) lumiꢀ
nescence. The introduction of the nitro group (L3)
leads to a noticeable decrease in luminescence intenꢀ
sity.
100
1
80
60
40
20
2
3
4
5
6
7
An important luminescence characteristic of comꢀ
pounds is their photostability. Figure 4 shows how the
luminescence intensity of ligands L2 and L4 and their
Nd(III) and Yb(III) complexes changes on continuꢀ
ous exposure to UV light. The luminescence of ligands
L2 and L4, like that of the other ligands, decreases to
an extent, whereas the luminescence of the acylpyraꢀ
zolonates rises in the first 10 min of exposure and
0
5
10
15
20
25
τ, min
Fig. 4. Luminescence intensity of the (
3–5) Yb(III) and ( ) Nd(III) in the complexes with (
L1, ( ) L2, ( )L4, and ( ) L5 vs. the time of exposure to
UV light ( = 365 nm) ( =
L1,L2,L4,L5
1, 2) ligands and
(
6
,
7
7)
remains unaltered (Nd
ually decreases (Yb L4) over the course of further
exposure to UV light. Exceptions are the complexes
· L1, Nd · L2, Yb · L2) or gradꢀ
4,
6
3
5
–5
·
λ
c
= 5
×
10 М;
c
Nd,Yb
–4
5
×
10 M).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

904
MESHKOVA et al.
Table 4. Effect of the second ligand (L')* on the luminescence intensity of the Yb(III) complexes with acylpyrazolones
L1–L 5 (
c
Yb = 2
×
10–5 M; cL1–L5 L' = 2 10–4 M)
×
and
I
, arb. units/(
I
(YbL1–L5)L'/
I
(Yb(L1–L5))
TOPO
Complex
–
Phen
bathoPhen
TPPO
Yb · L1
Yb · L2
Yb · L3
Yb · L4
Yb · L5
53
46
22
12
85
16/0.3
40/0.9
12/0.5
7/0.6
18/0.3
18/0.4
8/0.4
95/1.8
90/2.0
30/1.4
20/1.7
260/4.9
265/5.8
69/3.1
5/0.4
60/5.0
68/0.8
51/0.6
350/4.1
170/2.0
–1
–1
–1
–1
*
E (L') = 22130 cm (Phen), 22220 cm (bathoPhen), 20410 cm (TOPO), and 20620 cm (TPPO).
T1
Table 5. Absorption maxima and intensities for the Yb(III) complexes with L1, L3, and L5 in the absence and presence of
the second ligand
Complex
Yb · L1
λ
max, nm
A
Complex
Yb · L3
λ
max, nm
A
240.0
271.4
271.4
286.1
283.7
240.0
1.400
0.594
0.347
0.970
0.728
2.000
255.4
269.7
284.9
297.7
271.8
286.2
0.648
1.002
1.306
0.547
0.945
2.000
Yb · Phen
Yb · L3 · Phen
Yb · L3 + bathoPhen
Yb · L5
Yb · L1+ Phen
Yb · bathoPhen
Yb · L1 + bathoPhen
Yb · L1 · TPPO
Yb · L5 · Phen
Yb · L5 + bathoPhen
–5
Note:
c
=
c
= 1 × 10 M.
Yb
ligands
luminescence quenching effect, water molecules are tions of the Nd(III) and Yb(III) acylpyrazolonates
removed from the first coordination sphere of the leads to a sharp (9–20ꢀfold) decrease in luminescence
complex by introducing the second ligand, organic intensity, which can be caused by decomposition of
solvents, or surfactants or by increasing the hydrophoꢀ not only the suspension of the complex but also the
bicity of the ligands [10].
complex itself. Surfactants (cetylpyridinium chloride
(bromide), cetyltrimethylammonium bromide, ethoꢀ
nium, sodium dodecylculfate, Triton Xꢀ100, Bridgeꢀ35)
introduced into solutions of the complexes in concenꢀ
trations lower than or equal to the CMC have no effect
on or decrease the luminescence intensity of Nd(III)
and Yb(IIII) acylpyrazolonates.
Table 4 summarizes the luminescence intensities of
the Yb(III) complexes with all acylpyrazolones in the
absence and presence of the second ligand.
These data demonstrate that the strongest Yb(III)
luminescence rise for the complexes with L1–L5 is
observed when TOPO (by a factor of 1.4–4.1) or
TPPO (by a factor 2.0–5.8) coordinated through the
phosphoryl oxygen atom were introduced into them.
The 20–70% decrease in luminescence intensity for
the Yb(III) complexes with L1–L5 caused by the
introduction of Phen or bathoPhen into solutions was
unexpected. The assumption of their competing comꢀ
plexation was supported by the absorption spectra of
the Yb(III) complexes with L1, L3, L5, Phen, and
bathoPhen, both separately and in mixture (Table 5).
After the addition of these second ligands, the absorpꢀ
Thus, studying the formation and luminescenceꢀ
spectral properties of the Nd(III) and Yb(III) comꢀ
plexes with acylpyrazolones showed that the strongest
luminescence is exhibited by the complexes of Yb(III)
which has one emitting level and one groundꢀstate
level. Competing complexation revealed in the
Yb(III)–acylpyrazolone–Phen (bathoPhen) system
leads to a decrease in the luminescence intensity of
acylpyrazolonates. Mixedꢀligand complexes form
only in the presence of TOPO and TPPO, which is
responsible for the 2–5ꢀfold increase in luminescence
intensity.
tion maxima of Yb · Phen, Yb · bathoPhen, and Yb ·
(L1, L3, L5) complexes coincide, whereas the introꢀ
duction of TPPO (TOPO) into pyrazolonate solutions
does not change the spectral pattern and only leads to
a buildup of the absorption of the resulting mixedꢀ
ligand complexes.
ACKNOWLEDGMENTS
The introduction of organic solvents (ethanol,
We are grateful to G.V. Mal’tsev for his valuable
dioxane, acetonitrile, dimethyl sulfoxide) into soluꢀ comments on the results of this work.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 6 2011

IR LUMINESCENCE OF NEODYMIUM(III) AND YTTERBIUM(III) COMPLEXES
905
5. J. Kido and Y. Okamoto, Chem. Rev. 102, 2357 (2002).
REFERENCES
6. F. Marchetti, C. Pettinari, and R. Pettinari, Coord.
1. N. S. Poluektov, L. I. Kononenko, N. P. Efryushina,
and S. V. Bel’tyukova, Spectrophotometric and Luminesꢀ
cence Methods of Determination of Lanthanides (Naukꢀ
ova Dumka, Kiev, 1989) [in Russian].
Chem. Rev. 249, 2909 (2005).
7. N. P. Kuz’mina and S. V. Eliseeva, Zh. Neorg. Khim.
51 (1), 80 (2006) [Russ. J. Inorg. Chem. 51 (1), 73
(2006)].
8. C. Pettinari, F. Marchetti, R. Pettinari, et al., J. Chem.
Soc., Dalton Trans., 1409 (2002).
2. O. Renault and D.ꢀG. Moon, et al., Adv. Mater. 12
,
1591 (2000).
3. H. Xin, F. Y. Li, M. Shi, et al., J. Am. Chem. Soc. 125
,
9. I. P. Efimov, L. S. Voronets, L. G. Makarova, and
V. M. Peshkova, Vestn. Mosk. Univ., Ser. Khim., No. 4,
121 (1969).
7166 (2003).
4. M. A. Katkova, A. G. Vitukhnovskii, and M. N. Bochꢀ
karev, Usp. Khim. 74 (12), 1193 (2005).
10. S. B. Meshkova, J. Fluoresc. 10 (4), 333 (2000).
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