Luminescence of lanthanides in complexes with chromophoric crown ethers

Article abstract of DOI:10.1023/A:1022160007902

Spectral luminescence characteristics, viz., quantum yields and luminescence lifetime, of the Yb³⁺ and Nd³⁺ ions in aqueous-methanolic solutions of their complexes with chromophoric benzo-15-crown-5 derivatives were determined. The e

Full text of DOI:10.1023/A:1022160007902

Russian Chemical Bulletin, International Edition, Vol. 51, No. 12, pp. 2303—2305, December, 2002
2303
Luminescence of lanthanides in complexes with chromophoric crown ethers
ꢀ
Yu. V. Korovin, N. V. Rusakova, and Yu. A. Popkov
A. V. Bogatsky PhysicoꢀChemical Institute of the National Academy of Sciences of Ukraine,
8
6 Lustdorfskaya doroga, 65080 Odessa, Ukraine.
Fax: +38 (048 2) 65 2012. Eꢀmail: physchem@paco.net
Spectral luminescence characteristics, viz., quantum yields and luminescence lifetime, of
the Yb3+ and Nd ions in aqueousꢀmethanolic solutions of their complexes with chromophoric
benzoꢀ15ꢀcrownꢀ5 derivatives were determined. The efficient 4fꢀluminescence (λexc = 337 nm)
is due to the intramolecular transfer of the excitation energy from the chromophoric moiety of
the molecule to the Ln3+ ion.
3+
Key words: IR luminescence, ytterbium, neodymium, complexes, crown ethers.
Among all lanthanide ions (Ln3+), manifesting
advantage can be eliminated, to a great extent, in the case
of ligands, which shield, on the one hand, the complexꢀ
forming ion from the quenching effect of the solvent molꢀ
ecules and, on the other hand, favor the efficient transfer
3
+
4
(
1
fꢀluminescence, only some of them, in particular, Yb
λmax = 980 nm) and Nd3+ (λmax = 880, 1060, and
340 nm), are characterized by luminescence in comꢀ
3
+
plexes with organic ligands, which absorb the light preꢀ
dominantly in the visible spectral region. This is attribꢀ
uted to the fact that longꢀlived triplet (T) levels of the
most part of colored reagents have a higher energy than
of the excitation energy to the Ln ion.
In this work, we studied the IR luminescence of the
Yb3+ and Nd complexes with chromophoric crown
ethers 1 and 2, viz., ligands satisfying, to a great extent,
the above requirements.
3+
2
–1
lowꢀlying radiative levels of these ions ( F is 10200 cm
5
/2
3+
3
+
4
–1
for Yb , and F3 is 11500 cm for Nd ). However,
/2
the 4fꢀluminescence from these levels is quenched due to
Experimental
–
1
highꢀfrequency (3500 cm ) vibrations of the OH groups
of the solvent molecules, which enter the coordination
sphere of the complexes. As a consequence, they exhibit
fairly low luminescence characteristics of Ln3 . This disꢀ
The initial ytterbium and neodymium nitrates were preꢀ
pared as hexahydrates by the dissolution of weighted samples of
+ 1
the oxides (99.98% purity) in HNO followed by evaporation.
3
Ligands 1 and 2 were synthesized from 4´ꢀformylbenzoꢀ15ꢀ
crownꢀ5 (IBC Advanced Technologies, USA) and 2,6ꢀdimethylꢀ
phenol in the presence of TsOH and from 4´ꢀaminobenzoꢀ15ꢀ
crownꢀ5 (IBC Advanced Technologies, USA) and 2ꢀnaphthol,
2
respectively, using a known procedure. Ligand 1. Found (%):
C, 71.51; H, 6.98. C H O . Calculated (%): C, 71.40; H, 7.09.
31
36
7
Ligand 2. Found (%): C, 65.73; H, 5.99; N, 6.39. C H N O .
2
4
26
2
6
Found (%): C, 65.61; H, 6.08; N, 6.49. The characteristics of
the synthesized compounds coincided with the published data.
The lanthanide complexes were prepared by the interaction of
equimolar amounts of their hexahydrate nitrates and methanolic
solutions of 1 and 2 in the presence of triethyl orthoformate as
3
described previously. All complexes were isolated in the solid
state and characterized by luminescence, IR and UV specꢀ
troscopy.
IR spectra were recorded on an IRꢀ75 spectrometer in pelꢀ
lets with KBr. UV spectra were recorded on a Specord UVꢀVis
spectrometer in MeOH. The luminescence and luminescence
excitation spectra were obtained on an SDLꢀ1 spectrometer
with FEUꢀ62 and FEUꢀ79 photoelectron multipliers at 298 K.
All spectra were corrected with account for the spectral sensitivꢀ
ity of the FEU. A DKsShꢀ150 lamp was the source of spectral
excitation. The positions of the T levels of the ligands were
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2138—2140, December, 2002.
066ꢀ5285/02/5112ꢀ2303 $27.00 © 2002 Plenum Publishing Corporation
1

2304
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 12, December, 2002
Korovin et al.
determined from the lowꢀtemperature phosphorescence spectra
of the gadolimium complexes with these ligands. The relative
quantum yields of 4fꢀluminescence (φ) of the Yb3+ and Nd3+
ions in the complexes (solution of Zn tetraphenylporphyrin,
whose quantum yield is 0.03, was a reference) and the luminesꢀ
Table 1. Luminescence characteristics of the ytterbium and
neodymium complexes with chromophoric crown ethers 1 and 2
3
Complex
φ•10 *
τ/µs*
cence lifetime (τ) (an LGIꢀ21 N laser was the excitation source,
Yb—1
Yb—2
Nd—1
Nd—2
8.8
6.6
1.2
0.9
4.2
3.8
0.9
0.8
2
λmax = 337 nm, pulse duration 15 ns) were determined using a
4
published procedure.
Results and Discussion
*
The error of measurement was ±10%.
The complexes under study are stable for several days
in methanolic solutions at room temperature, which is
supported by the absence of changes in the absorption
spectra (Fig. 1, a). Almost complete coincidence of the
are presented in Table 1. As should be expected for the
complexes with the same ligands, for the Yb complexes
the quantum yield and lifetime of luminescence are higher
and, in addition, comparable with those for the ytterꢀ
bium and neodymium complexes with other macrocyclic
ligands.5 The molecular luminescence of the ligands
3
+
3+
4
fꢀluminescence excitation spectra for the Yb and Nd
complexes in combination with the absorption spectra
indicates that the excitation energy is transferred from the
organic moiety of the complex molecule (energies of the
(
λexc = 313 nm) characterized by a broad diffuse band in a
region of 475—560 nm (1) and 490—555 nm (2) is almost
completely quenched in the complexes. This can indicate
the efficiency of the intramolecular transfer of the excitaꢀ
tion energy.6
–
1
T levels are equal to 15850 and 16270 cm for ligands 1
and 2, respectively) to the radiative levels of the lanꢀ
thanides due to the intramolecular character of transfer.
All complexes studied exhibit the 4fꢀluminescence of
the Yb3+ and Nd ions (Fig. 1, b), decaying according to
the exponential law. Some characteristics of luminescence
The complex formation of lanthanide nitrates with
ligand 1 produces complexes with the metal to ligand
ratio equal to 1 : 1, which is confirmed by elemental
analysis data and characteristic changes in the IR spectra.
The latter are almost identical to those for the complexes
3+
D (rel. units)
1
0
.0
.5
7
a
with benzoꢀ15ꢀcrownꢀ5. This suggests the coordination
1
3
+
of the Ln ions to five O atoms of the macrocycle and
–
O atoms of two bidentate NO3 groups. It should espeꢀ
3
cially be emphasized that the IR spectra of the complexes
with ligand 1 has no absorption in the region from 3350 to
2
–1
3
300 cm characteristic of water molecules in the interꢀ
nal coordination sphere. Therefore, the coordination
number of ytterbium and neodymium is nine.
4
In the case of ligand 2, the 1 : 1 complexes were also
isolated. It could be expected that, in addition to the
crown ether cavity, one more lanthanide ion coordinates
to the O atoms of the naphthol group and to the N atom
of the diazo group. However, by analogy to the lanthanideꢀ
3
00
400
500
600
λ/nm
I (rel. units)
1
ꢀ(pyridylꢀ2′ꢀazo)naphtholꢀ2 complex, such a coordinaꢀ
1
0
.0
.5
8
b
tion can occur only at рН >6.
1
Taking into account that the Yb and Nd3+ ions in
the complexes with benzoꢀ15ꢀcrown do not virtually luꢀ
minesce and the efficiency of their 4fꢀluminescence is
3+
3
9
low in the complexes with sulfophenyl complexones
(
Phthalexone S, Xylenol Orange) and diazo dyes with the
sixꢀmembered heterocycle (1ꢀ(pyridylꢀ2′ꢀazo)ꢀnaphtholꢀ
, 1ꢀ(thiazolylꢀ2′ꢀazo)naphtholꢀ2), one can suggest that
the molecules of ligands 1 and 2 perform a dual function:
1) aromatic fragments are soꢀcalled "photoantennas," i.e.,
2
4
2
(
1
0
8
50
950
1050 1150 1250
λ/nm
accumulators of the excitation energy ; (2) crown moiꢀ
ety shields the complexꢀforming ion from vibrations of
О—Н of the solvent molecule. We found a similar effect
Fig. 1. Absorption (a) and 4fꢀluminescence (b) spectra of
Yb—1 (1 ), Yb—2 (2), Nd—1 (3), and Nd—2 (4) in MeOH at
98 K, 5.0•10 mol L
–
5
–1
11
2
.
for the luminescence of ytterbium cryptates.

Lanthanide complexes with crown ethers
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 12, December, 2002 2305
Thus, main requirements to the ligands, whose comꢀ
4. M. P. Tsvirko, G. F. Stelmakh, V. E. Pyatosin, K. N.
Solovyov, T. F. Kachura, A. S. Piskarskas, and R. A.
Gadonas, Chem. Phys., 1986, 106, 467.
3
+
plexes could provide an efficient luminescence of the Ln
ions in the nearꢀIR spectral region, are the following:
1) highly dentate character (О,Nꢀdonor atoms), (2) chroꢀ
mophoric groups ("photoantennas"), and (3) certain enꢀ
5
6
7
8
. Yu. Korovin and N. Rusakova, Rev. Inorg. Chem., 2001,
(
2
1, 299.
. M. Tsvirko, G. Stelmakh, V. Pyatosin, K. Solovyov, and
T. Kachura, Chem. Phys. Lett., 1980, 73, 80.
. M. Hiraoka, Crown Compounds. Their Characteristics and
Applications, Elsevier, Amsterdam, 1982, 351 pp.
. K. B. Yatsimirskii, N. A. Kostromina, Z. A. Sheka, N. K.
Davidenko, E. E. Kriss, and V. I. Ermolenko, Khimiya
kompleksnykh soedinenii redkozemel´nykh elementov [Chemꢀ
istry of Complexes of RareꢀEarth Elements], Naukova Dumka,
Kiev, 1966, Ch. 7, 432 (in Russian).
–
1
ergy of the T levels (at least 13500—14000 cm ).
This work was financially supported by the National
Academy of Sciences of Ukraine (Project No. 249/2001).
References
9
. Yu. Korovin and N. Rusakova, 7th Intern. Conf. on Methods
and Applications of Fluorescence (16—19 September, 2001),
Abstracts, Amsterdam, The Netherlands, 2001, 98.
1
. J.ꢀC. G. Bünzli, in Lanthanide Probes in Life, Chemical and
Earth Sciences. Theory and Practice, Eds. G. R. Choppin
and J.ꢀC. G. Bünzli, Elsevier, Amsterdam, 1989, 2, 89.
. T. Yamashita, H. Nakamura, M. Takagi, and K. Ueno, Bull.
Chem. Soc. Jpn., 1980, 53, 1550.
. Yu. V. Korovin, S. V. Shevchuk, V. A. Bacherikov, N. V.
Rusakova, E. A. Alekseeva, and A. I. Gren´, Zh. Neorg.
Khim., 2000, 45, 1513 [Russ. J. Inorg. Chem., 2000, 45, 1383
10. N. Sabbatini, M. Guardigli, and J.ꢀM. Lehn, Coord. Chem.
Rev., 1993, 123, 201.
11. Yu. V. Korovin, N. V. Rusakova, and Yu. A. Popkov,
Zh. Prikl. Spektrosc., 2002, 69, 79 [J. Appl. Spectr., 2002, 69
(Engl. Transl.)].
2
3
Received January 30, 2002;
(
Engl. Transl. )].
in revised form June 28, 2002