Photoluminescent tetrazolate-based Eu(III) complexes: An outstanding impact of aromatic phosphine oxide co-ligands on the photoluminescence quantum yields

Article abstract of DOI:10.5560/ZNB.2014-3275

New ternary Eu(III) 5-(2-pyridyl-1-oxide)tetrazolate complexes with phosphine oxide co-ligands have been synthesized and characterized by elemental analysis, and IR and 1H NMR spectroscopic techniques. The analytical data revealed that these complexes are

Full text of DOI:10.5560/ZNB.2014-3275

Photoluminescent Tetrazolate-based Eu(III) Complexes:
An Outstanding Impact of Aromatic Phosphine Oxide Co-ligands
on the Photoluminescence Quantum Yields
a
a,c
a
a
Marek Pietraszkiewicz , Suraj Mal , Oksana Pietraszkiewicz , Krzysztof Górski , and
b
Nitin Chelwani
a
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01224 Warsaw,
Poland
b
Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences,
P. O. Box 49, H-1525 Budapest, Hungary
Present address: Department of Chemistry, School of Sciences, Lovely Professional University,
c
Jalandhar – Delhi G. T. Road (NH-1), Phagwara, Punjab, India-144411
Reprint requests to M. Pietraszkiewicz. E-mail: mpietraszkiewicz@ichf.edu.pl
Z. Naturforsch. 2014, 69b, 239 – 247 / DOI: 10.5560/ZNB.2014-3275
Received September 30, 2013
New ternary Eu(III) 5-(2-pyridyl-1-oxide)tetrazolate complexes with phosphine oxide co-ligands
1
have been synthesized and characterized by elemental analysis, and IR and H NMR spectroscopic
techniques. The analytical data revealed that these complexes are mononuclear, and the central Eu(III)
ion is coordinated by three oxygen and three nitrogen atoms of the tetrazolate and two oxygen atoms
from the phosphine oxide ligands. The ancillary ligands increased remarkably the luminescence effi-
ciency of the Eu(III) tetrazolate.
Key words: Europium Tetrazolates, Phosphine Oxides, Photoluminescence, Quantum Yields,
Lifetime
Introduction
chromophores by transferring energy from the excited
states of the “antenna” to the emissive states of lan-
The unique properties of lanthanide complexes ex- thanide ions [11 – 13]. This process involves excita-
hibiting narrow emission bands upon excitation, long- tion of the ligand to a singlet state, radiationless in-
living luminescence lifetimes, emission over the vis- tersystem crossing to the triplet state and energy trans-
ible and near-IR (NIR) regions makes them very at- fer from the triplet state to the emissive level of the
tractive materials for various technologies. On account lanthanide cation. Further, the excited lanthanide ions
of their high photoluminescence quantum yields, lan- undergo radiative transitions to lower energy states
thanide complexes can be applied in light-emitting which are responsible for the characteristic multi-
devices [1 – 3], low-threshold lasers [4], optical am- ple narrow band emissions. For such a phenomenon
plifiers [5], displays, or biomedical imaging [6, 7]. to occur, one must take into account the energy of
Bredol and coworkers demonstrated the feasibil- the excited states of the organic chromophore used,
ity to manufacture highly photoluminescent hybrid which must be higher as compared to the emissive lev-
organic/inorganic materials – sol-gels incorporating els of the lanthanide ions [14 – 17]. Ligands such as
photoluminescent lanthanide complexes [8 – 10].
1,3-diketonates [18 – 20], carboxylates [21 – 23], and
The limiting features of lanthanide ions themselves analogs of 1,3-diketonates (pyrazolonates and isoxa-
are the low absorbance leading to a low value of the zolonates) [24, 25], have been extensively studied so
molar absorption coefficient and the spin- and parity- far to act as “antenna” for the lanthanide ions. A great
forbidden nature of f- f transitions that prevent di- number of different chromophores have been investi-
rect excitation. Such problems can be avoided by in- gated and studied to achieve better and brighter lan-
troducing organic ligands which act as the “antenna” thanide complex luminescence. The applicability of
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
Ph Ph
lanthanide complexes can be limited by: 1) vibronic
quenching of lanthanide complex emission by OH, NH
oscillators present in the 1 coordination sphere of
the Ln(III) cation, 2) low photoluminescence quantum
yield, and 3) low thermodynamic and kinetic stability.
Ph Ph
P
P
Ph
O
Ph
O
O
st
P
P
Me
Me
O
O
O
Ph
O
O
P
P
Ph
To overcome all such problems, ligands bearing suit- Ph
Ph
Ph
Ph
able chromophores forming thermodynamically stable
DPEPO
XSANTPO
OPPO
complexes with lanthanide ions are to be used. Coordi-
natively unsaturated lanthanide complexes frequently
display low photoluminescence quantum yields, due
Fig. 1. The phosphine oxides used as co-ligands.
to the presence of quenching molecules (water or dentate pyridine-tetrazolates as analogs of dipicolinate
alcohol). These quenchers can be replaced by sev- ligands [36].
eral neutral sensitizing auxiliary ligands. These co-
In a previous paper [37] we described the pho-
ligands can also act as an additional “antenna” and toluminescence properties of europium and terbium
can enhance the overall photoluminescence quantum tetrazolates. Herein we report the synthesis and
yield. A large number of highly coordinated com- photophysical studies of Eu(III) complexes with
plexes of lanthanide 1,3-diketonates containing ad- 5-(2-pyridyl-1-oxide)tetrazole (HPTO) and phosphine
ditional N-ligands such as 1,10-phenanthroline, 4,7- oxides as co-ligands: 4,8-bis(diphenylphosphinyl)-9,9-
0
disubstituted 1,10-phenanthrolines, 2,2 -bipyridine, dimethyl-xanthene dioxide (XANTPO), 1,2-bis(di-
0
0
4
,4 -disubstituted 2,2 -bipyridines, or 1,4-diaza-1,3- phenylphosphino)benzene dioxide) (OPPO) and
butadienes [18, 26, 27] have been successfully synthe- 2,2 -bis(diphenylphosphino)-diphenylether
0
dioxide
sized and used in photophysical studies. Phosphine ox- (DPEPO). The choice of these auxiliary ligands is due
ides display particularly high affinity for the complex- to their strong coordination ability with the lanthanide
ation of lanthanide cations. The square-antiprismatic ions and their structural rigidity. These ligands are
structure formed by introducing phosphine oxides into shown in Fig. 1.
lanthanide complexes also promotes the faster radia-
tive decay of the lanthanide ion, leading to an increase Result and Discussion
of the photoluminescence efficiencies due to an en-
5
7
hanced D → F transition [28 – 30].
Syntheses and characterization of complexes
0
2
Tetrazoles display pKa values in the range of
4
.2 – 4.4, similarly to carboxylic acids [31]. They are
The ligand HPTO and its neutral complex 1 were
excellent ligands for metal ion coordination [32, 33]. synthesized according to our previous work [37]. The
The water binding at lanthanide ions is prevented by complexes with the P-oxide co-ligands were synthe-
introducing multidentate tetrazole-based ligands con- sized according to Scheme 1.
taining terpyridine or bipyridine chromophores, pro-
Microanalysis of the products confirmed the
viding luminescent lanthanide complexes with good proposed stoichiometry. The bands observed at
−1
photoluminescence quantum yields [34, 35]. Quite 3000 – 3300 cm in the IR spectra of all complexes
recently, much higher photoluminescence quantum confirms the presence of water molecules, also re-
yields have been reported in solution and in the solid ported for other tetrazole-containing complexes. The
state for Eu(III) and Tb(III) complexes containing tri- water molecules are hydrogen-bonded to the tetrazole
Ph
O
Ph
Ph
N
N
OPPO, MeOH
Reflux, 24 h
N
N
O
O
P
P
Eu.(H O)
2
3.5
Eu
N
N
3
N
N
O
Ph
3
N
N
Scheme 1. Synthesis of ternary complexes.
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
241
100
(a)
Eu(PTO)
3
Eu(PTO) .XANTPO
3
Eu(PTO) .OPPO
3
75
-
CH Sym
3
P=O
50
25
0
100
200
300
400
500
600
700
0
Temperature( C)
600
800
1000
1200
1400
Fig. 3. Thermogravimetric curve for complex 2.
-
1
Wavenumbers (cm )
(
b)
oxide by the sharp bands at 450 and 400 cm 1, respec-
−
tively (Fig. 2).
The proton NMR spectra of complexes 1 – 4 showed
all the expected peaks of the PTO ligand. The signals
of the pyridine protons have been shifted upfield upon
coordination with the metal ion for complexes 1 – 4.
The TGA analysis shows the loss of water molecules
Eu-O
◦
below 70 C (4.1%, 6% and 3% for 2, 3 and 4, re-
spectively) confirming their presence in the outer coor-
dination sphere, followed by the loss of the respective
phosphine oxides and tetrazoles, which at last leads to
the formation of europium oxide (Fig. 3).
Eu-N
Ring deformation
300 400
Molecular structure modeling of complexes by the
600 MOPAC/AM1 model
200
500
-1
Wavenumbers (cm )
We have tried to optimize the molecular structure
Fig. 2 (color online). Mid- and far-IR spectra of complexes
– 3 (A) and of complex 1 (B).
of the synthesized europium(III) complexes by us-
ing the MOPAC/AM1 model with parameters for eu-
ropium [41]. The central Eu(III) ion in complexes 2 – 4
1
units, but not to the metal ions [38 – 40]. The shifts in possesses an eight-fold coordination environment, and
the P=O stretching frequencies of the phosphine ox- the geometry can be described as a square antiprism.
ide molecules in the presented complexes (from 1135 Lanthanide complexes with seven-, eight- or nine-
−
1
−1
to 1150 cm in 2, from 1155 to 1178 cm in 3 and fold coordination are well documented [42, 43]. Short
−
1
from 1135 to 1165 cm in 4) show the involvement P=O–Eu bonds (2.324 – 2.333 Å) were calculated for
of the phosphoryl oxygen atoms in the complex for- these complexes. They are distinctly shorter than those
mation with the Eu(III) ion. The shift of the band at found in the crystal structure of gadolinium 5-(2-
− −1
265 cm of the N–O stretching to 1360 cm indi- pyridyl-1-oxide)tetrazolate between Gd–OH (coordi-
2
1
1
cates that the N–O group is engaged in complex for- nated water, 2.450 Å) [41]. That suggests stronger in-
mation with the Eu(III) ion. The far-IR spectra reveal teractions of the phosphine oxides with the Eu(III) ion.
the coordination of the Eu(III) ion with the nitrogen Fig. 4 represents the calculated structure of the tetrazo-
atoms of tetrazole and the oxygen atoms of pyridine late complex with the XANTPO co-ligand.
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
1
.0
.8
.6
.4
.2
.0
0
0
0
0
0
250
300
350
400
Wavelength (nm)
1
.0
.8
.6
.4
0.2
0
Fig. 4 (color online). Optimized molecular structure of
complex 2.
0
0
The observed torsion angle in-between the PTO
and the phosphine oxide ligand suggests a distortion
around the Eu(III) ion by the introduced phosphine
oxide.
0.0
250
Photoluminescence properties of the Eu(III)
complexes
300
350
400
Wavelength (nm)
The room-temperature absorption and normalized
excitation spectra of complexes 2 – 4 are shown in
Fig. 5. The excitation spectra were obtained by moni-
toring the emission wavelength of Eu(III) at 612 nm by
using a xenon lamp. The excitation spectra of the com-
plexes exhibit a broad band between 250 and 325 nm,
1
.0
0.8
∗
0.6
0.4
which can be assigned to π-π electron transitions of
the ligands. The shape of the excitation spectra of the
complexes comply with that of the absorption spec-
tra, confirming the environment of Eu(III) by the main
ligand PTO and the corresponding phosphine oxides
used.
0.2
This is diagnostic of the typical sensitization of the
Eu(III) ion by ligands instead of direct excitation of the
lanthanide ion. The molar absorption coefficient values
for complexes 3 and 4 were found much higher than for
complex 1 (Table 1). This confirms that the sensitiza-
0
.0
2
50
300
350
400
Wavelength (nm)
Fig. 5 (color online). UV/Vis absorption (solid line) and ex-
citation spectra (λem = 612 nm) (dashed line) of complexes
tion of the Eu(III) ion by the ligands is very signifi- 2 (top), 3 (middle) and 4 (bottom) in acetonitrile solution at
cant and prevents the rapid deactivation of the excited room temperature.
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
243
5
Table 1. Absorption wavelength maxima (λ in nm) and mo- Table 2. Excitation wavelengths (λexc), D lifetimes (τobs),
0
−
1
−1
lar absorption coefficients (ε in cm mol ) for complexes photoluminescence quantum yields (Φ), KRAD and KNR for
1
– 4 in acetonitrile solution.
complexes 1 – 4 in acetonitrile solution at room temperature.
Complex
Wavelength
nm)
272
53
276
44
274
40
289
41
Molar absorption
coefficient (cm mol )
Complex
λexc
Φ
τobs
KRAD
(ms
0.21
0.37
0.23
0.26
KNR
−1
−
1
−1
(
−1
(
nm)
(%)
(ms)
)
(ms
)
1
2
3
4
27 400
43 000
54 730
126 430
40 960
111 085
47 260
90 700
1
2
3
4
284
262
260
271
13
73
36
38
0.66
1.99
1.59
1.45
1.30
0.14
0.40
0.43
2
2
2
more effective than direct excitation of the metal ion.
The presence of a single emission band of D → F
2
5
7
0
0
for te europium(III) complexes proves the existence of
state by the vibrations of the ligands and/or solvent a single chemical environment around the Eu(III) ion at
molecules.
7
a low symmetry site. The F level shows three main
1
The room temperature-normalized emission spectra overlapping components of almost equal intensity at
of the europium(III) complexes 1 – 4 under the excita- 588 – 598 nm that can be assigned to the allowed mag-
5
7
tion wavelengths 262, 260 and 271 nm are shown in netic dipole transitions, while the D → F transi-
0
4
Fig. 6. The emission spectra exhibit the characteris- tion gives rise to a strong band at 699 and two smaller
tic sharp peaks in the 575 – 725 nm region associated ones at 696 and 694 nm, attributed to the electric dipole
5
7
with the D → FJ transitions of the Eu(III) ion. The transitions. Furthermore, the transitions from the ex-
0
5
7
5
7
five major peaks of the D → F
transitions are cited D state to the FJ (J = 0, 1, 2) state (538 nm,
1
0
0−4
0
5
7
resolved, and the hypersensitive D → F transition 556 nm) were also evident (Fig. 6). The luminescence
2
is very intense, pointing to a highly polarizable chem- decay of the europium(III) complexes 1 – 4 was mea-
7
ical environment around the Eu(III) ion, which is re- sured in acetonitrile solution at the F site upon lig-
2
sponsible for the brilliant-red emission of these com- and excitation at room temperature and derived by fit-
plexes [43]. The absence of a broad emission band ting as a mono-exponential function. The calculated
resulting from organic ligands in the blue region in- values of luminescence decay for complexes 1 – 4 are
dicates the effective energy transfer from the ligands presented in Table 2. The longer lifetime observed for
to the central Eu(III) ion. The absence of any absorp- the ternary complexes 2 – 4, in contrast to complex 1,
tion band due to the f- f transitions of the Eu(III) ion confirms the replacement of water from the inner co-
proves that luminescence sensitization via ligands is ordination sphere of the Eu(III) ion. The shorter decay
(
a)
(b)
3.0
1.5
7
F2
2.5
5
1
D0
D
7
5
2
.0
.5
.0
.5
.0
1.0
0.5
F4
7
7
7
F1
F3
F0
4
3
2
1
1
1
1
D
5
0
1
D
5
0
0
.0
500
550
600
650
700
750
520
530
540
550
560
570
Wavelength (nm)
Wavelength (nm)
Fig. 6 (color online). Emission spectra of Eu(III) complexes 1 – 4 recorded in acetonitrile solution at room temperature for
5
7
5
7
D → FJ (J = 0 – 4) transitions (a), and D → FJ (J = 0 – 2) transitions for complex 2 (b).
0
1
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
lifetime observed for complex 1 can be attributed to the
vibronic oscillations shown by the coordinated water
molecules which promote the non-radiative decay as it
is well described for the tetrazole-containing hydrated
complexes [34 – 36].
3
2
2000
8000
(30800)
S
1
(
29100)
S
1
(27583)
5
(27724)
D
3
S
1
2
4000
0000
(24000)
(21483)
5
T
1
D
2
(19027)
5
2
(21312)
(21436)
T1
D1
T
1
5
D
0
Table 2 gives data for the radiative (KRAD) and non-
16000
12000
(17293)
radiative decay (KNR), the photoluminescence quan-
5
tum yields (Φ) for the D europium(III) ion excited
0
8
4
000
000
0
state and the luminescence decay lifetime (τ) for com-
plexes 1 – 4. Complex 1 exhibited a lower photolumi-
nescence efficiency due to quenching by vibronic os-
3+
XANTPO
PTO
Eu
OPPO
st
cillations of coordinated water molecules in the 1 co-
Fig. 7 (color online). Proposed energy transfer diagram in
ternary complexes.
ordination sphere of the Eu(III) ion. Complexes 2, 3
and 4 exhibit photoluminescence efficiencies by the
six- to three-fold higher than that of complex 1.
The low symmetry of the proposed square- nant energy transfer from the triplet state of the ligands
5
5
antiprismatic structure of the complexes with the phos- to the D and D emissive levels of the Eu(III) ion as
1
0
phine oxide co-ligands also enhances the radiative proven by the emission spectra (Fig. 6).
5
rates and quantum efficiencies by increasing the D →
0
7
F emission related to the odd parity factor [42]. In Conclusions
2
the present study, complex 2 exhibited a photolumines-
cence efficiency (73%) which is the highest reported to
Tetrazoles are a promising class of heterocyclic lig-
date for tetrazolate Eu(III) complexes. From our previ- ands that can sensitize effectively the luminescence of
ous experimental data the singlet and triplet state en- lanthanide ions upon UV excitation. The coordination
ergy values of the PTO ligand were calculated from of phosphine oxide expels water molecules from the
the phosphorescence spectra of the Gd(PTO) ·(H O)x first coordination sphere, leading to highly improved
3
2
complex [37]. On this basis we propose an energy photoluminescence of the ternary complexes. The pro-
transfer diagram for the ternary Eu(III) tetrazolate posed intra-molecular energy migration diagram indi-
complexes, in which the energy migration takes place cates an energy transfer from the triplet state of the
5
5
from the PTO ligand and the corresponding phos- ligand to the D and D levels of the Eu(III) ion.
1
0
phine oxides to the emissive level of the europium The photoluminescence quantum yields and decay life-
ion. Based on Reinhoudt’s empirical rule [44] the in- times of the complexes vary according to the nature
tersystem crossing process will be effective when ∆E of the co-ligand. The highest values of photolumines-
−
1
(
S −T ) is at least 5000 cm for all kinds of ligands. cence quantum yield and decay lifetime have been ob-
1
1
The triplet states of the ligands thus play an important served for complex 2 (73%, 1.99 ms). Thus our results
role in the energy transfer process which is also con- suggest that the XANTPO-coordinated 5-(2-pyridyl-1-
firmed by experimental evidences, such as back-energy oxide)tetrazolate-europium(III) complex may find an
transfer reported for cases where there is a small en- application in organic photonics and electronics.
ergy gap between the lowest triplet state of the chro-
mophore and the lanthanide emissive levels. Latva et Experimental Section
al. supported this suggestion by his extensive study on
Phosphines from Aldrich were used without further purifi-
terbium complexes giving an empirical rule stating that
cation. Solvents were of analytical reagent grade. IR spec-
ligand-to-metal energy transfer takes place only when
tra were recorded using a Perkin-Elmer 2000 spectrome-
5
−1
∆
E (T − DJ) is greater than 2000 cm , which results
1
1
ter. HNMR spectra were recorded in CDCl or [D ]DMSO
3
6
in a higher photoluminescence quantum yield [45].
Phosphine oxide ligands fulfill the required two condi-
tions for an effective energy transfer (Fig. 7, XANTPO
with a Bruker DRX 250 MHz spectrometer using TMS as
internal standard. Elemental analyses were performed with
a Vario EL III Heraeus instrument. TG-DSC measurements
ligand shown, but analogous energy flow for DPEPO). were carried out by using a TG-DSC 111 instrument (Se-
The energy diagram shows the effective and predomi- taram France).
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245
Synthesis of 5-(2-pyridyl-1-oxide)tetrazole (HPTO) and
[Eu(PTO) ·DPEPO·(H O) ] (4)
3
2
2
Eu(PTO) ·(H O) (1)
3
2
3.5
IR (KBr): ν = 3290 (O–H), 2988 (C–H arom.), 1500
N=N), 1260 (N–O), 1165 (P=O), 1026 (N–N), 746 (C–
The synthesis of HPTO and its europium complex were
carried out as described previously by us [31].
(
−1
1
H), 570 (P–C), 450 (Eu–N), 400 (Eu–O) cm . – H NMR
250 MHz, [D ]DMSO): δ = 6.67 – 7.75 (broad m, arom.). –
(
6
Synthesis of the phosphine oxides
C H N EuP O : calcd. C 52.10, H 3.56, N 16.88; found
5
4
44 15
2 8
The phosphine oxides were synthesized by oxidation of C 52.17, H 3.29, N 16,97. Yield 79%.
the corresponding phosphines. Calculated amounts of H O
2
2
Photophysical properties
(30%) were added slowly to the vigorously stirred THF so-
lution of the respective phosphine. Stirring was maintained
at room temperature for 2 h. After evaporation of THF, the
residue was treated with acetone-ethyl acetate to obtain the
respective phosphine oxide product as a precipitate. The pre-
cipitates thus obtained were filtered off and dried in a vac-
UV/Vis spectra were recorded with a Shimadzu UV-3100
spectrophotometer and corrected luminescence spectra (exci-
tation, emission and decay lifetime) with a Fluorolog 3 spec-
trofluorimeter using acetonitile of spectral grade as solvent
at room temperature. Calculations and measurements: Pho-
toluminescence quantum yields were determined to quan-
tify the complexes by using quinine sulfate as a standard
◦
uum. All melting points were above 360 C with decomposi-
tion.
1
XANTPO: H NMR (250 MHz, CDCl ): δ = 7.59 – 7.62
3
(
Φ = 0.52). A methodology described by Williams et al. [46]
(
(
d, 2H, Phen-H), 7.24 – 7.48 (m, 20H, Phen-H), 6.94 – 7.20
t, 2H, Phen-H), 6.74 – 6.84 (m, 2H, Phen-H), 1.70 (s, 6H,
and Eaton [47] was taken into account to measure and to
calculate the photoluminescence quantum yields of the com-
plexes in solution. It involves the use of well characterized
standard samples with known ΦST values.
2
Me). – MS (EI): m/z = 610. Yield 77%.
1
OPPO: H NMR (250 MHz, CDCl ): δ = 7.19 (m, 8H,
3
Phen-H), 7.35 (m, 12H, Phen-H), 7.57 (t, 2H, Phen-H), 7.75
Essentially, solutions of the standard and test samples with
identical absorbance at the same excitation wavelength can
be assumed to be absorbing the same number of photons.
Hence, a simple ratio of the integrated fluorescence intensi-
ties of the two solutions (recorded under identical conditions)
will yield the ratio of the quantum yield values. ΦX can be
calculated by using Eq. 1,
(
m, 2H, Phen-H). – MS (EI): m/z = 478. Yield 82%.
1
DPEPO: H NMR (250 MHz, CDCl ): δ = 7.75 – 7.64
3
(m, 9H, Phen-H), 7.42 (m, 13H, Phen-H), 7.05 – 7.04 (t, 2H,
Phen-H), 7.07 (t, 2H, Phen-H), 7.08 (t, 2H, Phen-H). – MS
EI): m/z = 570. Yield 84%.
(
Synthesis of the ternary complexes
ꢀ
ꢁ
All complexes were prepared by stirring equimolar
amounts of europium 5-(2-pyridyl-1-oxide)tetrazolate with
2
2
ΦX = ΦST (I /I ) η /η
(FST/FX)
(1)
X
ST
X
ST
the corresponding phosphine oxide in methanol for 24 h at
where ΦX and ΦST represent photoluminescence quantum
yield of lanthanide complexes (sample) and standard quinine
sulfate, respectively. The terms I and I represent the inte-
◦
7
0 C. The products were obtained after solvent evapora-
tion and recrystallization from an ethanol-hexane mixture.
◦
X
ST
All melting points were above 300 C with decomposition.
grated emission intensity of the complex and of the standard
under identical conditions, respectively. FST and FX mean
fractions of light absorbed by standard and sample. Radiative
and non-radiative constants (KRAD and KNR, respectively)
were calculated by Eqs. 2 and 3.
Eu(PTO) ·XANTPO·(H O) (2)
3
2
3
IR (KBr): ν = 3310 (O–H), 1460 (N=N), 1400 (CH3),
270 (N–O), 1150 (P=O), 1025 (N–N), 746 (C–H), 550 (P–
C), 450 (Eu–N), 400 (Eu–O) cm . – H NMR (250 MHz,
1
−1
1
[
–
D ]DMSO): δ = 6.59 – 7.95 (broad m, arom.), 1.56 (s, Me).
6
KRAD = Φ/τ
/τ = KRAD +KNR
(2)
(3)
C H EuP N O : calcd. C 52.54, H 3.87, N, 16.12;
57 50 15
2 9
1
found C 52.20, H 3.93, N 16.23. Yield 67%.
Acknowledgement
Eu(PTO) ·OPPO·(H O) (3)
3
2
4
IR (KBr): ν = 3305 (O–H), 1452 (N=N), 1370 (N–
This work was supported by the Project FP7 Marie Curie
C), 1270 (N–O), 1178 (P=O), 1030 (N–N ), 750 (C–H), Initial Training Network, Contract PITN-GA-2008-215399
−1
1
5
60 (P–C), 450 (Eu–N), 400 (Eu–O) cm . – H NMR “Cavity-confined Luminophores for Advanced Photonic Ma-
(
250 MHz, [D ]DMSO): δ = 6.92 – 7.71 (broad m, arom.). – terials: A Training Action for Young Researchers” (FINELU-
6
C H N EuP O : calcd. C 48.49, H 3.73, N 17.67; found MEN), and the Polish Ministry of Science & Higher Educa-
4
8
44 15
2 9
C 48.30, H 3.55, N 17.95. Yield 72%.
tion, grant no. 938/7. PR UE/2009/7.
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
[
[
[
[
1] V. L. Colvin, M. C. Schlamp, A. P. Alivisatos, Nature
los, H. I. S. Nogueira, Cryst. Growth Des. 2008, 8,
2505 – 2516.
1
994, 370, 354 – 357.
2] N. Tessler, V. Medvedev, M. Kazes, S. H. Kan, U. Ba- [24] R. Pavithran, N. S. Saleesh Kumar, S. Biju, M. L. P.
nin, Science 2002, 295, 1506 – 1508.
Reddy, S. A. Junior, R. O. Freire, Inorg. Chem. 2006,
45, 2184 – 2192.
[25] S. Biju, M. L. P. Reddy, A. H. Cowley, K. V. Vasude-
van, Cryst. Growth Des. 2009, 9, 3562 – 3569.
3] B. O. Dabousi, M. G. Bawendi, O. Onitsuka, M. F.
Rubner, Appl. Phys. Lett. 1995, 66, 1316 – 1318.
4] V. I. Klimov, A. A. Mikhailovsky, S. Xu, J. A. Hol-
lingsworth, C. A. Leatherdale, H. J. Eisler, M. G. Ba- [26] A. Bellusci, G. Barberio, A. Crispini, M. Ghedini, M.
wendi, Science 2000, 290, 314 – 317.
La Deda, D. Pucci, Inorg. Chem. 2005, 44, 1818 –
[5] M. T. Harrison, S. V. Kershaw, M. G. Burt, A. L. Ro-
1825.
gach, A. Kornowski, A. Eychmüller, H. Weller, Pure [27] J. A. Fernandes, R. A. S. Ferreira, M. Pillinger, L. D.
Appl. Chem. 2000, 72, 295 – 307.
Carlos, I. S. Goncalves, P. J. A. Ribeiro-Claro, Eur. J.
[6] B. Dubertret, P. Skourides, D. J. Norris, V. Noireaux,
Inorg. Chem. 2004, 3913 – 3919.
A. H. Brivanlou, A. Libchaber, Science 2002, 298, [28] Y. Wada, T. Ohkubo, M. Ryo, T. Nakarawa, Y. Hase-
1
759 – 1762.
gawa, S. Yanagida, J. Am. Chem. Soc. 2000, 122,
8583 – 8584.
[
[
[
7] M. P. Bruchez, M. Moronne, P. Gin, S. Weiss, A. P.
Alivisatos, Science 1998, 281, 2013 – 2016.
8] M. Bredol, T. Jüstel, S. Gutzov, Opt. Mater. 2001, 18,
[29] Y. Hasegawa, T. Ohkubo, K. Sogabe, Y. Kawamura,
Y. Wada, N. Nakashima, S. Yanagida, Angew. Chem.
Int. Ed. 2000, 39, 357 – 360.
3
37 – 341.
9] M. Bredol, U. Kynast, M. Boldhaus, C. Lau, Ber. [30] Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisa,
Bunsen-Ges. 1998, 102, 1557 – 1560.
10] M. Schem, M. Bredol, Thin Solid Films 2005, 474,
1 – 35.
11] J.-M. Lehn, Angew. Chem., Int. Ed. Engl. 1990, 29,
304 – 1319.
12] N. Sabbatini, M. Guardiglia, J.-M. Lehn, Coord. Chem.
Rev. 1993, 123, 201 – 228.
13] C. Piguet, J.-C. G. Bünzli, Chem. Soc. Rev. 1999, 28,
Y. Kai, S. Yanagida, J. Phys. Chem. A 2003, 107,
1697 – 1702.
[31] R. J. Herr, Bioorg. Med. Chem. 2002, 10, 3379 –
3393.
[32] H. Zhao, Z. R. Qu, H. Y. Ye, R. G. Xiong, Chem. Soc.
Rev. 2008, 37, 84 – 100.
[33] M. Dinca, A. F. Yu, J. R. Long, J. Am. Chem. Soc. 2006,
128, 8904 – 8913.
[
[
[
[
[
[
3
1
3
47 – 358.
14] R. G. Charles, E. P. Riedel, J. Inorg. Nucl. Chem. 1966,
8, 527 – 530.
[34] M. Giraud, E. S. Andreiadis, A. S. Fisyuk, R. Dema-
drille, J. Pecaut, D. Imbert, M. Mazzanti, Inorg. Chem.
2008, 47, 3952 – 3954.
2
15] R. Reisfeld, C. K. Jorgensen in Structure and Bonding, [35] E. S. Andreiadis, R. Demadrille, D. Imbert, J. Pecaut,
Vol. 77, (Eds.: R. Reisfeld, C. K. Jorgensen), Springer-
Verlag, Berlin, 1992, pp. 207 – 256.
16] S. Tobita, N. Arakawa, I. Tanaka, J. Phys. Chem. 1985,
M. Mazzanti, Chem. Eur. J. 2009, 15, 9458 – 9476.
[36] E. S. Andreiadis, D. Imbert, J. Pecaut, R. Demadrille,
M. Mazzanti, Dalton Trans. 2012, 41, 1268 – 1277.
[37] M. Pietraszkiewicz, S. Mal, O. Pietraszkiewicz, Opt.
Mater. 2012, 34, 1507 – 1512.
[
8
9, 5649 – 5654.
[
17] B. Alpha, R. Ballardini, V. Balzani, J.-M. Lehn, S. Pe-
rathoner, N. Sabbatini, J. Photochem. Photobiol. 1990, [38] D.-W. Fu, J. Dai, J.-Z. Ge, H.-Y. Ye, Z.-R. Qu, Inorg.
2, 299 – 306. Chem. Commun. 2010, 13, 282 – 285.
18] G. F. de Sá, O. L. Malta, C. de Mello Donegá, A. M. [39] W. Yang, X. Lin, A. J. Blake, C. Wilson, P. Hubberstey,
5
[
Simas, R. L. Longo, P. A. Santa-Cruz, E. F. da Silva, Jr.,
Coord. Chem. Rev. 2000, 196, 165 – 195.
N. R. Champness, M. Schroder, Cryst. Eng. Commun.
2009, 11, 67 – 81.
[
[
19] G. Vicentini, L. B. Zinner, J. Zukerman-Schpector, [40] H. Zhao, Z.-R. Qu, H.-Y. Ye, R.-G. Xiong, Chem. Soc.
K. Zinner, Coord. Chem. Rev. 2000, 196, 353 – 382. Rev. 2008, 37, 84 – 100.
20] M. D. McGehee, T. Bergstedt, C. Zhang, A. P. Saab, [41] R. O. Freire, G. B. Rocha, A. M. Simas, Inorg. Chem.
M. B. O’Regan, G. C. Bazan, V. I. Srdanov, A. J. Hee-
ger, Adv. Mater. 1999, 11, 1349 – 1354.
2005, 44, 3299 – 3310.
[42] S. Amine, M. Botta, M. Fasano, E. Terreno, Chem. Soc.
[
[
[
21] S. Sivakumar, M. L. P. Reddy, A. H. Cowley, K. V. Va-
Rev. 1998, 27, 19 – 29.
sudevan, Dalton Trans. 2010, 39, 776 – 786.
22] S. Raphael, M. L. P. Reddy, A. H. Cowley, M. Findlater,
Eur. J. Inorg. Chem. 2008, 4387 – 4394.
[43] F. A. Hart in Comprehensive Coordination Chemistry,
Vol. 3, (Eds.: G. Wilkinson, R. D. Gillard, J. A. Mc-
Cleverty), Pergamon Press, Oxford 1987, pp. 1059 –
1126.
23] P. C. R. Soares-Santos, L. Cunha-Silva, F. A. Almeida
Paz, R. A. Sá Ferreira, J. Rocha, T. Trindade, L. D. Car-
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M. Pietraszkiewicz et al. · Photoluminescent Tetrazolate-based Eu(III) Complexes
247
[
44] F. J. Steemers, W. Verboom, D. N. Reinhoudt, E. B. [46] A. T. R. Williams, S. A. Winfield, J. N. Miller, Analyst
Vander Tol, J. W. Verhoeven, J. Am. Chem. Soc. 1995, 1983, 108, 1067 – 1071.
17, 9408 – 9414. [47] D. F. Eaton, Pure Appl. Chem. 1988, 60, 1107 – 1114.
1
[45] M. Latva, H. Takalo, V. M. Mukkala, C. Matachescu,
J. C. Rodriguez-Ubis, J. Kanakare, J. Lumin. 1997, 75,
1
49 – 169.
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