A new tetrakis β-diketone ligand for NIR emitting LnIII ions: Luminescent doped PMMA films and flexible resins for advanced photonic applications

Article abstract of DOI:10.1039/c3tc31181c

A new antenna molecule containing four benzoyltrifluoroacetone (BTFA) moieties anchored to a single carbon atom and connected through four flexible methoxy groups, namely 1,1′-(4,4′-(2,2-bis((4-(4,4,4-trifluoro-3- oxobutanoyl)phenoxy)methyl) propane-1,3-diyl)bis(oxy)bis(4,1-phenylene))bis(4,4, 4-trifluorobutane-1,3-dione) [H₄L], has been designed and synthesized. Using this ligand, a series of homo- and hetero-metallic Ln ^III complexes of general formula [LnL]NBu₄ (where Ln = Sm (1), Gd (2), Er (3), Yb (4), Er_0.5Yb_0.5 (5), Er _0.5Gd_0.5 (6), Yb_0.5Gd_0.5 (7) and NBu₄ = tetrabutyl ammonium) have been isolated. All these complexes have high molar absorption coefficients (>40:000 M^-1 cm ^-1 around 330 nm in DMF) and display strong visible (Sm ^III) and/or, NIR (Sm^III, Er^III, Yb ^III) luminescence in solid state and in DMF solution upon irradiation at the ligand-centred bands in the range 250-400 nm. Furthermore, these complexes have been doped into PMMA matrices yielding highly luminescent, photo-stable films and flexible resins made of fibres with average diameter 300-400 nm. Photoluminescence studies show that the newly designed ligand is an adequate sensitizer for Sm^III, Yb^III and Er^III luminescence. The emission quantum yields and the luminescence lifetimes at room-temperature are 3.4 ± 0.5% and 79.1 ± 1 μs for Sm ^III and 2.6 ± 0.4% and 12.1 ± 0.1 μs for Yb ^III in solid state. Furthermore the overall quantum yields and lifetime measurements for the mixed metallic complex show that Yb^III → Er^III energy transfer occurs resulting in enhanced Er ^III emission.

Full text of DOI:10.1039/c3tc31181c

Journalof
Materials Chemistry C
Materials for optical and electronic devices
www.rsc.org/MaterialsC
Volume 1 | Number 42 | 14 November 2013 | Pages 6915–7118
ISSN 2050-7526
PAPER
Silvanose Biju, Jean-Claude G. Bünzli, Hwan Kyu Kim et al.
III
A new tetrakis β-diketone ligand for NIR emitting Ln ions: luminescent doped
PMMA films and flexible resins for advanced photonic applications

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Materials Chemistry C
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PAPER
A new tetrakis b-diketone ligand for NIR emitting LnIII
ions: luminescent doped PMMA films and flexible resins
for advanced photonic applications†
Cite this: J. Mater. Chem. C, 2013, 1,
6935
a
a
ab
a
*
*
*
and Hwan Kyu Kim
¨
Silvanose Biju, Yu Kyung Eom, Jean-Claude G. Bunzli
A new antenna molecule containing four benzoyltrifluoroacetone (BTFA) moieties anchored to a single
carbon atom and connected through four flexible methoxy groups, namely 1,10-(4,40-(2,2-bis((4-
(4,4,4-trifluoro-3-oxobutanoyl)phenoxy)methyl)
propane-1,3-diyl)bis(oxy)bis(4,1-phenylene))bis(4,4,4-
trifluorobutane-1,3-dione) [H4L], has been designed and synthesized. Using this ligand, a series of
homo- and hetero-metallic LnIII complexes of general formula [LnL]NBu4 (where Ln ¼ Sm (1), Gd (2), Er
(3), Yb (4), Er0.5Yb0.5 (5), Er0.5Gd0.5 (6), Yb0.5Gd0.5 (7) and NBu4 ¼ tetrabutyl ammonium) have been
isolated. All these complexes have high molar absorption coefficients (>40 000 Mꢀ1 cmꢀ1 around 330
nm in DMF) and display strong visible (SmIII) and/or, NIR (SmIII, ErIII, YbIII) luminescence in solid state and
in DMF solution upon irradiation at the ligand-centred bands in the range 250–400 nm. Furthermore,
these complexes have been doped into PMMA matrices yielding highly luminescent, photo-stable films
and flexible resins made of fibres with average diameter 300–400 nm. Photoluminescence studies show
that the newly designed ligand is an adequate sensitizer for SmIII, YbIII and ErIII luminescence. The
emission quantum yields and the luminescence lifetimes at room-temperature are 3.4 ꢁ 0.5% and
79.1 ꢁ 1 ms for SmIII and 2.6 ꢁ 0.4% and 12.1 ꢁ 0.1 ms for YbIII in solid state. Furthermore the overall
quantum yields and lifetime measurements for the mixed metallic complex show that YbIII / ErIII
energy transfer occurs resulting in enhanced ErIII emission.
Received 19th June 2013
Accepted 17th August 2013
DOI: 10.1039/c3tc31181c
www.rsc.org/MaterialsC
applications including telecommunications, medical diagnosis
and imaging, as well as in security inks and counterfeiting tags.2
Introduction
Initially, interest for near-infrared (NIR) emitting LnIII ions
stemmed from the development of optical bres, lasers and
ampliers1 since the NIR emission of ErIII around 1.5 mm is in
the so-called telecommunication “C” window. The subsequent
implementation of upconverted nanophosphors for the detec-
tion of cell and tissue antigens2 added a whole new eld of
applications for LnIII NIR luminescence. As a result, ions such
as ErIII and YbIII (emitting at 980 nm and a good sensitizer of
ErIII emission) are attracting considerable research attention
due to their characteristic luminescence properties.1,3 These
properties, coupled with the advantage of good signal trans-
mittance of NIR radiation by silica and biological tissues, make
them attractive for potential use in a number of photonic
Trivalent samarium is another lanthanide ion which has several
transitions in the range 800–1700 nm (ref. 4–6) along with
intense orange red luminescence in the visible region.4,7,8
Usually, the small absorption cross-sections of LnIII ions result
in inefficient emission from their 4f levels under direct excita-
tion unless powerful lasers are used. One of the most popular
ways to overcome this limitation is by complexing the LnIII ions
with organic ligands that sensitize the emission of the metal ion
by the well-known antenna effect.9–11 However NIR emitting
lanthanide complexes with organic ligands oen show low
emission efficiencies and shorter excited state lifetime values
compared to inorganic systems due to multiphonon de-excita-
tion caused by the coupling of the f levels with high-frequency
oscillators like O–H, N–H and C–H, present in the organic
ligands or in the solvent molecules.3,12 Careful selection of
solvents and clever design of ligands can easily minimize the
number of O–H and N–H groups around the LnIII ions but C–H
bonds are very difficult to eliminate from an organic molecule.
Fluorinated b-diketones are one among the most studied
antenna molecules for NIR emitting LnIII ions, in view of the
minimum number of C–H vibrators present; however the elec-
tron attractive nature of the C–F bonds oen reduces the
aDepartment of Advanced Materials Chemistry and WCU Center for Next Generation
Photovoltaic Systems, Korea University, Jochiwon-eup, Sejong-si, 339-700, Republic
of Korea. E-mail: hkk777@korea.ac.kr; drbijusilvanose@gmail.com; Fax: +82-44-
860-1331; Tel: +82-44-860-1493
b
´
´ ´
Institute of Chemical Sciences and Engineering, Ecole Polytechnique Federale de
Lausanne, BCH 1402, CH-1015 Lausanne, Switzerland. E-mail: jean-claude.bunzli@
ep.ch; Fax: +41 21 693 5550; Tel: +41 21 693 9821
† Electronic supplementary information (ESI) available: NMR, EDS and PL data.
See DOI: 10.1039/c3tc31181c
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coordination ability of these molecules.13,14 Moreover, in most
of the reports, bidentate b-diketonates result in the formation of
neutral tris LnIII complexes with the metal coordination sphere
completed by either solvent molecules with O–H vibrators or
neutral donors with large numbers of C–H oscillators.13,14
To solve this problem, we have designed a new uorinated
b-diketone podand (H4L) by combining four well known uo-
rinated benzoyltriuoroacetone (BTFA) moieties anchored to a
single carbon atom and connected by four methoxy groups to
ensure enough exibility for the four diketonates to be able to
simultaneously coordinate the metal ion. Indeed, this molecule
is expected to form octa-coordinated anionic LnIII-b-diketonates
similar to the tetrakis(b-diketonates) with bidentate ligands,
which are known to be more luminescent than the tris
complexes.15 The graing of four coordination units onto a
single framework is expected to lead to larger chelate effect and
therefore higher binding constants compared to the parent.
For practical applications in optical devices it is oen
advantageous to incorporate the luminescent LnIII centres into
inert hosts like silica matrices, which in addition to combining
the properties of both organic and inorganic compounds ensure
better long-term stability and easier processability.16 Covalent
graing of ligands onto the backbone of silica networks like
MCM-41,5,17 SBA-1517,18 and xerogels19 via Si–C bonds is one of
the most common methods for generating homogeneous
hybrid materials with high mechanical stability. McCoy et al.
developed pH sensitive hydrogels based on the EuIII-quinoline
cyclen conjugate complex.20 Recently our group has developed a
new class of organic–inorganic hybrids based on a hierarchi-
cally ordered mesoporous organosilica, which shows sensitized
emission from ErIII and YbIII centres.21 However the NIR lumi-
nescence efficiencies of LnIII complexes in silica matrices
remain unimpressive in view of the O–H oscillators present in
the second coordination sphere.22 Another class of hybrid
materials, namely lanthanide–polymer hybrids, which
combines the good luminescent properties of lanthanide
complexes with the excellent mechanical processing properties
of organic polymers, seems to be better suited and is therefore
attracting hey attention.1 These materials nd applications as
plastic optical bres, lasing materials, and optical ampliers.1 A
widely used polymer host for luminescent lanthanide
complexes is poly-(methyl methacrylate) (PMMA) which is a low-
cost, simply prepared polymer with excellent optical proper-
ties.23,24 Thus, in the present work, we have doped the newly
developed visible and NIR emitting complexes into this matrix
to get highly transparent lms that can also be electrospun into
resins consisting of uniform wires of diameter 300–400 nm. The
optical properties of the newly synthesized complexes and
hybrid materials are reported and discussed.
Scheme 1 Synthetic procedure for the ligand H4L.
microanalysis data for 1–7 demonstrate that the Ln3+ : L4ꢀ mole
ratio is 1 : 1 and that one molecule of counter ion (Bu4N+) is
present. The carbonyl stretching frequency ns(C]O) of H4L
(1600 cmꢀ1) shis to 1623–1626 cmꢀ1 in 1–7 along with the
appearance of a new peak in the range 1678–1681 cmꢀ1, thus
indicating coordination of the carbonyl groups to the LnIII
cation in each case. Furthermore, the presence of signals in the
range 2800–2900 cmꢀ1 due to the –CH2– groups and the signal
around 1015–1017 cmꢀ1, ns(C–N), conrm the presence of
+
NBu4 in all isolated complexes. The absence of any broad
bands around 3500 cmꢀ1 ns(O–H) in 1–7 proves that they are
anhydrous and, therefore, that all four b-diketonate moieties
are coordinated to the LnIII cations. The thermal stability of the
complexes was examined by means of thermogravimetric
analysis and typical thermograms are depicted in Fig. 1. All the
complexes display two distinct decomposition steps. The rst
one, around 100 ꢂC, occurs with weight losses of 1.5–2% and is
related to the removal of adsorbed solvent molecules. Further
thermal decomposition of 1–7 appears to be more complex,
ꢂ
with steps around 210, 400, 600 and 700 C corresponding to
the loss of organic groups and formation of the metal oxides.
The residual weight is between 15 and 16% that is approxi-
mately equal to the weight of rare-earth oxides (calcd: 12.7–
14.0%). Most importantly, the thermal stability of these
complexes is as high as 210 ꢂC and none of them shows distinct
weight losses in the range 150–175 ꢂC, as expected for
complexes without solvent molecules in the rst coordination
sphere.
Ligand-centred luminescence and energy levels
Results and discussion
Spectroscopic characterization of H4L and [LnL]NBu4 (1–7)
The complexes described in this study were soluble only in
highly polar solvents such as DMF and DMSO. The highly
The synthetic procedures adopted for the ligand H4L and its coordinating DMSO can destroy the LnIII coordination sphere in
LnIII complexes (1–7) are described in Schemes 1 and 2, LnIII-b-diketonates. Hence solution studies were conducted in
respectively. The 1H and 13C NMR spectra of H4L are presented the less coordinating DMF medium. The UV-vis absorption
in Fig. S1 and S2 (ESI†). Vibrational spectroscopy and spectra of ligand H4L and its LnIII complexes 1–4 in DMF
6936 | J. Mater. Chem. C, 2013, 1, 6935–6944
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Scheme 2 Synthetic procedure for lanthanide complexes [LnL]NBu4 [Ln ¼ Sm (1), Gd (2), Er (3), Yb (4), Er0.5Yb0.5 (5), Er0.5Gd0.5 (6), Yb0.5Gd0.5 (7)].
around 328 and 274 nm. The overall shapes of the absorption
spectra in DMF and PMMA are, however, similar and hence one
can assume that the absorbing species remain the same in both
media. A rst conclusion is that these complexes can efficiently
absorb UV radiations and may be interesting as UV-protection
coatings and/or wavelength-converting materials.
It is known that the energy absorbed by the ligand-centred
absorption bands in LnIII complexes can undergo intersystem
crossing leading to enhanced population of its lowest triplet
level and subsequent energy transfer to the nearby LnIII-centred
4f states.27 This mechanism works for most of the LnIII
Fig. 1 Thermogravimetric curves of LnIII complexes 1–7.
solutions (Fig. 2a) and in PMMA (Fig. 2b) were recorded at room
temperature. Relevant data are gathered in Table 1. The
absorption spectrum of H4L shows two maxima at 323 nm and
272 nm with large molar absorption coefficients (ꢃ40–
42 000 Mꢀ1 cmꢀ1) and a shoulder at 285 nm. The peak around
323 nm can be attributed to the singlet–singlet (1p–p*) enolic
transitions of the b-diketone moieties25 while the features at
lower wavelengths are due to singlet–singlet (1p–p*) transitions
in the phenyl rings.26 The absorption spectra of the LnIII
complexes are similar to that of H4L except for a blue shi of the
shoulder at 285 nm to 278 nm and a red shi of the 323 nm
absorption to 329 nm. This is in accordance with the fact that
the conjugation in the b-diketonate moieties becomes larger
upon coordination with LnIII ions. Furthermore the molar
absorption coefficients of the lowest-energy transition calcu-
lated for 1–4 (ꢃ42–44 000 Mꢀ1 cmꢀ1) are similar and close to the
value for the free ligand, pointing to the presence of one L4ꢀ
anion bonded to each LnIII cation. The energy of the singlet
state level of the ligand was calculated from the higher
absorption wavelength edge of the absorption spectrum of 2,
Fig. 2 UV-vis absorption spectra (298 K) of (a) the ligand and its LnIII-complexes
in DMF (c z 10ꢀ6 M) and (b) LnIII complexes doped into PMMA films (4 wt%); the
and is equal to 26 700 cmꢀ1 (375 nm). The absorption spectra of
thin lms of PMMA doped with 4 wt% of 1, 3 and 4 are broader
thickness of the films is not the same for all samples and varies from 0.6 to
than those in DMF solution with two well resolved signals 0.9 mm.
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Table 1 UV-vis absorption spectral data (298 K) of the ligand and its LnIII-
complexes in DMF (c z 2 ꢄ 10ꢀ6 M) and in PMMA films
transfer pathways can be predicted as follows; they are sketched
in Fig. 4. The energy difference between the 3p–p* state of L4ꢀ
and the receiving SmIII(4G5/2) level is ꢃ3400 cmꢀ1 and hence one
may expect a reasonably efficient sensitization of the lumines-
cence of this ion. In a similar way the Er(2H11/2) level located at
19 100 cmꢀ1 or other ErIII levels such as 4S3/2 or 4F9/2 can accept
energy from the triplet state of L4ꢀ; subsequent intra-ion non-
radiative processes can then lead to population of the emitting
4I13/2 level. The situation for YbIII is not simple and may involve
Compound
lmax/nm (3/Mꢀ1 cmꢀ1
)
H4L
1
2
3
323 (42 000), 272 (40 360)
329 (44 240), 270 (26 899)
329 (42 442), 270 (39 250)
329 (42 442), 270 (37 093)
329 (41 931), 270 (31 562)
328, 274
4
1/PMMA 4 wt%
3/PMMA 4 wt%
4/PMMA 4 wt%
a mechanism assisted through the divalent state by electron
328, 273
328, 273
transfer, which necessitates an energy of about 19 000 cmꢀ1
.
3
LnIII-centred photophysical properties of homometallic
complexes
complexes except the one containing GdIII because its lowest
8
excited level, S7/2, is located at 32 150 cmꢀ1, well above the
triplet states of most organic chromophores. Thus investigation
of the luminescence spectra of the GdIII complex 2 gives useful
information about the ligand states.28,29 Fig. 3 displays the
uorescence spectra of H4L and 2 at 298 K as well as the
phosphorescence spectrum of 2 at 77 K obtained by excitation at
their absorption maxima. As is evident from this gure, the
emission maximum of H4L (428 nm) is substantially red shied
In order to determine the best excitation wavelength for each
LnIII complex, excitation spectra were recorded by monitoring
the emission wavelengths at 645 nm (SmIII), 1545 nm (ErIII) and
983 nm (YbIII). The spectra recorded for solid-state samples are
in the luminescence and phosphorescence spectra of
2
(500 nm). However, the luminescence spectrum of 2 at 298 K
shows a shoulder around 430 nm corresponding to uorescence
emission that disappears completely in the phosphorescence
spectrum recorded at 77 K with a time delay of 0.05 ms. Thus
the emission band centred at 500 nm can be considered as the
emission from the triplet (3p–p*) state of bound L4ꢀ. The low-
temperature phosphorescence spectrum of 2 could be decom-
posed into four Gaussian components at 469 nm (21 321 cmꢀ1),
500 nm (20 000 cmꢀ1), 552 nm (18 115 cmꢀ1) and 633 nm
(15 797 cmꢀ1). The most energetic component is assigned to the
0-phonon transition. With this at hand, ligand-to-metal energy
Fig. 4 Energy diagram for L4ꢀ and relevant LnIII ions.
Fig. 3 (a) Corrected fluorescence spectra of H4L (red curve) and 2 (blue curve) at
298 K, in solid state, and (b) corrected phosphorescence spectrum of 2 at 77 K and
its decomposition into Gaussian components (dispersion in CDCl3, c z 10ꢀ5 M,
delay increment 0.05 ms, lex ¼ 330 nm); vertical scales are arbitrary units.
Fig. 5 Excitation spectra of LnIII complexes 1, 3, and 4 in solid state at 298 K;
emission monitored at 645 nm (1), 1545 nm (3) and 983 nm (4); vertical scale:
arbitrary units.
6938 | J. Mater. Chem. C, 2013, 1, 6935–6944
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shown in Fig. 5, while those measured in DMF solutions and in transitions, I(4G5/2 / H9/2)/I(4G5/2 / H7/2), is identical in all
PMMA matrices are displayed in Fig. S3 and S4, respectively media, within experimental errors: 3.86 in solid state, 3.83 in
(ESI†). All these spectra are dominated by typical ligand-centred DMF and 3.84 in PMMA. This indicates that the local environ-
broad bands covering the entire UV region with a tail extending ment around the SmIII ion remains the same in all samples.
6
6
into the blue, up to 400 nm. The excitation spectra of solid-state
The emission spectra of the ErIII and YbIII complexes 3 and 4
samples of 1, 3, and 4 present two maxima, one around 360– cover both the visible (ligand emission centred at 500 nm, Fig. S5,
370 nm and the other around 270–280 nm, as well as a shoulder ESI†) and the NIR spectral ranges (Fig. 7). While the visible
around 320 nm. In addition to these broad bands some faint f–f emission spectrum of 4 resembles the one of the GdIII complex, the
6
4
6
transitions are also observed: P5/2, M19/2 ) H5/2 at 418 nm spectrum of 3 features a structured dip at 520 nm which can
(SmIII),8 2H11/2 ) 4I15/2 at 522 nm and 4F9/2 ) 4I15/2 at 654 nm be assigned to absorption from the ErIII ion through the 2H11/2
)
(ErIII).30 The very low intensities of these bands compared to the 4I15/2 hypersensitive transition. This, together with the intensity of
ligand-centred bands suggest that an antenna mechanism is the ligand emission band being much smaller in both 3 and 4 than
operative in all complexes. The solid-state excitation spectrum in 2, clearly indicates that energy transfer from L4ꢀ to ErIII and YbIII
of the YbIII complex 4 shows an additional broad and faint band is operative. This conclusion is further conrmed by the lifetime of
centred at 500 nm that could reect a contribution from the the triplet state of L4ꢀ which, at 77 K, is reduced to <50 ms in
electron-transfer mechanism involving YbII. The excitation complexes 3 and 4 from 845 ꢁ 5 ms in the GdIII compound,
spectra recorded in DMF solution are similar for all LnIII ions pointing to the role of the triplet state as the feeding level.
but are substantially different in shape compared to the solid-
The NIR emission spectra of complexes 3 and 4 in the three
state spectra: the most prominent feature is at 314–318 nm, media studied are very similar at 298 K (Fig. 7) with bands in the
corresponding to the shoulder in the solid-state spectra, while range 1460–1640 nm (maximum at 1545 nm, shoulders at 1500
the two other maxima lie at 275–280 and 350–355 nm. The and 1600 nm) for 3 and 930–1090 nm (maximum at 983 nm,
spectra of 1, 3 and 4 in PMMA matrices resemble those in DMF shoulders at 1003 and 1026 nm) for 4. They are due to the
4
2
solution with, however, broader bands. No lanthanide-centred Er(4I13/2 / I15/2) and Yb(2F5/2 / F7/2) transitions with split-
excitation bands are seen in these two media, pointing to a ting attributable to crystal eld effects.5,17,31,32 Furthermore, a
more efficient antenna mechanism compared to solid state.
weak anti-Stoke band around 950 nm is also present in the
When excited through the ligand-centred band at 315 nm, room temperature emission spectrum of 4 but is absent from
the SmIII complex emits typical narrow f–f bands in both visible the 77 K spectrum, which conrms its “hot band” nature.33 The
and NIR spectral ranges (Fig. 6). The spectra obtained are spectra recorded at low temperature (Fig. 8) have better reso-
identical in shape and peak positions whatever the medium is. lution and crystal eld components are easily spotted at 1545,
4
The observed bands are assigned to transitions from the G5/2 1585, and 1615 nm for ErIII and 983, 1005, and 1030 nm for
6
excited state to the lower energy levels of HJ ( J ¼ 5/2, 7/2, 9/2, YbIII.30 The observation of only 3 crystal eld components for
6
and 11/2) in the visible8 and FJ ( J ¼ 5/2, 7/2, and 9/2)5 in the Yb(2F7/2) is compatible with a cubic arrangement of the coor-
NIR. In comparison with the magnetic dipole transition 4G5/2
/
dinating atoms around the metal ion. Finally, the solid-state
4
6
6H7/2 at 602 nm, the electric dipole transition G5/2 / H9/2 at sample of the YbIII complex shows visible-light sensitized NIR
645 nm is much more intense and is responsible for the orange- emission when excited at 500 nm, both at 298 K and 77 K.
red emission colour.7 The intensity ratio between these two
The efficiency of visible and NIR emission of complexes 1, 3,
and 4 can be examined in terms of overall quantum yields (Fov)
Fig. 7 Corrected NIR emission spectra of (a) 3, and (b) 4 at 298 K in solid state
(black curves, lex ¼ 365 nm), in DMF (blue curves; c ¼ 10ꢀ5 M, lex ¼ 315 nm) and in 4
wt% doped PMMA films (red curves, lex ¼ 365 nm): vertical scales: arbitrary units.
Fig. 6 Corrected emission spectra of 1 at 298 K in solid state (black curve, lex
¼
365 nm), in DMF (blue curve; c ¼ 10ꢀ5 M, lex ¼ 315 nm) and in a 4 wt%-doped
PMMA film (red curve, lex ¼ 365 nm); vertical scales: arbitrary units.
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Fig. 9 Decay profiles of complexes 1 (orange curve), 3 (red curve), and 4 (blue
Fig. 8 Corrected NIR emission spectra of (a) 3, and (b) 4 at 77 K in solid state
(black curves, lex ¼ 365 nm), and in DMF (blue curves; c ¼ 10ꢀ5 M, lex ¼ 315 nm):
vertical scales: arbitrary units.
curve), in solid state at 298 K.
environment around the metal ions remains the same, hence
proving that the complexes are stable in DMF solution. The Fov
and sobs data listed here for the YbIII complex 4 are, to the best of
our knowledge, the highest values reported for anhydrous YbIII
complexes with uorinated b-diketonates34 (Table 3). However,
these values are not as high as the values published for
complexes with benzoyl-substituted 8-hydroxyquinolines.35
Compared to [Yb(BTFA)phen], complex 4 shows 2.8 times larger
Fov and 1.2 times longer sobs in solution, which can be attributed
to the suppression of the formation of potential conformers
arising from rotations of the phenyl groups around a single
bond, which are restricted in L4ꢀ compared to BTFA.
One of the main disadvantages of PMMA lms or sheets is
their brittleness, due to the high glass transition temperature. To
remedy this problem, Binnemans and co-workers produced
exible polymer lms with high luminescence efficiencies by
blending the polymer with a plasticizer.23 It is also known that
when the diameter of polymeric bre materials is shrunk to sub-
micrometers or nanometers, there appear several amazing
characteristics such as a very large surface area to volume ratio,
exibility in surface functionalities, and superior mechanical
performance like stiffness and tensile strength compared with
any other known form of the material. These outstanding prop-
erties make the polymer nanobres optimal candidates for
several important applications.36 Thus PMMA solutions doped
with 4 wt% of complexes 1, 3, and 4 were electrospun to fabricate
exible resins. Electron microscopy images reveal the presence of
uniform wires of diameter 300–400 nm (Fig. 10). The photo-
luminescent properties of these wires are similar to those of
doped lms as demonstrated by the excitation and emission
spectra displayed in Fig. S6 (ESI†) and 11, respectively, as well as
by overall quantum yield and excited-state lifetime data (Table 2).
and excited state lifetimes (sobs). The overall quantum yield is
regulated by the sensitization efficiency of the antenna molecule
(fsen) and the intrinsic luminescence quantum yield of the LnIII
ion (fLn): Fov ¼ fsenfLn.4 Data for Fov for samples 1 and 4 have
been determined at room temperature and are listed in Table 2.
In the case of SmIII, transitions in the visible region only have
been taken into consideration. The excited-state lifetime of
complexes 1, 3, and 4 at 298 K (sobs) has been investigated by
exciting the samples using a 355 nm pulsed laser line and
monitoring the NIR transitions 4G5/2 / 6F5/2 at ꢃ953 nm (SmIII),
4I13/2 / 4I15/2 at ꢃ1545 nm (ErIII) and 2F5/2 / 2F7/2 at ꢃ983 nm
(YbIII), respectively. All the decay curves could be tted with
single exponential functions, consistent with the presence of a
single major luminescent species in the complexes. Calculated
values are given in Table 2 and typical decay proles obtained for
the solid-state samples are shown in Fig. 9. As expected, the SmIII
complex has the highest values in all media for Fov and sobs
compared to ErIII and YbIII while Fov could not be measured for
ErIII due to the too low emission intensity. Introduction of the
complexes into PMMA leads to mixed effects: it is benecial for
SmIII which then features the largest quantum yield measured,
but the excited state lifetime is shortened by about 8 and 20%
compared to solid state for SmIII and YbIII while it remains
constant for ErIII. On the other hand, there are no drastic
differences in lifetimes between solid-state samples and DMF
solutions for the three LnIII ions, suggesting that the local
Table
2
Excited-state lifetimes (sobs
)
and overall quantum yields (Fov
)
of
complexes 1, 3, and 4 at 298 K
3
1
4
LnIII-centred photophysical properties of heterometallic
compounds
The YbIII ion has one order of magnitude higher absorption
cross-section at 980 nm than ErIII. Hence co-doping materials
with both ErIII and YbIII ions is a usual method to improve the
Complex
Fov (%)
sobs (ms)
sobs (ms) Fov (%)
sobs (ms)
Solid
DMF
3.4 ꢁ 0.5 79.1 ꢁ 0.1 1.6 ꢁ 0.1 2.6 ꢁ 0.4 12.1 ꢁ 0.1
2.5 ꢁ 0.4 72.5 ꢁ 0.1 1.5 ꢁ 0.1 1.8 ꢁ 0.3 12.3 ꢁ 0.1
PMMA lm 4.0 ꢁ 0.6 72.7 ꢁ 0.1 1.6 ꢁ 0.1 n.d.
PMMA wires 4.0 ꢁ 0.6 73.1 ꢁ 0.1 1.6 ꢁ 0.1 n.d.
9.7 ꢁ 0.1
9.8 ꢁ 0.1
6940 | J. Mater. Chem. C, 2013, 1, 6935–6944
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Table 3 Photophysical data for YbIII-b-diketonate complexes at room temperature reported in the literaturea
Fov (%)
sobs (ms)
Complex
Solid State
Toluene
Solid state
Toluene
PMMA
Ref.
[YbL]NBu4 (4)
2.6 ꢁ 0.4
1.8 ꢁ 0.3b
1.1 ꢁ 0.1
1.20
0.88
0.65
0.88
0.98
0.92
12.1 ꢁ 0.1
12.3 ꢁ 0.1b
10.4
11.7
11.8
10.4
10.7
11.0
10.5
9.7 ꢁ 0.1
10.7
11.1
11.0
—
—
—
—
This work
13 and 34
[Yb(TTA)3(phen)]
[Yb(THFP)3(phen)]
[Yb(TTDFH)3(phen)]
[Yb(BTFA)3(phen)]
[Yb(BHFP)3(phen)]
[Yb(BTDFA)3(phen)]
[Yb(BHDFD)3(phen)]
1.6 ꢁ 0.2
12.01 ꢁ 0.02
—
—
—
—
—
—
—
—
—
—
—
—
34
34
34
34
34
34
a
TTA
¼
2-thenoyltriuoroacetone, THFP
¼
2-thenoylheptauoropentanone, TTDFO
¼
2-thenoyltridecyluorooctanone, BTFA
benzoyltridecyluorooctanone, BHDFD
¼
¼
benzoyltriuoroacetone,
BHFP
¼
benzoylheptauoropentanone,
BTDFO
¼
benzoylheptadecyluorodecanone, phen ¼ 1,10-phenanthroline. b Measured in DMF (c ¼ 10ꢀ5 M).
Fig. 11 Corrected emission spectra of 1, 3, and 4 doped into PMMA fibres (4 wt
%) at 298 K. Vertical scale: arbitrary units.
Fig. 10 SEM images of 1 (a), 3 (b) and 4 (c) doped PMMA resins (4 wt%).
Magnification: ꢄ 15 000, scale bar ¼ 1 mm (left); ꢄ 50 000, scale bar ¼ 200 nm
(right).
pumping efficiency of ErIII ions.14 Indirect excitation of the ErIII
ions occurs mainly via energy transfer from the Yb(2F5/2) level to
the Er(4I11/2, 4I13/2) levels. Thus we have synthesized the hetero-
bimetallic complex [Er0.5Yb0.5L]NBu4 (5) and, for comparison
purposes, [Er0.5Gd0.5L]NBu4 (6) and [Gd0.5Yb0.5L]NBu4 (7). The
atomic ratios between different lanthanides present in each of
the complexes were conrmed by EDS analysis (Fig. S7 and
Table S1, ESI†). The excitation spectra of 5 obtained by moni-
toring the emission signals around 1545 nm (ErIII) and 983 nm
(YbIII) are similar to those of its pure counterparts 3 and 4, and
are dominated by the ligand centred band with main maximum
at 365 nm (Fig. S8, ESI†). When excited at this wavelength, the
Fig. 12 Corrected emission spectra of 5–7 at 298 K in solid state, inset: ErIII
emission.
emission spectrum of 5 shows transitions related to both ErIII (ꢀ20%) is observed in comparison with that of complex 7. This
and YbIII centres (Fig. 12). The strength of the ErIII transition is fact is related to energy transfer between the YbIII and ErIII ions,
much weaker than that of the YbIII signal; however it has larger since the 4I13/2 level of ErIII (6500 cmꢀ1) lies ꢃ3500 cmꢀ1 below
luminescence intensity (+60%) than complex 6. On the other the Yb(2F5/2) level. This conclusion is substantiated by the
hand, a decrease in the intensity of the YbIII-centred emission values of overall quantum yields and excited state lifetimes: for
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Paper
YbIII, Fov ¼ 1.4 ꢁ 0.2% and sobs ¼ 9.4 ꢁ 0.1 ms are smaller than dry dimethylformamide (DMF, 20 mL) was stirred and heated at
ꢂ
the values obtained for 7 (Fov ¼ 1.6 ꢁ 0.2% and sobs ¼ 10.3 ꢁ 90 C for 96 h. The hot mixture was cooled, diluted with H2O
0.1 ms). On the other hand the excited-state lifetimes obtained (20 mL) and the product was extracted with CHCl3 (2 ꢄ 35 mL).
for the ErIII luminescence in complexes 5 (1.5 ꢁ 0.1 ms) and 6 The CHCl3 layer was washed with H2O and brine and was then
(1.6 ꢁ 0.1 ms) are identical, within experimental errors. The dried over anhydrous Na2SO4. The product was obtained as a
YbIII-to-ErIII energy transfer efficiency in the mixed metallic pale yellow solid by precipitation from hexane (250 mL). In the
complex 5 can be computed from fLn/Ln ¼1 ꢀ (c/c0)37,38 where second step the tetraacetylphenone synthesized in the rst step
c and c0 are the quantum yields or lifetimes of the YbIII(2F5/2
)
(1.25 mmol) and NaOMe (5 mmol) were added to 20 mL of dry
level in the presence and absence of acceptor, respectively. The tetrahydrofuran (THF) and stirred for 10 min at room temper-
fLn/Ln values obtained by taking these two parameters into ature. To this solution, ethyltriuoroacetate (5 mmol) was
account are in reasonable agreement: 12.5 and 8.9%, added dropwise in an inert atmosphere and stirred for 48 h. To
respectively.
the resulting solution, 50 mL of 2 M HCl were added, and the
mixture was extracted twice with dichloromethane (2 ꢄ 35 mL).
The organic layer was separated and dried over Na2SO4, and the
product was obtained by precipitation upon addition of hexane
(250 mL).
Conclusions
We have designed a novel podand featuring four uorinated b-
diketone arms derived from benzoyltriuoroacetone which
forms 1 : 1 complexes with trivalent lanthanide ions, saturating
their coordination sphere. Photoluminescence studies show
that the newly designed antenna molecule is highly efficient in
sensitizing SmIII (both in the visible and NIR ranges) and YbIII
luminescence and can provide sizable sensitization for ErIII
ions. The emission quantum yields and the luminescence life-
times at room-temperature obtained for the YbIII complex in the
present study are the highest among many YbIII complexes with
uorinated b-diketonate ligands. Furthermore YbIII / ErIII
energy transfer is used as a tool to improve the emission
intensity of the ErIII transition around 1.5 mm in a hetero-
bimetallic complex. The complexes can be easily doped into
PMMA matrices to give luminescent, photo-stable lms and
exible resins under the form of wires. In addition to these
interesting emission properties, the novel hybrid materials
reported here have large absorption coefficient in the entire UV
range and in the blue, up to 400 nm, that make them potential
candidates as UV-protection coatings, wavelength converting
materials in photovoltaics, or for optical amplication in the
eld of telecommunications.
H4L (pale yellow solid). Yield: 95%. Anal. calcd for
C
45H32F12O12 (992.71): C, 54.45; H, 3.25; found: C, 54.79; H,
3.39. FTIR (KBr, cmꢀ1): 3450 (ns O–H); 3071 (n Csp2H); 2956, 2886
(n Csp3H); 1600 (ns C]O); 1509, 1464, 1312 (n C]C); 1267, 1065
(ns C–O); 1172, 1145 (d C–H); 1110 (ns C–F); 845, 794 (d C–H); 704
1
(d CF3). H NMR (CDCl3, 300 MHz), d (ppm): 4.48 (8H, s), 6.48
(4H, s), 7.03 (8H, d; J ¼ 9.0), 2.92 (8H, d; J ¼ 8.7), 15.31 (4H, s:
broad). 13C NMR (CDCl3, 300 MHz) d (ppm): 44.99 (C); 66.52(–O–
CH2–); 91.78 (CO–CH–CO); 115.50, 126.38, 130.13, 163.05
(phenyl); 126.39 (CF3); 176.36, 188.72 (CO). m/z ¼ 1081.11 [M ꢀ
4H+ 4Na + H]+.
Synthesis of the LnIII complexes [LnL]NBu4
To an ethanolic suspension of H4L (10 mL), 4 mmol of aqueous
NaOH (2 M) were added at room temperature and the mixture
was stirred until complete dissolution of H4L. Required
volumes of aqueous LnIII nitrates were then added slowly and
the solution was diluted to 50 mL with THF. The reaction
ꢂ
mixture was then stirred for 6 h at 50 C. A solution of Bu4NBr
(1.05 mmol) in deionized water/THF (5/10 mL) was then added,
resulting in the formation of a precipitate (Scheme 2). Aer
stirring the mixture for 6 h at 50 ꢂC, the pale yellow solid
product was ltered, washed with n-hexane, and dried. The
obtained [LnL]NBu4 complexes were re-dissolved in DMF,
ltered and the ltrate was allowed to stand for a period of 3–4
weeks. The [LnL]NBu4 complexes were obtained as yellow
powders and were dried in a vacuum at 50 ꢂC for 2 days. Yield:
90–95%. The limited solubility of LnLNBu4 in common organic
solvents prevented the isolation of single crystals suitable for
X-ray analysis: the complexes are soluble only in DMF and
DMSO and efforts to grow single crystals from solvent combi-
nations involving DMF and DMSO were not successful.
Experimental section
Materials
Lanthanide(III) nitrate hexahydrates, 99.9%, were obtained
from Sigma Aldrich (Ln ¼ Sm, Gd, Er, Yb). 4-Hydroxy-
acetophenone 99.9% (Sigma Aldrich), 1,3-dibromo-2,
2-bis(bromomethyl)propane 99.9% (Sigma Aldrich), ethyl-
triuoroacetate 99.9% (Sigma Aldrich), tetra-n-butylammo-
niumbromide (C4H9)4NBr 99.9% (Acros Organics), polymethyl
methacrylate (PMMA) (Alfa Aesar), and sodium methoxide
99.9% (Sigma Aldrich) were used without further purication.
Solvents were dried using standard methods. All the other
chemicals used were of analytical reagent grade.
[SmL]NBu4 (1) (yellow solid). Yield: 92%. Anal. calcd for
C
61H64F12NO12Sm (1381.50): C, 53.03; H, 4.67; N, 1.01; found: C,
53.21; H, 4.79; N, 1.10. FTIR (KBr, cmꢀ1): 3072 (n Csp2H); 2964,
2940, 2878 (n Csp3H); 1681, 1623 (ns C]O); 1597, 1505, 1468,
Synthesis of the ligand H4L
The ligand H4L was prepared by a two-step process with an 1309 (n C]C); 1288, 1240 (ns C–O); 1173, 1125 (d C–H); 1118
overall yield of 95% (Scheme 1). In the rst step, a mixture of (ns C–F); 1019 (ns C–N); 842, 783 (d C–H); 703 (d CF3).
1,3-dibromo-2,2-bis(bromomethyl)propane
(1.25
mmol),
[GdL]NBu4 (2) (yellow solid). Yield: 95%. Anal. calcd for
4-hydroxyacetophenone (5 mmol), and K2CO3 (5.10 mmol) in
C
61H64F12GdNO12 (1388.39): C, 52.77; H, 4.65; N, 1.01; found: C,
6942 | J. Mater. Chem. C, 2013, 1, 6935–6944
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52.91; H, 4.80; N, 1.07. FTIR (KBr, cmꢀ1): 3071 (n Csp2H); 2965, YbIII, a solid state sample of [Yb(TTA)3(phen)] was used as
2938, 2876 (n Csp3H); 1678, 1625 (ns C]O); 1598, 1500, 1471, standard (Fov¼1.6%).13 The values reported are averages of 6
1308 (n C]C); 1288, 1244 (ns C–O); 1173, 1124 (d C–H); 1118 different measurements with an estimated error of ꢁ15%. NIR
(ns C–F); 1015 (ns C–N); 840, 781 (d C–H); 704 (d CF3).
luminescence lifetimes were measured with a previously
[ErL]NBu4 (3) (yellow solid). Yield: 95%. Anal. calcd for described instrumental setup.40 The PMMA lms were obtained
C
61H64 ErF12NO12 (1398.40): C, 52.39; H, 4.61; N, 1.00; found: C, by drop casting and the resins were prepared with the eS-Robot
52.51; H, 4.81; N, 1.05. FTIR (KBr, cmꢀ1): 3070 (n Csp2H); 2965, electrospinning system from NanoNc Co. Ltd, Korea. DMF
2940, 2877 (n Csp3H); 1678, 1626 (ns C]O); 1598, 1500, 1470, solutions of PMMA doped with 4 wt% of LnIII complexes were
1308 (n C]C); 1288, 1245 (ns C–O); 1173, 1124 (d C–H); 1118 (ns taken in a syringe with a needle of gauge 23 G and electrospun
C–F); 1017 (ns C–N); 840, 781 (d C–H); 704 (d CF3).
by applying a voltage of 8 kV between the solution and the
[YbL]NBu4 (4) (yellow solid). Yield: 95%. Anal. calcd for counter electrode kept at a distance of 10 cm.
C
61H64F12NO12Yb (1404.18): C, 52.18; H, 4.59; N, 1.00; found: C,
52.41; H, 4.77; N, 1.10. FTIR (KBr, cmꢀ1): 3069 (n Csp2H); 2965,
2939, 2877 (n Csp3H); 1678, 1625 (ns C]O); 1598, 1501, 1470,
Acknowledgements
1308 (n C]C); 1288, 1244 (ns C–O); 1173, 1124 (d C–H); 1118 This research was supported by the World Class University
(ns C–F); 1016 (ns C–N); 840, 781 (d C–H); 702 (d CF3). Program funded by the Ministry of Education, Science, and
[Er0.5Yb0.5L]NBu4 (5) (yellow solid). Yield: 95%. Anal. calcd Technology through the National Research Foundation of Korea
for C61H64Er0.5F12NO12Yb0.5 (1401.29): C, 52.28; H, 4.60; N, 1.00; (grant R31-2012-000-10035-0), and by a grant from Korea
found: C, 52.40; H, 4.70; N, 1.10. FTIR (KBr, cmꢀ1): 3071 University (2010). One of the authors (S. B.) thanks Collegiate
(n Csp2H); 2965, 2937, 2877 (n Csp3H); 1678, 1625 (ns C]O); 1599, Education Dept. and Dept. of Higher Education Govt. of Kerala,
1500, 1470, 1308 (n C]C); 1288, 1246 (ns C–O); 1173, 1124 (d India for granting leave without allowance for doing post-
C–H); 1118 (ns C–F); 1015 (ns C–N); 841, 781 (d C–H); 704 (d CF3). doctoral research.
[Er0.5Gd0.5L]NBu4 (6) (yellow solid). Yield: 95%. Anal. calcd
for C61H64 Er0.5F12 Gd0.5NO12 (1393. 40): C, 52.58; H, 4.63; N,
Notes and references
1.01; found: C, 52.80; H, 4.75; N, 1.06. FTIR (KBr, cmꢀ1): 3071
(n Csp2H); 2965, 2938, 2878 (n Csp3H); 1678, 1626 (ns C]O); 1598,
1500, 1472, 1308 (n C]C); 1288, 1244 (ns C–O); 1173, 1124 (d C–
H); 1119 (ns C–F); 1015 (ns C–N); 840, 781 (d C–H); 703 (d CF3).
[Yb0.5Gd0.5]LNBu4 (7) (yellow solid). Yield: 95%. Anal. Calcd
for C61H64F12Gd0.5NO12Yb0.5 (1396. 29): C, 52.47; H, 4.62; N,
1.00; found: C, 52.72; H, 4.81; N, 1.10. FTIR (KBr, cmꢀ1): 3070
(n Csp2H); 2966, 2938, 2877 (n Csp3H); 1679, 1626 (ns C]O); 1598,
1500, 1470, 1308 (n C]C); 1288, 1245 (ns C–O); 1174, 1124 (d
C–H); 1118 (ns C–F); 1016 (ns C–N); 840, 781 (d C–H); 705 (d CF3).
1 K. Kuriki, Y. Koike and Y. Okamoto, Chem. Rev., 2002, 102,
2347–2356.
2 H. J. M. A. A. Zijlmans, J. Bonnet, J. Burton, K. Kardos, T. Vail,
R. S. Niedbala and H. J. Tanke, Anal. Biochem., 1999, 267, 30–36.
¨
3 S. Comby and J.-C. G. Bunzli, in Handbook on the Physics and
Chemistry of Rare Earths, ed. K. A. Gschneidner Jr, J.-C. G.
¨
Bunzli and V. K. Pecharsky, Elsevier, 2007, pp. 217–470.
4 S. Quici, M. Cavazzini, G. Marzanni, G. Accorsi, N. Armaroli,
B. Ventura and F. Barigelletti, Inorg. Chem., 2005, 44, 529–
537.
5 L.-N. Sun, J.-B. Yu, H.-J. Zhang, Q.-G. Meng, E. Ma, C.-Y. Peng
and K.-Y. Yang, Microporous Mesoporous Mater., 2007, 98,
156–165.
6 B. Chu, W. L. Li, Z. R. Hong, F. X. Zang, H. Z. Wei,
D. Y. Wang, M. T. Li, C. S. Lee and S. T. Lee, J. Phys. D:
Appl. Phys., 2006, 39, 4549–4552.
7 K. Miyata, T. Nakagawa, R. Kawakami, Y. Kita, K. Sugimoto,
T. Nakashima, T. Harada, T. Kawai and Y. Hasegawa, Chem.–
Eur. J., 2011, 17, 521–528.
8 X. Y. Chen, M. P. Jensen and G. K. Liu, J. Phys. Chem. B, 2005,
109, 13991–13999.
Methods
Elemental analyses were performed with a Perkin-Elmer Series 2
Elemental Analyzer 2400. A Perkin-Elmer Spectrum One FT-IR
spectrometer using KBr (neat) was used to obtain the IR spectral
data. Mass spectrum of the ligand H4L was recorded on a JEOL
JSM 600 fast atom bombardment high resolution mass spec-
trometer (FABMS) and the thermogravimetric analyses were
performed on a TGA-50H instrument (Shimadzu, Japan). SEM
and EDS analyses were performed on a JEOL JSM-5600LV
microscope. Absorption spectra of the ligands and complexes
were recorded in DMF solution and PMMA lms on a UV-2450
9 S. I. Weissman, J. Chem. Phys., 1942, 10, 214–217.
spectrophotometer (Shimadzu). Photoluminescence spectra 10 N. Sabbatini, M. Guardigli and J.-M. Lehn, Coord. Chem. Rev.,
were collected on a Fluorolog FL 3-22 spectrometer from 1993, 123, 201–228.
Horiba-Jobin Yvon-Spex equipped for both visible and NIR 11 J.-M. Lehn, Angew. Chem., Int. Ed., 1990, 29, 1304–1319.
measurements and were corrected for the instrumental func- 12 I. Hernandez, Y.-X. Zheng, M. Motevalli, R. H. C. Tan,
tion. NIR luminescence studies were conducted under Ar
atmosphere. Powdered samples were put into 2 mm i.d. quartz
W. P. Gillin and P. B. Wyatt, Chem. Commun., 2013, 49,
1933–1935.
¨
capillaries. The PMMA lms with size ꢃ10 ꢄ 5 mm were used as 13 L. N. Puntus, K. J. Schenk and J.-C. G. Bunzli, Eur. J. Inorg.
such. Overall quantum yield data for SmIII in the visible spectral
Chem., 2005, 4739–4744.
range and for YbIII in NIR were acquired at rt on the same 14 Q. Zhong, H. Wang, G. Qian, Z. Wang, J. Zhang, J. Qiu and
instrument using a home-modied integrating sphere;39 for
M. Wang, Inorg. Chem., 2006, 45, 4537–4543.
This journal is ª The Royal Society of Chemistry 2013
J. Mater. Chem. C, 2013, 1, 6935–6944 | 6943

View Article Online
Journal of Materials Chemistry C
Paper
15 K. Binnemans, Chem. Rev., 2009, 109, 4283–4374.
16 B. Yan, RSC Adv., 2012, 2, 9304–9324.
29 N. S. Baek, M. K. Nah, Y. H. Kim and H. K. Kim, J. Lumin.,
2007, 127, 707–712.
¨
17 L.-N. Sun, H.-J. Zhang, C.-Y. Peng, J.-B. Yu, Q.-G. Meng, 30 C. Reinhard and H. U. Gudel, Inorg. Chem., 2002, 41, 1048–
L.-S. Fu, F.-Y. Liu and X.-M. Guo, J. Phys. Chem. B, 2006,
110, 7249–7258.
18 L.-N. Sun, H.-J. Zhang, J.-B. Yu, S.-Y. Yu, C.-Y. Peng, S. Dang,
X.-M. Guo and J. Feng, Langmuir, 2008, 24, 5500–5507.
1055.
31 L.-N. Sun, J.-B. Yu, G.-L. Zheng, H.-J. Zhang, Q.-G. Meng,
C.-Y. Peng, L.-S. Fu, F.-Y. Liu and Y.-N. Yu, Eur. J. Inorg.
Chem., 2006, 3962–3973.
19 B. Tong, S. Wang, Y. Meng and B. Wang, Photochem. 32 J. Zhang and S. Petoud, Chem.–Eur. J., 2008, 14, 1264–1272.
¨
33 F. R. Gonçalves e Silva, O. L. Malta, C. Reinhard, H.-U. Gudel,
Photobiol. Sci., 2007, 6, 519–520.
¨
20 C. P. McCoy, F. Stomeo, S. E. Plush and T. Gunnlaugsson,
Chem. Mater., 2006, 18, 4336–4343.
C. Piguet, J. E. Moser and J.-C. G. Bunzli, J. Phys. Chem. A,
2002, 106, 1670–1677.
21 S. Biju, Y. K. Eom, J.-C. G. Bunzli and H. K. Kim, J. Mater. 34 M. P. Tsvirko, S. B. Meshkova, V. Y. Venchikov,
Chem. C, 2013, 1, 3454–3466.
Z. M. Topilova and D. V. Bol'shoi, Opt. Spectrosc., 2001, 90,
669–673.
22 A. Mech, A. Monguzzi, F. Meinardi, J. Mezyk, G. Macchi and
R. Tubino, J. Am. Chem. Soc., 2010, 132, 4574–4576.
23 K. Lunstroot, K. Driesen, P. Nockemann, L. Viau,
¨
35 N. M. Shavaleev, R. Scopelliti, F. Gumy and J.-C. G. Bunzli,
Inorg. Chem., 2009, 48, 7937–7946.
P. H. Mutin, A. Vioux and K. Binnemans, Phys. Chem. 36 Z.-M. Huanga, Y.-Z. Zhangb, M. Kotakic and S. Ramakrishna,
Chem. Phys., 2010, 12, 1879–1885. Comp. Sci. Technol., 2003, 63, 2223–2253.
24 Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisa, Y. Kai 37 S. Biju, D. B. Ambili Raj, M. L. P. Reddy, C. K. Jayasankar,
and S. Yanagida, J. Phys. Chem. A, 2003, 107, 1697–1702.
25 S. Biju, D. B. A. Raj, M. L. P. Reddy and B. M. Kariuki, Inorg.
Chem., 2006, 45, 10651–10660.
26 H.-F. Li, P.-F. Yan, P. Chen, Y. Wang, H. Xu and G.-M. Li,
Dalton Trans., 2012, 41, 900–907.
A. H. Cowley and M. Findlater, J. Mater. Chem., 2009, 19,
1425–1432.
38 D. Ananias, M. Kostova, F. A. Almeida Paz, A. Ferreira,
L. D. Carlos, J. Klinowski and J. Rocha, J. Am. Chem. Soc.,
2004, 126, 10410–10417.
¨
27 G. A. Crosby, R. E. Whan and R. M. Alire, J. Chem. Phys., 1961, 39 A. Aebischer, F. Gumy and J.-C. G. Bunzli, Phys. Chem. Chem.
34, 743–748. Phys., 2009, 11, 1346–1353.
28 S. Biju, M. L. P. Reddy, A. H. Cowley and K. V. Vasudevan, 40 N. M. Shavaleev, R. Scopelliti, F. Gumy and J.-C. G. Bunzli,
J. Mater. Chem., 2009, 19, 5179–5187. Inorg. Chem., 2008, 47, 9055–9068.
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This journal is ª The Royal Society of Chemistry 2013