Synthesis and characterisation of a novel europium(iii)-containing heptaisobutyl-POSS

Article abstract of DOI:10.1039/c4nj00157e

A novel luminescent metal-containing POSS, bearing in the structure the europium ion, was synthesized and characterized. The corner-capping reaction between the partially condensed isobutyl-POSS (molecular formula (C ₄H₉)₇Si₇O₉(OH) ₃) and the anhydrous EuCl₃, under basic conditions, led to a completely condensed Eu(iii)-containing POSS. The molecular compound involves THF molecules, coming from the reaction medium, in the coordination sphere on Eu(iii). A deep optical characterization demonstrated that the Eu(iii)-POSS sample is characterized by a quantum efficiency of ca. 14% and high photostability. Both these properties render this molecular platform an ideal candidate for the construction of luminescent devices and light-harvesting systems. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4nj00157e

NJC
View Article Online
View Journal | View Issue
PAPER
Synthesis and characterisation of a novel
europium(III)-containing heptaisobutyl-POSS†
Stefano Marchesi,a Fabio Carniatoa and Enrico Boccaleri*ab
Cite this: New J. Chem., 2014,
38, 2480
A novel luminescent metal-containing POSS, bearing in the structure the europium ion, was synthesized and
characterized. The corner-capping reaction between the partially condensed isobutyl-POSS (molecular
formula (C4H9)7Si7O9(OH)3) and the anhydrous EuCl3, under basic conditions, led to a completely condensed
Eu(III)-containing POSS. The molecular compound involves THF molecules, coming from the reaction
medium, in the coordination sphere on Eu(III). A deep optical characterization demonstrated that the
Eu(III)-POSS sample is characterized by a quantum efficiency of ca. 14% and high photostability. Both
these properties render this molecular platform an ideal candidate for the construction of luminescent
devices and light-harvesting systems.
Received (in Victoria, Australia)
30th January 2014,
Accepted 4th March 2014
DOI: 10.1039/c4nj00157e
www.rsc.org/njc
POSS can react with a large variety of metal centres (in the form of
alkoxides or chlorides), thus affording a completely condensed
1. Introduction
Polyhedral oligomeric silsesquioxanes (POSS) are a class of metal-silsesquioxane species (M-POSS).13–17
condensed three dimensional oligomeric organosiliceous com-
The ‘‘Periodic Table of metal-containing POSS’’ already covers
pounds with the cage framework having different geometries numerous chemical elements spanning from alkali metals to
and symmetries. As a general feature, the molecular structure transition and lanthanide ions and the chemistry of these solids
of these compounds consists of silicon atoms bonded to one- continues to be an area of vigorous research activity. Very recently,
and-a-half oxygen (‘‘sesqui-’’) and hydrocarbon (‘‘-ane’’) moieties lanthanide-containing POSS (Ln-POSS) have attracted interest
(herein denoted as R), leading to (RSiO1.5) bond units. The most because of their potential use in homogeneous/heterogeneous
common materials are cubic systems, with general formula catalysis and the biomedical field. Indeed, different Ln-POSS
1–3
R8Si8O12
.
containing Ce(III),18 Er(III),19 and Gd(III)20 with definite architecture
POSS molecules due to their high chemical versatility, good have been explored. Nevertheless, as a general comment, informa-
stability and molecular size have attracted growing interest in the tion on well-characterized lanthanide silsesquioxane derivatives is
last decade as hybrid nanostructured 3D nanomaterials, finding still quite limited. Furthermore, luminescent metal centres such
applications in several fields, spanning from catalysis,4–6 to bio- as europium, to the best of our knowledge, have not been deeply
medical7,8 and diagnostic uses,9,10 to the preparation of nano- investigated in combination with molecular POSS structures.
composite materials with improved physico-chemical features.11,12
It is worth noting that luminescent lanthanides are well
Besides fully condensed polyhedral silsesquioxanes that are known as efficient luminophores when combined with specific
generally identified with a cubic R8Si8O12 structure, open-corner ‘‘antenna’’ groups (typically based on aromatic functionalities),
POSS compounds, structurally related to cubic systems where a Si which emit a long-living narrow band of practically monochromatic
vertex is removed leaving incompletely condensed silanol groups radiation through the strong optical absorption in the ultraviolet
(with general formula R7Si7O9(OH)3), seem to be currently more region. However, they have not so far been used extensively in
interesting, because of their capability to link different function- practical applications mainly due to their poor thermal stability and
alities through the reaction with specific organosilane and low mechanical resistance. The encapsulation of these lanthanide
heteroelement precursors. In particular, partially condensed ions, through anchoring and embedding procedures, into sol–
gel-derived materials21 can circumvent these shortcomings and
a Dipartimento di Scienze e Innovazione Tecnologica, Centro Interdisciplinare
can therefore lead to lanthanide-based luminescent materials.
Following this idea, a novel Eu(III)-containing POSS (hereafter
named Eu(III)-POSS) was synthesized in this manuscript, starting
from a partially condensed isobutyl-POSS. The structure and the
optical properties of this molecule were investigated in view of its
potential use in conversion devices such as LEDs, light emitting
sensors and imaging diagnostic probes.
`
NanoSistemi, Universita del Piemonte Orientale, Viale Teresa Michel 11,
15121 Alessandria, Italy. E-mail: enrico.boccaleri@unipmn.it;
Fax: +39 0131360250; Tel: +39 0131260264
b Nova Res S.r.l. – Via G. Bovio, 6 – 28100 Novara, Italy. E-mail: info@novares.org;
Web: www.novares.org; Fax: +39 0321 1850924; Tel: +39 0321 1850492
† Electronic supplementary information (ESI) available: Details of the physico-
chemical characterization of Eu(III)-POSS. See DOI: 10.1039/c4nj00157e
2480 | New J. Chem., 2014, 38, 2480--2485
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
Paper
NJC
2. Experimental section
2.1 Materials
at 320 and 395 nm. Eu(III)-POSS was characterized in solid state
form and in CHCl3 solution. Time-resolved measurements were
performed by using the time-correlated single-photon counting
(TCSPC) option. A 370 nm spectraLED laser was used to excite the
sample. Signals were collected using an IBH DataStation Hub
photon counting module. Data analysis was performed using the
commercially available DAS6 software (HORIBA Jobin Yvon IBH).
Heptaisobutyl-trisilanol POSS (1), provided by Nova Res S.r.l.
(Novara, Italy), was used as a precursor for the preparation
of Eu(III)-POSS. In general, all solvents, freshly opened, were
used without any further purification. Particular care was taken
only for THF, that was purified before use by distillation on
Na/benzophenone to remove traces of radicals and water.
Eu(III)-POSS synthesis. Anhydrous EuCl3 (170 mg, 0.66 mmol,
Sigma Aldrich) was added with vigorous stirring to a solution of
3. Results and discussion
(1) (500 mg, 0.63 mmol) in 90 mL of anhydrous distilled THF, in Eu(III)-POSS was prepared following the synthetic procedure
the presence of 272 mL of triethylamine (Et3N Z99%, Sigma adopted in the literature by Edelmann et al. to synthesize the
Aldrich). The reaction solution was carefully purged with nitrogen. parent Ce(III)-POSS and Er(III)-POSS samples.18,19 In detail, Eu(III)-
The temperature was increased to 50 1C and the mixture stirred POSS synthesis was performed in a single step, through the
for 24 h. Finally, the solvent was evaporated until a white corner-capping reaction of a partially condensed silsesquioxane,
powder was obtained. The sample was washed with water and the heptaisobutyl-trisilanol POSS (1), with anhydrous EuCl3 in
THF in order to remove a large part of un-reacted residues and distilled THF and in the presence of triethylamine (Et3N). The
by-products, thus obtaining the Eu(III)-POSS sample (2).
reaction was carried out at 50 1C, under nitrogen flow, for 24 hours
(Scheme 1). A white powder was obtained and washed with water
and THF solvent in order to remove a large fraction of un-reacted
residues and by-products. The Eu(III)-POSS sample (2) was success-
fully obtained. A schematic view of a possible chemical structure of
the Eu(III)-POSS sample is reported in Scheme 1.
2.2 Characterization
The 13C NMR spectrum of Eu(III)-POSS, dissolved in CDCl3, was
recorded using a JEOL Eclipse Plus spectrometer equipped with
a 9.4 T magnet.
The occurrence of the corner-capping reaction of the open cage
POSS was monitored by FT-IR spectroscopy. The IR spectrum of
the Eu(III)-POSS sample, recorded in KBr pellets, was compared
to the vibrational profile of the reactant heptaisobutyl-POSS (1)
(Fig. 1). The two compounds show very similar IR features
in the region of the stretching and bending modes of the
isobutyl chains and of the nas(Si–O–Si) of the cage framework
(1500–1100 cmÀ1). This is proof that the POSS cage structure
was essentially preserved from the chemical point of view
during the corner-capping reaction. Nevertheless, it is worth
noting that the band centred at 1100 cmÀ1 (nas(Si–O–Si)) in the
IR spectrum of the product (2) (Fig. 1, down curve) appeared
slightly broadened in comparison to the vibrational profile of
the reactant POSS (1). This result could be indicative of a local
alteration of the cage symmetry occurring in the presence of the
coordinated metal centre.
The amount of carbon and nitrogen was detected by using
the EuroVector CHN analyzer ‘‘EA3000’’.
29Si solid state NMR spectra were acquired on a Bruker
Avance III 500 spectrometer and a wide bore 11.7 Tesla magnet
with operational frequencies of 99.35 MHz for 29Si. A 4 mm
triple resonance probe was employed in all the experiments and
the samples were packed in a zirconia rotor and spun at an MAS
rate of 5 kHz. The magnitude of the radio frequency field was
42 kHz and the relaxation delay between accumulations
was 120 s.
Infrared (IR) spectra of solid samples in KBr pellets were
recorded in the range 4000–400 cmÀ1 with 4 cmÀ1 resolution,
by using a Bruker Equinox 55 spectrometer.
The XRF analysis was carried out using the Rigaku NEX QC
(QC1036) Benchtop Energy Dispersive X-ray Fluorescence (EDXRF)
spectrometer, equipped with a 50 kV (4 watt) X-ray tube.
MALDI-TOF analysis was performed using the Mass Spectro-
meter Voyager DE Pro (AB-Sciex). For MALDI-TOF analysis,
3,5-dimethoxy cinnamic acid (sinapinic acid) (LaserBio Labs,
Sophia-Antipolis Cedex, France) was used as a matrix in a con-
centration of 10 mg mLÀ1 in 50 : 50 acetonitrile : water 0.1% TFA.
Typically the 10 mL sample was mixed with 10 mL matrix solution, of
which 1 mL was deposited on the appropriate target. After thorough
drying in the dark, 100 shots per spectrum were acquired.
The MALDI-MS spectral data were processed using the Data
Explorer software from AB-Sciex.
The most important differences between the two samples fall
in the 3500–3000 cmÀ1 and 1000–500 cmÀ1 IR ranges (Fig. 1).
Photoexcitation and photoluminescence emission spectra were
recorded on a Horiba Jobin-Yvon Model IBH FL-322 Fluorolog 3
spectrometer equipped with a 450 W xenon arc lamp, double-
grating excitation and emission monochromators (2.1 nm mmÀ1
dispersion; 1200 grooves per mm), and a Hamamatsu Model R928
Scheme 1 Schematic view of the corner-capping reaction of the hepta-
isobutyl-trisilanol POSS (1) with an anhydrous europium salt, thus obtaining
photomultiplier tube. PL spectra were recorded under irradiation the Eu(III)-POSS (2) sample.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2480--2485 | 2481

View Article Online
NJC
Paper
Fig. 1 IR spectra of heptaisobutyl-POSS (up curve) and Eu(III)-POSS
(down curve).
Fig. 2 29Si MAS NMR spectra of heptaisobutyl-POSS (a) and Eu(III)-POSS (b).
In particular, the vibrational profile of sample 1 shows two
Moreover, two new peaks clearly appear in the À100 to
absorptions at 890 cmÀ1 and 3250 cmÀ1, relative to the stretch- À120 ppm range and can be attributed to the silicon sites
ing modes of Si–OH and O–H groups, respectively, that are directly coordinated to Eu3+ ions.
almost completely absent in 2, where the cage is completely
As a general comment, all 29Si NMR signals are broadened
condensed.22 The presence of additional bands, i.e. at 1030 and as a consequence of both the strong paramagnetic nature of the
800 cmÀ1, in the spectrum of 2 indicates the presence of THF Eu(III) centre and the alteration of the cage symmetry promoted
molecules coordinated to the metal centre, as can be assigned to by the corner-capping reaction.
the asymmetric and symmetric modes of the –C–O–C– bonds.
Additional information on the chemical structure of the
An absorption at 1260 cmÀ1 relative to the C–N stretching mode Eu(III)-POSS sample was obtained by MALDI-TOF analysis. The
of the Et3N, derived from the synthesis procedure, was also mass spectrum of 2 shows an intense peak at ca. 1205 (m/z)
observed. The quantity of the triethylamine byproduct was (Fig. S3, ESI†). This value is in agreement with the molecular
estimated by CHN analysis. An amount of ca. 4 wt% was detected weight of a monomeric structure in which the Eu3+ ion is
in the final material.
IR data have been supported by NMR spectroscopy applied coordination sphere with THF (as indicated by the 13C NMR
to 13C and 29Si nuclei.
spectrum) and probably water molecules derived from the
bound to the Si–O– units of the POSS cage, expanding its
The high resolution 13C-NMR spectrum of product 2, dis- purification treatments. An intense peak at ca. 1430 m/z was
solved in CDCl3 (see Fig. S1 in the ESI†), shows peaks at 30.0, also observed and correlated to the molecular weight of Eu(III)-
23.9, and 8.6 ppm, ascribed to –CH2, –CH, and –CH3 carbon of POSS bound to the sinapinic acid matrix, used to stabilized the
the isobutyl groups bound to the siliceous framework (Fig. S1, sample prior to the analysis. No evidence of dimeric or multi-
ESI†). Additional signals at 65.8 and 68.0 ppm are also observed meric species, often detected for parent Ln-containing POSS, is
and are ascribed to the –H2C–O of both free and coordinated observed for the Eu(III)-POSS sample prepared in this work.
(through the formation of the Eu–O–CH2 bond) THF molecules More insights into the chemical structure of this sample could
to the metal centre, respectively. In addition, peaks at ca. 15 be obtained through single-crystal X-ray diffraction analysis,
and 45 ppm are also present and assigned to the presence of but POSS functionalized with highly mobile isobutyl groups are
the triethylamine by-product derived from the synthesis reac- often unsuitable for this analysis due to their poor tendency
tion (see also IR data described above).
to crystallise into appropriately sized crystals, as observed in
Silicon site distribution in the Eu(III)-POSS sample was our case.
monitored by solid-state MAS-NMR spectroscopy, because of
The photophysical properties of Eu(III)-POSS were finally
the poor solubility of the product in conventional deuterated investigated. The excitation spectrum of 2 dissolved in CHCl3
solvents. The 29Si-MAS NMR spectrum of the heptaisobutyl-POSS was collected around the most intense emission line of Eu3+
shows two well defined signals at À58 ppm (with an abundance at lem = 615 nm (Fig. 3A). The excitation spectrum shows in
of 47%, calculated by the integration of the deconvoluted band), addition to the narrow peaks relative to the characteristic intra-
relative to the three silicon sites bound to the –OH groups, and at 4f6 electronic transitions of Eu3+ (as assigned in the spectra),24
À68 ppm (ascribed to the remaining Si atoms of the POSS cage, a broad absorption band from 250 to 350 nm with maximum
with an abundance of 53%) (Fig. 2, curve a). The band at located at 320 nm (Fig. 3A). This absorption, observed both for
À58 ppm, previously assigned to the silanol species of the partially the sample measured in solid state form (see Fig. S4, ESI†) and
condensed POSS,23 drastically decreases in intensity in the 29Si in chloroform solution, was ascribed to the absorption of the
NMR spectrum of the Eu(III)-POSS product (abundance of 6.4%), as host matrix.
a consequence of the almost complete closure of the cage with the
The photoluminescence spectra of Eu(III)-POSS dissolved
metal site (Fig. 2, curve b). The presence of the Eu3+ ion in the in chloroform were measured by exciting the sample at two
POSS cage was also supported by the XRF analysis carried out on different excitation wavelengths, 320 nm (wavelength relative to
5
the Eu(III)-POSS sample (data reported in the ESI,† Fig. S2).
the absorption of both the Eu3+ (7F0 - H3–7 transitions) and
2482 | New J. Chem., 2014, 38, 2480--2485
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
Paper
NJC
Table 1 Asymmetry factor, experimental 5D0 lifetime, the Eu3+ quantum
efficiency value of the Eu(III)-POSS sample
Asymmetry
factor (R)
t
1/t0
t0
(ms)
FEu
(%)
(ms)
(msÀ1
)
Eu(III)-POSS
7
2.2 (lexc = 395)
3.8 (lexc = 320)
0.34
0.42
2.37
14.3
5D0 - F2 transition, suggests that the chemical environment
of the Eu3+ ion in Eu(III)-POSS is characterized by a low sym-
metry degree.26 The asymmetry factor of Eu(III)-POSS is 2.2 when
the sample is excited at lex = 395 nm and 3.8 when irradiated at
320 nm, thus indicating that the Eu(III) ion is characterized
in this matrix by a low symmetric coordination environment
(see Table 1).
The discussion only involves tendencies, as the method of
determining the asymmetry with the 5D0
- -
7F2/5D0 7F1
intensity ratio does not allow relying on the exact values.
In order to further investigate the luminescence performance
of the sample, the lifetime of excited states of Eu3+ ions in 2 was
also measured. The decay curve of the 5D0 level is well-
reproduced by means of a mono-exponential function. The
lifetime value is determined to be 0.34 ms (Table 1), in agree-
ment with the results obtained for parent solids based on silica-
type or aluminosilicate matrices (mesoporous silicas, zeolites. . .)
(Fig. 4).27
Fig. 3 (A) Excitation spectrum of Eu(III)-POSS in CHCl3 around the most
intense emission line of Eu3+ at lem = 615 nm; (B) emission spectra of Eu(III)-
POSS under irradiation at 320 nm (solid curve) and 395 nm (dash line).
The 5D0 quantum efficiency (F) is estimated taking into
account the emission spectrum and the lifetime of the 5D0 state
and by using the following eqn (1):28
the host matrix) and 395 nm (only typical of the Eu3+ ion
5
(7F0 - L6 transition)), respectively (Fig. 3B).
In both cases, the emission spectra are composed of very
narrow emission peaks relative to the intra-4f6 electronic levels
FLn = t/t0
(1)
of Eu3+ (5D0
-
7FJ (J = 0–4)).24 However, the intensity of
where t and t0 are the lifetime and the radiative lifetime of the
Eu3+ luminescence, respectively.
the peak at 615 nm, which is ascribed to the hypersensitive
5D0 7F2 transition, appears to be more intense when the
-
Eqn (2) provides a means to calculate the radiative lifetime
directly from the corrected emission spectrum without the
intervention of the Judd–Ofelt theory.29
sample is irradiated at 320 nm (Fig. 3B).
It is worth noting that the photoluminescence spectrum of
the sample irradiated at 320 nm showed a weak band at 579 nm
(well evident in the PL spectrum of Eu(III)-POSS in the solid
1/t0 = AMD,0n3(Itot/IMD
)
(2)
5
7
state (see Fig. S4B, ESI†)) related to the D0 - F0 transition,
unique for a given chemical environment, since both the initial
and final states are non-degenerate. The number of compo-
nents observed for this transition is then related to the number
of chemically distinct environments of the Eu3+ ion and the
transition has been used both in excitation and emission as a
probe of sample homogeneity. It is clear that there is only one
band in our case, consistent with the presence of a single
predominant environment.
In this equation, n is the refractive index of the solvent
(CHCl3), AMD,0 is the spontaneous emission probability for the
5D0 - 7F1 transition in vacuo, and Itot/IMD is the total area of the
Site geometrical aspects can be evaluated using the PL
results. The asymmetry factor (R), which is the ratio of the
5
7
integrated intensity of the D0 - F2 (peak at 615 nm) transi-
5
7
tion to the D0 - F1 transition (signal at 592 nm), has been
widely used as an indicator of Eu3+ site symmetry and it tends
to zero when the excited ions are located at a symmetry site. It is
believed that the value of R becomes larger as the interaction
of Eu3+ with its neighbours becomes stronger and the Eu3+ site
symmetry becomes lower.25 The presence of a very intense peak
Fig. 4 PL intensity decay over time of the Eu(III)-POSS sample dissolved in
at 615 nm in the PL spectrum of 2, relative to the electric dipole CHCl3 under irradiation at 370 nm (–J–).
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2480--2485 | 2483

View Article Online
NJC
Paper
Acknowledgements
`
Dr Francesco Marsano and Dr Claudio Cassino (DiSIT – Universita
del Piemonte Orientale) are kindly acknowledged for the collection
of MALDI-TOF and NMR data, respectively.
Notes and references
1 R. H. Baney, M. Itoh, A. Sakakibara and T. Suzuki, Chem.
Rev., 1995, 95, 1409.
2 P. G. Harrison, J. Organomet. Chem., 1997, 542, 141.
3 P. P. Pescarmona and T. Maschmeyer, Aust. J. Chem., 2001,
54, 583.
4 S. H. Phillips, T. S. Haddad and S. J. Tomczak, Curr. Opin.
Solid State Mater. Sci., 2005, 8, 21.
Fig. 5 Photostability test on Eu(III)-POSS solution in CHCl3 irradiated
at 395 nm.
5 R. Duchateau, Chem. Rev., 2002, 102, 3525; V. Lorenz and
F. T. Edelmann, Z. Anorg. Allg. Chem., 2004, 630, 1147;
V. Lorenz and F. T. Edelmann, Adv. Organomet. Chem.,
2005, 53, 101.
(corrected) Eu3+ emission spectrum to the area of the 5D0 - 7F1
band. It was theoretically calculated and experimentally verified
that AMD,0 has a value of 14.65 sÀ1 29
.
6 H. C. L. Abbenhuis, Chem.–Eur. J., 2000, 6, 25.
7 J. D. Lichtenhan, Comments Inorg. Chem., 1995, 17, 115.
8 R. W. J. M. Hanssen, R. A. van Santen and H. C. L. Abbenhuis,
Eur. J. Inorg. Chem., 2004, 675.
9 F. J. Feher and J. F. Walzer, Inorg. Chem., 1991, 30, 1689.
10 V. Lorenz, A. Fischer, S. Gießmann, J. W. Gilje, Y. Gun’ko,
K. Jacob and F. T. Edelmann, Coord. Chem. Rev., 2000,
206–207, 321.
The intrinsic quantum efficiency of europium (FLn), based
on the emission spectra obtained in solution under irradiation
at 320 nm and on the value of the lifetime previously obtained,
was calculated to be 14.3% (Table 1), in agreement with the
data obtained for other Eu3+-containing silica frameworks.24
In order to further investigate the photostability of the
hybrid material in CHCl3 solution, bleaching tests have been
performed (Fig. 5). Photodegradation of the Eu(III)-POSS sample
is strongly limited (ca. 5%) after 1 h of light irradiation at
395 nm, confirming that the sample is characterized by high
photostability.
11 R. Duchateau, Chem. Rev., 2002, 102, 3525.
12 J. Annand, H. C. Aspinall and A. Steiner, Inorg. Chem., 1999,
38, 1931.
13 V. Lorenz, S. Giessmann, Y. K. Gun’ko, A. K. Fischer, J. W.
Gilje and F. T. Edelmann, Angew. Chem., 2004, 116, 4703;
V. Lorenz, S. Giessmann, Y. K. Gun’ko, A. K. Fischer,
J. W. Gilje and F. T. Edelmann, Angew. Chem., Int. Ed.,
2004, 43, 4603.
4. Conclusions
In conclusion, the synthesis and characterization of a novel
completely condensed Eu3+-containing POSS (Eu(III)-POSS) are 14 F. J. Feher, T. A. Budzichowski, K. Rahimian and J. W. Ziller,
reported in this work. A detailed investigation of the physico-
chemical properties of the Eu(III)-POSS sample, by NMR applied 15 M. Crocker, R. H. M. Herold, A. G. Orpen and M. T. A.
to 13C and 29Si nuclei, FT-IR and MALDI-TOF analyses, has
Overgaag, J. Chem. Soc., Dalton Trans., 1999, 3791.
provided information on the reaction steps and on the nature 16 K. Wada, M. Bundo, D. Nakabayashi, N. Itayama, T. Kondo
of the final product and highlighted that the synthetic protocol and T. Mitsudo, Chem. Lett., 2000, 628.
can be selective towards the preparation of Ln-containing POSS. 17 M. Chabanas, E. A. Quadrelli, B. Fenet, C. Coperet, J. Thivolle-
J. Am. Chem. Soc., 1992, 114, 3859.
Structural and spectroscopic results indicated that the Eu3+ ion
caps the POSS unit by the dangling oxygen groups of the open
corner and expands its coordination sphere by linking THF
molecules (from the reaction medium).
Cazat, J. M. Basset, A. Lesage and L. Emsley, Angew. Chem.,
2001, 113, 4625; M. Chabanas, E. A. Quadrelli, B. Fenet,
C. Coperet, J. Thivolle-Cazat, J. M. Basset, A. Lesage and
L. Emsley, Angew. Chem., Int. Ed., 2001, 40, 4493.
From the optical point of view, the compound presented 18 Y. K. Gun’ko, R. Reilly, F. T. Edelmann and H.-G. Schmidt,
interesting luminescent properties. Eu(III)-POSS was charac- Angew. Chem., Int. Ed., 2001, 40(7), 1279.
terized by a quantum efficiency of ca. 14%, in agreement with 19 V. Lorenz, S. Blaurock, C. G. Hrib and F. T. Edelmann,
parent samples based on silica matrices, and high photostabil- Eur. J. Inorg. Chem., 2010, 2605.
ity to photobleaching. These features along with the molecular 20 M. Tan, Z. Ye, E.-K. Jeong, X. Wu, D. L. Parker and Z.-R. Lu,
size and the high versatility derived from the presence of organic Bioconjugate Chem., 2011, 22, 931.
groups bound to the POSS cage, which can be opportunely 21 L. Liu, H. Lu, H. Wang, Y. Bei and S. Feng, Appl. Organomet.
modified or functionalized, render the Eu(III)-POSS sample a Chem., 2009, 23, 429.
potential candidate for the development of luminescent probes 22 F. Carniato, E. Boccaleri, L. Marchese, A. Fina, D. Tabuani
and light-harvesting systems.
and G. Camino, Eur. J. Inorg. Chem., 2007, 585.
2484 | New J. Chem., 2014, 38, 2480--2485
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014

View Article Online
Paper
NJC
23 F. Carniato, E. Boccaleri and L. Marchese, Dalton Trans., 27 X. Guo, H. Guo, L. Fu, H. Zhang, L. D. Carlos, R. Deng and
2008, 36. J. Yu, J. Photochem. Photobiol., A, 2008, 200, 318.
24 Y. Wang and N. Lin, Photochem. Photobiol. Sci., 2011, 28 S. I. Klink, G. A. Hebbink, L. Grave, P. G. B. Oude Alink,
10, 42.
F. C. J. M. van Veggel and M. H. V. Werts, J. Phys. Chem. A,
2002, 106, 3681.
29 M. H. V. Werts, Luminescent Lanthanide Complexes, Visible Light
Sensitised Red and Near-Infrared Luminescence, PhD thesis,
The Netherlands, 2000.
25 S. F. Tang, A. Babai and A. V. Mudring, Angew. Chem.,
Int. Ed., 2008, 47, 7631.
26 P. Zhang, Y. Wang, H. Liu and Y. Chen, J. Mater. Chem.,
2011, 21, 18462.
This journal is ©The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2014
New J. Chem., 2014, 38, 2480--2485 | 2485