Luminescent Nanothermometers Obtained by Post-Synthetic Modification of Metal-Organic Framework MIL-68

Article abstract of DOI:10.1002/ejic.201900110

Metal-organic frameworks (MOFs) bearing lanthanide ions are excellent platforms for designing luminescent thermometers. However, so far, post-synthetic modification of MOFs linkers has not been explored as a route to produce such thermometers, despite its

Full text of DOI:10.1002/ejic.201900110

DOI: 10.1002/ejic.201900110
Full Paper
Luminescent Nanothermometers
Luminescent Nanothermometers Obtained by Post-Synthetic
Modification of Metal-Organic Framework MIL-68
Reda M. Abdelhameed,[a,b,c] Duarte Ananias,[a] Artur M. S. Silva,[b] and João Rocha*[a]
Abstract: Metal-organic frameworks (MOFs) bearing lanthan- cally modified via a cross-linking reaction with 1,4-Bis{4-[(E)-3-
ide ions are excellent platforms for designing luminescent ther- (N,N-dimethylamino)prop-2-enoyl]phenoxy}butane (HL), fol-
mometers. However, so far, post-synthetic modification of MOFs lowed by coordination to Eu3+ and Tb3+ ions. The luminescence
linkers has not been explored as a route to produce such ther- properties of the material were assessed. Tb90Eu10-MIL-68-HL
mometers, despite its potential to design the lanthanide coordi- was found to be an excellent cryogenic (< 100 K) ratiometric
nation sphere and, thus, tune the emission properties of the luminescent nanothermometer exhibiting a maximum relative
material. Here, nanocrystals of MIL-68-NH2 were post-syntheti- sensitivity of 9.4 % K–1 at 12 K.
Introduction
ity.[11] It is also a good adsorbent for H2, CO2,[11] and rhod-
amine B,[12] and is a photocatalyst in the reduction of CrVI to
CrIII.[13]
Metal-organic frameworks (MOFs) are hybrid materials built up
from organic linkers and metal ions.[1] Certain MOFs features,
such as a high surface area, large pore volume and a widely
tuneable composition make them promising materials for many
applications including gas storage[2] and separation,[3] cataly-
sis[4] and photocatalysis,[5] optical,[6] and in the biomedical
area.[7] Recently, post-synthetic modification, i.e., the modifica-
tion of a MOF after its synthesis preserving the essential fea-
tures of the framework structure, was used as a route to obtain
light emitting materials via coordination of the parent MOF to
a trivalent lanthanide ion (Ln3+).[8] These materials have, among
other, the ability to sense with high sensitivity certain metal
ions in solution.[9]
MOF MIL-68, first reported by the group of Férey,[10] consists
of infinite trans-connected chains of octahedral units MO4(OH)2
(M = Ga or In), linked to each other via the terephthalate li-
gands, generating triangular (ca. 6.0 Å wide) and hexagonal (ca.
16.0 Å) one-dimensional channels (Figure S1). MIL-68 amino-
functionalized at the terephthalate ligand (MIL-68-NH2), later
disclosed,[11] is of particular interest because it opens up a sim-
ple route for post-synthetic modification. MIL-68-NH2 has a BET
surface area in excess of 1200 m2 g–1 and a good thermal stabil-
Measuring temperature with accuracy is of interest in a
broad range of areas, such as industrial manufacturing and
monitoring processes, health, and safety. Molecular luminescent
thermometers have advantages over the traditional liquid-filled
and bimetallic thermometers, because they exhibit high spatial
resolution and sensitivity, fast response, are essentially non-in-
vasive, and are inert to strong electric or magnetic fields.[14]
MOFs are excellent platforms for designing luminescent ther-
mometers. Work on the development of lanthanide-bearing
MOFs luminescent thermometers based on the intensity ratio
of two separate electronic emissions, providing self-calibrated
temperature readout, has been reviewed.[15]
Surprisingly, to the best of our knowledge, the post-synthetic
modification of MOFs linkers has not yet been explored as an
avenue to produce lanthanide-bearing luminescent thermome-
ters, despite its potential to rationally tune the lanthanide coor-
dination sphere and, thus, the emission properties of the mate-
rial. As a proof of concept, here MIL-68-NH2 was post syntheti-
cally modified via a cross-linking reaction followed by coordina-
tion to Eu3+ and Tb3+, in appropriate ratios. The ensuing dual
emission allowed ratiometric temperature sensing with consid-
erable sensitivity in the cryogenic range (< 100 K).
[a] Department of Chemistry, CICECO-Aveiro Institute of Materials, University
of Aveiro,
3810-193 Aveiro, Portugal
E-mail: rocha@ua.pt
http://www.ciceco.ua.pt/jr
Results and Discussion
Synthesis of MIL-68-NH2
[b] Department of Chemistry, QOPNA, University of Aveiro,
3810-193 Aveiro, Portugal
MIL-68-NH2 was prepared by addition of indium nitrate to 2-
aminoterephthalic acid in the presence of DMF at room temper-
ature. A solution of DABCO (1,4-diazabicyclo[2.2.2]octane) in
DMF was added drop wise to this solution yielding a white
crystalline powder. The chemical formula of MIL-68-NH2 ascer-
tained from elemental analysis was [In(OH)(C8H5NO4)].
E-mail: artur.silva@ua.pt
https://sites.google.com/site/artursilvaua/
[c] Applied Organic Chemistry Department, National Research Centre,
33 EL Bohouth st., Dokki, Giza, Egypt
E-mail: reda_nrc@yahoo.com
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201900110.
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Synthesis and Molecular Structure of HL
composition of MIL-68-HL was In(OH)(C19H14NO6). Thus, one
molecule of HL linker binds to two aminoterephthalate mole-
cules.
HL linker was synthesized using α,ω-bis(4-acetylphenoxy)-
butane as starting material, obtained by reacting the potassium
salt (following treatment of 4-hydroxyacetophenone with
ethanolic potassium hydroxide) with butane dibromobutane in
boiling DMF. Solvent-less heating of this compound with DMF/
DMA afforded the corresponding bis(enaminone) derivative
In absence of suitable single crystals, the determination of
the unit-cell parameters of MIL-68-NH2 and ensuing modified
materials was carried out from powder X-ray diffraction. No
significant differences were observed between MIL-68-NH2,
MIL-68-HL, Eu-MIL-68-HL, Tb-MIL-68-HL, Tb90Eu10-MIL-68-HL
(Figure 1). The pattern of MIL-68-NH2 was indexed in the ortho-
rhombic system (Cmcm space group) with the following
cell parameters: a = 21.782 Å, b = 37.804 Å, c = 7.215 Å,
V = 5941.2 Å3, and Figure of Merit F(n = 30) = 37.0.[11]
1
(Figure S2). H NMR spectra of HL show one singlet at δ = 3.0
due to the N,N dimethylamino protons, and two doublets at
δ = 5.7 and δ = 7.8 characteristic of olefinic–CH=CH-N protons
with the same coupling constant J = 12 Hz (typical for trans-
configuration), in addition to the other butane and aromatic
moieties resonances.
Using ChemBio3D, the molecular structure of HL was pre-
dicted with mode MM2 (Energy Minimization with hindered ro-
tation). As shown in Figure S3, the distance between the two
terminal nitrogen atoms is 14.3 Å, suggesting the HL molecule
may me admitted into MIL-68-NH2 channels.
Post-Synthetic Cross-Linking Modification of MIL-68-NH2
MIL-68-NH2 was chemically cross-linked to the HL linker
1
(Scheme 1). Proof for the modification is forthcoming from H
NMR spectra, after sample digestion (DCl/D2O/[D6]DMSO) (Fig-
ures S4–11), which display the linker resonances [7.35 (δ, 1H,
J 8.3 and 1.3 Hz, H-4), 7.62 (δ, 1H, J 1.3 Hz, H-1), 7.85 (δ, 1H,
J 8.3 Hz, H-5)], while the peaks at δ = 6.85 and δ = 7.50 are
ascribed to the HL aromatic ring. The aliphatic methylene group
resonates at δ = 3.2 (s, 2H, -CH2). 1H peaks integration indicates
a modification rate of ca. 100 %. HMBC, COSY, NOSY, HSQC pro-
vide further proof for MOFs modification. According to NMR,
Fourier transform infrared and elemental analysis, the chemical
Figure 1. Powder X-ray diffraction patterns of a) MIL-68-NH2, b) MIL-68-HL,
c) Eu-MIL-68-HL, d) Tb-MIL-68-HL, e) Tb90Eu10-MIL-68-HL.
Consider the infrared spectra in Figure 2. MIL-68-NH2 exhibits
the typical bands of the carboxylic acid function in the region
of 1400–1700 cm–1. The absorption band of the carboxyl
groups of the ligand coordinated to the indium metal appears
at 1558 cm–1. Moreover, the presence of occluded DMF mole-
cules is also evidenced by the C=O band at 1671 cm–1.
Figure 2. FTIR spectra of MIL-68-NH2, MIL-68-HL, Tb90Eu10-MIL-68-HL.
The band at 1256 cm–1 is ascribed to the N–C stretching vibra-
tion and the two weak peaks at 3380 and 3472 cm–1 to NH2
symmetric and asymmetric stretching vibrations. Importantly, the
Scheme 1. Post-synthetic modification of MIL-68-NH2 with HL, followed by
the complexation of MIL-68-HL with Ln3+ ions. The exact nature of the Ln3+
coordination sphere is unknown.
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carbonyl group of MIL-68-HL is observed at 1727 cm–1 but ab-
sent from the Ln-bearing samples, supporting carbonyl Ln-coor-
dination. The following chemical compositions of Ln-bearing
samples were determined by energy-dispersive X-ray spectro-
scopy (EDS) and elemental analysis: In(OH)(C29H43N3EuO17S5);
In(OH)(C29H43N3TbO17S5), In(OH)(C29H43N3Eu0.9Tb0.1O17S5) for, re-
spectively, Eu-MIL-68-HL, Tb-MIL-68-HL and Tb90Eu10-MIL-68-HL.
The ratio between indium, and europium and terbium was deter-
mined by EDS and confirmed by atomic absorption spectro-
scopy.
TEM and SEM images of MIL-68-NH2, Eu-MIL-68-HL, Tb-MIL-
68-HL and Tb90Eu10-MIL-68-HL are shown in, respectively, Fig-
ure 3 and S12. MIL-68-NH2 presents itself as thin sheets from
tens to hundred nanometres wide. Following HL-modification
and Ln-coordination, rods are observed, 100–200 nm wide.
Figure 4. Excitation spectra of Eu-MIL-68-HL (λEm. = 613.5 nm) and Tb-MIL-68-
HL (λEm. = 545 nm) recorded at 295 K.
emission spectrum of Eu-MIL-68-HL shows a dominance of the
5D0→7F2 over the 5D0→7F1 transition, a unique 5D0→7F0 transi-
tion, and exhibits three and five Stark components for the
5
5D0→7F1 and D0→7F2 transitions. These features indicate the
presence of a single low-symmetry Ln3+ local environment. The
emission spectrum of Tb90Eu10-MIL-68-HL recorded at 295 K un-
der ambient pressure consists on, essentially, the overlap of the
Eu-MIL-68-HL and Tb-MIL-68-HL spectra (Figure S13).
Figure 3. TEM images of a) MIL-68-NH2, b) Eu-MIL-68-HL, c) Tb-MIL-68-HL,
d) Tb90Eu10-MIL-68-HL.
Luminescence Thermometry
The excitation spectra of Eu-MIL-68-HL and Tb-MIL-68-HL were
recorded at room temperature (ca. 295 K) monitoring the
strongest Eu3+ 5D0→7F2, and the Tb3+ 5D4→7F5 emission transi-
tions (Figure 4). Both spectra are dominated by a broad UV
band (240–330 nm) attributed to a superposition of the π–π*
transitions of the organic ligands and a ligand-to-metal charge-
transfer band. The additional sharp lines in the spectra of
Eu-MIL-68-HL and Tb-MIL-68-HL are ascribed to the intra-4f6
Figure 5. Emission spectra of Eu-MIL-68-HL and Tb-MIL-68-HL recorded at
295 K with the excitation fixed at 312 nm.
However, when the sample is submitted to a 5 × 10–3 mbar
vacuum the corresponding emission spectrum completely
changes (Figure S13) witnessing
a phase transformation
prompted by the release of the solvent molecules from the po-
rous structure. Consequently, to prevent any phase transforma-
tion under high vacuum, in the low temperature measurements
5
5
7F0,1→5D1-4, L6 and G2-6 transitions of Eu3+, and to the intra-
5
4f8 7F6→5D2-4 and GJ transitions of Tb3+
.
The emission spectra of Eu-MIL-68-HL and Tb-MIL-68-HL re- the vacuum system was initialized at a temperature below
corded at 295 K and excited at 312 nm (ligand band) are shown 260 K, allowing to freeze the sample. At the very low pressure
in Figure 5. The sharp Eu3+ and Tb3+ emission lines are assigned (5 × 10–6 mbar) used on the temperature dependent measure-
to the 5D0→7F0-4 and 5D4→7F6-0 transitions, respectively. The ments the as-synthesised sample is only stable up to 240 K.
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The excitation spectra of Tb90Eu10-MIL-68-HL, at ambient into absolute temperature T. For each temperature, four consec-
temperature and 12 K, were monitored both in the Eu3+ utive emission spectra were collected and used to determine
(5D0→7F2 at 613.5 nm) and Tb3+ (5D4→7F5 at 545 nm) strongest the average thermometric parameter and the corresponding
transitions (Figure S14). While the 295 K spectrum monitoring standard deviation (95 % confidence). ITb and IEu parameters
the Tb3+ emission is similar to the spetrum of Tb-MIL-68-HL were determined by integrating the emission spectra in the
(Figure 4), the spectrum monitoring the Eu3+ emission shows a 535–557 nm and 605–629 nm wavelength intervals, respec-
prominence of the Tb3+ intra 4f lines over the Eu3+ ones. This tively. Figure 6b exhibits the distinct ITb and IEu temperature
is clear evidence for Tb3+-to-Eu3+ energy transfer, which dependence. The Tb3+ emission decreases in the temperature
enabled the ratiometric thermometry. For that, an excitation range studied, particularly in the 12–60 K interval where it
wavelength of 312.3 nm was selected, on the ligand-to-Ln3+ shows logarithmic temperature dependence, reaching at 240 K
energy-transfer UV band, corresponding to the minimum over- 19 % of the emission observed at 12 K. In contrast, the Eu3+
lap of the Tb3+ and Eu3+ 12 K excitation spectra, and very close emission increases 1.6-fold from 12 K to 240 K. The decrease of
to the Tb3+ and Eu3+ excitation maxima at room-temperature the Tb3+ emission and concomitant increase of the Eu3+ emis-
(Figure S14). Therefore, the 312.3 nm excitation afforded a good sion is evidence for a thermally activated Tb3+-to-Eu3+ energy
emission output and maximized the temperature sensitivity of transfer. In accord, whereas the Eu3+ 5D0 decay curves are single
the system.
exponentials with the corresponding emission lifetimes slightly
decreasing from 12 K (0.56 0.01 ms) to 295 K (0.50 0.01 ms),
the Tb3+ 5D4 decay curves are obviously not single exponentials
and the corresponding averaged lifetime strongly decreases
The temperature dependence of Tb90Eu10-MIL-68-HL emis-
sion in the 12–240 K range, with the excitation fixed at
312.3 nm, is shown in Figure 6a.
Figure 6. a) Emission spectra of Tb90Eu10-MIL-68-HL in the 12–240 K range
with the excitation fixed at 312.3 nm. b) Corresponding temperature depend-
ence of ITb (green) and IEu (red) parameters.
Figure 7. a) Variation of Δ as a function of temperature in the 12–240 K range
for Tb90Eu10-MIL-68-HL excited at 312.3 nm. The solid line is the calibration
curve obtained by fiting the experimental data to equation (4) (r2 > 0.999).
The integrated areas of the green 5D4→7F5 (ITb), and red
5D0→7F2 (IEu) transitions were used to define the thermometric
parameter Δ = ITb/IEu and to convert the emission intensities
The error in Δ results from the propagation of the errors in ITb and IEu
.
b) Corresponding relative thermal sensitivity in the same temperature range.
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Synthesis of MIL-68-NH2: MIL-68-NH2 was obtained by precipita-
tion. 0.325 g (1.08 mmol) of indium nitrate and 0.227 g (1.25 mmol)
of 2-aminoterephthalic acid were dissolved in 20 mL of DMF. The
reaction mixture was stirred for 5 min, then 1 mL (1.38 mmol) of
from 0.82 ms to 0.31 ms, in the same temperature range (Figure
S15).
Figure 7a shows the temperature dependence of the ther-
mometer parameter Δ in the 12–240 K range for Tb90Eu10-MIL-
68-HL. The data is well fitted by the classical Mott–Seitz model
considering two competitive non-radiative recombination chan-
nels:[15,16]
where Δ0 is the Δ parameter at T = 0 K, α = W0/WR is the ratio
between the non-radiative (W0 at T = 0 K) and radiative (WR)
rates, and ΔE1 and ΔE2 are the activation energies for the two
non-radiative channels. Fitting the experimental Δ values with
1.38
M DABCO solution (0.192 g of DABCO in 1 mL of DMF) was
added dropwise. The reaction mixture was stirred for 20 h at room
temperature. The precipitate obtained was washed with DMF then
soaked in CHCl3 for 24 h. filter and dry in air. 1H NMR 300 MHz,
(DCl/D2O/[D6]DMSO) δ: 7.06 (d, 1H, J = 8.2Hz), 7.40 (s, 1H), 7.79 (d,
1H, J = 8.2Hz).
Synthesis of HL (1,4-Bis{4-[(E)-3-(N,N-dimethylamino)prop-2-
enoyl]phenoxy}butane): 4- Hydroxyacetophenone (20 mmol) was
dissolved in a hot ethanolic KOH solution [prepared by dissolving
1.12 g (20 mmol) of KOH in 20 mL of absolute ethanol], and the
solvent was then removed in vacuo. The remaining material was
dissolved in DMF (15 mL) and butane dibromides (10 mmol) added.
The reaction mixture was refluxed for 5 minutes during which KCl
was separated. The solvent was then removed in vacuo and the
remaining material poured over crushed ice. The solid obtained was
recrystallized from ethanol to give colourless crystals. A mixture of
bis(acetyl) derivatives (10 mmol) and dimethylformamide-dimeth-
ylacetal (DMF/DMA) (5.4 g, 45 mmol) was refluxed for 10 h. The
reaction mixture was left to cool to room temperature and the re-
sulting yellow solid products were collected by filtration, washed
with ethanol, dried, and finally recrystallized from ethanol to afford
the corresponding bis(enaminone) derivatives as pale yellow
Equation (1) yields Δ0 = 1.51 0.04, α1 = 10.3 0.2, ΔE1
=
21.1 0.3 cm–1, α2 = 26.5 2.2 and ΔE2 = 249 13 cm–1.
(1)
The two non-radiative recombination channels responsible
for the temperature sensing, associated with ΔE1 and ΔE2, are
presumably the Tb3+-to-Eu3+ energy transfer and the energy
migration between two neighbouring Tb3+ sites. The relative
sensitivity, Sr = (∂Δ/∂T)/Δ,[17] a figure of merit used to compare
the performance of thermometers, is plotted in Figure 7b.
Tb90Eu10-MIL-68-HL presents a maximum relative sensitivity (Sm)
of 9.4 %K–1 at 12 K, which gradually decreases with the temper-
ature increase reaching a value of 1 %K–1 at 52.3 K and a mini-
mum of 0.26 %K–1 at 240 K.
Tb90Eu10-MIL-68-HL presents the second best Sm reported so
far for ratiometric luminescent thermometers operative in the
cryogenic temperature range (T < 100 K).[16,18] Concerning the
Sm parameter, Tb90Eu10-MIL-68-HL is only outperformed by
Tb0.95Eu0.05HY (HY = 5-hydroxy-1,2,4-benzenetricarboxylic acid),
with Sm of 31.0 %K–1 at 4 K.[18a]
crystals respectively. Yield 2.49
g (57 %); m.p. 200–202 °C;
IR (KBr) 1640 cm–1 (C=O), 1600 cm–1 (C=C); 1H NMR (CDCl3) 2.0
(d, 4H, OCH2CH2CH2CH2O), 3.02 (s, 12H,4 NCH3), 4.1 (s, 4H,
OCH2CH2CH2CH2O), 5.71 (d, J = 12Hz, 2H, 2 N-CH=CH-CO), 6.90
(d, J = 9 Hz, 4H, ArH),7.78 (d, J = 12 Hz, 2H, 2N-CH=CH-CO), 7.89 (d,
J = 9 Hz, 4H, ArH); Anal. for C26H32N2O4 Calcd: C, 71.53; H, 7.39; N,
6.42; found C, 71.80; H, 7.22; N, 6.18 %.
Synthesis of MIL-68-HL: A CHCl3 solution of HL reagent (0.6 g,
6 mmol) was added dropwise at room temperature to MIL-68-NH2
(1.0 g, 3.3 mmol NH2 equivalents). The resulting mixture was sealed
and kept for 3 days at 70 °C. The powder was washed with CHCl3
three times and dried at 75 °C in a oven.
Conclusions
Synthesis of Ln-MIL-68-HL: A sample MIL-68-HL (3.10 g, 3 mmol)
was dispersed in three vials containing mixed solvent from ethanol/
DMSO (90:10 v/v) (15 mL). To each portion of this mixture, a solu-
tion of Eu(NO3)3·6H2O (0.366 g, 1 mmol) or Tb(NO3)3·6H2O (0.373 g,
1 mmol) or mixed lanthanide from Eu(NO3)3·6H2O (0.0366 g,
0.1 mmol) and Tb(NO3)3·6H2O (0.335 g, 0.9 mmol) was added drop-
wise at room temperature and the mixture was stand for 5 days.
The sample was washed twice with ethanol and dried in air.
In conclusion, post-synthetic modification of Ln-based Metal-
Organic Frameworks has been shown to be a suitable tool to
design ratiometric luminescent nanothermometers. This con-
cept was illustrated with MIL-68-NH2, by cross-linking with an
appropriate ligand (HL) and coordinating to Eu3+ and Tb3+
.
Tb90Eu10-MIL-68-HL is a new cryogenic ratiometric luminescent
thermometer with a very good maximum relative sensitivity of
9.4 % K–1 at 12 K, which is the second best reported so far for
related temperature sensors. Many other wide-pore MOFs and
Characterization: Powder X-ray diffractograms were collected on a
X′Pert MPD Philips diffractometer (Cu-Kα X-radiation at 40 kV and
50 mA). EDS measurements were carried out on a Hitachi SU-70
a variety of cross-linking molecules are available to engineer fitted with a field emission gun. Optical microscopy images were
obtained on a Leica EZ4HD Digital Microscope-3.0 Megapixel. Fou-
rier transform infrared spectra were measured in the transmission
mode on a Mattson 5000 in the range 4000–350 cm–1. The pellets
were prepared by adding 1–2 mg of MOFs to 200 mg of KBr. The
mixture was compressed at a pressure of 10 kPa to form transparent
pellets. CNH contents were determined on a LECO CHNS-932 ele-
mental analyser. Solution NMR spectra were recorded on a Bruker
Avance 300 spectrometer (300 MHz) using a solution prepared by
digesting 7 mg of sample in [D6]dimethyl sulfoxide (500 μL) and
dilute DCl (100 μL, 35 % DCl).
luminescent thermometers. Work along these lines is in
progress.
Experimental Section
Materials: 2-Aminoterephthalic acid (99 %, Aldrich), indium
nitrate hydrate (Merck), N,N-dimethylformamide (DMF, 99.9 %,
Aldrich), chloroform (99.5 %, Aldrich), 4-Hydroxyacetophenone
(99 %, Aldrich), europium nitrate hexahydrate [Eu(NO3)3·6H2O]
(99.99 %, Aldrich), terbium nitrate hexahydrate [Tb(NO3)3·6H2O]
(99.99 %, Aldrich).
Photoluminescence: The emission and excitation spectra were re-
corded on a modular double grating excitation spectrofluorimeter
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Acknowledgments
Thanks are due to University of Aveiro and FCT/MEC for the
financial support to the QOPNA research project (FCT UID/QUI/
00062/2019) and to the CICECO-Aveiro Institute of Materials
(POCI-01-0145-FEDER-007679; FCT UID/CTM/50011/2019), fi-
nanced by national funds and when appropriate co-financed
by FEDER under the PT2020 Partnership Agreement, and to the
Portuguese NMR Network. We further wish to thank STDF
(project number 25313) for the grant given to R. M. Abdelham-
eed.
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Chem. Eur. J. 2018, 24, 11926–11935.ORCID MISSINGDuarte Ananias
Keywords: Metal-organic frameworks · Lanthanides · Post-
synthetic modification · Luminescent thermometry
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Received: January 28, 2019
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Luminescent Nanothermometers
R. M. Abdelhameed, D. Ananias,
A. M. S. Silva, J. Rocha* ................... 1–7
Luminescent
Nanothermometers
Obtained by Post-Synthetic Modifi-
cation of Metal-Organic Framework
MIL-68
Nanocrystals of MIL-68-NH2 was suc- tion. The obtained material makes an
cessfully modified by post-synthetic excellent cryogenic (< 100 K) ratiomet-
modification via a cross-linking reac- ric luminescent nanothermometer.
DOI: 10.1002/ejic.201900110
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim