Photoluminescence of Binary and Ternary Europium-based Polyhedral Oligomeric Silsesquioxane and Sol–Gel Complexes

Full text of DOI:10.1002/bkcs.12081

Communication
DOI: 10.1002/bkcs.12081
BULLETIN OF THE
P. H. Bindu et al.
KOREAN CHEMICAL SOCIETY
Photoluminescence of Binary and Ternary Europium-based Polyhedral
Oligomeric Silsesquioxane and Sol–Gel Complexes
†
‡
§
¶,*
Pardeshi Hima Bindu, Begari Prem Kumar, Raghuveer Sherial, Avvaru Praveen Kumar, Bui
∥
∥
The Huy, and Yong-Ill Lee
†
Telangana Tribal Welfare Residential Degree College, Suryapet, Telangana, 508213, India
‡
Research and Development, Tata Steel Limited, Janshedpur, Jharkhand, 831001, India
§
Sai Life Sciences Limited, IKP, Shameerpet, Hyderabad, Telangana, 500078, India
¶
Department of Applied Chemistry, School of Applied Natural Science, Adama Science and Technology
University, Adama, Ethiopia. *E-mail: drkumar.kr@gmail.com
Department of Chemistry, Changwon National University, Changwon 641-773, Republic of Korea
∥
Received April 26, 2020, Accepted July 8, 2020
Keywords: Europium hybrid complexes, Ternary and binary complexes, POSS, Sol–gel method
Development of the organic–inorganic hybrid materials is
the interesting nanomaterials of light emitting because o1f
their good chemical, mechanical, and thermal stability.
The lanthanide material that possess narrow and weak
absorption bands hard to give luminescence by direct exci-
might have spectacular influence on their physical and
functional properties, such as mechanical and thermal
10,11
properties.
In this work, we have selected N-(3-(triethoxysilyl)pro-
0
pyl)-[1,1 -biphenyl]-4-carboxamide (BiPTMS) and bipheny
2
tation. Generally, lanthanide ions, which possess intense
l-POSS (Biph-POSS) as bridging monomers and
1,10-phenanthroline (phen) as a co-ligand to sensitize the
luminescence of europium ions. We synthesized new binary
and ternary complexes of POSS material (homogeneous
material) which are soluble in most of the organic solvents
and sol–gel complexes (heterogeneous material) are insolu-
ble in organic solvents. As-synthesized complexes are char-
acterized and the photoluminescence property of POSS
hybrid materials (Eu-Bip-Si and Eu-Bip-POSS) and sol–gel
material (Eu-Bip-Phe-Si and Eu-Bip-Phe-POSS) are com-
pared and discussed. The europium-based binary and ter-
nary complexes are shown Figure 1.
and broad absorption bands, are chelated with organic
3
ligands to increase absorption. The intramolecular energy
transfer takes place via excited state of ligand to emitting
level of lanthanide, which generates metal-centered lumi-
4
nescence, called antenna effect.
The synthesis of luminescence hybrid material by the
sol–gel method is a convenient source to set up complexes
of luminescent lanthanide and this method can be possible
to perform at ambient temperatures but having a disadvan-
tage of less solubility of these lanthanide complexes. This
indicates a comparatively low-doped concentration of sol–
gel matrix only can be received, apart from this there is a
possibility to form cluster which in turn to get poor lumi-
Results and Discussion
5
nescent material. To solve the drawback of sol–gel mate-
rial, replace with polyhedral oligomeric silsesquioxane
Initially, Biph-POSS (7) was prepared by condensation of
isobutyl trimethoxysilane in the presence of LiOH to get
1,3,5,7,9,11,14-heptaisobutyl-tricyclo[7,3,3,15,14]heptasilo
xane-3,7,11-trisilanol (incompletely condensed product, tri-
silanol isobutyl-POSS) (5). Subsequently, 3-aminopropyltri
methoxysilane was applied to corner capping reaction to
(POSS) moieties to increase the solubility of the lanthanide
complexes. In order to get an effective luminescent mate-
rial, un-reacted europium salt present in the complex can be
6
removed by dissolving in organic solvents.
POSS is a unique modifier to superior materials because
7
0
it has the stability which acquired by 3D structure. POSS
get NH -POSS (6). This NH -POSS reacted with [1,1 -
2
2
molecules possess a rigid inorganic core which furnishes
thermal and photo-stability, high stiffness, the organic
groups at the corner provide processability, compatibility as8
well as excellent solubility as compared to other materials.
A number of POSS-based functional nanomaterials, includ-
ing, light-emitting materials, ionic liquids, liquid crystals,
biphenyl]-4-carbonyl chloride (Biph) in the presence of
pyridine and anhydrous ether as a solvent to form a func-
tional bridge molecule of Biph-POSS (7) (Scheme 1) 70%
1
yield. Biph-POSS was characterized by
H
NMR
(Figure S1, Supporting Information), where the peaks at δ
8.30 (d, J = 8.33 Hz, 2H, Ar H), 7.49–7.56 (m, 4H,
Ar H) and 7.26–7.43 (m, 3H, Ar H) indicate the presence
9
and dental materials have been demonstrated. The reported
0
materials are mono and/or octa-substituted POSS com-
pounds. The POSS moieties that have internalized to other
materials like polymers, organic molecules, and so forth
of 1,1 -biphenyl. The peak at 5.98 (bs, 1H) indicate the
presence of NH proton. The peak at δ 2.89 (m, 2H,
NHCH ) indicate the existence of N-attached CH2 and
2
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1
20
00
120
Eu-biph-Phe-POSS
Eu-biph-phe-Si
1
100
80
60
40
20
8
6
4
2
0
0
0
0
0
0
0
200
400
600
800
1000
0
200
400
600
800
1000
120
120
Eu-biph-POSS
Eu-biph-Si
1
00
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperature o
C)
Temperature ( C)
o
(
Figure 2. TGA curves of Eu hybrid complexes.
Eu-Biph-Phe-Si, Eu-Biph-POSS, and Eu-Biph-Si, respec-
ꢀ
tively. The initial loss of weight below 200 C is ascribed to
evaporation of residual solvent and physically adsorbed
water through partial dehydroxylation. From TGA curves,
it has been observed that major weight loss is occurred
Figure 1. Structures of Eu-Biph-Phe-POSS (1), Eu-Biph-Phe-Si
(2), Eu-Biph-POSS (3) and Eu-Biph-Si (4) complexes.
ꢀ
between 200 and 500 C. This can be assigned to the ther-
peaks at δ 1.58–1.87(m, 9H, N C CH2− and C CH ),
.72–0.95 (m, 42H, CH(CH ) ), 0.38–0.68 (m, 18H,
mal degradation of organo-silicate framework, which
12
0
includes cleavage of C C, C N and Si C bonds. The
3
2
ꢀ
CH Si) indicate the existence of isobutyl-POSS moieties,
weight loss of Eu-complexes between 350 and 500 C could
2
0
which is bridged to [1,1 -biphenyl]-4-carbonyl chloride
be due to the decompositions of the SiO residuals and the
2
moiety (Supporting Information Scheme S1). 3-
Aminopropyltrimethoxysilane reacts with [1,1 -biphenyl]-
Si O Si structure of the cage. Then, no significant weight
loss is occurred when the temperature was above 500 C,
0
ꢀ
which implies the thermal stability of binary and ternary
4-carbonyl chloride (Biph) in the presence of pyridine to
europium-based POSS and sol–gel complexes.
form Biph-Si (8) in 70% yield (Scheme 1). This compound
was characterized by H NMR and C-NMR (Supporting
Information Figure S2).
1
13
FTIR Analysis
Thermogravimetric Analysis
The FTIR of Eu-Biph-Phe-POSS (1), Eu-Biph-Phe-Si (2),
Eu-Biph-POSS (3), and Eu-Biph-Si (4) are presented in
Thermogravimetric curves of Eu-Biph-Phe-POSS, Eu-Biph-
Phe-Si, Eu-Biph-POSS, and Eu-Biph-Si complexes are
shown in Figure 2. A total mass loss of around 64%, 66%,
90
75
60
Eu-Biph-Phe-POSS
Eu-Bph-Phe-Si
5
4
0
0
C=O-Eu
58%, and 52% have been noticed for Eu-Biph-Phe-POSS,
60
Ar-CH
NH
C=O-Eu
Ar-CH
CH
NH
CH
45
Ar-CH
Ar-C=C
3
0
30
20
C=C
Si-C
Si-O-Si
15
Si-C
Si-O-Si
0
500
1000 1500 2000 2500 3000 3500 4000 500 1000 1500 2000 2500 3000 3500 4000
7
0
8
7
6
5
4
0
0
0
0
0
Eu-Biph-POSS
Eu-Biph-Si
60
Amide N-H
NH-C=O-Eu
Ar C=C
5
0
Ar C-H
bending
N-H
Ar C-H & Alkyl C-H
Ar C-H Si-C
bending
Si-C
Alkyl C-H and Ar C-H
Ar C=C
40
NH-C=O-Eu
Si-O-Si
1000 1500 2000 2500 3000 3500 4000 500
Si-O-Si
1000 1500 2000 2500 3000 3500 4000
5
00
-
1
-1
Wavenumber (cm
)
Wavenumber (cm
)
Scheme 1. Synthesis of Eu-Biph-Phe-POSS (1)
Figure 3. FTIR data of Eu hybrid complexes.
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Figure 3. The FTIR spectra of all four complexes showed a
FE-SEM and EDX Analysis
−
1
bright band at ~1640 cm corresponding to v(Amide
−
1
C O). A stretching vibration at 3300 cm was detected
for amide v(N H), that is supported for the formation of
C O Eu of europium complex, suggests the involvement
of oxygen from amide group in the complexation. The
The surface morphology of europium hybrid complexes
was studied by FE-SEM and the microstructural features of
the respective Eu-complexes are presented in Figure 4. A
clear formation of clumps has been observed in the FE-
SEM images and these clumps comprise bigger microstruc-
ture. Further, these clumps are dispersed homogenously on
the surface of Eu-hydrid powders. These Eu-hydrid com-
plexes are homogeneous molecular-based materials which
linked up between organic phase and inorganic phase
through strong chemical bonds, which leads to a complexed
−
1
bands from 2879 to 2990 cm are mostly because of v
(
C H) stretching vibration on the trident organic arms of
−
1
POSS. The peaks at 1203, 1195 and 1074, 1078 cm
belongs to v(Si O Si) and v(Si C) stretching vibrations,
respectively, which indicate POSS moiety’s stability
throughout the process.
13
molecular. EDX experiments were performed to support
the europium presence in the all Eu-hybrid complexes. The
EDX analyses over the total region of the surface in all the
samples clearly affirm the existence of Eu, Si, O, and N
elements of Eu-hybrid complexes.
Photoluminescence of Eu-Hybrid Complexes
The luminescent excitation spectrum of Eu-Biph-Phe-POSS
and Eu-Biph-Phe-Si samples was recorded at room temper-
ature and monitored at a wavelength of 617 nm and pres-
ented in Figure 5. The spectra comprise of broad bands and
3+
sharp lines, which attribute to f–f transition of Eu . The
broad band at 300–375 nm can relate to Si in host absorp-
tion band. This band overlapped excitation peaks from
7
5
7
5
7
5
F ! H , F ! D and F ! G
transitions of
2-6
0
3
3-7
0,1
4
0
+
3+
Eu ions. Figure 5(a) shows f–f transitions of Eu ions,
7
5
7
5
which are attributed to F ! L at 397 nm, F ! D at
0
6
0
3
7
5
4
16 nm and F ! D at 465 nm. In the case of Eu-Biph-
0
2
POSS and Eu-Biph-Si, the excitation spectra were
expanded to short wavelength, as shown in Figure 5
(c) and (d).
1
1
5
2
9
6
3
0
400
300
200
100
0
(a)
(b)
Eu-Biph-Phe-POSS
Eu-Biph-phe-Si
200
250
300
350
400
450
500
550
200
240
280
320
360
400
60
15
Eu-Biph-POSS
(c)
Eu-Biph-Si
(d)
1
2
9
6
3
0
45
30
15
0
200
240
280
320
360
400 200
240
280
320
360
400
Wavelength (cm-1
)
Wavelength (cm-1
)
Figure 5. Excitation spectra of (a) Eu-Biph-Phe-POSS, (b) Eu-
Biph-Phe-Si, (c) Eu-Biph-POSS and (d) Eu-Biph-Si hybrid
complexes.
Figure 4. FE-SEM and EDX of Eu hybrid complexes 1–4 from
top to bottom, respectively.
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triethoxysilane was provided by Acros Organics (Fair Lawn,
NJ, USA). The solvents and other reagents used in the work
were obtained from TCI Chem. Ltd. (Tokyo, Japan).
(a)
Methods
Synthesis of Trisilanolisobutyl-POSS (5).
Isobutyl
trimethoxysilane (1 eq) was dissolved in acetone (4 vol), to
this added distilled water (0.80 eq) and lithium hydroxide
monohydrate (0.45 eq.) and refluxed for 20 h with vigorous
stirring. The resulting solution was acidified with 1 M HCl
(4 vol) and a solid precipitated out during addition. Filtered
the solid, washed with acetonitrile (5 vol), suck dried for
ꢀ
3
0 min and then dried under vacuum at 45 C for 4 h to
give 74% yield.
Proton NMR in CDCl with 400 MHz of 5: δ 0.64–0.54
(b)
3
(
(
m, 14H, -CH -), 0.98–0.92 (m, 42H, (CH ) ), 1.91–1.78
m, 7H, CH ) and 6.66 (bs, 3H, OH).
2
3 2
Synthesis of NH -POSS (6).
Added 3-aminopropyl
2
trimethoxysilane (1 eq) and tetraethyl ammonium hydrox-
ide (20% methanol solution) to solution of
a
trisilanolisobutyl-POSS (1 eq) in ethanol (6 vol) and stirred
ꢀ
the reaction mass for 36 h at 20 C. The solvent (ethanol)
was evaporated from the resultant solution to get a solid.
This solid was washed with acetonitrile (5 vol), suck dried
ꢀ
for 30 min and then dried under vacuum at 45 C 30 min
ꢀ
and then dry under vacuum at 45 C to obtain 77% yield as
a white solid (Scheme 1).
Proton NMR in CDCl with 400 MHz of 6: δ 0.6 (t,
3
SiCH , 16H), 0.9 (d, CH(CH ) , 42H), 1.7–1.9 (m,
2
3 2
Figure 6. Emission spectra of (a) ternary and (b) binary Eu hybrid
complexes.
CH CH, CH CH , 7H) and 2.6 (t, CH NH ,2H).
2
2
2
2
2
Synthesis of BiPh-POSS (7). Dissolved BiPh (1 eq) in
vol. of dry ether under N2 atmosphere.
5
3+
It is known that photoluminescence spectra of Eu ions
Heptaisobutyloctasiloxane propylamine (NH -POSS) (1 eq)
2
5
7
exhibit emission bands which represented to D ! F
0
J
and pyridine (4 eq) were dissolved in 4 vol. of ether and
added drop wise to the BiPh solution while stirring. The
reaction mass was stirred for 4 h at room temperature under
3
+
(
J = 0–6) transitions of Eu ions. In this study, the peaks
5
7
located at 616, 595 and 581 nm related to D ! F ,
0
2
5
7
5
7
D ! F and D ! F , respectively (Figure 6(a)). In
0
1
0
0
N atmosphere. After completion of the reaction, the pyri-
2
the case of Eu-Biph-POSS sample, the intensity of peak of
dine hydrochloride salt was filtered. The filtrate was evapo-
5
7
5
81 nm is very weak (Figure 6(b)) although D ! F is
ꢀ
0
0
rated under vacuum at 45 C to get white solid in 70% yield
forbidden by the ΔJ selection rules. This observed peak is
associated to J-mixing that induced by the perturbation of
crystal field. The photoluminescence intensities of Eu-
Biph-Phe-POSS and Eu-Biph-POSS samples are stronger
than those of Eu-Biph-Phe-Si and Eu-Biph-Si, respectively.
The reason can be related to rigid silica cube, nonplanar
(Scheme 1).
Proton NMR in CDCl with 400 MHz of 7: δ 8.29 (d,
3
J = 7.5 Hz, 2H, Ar H), 7.95 (t, J = 7.5 Hz, 1H, Ar H),
.34–3.49 (m, 4H, NHCH ), 2.86 (bs, 2H, NH), 1.56–1.89
3
2
(
m, 21H, CH CH CH ), 0.81–0.93 (m, 84H, CH(CH ) ),
2 2 2 3 2
0
.48–0.56 (m, 36H, CH Si).
2
structure and as
POSS.
a
high-performance electrolyte of
Carbon-13 NMR (CDCl ): δ 167.2 (Amide), 144.6
Aromatic), 140.4 (Aromatic), 133.5 (Aromatic), 130.3
Aromatic), 128.8 (Aromatic), 127.8 (Aromatic), 127.2
3
9
,14–16
(
(
Experimental
(Aromatic), 126.8 (Aromatic), 42.3 (N C ), 29.7
( C Si), 25.6 (CH ), 23.8 ( C Si), 23 (N CH2 C ),
(
3
Materials.
Tetraethyl orthosilicate (TEOS), isobutyl
22.4 (C(CH3).
trimethoxysilane, 1,10-phenanthroline, pyridine, 4-biphenyl
carbonyl chloride (BiPh) and Eu(NO ) .6H O were pur-
chased from Sigma-Aldrich (St. Louis, MO, USA) and were
Synthesis of the Ternary Hybrid Material Eu-Biph-Phe-
POSS (1). Dissolved 1,10-phenanthroline (2 eq) and BiPh-
POSS (4 eq) in 5 vol. of absolute ethanol while stirring.
Added solid Eu(NO ) .6H O (1 eq) to the above solution.
3
3
2
used without any further purification. The (3-aminopropyl)
3
3
2
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Stirred the solution for 24 h and evaporated the solvent by
vacuum rotary vapor to get a white solid (Scheme 1). To
confirm the reaction, white solid was checked under UV-
lamp to get red emitting light.
Characterization Techniques. FTIR (6300 Spectrometer,
JASCO, Japan) analysis was carried out in the range of
400–4000 cm− using a resolution of 0.07 cm . The pellet
method was used to prepare the samples. The spectrum was
recorded with an average of 10 scans. The nuclear magnetic
resonance (NMR) study for all synthesized samples was
performed by NMR spectrometer (Avance 400; Bruker,
1
−1
Synthesis of N-(3-(triethoxysilyl) propyl)-[1,1’-biphenyl]-
4-carboxamide (8). Dissolved BiPh (1 eq) in 5 vol. of
ether under N atmosphere and added drop wise to a solu-
2
tion of amino propylsilane (1 eq) and pyridine (4 eq) in
Germany) using CDCl as a solvent. Field-emission scan-
3
4
vol. of ether. The reaction mass was stirred for 4 h at
ning electron microscope (FE-SEM, MIRA II, TESCON,
Czech) was executed to see the surface morphology of the
samples. The elemental analysis was carried out using
energy dispersive X-ray analysis (EDXA; Oxford, USA) to
support the europium presence in the samples. Ther-
mogravimetric analysis (TGA) experiments were performed
using a SDT Q200 (USA) instrument under a flow of nitro-
gen gas. A Shimadzu, Japan photoluminescence spectro-
photometer (RF-5301) was used to examine the excitation
and emission characteristics of the europium complexes.
room temperature under N atmosphere. The reaction mass
2
was filtered to remove pyridine hydrochloride salt after
completion of the reaction. The filtrate was concentrated
under vacuum rotary evaporator to get a crude mass. Then
the product was purified by column chromatography to
yield a white solid of 70% yield (Supporting Information
Scheme S1).
Proton NMR (CDCl3, 400 MHz) of 8: δ 7.86 (dd,
J = 8.5, 7.0 Hz, 4H, Ar H), 7.47 (t, J = 7.3, 7.5 Hz 2H,
Ar H), 7.39 (t, J = 7.3 Hz, 1H, Ar H), 6.56 (bs, 1H),
Acknowledgments. Publication cost of this paper was
supported by the Korean Chemical Society.
3.84 (q, J = 7.0, 6.8 Hz, 6H), 3.50 (q, J = 6.5, 6.0 Hz, 2H),
1.79 (p, 7.07, 13.89 Hz, 2H), 1.23 (t, J = 7.0 Hz, 9H) and
0.74 (t, J = 8.0, 2H).
1
3
Supporting Information. Additional supporting informa-
tion may be found online in the Supporting Information
section at the end of the article.
CNMR (CDCl ): δ 167.1 (Amide), 144 (Aromatic),
3
1
1
1
40.1 (Aromatic), 133.58 (Aromatic), 128.9 (Aromatic),
27.94 (Aromatic), 127.41 (Aromatic), 127.2 (Aromatic),
27.17 (Aromatic), 58.5 (O-CH -), 42.2 (CH -N), 22.9
2
2
(
CH ), 18.3 (CH (OEt)), 7.84 (CH (Si)).
2 3 2
References
Synthesis of Sol–Gel-based Hybrid Eu-Biph-Phe-Si (2).
Dissolved BiPh-Si (4 eq) and 1,10-phenanthroline (2 eq) in
1
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2
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3
2
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3
2
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Information Scheme S2). To confirm the reaction, white
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vol. of dry ethanol along with stirring. Added approxi-
1
1
mately one-third amount of Eu(NO ) .6H O to the solution.
3
3
2
Then added tetraethyl orthosilicate and deionized water
drop wise. After 2 h of stirring, added one drop of dilute
HCl to promote hydrolysis. The mixture was then trans-
1
4. K. Tanaka, F. Ishiguro, J. Jong-Hwan, H. Tatsuhiro, Y.
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ferred to a RB flask and kept for reflux at 60 C for 16 h.
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Bull. Korean Chem. Soc. 2020
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