The first example of Tb3-containing metallopolymer-type hybrid materials with efficient and high color-purity green luminescence

Article abstract of DOI:10.1039/c5dt00141b

In the series of homo-leptic trinuclear complexes {[Ln₃(L)₄Cl₄(MeOH)(H₂O)]·Cl} (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4) self-assembled from the allyl-modified benzimidazole-type ligand HL (4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol) and LnCl₃·6H₂O, a suitable energy level match endows efficient green luminescence (Φ_overall = 72%) of Tb₃-arrayed complex 3. The copolymerization between each of these complex monomers 1-4 and CC-containing MMA (methyl methacrylate) or NBE (norbornene) shows that degradative chain transfer of the terminal four flexible allyl groups within restrains their radical polymerization with MMA while it does not hinder their effective ring-opening metathesis polymerization (ROMP) with NBE. Thus, two kinds of PMMA-supported doping hybrid materials 1@PMMA, 2@PMMA, 3@PMMA and 4@PMMA and PNBE-supported metallopolymer-type hybrid materials Poly(NBE-1), Poly(NBE-2), Poly(NBE-3) and Poly(NBE-4) are obtained, respectively. Especially for both 3@PMMA and Poly(NBE-3) with high color-purity characteristic green emission of Tb³⁺ ions, improved physical properties including significantly enhanced luminescence (Φ_overall = 76% or 83%) are observed, and covalent-bonding endows a higher-concentration self-quenching as compared to physical doping. This journal is

Full text of DOI:10.1039/c5dt00141b

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Manuscript for Dalton Trans.
First example of Tb3ꢀcontaining metallopolymerꢀtype hybrid
materials with efficient and high colorꢀpurity green
luminescence
Zhao Zhang,a Heini Feng,a Lin Liu,a Chao Yu,a Xingqiang Lü,*a Xunjin Zhu,b
WaiꢀKwok Wong,b Richard A. Jones,c Mei Pand and Chengyong Su*d
aSchool of Chemical Engineering, Shaanxi Key Laboratory of Degradable Medical
Material, Northwest University, Xi’an 710069, Shaanxi, P. R. China
bDepartment of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong,
Hong Kong, P. R. China
cDepartment of Chemistry and Biochemistry, The University of Texas at Austin, 1 University
Station A5300, Austin, TX 78712ꢀ0165, United States
dMOE Laboratory of Bioinoragnic and Synthetic Chemistry/KLGH EI of Environment and
Energy Chemistry, School of Chemistry and Chemical Engineering, Sun YatꢀSen University,
Guangzhou 510275, Guangdong, China
To whom correspondence should be addressed.
*Xingqiang Lü: 86ꢀ29ꢀ88302312(o); Eꢀmail: lvxq@nwu.edu.cn
*Chengyong Su: 86ꢀ20ꢀ84115178(o); Eꢀmail: cesscy@mail.sysu.edu.cn
1

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Abstract
In the series of homoꢀleptic trinuclear complexes {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln = La, 1;
Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4) selfꢀassembled from the allylꢀmodified
benzimidazoleꢀtype ligand HL (4ꢀallylꢀ2ꢀ(1Hꢀbenzo[d]imidazolꢀ2ꢀyl)ꢀ6ꢀmethoxyphenol) and
LnCl3·6H2O, the suitable energy level match endows the efficient green luminescence (Фoverall
= 72%) of the Tb3ꢀarrayed complex 3. The copolymerization between each of these complex
monomers 1ꢀ4 with C=Cꢀcontaining MMA (methyl methacrylate) or NBE (norborene) shows
that the degradative chain transfer of the terminal four flexible ally groups within restrains
their radical polymerization with MMA while does not hinder their effective ringꢀopening
metathesis polymerization (ROMP) with NBE. Thus, two kinds of PMMAꢀsupported doping
hybrid materials 1@PMMA, 2@PMMA, 3@PMMA and 4@PMMA and PNBEꢀsupported
metallopolymerꢀtype hybrid materials Poly(NBEꢀ1), Poly(NBEꢀ2), Poly(NBEꢀ3) and
Poly(NBEꢀ4) are obtained, respectively. Especially for both 3@PMMA and Poly(NBEꢀ3)
with high colorꢀpurity characteristic green emission of Tb3+ ion, the improved physical
properties including the significantly enhanced luminescence (Фoverall = 76 % or 83%) are
observed, and the covalentlyꢀbonding endows the higherꢀconcentration selfꢀquenching as
compared to the physical doping.
Keyword: PMMAꢀsupported doping or PNBEꢀsupported metallopolymerꢀtype hybrid
material; Tb3ꢀarrayed benzimidazoleꢀtype complex; Radical polymerization or ROMP;
Energy transfer
2

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1. Introduction
Due to the large Stokes shift, msꢀgrade long lifetime and characteristic narrow lineꢀlike
emission of Eu3+ or Tb3+ ion, there has been a growing interest on the development of new
kinds of high colorꢀpurity Eu3+ꢀ (red) or Tb3+ꢀbased (green) optical materials with potential
applications in organic lightꢀemitting diodes (OLEDs),1 white lightꢀemitting devices,2
colorꢀtuning pigments3 or biological fluoroꢀimmunoassay.4 However, limited by the forbidden
parity from fꢀf transitions of these two inorganic Ln3+ ions, the molar absorption coefficients
are normally very low (ε
= 0.01ꢀ10 Mꢀ1cmꢀ1). From the viewpoint of effective sensitization,
suitable chromophore is required to allow for indirect population of those Ln3+ ions’ emissive
excited states through ligand excitation (“antenna effect”).5 For this purpose, the compatibility
between the excited state level of the chromophore and the accepting level of the
corresponding Ln3+ ion should be realized6 in these luminescent Ln3+ꢀcomplexes besides the
avoidance of the nonꢀradiative deactivation by OHꢀ, NHꢀ or CHꢀoscillators around the Ln3+
ion.7 Nevertheless, the Ln3+ꢀcomplexes generally present low thermal stability and poor
mechanical property, giving rise to another parallel challenge.
In order to overcome these deficiencies and simultaneously improve the photoꢀphysical
property of these Ln3+ꢀcomplexes, one of simple while effective solutions is through physical
doping into a host inorganic or organic polymeric matrix.8 On the other hand, an alternative
approach is to trapping the Ln3+ꢀcomplex into a silicaꢀbased host9 or a polymer backbone10
with covalent bonds for the formation of graftingꢀtype inorganicꢀorganic hybrid materials. By
contrast, Ln3+ꢀcontaining metallopolymers,11 as a unique class of grafted hybrid materials,
possess both the beneficial property of the inorganic Ln3+ ions and the attractive features
3

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including mechanical strength, flexibility, ease of processing and low cost of organic
polymers. This advantage, especially compared with Ln3+ꢀcontaining doping hybrid materials,
endows the ability to effectively resolve the high homogeneity and clustering of emitters and
makes them more ideal as optoelectronic materials. Till now, to the best of our knowledge, the
developed Ln3+ꢀcontaining metallopolymers are usually limited from the mononuclear
Ln3+ꢀcomplexes through coupling,12 ringꢀopening polymerization,13 radical polymerization14
or electroꢀpolymerization,15 and few systems fabricated from dꢀf heterometallic16 or fꢀf
polymetallic complexes.17 In our recent reports, through the radical copolymerization of the
divinylꢀmodified ZnLn or Zn2Ln (Ln = Nd, Yb or Er) Salenꢀtype Schiffꢀbase complex
monomer and another C=Cꢀcontaining monomer, two examples of nearꢀinfrared (NIR)
luminescent ZnLn16b, 16c or Zn2Lnꢀcontaining16d metallopolymers are constructed. Moreover,
another example of NIR luminescent metallopolymers based on allylꢀmodified Ln4(Salen)4
(Ln = Nd or Yb) complexes is successfully built by the controlled ringꢀopening metathesis
polymerization (ROMP) with norborene (NBE).17 In the two kinds of metallopolymers, the
additive electronic communication between the homoꢀ or heteroꢀmultiple metal centers
actually induces more efficient energy transfer. In consideration of the relatively higher first
excited state (17286 cmꢀ1, 5D0 for Eu3+; 20545 cmꢀ1, 5D4 for Tb3+) of visible luminescent Eu3+
4
2
4
or Tb3+ ion than that (11257 cmꢀ1, F3/2 for Nd3+; 10400 cmꢀ1, F5/2 for Yb3+, 6610 cmꢀ1, I13/2
for Er3+) of NIR luminescent Nd3+, Yb3+ or Er3+ ion,18 new organic ligands also with
unsaturated C=C functions while not vinylꢀ or allylꢀmodified Salenꢀtype Schiffꢀbase ligands
need to be designed, where the polymerizable multiꢀmetallic Eu3+ or Tb3+ complex monomer
3
with higher πꢀπ* energy level matched well with the first excited state of Eu3+ or Tb3+ ion
4

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can also be copolymerized with other C=Cꢀcontaining monomers. Thus, new
polymetallicꢀcontaining metallopolymers with Eu3+ꢀ or Tb3+ꢀbased high colorꢀpurity visible
emission are expected. Herein, through the selfꢀassembly of the allylꢀmodified
benzimidazoleꢀtype ligand HL and LnCl3·6H2O (Ln = La, Eu, Tb or Gd), a series of
homoꢀleptic trinuclear complexes {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln = La, 1; Ln = Eu, 2;
Ln = Tb, 3 or Ln = Gd, 4) are obtained, respectively. The series of Ln3ꢀarrayed (Ln = Eu or Tb)
complex monomers with four terminal allyl groups should be copolymerized with MMA or
NBE, and thus, the first example of high colorꢀpurity Eu3+ꢀ or Tb3+ꢀbased trimetallic emissive
metallopolymers could be anticipated.
2. Experimental
Materials and methods
High performance liquid chromatography (HPLC) grade tetrahydrofuran (THF) was
purchased from Fisher Scientific and purified over solvent columns. Other solvents were used
as received from Sigma Aldrich and stored over 3 Å activated molecule sieves. Methyl
methacrylate (MMA) was dried over CaH2, distilled and stored under dried N2 prior to use.
Azobis(isobutyronitrile) (AIBN) was purified by recrystallization twice from absolute MeOH
prior to use. Other chemicals containing HoveydaꢀGrubbs II (HꢀGrubbs II) and norborene
(NBE) were commercial products of reagent grade and were used without further purification.
All manipulations of air and water sensitive compounds were carried out under dried N2 using
the standard Schlenk line techniques. Elemental analyses were performed on a PerkinꢀElmer
240C elemental analyzer. Infrared spectra were recorded on a Nicolet NagnaꢀIR 550
5

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1
spectrophotometer in the region 4000ꢀ400 cmꢀ1 using KBr pellets. H NMR spectra were
recorded on a JEOL EX 400 spectrometer with SiMe4 as internal standard in CD3CN, CDCl3
and/or DMSOꢀδ6 at room temperature. ESIꢀMS was performed on a Finnigan LCQDECA XP
HPLCꢀMSn mass spectrometer with a mass to charge (m/z) range of 4000 using a standard
electrospray ion source and MeCN as solvent. Electronic absorption spectra in the UV/Visible
region and diffuse reflection (DR) spectra were recorded with a Cary 300 UV
spectrophotometer, steadyꢀstate visible fluorescence and PL excitation spectra were recorded
on a Photon Technology International (PTI) Alpha scan spectrofluorometer, and visible decay
spectra were recorded on a picoꢀN2 laser system (PTI Time Master). The quantum yield
(Фoverall) of visible luminescence for each sample in solution was determined by the relative
comparison procedure, using a reference of a known quantum yield (quinine sulfate in dilute
H2SO4 solution, Фr = 0.546). The quantum yield (Фoverall) of visible luminescence for each
solid state sample was determined by absolute method using an integrating sphere19 (150 nm
diameter, BaSO4 coating) on Edingburgh Instrument FLS928. Three parallel measurements
were carried out for each sample, so that the presented Фoverall value corresponds to the
arithmetic mean value with the estimated errors of 10%. Gel permeation chromatography
(GPC) analyses of the polymers were performed using a Waters 1525 binary pump coupled to
a Waters 2414 refractive index detector with HPLC THF as the eluant on American Polymer
Standard 10
using polystyrene standards. The powder Xꢀray diffraction (PXRD) patterns were recorded on
a D/MaxꢀIIIA diffractometer with graphiteꢀmonochromatized Cu Kα radiation ( = 1.5418 Å).
ꢀm particle size, linear mixed bed packing columns. The GPC was calibrated
λ
Thermogravimetric (TG) analyses were carried out on a NETZSCH TG 209 instrument under
6

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flowing nitrogen by heating the samples from 25 to 600 °C.
Synthesis of 5ꢀallyꢀ2ꢀhydroxyꢀ3ꢀmethoxyꢀbenzaldehyde
5ꢀAllyꢀ2ꢀhydroxyꢀ3ꢀmethoxyꢀbenzaldehyde was obtained by the Williamson synthesis from
oꢀvanillin (6.08 g, 40 mmol) and allyl bromide (12.0 mL, 140 mmol) as the starting
materials in the presence of anhydrous K2CO3 (11.06 g, 80 mmol) and the subsequent para
Claisen rearrangement according to a wellꢀestablished procedure from the literature.17 Yield:
3.92 g, 51%. Element analysis (%): calcd for C11H12O3 (192.21): C, 68.74; H, 6.29. Found: C,
1
68.72; H, 6.34. H NMR (400 MHz, CDCl3): δ (ppm) 11.10 (s, 1H, ꢀOH), 9.90 (s, 1H,
ꢀCHO), 6.99 (s, 1H, ꢀPh), 6.95 (s, 1H, ꢀPh), 5.97 (m, 1H, ꢀCH=C), 5.13 (m, 2H, =CH2), 3.91
(s, 3H, ꢀOMe), 3.38 (s, 2H, ꢀCH2).
Synthesis of diallylꢀmodified Salenꢀtype Schiffꢀbase precursor H2L0 (H2L0
N,N’ꢀbis(5ꢀallylꢀ3ꢀmethoxyꢀsalicylidene)phenyleneꢀ1,2ꢀdiamine)
=
To a stirred solution oꢀphenylenediamine (0.55 g, 5 mmol) in absolute EtOH (20 mL),
5ꢀallyꢀ2ꢀhydroxyꢀ3ꢀmethoxyꢀbenzaldehyde (1.92 g, 10 mmol) was added, and the resultant
mixture was continuously stirred under N2 atmosphere at room temperature for 12 h. The
insoluble red precipitate was filtered and washed with cold diethyl ether to give a red
polycrystalline solid. Yield: 1.46 g, 64%. Element analysis (%): calcd for C28H28N2O4
(456.64): C, 73.66; H, 6.18; N 6.14. Found: C, 73.75; H, 6.15; N, 6.06. FTꢀIR (KBr, cmꢀ1):
3320 (b), 3070 (w), 2993 (w), 2943 (w), 2898 (w), 2839 (w), 1620 (s), 1581 (m), 1475 (s),
1394 (m), 1344 (w), 1267 (vs), 1230 (w), 1209 (w), 1161 (m), 993 (s), 966 (w), 908 (m), 840
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1
(w), 800 (w), 746 (w), 686 (w), 600 (w), 545 (w), 503 (w), 480 (w). H NMR (400 MHz,
CD3CN): (ppm) 13.16 (s, 2H, ꢀOH), 8.71 (s, 2H, ꢀCH=N), 7.37 (m, 4H, ꢀPh), 6.94 (s, 4H,
ꢀPh), 6.01 (m, 2H, ꢀCH=C), 5.10 (m, 4H, =CH2), 3.86 (s, 6H, ꢀOMe), 3.36 (m, 4H, ꢀCH2).
δ
Synthesis
of
allylꢀmodified
benzimidazoleꢀtype
ligand
HL
(HL
=
4ꢀallylꢀ2ꢀ(1Hꢀbenzo[d]imidazolꢀ2ꢀyl)ꢀ6ꢀmethoxyphenol)
The solution of the diallylꢀmodified Salenꢀtype Schiffꢀbase precursor H2L0 (4.56 g, 10 mmol)
in absolute MeOH (20 mL) was refluxed under N2 atmosphere for 36 h, where the color of the
solution changed from dark red to brown and white. After cooling to room temperature, the
volatile materials were removed under vacuum, and the colorless solid residue (HL) remained
was washed with absolute EtOH and dried under vacuum. Yield: 1.96 g, 70%. Element
analysis (%): calcd for C17H16N2O2 (280.33): C, 72.84; H, 5.75; N, 9.99. Found: C, 72.76; H,
5.87; N, 9.91. FTꢀIR (KBr, cmꢀ1): 3651 (w), 3524 (w), 3464 (w), 3067 (w), 2970 (w), 2928
(w), 2907 (w), 2837 (w), 2766 (w), 2731 (w), 2654 (w), 2596 (w), 2531 (w), 2486 (w), 2293
(w), 2259 (w), 2212 (w), 2116 (w), 2021 (w), 1977 (w), 1933 (w), 1894 (w), 1846 (w), 1827
(w), 1776 (w), 1722 (w), 1624 (s), 1599 (m), 1499 (s), 1454 (s), 1398 (s), 1342 (w), 1254 (vs),
1146 (s), 1063 (s), 997 (s), 964 (w), 914 (m), 851 (m), 800 (m), 748 (m), 681 (w), 615 (m),
548 (w), 494 (w), 434 (w). 1H NMR (400 MHz, CD3CN):
δ (ppm) 12.99 (s, 1H, ꢀNH), 11.09
(s, 1H, ꢀOH), 7.72 (d, 1H, ꢀPh), 7.60 (d, 1H, ꢀPh), 7.31 (m, 3H, ꢀPh), 6.94 (s, 1H, ꢀPh), 6.09
(m, 1H, ꢀCH=C), 5.17 (m, 2H, =CH2), 3.90 (s, 3H, ꢀOMe), 3.44 (d, 2H, ꢀCH2).
Synthesis of homoꢀleptic trinuclear complexes {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln = La,
8

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1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4)
The CH2Cl2ꢀMeOH solution (10 mL, V/V = 1/1) containing HL (168 mg, 0.6 mmol) and
Et3N (84 L, 0.6 mmol) was stirred for 30 min at RT, then a solution of LnCl3·6H2O (0.6
ꢀ
mmol, Ln = La, 212 mg; Ln = Eu, 220 mg; Ln = Tb, 224 mg or Ln = Gd, 223 mg) in absolute
MeOH (5 mL) was added and the mixture was refluxed under N2 atmosphere for 3 h,
respectively. After cooling to RT, the resultant respective clear yellow solution was filtered,
and diethyl ether was allowed to diffuse slowly into the filtrate at RT. Pale yellow
microcrystalline products were obtained in about two weeks, respectively.
For 1: Yield: 193 mg, 73%. Element analysis (%): calcd for C69H66N8O10Cl5La3 (1761.31):
C, 47.05; H, 3.78; N, 6.36. Found: C, 47.15; H, 3.94; N, 6.28. FTꢀIR (KBr, cmꢀ1): 3380 (b),
3220 (s), 2977 (s), 2940 (s), 2740 (m), 2679 (s), 2491 (w), 1620 (s), 1570 (s), 1507 (vs), 1465
(s), 1430 (s), 1399 (m), 1351 (m), 1276 (m), 1246 (s), 1211 (m), 1171 (w), 1133 (m), 1057 (s),
1039 (w), 1010 (w), 994 (s), 917 (w), 851 (m), 820 (w), 770 (s), 748 (s), 683 (w), 654 (w),
623 (w), 585 (w), 569 (w), 530 (w), 498 (w). 1H NMR (400 MHz, DMSOꢀδ6): δ (ppm) 13.17
(s, 4H, ꢀNH), 8.24 (m, 1H, ꢀOH), 7.79 (m, 2H, ꢀPh), 7.71 (m, 4H, ꢀPh), 7.61 (m, 2H, ꢀPh),
7.49 (m, 4H, ꢀPh), 7.39 (m, 3H, ꢀPh), 7.27 (m, 3H, ꢀPh), 7.18 (m, 6H, ꢀPh), 6.03 (m, 4H,
ꢀCH=C), 5.13 (m, 8H, =CH2), 3.87 (s, 3H, MeOH), 3.83 (s, 12H, ꢀOMe), 3.33 (s, 8H, ꢀCH2).
ESIꢀMS (in MeCN) m/z: 1725.86 (100%), [MꢀCl]+; 1762.32 (18%), [M+H]+.
For 2: Yield: 192 mg, 71%. Element analysis (%): calcd for C69H66N8O10Cl5Eu3 (1800.48):
C, 46.03; H, 3.69; N, 6.22. Found: C, 46.06; H, 3.82; N, 6.15. FTꢀIR (KBr, cmꢀ1): 3373 (b),
3210 (m), 2945 (m), 2841 (m), 1622 (s), 1571 (s), 1522 (m), 1487 (vs), 1463 (s), 1445 (s),
1424 (s), 1345 (m), 1307 (w), 1280 (m), 1243 (s), 1202 (m), 1140 (m), 1057 (s), 1012 (w),
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1000 (s), 957 (w), 910 (m), 865 (w), 850 (w), 817 (m), 766 (s), 748 (s), 686 (w), 654 (w), 624
(w), 574 (w), 499 (w). ESIꢀMS (in MeCN) m/z: 1765.02 (100%), [MꢀCl]+; 1801.48 (16%),
[M+H]+.
For 3: Yield: 189 mg, 69%. Element analysis (%): calcd for C69H66N8O10Cl5Tb3 (1821.37):
C, 45.50; H, 3.65; N, 6.15. Found: C, 45.47; H, 3.74; N, 6.10. FTꢀIR (KBr, cmꢀ1): 3390 (b),
3227 (m), 2975 (m), 2941 (m), 2737 (m), 2677 (m), 2490 (w), 1621 (s), 1570 (s), 1507 (s),
1495 (vs), 1464 (s), 1431 (m), 1398 (m), 1350 (w), 1278 (w), 1245 (s), 1211 (w), 1171 (w),
1133 (w), 1057 (m), 1037 (w), 995 (s), 917 (w), 825 (w), 821 (w), 770 (s), 747 (m), 688 (w),
655 (w), 623 (w), 589 (w), 502 (w). ESIꢀMS (in MeCN) m/z: 1785.92 (100%), [MꢀCl]+;
1822.38 (13%), [M+H]+.
For 4: Yield: 185 mg, 68%. Element analysis (%): calcd for C69H66N8O10Cl5Gd3 (1816.35):
C, 45.63; H, 3.66; N, 6.17. Found: C, 45.97; H, 3.81; N, 6.08. FTꢀIR (KBr, cmꢀ1): 3378 (b),
3219 (m), 2977 (m), 2941 (m), 2739 (m), 2679 (m), 2492 (w), 1620 (s), 1571 (s), 1507 (s),
1465 (vs), 1434 (s), 1399 (m), 1352 (m), 1278 (m), 1246 (s), 1211 (m), 1170 (w), 1133 (m),
1057 (s), 1037 (w), 1010 (w), 995 (s), 917 (w), 852 (m), 820 (w), 771 (s), 748 (s), 687 (w),
654 (w), 623 (w), 589 (w), 569 (w), 531 (w), 499 (w). ESIꢀMS (in MeCN) m/z: 1780.89
(100%), [MꢀCl]+; 1817.35 (14%), [M+H]+.
Determination of the crystal structure
Single crystals for 3·2MeOH·4H2O of suitable dimensions were mounted onto thin glass
fibers. All the intensity datas were collected on a Bruker SMART CCD diffractometer
(MoꢀKα radiation and
λ
= 0.71073 Å) in Φ and ω scan modes. Structures were solved by
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Direct methods followed by difference Fourier syntheses, and then refined by fullꢀmatrix
leastꢀsquares techniques against F2 using SHELXTL.20 All other nonꢀhydrogen atoms were
refined with anisotropic thermal parameters. Absorption corrections were applied using
SADABS.21 All hydrogen atoms were placed in calculated positions and refined isotropically
using a riding model. Crystallographic data and refinement parameters for the complexes are
presented in Table 1. Relevant atomic distances and bond angles are collected in Table 1S.
CCDC reference number 1035177 is for 3·2MeOH·4H2O.
Synthesis of PMMAꢀsupported doping hybrid materials 1@PMMA, 2@PMMA,
3@PMMA and 4@PMMA
The
homogeneous
polymerization
of
MMA
and
each
of
complexes
{[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4) with a
stipulated feeding molar ratio (200:1, 400:1, 600:1 or 800:1) in activation with AIBN was
carried out in a FisherꢀPorter glass reactor and protected by dried N2 according to the typical
procedure.22 A mixture of MMA (2.7 mL, 25.3 mmol) in activation with AIBN (37.6 mg, 1.5
mol % of MMA) and {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (0.063 mmol; Ln = La (1), 111 mg;
Ln = Eu (2), 114 mg; Ln = Tb (3), 115 mg or Ln = Gd (4), 116 mg) was dissolved in dry
xylene (30 mL), and the resultant homogeneous solution was purged with N2 for 10 min and
sealed under a reduced N2 atmosphere. The solution was heated to 60 °C with continuous
stirring for 24 h. The viscous mixture was diluted with dry THF (20 mL) and precipitated
with absolute diethyl ether (50 mL) for three times. The resulting solid products were
collected by filtration and dried at 45 oC under vacuum to constant weight, respectively.
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For 1@PMMA (400:1): Yield: 91%. FTꢀIR (KBr, cmꢀ1): 3631 (w), 3381 (m), 3221 (w),
3300 (w), 2996 (m), 2949 (m), 2844 (w), 1732 (vs), 1625 (m), 1570 (w), 1505 (w), 1460 (m),
1390 (s), 1348 (w), 1309 (w), 1255 (w), 1201 (w), 1058 (w)，1045 (w), 1018 (w), 1002 (w),
960 (w), 867 (w), 823 (w), 767 (m), 746 (m), 684 (w), 658 (w), 585 (w), 555 (w), 514 (w),
466 (w). 1H NMR (400 MHz, DMSOꢀ
δ6ꢀCDCl3, v/v = 10:1): δ (ppm) 13.12 (s, 4H, ꢀNH), 8.20
(m, 1H, ꢀOH), 7.78 (m, 2H, ꢀPh), 7.70 (m, 4H, ꢀPh), 7.61 (m, 2H, ꢀPh), 7.48 (m, 4H, ꢀPh),
7.38 (m, 3H, ꢀPh), 7.27 (m, 3H, ꢀPh), 7.17 (m, 6H, ꢀPh), 6.01 (m, 4H, ꢀCH=C), 5.11 (m, 8H,
=CH2), 3.86 (s, 3H, MeOH), 3.83 (s, 12H, ꢀOMe), 3.56 (s, 330H, ꢀCOOMe), 3.32 (s, 8H,
ꢀCH2), 1.85 (b, 220H, ꢀCH2), 0.91 (m, 330H, ꢀCH3).
For 2@PMMA (400:1): Yield: 90%. FTꢀIR (KBr, cmꢀ1): 3624 (w), 3383 (m), 3219 (w),
3301 (w), 3070 (w), 2996 (m), 2950 (m), 2841 (w), 1731 (vs), 1624 (m), 1570 (w), 1501 (w),
1466 (w), 1391 (s), 1345 (w), 1308 (w), 1252 (w), 1200 (w), 1059 (w)，1041 (w), 1017 (w),
1000 (w), 966 (w), 868 (w), 820 (w), 765 (m), 746 (m), 681 (w), 650 (w), 580 (w), 551 (w),
510 (w), 461 (w).
For 3@PMMA (200:1, 400:1, 600:1 and 800:1): Yield: 83% (200:1); 89% (400:1); 91%
(600:1); 92% (800:1). FTꢀIR (KBr, cmꢀ1): 3620 (w), 3379 (m), 3222 (w), 3301 (w), 2998 (m),
2948 (m), 2841 (w), 1731 (vs), 1621 (m), 1570 (w), 1507 (w), 1460 (m), 1391 (s), 1345 (w),
1309 (w), 1256 (w), 1201 (w), 1056 (w), 1048 (w), 1017 (w), 1002 (w), 962 (w), 867 (w), 823
(w), 764 (m), 746 (m), 686 (w), 658 (w), 581 (w), 551 (w), 514 (w), 462 (w).
For 4@PMMA (400:1): Yield: 88%. FTꢀIR (KBr, cmꢀ1): 3627 (w), 3380 (m), 3220 (w),
3305 (w), 3070 (w), 2997 (m), 2949 (m), 2842 (w), 1732 (vs), 1625 (m), 1571 (w), 1505 (w),
1460 (w), 1392 (s), 1347 (w), 1309 (w), 1254 (w), 1201 (w), 1057 (w)，1046 (w), 1018 (w),
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1002 (w), 961 (w), 867 (w), 822 (w), 767 (m), 743 (m), 684 (w), 652 (w), 585 (w), 554 (w),
512 (w), 465 (w).
Synthesis of PNBEꢀsupported metallopolymerꢀtype hybrid materials Poly(NBEꢀ1),
Poly(NBEꢀ2), Poly(NBEꢀ3) and Poly(NBEꢀ4)
The homogeneous copolymerization of NBE and each of complexes 1ꢀ4 with a stipulated
feeding molar ratio (200:1, 400:1, 600:1 or 800:1) in activation with HꢀGrubbs II was carried
out in a FisherꢀPorter glass reactor and protected by dried N2. To a solution of the complex
{[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (0.02 mmol, Ln = La (1), 35.4 mg; Ln = Eu (2), 35.8 mg;
Ln = Tb (3), 36.2 mg or Ln = Gd (4), 36.4 mg) in dry CHCl3 (30 mL), NBE (8 mmol, 752 mg)
and HꢀGrubbs II (1.5 molꢀ% of NBE; 11.3 mg, added in three times: 7 mg, 2.3 mg and 2 mg,
respectively) were added, and the resultant homogeneous solution was purged with N2 for 10
min and sealed under a reduced N2 atmosphere. The mixture was stirred at RT for 72 h.
Subsequently, ethyl vinyl ether (1 mL) was added to quench the reaction. Each of the obtained
products was precipitated as viscous substance by slow dropping into cold EtOH. The
o
resulting solids were collected by filtration and dried at 45 C under vacuum to constant
weight, respectively.
For Poly(NBEꢀ1) (400:1): Yield: 79%. FTꢀIR (KBr, cmꢀ1): 3313 (b), 2943 (m), 2862 (s),
2733 (w), 2603 (m), 2530 (w), 2495 (w), 1994 (w), 1772 (m), 1710 (m), 1662 (w), 1616 (w),
1490 (s), 1448 (s), 1348 (w), 1257 (s), 1205 (m), 1145 (w), 1037 (s), 966 (vs), 912 (w), 864
(w), 821 (s), 744 (w), 698 (vs), 671 (w), 580 (w), 497 (w), 439 (w). 1H NMR (400 MHz,
DMSOꢀ
δ
6ꢀCDCl3, v/v = 10:1): δ (ppm) 13.17 (s, 4H, ꢀNH), 8.28 (m, 1H, ꢀOH), 7.60 (b, 8H,
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ꢀPh), 7.53 (b, 2H, ꢀPh), 7.46 (b, 2H, ꢀPh), 7.25 (b, 8H, ꢀPh), 7.06 (b, 1H, ꢀPh), 6.86 (b, 2H,
ꢀPh), 6.78 (b, 1H, ꢀPh), 5.72 (m, 4H, ꢀPh), 5.54 (b, 4H, ꢀCH=C), 5.27 (s, 150H, ꢀCH=CHꢀ (Z)),
5.14 (s, 150H, ꢀCH=CHꢀ (E)), 4.90 (d, 4H, ꢀCH=CH2), 4.79 (d, 4H, ꢀCH=CH2), 3.94 (m, 3H,
MeOH), 3.93 (m, 12H, ꢀOMe), 3.36 (m, 8H, ꢀCH2ꢀC=C), 2.72 (s, 150H, ꢀCH), 2.37 (s, 150H,
ꢀCH), 1.73 (m, 450H, ꢀCH2), 1.28 (s, 300H, ꢀCH2), 0.95 (m, 150H, ꢀCH2).
For Poly(NBEꢀ2) (400:1): Yield: 74%. FTꢀIR (KBr, cmꢀ1): 3310 (b), 2941 (m), 2862 (s),
2735 (w), 2600 (m), 2534 (w), 2492 (w), 1990 (w), 1773 (m), 1713 (m), 1660 (w), 1614 (w),
1495 (s), 1447 (s), 1345 (m), 1255 (s), 1204 (m), 1149 (w), 1036 (s), 967 (vs), 910 (w), 865
(w), 818 (w), 747 (w), 674 (w), 580 (w), 493 (w), 431 (w).
For Poly(NBEꢀ3) (200:1, 400:1, 600:1 or 800:1): Yield: 55% (200:1); 77% (400:1); 82%
(600:1); 85% (800:1). FTꢀIR (KBr, cmꢀ1): 3313 (b), 2945 (m), 2862 (s), 2734 (w), 2603 (m),
2530 (w), 2496 (w), 1994 (w), 1773 (m), 1710 (m), 1660 (w), 1616 (w), 1491 (s), 1448 (s),
1347 (m), 1257 (s), 1206 (m), 1145 (w), 1036 (s), 968 (vs), 912 (w), 864 (w), 820 (w), 743
(w), 670 (w), 580 (w), 497 (w), 438 (w).
For Poly(NBEꢀ4) (400:1): Yield: 73%. FTꢀIR (KBr, cmꢀ1): 3311 (b), 2943 (m), 2860 (s),
2733 (w), 2601 (m), 2530 (w), 2490 (w), 1994 (w), 1772 (m), 1711 (m), 1662 (w), 1616 (w),
1491 (s), 1448 (s), 1347 (m), 1257 (s), 1205 (m), 1148 (w), 1037 (s), 965 (vs), 912 (w), 864
(w), 820 (w), 745 (w), 671 (w), 582 (w), 497 (w), 438 (w).
3. Results and discussion
Synthesis and characterization of the ligand HL and its series of complex monomers
{[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4)
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As shown in Scheme 1, 5ꢀallyꢀ2ꢀhydroxyꢀ3ꢀmethoxyꢀbenzaldehyde was synthesized by the
Williamson synthesis and the subsequent para Claisen rearrangement with oꢀvanillin and allyl
bromide as the starting materials in the presence of anhydrous K2CO3 as the literature.17 The
diallylꢀmodified Salenꢀtype Schiffꢀbase precursor H2L0 was obtained from the condensation
reaction of oꢀphenylenediamine with 5ꢀallyꢀ2ꢀhydroxyꢀ3ꢀmethoxyꢀbenzaldehyde in a 1:2
molar ratio, while in refluxing absolute MeOH, the precursor H2L0 was successfully
converted into the offꢀwhite benzimidazoleꢀtype ligand HL in a good yield of 70%.
Furthermore, reaction of the allylꢀmodified benzimidazoleꢀtype ligand HL and LnCl3·6H2O
(Ln = La, Eu, Tb or Gd) in different metal to ligand molar ratios (1:1, 4:3 1:2 or 1:4) afforded
the similar series of homoꢀleptic trinuclear complexes {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln =
La, 1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4), respectively, despite the slight difference of
yields. Similar to the good solubility of the allylꢀmodified benzimidazoleꢀtype ligand HL in
common organic solvents except for water, complexes 1ꢀ4 are also soluble in slightlyꢀpolar
organic solvents due to the introduction of flexible allyl groups together with the charge of the
two components (the cationic [Ln3(L)4Cl4(MeOH)(H2O)]+ part and one free Clꢀ anion) in each
of the four complexes.
[Scheme 1 inserted here]
The Schiffꢀbase precursor H2L0, the benzimidazoleꢀtype ligand HL and its series of
1
complexes 1ꢀ4 were well characterized by EA, FTꢀIR, H NMR and ESIꢀMS. In the FTꢀIR
spectra, two characteristic strong absorptions at 1620ꢀ1624 and 993ꢀ1000 cmꢀ1 attributed to
the
ν vibration and the ω vibration of the terminal active =CH2 groups from allyl substituents
were observed for the precursor H2L0, the ligand HL and complexes 1ꢀ4, respectively. As to
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1
the H NMR spectrum identification of the precursor H2L0 or the ligand HL, the similar
intraꢀmolecular resonanceꢀassisted hydrogen bonded (RAHB) OꢀH···N proton resonance (
13.16 ppm for H2L0 or
= 11.09 ppm for HL) and the wellꢀkept proton resonances ( = 6.01,
5.10 and 3.36 ppm for H2L0 or
= 6.09, 5.17 and 3.44 ppm for HL) of the functional allyl
groups were exhibited. Nevertheless, the replacement of the typical ꢀCH=Nꢀ proton resonance
δ
=
δ
δ
δ
(
δ
= 8.71 ppm) for the precursor H2L0 with the typical ꢀNH proton resonance (
δ = 12.99 ppm)
1
for the ligand HL endowed their distinctive difference between. The H NMR spectrum
(shown in Figure 1) of the antiꢀferromagnetic trinuclear La3ꢀarrayed complex 1, due to the
coordination of La3+ ions, showed a slightly spread shift (
proton resonances of the ligands relative to that of the free ligand HL (
ppm). Moreover, besides the persistence of proton resonances ( = 6.03, 5.13 and 3.33 ppm)
for the terminal allyl groups of complex 1, the presence of new proton resonances ( = 8.24
δ
from 13.17 to 3.33 ppm) of the
δ
from 12.99 to 3.44
δ
δ
and 3.87 ppm) from one coordinated MeOH molecule, together with the slight shift of the
proton resonances of four coordinated ligands also confirmed the formation of La3ꢀarrayed
complex 1. The ESIꢀMS spectra of the series of complexes 1ꢀ4 displayed the similar patterns
and exhibited the strong mass peak at m/z 1725.86 (1), 1765.02 (2), 1785.92 (3) or 1780.89 (4)
assigned to the major species of [Ln3(L)4Cl4(MeOH)(H2O)]+ of complexes 1ꢀ4, respectively.
These observations further indicate that each of discrete homoꢀleptic Ln3ꢀarrayed units is
retained in the corresponding dilute MeCN solution.
[Figure 1 inserted here]
The solid state structure of 3·2MeOH·4H2O as the representative of complexes 1ꢀ4 was
determined by singleꢀcrystal Xꢀray diffraction analysis, and its crystallographic data and
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selected bond parameters are presented in Tables 1 and 1S, respectively. Complex
3·2MeOH·4H2O crystallizes in the triclinic space group Pꢀ1. For 3·2MeOH·4H2O, the
smallest symmetric unit is composed of one cation [Tb3(L)4Cl4(MeOH)(H2O)]+, one free Clꢀ
anion, two solvates MeOH and four solvates H2O. As shown in Figure 2, four deprotonated
(L)ꢀ ligands chelate to three Tb3+ ions with a nonꢀlinear linkage (Tb1ꢀTb2ꢀTb3 angle of
144.51(5)°), where the central Tb3+ ion (Tb2) is bridged by two phenolic O atoms (O1 and O5
or O3 and O7) from the corresponding two deprotonated (L)ꢀ ligands to the two terminal Tb3+
ions (Tb1 or Tb3), respectively. The three Tb3+ ions exhibit three kinds of different
coordination environments, where the unique central Tb3+ ion (Tb2) is eightꢀcoordinate and
bound by two sets of the pheonlic O atom (O5 or O7) and the methoxy O atom (O6 or O8)
from two different deprotonated (L)ꢀ ligands and two sets of the imidazole N (N2 or N4) and
the pheonlic O atom (O1 or O3) from the other two different deprotonated (L)ꢀ ligands.
However, both of the two terminal Tb3+ ions (Tb1 and Tb3) with the slightly different
coordination environments are sevenꢀcoordinate: in addition to the imidazole N (N6 or N8)
and the pheonlic O atom (O5 or O7) from one deprotonated (L)ꢀ ligand and the pheonlic O
atom (O1 or O3) and the methoxy O atom (O2 or O4) from another deprotonated (L)ꢀ ligand,
it saturate its coordination sphere from two coordinated Clꢀ anions (Cl1 and Cl2 or Cl3 and
Cl4) and one O10 atom from the coordinated H2O or one O9 atom from the coordinated
MeOH molecule, respectively. Two unique Tb···Tb distances of 3.8563(35) and 3.8368(37) Å
are between the central Tb3+ ion (Tb2) and the two terminal Tb3+ ions (Tb1 and Tb3),
respectively. In addition to the weak N1ꢀH1···Cl5 Hꢀbonding (3.045(2) Å, shown in Figure
1S) between the free Clꢀ anion (Cl5) for charge balance with one deprotonated (L)ꢀ ligand,
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free solvates MeOH and H2O are not bound to the homoꢀleptic framework, and they exhibit
no observed interactions with the host structure. It is worth noting that the homoꢀleptic
trinuclear host structure in 3·2MeOH·4H2O is distinctively different from the reported
structures of mononuclear Lnꢀarrayed or homoꢀleptic binuclear Ln2ꢀarrayed complexes23
while comparable to Clꢀꢀdependent homoꢀleptic Ln3ꢀarrayed structure24 based on the analogue
Brꢀmodified benzimidazoleꢀtype ligand. This result shows that the discrete homoꢀleptic
Ln3ꢀarrayed host structure of complex 3·2MeOH·4H2O is stable and not strictly relied on the
stoichiometries as the literature,23 especially with the involvement of electronꢀdonating allyl
while not electronꢀwithdrawing Br group. Moreover, all the four functional allyl groups with
the C=C bond lengths of 1.297(10)ꢀ1.304(19) Å for the typical C=C bonds in complex
3·2MeOH·4H2O are well retained.
[Figure 2 inserted here]
Photophysical property and energy transfer of the series of complexes
{[Ln3(L)4Cl4(MeOH)(H2O)]·Cl} (Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4) in solution
The photophysical property of the ligand HL and its complexes 2ꢀ4 has been examined in
dilute MeCN solution at RT or 77 K, and summarized in Table 2 and Figures 3ꢀ4. As shown in
Figure 3, similar ligandꢀcentered solution absorptions (224ꢀ226, 296ꢀ300 and 330ꢀ332 nm) of
complexes 2ꢀ4 in the UVꢀvisible region are observed, where all the intraꢀligand lowꢀenergy
πꢀπ* transition absorptions are redꢀshifted upon coordination of Ln3+ ions compared to that
(324 nm) of the free ligand HL. For complex 2, photo excitation (λex = 359 nm) of the
chromophore just gives rise to weak residual visible emission (λem = 428 nm) assigned to the
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πꢀπ* ligand transition, and no characteristic Eu3+ꢀbased lineꢀlike emissions are observed. In
contrast, for complex 3, as shown in Figure 4, the ligandꢀcentered emission is not detectable
in the emission spectrum, while the strong characteristic ligandꢀfield splitting emissions of
Tb3+ ion from the emitting level (5D4) to the ground multiple 7FJ (J = 6, 5, 4, 3) are exhibited,
5
7
respectively. The strongest emission (λem = 543 nm) based on the hyperꢀsensitive D4 → F5
transition, together with the second maximum peak at 488 nm corresponding to the 5D4 → 7F6
transition, endows the bright green solution luminescence with a CIE (Commission
International De L’Eclairage) chromatic coordinate x = 0.304 and y = 0.599 for complex 3.
[Figures 3ꢀ4 inserted here]
It is of special interest to explore the detailed mechanism of energy transfer process for
the two complexes 2ꢀ3. As a suitable reference compound, the Gd3ꢀarrayed complex 4 allows
the further study of the chromophore luminescence in the absence of energy transfer, because
the Gd3+ ion has no energy levels below 32150 cmꢀ1, and therefore cannot accept any energy
from the excited state of the chromophore.25 Different from the typical fluorescence (λem
426 and = 1.51 ns) at RT, as shown in Figure 2S, complex 4 exhibits the phosphorescence
em = 433 and = 29.4
s) at 77 K, from which the triplet (3πꢀπ*) energy level at 23095 cmꢀ1
=
τ
(
λ
τ
ꢀ
is obtained. With regard to the singlet (1πꢀπ*) energy level (28736 cmꢀ1) estimated by the
lower wavelength of its UVꢀvisible absorbance edge, so the larger energy gap ꢁE1 (5641 cmꢀ1,
1πꢀπ* ꢀ3πꢀπ*) than 5000 cmꢀ1, as shown in Figure 5, endows the effective interꢀsystem
crossing process according to Reinhouldt’s empirical rule.26 Further through checking the
3
energy level match between the ligandꢀbased πꢀπ* energy level (23095 cmꢀ1) and the first
excited state level of Eu3+ or Tb3+ ion, in spite of the energy gap (ꢁE2 = 5809 nm) for complex
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2, it is actually large enough to go beyond the reasonable range of 2500ꢀ4000 cmꢀ1 from
Latva’s empirical rule.27 The possible heavy nonꢀradiative deactivation results in the complete
quenching of the characteristic Eu3+ꢀbased emissions. As to complex 3, the relatively smaller
energy gap (ꢁE2 = 2550 nm) within the ideal 2500ꢀ4500 cmꢀ1 range27 confirms the suitability
of the allylꢀmodified benzimidazoleꢀtype ligand HL as a sensitizer for Tb3+ ion. The Tb3+ ion
(5D4) lifetime of complex 3 (Figure 6) under excitation of 346 nm is measured to be τobs
=
104.54
ꢀ
s, which is not one of the longest so for reported Tb3+ꢀcomplexes,28 while the
attractive high quantum yield (Фoverall, 72%) for complex 3 in solution is obtained. This should
be mainly attributed to the suitable energy level match and the additive electronic
communication between three Tb3+ centers in complex 3 despite the vibrationic quenching7
from OHꢀcontaining oscillators (MeOH and H2O) in the inner coordination spheres of the two
terminal Tb3+ ions.
[Figures 5ꢀ6 inserted here]
Synthesis and characterization of PMMAꢀsupported doping hybrid materials
1@PMMA, 2@PMMA, 3@PMMA and 4@PMMA and PNBEꢀsupported
metallopolymerꢀtype hybrid materials Poly(NBEꢀ1), Poly(NBEꢀ2), Poly(NBEꢀ3) and
Poly(NBEꢀ4)
In consideration of the excellent performance of PMMA as one of the popular polymer
matrices with low cost, low optical absorbance and good mechanical property,29 it is of
interest to explore the radical polymerization behaviors of the series of Ln3ꢀarrayed
complexes 1ꢀ4 containing four active allyl groups as the complex monomers like those16
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containing active vinyl groups with MMA in activation with AIBN. To our dismay, the
copolymerization does not effectively occur as expected, where each of complexes 1ꢀ4 is just
physically doped into the in situ formed PMMA matrix from homoꢀpolymerization of MMA,
exclusively giving the series of PMMAꢀsupported doping hybrid materials 1@PMMA,
2@PMMA, 3@PMMA and 4@PMMA, as shown in Scheme 2, respectively. As to the
isolated hybrid materials, in the FTꢀIR spectra from the simple combination of characteristic
absorptions from each of 1ꢀ4 and PMMA, the intense absorption band at 1731ꢀ1732 cmꢀ1
attributed to the
ν(C=O) vibration of PMMA appears, and the characteristic absorptions at
1621ꢀ1625 and 1000ꢀ1002 cmꢀ1 assigned to the
ν
(allyl) vibration and the (allyl) vibration of
ω
complexes 1ꢀ4 are weakened while well kept due to the low concentration doping.
Nevertheless, the absence of the band absorptions in the range of 3373ꢀ3390 cmꢀ1 attributed to
the coordinated MeOH and H2O in complexes 1ꢀ4, together with the slight blueꢀshift by 3ꢀ4
cmꢀ1 of (C=O) vibrations (1731ꢀ1732 cmꢀ1) of 1@PMMA, 2@PMMA, 3@PMMA and
ν
4@PMMA than that (1728 cmꢀ1) of pure PMMA indicates that the two coordinated MeOH
and H2O should be replaced by carbonyl groups from PMMA through physical doping (also
shown in Scheme 2). Especially based on the 1H NMR spectrum (also shown in Figure 1) of
antiꢀferromagnetic 1@PMMA, the well combined and almost no shifted proton resonances of
the coordinated benzimidazoleꢀtype ligand (L)ꢀ and PMMA are unambiguously identical to
those of complex 1 and PMMA, respectively. The results indicate that the series of complexes
1ꢀ4 with active allyl groups can not be copolymerized with MMA in presence of AIBN
through the freeꢀradical mechanism,16 probably due to the degradative chain transfer30 of the
flexible allyl groups, from which lower reactivity of the resonanceꢀstabilized monomeric
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radical formed from those complex monomers than that of MMA leads much less tendency to
1
initiate a new polymer chain. It is of special notice that the quantitative H NMR analysis of
1@PMMA further shows the distinctively lower molar ratio of 110:1 than the initial feed
molar ratio (400:1) of MMA with 1, which should be due to the loss of MMA from
oligometric PMMA.
[Scheme 2 inserted here]
Assisted by the success of homoꢀpolymerization of NBE or it derivatives31 and their
copolymerization17,32 with many other C=Cꢀcontaining (including ally groups) functional
monomers using the typical ROMP in activation with Grubbsꢀtype catalysts, the
copolymerization of the series of Ln3ꢀarrayed complexes 1ꢀ4 containing four active allyl
groups with NBE were carried out in absolute CHCl3 at RT in activation with HꢀGrubbs II
(also in Scheme 2). Undoubtedly, all the copolymerizations were complete after 72 h as
expected, from which each of the benzimidazoleꢀbased Ln3ꢀarrayed unit with four functional
allyl groups is covalently bonded to the PNBE polymeric backbone, thus the first example of
metallopolymers based on the homoꢀtrinuclear Ln3ꢀarrayed units is constructed to date. The
isolated metallopolymerꢀtype hybrid materials Poly(NBEꢀ1), Poly(NBEꢀ2), Poly(NBEꢀ3)
and Poly(NBEꢀ4) with Wolf Type II fashion33 are also well characterized by FTꢀIR, 1H NMR
and GPC. In the FTꢀIR spectra, the characteristic absorptions of unsaturated C=C bonds from
1
allyl groups of complexes 1ꢀ4 completely disappear. The H NMR spectrum analysis of the
antiꢀferromagnetic Poly(NBEꢀ1) (also shown in Figure 1) shows the combined proton
resonances (δ
= 13.17 to 0.95 ppm) of the coordinated benzimidazoleꢀtype ligand (L)ꢀ and
NBE, where the proton resonances of new ꢀCH=CHꢀ within at 5.54 ppm and the terminal
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ꢀC=CH2 at 4.90 and 4.79 ppm from NBEꢀringꢀopening groups of 1, together with those of the
Zꢀmode ꢀCH=CHꢀ at 5.27 ppm and the Eꢀmode ꢀCH=CHꢀ at 5.14 ppm from PNBE, are
displayed, respectively. As shown in Table 2S, the numberꢀaverage molecular weights (Mn)
and polydispersity indexes (PDI = Mw/Mn) of the series of PNBEꢀsupported grafting hybrid
materials from different feeding molar ratios are in the range of 20020ꢀ25592 g/mol and
2.11ꢀ2.58, respectively, where those relatively lower molecular weights in the 104 g/mol
magnitude could endow the good solubility and the facilitated filmꢀforming. Especially for
the obtained hybrid materials Poly(NBEꢀ3) from different feeding molar ratios (200:1, 400:1,
600:1 and 800:1) with NBE to 3, there has an almost linear relationship between the
molecular weights and the feeding molar ratios, suggesting a randomꢀbonding while
homogeneous distribution of 3 alone the polymeric backbone.34
PXRD patterns of the two series of {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl}ꢀcontaining doping
and grafting hybrid materials (as shown in Figures 7a and 7b) show only amorphous peaks of
PMMA and PNBE, respectively. It suggests that in the two kinds of hybrid materials with the
good filmꢀforming property, the Ln3ꢀarrayed benzimidazoleꢀtype complex unit is
homogeneously distributed into the PMMA matrix with complicated weak interactions or the
PNBE matrix with strong covalentlyꢀbonds between, respectively, especially on the condition
of low concentrations. Moreover, TG analysis of the series of PMMAꢀsupported doping
hybrid materials shows an increase of about 25 °C for the Tonset in comparison with the pure
PMMA, as shown in Figure 8, and a relatively slight increase (15 °C) is observed for another
series of PNBEꢀsupported metallopolymerꢀtype hybrid materials as compared with pure
PNBE. However, the decomposition with maxima around much higher temperature interval
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(452ꢀ458 °C) for the PNBEꢀsupported metallopolymerꢀtype hybrid materials than that
(366ꢀ372 °C) for the PMMAꢀsupported doping hybrid materials is exhibited, and both are
distinctively higher than that (278 °C) of the representative complex 3. These observations
further demonstrate that the thermal stabilities of the two kinds of hybrid materials are
essentially improved by doping or grafting, and the metallopolymerꢀtype hybrid materials are
more stable in relative to those physical doping hybrid materials.
[Figures 7 and 8 inserted here]
Photophysical properties of the two series of hybrid materials 2@PMMA, 3@PMMA
and 4@PMMA and Poly(NBEꢀ2), Poly(NBEꢀ3) and Poly(NBEꢀ4) in solid state
For the two series of hybrid materials, their photophysical properties in solid state at RT or 77
K have been examined, and also summarized in Table 2 and Figures 9ꢀ12 and 2S. As shown
in Figure 9, the DR spectra of both the PMMAꢀsupported doping and PNBEꢀsupported
metallopolymerꢀtype hybrid materials from complexes 2ꢀ4 exhibit the relatively broader
absorption bands than those of complexes 2ꢀ4 in solution, where the absorptions at 212ꢀ214,
298ꢀ304 and 347ꢀ350 nm or 208ꢀ210, 222ꢀ224, 303ꢀ304 and 341ꢀ344 nm in the UVꢀvisible
region should be assigned to electronic transitions from the organic moieties of both the
coordinated benzimidazoleꢀtype ligands and PMMA or PNBE, respectively. Due to the
characteristic absorption bands of Eu3+, Tb3+ or Gd3+ ion commonly appearing above 1000
nm,35 they are not discerned in the corresponding samples. Upon excitation of the
chromophore’s absorption band (λex = 346 nm for 2@PMMA or λex = 343 nm for
4@PMMA), both 2@PMMA and 4@PMMA in solid state also exhibit the ligandꢀbased
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emissions shown in Figure 10, and 3@PMMA also gives rise to the strong characteristic
7
ligandꢀfield splitting while also high colorꢀpurity green emissions (5D4 → FJ, J = 6, 5, 4, 3
shown in Figure 11a and a CIE coordinate of x = 0.302 and y = 0.598 shown in Figure 12) of
Tb3+ ion. Especially for the solid 3@PMMA, the lifetime value (
τ = 291.50 ꢀs also shown in
Figure 6) is found to distinctively increase in relative to that of complex 3 in solution, which
should be assigned to the newly coupling interactions between ꢀC=O of PMMA with the
OHꢀcontaining oscillators around Tb3+ ions to suppress the multiphonon relaxation.36
Similarly, for the PNBEꢀsupported metallopolymerꢀtype hybrid material Poly(NBEꢀ3), the
ligandꢀcentered emission is also completely quenched, and the stronger high colorꢀpurity
green emission with a CIE coordinate of x = 0.301 and y = 0.600 (also shown in Figure 12) of
Tb3+ ion is observed, as shown in Figure 11b.
[Figures 9ꢀ12 inserted here]
It is worth noting that the maximum excitation positions (λex = 383 nm for Poly(NBEꢀ2),
λex = 395 nm for Poly(NBEꢀ3) or λex = 381 nm for Poly(NBEꢀ4)) for the PNBEꢀsupported
grafting hybrid materials in solid state are all distinctively redꢀshifted as compared to the
solution spectra of complex monomers 2ꢀ4 or the solid spectra of the PMMAꢀsupported
doping hybrid materials. This result, together with the slight redꢀshift of the ligandꢀcentered
emission for Poly(NBEꢀ2) or Poly(NBEꢀ4), suggests the increased conjugation from the
formation of covalentlyꢀbonded metallopolymers.37 Moreover, the extension of the
PNBEꢀbased backbone for Poly(NBEꢀ3), changes the ligand electric fields around the Tb3+
ions, leading to the further increase of lifetime value (τ = 451.04 ꢀs also shown in Figure 6).
From the viewpoint of energy transfer, the weak coupling interactions in 3@PMMA or the
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strong covalentlyꢀbonding in Poly(NBEꢀ3) probably could recombine the charge carrier at
Tb3+ꢀrelated trap site35 in the corresponding polymer matrix, endowing the effective decrease
3
of the πꢀπ* energy level (22222 cmꢀ1 or 21978 cmꢀ1) of the chromophore to strengthen the
ligandsꢀtoꢀmetal energy transfer. These results based on more suitable energy match (also
shown in Figure 5) are well in accordance with the relatively larger quantum yields (Фoverall
76% for 3@PMMA or 83% for Poly(NBEꢀ3)). Noticeably, the emission spectra of both
3@PMMA ( ex = 370 nm) and Poly(NBEꢀ3) ( ex = 395 nm) from the Tb3ꢀarrayed complex 3
,
λ
λ
at a variety of feeding molar ratios (200:1, 400:1, 600:1 and 800:1), exhibit the same
wellꢀdefined emission peaks characteristic of the 5D4 → 7FJ (J = 6, 5, 4, 3) transitions of Tb3+
ion, as shown in Figure 11. Although there has an almost linear relationship between the
hyperꢀsensitive emission intensity and the feeding molar ratio, the concentration
selfꢀquenching36 for the series of doping hybrid materials 3@PMMA at 400:1 is effectively
prevented from the formation of uniform grafting hybrid materials Poly(NBEꢀ3).
4. Conclusion
Through the selfꢀassembly from the allylꢀmodified benzimidazoleꢀtype ligand HL and
LnCl3·6H2O, a series of homoꢀleptic Ln3ꢀarrayed complexes {[Ln3(L)4Cl4(MeOH)(H2O)]·Cl}
(Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3 or Ln = Gd, 4) are obtained, respectively, in which energy
transfer mechanism reveals the suitable energy level match for the Tb3ꢀarrayed complex 3
with efficient green luminescence (Фoverall = 72%). Moreover, each of these complex
monomers 1ꢀ4 cannot be copolymerized with MMA from the radical polymerization, while
can be effectively copolymerized with NBE through ROMP, giving two kinds of
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PMMAꢀsupported doping hybrid materials 1@PMMA, 2@PMMA, 3@PMMA and
4@PMMA and PNBEꢀsupported metallopolymerꢀtype hybrid materials Poly(NBEꢀ1),
Poly(NBEꢀ2), Poly(NBEꢀ3) and Poly(NBEꢀ4) respectively. For both 3@PMMA and
Poly(NBEꢀ3) with high colorꢀpurity characteristic emissions of Tb3+ ion, the significantly
improved physical properties, such as thermal stability, filmꢀforming property and the
luminescent property, are exhibited, and the covalentlyꢀbonding endows the
higherꢀconcentration (up to 400:1) selfꢀquenching. This result suggests that these hybrid
materials especially the metallopolymerꢀtype hybrid materials can be used as green
luminescent optical fibers for practical applications of high colorꢀpurity polymerꢀbased
OLEDs.
Supporting information
The synthesis and characterization of PMMA in activation with AIBN and PNBE in
activation with HꢀGrubbs II in Supporting information; the selected bond lengths (Å) and
bond angles (°) for 3·2MeOH·4H2O and GPC data of the samples of PMMA, PNBE and the
series of metallopolymers Poly(NBEꢀ1), Poly(NBEꢀ2), Poly(NBEꢀ3) and Poly(NBEꢀ4) in
Tables 1ꢀ2S; Perspective drawing of the weak N1ꢀH1···Cl5 Hꢀbonding (3.045(2) Å)
interaction between the host framework and the free Cl5 in complex 3·2MeOH·4H2O and the
visible emission and excitation spectra of complex 4 in MeCN solution at 1 × 10ꢀ5 M and the
hybrid materials 4@PMMA and Poly(NBEꢀ4) with the feeding molar ratio of 400:1 in solid
state at 77 K in Figures 1ꢀ2S, respectively.
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Acknowledgements
This work is funded by the National Natural Science Foundation (21373160, 91222201,
21173165), the Program for New Century Excellent Talents in University from the Ministry
of Education of China (NCETꢀ10ꢀ0936), the research fund for the Doctoral Program
(20116101110003) of Higher Education, the Science and Technology and Innovation Project
(2012KTCQ01ꢀ37) of Shaanxi Province, Graduate Innovation and Creativity Fund (Visiting
Learner) of Northwest University in P. R. of China.
References
1 (a) J. Kido and Y. Okamoto, Chem. Rev., 2002, 102, 2357; (b) M. A. Katkova and M. N.
Bochkarev, Dalton Trans., 2010, 39, 6599.
2 (a) S. Sivakumar, F. C. J. M. Van Veggel and M. Raudsepp, J. Am. Chem. Soc., 2005, 127,
12464; (b) Q.ꢀL. Dai, M. E. Foley, C. J. Breshike, A. Lita, S. Adrian and G. F. Strouse, J.
Am. Chem. Soc., 2011, 133, 15475; (c) M. M. Shang, C. X. Li and J. Lin, Chem. Soc. Rev.,
2014, 43, 1372.
3 (a) F. Wang, Y. Han, C. S. Lim, Y. H. Lu, J. Wang, J. Xu, H. Y. Chen, C. Zhang, M. H. Hong
and X. G. Liu, Nature, 2010, 463, 1061; (b) L. Armelao, S. Quici, F. Barigelletti, G. Accorsi,
G. Bottaro, M. Cavazzini and E. Tondello, Coord. Chem. Rev., 2010, 254, 487; (c) S. Roy,
A. Chakraborty and T. K. Maji, Coord. Chem. Rev., 2014, 273ꢀ274, 139; (d) T. W. Duan
and B. Yan, J. Mater. Chem. C, 2014, 2, 5098.
4 (a) J.ꢀC. G. Bünzli, Chem. Rev., 2010, 110, 2729; (b) X. H. Wang, H. B. Chang, J. Xie, B. Z.
Zhao, B. T. Liu, S. L. Xu, W. B. Pei, N. Ren, L. Huang and W. Huang, Coord. Chem. Rev.,
28

Page 29 of 45
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00141B
273ꢀ274, 201; (c) M. C. Heffem, L. M. Matosziuk and T. J. Meade, Chem. Rev., 2014, 114,
4496.
5 E. G. Moore, A. P. S. Samuel and K. N. Raymond, Acc. Chem. Res., 2009, 42, 542.
6 P. A. Tanner and C.ꢀK. Duan, Coord. Chem. Rev., 2010, 254, 3026.
7 J.ꢀC. G. Bünzli and S. V. Eliseeva, in Springer Series on Fluorescence, Vol. 7, Lanthanide
Spectroscopy, Materials, and Bioꢀapplications, ed. P. Hänninen and H. Härmä, Springer
Verlag, Berlin, Germany, 2010, vol. 7, ch. 2.
8 (a) B. Yan, RSC Adv., 2012, 2, 9304; (b) L. D. Carlos, R. A. S. Ferreira, V. De Zea
Bermudez, B. JulianꢀLopez and P. Escribano, Chem. Soc. Rev., 2011, 40, 536.
9 K. Binnemans, Chem. Rev., 2009, 109, 4283.
10 J. Feng and H. J. Zhang, Chem. Soc. Rev., 2013, 42, 387;
11 J. M. Stanley and B. J. Holliday, Coord. Chem. Rev., 2012, 256, 1520.
12 (a) J. Pei, X. L. Liu, W. L. Yu, Y. H. Lai, Y. H. Liu and R. Cao, Macromolecules, 2002, 35,
7274; (b) A. Balamurugan, M. L. P. Reddy and M. Jayakannan, J. Phys. Chem. B, 2009,
113, 14128.
13 A. Meyers, A. Kimyonok and M. Weck, Macromolecules, 2005, 38, 8671.
14 (a) Q. Ling, Y. Song, S. J. Ding, C. Zhu, D. S. H. Chan, D.ꢀL. Kwong, E.ꢀT. Kang and
K.ꢀG. Neoh, Adv. Mater., 2005, 17, 455; (b) H. Xu, R. Zhu, P. Zhao and W. Huang, J. Phys.
Chem. C, 2011, 115, 15627.
15 X. Y. Chen, X. P. Yang and B. J. Holliday, J. Am. Chem. Soc., 2008, 130, 1546.
16 (a) J. F. Li, F. Y. Song, L. Wang, J. M. Jiao, Y. X. Cheng and C. J. Zhu, Macromol. Rapid
Commun., 2012, 33, 1268; (b) Z. Zhang, W. X. Feng, P. Y. Su, X. Q. Lü, J. R. Song, D. D.
29