Unusual Aggregation Arrangement of Eu-Containing Polyoxometalate

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Unusual Aggregation Arrangement of Eu-Containing Polyoxometalate Hybrid in a Protic Ionic Liquid with Improved Luminescence Property Nana Lei, Sijing Yi, Jiao Wang, Qintang Li, and Xiao Chen J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.7b10701 • Publication Date (Web): 04 Dec 2017 Downloaded from http://pubs.acs.org on December 7, 2017

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The Journal of Physical Chemistry

Unusual Aggregation Arrangement of Eu-Containing Polyoxometalate Hybrid in a Protic Ionic Liquid with Improved Luminescence Property Nana Lei,a a

Sijing Yi,b Jiao Wang,a

Qintang Li,c

Xiao Chen a,*

Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan, 250100, China b

c

College of Art and Sciences, Shanxi Agricultural University, Taigu, 030801, China

State Key Laboratory of Cultivation Base for Nonmetal Composites and Functional Materials,

School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang, 621010, China

*Corresponding author: Xiao Chen Address: Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan, 250100, China E–mail: [email protected]. Tel.: +86–531–88365420. Fax: +86–531–88564464.

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The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Hybridization of polyoxometalates (POMs) with cationic surfactants offers the opportunity to greatly improve their functionalities as well as processabilities. Here, a surfactant-encapsulated Eu-containing POM complex (SEP) was formed via electrostatic interaction between 1-octadecyl-3-methylimidazolium bromide (OB) and Na9(EuW10O36)·32H2O (EuW10). SEP was firstly self-assembled in a protic ionic liquid to prepare the soft aggregates to fundamentally avoid the fluorescence quenching by water molecules. The structures and photophysical properties of SEP or aggregates were investigated thoroughly by NMR and FTIR spectroscopy, optical and electron microscopy, small-angle X-ray scattering and fluorescence measurements. The formed gel-like aggregates were found to compose of three-dimensional networks of micro-ribbons with an interdigitated layered molecular packing of SEP, which was different from the usual inverse bilayer model of POM hybrids in common organic solvents. Compared to EuW10 solid or its aqueous solution, both SEP and its aggregates exhibited intense red luminescence with much improved lifetime and quantum efficiency. In addition, the soft aggregates exhibited an efficient energy transfer and an obviously enhanced monochromaticity, owning to the organized arrangement of EuW10 units and a confined microenvironment to isolate them from each other between adjacent layers. The obtained results will not only present a useful reference to the aggregation behavior of POM hybrids in ionic liquids, but also provide an easy way to design EuW10 luminescent soft materials based on the nonaqueous media.


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1. Introduction Recently, the functional luminescent materials are emerging as an attractive research subject because of their versatile electro-optical applications, such as light-emitting diodes (LEDs), luminescent solar concentrators, photovoltaic cells, biological fluorescent probes and switches.1,2 Among a variety of light-emitting units, the lanthanide-containing luminescent materials have aroused substantial interests for decades due to their intriguing photoluminescent properties of narrow emission bands, large Stokes shifts, long lifetimes (µs ~ ms range), high quantum yield, tunable emission and exceptional monochromaticity.3 Much work concerning luminescence of lanthanide ions has been concentrated on their complexes like those with β-diketonate ligands for their excellent optical properties.4 However, their uses are limited due to the poor mechanical properties and thermal or chemical instabilities in complexes.5 As a potential way to overcome these defects, the lanthanide-containing POMs with excellent luminescence efficiency and superior mechanical properties have been drawing more and more attention owing to their promising applications.6 As discrete polyanion oxide nanoclusters of transition metals, the POMs themselves have demonstrated widespread potential applications in catalysis, photo- and electro-chromic devices, medicine and sensing, etc.7 However, the practical POMs-based materials are quite limited due to the poor processability in their inorganic crystalline or amorphous powders. Meanwhile, as light-emitting units, the lanthanide-containing POMs also suffer from the weakened luminescence efficiency in aqueous solution due to the quenching by water molecules and the incompatibility with hydrophobic organic matrices. By encapsulation with cationic surfactants, polymers or biomolecules, these POMs could become more processable in solution to form diverse supramolecular aggregates like micelles, vesicles, fibers, tubes, belts, liquid crystals and films, 3 ACS Paragon Plus Environment


which might enhance their functionalities through the synergistic effect of two components.8-14 For cationic surfactant or biomolecule-encapsulated POMs, Wu’s group has carried out systematic investigations in water or organic solvents,8,9 including the use of lanthanide-containing POMs as bio- and medical luminescence probes.10 For example, they found that the Eu-containing POM could selectively bind basic amino acids through electrostatic interaction and hydrogen bonding, which then significantly induced the emission enhancement of Eu3+ in aqueous solution. Such an effect was also used to discriminate the peptides from different human papillomaviruses (HPVs) subtype.15 Using the similar luminescence unit and double hydrophilic block copolymers, Zhang and Wan et al. constructed hybrid assemblies of core–shell micelles and hydrogels with enhanced emissions through electrostatic interaction.11,12 Then, they designed a new type of recyclable supramolecular chemosensor for efficient detection of carbon dioxide based on a luminescent Dy-containing POM and a block copolymer with CO2 sensitivity.16 Recently, Yu et al. reported preparation of hybrid spheres with excellent photophysical properties by an Eu-containing POM and cationic Gemini surfactants, which might be used as a supramolecular fluorescence chemsensor for H2S detection.13 Different from these assembling ways, however, Song et al. fabricated well-ordered and ultra-thin films displaying anisotropic red luminescence using an Eu-containing POM (EuW10) and exfoliated Mg-Al layered double hydroxide (LDH) monolayers via a layer-by-layer technique. Each LDH monolayer provided EuW10 with a confined and protective microenvironment to induce orientation effect of guest molecules.14 Granadeiro and Balula et al. reported the incorporation of an Eu-containing POM within the porous channels of periodic mesoporous organosilica through electrostatic interaction to produce a luminescent material exhibiting a strong red emission under UV irradiation and an efficient energy transfer process to the lanthanide emitting center.17 4 ACS Paragon Plus Environment

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Generally speaking, although excellent photoluminescent properties could be obtained from above mentioned lanthanide-containing POMs, there still existed the limit of fluorescence quenching by water molecules when the assemblies were fabricated in aqueous environment. To overcome this difficulty, the ordered molecular aggregates with cationic surfactants, polymers or biomolecules had been designed and the quenching were suppressed to a certain extent.11-16 Meanwhile, using nonaqueous solvents as media to replace water was also a good choice to fundamentally avoid the water-induced quenching.18,19 For this aim, the ionic liquids (ILs) show much potential as self-assembling media for their excellent properties such as negligible vapor pressure, non-flammability, wide liquid range, tunable solvation ability for various organic and inorganic substances, and the fine tunabilities of structure and property. Specially, ILs are nearly colorless or transparent through almost the whole visible and near-infrared spectral regions, making them much suitable as optical solvents. The lanthanide-doped ionic liquids have therefore become an interesting research topic and new luminescent ‘soft’ materials.19-21 In addition, ILs have behaved as promising nonaqueous media for designing abundant ordered aggregates with high thermostabilities.22,23 The novel luminescent soft materials from IL-mediated lyotropic liquid crystals (LLCs) doped with europium complexes were therefore prepared in our group, which exhibited much improved energy transfer efficiency and stability of europium complex.24,25 However, to our best knowledge, there is still no report on supramolecular assembilies of lanthanide-containing POMs hybrid in ILs for their emission enhancement. For this motivation, we here investigate the aggregation behavior and photophysical property of the composite luminescent soft material from an Eu-containing POM (Na9(EuW10O36)·32H2O, EuW10) in a protic IL (ethylammonium nitrate, EAN) with the aid of a long chain surfactant, 5 ACS Paragon Plus Environment


1-octadecyl-3-methylimidazolium bromide ([C18mim]Br, OB). The schematic of EuW10 and chemical structure of OB were shown in Figure 1. EuW10 was employed owing to its highest quantum yield and longest lifetime among known luminescent POMs.26 By initially forming surfactant-encapsulated EuW10 complex (SEP) through electrostatic interaction between the imidazolium cation of OB and the EuW10 polyanion nanoclusters, the amphiphilic building blocks were formed (Figure 1). It can then be expected that such luminescent ordered architectures based on SEP and EAN may present better photophysical property than those of POM-containing aggregates formed in water.

Figure 1. Schematic representation of polyhedral EuW10, chemical structure of OB and SEP complex.

2. Experimental section 2.1. Materials Na9(EuW10O36)·32H2O (EuW10) was prepared according to the procedures described by Sugesta and Yamase.26 1-octadecyl-3-methylimidazolium bromide (OB) was synthesized through the reaction of 1-methylimidazole and an excess amount of 1-octadecyl bromide based on the reported methods.27 EAN was obtained following the steps introduced by Evans et al.28 The products purities were ascertained using 1H-NMR in DMSO-d6 and high-resolution mass spectrometry (see the Supporting Information for details). High-purity water with a resistivity of 18.4 MΩ⋅cm was obtained from a FLOM water purification system (Qingdao).


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2.2. Synthesis of OB encapsulated EuW10 complex (SEP) Based on the charge balance (OB / EuW10 molar ratio as 9:1), the EuW10 aqueous solution (9.6 mL, 3 mM) was added into that of OB (86.1 mL, 3 mM) with stirring at room temperature. After two hours, the produced white precipitates (solid SEP powder) were collected by centrifugation and then washed 2 times with deionized water. The final product was dried with a lyophilizer overnight. Its composition was verified in detail using 1H-NMR in DMSO-d6, FTIR, TGA and elementary analysis. The results of TGA and elementary analysis were as following. Anal. Calcd. for SEP (C198H391N18O38EuW10, 5662.7): C, 42.29; H, 7.01; N, 4.48. Found: C, 41.86; H, 6.74; N, 4.13. As a mass loss of 0.74% occurred in the range of 30-150 °C from TGA (Figure S1), which resulted from crystal water, (OB)9(EuW10O36)·2H2O was speculated as the chemical formula of SEP. 2.3. Preparation of SEP soft aggregates Typically, a desired amount of SEP was weighed and dissolved in EAN (1 mL) by slightly heating in a screw-cap vial. Then the clear solution became opaque and much viscous upon cooling slowly to room temperature. Generally, the samples were equilibrated at 25 °C for at least 4 weeks before further investigation. For comparison, the samples of OB assembled in EAN were prepared in a similar manner. 2.4. Characterization methods

Thermogravimetry The SEP complex was transferred into an open platinum crucible and analyzed on a Mettler Toledo TGA/DSC1 with a heating rate of 5 °C·min-1 from 25 to 900 °C under a nitrogen atmosphere. 7 ACS Paragon Plus Environment


Optical and fluorescence microscopy To get initial aggregate morphology images, the normal or polarized optical microscopy (POM) observations were carried out on a Motic B2 microscope with a CCD camera (Panasonic Super Dynamic II WV-CP460). An inverted fluorescence microscope (Model IX81, Olympus, Japan) was also used for luminescent soft aggregates.

Transmission and scanning electron microscopy The detailed soft aggregate morphology was observed by transmission electron microscopy (TEM) on a Hitachi 100CX-II operating at 100 kV. More in situ aggregate morphology was observed by the freeze-fracture TEM. The fracturing and replication were performed on EM BAF060 (Leica, Germany) at a temperature of −150 °C. A small amount of sample was placed on a specimen holder, which was frozen by plunging the holder into the liquid propane cooled by liquid nitrogen. Pt/C was deposited at an angle of 45 ° to shadow the replicas and C was deposited at an angle of 90 ° to consolidate the replicas. The resulting replicas were observed with a Hitachi 100CX-II operating at 100 kV. High-resolution transmission electron microscopy (HR-TEM) images were recorded on a HRTEM JEOL 2100 system operating at 200 kV. Three dimensional morphology observation and composition judgment were taken by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) on a Hitachi SU8010 operated at 5.0 kV. To make the sample suitable for TEM and SEM measurements, the aggregates were firstly immersed in acetone to remove EAN for five days and the acetone was replaced every 12 hours. Then the acetone was changed to water and the samples were dried via vacuum freeze drying.29, 30

Small-angle X-ray scattering 8 ACS Paragon Plus Environment

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To get more direct structural information, the SAXS measurements were performed on a SAXSess mc2 X-ray scattering system (Anton Paar) operated at 50 kV and 40 mA. The distance from the detector to the sample was 264.5 mm and the wavelength of X-ray used in the measurements was 0.1542 nm (Cu Kα). The exposure time of all samples was 20 minutes.

Fluorescence spectroscopy Steady state fluorescence spectra and lifetime of the samples were recorded on an Edinburgh Instruments FLS920 luminescence spectrometer equipped with a 450 W xenon lamp and a µF920 microsecond flash lamp. The luminescence lifetime was measured via monitoring the luminescence intensity decaying with time at the 5D0→7F2 transition of Eu3+.

Fourier transformed infrared spectroscopy FTIR spectra were recorded from 400 to 4000 cm-1 with a resolution of 4 cm-1 using an Alpha-T spectrometer (Bruker). For the solid powder, a small amount of it was added into KBr salt and the mixture was compressed into a transparent disk.

3. Results and discussion 3.1. Structural characterization for SEP complex As described in experimental section, the supramolecular complex (SEP) prepared mainly by electrostatic interaction between an anionic Weakley-type polyoxometalate (EuW10) and a long chain cationic surfactant (OB) was basically composed of one anionic EuW10 cluster and nine imidazolium cations of OB with a structure model shown in Figure 1. To identify the binding position of OB with EuW10, the complex was characterized by 1H-NMR spectroscopy with the results for SEP and OB shown in Figure 2a. It was observed that, the spectrum for SEP showed 9 ACS Paragon Plus Environment


similar resonance signals to those of pure OB, indicating the maintenance of integrated structure of OB during the encapsulation process. Two proton bands of the imidazolium ring from pure OB (bands 1 & 2 in Figure 2a), however, were shifted toward high field by 0.06 and 0.02 ppm for SEP, respectively. This was attributed to the electrostatic interaction between imidazolium cation and negatively charged EuW10, leading to an increase in the electron density of protons from imidazolium ring.31 Considering the fact that the chemical shifts of the proton signals are sensitive to the local physical and chemical environment, the imidazolium cation headgroup of OB should bind to the negative charged cluster. The existence and keeping of Weakley structure of EuW10 in SEP were certified from their characteristic vibration bands in FT-IR spectrum. As shown in Figure 2b, the characteristic vibration bands of EuW10 at 943 and 846 cm−1 were assigned to ν (W=Od) and ν (W−Ob−W), respectively. Those at 788 and 706 cm−1 were ascribed to ν (W−Oc−W), where Ob and Oc represented the bridged oxygen atoms of two octahedra sharing a corner and an edge, respectively, while Od denoted the terminal oxygen.32 For the SEP complex, the characteristic bands of EuW10 still existed, indicating that its structure remained intact in the hybrid. However, these bands were shifted to 935, 844, 776, and 713 cm−1, respectively, which illustrated the intense electrostatic interaction between OB and EuW10. The reduced W=Od vibration frequencies confirmed the existence of hydrogen bonding interaction between the two components, since the involvement of terminal oxo ligand of EuW10 cluster in hydrogen bonding slightly elongated the bond length of W=Od, and consequently lowered its vibration frequencies.33 In addition, the peaks located at 3000–2800 cm−1 were assigned to saturated C–H stretching of aliphatic groups from OB, whereas those from the unsaturated C–H stretching of imidazolium ring were observed in 3100–3000 cm−1.34 It was observed that the unsaturated C–H stretching bands in SEP (3087 cm−1) displayed slight change compared to that from pure OB (3072 cm−1). On the other hand, the C–C stretching band at 1177 cm−1 and the C–N 10 ACS Paragon Plus Environment

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stretching peak at 1472 cm−1 assigned to imidazolium ring of pure OB were found to move to 1170 and 1467 cm−1, respectively in SEP. These changes further implied that the electrostatic interaction certainly happened between the imidazolium cation headgroup of OB and the negative charged EuW10 cluster.

Figure 2. 1H-NMR spectra of OB and SEP in DMSO-d6 (a) and FTIR spectra of pure OB, EuW10 and SEP in KBr pellets (b).

3.2. Soft aggregates of SEP formed in EAN To explore and better understand the luminescent properties of constructed soft materials, the aggregation behaviors of OB encapsulated EuW10 complex (SEP) in EAN were firstly investigated. To have a comprehensive understanding on SEP aggregation mechanism, the aggregates formed by OB itself were also investigated. Both SEP and OB exhibited good self-assembling capabilities in EAN, where the opaque and 11 ACS Paragon Plus Environment


much viscous samples were observed at room temperature. The SEP complex formed gel-like aggregates at a concentration even as low as 5.66 wt% (weight percentage). On this base, the SEP samples at three concentrations (5.66, 10.71 and 16.67 wt%) were selected for aggregation mechanism and photophysical property study, corresponding to three equivalent OB concentrations (3.86, 7.44 and 11.82 wt% ) in EAN. For self-aggregation of OB, it was not difficult to understand due to its amphiphilicity. However, the EuW10 itself was insoluble in EAN whatever being treated with heating or sonication. It was because the solvophobic interaction by peripheral alkyl tails of OB in SEP that the POM hybrid became amphiphilic with the solvophilic head containing EuW10 polyanion and imidazolium cations, which made SEP soluble and self-assemble in EAN through hydrogen bonding and electrostatic forces.

Aggregate morphologies and microstructures The preliminary microstructures of formed aggregates were observed by optical microscopy. Figure 3 showed the mapped images under or without polarized light for gel-like samples formed by SEP or OB in EAN. As shown in Figure 3a&b, three-dimensional networks by micro-fibers with an average width of 2 µm and different lengths were seen for both systems. These fibers exhibited strong birefringence when observed under polarized light (Figure 3c&d), demonstrating the anisotropic nature of aggregate structures. The similar aggregate morphologies for SEP or OB in EAN indicated their similar aggregate structures. However, the careful observations indicated that the micro-fibers for OB/EAN aggregates were longer than those for SEP/EAN system, which might suggest certain order deterioration of formed aggregates in the latter system to hinder their further extension. Moreover, it was also observed that the aggregated micro-fibers became more compact and larger with increasing concentrations of SEP or OB, just as shown in Figure S2 for the 12 ACS Paragon Plus Environment

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SEP/EAN system.

Figure 3. Optical microscopic images without (top) and under (bottom) polarized light for 10.71 wt% SEP/EAN (a)&(c) and 7.44 wt% OB/EAN (b)&(d).

To get more structural information for these aggregates, the samples formed by SEP in EAN were further observed by TEM, SEM and FF-TEM. The obtained typical images for the sample at 10.71 wt% SEP in EAN were shown in Figure 4 and Figure S3. It was clearly observed from TEM and SEM images (Figure S3a&b) that the micro-fibers to form three-dimensional networks in EAN were practically micro-ribbons with certain rigidity. Meanwhile, the much shorter lengths of micro-ribbons than those in Figure 3a and large amounts of smaller plates suggested certain aggregate damages caused by the solvent exchange to remove EAN for electron microscope measurements. However, the dominating aggregate lamellar structures were still kept as confirmed by FF-TEM and SAXS measurements. The result from X-ray energy dispersive spectroscopy (EDS) shown in Figure S3c displayed obvious signals of C, N, W and Eu for these micro-ribbons, indicating the presence of SEP. The incorporation of EuW10 into the micro-ribbons was also evidenced from fluorescence microscopy observation, where the luminescent micro-fibers could be seen (Figure S4). These ribbons seemed packed by thin lamellaes as confirmed by FF-TEM image 13 ACS Paragon Plus Environment


(Figure 4a), where a large number of layers were identified. Further observation by HR-TEM with the result shown in Figure 4b revealed that the lamellar ribbons were composed of alternatively arranged bright and dark streaks under bright-field conditions, corresponding to imidazolium cation layer and EuW10 layer, respectively. Here, the repeated layer spacing free from EAN was checked from selected regions as about 3.9 nm. The image at a higher resolution for thin lamellae in Figure 4c demonstrated good dispersion of EuW10 nanoclusters, where EuW10 appeared as black dots with a diameter of 1 to 2 nm, in agreement with the size of a EuW10 cluster determined by crystal structure parameters.26 The similar lamellar structures were also seen from the FF-TEM image for the 7.44 wt% OB/EAN sample (Figure S5). Therefore, it was easily considered that the aggregates formed by SEP or OB in EAN might have similar microstructures, perhaps due to the similar dominating intermolecular forces, i.e. solvophobic interactions.

Figure 4. FF-TEM (a), HR-TEM edge (b) and face (c) images for 10.71 wt% SEP/EAN sample.

SAXS measurement and self-assembly mechanism How about the molecular packing and self-assembly mechanism of SEP in such a lamellar structure? To answer this question, the SAXS patterns for these SEP or OB aggregate samples were measured with the results shown in Figure 5. As reported before, the long alkyl surfactant with imidazolium headgroup could self-assemble in EAN to form aggregates of lamellar phase.27,35 For OB used here, its aggregate SAXS patterns exhibited two scattering peaks at different 14 ACS Paragon Plus Environment

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concentrations (Figure 5a). The scattering factor ratios of 1st and 2nd peaks (q1/q2) were nearly 1:2, indicating a lamellar structure of the aggregates, in good agreement with that from FF-TEM observation (Figure S5). The repeated layer spacing (d) including the thicknesses of OB bilayer and EAN solvent layer 36 was then calculated to be 7.0 nm from the scattering factor of the first peak (d = 2π/q1), nearly independent of the OB concentration.37,38 For SEP/EAN system, however, only one obvious scattering peak was shown in Figure 5b, indicating that the existence of EuW10 in SEP deteriorated the order of layered aggregates. The d value was also calculated as 7.0 nm and did not change at different SEP concentrations. The nearly same repeated layer spacings in two systems fundamentally demonstrated that the aggregates formed by SEP or OB in EAN should have similar lamellar structures. Think back to the HR-TEM image shown in Figure 4b, where the SEP bilayer thickness free from EAN was mapped as about 3.9 nm. Thus, the EAN solvent layer was about 3.1 nm for SEP/EAN system, much larger than the POM average diameter.26

Figure 5. SAXS patterns of OB/EAN (a) and SEP/EAN (b) at three different concentrations and 25 °C.

What caused SEP or OB to self-assemble in EAN to form micro-ribbons with lamellar structures? Why were the aggregates formed by SEP in EAN less organized than those of OB/EAN system? To get answers to these questions, the dominant intermolecular forces should be disclosed clearly. As investigated before, the long alkyl surfactant with imidazolium headgroup could 15 ACS Paragon Plus Environment


self-assemble in EAN to form lamellar phase mainly through the hydrogen bonding and solvophobic interactions.27,35 The similar roles should be played here to facilitate OB to form gel-like samples in EAN at lower concentrations. The importance of solvophobic interaction to dominate lamellae formation was also certified by a parallel control experiment, where the 1-hexadecyl-3-methylimidazolium bromine ([C16mim]Br) with a little shorter alkyl chain than OB was used and only clear solutions without any large aggregate were formed in EAN at equivalent concentrations. As for the growth of 1D anisotropic assemblies, however, it should be related to the directional noncovalent forces like π-π stacking and hydrogen bonding.33,39 For example, Yan et al. discovered the dominant role of trace amounts of hydrogen-bond-forming solvent for mediation of dipeptide self-assembly to form fibers.40 In the studied OB/EAN system here, the EAN molecule preferred to interact with OB headgroup through hydrogen bonding produced either between O atoms in NO3and H atoms of imidazolium ring or between H atoms in CH3CH2NH3+ and N atoms of imidazolium headgroup.27,35 If using a nonprotic ionic liquid, 1-butyl-3-methylimidazolium terafluoroborate ([Bmim]BF4), however, OB only formed opaque gel-like samples with much shorter lamellar aggregates owning to the lack of solvent-bridged hydrogen bonding (Figure S6). Therefore, the strong solvophobic interactions and the directional hydrogen bonding should be responsible for the production of micro-ribbons with lamellar structures in OB/EAN system. With the time increase, the gradually interweaving of micro-ribbons endowed the samples with high viscosities. In spite of being less ordering than OB/EAN system, the similar lamellar aggregates formed by SEP in EAN should originate from the similar dominating intermolecular interactions. Based on all the obtained results, a mechanism model for SEP self-assembling in EAN was proposed, which was shown in Figure 6. As a unique building block, SEP is capable of rearranging the peripheral covered 16 ACS Paragon Plus Environment

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surfactants to change its amphiphilicity. For example, Wu et al. have observed that the inverse bilayer model with the POM located at the middle of the sandwich structure in organic solution could transform into another model where the surfactants adopted a regular bilayer form with POM clusters covering it as the counterions in water.9 In our situation here, EAN, as a protic ionic liquid, possesses a number of similarities to water and thus has ability to form a three dimensional hydrogen-bonding network. Therefore, with the help of solvophobic interactions of the alkyl chain, solvent mediated hydrogen bonding and electrostatic interactions of polar head groups in EAN, the peripheral surfactants of SEP rearranged and adopted a regular bilayer form with EuW10 polyanions covering it as the counterions. The produced lamellar structure was just as the model illustrated in Figure 6a. Compared with the solvophobic chain length of OB (2.3 nm) calculated at the B3LYP/6-31G(d, p) level using the density functional theory (DFT) calculation and the lateral height of EuW10 (0.8 nm), the thickness of one SEP layer free from EAN solvent (3.9 nm, Figure 4b) was larger than the length sum of above two components but less than twice of it. Consequently, the interdigitated arrangement of OB alkyl chains might be reasonable (Figure 6a).37,38,41 Such formed lamellar aggregates further stacked into long micro-ribbons through the directional hydrogen bonding (Figure 6b). The three-dimensional networks of micro-ribbons would be gradually formed to solidify the EAN solvents (Figure 6c). It should be mentioned that the ordering of aggregates formed by SEP in EAN was worse than that of OB/EAN system in spite of possessing the similar lamellar structures. As polyanionic nanocluster counterions, EuW10 would form hydrogen bonding and electrostatic forces with imidazolium cations. Thus, the adsorbed EuW10 on the surface of OB bilayer might produce disturbance on the packing ordering of imidazolium rings through certain steric hindrance.



Figure 6. Schematic representation for the lamellar arrangement of SEP complex (a) in an aggregated micro-ribbon model (b); and the formed luminescent three-dimensional networks in EAN (c).

3.3. The photophysical properties of SEP aggregates The excitation and emission spectra for such SEP/EAN aggregates were measured to explore the effect of organized micro-environment on the luminescence efficiency. Figure 7a exhibited the excitation spectra of EuW10 at different aggregated states. As we can see, a strong excitation band assigned to the ligand to metal charge transfer (LMCT) transition of O→W for EuW10 (304 nm) was observed to move to 283 nm for SEP and roughly 270 nm for SEP/EAN system owning to the surface environment change of Eu3+. This charge transfer band usually plays an important role for EuW10 luminescence since the photoexcitation of this transition could lead to an intramolecular energy transfer from the O→W LMCT excited state to the 5D0 emitting state of Eu3+. The electron originated from the 5D0 excited state would relax to the 7Fj ground state, ultimately generating the characteristic luminescence of Eu3+.42 Therefore, such a process should be strongly affected by surrounding ligand configuration.43 In SEP here, the strong electrostatic interaction between the imidazolium cations of OB and EuW10 would modify the coordination environment of Eu3+ and alter the LMCT transition process. The self-assembly of SEP in EAN, however, would further 18 ACS Paragon Plus Environment

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change the micro-environment of EuW10 and cause an excitation wavelength blue shift again. Moreover, all the narrow peaks in Figure 7a presented from 350 to 500 nm were originated from the characteristic 4f 6 transitions of Eu3+ ion, i.e. 395 nm (7F0→5L6), 416 nm (7F0→5D3) and 465 nm (7F0→5D2).44 Obviously, the relatively reduced excitation intensities of characteristic 4f6 shell transitions for SEP and corresponding aggregates in EAN indicated a more efficient intramolecular energy transfer from O→W LMCT band to Eu3+.45 It was possible that the organic matrix around EuW10 reduced the delocalization of d1 electron to result in a more efficient transition.46

Figure 7. Excitation (a) and emission (b) spectra of EuW10 at different aggregated states. Excitation spectra were obtained by examining 5D0→7F2 transition and emission spectra were measured under excitation into the LMCT states.

Figure 7b displayed the corresponding emission spectra under excitation into the LMCT states, where the characteristic 5D0→7Fj (j = 0, 1, 2, 3, 4) transitions of Eu3+ were observed.44 It is generally accepted that the 5D0→7F0 transition (579 nm) of Eu3+ is strictly forbidden in a symmetric field. Therefore, the clear bands occurred near 579 nm in Figure 7b indicated the low symmetry environments around Eu3+ respectively in EuW10, SEP and SEP/EAN systems and there existed no inversion center.44 As a magnetic dipole transition, the intensity of 5D0→7F1 was hardly changed from the microenvironment alteration of Eu3+. For this reason, all measured emission spectra were normalized to the 5D0→7F1 transition to compare the other band changes. On the contrary, the 19 ACS Paragon Plus Environment


5

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D0→7F2 electric dipole transition was more sensitive to surrounding environment of Eu3+ with its

intensity increased at reduced coordination symmetry. Therefore, the transition intensity ratio of 5

D0→7F2 to 5D0→7F1, referred as I(0→2)/I(0→1), could be used to evaluate such a symmetry change

under different conditions.47 Taking the 5D0→7F1 transition as a criterion, the stronger intensity of 5

D0→7F2 transition indicated a higher asymmetry environments around Eu3+. Table 1 listed the photophysical properties for all investigated samples. It was found that the

I(0→2)/I(0→1) value increased from 0.73 for EuW10 to 1.25 for SEP amorphous powder. Such increased intensity ratios have also been reported previously in organic and polymer matrices possibly due to uniform dispersion and fixation of EuW10.46 After self-assembled in EAN, this ratio was further increased to 1.78 at a SEP concentration of 16.67 wt%. Such a tendency indicated an enhanced asymmetry of Eu3+ coordination and monochromaticity, which was attributed to the anisotropic distribution of EuW10 in formed lamellar aggregates. Moreover, only a slight increase of coordination asymmetry degree was observed with further increasing SEP concentration in EAN, possibly due to little ordering improvement under the stronger electrostatic forces between EuW10 at higher concentration. Table 1. The Photophysical Properties of EuW10 at Different Aggregated States

I(0→2) / I(0→1)

τ

kr

knr

η

[ms]

[ms-1]

[ms-1]

[%]

EuW10

0.73

2.93

0.17

0.17

50.92

SEP

1.25

3.56

0.21

0.07

75.12

SEP/EAN (5.66 wt%)

1.57

3.08

0.24

0.09

72.65

(10.71 wt%)

1.68

2.79

0.24

0.13

65.84

(16.67 wt%)

1.78

2.74

0.24

0.12

66.91

samples


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In addition, for a better understanding of Eu3+ local coordination structure changes, the fluorescence decay curves of 5D0→7F2 emission for all samples were measured. The fluorescence lifetimes (τ) were therefore obtained by fitting the decay profiles with a double-exponential function. As seen in Table 1, the τ value of SEP amorphous powder (3.56 ms) was increased significantly when compared with that of pure EuW10 (2.93 ms), which was ascribed to more effective isolation and fixation of EuW10 clusters by OB to reduce the nonradiative vibration inactivation.48 As a comparison, the Eu-containing POM complexes with quaternary ammonium surfactants usually have shorter τ values than those of corresponding Eu-POMs.43,45 This was attributed to the strong interactions between the quaternary ammonium headgroup and Eu-containing POMs, which might affect the intramolecular fluorescence resonant energy transfer between WO6 octahedron and Eu3+, leading to certain fluorescence quenching.32,42,43,49 For aggregates in EAN, however, the fluorescence lifetimes were shortened more at higher concentrations of SEP, possibly originated from nonradiative vibrational deactivation of EuW10 because of the soft support nature of aggregates as well as concentration quenching. Nevertheless, the lowest τ value here for aggregate sample at 16.67wt% SEP concentration (2.79 ms) was still better than those reported even in solidlike matrix like the copolymer hybrids containing EuW10 (τ = 1.50 ms) and the ultra-thin films based on layered double hydroxides and EuW10 (τ = 2.22 ms).14,45 Moreover, the soft aggregates constructed in EAN here also exhibited much longer lifetimes than those for luminescent hybrid nanoparticles or vesicles containing EuW10 in water.13,50 All these further demonstrated the effective isolation and fixation of EuW10 clusters by OB and advantages of EAN as medium to fundamentally avoid the water-induced quenching. Based on the fluorescence lifetimes and emission spectra, the rate constants of radiative (kr) or nonradiative (knr) and the quantum efficiency (η) of 5D0 excited state were determined (see the 21 ACS Paragon Plus Environment


Supporting Information for details), which were also summarized in Table 1. Compared to pure EuW10, the values of a relatively higher kr along with a lower knr were observed for SEP amorphous powder. Thus a relatively higher η value was obtained, suggesting a better energy transfer efficiency due to homogeneous distribution and confinement of EuW10 to weaken the concentration and collision quenching.51 Consistent with the trend of lifetime change, the η values of SEP/EAN samples were a little smaller than that of SEP, but still larger than that of pure EuW10 solid, which could be understood from the changes of kr and knr. As shown in Table 1, though possessing higher kr values, the knr values of SEP/EAN samples increased faster, which further demonstrated their stronger nonradiative vibrational deactivation due to the soft matrix nature. Ultimately the relatively lower η values were obtained. In addition, the slightly decreased lifetimes as well as quantum efficiency values with increasing concentration of SEP in EAN were possibly due to the concentration quenches.

4. Conclusions In summary, the luminescent soft materials containing EuW10 have been constructed through a convenient self-assembling method of SEP in EAN. The lyotropic aggregate structure accompanying with their luminescence properties have been studied in detail. Investigations showed that SEP formed gel-like samples in EAN at a concentration even as low as 5.66 wt%, which were composed of micro-ribbons with lamellar structures. Through the hydrogen bonding and solvophobic interactions in EAN, the peripheral surfactants of SEP rearranged and adopted a regular interdigitated bilayer form with EuW10 polyanions covering it as the counterions, which was totally different from the usual inverse bilayer model with the POM located at the middle of the sandwich structure in organic solution.8,9 Meanwhile, it was further confirmed that using EAN as


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the self-assembling solvent could basically avoid the quenching from water molecules to improve the luminescence performance as observed from our previously study.24,25 The produced SEP complex presented better monochromaticity than EuW10 due to the stronger interactions between Eu3+ and its microenvironment.52 Meanwhile, the luminescence lifetime and quantum efficiency of SEP were much improved owning to the good isolation and confinement of EuW10 by imidazolium surfactant to limit the nonradiative vibration inactivation. The obtained photophysical parameters of SEP were also much better than those of reported quaternary ammonium surfactants encapsulated Eu-containing POM complexes.43,45 The soft SEP aggregates in EAN, however, further improved the dispersion of EuW10 in an IL-based matrix and exhibited an efficient energy transfer and enhanced monochromaticity. Though having a slight reduction compared to SEP, these luminescent properties of soft aggregates were comparable to or even better than those Eu-POM hybrids by solid matrices possibly owning to the enhanced isolation effect and nonaqueous environment.13,14,45,49 Moreover, the produced luminescent soft materials, retaining the physicochemical nature of EAN, are easily shaped to prepare coatings or rods, making them potential to be used in optical devices. Therefore, the findings herein not only supplemented the aggregation behavior of POMs hybrid in ILs, but also provided a stable and biocompatible self-assembling matrix. The structure tunability of ILs could make such fabricated luminescent soft materials with versatility to meet more demands, like the construction of well-organized films of Eu-containing POMs by introducing polymerizable ILs.

Supporting information Details on the purities characterizations of synthesized products are included. The optical and electron microscopy images for aggregate morphologies and calculation methods of photophysical parameters are also provided. This material is available via the Internet at http://pubs.acs.org. 23 ACS Paragon Plus Environment


Acknowledgements This work was financially supported by the National Natural Science Foundation of China (21373127 and 21673129). The authors are very thankful to Zhaozhen Cao for her assistance in photophysical properties characterizations and useful discussions. References (1) Irie, M.; Fukaminato, T.; Sasaki, T.; Tamai, N.; Kawai, T. Organic Chemistry: a Digital Fluorescent Molecular Photoswitch. Nature 2002, 420, 759-760. (2) Sirringhaus, H. Device Physics of Solution-Processed Organic Field-Effect Transistors. Adv. Mater. 2005, 17, 2411-2425. (3) Binnemans, K. Lanthanide-Based Luminescent Hybrid Materials. Chem. Rev. 2009, 109, 4283-4374. (4) Biju, S.; Xu, L. J.; Sun, C. Z.; Chen, Z. N. White OLEDs Based on a Novel Eu III-Tetrakis-β-Diketonate Doped into 4, 4′-N, N′-Dicarbazolebiphenyl as Emitting Material. J. Mater. Chem. C 2015, 3, 5775-5782. (5) Feng, J.; Zhang, H. J. Hybrid Materials Based on Lanthanide Organic Complexes: a Review. Chem. Soc. Rev. 2013, 42, 387-410. (6) Granadeiro, C. M.; de Castro, B.; Balula, S. S.; Cunha-Silva, L. Lanthanopolyoxometalates: From the Structure of Polyanions to the Design of Functional Materials. Polyhedron 2013, 52, 10-24. (7) Long, D. L.; Burkholder, E.; Cronin, L. Polyoxometalate Clusters, Nanostructures and Materials: from Self Assembly to Designer Materials and Devices. Chem. Soc. Rev. 2007, 36, 105-121. (8) Li, H. L.; Sun, H.; Qi, W.; Xu, M.; Wu, L. X. Onionlike Hybrid Assemblies Based on 24 ACS Paragon Plus Environment

Page 24 of 31

Page 25 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Surfactant-Encapsulated Polyoxometalates. Angew. Chem. Int. Ed. 2007, 46, 1300-1303. (9) Yan, Y.; Li, B.; Li, W.; Li, H. L.; Wu, L. X. Controllable Vesicular Structure and Reversal of a Surfactant-Encapsulated Polyoxometalate Complex. Soft Matter 2009, 5, 4047-4053. (10) Gao, P. F.; Wu, Y. Q.; Wu, L. X. Co-Assembly of Polyoxometalates and Peptides towards Biological Applications. Soft matter 2016, 12, 8464-8479. (11) Zhang, J.; Liu, Y.; Li, Y.; Zhao, H. X.; Wan, X. H. Hybrid Assemblies of Eu-Containing Polyoxometalates and Hydrophilic Block Copolymers with Enhanced Emission in Aqueous Solution. Angew. Chem. Int. Ed. 2012, 51, 4598-4602. (12) Wei, H. B.; Du, S. M.; Liu, Y.; Zhao, H. X.; Chen, C. Y.; Li, Z. B.; Lin, J.; Zhang, Y.; Zhang, J.; Wan, X. H. Tunable, Luminescent, and Self-healing Hybrid Hydrogels of Polyoxometalates and Triblock Copolymers Based on Electrostatic Assembly. Chem. Commun. 2014, 50, 1447-1450. (13) Guo, Y. X.; Gong, Y. J.; Qi, L. B.; Gao, Y. A.; Yu, L. A Polyoxometalate-Based Supramolecular Chemosensor for Rapid Detection of Hydrogen Sulfide with Dual Signals. J. Colloid Interface Sci. 2017, 485, 280-287. (14) Xu, J. H.; Zhao, S.; Han, Z. Z.; Wang, X. T.; Song, Y. F. Layer-by-layer Assembly of Na9(EuW10O36)·32H2O and Layered Double Hydroxides Leading to Ordered Ultra-Thin Films: Cooperative Effect and Orientation Effect. Chem. Eur. J. 2011, 17, 10365-10371. (15) Zhang, T.; Fu, D. Y.; Wu, Y. Q.; Wang, Y. Z.; Wu, L. X. Potential Applications of Polyoxometalates for the Discrimination of Human Papillomavirus in Different Subtypes. Dalton Trans. 2016, 45, 15457-15463. (16) Wei, H. B.; Zhang, J. L.; Shi, N.; Liu, Y.; Zhang, B.; Zhang, J.; Wan, X. H. A Recyclable Polyoxometalate-Based Supramolecular Chemosensor for Efficient Detection of Carbon Dioxide. Chem. Sci. 2015, 6, 7201-7205. 25 ACS Paragon Plus Environment


(17) Granadeiro, C. M.; Ribeiro, S. O.; Kaczmarek, A. M.; Cunha-Silva, L.; Almeida, P. L.; Gago, S.; Deun, R. V.; de Castro, B.; Balula, S. S. A Novel Red Emitting Material Based on Polyoxometalate@ Periodic Mesoporous Organosilica. Microporous Mesoporous Mater. 2016, 234, 248-256. (18) Kropp, J. L.; Windsor, M. W. Luminescence and Energy Transfer in Solutions of Rare-Earth Complexes. I. Enhancement of Fluorescence By Deuterium Substitution. J. Phys. Chem. 1965, 42, 1599-1608. (19) Binnemans, K. Lanthanides and Actinides in Ionic Liquids. Chem. Rev. 2007, 107, 2592-2614. (20) Nockemann, P.; Beurer, E.; Driesen, K.; Van Deun, R.; Van Hecke, K.; Van Meervelt, L.; Binnemans, K. Photostability of a Highly Luminescent Europium β-diketonate Complex in Imidazolium Ionic Liquids. Chem. Commun. 2005, 34, 4354-4356. (21) Li, H. R.; Shao, H. F.; Wang, Y. G.; Qin, D. S.; Liu, B. Y.; Zhang, W. J.; Yan, W. D. Soft Material with Intense Photoluminescence Obtained by Dissolving Eu2O3 and Organic Ligand into a Task-Specific Ionic Liquid. Chem. Commun. 2008, 41, 5209-5211. (22) Sharma, S. C.; Atkin, R.; Warr, G. G. The Effect of Ionic Liquid Hydrophobicity and Solvent Miscibility on Pluronic Amphiphile Self-Assembly. J. Phys. Chem. B 2013, 117, 14568-14575. (23) Li, Q. T.; Yao, M. H.; Yue, X.; Chen, X. Effects of a Spacer on the Phase Behavior of Gemini Surfactants in Ethanolammonium Nitrate. Langmuir 2017, 33, 4328-4336. (24) Yi, S. J.; Wang, J.; Chen, X. Enhanced Energy Transfer Efficiency and Stability of Europium β-Diketonate Complex in Ionic Liquid-Based Lyotropic Liquid Crystals. Phy. Chem. Chem. Phy. 2015, 17, 20322-20330. (25) Yi, S. J.; Yao, M. H.; Wang, J.; Chen, X. Highly Luminescent and Stable Lyotropic Liquid Crystals Based on a Europium β-Diketonate Complex Bridged by an Ethylammonium Cation. Phys. 26 ACS Paragon Plus Environment

Page 26 of 31

Page 27 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Chem. Chem. Phys. 2016, 18, 27603-27612. (26) Sugeta, M.; Yamase, T. Crystal Structure and Luminescence Site of Na9(EuW10O36)·32H2O. Bull. Chem. Soc. Jpn. 1993, 66, 444-449. (27) Zhao, Y. R.; Chen, X.; Wang, X. D. Liquid Crystalline Phases Self-Organized from a Surfactant-Like Ionic Liquid C16mimCl in Ethylammonium Nitrate. J. Phys. Chem. B 2009, 113, 2024-2030. (28) Evans, D. F.; Chen, S. H.; Schriver, G. W.; Arnett, E. M. Thermodynamics of Solution of Nonpolar Gases in a Fused Salt. Hydrophobic Bonding Behavior in a Nonaqueous System. J. Am. Chem. Soc. 1981, 103, 481-482. (29) Yu, Q. L.; Wu, Y.; Li, D. M.; Cai, M. R.; Zhou, F.; Liu, W. M. Supramolecular Ionogel Lubricants with Imidazolium-Based Ionic Liquids Bearing the Urea Group as Gelator. J. Colloid Interface Sci. 2017, 487, 130-140. (30) Wang, X. L.; Zhang, Z.; Cao, Y.; Hao, J. C. Ionogels of Pseudogemini Supra-Amphiphiles in Ethylammonium Nitrate: Structures and Properties. J. Colloid Interface Sci. 2017, 491, 64-71. (31) Li, H. L.; Yang, Y.; Wang, Y. Z.; Li, W.; Bi, L. H.; Wu, L. X. In Situ Fabrication of Flower-Like Gold

Nanoparticles

in

Surfactant-Polyoxometalate-Hybrid

Spherical

Assemblies. Chem.

Commun. 2010, 46, 3750-3752. (32) Jiang, M.; Liu, M. H. A Photoluminescent Switch Based on the Hybrid Organized Molecular Films of Decatungsteuropate and Some Amphiphiles. J. Colloid Interface Sci. 2007, 316, 100-106. (33) Yin, P. C.; Bayaguud, A.; Cheng, P.; Haso, F.; Hu, L.; Wang, J.; Vezenov, D.; Winans, R. E.; Hao, J.; Li, T. et al. Spontaneous Stepwise Self-Assembly of a Polyoxometalate-Organic Hybrid into Catalytically Active One-Dimensional Anisotropic Structures. Chem. Eur. J 2014, 20, 9589-9595. 27 ACS Paragon Plus Environment


Page 28 of 31

(34) Wang, G. Y.; Wang, Y. Y.; Wang, X. H. Aggregation Behaviors of Mixed Systems for Imidazole Based Ionic Liquid Surfactant and Triton X-100. J. Mol. Liq. 2017, 232, 55-61. (35) Zhao, M. W.; Gao, Y. A.; Zheng, L. Q. Lyotropic Liquid Crystalline Phases Formed in Binary Mixture

of

1-Tetradecyl-3-Methylimidazolium

Chloride/Ethylammonium

Nitrate

and

Its

Application in the Dispersion of Multi-Walled Carbon Nanotubes. Colloids Surf. A 2010, 369, 95-100. (36) Long, P. F.; Yan, H.; Guo, X. H.; Hao, J. C. Lyotropic Liquid Crystal Phases of Lithium Perfluorinated Fatty Acid Salts in Aqueous Solutions and Molecular Dynamics Study of the Lamellar Phase. J. Fluorine Chem. 2012, 135, 315-322. (37) Cheng, N.; Hu, Q. Z.; Bi, Y. H.; Xu, W. W.; Gong, Y. J.; Yu, L. Gels and Lyotropic Liquid Crystals: Using an Imidazolium-Based Catanionic Surfactant in Binary Solvents. Langmuir 2014, 30, 9076-9084. (38) Wang, X. L.; Yang, Q.; Cao, Y. X.; Hao, H. B.; Zhou, J. H.; Hao, J. C. Metallosurfactant Ionogels in Imidazolium and Protic Ionic Liquids as Precursors to Synthesize Nanoceria as Catalase Mimetics for the Catalytic Decomposition of H2O2. Chem. Eur. J 2016, 22, 17857-17865. (39) Rosnes, M. H.; Musumeci, C.; Pradeep, C. P.; Mathieson, J. S.; Long, D. L.; Song, Y. F.; Pignataro, B.; Cogdell, R.; Cronin, L. Assembly of Modular Asymmetric Organic-Inorganic Polyoxometalate Hybrids into Anisotropic Nanostructures. J. Am. Chem. Soc. 2010, 132, 15490-15492. (40) Wang, J.; Liu, K.; Yan, L. Y.; Wang, A. H.; Bai, S.; Yan, X. H. Trace Solvent as a Predominant Factor to Tune Dipeptide Self-Assembly. ACS nano 2016, 10, 2138-2143. (41) Ramakanth, I.; Ramesh, N.; Patnaik, A. Fibrous Gels of Cetylpyridinium Chloride in Binary Solvent Mixtures: Structural Characteristics and Phase Behaviour. J. Mater. Chem. 2012, 22, 28 ACS Paragon Plus Environment

Page 29 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17842-17847. (42) Wang, X. T.; Wang, J. Q.; Tsunashima, R.; Pan, K.; Cao, B.; Song, Y. F. Electrospun Self-Supporting

Nanocomposite

Films

of

Na9(EuW10O36)·32H2O/PAN

as

pH-Modulated

Luminescent Switch. Ind. Eng. Chem. Res. 2013, 52, 2598-2603. (43) Zhang, T. R.; Spitz, C.; Antonietti, M.; Faul, C. F. Highly Photoluminescent Polyoxometaloeuropate-Surfactant Complexes by Ionic Self-Assembly. Chem. Eur. J 2005, 11, 1001-1009. (44) Binnemans, K. Interpretation of Europium (III) Spectra. Coord. Chem. Rev. 2015, 295, 1-45. (45) Li, H. L.; Qi, W.; Li, W.; Sun, H.; Bu, W. F.; Wu, L. X. A Highly Transparent and Luminescent Hybrid Based on the Copolymerization of Surfactant-Encapsulated Polyoxometalate and Methyl Methacrylate. Adv. Mater. 2005, 17, 2688-2692. (46) Bu, W. F.; Li, H. L.; Li, W.; Wu, L. X.; Zhai, C. X.; Wu, Y. Q. Surfactant-Encapsulated Europium-Substituted Heteropolyoxotungstates: Structural Characterizations and Photophysical Properties. J. Phys. Chem. B 2004, 108, 12776-12782. (47) Wang, L. H.; Wang, W.; Zhang, W. G.; Kang, E. T.; Huang, W. Synthesis and Luminescence Properties of Novel Eu-Containing Copolymers Consisting of Eu (III)-Acrylate-β-Diketonate Complex Monomers and Methyl Methacrylate. Chem. Mater. 2000, 12, 2212-2218. (48) Yi, S. J.; Li, Q. T.; Liu, H. G.; Chen, X. Reverse Lyotropic Liquid Crystals from Europium Nitrate and P123 with Enhanced Luminescence Efficiency. J. Phys. Chem. B 2014, 18, 11581-11590. (49) Wang, Z. L.; Zhang, R. L.; Ma, Y.; Peng, A. D.; Fu, H. B.; Yao, J. N. Chemically Responsive Luminescent

Switching

in

Transparent

Flexible

Self-Supporting

Nanocomposite Thin Films. J. Mater. Chem. 2010, 20, 271-277. 29 ACS Paragon Plus Environment

[EuW10O36]9--Agarose


(50) Zhang, H.; Guo, L. Y.; Xie, Z. C.; Xin, X.; Sun, D.; Yuan, S. L. Tunable Aggregation-Induced Emission of Polyoxometalates via Amino Acid-Directed Self-Assembly and Their Application in Detecting Dopamine. Langmuir 2016, 32, 13736-13745. (51) Lunstroot, K.; Driesen, K.; Nockemann, P.; Viau, L.; Mutin, P. H.; Vioux, A.; Binnemans, K. Ionic Liquid as Plasticizer for Europium (III)-Doped Luminescent Poly (Methyl Methacrylate) Films, Phys. Chem. Chem. Phys. 2010, 12, 1879-1885. (52) Chen, X.; Wang, Y. R.; Chai, R.; Xu, Y.; Li, H. R.; Liu, B. Y. Luminescent Lanthanide-Based Organic/Inorganic Hybrid Materials for Discrimination of Glutathione in Solution and within Hydrogels. ACS Appl. Mater. Interfaces 2017, 9, 13554-13563.


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TOC Graphic


Unusual Aggregation Arrangement of Eu-Containing Polyoxometalate

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