- Email: [email protected]
Synthesis and fluorescent properties of europium–polymer complexes containing 1,10-phenanthroline
Synthetic Metals 159 (2009) 1557–1562
Contents lists available at ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Synthesis and fluorescent properties of europium–polymer complexes containing 1,10-phenanthroline Xingyu Liu, Yulin Hu, Baoyan Wang, Zhixing Su ∗ Institute of Polymer and Engineering, College of Chemistry and Chemical Engineering, Lanzhou University, Tianshui South Road 222, Lanzhou 730000, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 8 May 2008 Received in revised form 14 April 2009 Accepted 16 April 2009 Available online 20 May 2009 Keywords: 5-Acrylamido-1,10-phenanthroline Rare earth Fluorescence Polymer complex
a b s t r a c t In this paper, 5-acrylamido-1,10-phenanthroline (AP) was synthesized, then the luminescence material containing Eu–polymer complexes were obtained by two methods. The polymer structure and properties were characterized by FT-IR, UV, fluorescence spectra, DSC, GPC, ICP and XRD. Compared with the two methods the rare earth ions-containing polymers, we obtained copolymer B by the second one that had high and stable fluorescence intensity with the Eu content 0.31%. Comparing the two results via different methods, we have set down the useful basement for the study of the luminescence material containing Eu–polymer complexes. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Luminescent rare earth complexes have attracted considerable attentions for organic electroluminescent (EL) devices [1–5] as well as for optical microcavity emitters [6,7] owing to their inherent extremely sharp emission bands and potentially high internal quantum efficiency. However, there are many problems for the rare earth complexes that have small molecular weight such as the instability in organic solution and poor compatibility with other materials [8]. Thus, the broad application of rare earth-containing polymers has been attracted significant attention in the past decade [9–12]. In comparison with small molecular weight rare earth complexes, besides the advantage of the desired mechanical flexibility, polymer-based rare earth luminescent materials can be soluble or fused processable, which is attractive for optical [13,14] and electronic [15,16] applications. Recently, one method to synthesize rare earth-containing polymers materials is the direct reaction of the polymer ligands with rare earth ions [17–20]. Another method to obtain rare earthcontaining polymers is the copolymerization of rare earth metalcontaining monomers and polymeric monomers [21–23]. In this paper, the monomer of 5-acrylamido-1,10-phenanthroline was synthesized from 1,10-phenanthroline via nitration, reduction and acylation with acrylic chloride to introduce a terminal double bond capable to copolymerize with monomers [24], as
∗ Corresponding author. Tel.: +86 0931 8912391; fax: +86 0931 8912582. E-mail address: [email protected] (Z. Su). 0379-6779/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2009.04.013
illustrated in Scheme 1. The fluorescent Eu-containing polymer materials using AP as ligands was synthesized by the two different methods as described in detail in the experimental part. The fluorescence behaviors of the two products were investigated and the differences between them were discussed in detail. 2. Experimental 2.1. Materials Eu2 O3 (99.99 wt%) was purchased from Gansu rare earth group Co., Ltd. and used without further purification. Methyl methacrylate was purified before use. 2,2-Azoisobutyronitrile (AIBN) was recrystallized twice from methanol. Polymethyl methacryate (PMMA) was produced by our laboratory. Other chemicals were analytical grade. 2.2. Synthesis of tris(5-acrylamido-1,10-phenanthroline) europium–Eu(AP)3 The complexation reaction between AP and europium chloride follows standard methods. A sample of 400 mg (1.61 mmol) of AP was dissolved in 15 mL methylenechloride, a solution of EuCl3 ·6H2 O (103.4 mg, 0.4 mmol) in 5 mL of anhydrous ethanal was successively add to the solution of AP. The mixture was refluxed at 45 ◦ C for 6.5 h to ensure completion of the reaction. Upon completion of the reaction, the solvent was evaporated under reduced pressure, and the residual brown-yellow precipitate was filtered and washed with distilled water to remove impurities. Further purifica-
1558
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
Scheme 1. Preparation of 5-nitro-1,10-phenanthrolin, 5-amino-1,10-phenanthrolin (phen-NH2 ) and 5-acrylamido-1,10-phenanthrolin (AP).
tion was accomplished by recrystallization from an acetone/water mixture (4/1, v/v), yield ≈ 80%. The polymer cannot be soluble in THF, acetone, methanol and ethanol, but in DMF, as illustrated in Scheme 2. Elemental analysis (calculated/found) for the dried dye (C45 H33 N9 O3 EuCl2 ; MW 970.7): C, 55.68/54.90; H, 3.43/3.77; N, 12.99/12.26; the content of Eu in Eu(AP)3 was determined by ICP (calculated/found): Eu (15.66/15.64). IR(KBr), (cm−1 ): 3365 (N–H ); 1655 (C O ); 1620 (C C ); 1534 (C C+C N ); 1418 (C N ); 1248 (C–N ); 894, 798, 733 (ıC–H ). 2.3. Synthesis of copolymer 5-acrylamido-1,10-phenanthroline (AP) with methyl methacrylate (MMA) (poly(MMA-co-AP))(A) The mixture of AP (0.18 mmol) monomer and MMA (1.4 mmol), initiator AIBN (3.0 × 10−3 mol/L) was dissolved in DMF, and added into a glass polymerization tube. The homogeneous solution was degassed and sealed under vacuum. The polymerization was carried out by heating the sealed tube at 80 ◦ C for 6 h. The viscous homogeneous solution was then dissolved in DMF and poured into 200 mL of methanol with stirring. The process was repeated twice and finally dried under vacuum at 50 ◦ C for 24 h to afford powder polymer. The polymer was easily soluble in chloroform, acetone, THF and DMF, as illustrated in Scheme 2. The structure can be characterized by IR, and the content can be measured by UV (CHCl3 as solution), the measured value of the AP content is 2.35% (wt%). The average molecular weight of copolymer B is Mn = 4.1 × 104 g/mol, Mw /Mn = 1.33, Tg = 102.5 ◦ C. UV: ab = 270 nm. IR (KBr), (cm−1 ): 1732 (C O); 1678 (C O-AP); 1276; 1247; 1194; 1150 (C–C–O–C); 2954 (C–H). 2.4. Synthesis of copolymers of Eu(AP)3 with methyl methacrylate (MMA) (poly(MMA-co-Eu(AP)3 ))(B)
in methanol twice and finally dried under vacuum at 50 ◦ C for 24 h to afford powder polymers. This polymer dissolved in DMF easily, as illustrated in Scheme 2. The Eu content in the copolymers is in the range of 0.086–0.31% (wt%), as listed in Table 2. IR (KBr), (cm−1 ): 1731 (C O); 1272; 1243; 1194; 1148 (C–C–O–C); 2953 (C–H). 2.5. Synthesis of the europium-doped polymethyl methacrylate thin films Eu(AP)3 (9.08 mmol) and PMMA (57.0 mg) were dissolved in 10 mL of DMF, and mixed the DMF containing some concentration PMMA. The mixture solution was poured into on the glass and the film was obtained after dried, finally dried in vacuum chamber. 2.6. Instruments FT-IR were recorded on a Nicolet NEXUS 670FTIR spectrometer by dispersing samples in KBr disks; the fluorescent emission spectrum were recorded on Perkin-Elmer LS 55 fluorescent; UV spectra were taken using on Lambda 35 UV spectrometer (PerkinElmer); the element analysis were carried out by GmbH VarioEL element analysis; the content of Eu complexes were measure by IRIS ER-S WP-1 plasma emission (ICP); DSC measurements were performed at a heating rate of 10 ◦ C/min under nitrogen with a Sapphire DSC Differential Scanning Calorimeter (PerkinElmer). Gel permeation chromatography (GPC) analysis was conducted with a GPCV2000 system using polystyrene as standard and THF as the eluen; X-ray diffraction spectra were conducted on Kristalloflex XRD-5000 X-ray diffraction. 3. Results and discussion 3.1. FT-IR spectral characterization
The mixture of Eu(AP)3 monomer and MMA (1.07 mol/L) in certain ratios, a small amount of initiator AIBN (3.0 × 10−3 mol/L), and solvent DMF was mixed and added into a glass polymerization tube. The homogeneous solution was degassed and sealed under vacuum. The polymerization was carried out by heating the sealed tube at 80 ◦ C for 5 h. The viscous homogeneous solution was then dissolved in DMF and poured into 200 mL of methanol with stirring. The resulting precipitate was redissolved in DMF and reprecipitated
The FT-IR spectra of ligands and complex are recorded in the range of 400–4000 cm−1 . The main absorption bands are listed in Table 1. The FT-IR spectra of ligand 5-acrylamido-1,10phenanthroline (AP) shows that, the C C + C N stretching vibration of aromatic ring for the products Phen-NH2 and AP was 1560 and 1539 cm−1 , respectively. It shows that the band of the stretching vibration decreases with the increase of the electron-donate capa-
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
1559
Scheme 2. Preparation of tris(5-acrylamido-1,10-phenanthroline) europium chloride (Eu(AP)3 ), copolymers poly(MMA-co-AP)(A) and poly(MMA-co-Eu(AP)3 )(B).
bility of the substitute. The N–H stretching vibration of Phen-NH2 was at 3416 and 3322 cm−1 . The N–H stretching vibration of AP shifted to 3427 cm−1 . The C O stretching vibration of amido was at 1682 cm−1 which overlapped the band of C C stretching vibration.
The FT-IR spectrum of the complex tris(5-acrylamido-1,10phenanthroline) europium chloride (Eu(AP)3 ) shows that the C C + C N stretching vibration of aromatic ring in the complex are shifted to low frequencies from 1539 to 1534 cm−1 and the C N and
Table 1 Important IR absorption band of the ligand and complex (cm−1 ). IR (cm−1 )
C Phen-NH2 AP Eu(AP)3
C
1636, 1505, 1453 1621 1620
ıC–H
C
882, 842, 739 878, 800, 741 894, 798, 733
1591, 1426 1407 1418
N
C
C+C N
1560 1539 1534
C–N
N–H
C
1270 1227 1248
3416, 3322 3427 3365
1682 1655
O
1560
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
Table 2 Properties of the Eu-containing copolymers. No.
Eu(AP)3 content in the feed (g)
Ratio of MMA/Eu(AP)3 (%)
Eu (%)
Tg (◦ C)
Mw (×104 )
Mw /Mn
1. 2. 3. 4. 5.
0.1027 0.0867 0.0773 0.0444 0.0269
9.348 11.073 12.419 21.622 35.688
0.31 0.22 0.20 0.19 0.086
124.2 124.5 117.2 124.2 123.4
1.69
1.23
1.94
1.43
2.26
1.29
C–N stretching vibration of aromatic ring in the complex are red shifted from 1407 and 1227 cm−1 to 1418 and 1248 cm−1 , respectively. The bending vibrations of aromatic ring are also shifted, from 878, 800, and 741 cm−1 to 894, 798, and 733 cm−1 . The N–H stretching vibration of the complex are shifted to low frequencies, from 3427 to 3365 cm−1 . Weak band at 417 cm−1 corresponding to the Eu–N stretching vibration was observed. These results suggested that the coordination bonds were formed between the Eu3+ ion and ligand AP in the complex. The FT-IR spectrum of copolymer A shows that the C O stretching vibration of MMA at 1732 cm−1 is absent and the stretching vibration of C–C–O–C at 1276, 1247, 1194, and 1150 cm−1 appears. The C–O stretching vibration of monomer AP is at 1678 cm−1 and the C–H stretching vibration at 2954 cm−1 . These results suggest that the structure of polymer are similar to that of PMMA because the low content of AP in copolymer. The FT-IR spectrum of copolymer B is similar to that of copolymer A because the content of Eu is too low. It indicates that there are a lot of MMA chains in the backbone of copolymer B. So the properties of the products are similar to that of MMA and show good solubilities in THF and DMF.
cultly. The Tg of copolymer A is much higher than that of copolymer B (117.2–124.5 ◦ C).
3.2. Thermal properties
3.3. UV properties
As shown in Table 2 and Fig. 1, the Eu content decreases from No. 1 to No. 5 (Eu(AP)3 singlet decreases steadly), the value of Tg decreases slowly with the decrease of the Eu content from 117.2 to 124.5 ◦ C. The chains of the polymer have star-like structure. The higher the Eu content, the more complex the rigid structure. And this limits the movement of copolymers chain. The Tg content of copolymers B increases with the increase of the content of Eu. Due to the little difference of Eu content in samples 1–5 (Eu = 0.086–0.31%), Tg content is just little higher than that of PMMA. But there is no distinct difference among the five samples. Tg of copolymer A is 102.5 ◦ C and Eu3+ makes the chain to move diffi-
Figs. 2–4 shows the UV spectra of copolymers A and B, ligand AP and complex Eu(AP)3 . In Fig. 2, the absorption spectra of copolymer A and ligand AP are similar and they have two absorption peaks at about 270 and 321 nm. It is due to the energy absorption depended on AP after obtaining copolymer A. Furthermore, it is mainly depended on the electron transition of → * in ligand AP. Namely the energy absorbed by AP was transformed to Eu3+ ion. The energy transformed by copolymers B was much less. The UV absorption spectrum of Eu(AP)3 in DMF has shown in Fig. 3. The red shift of absorption peak is due to → * transitions of AP (270, 321 nm), the absorptions of Eu(AP)3 are at 276 and 324 nm. The absorption of copolymer B (Fig. 4) at 270 and 322 nm are close to that of ligand. It shows that the absorption is mainly caused by
Fig. 1. DSC curves of poly(MMA-co-AP)(A) and poly(MMA-co-Eu(AP)3 )(B) (samples 1–5).
Fig. 2. Absorbance spectrum of AP (a) and poly(MMA-co-AP)(A) (b) in DMF.
Fig. 3. Absorbance spectrum of Eu(AP)3 in DMF.
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
1561
Fig. 4. Absorbance spectrum of poly(MMA-co-Eu(AP)3 )(B) in DMF. Fig. 6. Excitation (—) and emission (- - -) spectra of complex Eu(AP)3 solid.
the intermolecular energy transfer of the ligand in the backbone of the copolymer B. 3.4. Fluorescence properties The excitation and emission peaks of AP in DMF were 311 and 420 nm, respectively. The excitation and emission peaks of copolymer A in DMF are 311 and 417 nm, respectively. Obviously, it is showed that the fluorescence of the copolymer A was caused by the fluorphore AP. The excitation and emission spectra of complex Eu(AP)3 in DMF were shown in Fig. 5. The excitation peak is 350 nm. The emission peaks at 580, 595 and 617 nm, are attributed to the 5 D0 → 7 F0 , 5 D → 7 F , and 5 D → 7 F transitions, respectively. The excitation 0 1 0 2 peak of the complex Eu(AP)3 in solid state is 334 nm, and the corresponding emission peaks center at 595 and 617 nm as shown in Fig. 6. The excitation peak of the europium-doped copolymer A in acetone solution is 336 nm. The emission peaks are 598 and 618 nm which can be attributed to the 5 D0 → 7 F1 , 5 D0 → 7 F2 transitions, respectively. It shows that the energy transfer from the polymer ligand to Eu3+ takes place and exhibits the fluorescent characteristic of Eu3+ . AP of copolymer A can increase the emission property of Eu3+ , while its fluorescent is less than that of copolymer B (Eu = 0.31%). So we added N-methyl pyrrolidine (NMP) in binary complex as second ligand and obtained ternary complex. The emission property of ternary complex is much stronger than that of binary complex.
Fig. 5. Excitation (—) and emission (- - -) spectra of complex Eu(AP)3 in DMF.
It indicates that there is corporation action between two ligands in ternary complex. Small molecular ligand increases the coordination number of rare earth ions. The range of conjugated bond complex gets wide and increases the fluorescent emission of Eu3+ . More particularly in ternary complex, the small molecular ligand NMP is main energy donor. The triplet-state level is higher than that of the resonance energy level (5 D0 ) of Eu3+ ion, the more efficient the intermolecular energy transfers. The excitation peak of copolymer B in DMF is 331 nm and the emission peaks centered at 576, 589 and 619 nm, assigned to 5 D0 → 7 F0 , 5 D0 → 7 F1 , and 5 D0 → 7 F2 transitions, respectively. Among the peaks, the emission at 619 nm from the 5 D0 → 7 F2 electric dipole transition is the strongest, suggesting low symmetry around the Eu3+ ion in the Eu-copolymers and monomers. Because the forbidden 5 D0 → 7 F2 electric dipole transition is the sensitive to the coordinative environment of Eu3+ ion, the asymmetric microenvironment causes the polarization of the Eu3+ ion under the influence of the electric field of the surrounding ligands, which increase the probability for the electric dipole transition. 3.5. XRD analysis Fig. 7 shows the X-ray diffraction pattern for different Eu contents. In the atactici PMMA, there were three broad diffraction peaks centered at 13.86◦ , 29.49◦ and 41.46◦ . In the copolymer B,
Fig. 7. X-ray diffraction pattern: (a) Eu(AP)3 , (b) 3.1% Eu(AP)3 /PMMA, (c) 0.086% poly(MMA-co-Eu(AP)3 ), (d) 0.31% poly(MMA-co-Eu(AP)3 ) and (e) PMMA.
1562
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
the diffraction intensity of three main noncrystalline peaks did not increase obviously with the increase of Eu content. Because a little difference of Eu content in copolymer B, their X-ray diffractions were similar. In Eu(AP)3 /PMMA, the three diffraction peaks of PMMA got weak and occurred apparently crystalline peak. From the XRD spectrum, when Eu(AP)3 uniformly dispersed, the result was better than Eu(AP)3 -doped PMMA. Both the long range and relative short range periodic arrangement of atoms and atomic groups are disturbed Eu(AP)3 moiety into polymer chains. As to Eu(AP)3 -doped PMMA systems, only the long range regularity is disturbed. The copolymers are possible to adopt conformation and tactility that is less favour the ligand interaction and excitation migration. As a result a much greater part of the excitation is transferred to Eu3+ under UV radiation. The special conformation is just the driving force that causes the highly fluorescent property. 4. Conclusions 5-Acrylamido-1,10-phenanthroline (AP) was synthesized, and the luminescence material containing Eu–polymer complexes were obtained by two different methods. One was prepared by the direct coordination among AP units, N-methyl pyrrolidine and europium ions; another was synthesized by the direct copolymerization of Eu-complex monomer containing 1,10-phenanthroline with methyl methacryate. We obtained the material, by the second method, which had high and stable fluorescence intensity with the Eu content 0.31%. And the polymer complexes have advantages over Eu(AP)3 -doped polymers in that: (a) the polymer complexes exhibit more intense Eu typical fluorescence; (b) in polymer complexes, Eu(AP)3 moiety is dispersed much more uniformly, which is very important in optical applications. By comparing the two results via different methods, we have set down the useful basement for the study of the luminescence material containing Eu–polymer complexes.
Acknowledgement One of the authors (Xingyu Liu) wishes to thank Prof. Zhixing Su for his kind corporation at Lanzhou University. References [1] J.J. Ding, H.F. Jiu, J. Bao, J.C. Lu, W.R. Gui, Q.J. Zhang, C. Gao, J. Comb. Chem. 7 (2005) 69–72. [2] H. Xin, M. Shi, X.M. Zhang, F.Y. Li, Z.Q. Bian, K. Ibrahim, F.Q. Liu, C.H. Huang, Chem. Mater. 15 (2003) 3728–3733. [3] H. Suzuki, Res. Adv. Appl. Phys. 3 (2003) 11–25. [4] H. Suzuki, M. Notomi, A. Yokoo, Polym. Adv. Technol. 15 (2004) 75–80. [5] H. Suzuki, J. Photochem. Photobiol. A: Chem. 166 (2004) 155–161. [6] T. Tsutsui, N. Takada, S. Saito, Appl. Phys. Lett. 65 (1994) 1868–1870. [7] S. Dirr, S. Wiese, H.H. Johannes, D. Ammermann, A. Bõhler, W. Grahn, W. Kowalsky, Synth. Met. 91 (1997) 53–56. [8] Q. Li, T. Li, J.G. Wu, J. Phys. Chem. B 105 (2001) 12293–12296. [9] L.H. Wang, W. Wang, W.G. Zhang, E.T. Kang, W. Huang, Chem. Mater. 12 (2000) 2212–2218. [10] L.Y. Zhu, X.F. Tong, M.Z. Li, E.J. Wang, J. Phys. Chem. B 105 (2001) 2461–2464. [11] J. Xu, X.H. Huang, N.L. Zhou, J.S. Zhang, J.Ch. Bao, T.H. Lu, C. Lia, Mater. Lett. 58 (2004) 1938–1942. [12] M.J. Tapia, H.D. Burrows, J.M. García, F. García, A.A.C.C. Pais, Macromolecules 37 (2004) 856–862. [13] L.H. Sloo, A. Polman, S.I. Klink, G.A. Hebbink, L. Grave, F.C.J.M. van Veggel, D.N. Reinhoudt, J.W. Hofstraat, Opt. Mater. 14 (2000) 101–107. [14] N. Sabbatini, M. Guardigli, J.M. Lehn, Coord. Chem. Rev. 123 (1993) 201–208. [15] Q.J. Zhang, P. Wang, X.F. Sun, Y. Zhai, P. Dai, Appl. Phys. Lett. 72 (1998) 407–409. [16] R.J. Mears, L. Reekie, S.B. Poole, D.N. Payne, Electron. Lett. 22 (1986) 159–160. [17] Q.M. Wang, B. Yan, J. Photochem. Photobiol. A: Chem. 177 (2006) 1–5. [18] P. Lenaerts, A. Storms, J. Mullens, J. D’Haen, C. Gorller-Walrand, K. Binnemans, K. Driesen, Chem. Mater. 17 (2005) 5194–5201. [19] P. Lenaerts, K. Driesen, R. Van Deun, K. Binnemans, Chem. Mater. 17 (2005) 2148–2154. [20] I. Tomoyuki, H. Tetsuji, K. Noriyuki, M. Akira, I. Kenzo, Polymer 44 (2003) 2927–2932. [21] C.X. Du, Y. Xu, L. Ma, W.L. Li, J. Alloys Compd. 265 (1998) 81–86. [22] L.H. Wang, W. Wang, W.G. Zhang, E.T. Kang, et al., Chem. Mater. 12 (2000) 2212–2218. [23] Q.D. Ling, M.J. Yang, Z.F. Wu, et al., Polymer 42 (2001) 4605–4610. [24] K.P. McNamara, X.P. Li, A.D. Stull, Z. Rosenzweig, Anal. Chim. Acta 361 (1998) 73–83.
Contents lists available at ScienceDirect
Synthetic Metals journal homepage: www.elsevier.com/locate/synmet
Synthesis and fluorescent properties of europium–polymer complexes containing 1,10-phenanthroline Xingyu Liu, Yulin Hu, Baoyan Wang, Zhixing Su ∗ Institute of Polymer and Engineering, College of Chemistry and Chemical Engineering, Lanzhou University, Tianshui South Road 222, Lanzhou 730000, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 8 May 2008 Received in revised form 14 April 2009 Accepted 16 April 2009 Available online 20 May 2009 Keywords: 5-Acrylamido-1,10-phenanthroline Rare earth Fluorescence Polymer complex
a b s t r a c t In this paper, 5-acrylamido-1,10-phenanthroline (AP) was synthesized, then the luminescence material containing Eu–polymer complexes were obtained by two methods. The polymer structure and properties were characterized by FT-IR, UV, fluorescence spectra, DSC, GPC, ICP and XRD. Compared with the two methods the rare earth ions-containing polymers, we obtained copolymer B by the second one that had high and stable fluorescence intensity with the Eu content 0.31%. Comparing the two results via different methods, we have set down the useful basement for the study of the luminescence material containing Eu–polymer complexes. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Luminescent rare earth complexes have attracted considerable attentions for organic electroluminescent (EL) devices [1–5] as well as for optical microcavity emitters [6,7] owing to their inherent extremely sharp emission bands and potentially high internal quantum efficiency. However, there are many problems for the rare earth complexes that have small molecular weight such as the instability in organic solution and poor compatibility with other materials [8]. Thus, the broad application of rare earth-containing polymers has been attracted significant attention in the past decade [9–12]. In comparison with small molecular weight rare earth complexes, besides the advantage of the desired mechanical flexibility, polymer-based rare earth luminescent materials can be soluble or fused processable, which is attractive for optical [13,14] and electronic [15,16] applications. Recently, one method to synthesize rare earth-containing polymers materials is the direct reaction of the polymer ligands with rare earth ions [17–20]. Another method to obtain rare earthcontaining polymers is the copolymerization of rare earth metalcontaining monomers and polymeric monomers [21–23]. In this paper, the monomer of 5-acrylamido-1,10-phenanthroline was synthesized from 1,10-phenanthroline via nitration, reduction and acylation with acrylic chloride to introduce a terminal double bond capable to copolymerize with monomers [24], as
∗ Corresponding author. Tel.: +86 0931 8912391; fax: +86 0931 8912582. E-mail address: [email protected] (Z. Su). 0379-6779/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2009.04.013
illustrated in Scheme 1. The fluorescent Eu-containing polymer materials using AP as ligands was synthesized by the two different methods as described in detail in the experimental part. The fluorescence behaviors of the two products were investigated and the differences between them were discussed in detail. 2. Experimental 2.1. Materials Eu2 O3 (99.99 wt%) was purchased from Gansu rare earth group Co., Ltd. and used without further purification. Methyl methacrylate was purified before use. 2,2-Azoisobutyronitrile (AIBN) was recrystallized twice from methanol. Polymethyl methacryate (PMMA) was produced by our laboratory. Other chemicals were analytical grade. 2.2. Synthesis of tris(5-acrylamido-1,10-phenanthroline) europium–Eu(AP)3 The complexation reaction between AP and europium chloride follows standard methods. A sample of 400 mg (1.61 mmol) of AP was dissolved in 15 mL methylenechloride, a solution of EuCl3 ·6H2 O (103.4 mg, 0.4 mmol) in 5 mL of anhydrous ethanal was successively add to the solution of AP. The mixture was refluxed at 45 ◦ C for 6.5 h to ensure completion of the reaction. Upon completion of the reaction, the solvent was evaporated under reduced pressure, and the residual brown-yellow precipitate was filtered and washed with distilled water to remove impurities. Further purifica-
1558
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
Scheme 1. Preparation of 5-nitro-1,10-phenanthrolin, 5-amino-1,10-phenanthrolin (phen-NH2 ) and 5-acrylamido-1,10-phenanthrolin (AP).
tion was accomplished by recrystallization from an acetone/water mixture (4/1, v/v), yield ≈ 80%. The polymer cannot be soluble in THF, acetone, methanol and ethanol, but in DMF, as illustrated in Scheme 2. Elemental analysis (calculated/found) for the dried dye (C45 H33 N9 O3 EuCl2 ; MW 970.7): C, 55.68/54.90; H, 3.43/3.77; N, 12.99/12.26; the content of Eu in Eu(AP)3 was determined by ICP (calculated/found): Eu (15.66/15.64). IR(KBr), (cm−1 ): 3365 (N–H ); 1655 (C O ); 1620 (C C ); 1534 (C C+C N ); 1418 (C N ); 1248 (C–N ); 894, 798, 733 (ıC–H ). 2.3. Synthesis of copolymer 5-acrylamido-1,10-phenanthroline (AP) with methyl methacrylate (MMA) (poly(MMA-co-AP))(A) The mixture of AP (0.18 mmol) monomer and MMA (1.4 mmol), initiator AIBN (3.0 × 10−3 mol/L) was dissolved in DMF, and added into a glass polymerization tube. The homogeneous solution was degassed and sealed under vacuum. The polymerization was carried out by heating the sealed tube at 80 ◦ C for 6 h. The viscous homogeneous solution was then dissolved in DMF and poured into 200 mL of methanol with stirring. The process was repeated twice and finally dried under vacuum at 50 ◦ C for 24 h to afford powder polymer. The polymer was easily soluble in chloroform, acetone, THF and DMF, as illustrated in Scheme 2. The structure can be characterized by IR, and the content can be measured by UV (CHCl3 as solution), the measured value of the AP content is 2.35% (wt%). The average molecular weight of copolymer B is Mn = 4.1 × 104 g/mol, Mw /Mn = 1.33, Tg = 102.5 ◦ C. UV: ab = 270 nm. IR (KBr), (cm−1 ): 1732 (C O); 1678 (C O-AP); 1276; 1247; 1194; 1150 (C–C–O–C); 2954 (C–H). 2.4. Synthesis of copolymers of Eu(AP)3 with methyl methacrylate (MMA) (poly(MMA-co-Eu(AP)3 ))(B)
in methanol twice and finally dried under vacuum at 50 ◦ C for 24 h to afford powder polymers. This polymer dissolved in DMF easily, as illustrated in Scheme 2. The Eu content in the copolymers is in the range of 0.086–0.31% (wt%), as listed in Table 2. IR (KBr), (cm−1 ): 1731 (C O); 1272; 1243; 1194; 1148 (C–C–O–C); 2953 (C–H). 2.5. Synthesis of the europium-doped polymethyl methacrylate thin films Eu(AP)3 (9.08 mmol) and PMMA (57.0 mg) were dissolved in 10 mL of DMF, and mixed the DMF containing some concentration PMMA. The mixture solution was poured into on the glass and the film was obtained after dried, finally dried in vacuum chamber. 2.6. Instruments FT-IR were recorded on a Nicolet NEXUS 670FTIR spectrometer by dispersing samples in KBr disks; the fluorescent emission spectrum were recorded on Perkin-Elmer LS 55 fluorescent; UV spectra were taken using on Lambda 35 UV spectrometer (PerkinElmer); the element analysis were carried out by GmbH VarioEL element analysis; the content of Eu complexes were measure by IRIS ER-S WP-1 plasma emission (ICP); DSC measurements were performed at a heating rate of 10 ◦ C/min under nitrogen with a Sapphire DSC Differential Scanning Calorimeter (PerkinElmer). Gel permeation chromatography (GPC) analysis was conducted with a GPCV2000 system using polystyrene as standard and THF as the eluen; X-ray diffraction spectra were conducted on Kristalloflex XRD-5000 X-ray diffraction. 3. Results and discussion 3.1. FT-IR spectral characterization
The mixture of Eu(AP)3 monomer and MMA (1.07 mol/L) in certain ratios, a small amount of initiator AIBN (3.0 × 10−3 mol/L), and solvent DMF was mixed and added into a glass polymerization tube. The homogeneous solution was degassed and sealed under vacuum. The polymerization was carried out by heating the sealed tube at 80 ◦ C for 5 h. The viscous homogeneous solution was then dissolved in DMF and poured into 200 mL of methanol with stirring. The resulting precipitate was redissolved in DMF and reprecipitated
The FT-IR spectra of ligands and complex are recorded in the range of 400–4000 cm−1 . The main absorption bands are listed in Table 1. The FT-IR spectra of ligand 5-acrylamido-1,10phenanthroline (AP) shows that, the C C + C N stretching vibration of aromatic ring for the products Phen-NH2 and AP was 1560 and 1539 cm−1 , respectively. It shows that the band of the stretching vibration decreases with the increase of the electron-donate capa-
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
1559
Scheme 2. Preparation of tris(5-acrylamido-1,10-phenanthroline) europium chloride (Eu(AP)3 ), copolymers poly(MMA-co-AP)(A) and poly(MMA-co-Eu(AP)3 )(B).
bility of the substitute. The N–H stretching vibration of Phen-NH2 was at 3416 and 3322 cm−1 . The N–H stretching vibration of AP shifted to 3427 cm−1 . The C O stretching vibration of amido was at 1682 cm−1 which overlapped the band of C C stretching vibration.
The FT-IR spectrum of the complex tris(5-acrylamido-1,10phenanthroline) europium chloride (Eu(AP)3 ) shows that the C C + C N stretching vibration of aromatic ring in the complex are shifted to low frequencies from 1539 to 1534 cm−1 and the C N and
Table 1 Important IR absorption band of the ligand and complex (cm−1 ). IR (cm−1 )
C Phen-NH2 AP Eu(AP)3
C
1636, 1505, 1453 1621 1620
ıC–H
C
882, 842, 739 878, 800, 741 894, 798, 733
1591, 1426 1407 1418
N
C
C+C N
1560 1539 1534
C–N
N–H
C
1270 1227 1248
3416, 3322 3427 3365
1682 1655
O
1560
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
Table 2 Properties of the Eu-containing copolymers. No.
Eu(AP)3 content in the feed (g)
Ratio of MMA/Eu(AP)3 (%)
Eu (%)
Tg (◦ C)
Mw (×104 )
Mw /Mn
1. 2. 3. 4. 5.
0.1027 0.0867 0.0773 0.0444 0.0269
9.348 11.073 12.419 21.622 35.688
0.31 0.22 0.20 0.19 0.086
124.2 124.5 117.2 124.2 123.4
1.69
1.23
1.94
1.43
2.26
1.29
C–N stretching vibration of aromatic ring in the complex are red shifted from 1407 and 1227 cm−1 to 1418 and 1248 cm−1 , respectively. The bending vibrations of aromatic ring are also shifted, from 878, 800, and 741 cm−1 to 894, 798, and 733 cm−1 . The N–H stretching vibration of the complex are shifted to low frequencies, from 3427 to 3365 cm−1 . Weak band at 417 cm−1 corresponding to the Eu–N stretching vibration was observed. These results suggested that the coordination bonds were formed between the Eu3+ ion and ligand AP in the complex. The FT-IR spectrum of copolymer A shows that the C O stretching vibration of MMA at 1732 cm−1 is absent and the stretching vibration of C–C–O–C at 1276, 1247, 1194, and 1150 cm−1 appears. The C–O stretching vibration of monomer AP is at 1678 cm−1 and the C–H stretching vibration at 2954 cm−1 . These results suggest that the structure of polymer are similar to that of PMMA because the low content of AP in copolymer. The FT-IR spectrum of copolymer B is similar to that of copolymer A because the content of Eu is too low. It indicates that there are a lot of MMA chains in the backbone of copolymer B. So the properties of the products are similar to that of MMA and show good solubilities in THF and DMF.
cultly. The Tg of copolymer A is much higher than that of copolymer B (117.2–124.5 ◦ C).
3.2. Thermal properties
3.3. UV properties
As shown in Table 2 and Fig. 1, the Eu content decreases from No. 1 to No. 5 (Eu(AP)3 singlet decreases steadly), the value of Tg decreases slowly with the decrease of the Eu content from 117.2 to 124.5 ◦ C. The chains of the polymer have star-like structure. The higher the Eu content, the more complex the rigid structure. And this limits the movement of copolymers chain. The Tg content of copolymers B increases with the increase of the content of Eu. Due to the little difference of Eu content in samples 1–5 (Eu = 0.086–0.31%), Tg content is just little higher than that of PMMA. But there is no distinct difference among the five samples. Tg of copolymer A is 102.5 ◦ C and Eu3+ makes the chain to move diffi-
Figs. 2–4 shows the UV spectra of copolymers A and B, ligand AP and complex Eu(AP)3 . In Fig. 2, the absorption spectra of copolymer A and ligand AP are similar and they have two absorption peaks at about 270 and 321 nm. It is due to the energy absorption depended on AP after obtaining copolymer A. Furthermore, it is mainly depended on the electron transition of → * in ligand AP. Namely the energy absorbed by AP was transformed to Eu3+ ion. The energy transformed by copolymers B was much less. The UV absorption spectrum of Eu(AP)3 in DMF has shown in Fig. 3. The red shift of absorption peak is due to → * transitions of AP (270, 321 nm), the absorptions of Eu(AP)3 are at 276 and 324 nm. The absorption of copolymer B (Fig. 4) at 270 and 322 nm are close to that of ligand. It shows that the absorption is mainly caused by
Fig. 1. DSC curves of poly(MMA-co-AP)(A) and poly(MMA-co-Eu(AP)3 )(B) (samples 1–5).
Fig. 2. Absorbance spectrum of AP (a) and poly(MMA-co-AP)(A) (b) in DMF.
Fig. 3. Absorbance spectrum of Eu(AP)3 in DMF.
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
1561
Fig. 4. Absorbance spectrum of poly(MMA-co-Eu(AP)3 )(B) in DMF. Fig. 6. Excitation (—) and emission (- - -) spectra of complex Eu(AP)3 solid.
the intermolecular energy transfer of the ligand in the backbone of the copolymer B. 3.4. Fluorescence properties The excitation and emission peaks of AP in DMF were 311 and 420 nm, respectively. The excitation and emission peaks of copolymer A in DMF are 311 and 417 nm, respectively. Obviously, it is showed that the fluorescence of the copolymer A was caused by the fluorphore AP. The excitation and emission spectra of complex Eu(AP)3 in DMF were shown in Fig. 5. The excitation peak is 350 nm. The emission peaks at 580, 595 and 617 nm, are attributed to the 5 D0 → 7 F0 , 5 D → 7 F , and 5 D → 7 F transitions, respectively. The excitation 0 1 0 2 peak of the complex Eu(AP)3 in solid state is 334 nm, and the corresponding emission peaks center at 595 and 617 nm as shown in Fig. 6. The excitation peak of the europium-doped copolymer A in acetone solution is 336 nm. The emission peaks are 598 and 618 nm which can be attributed to the 5 D0 → 7 F1 , 5 D0 → 7 F2 transitions, respectively. It shows that the energy transfer from the polymer ligand to Eu3+ takes place and exhibits the fluorescent characteristic of Eu3+ . AP of copolymer A can increase the emission property of Eu3+ , while its fluorescent is less than that of copolymer B (Eu = 0.31%). So we added N-methyl pyrrolidine (NMP) in binary complex as second ligand and obtained ternary complex. The emission property of ternary complex is much stronger than that of binary complex.
Fig. 5. Excitation (—) and emission (- - -) spectra of complex Eu(AP)3 in DMF.
It indicates that there is corporation action between two ligands in ternary complex. Small molecular ligand increases the coordination number of rare earth ions. The range of conjugated bond complex gets wide and increases the fluorescent emission of Eu3+ . More particularly in ternary complex, the small molecular ligand NMP is main energy donor. The triplet-state level is higher than that of the resonance energy level (5 D0 ) of Eu3+ ion, the more efficient the intermolecular energy transfers. The excitation peak of copolymer B in DMF is 331 nm and the emission peaks centered at 576, 589 and 619 nm, assigned to 5 D0 → 7 F0 , 5 D0 → 7 F1 , and 5 D0 → 7 F2 transitions, respectively. Among the peaks, the emission at 619 nm from the 5 D0 → 7 F2 electric dipole transition is the strongest, suggesting low symmetry around the Eu3+ ion in the Eu-copolymers and monomers. Because the forbidden 5 D0 → 7 F2 electric dipole transition is the sensitive to the coordinative environment of Eu3+ ion, the asymmetric microenvironment causes the polarization of the Eu3+ ion under the influence of the electric field of the surrounding ligands, which increase the probability for the electric dipole transition. 3.5. XRD analysis Fig. 7 shows the X-ray diffraction pattern for different Eu contents. In the atactici PMMA, there were three broad diffraction peaks centered at 13.86◦ , 29.49◦ and 41.46◦ . In the copolymer B,
Fig. 7. X-ray diffraction pattern: (a) Eu(AP)3 , (b) 3.1% Eu(AP)3 /PMMA, (c) 0.086% poly(MMA-co-Eu(AP)3 ), (d) 0.31% poly(MMA-co-Eu(AP)3 ) and (e) PMMA.
1562
X. Liu et al. / Synthetic Metals 159 (2009) 1557–1562
the diffraction intensity of three main noncrystalline peaks did not increase obviously with the increase of Eu content. Because a little difference of Eu content in copolymer B, their X-ray diffractions were similar. In Eu(AP)3 /PMMA, the three diffraction peaks of PMMA got weak and occurred apparently crystalline peak. From the XRD spectrum, when Eu(AP)3 uniformly dispersed, the result was better than Eu(AP)3 -doped PMMA. Both the long range and relative short range periodic arrangement of atoms and atomic groups are disturbed Eu(AP)3 moiety into polymer chains. As to Eu(AP)3 -doped PMMA systems, only the long range regularity is disturbed. The copolymers are possible to adopt conformation and tactility that is less favour the ligand interaction and excitation migration. As a result a much greater part of the excitation is transferred to Eu3+ under UV radiation. The special conformation is just the driving force that causes the highly fluorescent property. 4. Conclusions 5-Acrylamido-1,10-phenanthroline (AP) was synthesized, and the luminescence material containing Eu–polymer complexes were obtained by two different methods. One was prepared by the direct coordination among AP units, N-methyl pyrrolidine and europium ions; another was synthesized by the direct copolymerization of Eu-complex monomer containing 1,10-phenanthroline with methyl methacryate. We obtained the material, by the second method, which had high and stable fluorescence intensity with the Eu content 0.31%. And the polymer complexes have advantages over Eu(AP)3 -doped polymers in that: (a) the polymer complexes exhibit more intense Eu typical fluorescence; (b) in polymer complexes, Eu(AP)3 moiety is dispersed much more uniformly, which is very important in optical applications. By comparing the two results via different methods, we have set down the useful basement for the study of the luminescence material containing Eu–polymer complexes.
Acknowledgement One of the authors (Xingyu Liu) wishes to thank Prof. Zhixing Su for his kind corporation at Lanzhou University. References [1] J.J. Ding, H.F. Jiu, J. Bao, J.C. Lu, W.R. Gui, Q.J. Zhang, C. Gao, J. Comb. Chem. 7 (2005) 69–72. [2] H. Xin, M. Shi, X.M. Zhang, F.Y. Li, Z.Q. Bian, K. Ibrahim, F.Q. Liu, C.H. Huang, Chem. Mater. 15 (2003) 3728–3733. [3] H. Suzuki, Res. Adv. Appl. Phys. 3 (2003) 11–25. [4] H. Suzuki, M. Notomi, A. Yokoo, Polym. Adv. Technol. 15 (2004) 75–80. [5] H. Suzuki, J. Photochem. Photobiol. A: Chem. 166 (2004) 155–161. [6] T. Tsutsui, N. Takada, S. Saito, Appl. Phys. Lett. 65 (1994) 1868–1870. [7] S. Dirr, S. Wiese, H.H. Johannes, D. Ammermann, A. Bõhler, W. Grahn, W. Kowalsky, Synth. Met. 91 (1997) 53–56. [8] Q. Li, T. Li, J.G. Wu, J. Phys. Chem. B 105 (2001) 12293–12296. [9] L.H. Wang, W. Wang, W.G. Zhang, E.T. Kang, W. Huang, Chem. Mater. 12 (2000) 2212–2218. [10] L.Y. Zhu, X.F. Tong, M.Z. Li, E.J. Wang, J. Phys. Chem. B 105 (2001) 2461–2464. [11] J. Xu, X.H. Huang, N.L. Zhou, J.S. Zhang, J.Ch. Bao, T.H. Lu, C. Lia, Mater. Lett. 58 (2004) 1938–1942. [12] M.J. Tapia, H.D. Burrows, J.M. García, F. García, A.A.C.C. Pais, Macromolecules 37 (2004) 856–862. [13] L.H. Sloo, A. Polman, S.I. Klink, G.A. Hebbink, L. Grave, F.C.J.M. van Veggel, D.N. Reinhoudt, J.W. Hofstraat, Opt. Mater. 14 (2000) 101–107. [14] N. Sabbatini, M. Guardigli, J.M. Lehn, Coord. Chem. Rev. 123 (1993) 201–208. [15] Q.J. Zhang, P. Wang, X.F. Sun, Y. Zhai, P. Dai, Appl. Phys. Lett. 72 (1998) 407–409. [16] R.J. Mears, L. Reekie, S.B. Poole, D.N. Payne, Electron. Lett. 22 (1986) 159–160. [17] Q.M. Wang, B. Yan, J. Photochem. Photobiol. A: Chem. 177 (2006) 1–5. [18] P. Lenaerts, A. Storms, J. Mullens, J. D’Haen, C. Gorller-Walrand, K. Binnemans, K. Driesen, Chem. Mater. 17 (2005) 5194–5201. [19] P. Lenaerts, K. Driesen, R. Van Deun, K. Binnemans, Chem. Mater. 17 (2005) 2148–2154. [20] I. Tomoyuki, H. Tetsuji, K. Noriyuki, M. Akira, I. Kenzo, Polymer 44 (2003) 2927–2932. [21] C.X. Du, Y. Xu, L. Ma, W.L. Li, J. Alloys Compd. 265 (1998) 81–86. [22] L.H. Wang, W. Wang, W.G. Zhang, E.T. Kang, et al., Chem. Mater. 12 (2000) 2212–2218. [23] Q.D. Ling, M.J. Yang, Z.F. Wu, et al., Polymer 42 (2001) 4605–4610. [24] K.P. McNamara, X.P. Li, A.D. Stull, Z. Rosenzweig, Anal. Chim. Acta 361 (1998) 73–83.