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A novel terbium complex using oxadiazole derivative as a neutral ligand: Synthesis and properties
Chinese Chemical Letters 18 (2007) 573–576 www.elsevier.com/locate/cclet
A novel terbium complex using oxadiazole derivative as a neutral ligand: Synthesis and properties Yu Liu a,b, Kong Qiang Xing b, Ji Yong Deng a, Mei Xiang Zhu a, Xia Yu Wang a, Wei Guo Zhu a,* b
a College of Chemistry, Xiangtan University, Xiangtan 411105, China Department of Chemistry, Qiongzhou University, Wuzhishan 572200, China
Received 10 November 2006
Abstract A novel terbium complex using 1,3,4-oxadiazole derivative as a neutral ligand was synthesized and characterized. Its thermal stability and photoluminescent properties were studied. The strong emission peaked at 546 nm with a full width at half maximum of 5 nm was observed in the pure terbium complex film under excitation of 328 nm light, which is attributed to the characteristic emission of terbium ion. The good thermal stability and intense sharp emission of this terbium complex display its potential application in electroluminescence devices. # 2007 Wei Guo Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Terbium complex; 1,3,4-Oxadiazole; Synthesis; Photoluminescence
Organic and polymer light-emitting devices (OLEDs and PLEDs) have attracted a great deal of attention because of their potential applications in flat panel displays [1–3]. Their electroluminescence (EL) wavelengths span whole visible spectrum. However, their emission spectra typically exhibit a full width at half maximum (FWHM) of 50– 200 nm due to the effects associated with inhomogeneous broadening and the presence of a vibronic progression [4]. It is very important to obtain efficient pure emission from OLEDs and PLEDs in order to realize full color displays. Owing to the unique protected f-electronic configuration by the completely filled s and p orbitals, organolanthanide complexes cannot only generate extremely pure emission, but also afford theoretically 100% quantum efficiency for emission [5]. Hence, organolanthanide complexes are believed to be a class of promising luminescent materials to exhibit sharp emission in the devices. However, up to now, organolanthanide complexes have not exhibited satisfactory luminescent efficiency in the devices as expected yet [6–13]. One main reason for the low efficiency is that organolanthanide complexes have the poor ability to transport charge carriers, which results in the unbalanced injection and transport of charge carriers. In order to achieve organolanthanide complexes with the improved carrier-transporting properties, some research groups recently focused on the design of the functionalized organolanthanide complexes by incorporating the ligands with carriertransporting properties into the complexes [9–11]. Much progress was made in developing the new functionalized organolanthanide complexes in which the diketones ligands contain electron-transporting groups [10,11].
* Corresponding author. E-mail address: [email protected] (W.G. Zhu). 1001-8417/$ – see front matter # 2007 Wei Guo Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.03.028
574
Y. Liu et al. / Chinese Chemical Letters 18 (2007) 573–576
In this paper, we reported our initial effort to achieve a novel functionalized terbium complex using an oxadiazole derivative as the neutral ligand. As oxadiazol derivatives are well known units with electrontransporting property, the terbium complex containing the oxadiazol derivative is expected to be good optoelectronic properties. Hence, we designed and synthesized the novel terbium complex, tris(acetylacetonato)[2(4-methoxy)phenyl-5-(2-pyridyl)-1,3,4-oxadiazol]terbium(III) [Tb(acac)3(MeO-OXD)]. The photoluminescence (PL) and thermal stability properties of Tb(acac)3(MeO-OXD) were studied. The synthesis of this novel terbium complex is depicted in Scheme 1. 1. Experimental 2-(4-Methoxylphenyl)-5-(2-pyridinyl)-1,3,4-oxadiazole (MeO-OXD) was synthesized according to the literature [12]. m.p. 154–156 8C. 1H NMR (400 Hz, CDCl3, d ppm): 8.83 (d, 1H, J = 2.0 Hz), 8.32 (d, 1H, J = 3.6 Hz), 8.17 (d, 2H, J = 8.64 Hz), 7.92 (t, 1H, J = 8.68 Hz), 7.48 (s, 1H), 7.04 (d, 2H, J = 8.68 Hz), 3.89 (s, 3H). GC–MS: (M+, 252). IR (KBr, cm1): 1585, 832, 790. Synthesis of Tb(acac)3(MeO-OXD): a solution of acetylacetone (0.150 g, 1.5 mmol) and MeO-OXD (0.126 g, 0.50 mmol) and ethanol (30 mL) was neutralized with a solution of sodium hydroxide (1.0 mol/L) in a flask under nitrogen atmosphere. A solution of terbium chloride (0.5 mmol) and water (1.5 mL) was then added dropwise into the flask with stirring. The mixed solution was stirred at 65–70 8C for 3.0 h. The formed white precipitate was filtered and washed with warm aqueous ethanol (1:1) for several times, and recrystallized from a mixed solvent of chloroform and petroleum (1:2) to afford Tb(acac)3(MeO-OXD) with a yield of 58.0%, m.p. 275–277 8C. TbC29H35N3O8 calcd. (%): C 48.88, H 4.95, N 5.90; found (%): C 48.75, H 4.90, N 5.84. All 1H NMR spectra were acquired at a Bruker Dex-400 NMR instrument using CDCl3 as a solvent. GC–MS data were obtained using a Trace GC–MS-2000 System (Finnigan). Elemental analysis was performed with a Perkin-Elmer 240 instrument. The films of the pure terbium complexes were formed on the quartz under pressure. PL spectrum was recorded on a fluorescence spectrophotometer (HITACHI-850) under excitation of 325 nm line. Thermogravimetic analysis (TGA) was carried out using NETZSCH STA449 from 25 to 700 8C at a heating rate of 10 8C/min under nitrogen. Differential scanning calorimetry (DSC) measurement was carried out using the NETZSCH DSC 204 instrument from 25 to 700 8C at a heating rate of 30 K/min under nitrogen. 2. Results and discussion The thermal properties of the terbium complex were determined by thermogravimetry (TG) and differential scanning calorimetry analysis. The TGA and DSC curves of the complex are shown in Fig. 1. The endothermic peak appeared at 355.4 8C in the DSC curve. No weight loss was observed up to 330 8C in the TG curve. The terbium complex was decomposed and had a weight loss of 65.5% at 370 8C. This is attributed to the remove of the neutral MeO-OXD ligand from the terbium complex. Compared with tris(acetylacetonato)[1,10-phenanthroline]terbium(III)
Scheme 1. Synthetic route of Tb(acac)3(MeO-OXD).
Y. Liu et al. / Chinese Chemical Letters 18 (2007) 573–576
575
Fig. 1. The TGA and DSC curves of Tb(acac)3(MeO-OXD).
[Tb(acac)3(phen)], Tb(acac)3(MeO-OXD) possessed a higher decomposition temperature [13], indicating that Tb(acac)3(MeO-OXD) demonstrates a better thermal stability. Fig. 2 (inset) shows the excitation spectrum of the terbium complex-based film. A maximum excitation wavelength of 328.8 nm with a shoulder at 382 nm was observed in the excitation spectrum. The emission spectra of the Tb(acac)3(MeO-OXD)- and Tb(acac)3(Phen)-based films were recorded under excitation of 328.8 nm light in Fig. 2. Four peaks at 490, 546, 584 and 618 nm are exhibited, which are assigned to 5D4 ! 7F6, 5D4 ! 7F5, 5D4 ! 7F4, and 5 D4 ! 7F3 transitions of Tb3+ ion, respectively [14,15]. The dominating monochromatic emission peaked at 546 nm has a full width at half maximum of 5 nm. This emission spectrum is almost identical to those from Tb(acac)3(Phen) [14] and tris(acetylacetonato)[4,7-diphenyl-1,10-phenanthroline]terbium(III) [Tb(acac)3(bath)] [15]. This indicates that the oxadiazole derivative replaced phenanthroline as a neutral ligand has no influence on the emission color of the terbium complex. In order to understand the emission intensity of Tb(acac)3(MeO-OXD), the emission spectrum of the pure Tb(acac)3(phen) film was measured. The enhanced emission intensity of the pure Tb(acac)3(MeO-OXD) film was showed in Fig. 2, which benefits its high-efficiency emission in electroluminescent devices. In addition, Tb(acac)3(MeO-OXD) is believed to have good carrier-transporting property due to the effect of the neutral MeOOXD ligand based on the observation reported by Huang group [11]. Hence the terbium complex with the neutral oxadiazole ligand is expected to be a class of promising electroluminescent materials in OLEDs and PLEDs based on its good thermal stability, pure emission, strong emission intensity and the potential carrier-transporting ability.
Fig. 2. The excitation and emission spectra of the pure terbium complexes films.
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Y. Liu et al. / Chinese Chemical Letters 18 (2007) 573–576
In conclusion, a novel terbium complex, Tb(acac)3(MeO-OXD), was obtained. Its high thermal stability and intense emission at 546 nm with a full width at half maximum of 5 nm were observed. The initial study indicates that the terbium complex should be an efficient green-emitting material used in the electroluminescent devices with pure emission. Some further studies on the EL properties of the terbium complex in the devices are currently ongoing for supporting our consideration. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 50473046), and the Science Foundation of the Ministry of Education of China (No. 204097), and the Outstanding Youth Foundation of Hunan Province (No. 04JJ1002), and the Science Foundation of the Department of Hunan Province (No. 03A049), the University Foundation of the Education Department of Hainan Province (No. HJKJ 200425) and the Hunan Provincial Natural Science Foundation (No. 06JJ2008). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
C.W. Tang, S.A. VanSlyke, J. Appl. Phys. Lett. 51 (1987) 913. J.H. Burroughes, D.D.C. Bradley, A.R. Brown, et al. Nature 347 (1990) 539. M.A. Baldo, D.F. O’Brien, Y. You, et al. Nature 395 (1998) 151. J. Pei, X.L. Liu, W.L. Yu, Y.H. Lai, Y.H. Niu, Y. Cao, Macromolecules 35 (2002) 7274. J. Kido, Y. Okamor, Chem. Rev. 102 (2002) 2357. T.W. Canzler, J. Kido, Org. Electron. 7 (2006) 29. M. Shi, F. Li, T. Yi, D. Zhang, H. Hu, C. Huang, Inorg. Chem. 44 (2005) 8929. T. Oyamada, Y. Kawamura, T. Koyama, H. Sababe, C. Adachi, Adv. Mater. 16 (2004) 1082. E. Satathtos, L. Panayiotidou, P. Lianos, A.D. Keramidas, Thin Solid Films 496 (2006) 489. J. Wang, R. Wang, J. Yang, et al. J. Am. Chem. Soc. 123 (2001) 6179. H. Xin, F.Y. Li, M. Shi, Z.Q. Bian, C.H. Huang, J. Am. Chem. Soc. 125 (2003) 7166. Z.L. Wu, M.X. Zhu, Y. Liu, et al. Chin. Chem. Lett. 16 (2005) 241. L.R. Melby, N.J. Rose, E. Abramsonan, D.J.C. Caris, J. Am. Chem. Soc. 86 (1964) 5117. Y. Zheng, J. Lin, Y. Liang, et al. Mater. Lett. 54 (2002) 424. Y. Zheng, J. Lin, Y. Liang, et al. Opt. Mater. 20 (2002) 273.
A novel terbium complex using oxadiazole derivative as a neutral ligand: Synthesis and properties Yu Liu a,b, Kong Qiang Xing b, Ji Yong Deng a, Mei Xiang Zhu a, Xia Yu Wang a, Wei Guo Zhu a,* b
a College of Chemistry, Xiangtan University, Xiangtan 411105, China Department of Chemistry, Qiongzhou University, Wuzhishan 572200, China
Received 10 November 2006
Abstract A novel terbium complex using 1,3,4-oxadiazole derivative as a neutral ligand was synthesized and characterized. Its thermal stability and photoluminescent properties were studied. The strong emission peaked at 546 nm with a full width at half maximum of 5 nm was observed in the pure terbium complex film under excitation of 328 nm light, which is attributed to the characteristic emission of terbium ion. The good thermal stability and intense sharp emission of this terbium complex display its potential application in electroluminescence devices. # 2007 Wei Guo Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Terbium complex; 1,3,4-Oxadiazole; Synthesis; Photoluminescence
Organic and polymer light-emitting devices (OLEDs and PLEDs) have attracted a great deal of attention because of their potential applications in flat panel displays [1–3]. Their electroluminescence (EL) wavelengths span whole visible spectrum. However, their emission spectra typically exhibit a full width at half maximum (FWHM) of 50– 200 nm due to the effects associated with inhomogeneous broadening and the presence of a vibronic progression [4]. It is very important to obtain efficient pure emission from OLEDs and PLEDs in order to realize full color displays. Owing to the unique protected f-electronic configuration by the completely filled s and p orbitals, organolanthanide complexes cannot only generate extremely pure emission, but also afford theoretically 100% quantum efficiency for emission [5]. Hence, organolanthanide complexes are believed to be a class of promising luminescent materials to exhibit sharp emission in the devices. However, up to now, organolanthanide complexes have not exhibited satisfactory luminescent efficiency in the devices as expected yet [6–13]. One main reason for the low efficiency is that organolanthanide complexes have the poor ability to transport charge carriers, which results in the unbalanced injection and transport of charge carriers. In order to achieve organolanthanide complexes with the improved carrier-transporting properties, some research groups recently focused on the design of the functionalized organolanthanide complexes by incorporating the ligands with carriertransporting properties into the complexes [9–11]. Much progress was made in developing the new functionalized organolanthanide complexes in which the diketones ligands contain electron-transporting groups [10,11].
* Corresponding author. E-mail address: [email protected] (W.G. Zhu). 1001-8417/$ – see front matter # 2007 Wei Guo Zhu. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.03.028
574
Y. Liu et al. / Chinese Chemical Letters 18 (2007) 573–576
In this paper, we reported our initial effort to achieve a novel functionalized terbium complex using an oxadiazole derivative as the neutral ligand. As oxadiazol derivatives are well known units with electrontransporting property, the terbium complex containing the oxadiazol derivative is expected to be good optoelectronic properties. Hence, we designed and synthesized the novel terbium complex, tris(acetylacetonato)[2(4-methoxy)phenyl-5-(2-pyridyl)-1,3,4-oxadiazol]terbium(III) [Tb(acac)3(MeO-OXD)]. The photoluminescence (PL) and thermal stability properties of Tb(acac)3(MeO-OXD) were studied. The synthesis of this novel terbium complex is depicted in Scheme 1. 1. Experimental 2-(4-Methoxylphenyl)-5-(2-pyridinyl)-1,3,4-oxadiazole (MeO-OXD) was synthesized according to the literature [12]. m.p. 154–156 8C. 1H NMR (400 Hz, CDCl3, d ppm): 8.83 (d, 1H, J = 2.0 Hz), 8.32 (d, 1H, J = 3.6 Hz), 8.17 (d, 2H, J = 8.64 Hz), 7.92 (t, 1H, J = 8.68 Hz), 7.48 (s, 1H), 7.04 (d, 2H, J = 8.68 Hz), 3.89 (s, 3H). GC–MS: (M+, 252). IR (KBr, cm1): 1585, 832, 790. Synthesis of Tb(acac)3(MeO-OXD): a solution of acetylacetone (0.150 g, 1.5 mmol) and MeO-OXD (0.126 g, 0.50 mmol) and ethanol (30 mL) was neutralized with a solution of sodium hydroxide (1.0 mol/L) in a flask under nitrogen atmosphere. A solution of terbium chloride (0.5 mmol) and water (1.5 mL) was then added dropwise into the flask with stirring. The mixed solution was stirred at 65–70 8C for 3.0 h. The formed white precipitate was filtered and washed with warm aqueous ethanol (1:1) for several times, and recrystallized from a mixed solvent of chloroform and petroleum (1:2) to afford Tb(acac)3(MeO-OXD) with a yield of 58.0%, m.p. 275–277 8C. TbC29H35N3O8 calcd. (%): C 48.88, H 4.95, N 5.90; found (%): C 48.75, H 4.90, N 5.84. All 1H NMR spectra were acquired at a Bruker Dex-400 NMR instrument using CDCl3 as a solvent. GC–MS data were obtained using a Trace GC–MS-2000 System (Finnigan). Elemental analysis was performed with a Perkin-Elmer 240 instrument. The films of the pure terbium complexes were formed on the quartz under pressure. PL spectrum was recorded on a fluorescence spectrophotometer (HITACHI-850) under excitation of 325 nm line. Thermogravimetic analysis (TGA) was carried out using NETZSCH STA449 from 25 to 700 8C at a heating rate of 10 8C/min under nitrogen. Differential scanning calorimetry (DSC) measurement was carried out using the NETZSCH DSC 204 instrument from 25 to 700 8C at a heating rate of 30 K/min under nitrogen. 2. Results and discussion The thermal properties of the terbium complex were determined by thermogravimetry (TG) and differential scanning calorimetry analysis. The TGA and DSC curves of the complex are shown in Fig. 1. The endothermic peak appeared at 355.4 8C in the DSC curve. No weight loss was observed up to 330 8C in the TG curve. The terbium complex was decomposed and had a weight loss of 65.5% at 370 8C. This is attributed to the remove of the neutral MeO-OXD ligand from the terbium complex. Compared with tris(acetylacetonato)[1,10-phenanthroline]terbium(III)
Scheme 1. Synthetic route of Tb(acac)3(MeO-OXD).
Y. Liu et al. / Chinese Chemical Letters 18 (2007) 573–576
575
Fig. 1. The TGA and DSC curves of Tb(acac)3(MeO-OXD).
[Tb(acac)3(phen)], Tb(acac)3(MeO-OXD) possessed a higher decomposition temperature [13], indicating that Tb(acac)3(MeO-OXD) demonstrates a better thermal stability. Fig. 2 (inset) shows the excitation spectrum of the terbium complex-based film. A maximum excitation wavelength of 328.8 nm with a shoulder at 382 nm was observed in the excitation spectrum. The emission spectra of the Tb(acac)3(MeO-OXD)- and Tb(acac)3(Phen)-based films were recorded under excitation of 328.8 nm light in Fig. 2. Four peaks at 490, 546, 584 and 618 nm are exhibited, which are assigned to 5D4 ! 7F6, 5D4 ! 7F5, 5D4 ! 7F4, and 5 D4 ! 7F3 transitions of Tb3+ ion, respectively [14,15]. The dominating monochromatic emission peaked at 546 nm has a full width at half maximum of 5 nm. This emission spectrum is almost identical to those from Tb(acac)3(Phen) [14] and tris(acetylacetonato)[4,7-diphenyl-1,10-phenanthroline]terbium(III) [Tb(acac)3(bath)] [15]. This indicates that the oxadiazole derivative replaced phenanthroline as a neutral ligand has no influence on the emission color of the terbium complex. In order to understand the emission intensity of Tb(acac)3(MeO-OXD), the emission spectrum of the pure Tb(acac)3(phen) film was measured. The enhanced emission intensity of the pure Tb(acac)3(MeO-OXD) film was showed in Fig. 2, which benefits its high-efficiency emission in electroluminescent devices. In addition, Tb(acac)3(MeO-OXD) is believed to have good carrier-transporting property due to the effect of the neutral MeOOXD ligand based on the observation reported by Huang group [11]. Hence the terbium complex with the neutral oxadiazole ligand is expected to be a class of promising electroluminescent materials in OLEDs and PLEDs based on its good thermal stability, pure emission, strong emission intensity and the potential carrier-transporting ability.
Fig. 2. The excitation and emission spectra of the pure terbium complexes films.
576
Y. Liu et al. / Chinese Chemical Letters 18 (2007) 573–576
In conclusion, a novel terbium complex, Tb(acac)3(MeO-OXD), was obtained. Its high thermal stability and intense emission at 546 nm with a full width at half maximum of 5 nm were observed. The initial study indicates that the terbium complex should be an efficient green-emitting material used in the electroluminescent devices with pure emission. Some further studies on the EL properties of the terbium complex in the devices are currently ongoing for supporting our consideration. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 50473046), and the Science Foundation of the Ministry of Education of China (No. 204097), and the Outstanding Youth Foundation of Hunan Province (No. 04JJ1002), and the Science Foundation of the Department of Hunan Province (No. 03A049), the University Foundation of the Education Department of Hainan Province (No. HJKJ 200425) and the Hunan Provincial Natural Science Foundation (No. 06JJ2008). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
C.W. Tang, S.A. VanSlyke, J. Appl. Phys. Lett. 51 (1987) 913. J.H. Burroughes, D.D.C. Bradley, A.R. Brown, et al. Nature 347 (1990) 539. M.A. Baldo, D.F. O’Brien, Y. You, et al. Nature 395 (1998) 151. J. Pei, X.L. Liu, W.L. Yu, Y.H. Lai, Y.H. Niu, Y. Cao, Macromolecules 35 (2002) 7274. J. Kido, Y. Okamor, Chem. Rev. 102 (2002) 2357. T.W. Canzler, J. Kido, Org. Electron. 7 (2006) 29. M. Shi, F. Li, T. Yi, D. Zhang, H. Hu, C. Huang, Inorg. Chem. 44 (2005) 8929. T. Oyamada, Y. Kawamura, T. Koyama, H. Sababe, C. Adachi, Adv. Mater. 16 (2004) 1082. E. Satathtos, L. Panayiotidou, P. Lianos, A.D. Keramidas, Thin Solid Films 496 (2006) 489. J. Wang, R. Wang, J. Yang, et al. J. Am. Chem. Soc. 123 (2001) 6179. H. Xin, F.Y. Li, M. Shi, Z.Q. Bian, C.H. Huang, J. Am. Chem. Soc. 125 (2003) 7166. Z.L. Wu, M.X. Zhu, Y. Liu, et al. Chin. Chem. Lett. 16 (2005) 241. L.R. Melby, N.J. Rose, E. Abramsonan, D.J.C. Caris, J. Am. Chem. Soc. 86 (1964) 5117. Y. Zheng, J. Lin, Y. Liang, et al. Mater. Lett. 54 (2002) 424. Y. Zheng, J. Lin, Y. Liang, et al. Opt. Mater. 20 (2002) 273.