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Emission properties of Sm(III) complex having ten-coordination structure
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Thin Solid Films 516 (2008) 2704 – 2707 www.elsevier.com/locate/tsf
Emission properties of Sm(III) complex having ten-coordination structure Yasuchika Hasegawa a,⁎, Shin-ichi Tsuruoka b , Takahiko Yoshida b , Hideki Kawai c , Tsuyoshi Kawai a a
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan b USHIO Chemix, Co Ltd., 2252-1 Goudo, Omaezaki, Shizuoka, 437-1613, Japan c Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8011, Japan Available online 1 May 2007
Abstract Sammarium(III) complex having ten-coordination structure, bis-(1,10-phenanthroline)tris-(hexafluoroacetylacetonato)samarium(III) (Sm(hfa)3 (phen)2) was prepared by chelation of tris-(hexafluoroacetylacetonato) samarium(III) (Sm(hfa)3(H2O)2) with 1,10-phenantroline (phen). The characteristic ten-coordination structure of Sm(hfa)3(phen)2 was determined by 1H NMR and elemental analyses. Strong deep-red emission (λmax=643 nm) and narrow emission band (FWHM=5 nm) of Sm(hfa)3(phen)2 originated from electronic allowed transition from characteristics ten coordinate structure. The emission quantum yields Sm(hfa)3(phen)2 excited at absorption bands of ligands and Sm(III) ion were found to be 0.36 and 1.4%, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Chemical synthesis; Luminescence; Samarium
1. Introduction Lanthanide(III) ions have been extensively studied as the attractive luminescent center for display devices, because of their highly monochromatic clear emission with FWHM smaller than 7 nm [1]. The monochromatic emission of lanthanide(III) ion mainly comes from the f–f transitions with no Storks shift [2]. The emission wavelength of lanthanide(III) is in principal independent of the crystal or ligand field because of characteristic feature of the f–f transition. Thus, tuning of the emission wavelength of a lanthanide ion is almost impossible. For example, the orange–red emission (615 nm) of Eu(III) ion which is well-known red element for display cannot be manipulated to the deep-red color emission (around 650 nm). Luminescent materials having narrow deep-red emission are strongly desired for high-quality display devices. For this purpose, we here focus on Sm(III) ion as a luminescent center. The emission bands of Sm(III) ion are assigned to 4G5/2 → 6H5/2 (zero–zero band), 4G5/2 → 6H7/2 (magnetic dipole transition), 4 G5/2 → 6H9/2 (electric dipole transition) and 4G5/2 → 6H11/2 (forbidden) [3]. Sm(III) complex with characteristic asymmetric ⁎ Corresponding author. Tel./fax: +81 743 6171. E-mail address: [email protected] (Y. Hasegawa). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.04.138
structures is expected to have increased radiation probability and emission quantum yield, since the 4G5/2 → 6H9/2 electric dipole transition would be partly allowed with the odd parity of the transition process. Recently, Ohmori and some of the present authors have demonstrated the deep-red emission from organic EL device by using a Sm(III) complex [4]. In the present study, we report on a new Sm(III) complex with ten-coordination structure for developing luminescent materials having narrow deep-red emission. The Sm(III) complex has two 1,10-phenanthroline ligands as shown in Fig. 1, which was designed taking some Eu(III)-phenanthroline complexes showing clear fluorescence into consideration [5]. The ten-coordination structure of the Sm(III) complex was determined by 1H NMR and elemental analyses. The emission spectrum, the emission quantum yield and the emission lifetime of the Sm(III) complex with ten-coordination structure in organic media are demonstrated for the first time. 2. Experimental details 2.1. Apparatus Infrared spectra used to identify synthesized materials were obtained with a Shimadzu FTIR-8300 spectrometer. Elemental
Y. Hasegawa et al. / Thin Solid Films 516 (2008) 2704–2707
Fig. 1. Chemical structure of bis(1,10-phenanthroline)tris-(hexafluoroacetylacetonato)sammarium(III) (Sm(hfa-H)3 (phen)2).
analyses were performed with a J-Science Lab JM10. 1H NMR data were obtained with a Varian Mercury plus 400 MHz spectrometer and were determined using tetramethylsilane (TMS) as an internal standard.
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corrected for detector sensitivity and lamp intensity variations. Emission lifetimes were measured with the third harmonics (355 nm) of Q switched Nd:YAG laser (Spectra Physics, INDI-50, FWHM = 5 ns, λ=1064 nm) and a photomultiplier (Hamamatsu photonics, R5108, response time = 1.1 ns). Nanosecond light pulses used to produce excitations in the samples (λ = 481 nm, power = 0.1 mJ) were generated by a dye laser (USHO optical systems DL-50, dye = coumarin 120). Emissions from the samples were filtered using a low-cut filter (Sigma SCF-50S52Y) placed in front of the detector. Nd:YAG response was monitored with a digital oscilloscope (Sony Tektronix, TDS3052, 500 MHz) synchronized to the single pulse excitation. Quantum yields were determined using a standard integrating sphere (diameter 6 cm) [6,7]. Optical path length of the cell was 5 mm. Quantum yields of rhodamine 6G in ethanol (1.0 × 10− 7 M, excitation wavelength = 510 nm, emission quantum yield = 95%) determined by the present procedure agreed well with reported value [8]. 3. Results and discussion
2.2. Materials
3.1. Coordination structure
Sammarium(III) chloride (99.5%), 1,1,1,5,5,5-hexafluoro2,4-pentanedione (hfa-H2) and 1,10-phenanthroline (phen) were purchased from Wako Pure Chemical Industries Ltd. Acetoned6 (CD3COCD3, 99.8%) was obtained from Aldrich Chemical Company Inc. All other chemicals were reagent grade and were used as received.
The coordination structure of Sm(III) complex was determined by 1H NMR measurement. The 1H NMR spectrum was shown in Fig. 2. The signals of the Sm(III) complex at around 8.5, 8.0, 7.6, 7.5 ppm were different from those of corresponding 1,10-phenanthroline and were assigned to signals of coordinated 1,10-phenanthroline (signals A). We also observed the signal of hexafluoroacetylacetonato ligands at 6.7 ppm (signal B). Integral proportion of signals A to signal B in the 1H NMR spectrum was found to be sixteen to three. The proportion indicates that the Sm(III) complex has two 1,10-phenanthroline (8H) and three hexafluoroacetylacetonato ligands (1H) in the deuterated acetone. The 1H NMR measurement of the Sm(III) complex gave empirical formula of SmC39H19O6F18N4 which agreed well with that determined by elemental analysis. From these analyses, the coordination site of the Sm(III) complex was determined to be a ten-coordination structure, Sm(hfa)3(phen)2.
2.3. Preparation of bis(1,10-phenanthroline)tris-(hexafluoroacetylacetonato)sammarium(III) (Sm(hfa-H)3(phen)2) Ethanol (30 ml) containing 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2.39 g, 11.5 mmol), 1,10-phenanthroline (phen) (2.07 g, 11.5 mmol) and potassium hydroxide (0.46 g, 11.5 mmol) was stirred. A solution of Sammarium chloride (1.4 g, 3.84 mmol) in water (5 ml) was added dropwise to the above solution and reacted at 60 °C for 2 h. The reaction mixture was concentrated and obtained mixture was washed with toluene/ water several times. The organic layer was separated, dried by anhydrous magnesium sulfate and concentrated. Recrystallization from water/methanol gave crystals of Sm(hfa-H)3(phen)2. Yield: 50–60%. IR(KBr): 1658 (st, C=O), 1529 (st, C=C), 1211 and 1197 (st, C–F) cm− 1. 1H NMR (CD3COCD3) δ=8.5 (4H, Ar), 8.0 (4H, Ar), 7.6 (4H, Ar), 7.5 (4H, Ar) and 6.7 (s, 3H, C-H) ppm. Anal. Calcd for SmC39H19O6F18N4: C, 41.38; H, 1.69; N: 4.95%. Found: C, 41.09; H, 1.68; N, 4.94%. Decomposition point: 288 °C. 2.4. Optical measurements Solution (0.01 M) of the Sm(III) complex was prepared in 1 ml of acetone and was degassed with nitrogen for optical measurements. Emission spectra were measured at room temperature using an ACTON research corporation SpectraPro 2300i system with a CCD detector (Roper PIXIS 100). The spectra were
Fig. 2. 1H NMR spectrum of Sm(hfa-H)3 (phen)2 in acetone-d6.
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Y. Hasegawa et al. / Thin Solid Films 516 (2008) 2704–2707
Generally, geometrical structure of lanthanide(III) complexes shows eight-coordination square anti-prism without inverted center [7]. According to the ten-coordination structure of lanthanide(III) complexes, extended square anti-prism structure without inverted center of La(III) complex have been reported [9]. The present Sm(III) complex having tencoordination structure should have no inverted center in the crystal field, resulting in an increase in electron transitions in the 4f orbitals due to odd parity. 3.2. Emission properties in organic media The emission spectrum of the Sm(III) complex in acetone was measured for the excitation at 380 nm (π−π⁎ transition of the hexafluoroacetylacetonato ligands). The emission spectrum was shown in Fig. 3a. The emission bands were observed at 562, 592, 643 and 705 nm and are attributed to f–f transitions 4G5/2 → 6H5/2 (zero–zero band: forbidden transition), 4G5/2 → 6H7/2 (magnetic dipole transition), 4G5/2 → 6H9/2 (electric dipole transition) and 4 G5/2 → 6H11/2 (forbidden transition), respectively. Spectra in Fig. 3a were normalized with respect to the 4G5/2 → 6H7/2 (magnetic dipole transition). 4G5/2 → 6H9/2 transition intensity was eight times larger than 4G5/2 → 6H7/2 transition intensity. The full width at half maxim (FWHM) of the 4G5/2 → 6H9/2 transition was found to be 5 nm. The narrow and strong emission of the 4G5/2 → 6H9/2 transition is due to asymmetric ten-coordination structure related to the special odd parity.
In order to confirm the emission from single Sm(hfa)3(phen)2 in liquid media, we carried out the emission lifetime measurement. The emission decay of Sm(III) complex in acetone is shown in Fig. 3b. Single exponential decay emission indicated the presence of a single luminescent site in acetone and homogeneity of the sample. Emission lifetime was determined from the slope of logarithmic plot of decay profile. The emission lifetime of the Sm(III) complex was found to be 0.054 ms. The value is similar to the reported value of nona-coordinated Sm (III) complex (around 0.040 ms) [10]. The total quantum yield of 4 G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions excited at absorption bands of the ligands (380 nm: π−π⁎ transition) and Sm(III) ion (480 nm: f–f transition) in acetone was found to be 0.36 and 1.4%, respectively. The emission quantum yield excited at ligand absorption of Sm(hfa)3 (phen)2 is larger than those of reported Sm(III) complexes (around 0.16%) [10]. Recently, luminescent lanthanide(III) complex, pyrazolone Eu(III) complex, for EL devices have been also reported [11]. The emission quantum yields excited at absorption bands of the ligands and Eu(III) ion in acetonitrile were reported to be 0.31 and 1.9%, respectively. These emission quantum yields of Sm(hfa)3(phen)2 are on similar order to those of corresponding pyrazolone Eu(III) complex. Generally, the emission quantum yields of Sm(III) complexes are much smaller than those of Eu(III) complexes because of smaller energy gap of Sm(III) ions (Sm(III): 7500 cm− 1, Eu(III): 12500 cm− 1) [1,2]. The excited state of Sm(III) ion having smaller energy gap is quenched by high-vibrational O–H bonds of coordination water, easily [6]. The effective emission quantum yield of Sm(hfa)3 (phen)2 would be due to characteristic ten-coordination structure without water molecules which lead to radiationless transition via vibrational relaxation. Furthermore, luminescent polymer thin film (PMMA) was successfully fabricated by incorporating the Sm(III) complex. From these results, ten coordinated Sm(III) complex having narrow deep-red emission would be regarded as attractive for new luminescent lanthanide(III) complex. 4. Conclusion We synthesized a new Sm(III) complex with ten-coordination structure, for developing luminescent materials having narrow deep-red emission. These emission quantum yields of the Sm (III) complex are on similar order to those of corresponding pyrazolone Eu(III) complex for EL devices. The emission quantum yields of luminescent lanthanide(III) complexes are also affected by vibrational structure of the surrounding media (host matrix). Especially, introduction of low-vibrational fluorinated polymers as a matrices leads to enhancement of the emission quantum yields of the lanthanide(III) complexes [7,12]. Luminescent materials using fluorine polymer containing Sm (hfa)3(phen)2 are desirable for developing applications in novel organic Sm(III) devices such as full-color displays. Acknowledgments
Fig. 3. (a) Emission spectrum of Sm(hfa-H)3 (phen)2 in acetone-d6 (2 × 10− 2 M, excitation at 380 nm). (b) Emission decay profile of Sm(hfa-H)3 (phen)2 in acetone-d6 (2 × 10− 2 M) shown in logarithmic scale.
This work was supported partly by a Grant-in-Aid for Scientific Research on Priority Area A of “Panoscopic
Y. Hasegawa et al. / Thin Solid Films 516 (2008) 2704–2707
Assembling and High Ordered Functions for Rare Earth Materials” from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. References [1] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag, New York, 1994. [2] F. Gan, Laser Materilas, World Scientific, Singapore, 1995, p. 70. [3] M.P.O. Wolbers, F.C.J.M. van Veggel, B.H.M. Snellink-Ruel, J.W. Hofdtraat, F.A.J. Geurts, D.N. Reinhoudt, J. Chem. Soc. Perkin Trans. 2 (1998) 2141. [4] Z. Kin, Y. Hino, H. Kajii, Y. Hasegawa, T. Kawai, Y. Ohmori, Trans. Mater. Res. Soc. Jpn. (in press).
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[5] J. Fang, C. Choy, D. Ma, E. Ou, Thin Solid Films 515 (4) (2006) 2419. [6] Y. Hasegawa, T. Ohkubo, K. Sogabe, Y. Kawamura, Y. Wada, N. Nakashima, S. Yanagida, Angew. Chem. Int. Ed. 39 (2000) 357. [7] Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisa, Y. Kai, S. Yanagida, J. Phys. Chem. A 107 (2003) 1697. [8] R.F. Kubin, A.N. Fletcher, J. Lumin. 27 (1982) 455. [9] D.R. van Staveren, G.A. van Albada, J.G. Haasnoot, H. Kooijman, A.M. M. Lanfredi, P.J. Nieuwenhuizen, A.L. Spek, F. Ugozzoli, T. Weyhermuuller, J. Reedijk, Inorg. Chim. Acta 315 (2001) 163. [10] F.R.G. Silva, O.L. Malta, C. Reinhard, H. Güdel, C. Poguet, J.E. Moser, J.G. Bünzli, J. Phys. Chem. A 106 (2002) 1670. [11] M. Shi, F. Li, T. Yi, D. Zhang, H. Hu, C. Huang, Inorg. Chem. 44 (2005) 8929. [12] Y. Hasegawa, K. Sogabe, Y. Wada, T. Kitamura, N. Nakashima, S. Yanagida, Chem. Lett. (1999) 35.
Thin Solid Films 516 (2008) 2704 – 2707 www.elsevier.com/locate/tsf
Emission properties of Sm(III) complex having ten-coordination structure Yasuchika Hasegawa a,⁎, Shin-ichi Tsuruoka b , Takahiko Yoshida b , Hideki Kawai c , Tsuyoshi Kawai a a
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan b USHIO Chemix, Co Ltd., 2252-1 Goudo, Omaezaki, Shizuoka, 437-1613, Japan c Research Institute of Electronics, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8011, Japan Available online 1 May 2007
Abstract Sammarium(III) complex having ten-coordination structure, bis-(1,10-phenanthroline)tris-(hexafluoroacetylacetonato)samarium(III) (Sm(hfa)3 (phen)2) was prepared by chelation of tris-(hexafluoroacetylacetonato) samarium(III) (Sm(hfa)3(H2O)2) with 1,10-phenantroline (phen). The characteristic ten-coordination structure of Sm(hfa)3(phen)2 was determined by 1H NMR and elemental analyses. Strong deep-red emission (λmax=643 nm) and narrow emission band (FWHM=5 nm) of Sm(hfa)3(phen)2 originated from electronic allowed transition from characteristics ten coordinate structure. The emission quantum yields Sm(hfa)3(phen)2 excited at absorption bands of ligands and Sm(III) ion were found to be 0.36 and 1.4%, respectively. © 2007 Elsevier B.V. All rights reserved. Keywords: Chemical synthesis; Luminescence; Samarium
1. Introduction Lanthanide(III) ions have been extensively studied as the attractive luminescent center for display devices, because of their highly monochromatic clear emission with FWHM smaller than 7 nm [1]. The monochromatic emission of lanthanide(III) ion mainly comes from the f–f transitions with no Storks shift [2]. The emission wavelength of lanthanide(III) is in principal independent of the crystal or ligand field because of characteristic feature of the f–f transition. Thus, tuning of the emission wavelength of a lanthanide ion is almost impossible. For example, the orange–red emission (615 nm) of Eu(III) ion which is well-known red element for display cannot be manipulated to the deep-red color emission (around 650 nm). Luminescent materials having narrow deep-red emission are strongly desired for high-quality display devices. For this purpose, we here focus on Sm(III) ion as a luminescent center. The emission bands of Sm(III) ion are assigned to 4G5/2 → 6H5/2 (zero–zero band), 4G5/2 → 6H7/2 (magnetic dipole transition), 4 G5/2 → 6H9/2 (electric dipole transition) and 4G5/2 → 6H11/2 (forbidden) [3]. Sm(III) complex with characteristic asymmetric ⁎ Corresponding author. Tel./fax: +81 743 6171. E-mail address: [email protected] (Y. Hasegawa). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.04.138
structures is expected to have increased radiation probability and emission quantum yield, since the 4G5/2 → 6H9/2 electric dipole transition would be partly allowed with the odd parity of the transition process. Recently, Ohmori and some of the present authors have demonstrated the deep-red emission from organic EL device by using a Sm(III) complex [4]. In the present study, we report on a new Sm(III) complex with ten-coordination structure for developing luminescent materials having narrow deep-red emission. The Sm(III) complex has two 1,10-phenanthroline ligands as shown in Fig. 1, which was designed taking some Eu(III)-phenanthroline complexes showing clear fluorescence into consideration [5]. The ten-coordination structure of the Sm(III) complex was determined by 1H NMR and elemental analyses. The emission spectrum, the emission quantum yield and the emission lifetime of the Sm(III) complex with ten-coordination structure in organic media are demonstrated for the first time. 2. Experimental details 2.1. Apparatus Infrared spectra used to identify synthesized materials were obtained with a Shimadzu FTIR-8300 spectrometer. Elemental
Y. Hasegawa et al. / Thin Solid Films 516 (2008) 2704–2707
Fig. 1. Chemical structure of bis(1,10-phenanthroline)tris-(hexafluoroacetylacetonato)sammarium(III) (Sm(hfa-H)3 (phen)2).
analyses were performed with a J-Science Lab JM10. 1H NMR data were obtained with a Varian Mercury plus 400 MHz spectrometer and were determined using tetramethylsilane (TMS) as an internal standard.
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corrected for detector sensitivity and lamp intensity variations. Emission lifetimes were measured with the third harmonics (355 nm) of Q switched Nd:YAG laser (Spectra Physics, INDI-50, FWHM = 5 ns, λ=1064 nm) and a photomultiplier (Hamamatsu photonics, R5108, response time = 1.1 ns). Nanosecond light pulses used to produce excitations in the samples (λ = 481 nm, power = 0.1 mJ) were generated by a dye laser (USHO optical systems DL-50, dye = coumarin 120). Emissions from the samples were filtered using a low-cut filter (Sigma SCF-50S52Y) placed in front of the detector. Nd:YAG response was monitored with a digital oscilloscope (Sony Tektronix, TDS3052, 500 MHz) synchronized to the single pulse excitation. Quantum yields were determined using a standard integrating sphere (diameter 6 cm) [6,7]. Optical path length of the cell was 5 mm. Quantum yields of rhodamine 6G in ethanol (1.0 × 10− 7 M, excitation wavelength = 510 nm, emission quantum yield = 95%) determined by the present procedure agreed well with reported value [8]. 3. Results and discussion
2.2. Materials
3.1. Coordination structure
Sammarium(III) chloride (99.5%), 1,1,1,5,5,5-hexafluoro2,4-pentanedione (hfa-H2) and 1,10-phenanthroline (phen) were purchased from Wako Pure Chemical Industries Ltd. Acetoned6 (CD3COCD3, 99.8%) was obtained from Aldrich Chemical Company Inc. All other chemicals were reagent grade and were used as received.
The coordination structure of Sm(III) complex was determined by 1H NMR measurement. The 1H NMR spectrum was shown in Fig. 2. The signals of the Sm(III) complex at around 8.5, 8.0, 7.6, 7.5 ppm were different from those of corresponding 1,10-phenanthroline and were assigned to signals of coordinated 1,10-phenanthroline (signals A). We also observed the signal of hexafluoroacetylacetonato ligands at 6.7 ppm (signal B). Integral proportion of signals A to signal B in the 1H NMR spectrum was found to be sixteen to three. The proportion indicates that the Sm(III) complex has two 1,10-phenanthroline (8H) and three hexafluoroacetylacetonato ligands (1H) in the deuterated acetone. The 1H NMR measurement of the Sm(III) complex gave empirical formula of SmC39H19O6F18N4 which agreed well with that determined by elemental analysis. From these analyses, the coordination site of the Sm(III) complex was determined to be a ten-coordination structure, Sm(hfa)3(phen)2.
2.3. Preparation of bis(1,10-phenanthroline)tris-(hexafluoroacetylacetonato)sammarium(III) (Sm(hfa-H)3(phen)2) Ethanol (30 ml) containing 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (2.39 g, 11.5 mmol), 1,10-phenanthroline (phen) (2.07 g, 11.5 mmol) and potassium hydroxide (0.46 g, 11.5 mmol) was stirred. A solution of Sammarium chloride (1.4 g, 3.84 mmol) in water (5 ml) was added dropwise to the above solution and reacted at 60 °C for 2 h. The reaction mixture was concentrated and obtained mixture was washed with toluene/ water several times. The organic layer was separated, dried by anhydrous magnesium sulfate and concentrated. Recrystallization from water/methanol gave crystals of Sm(hfa-H)3(phen)2. Yield: 50–60%. IR(KBr): 1658 (st, C=O), 1529 (st, C=C), 1211 and 1197 (st, C–F) cm− 1. 1H NMR (CD3COCD3) δ=8.5 (4H, Ar), 8.0 (4H, Ar), 7.6 (4H, Ar), 7.5 (4H, Ar) and 6.7 (s, 3H, C-H) ppm. Anal. Calcd for SmC39H19O6F18N4: C, 41.38; H, 1.69; N: 4.95%. Found: C, 41.09; H, 1.68; N, 4.94%. Decomposition point: 288 °C. 2.4. Optical measurements Solution (0.01 M) of the Sm(III) complex was prepared in 1 ml of acetone and was degassed with nitrogen for optical measurements. Emission spectra were measured at room temperature using an ACTON research corporation SpectraPro 2300i system with a CCD detector (Roper PIXIS 100). The spectra were
Fig. 2. 1H NMR spectrum of Sm(hfa-H)3 (phen)2 in acetone-d6.
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Y. Hasegawa et al. / Thin Solid Films 516 (2008) 2704–2707
Generally, geometrical structure of lanthanide(III) complexes shows eight-coordination square anti-prism without inverted center [7]. According to the ten-coordination structure of lanthanide(III) complexes, extended square anti-prism structure without inverted center of La(III) complex have been reported [9]. The present Sm(III) complex having tencoordination structure should have no inverted center in the crystal field, resulting in an increase in electron transitions in the 4f orbitals due to odd parity. 3.2. Emission properties in organic media The emission spectrum of the Sm(III) complex in acetone was measured for the excitation at 380 nm (π−π⁎ transition of the hexafluoroacetylacetonato ligands). The emission spectrum was shown in Fig. 3a. The emission bands were observed at 562, 592, 643 and 705 nm and are attributed to f–f transitions 4G5/2 → 6H5/2 (zero–zero band: forbidden transition), 4G5/2 → 6H7/2 (magnetic dipole transition), 4G5/2 → 6H9/2 (electric dipole transition) and 4 G5/2 → 6H11/2 (forbidden transition), respectively. Spectra in Fig. 3a were normalized with respect to the 4G5/2 → 6H7/2 (magnetic dipole transition). 4G5/2 → 6H9/2 transition intensity was eight times larger than 4G5/2 → 6H7/2 transition intensity. The full width at half maxim (FWHM) of the 4G5/2 → 6H9/2 transition was found to be 5 nm. The narrow and strong emission of the 4G5/2 → 6H9/2 transition is due to asymmetric ten-coordination structure related to the special odd parity.
In order to confirm the emission from single Sm(hfa)3(phen)2 in liquid media, we carried out the emission lifetime measurement. The emission decay of Sm(III) complex in acetone is shown in Fig. 3b. Single exponential decay emission indicated the presence of a single luminescent site in acetone and homogeneity of the sample. Emission lifetime was determined from the slope of logarithmic plot of decay profile. The emission lifetime of the Sm(III) complex was found to be 0.054 ms. The value is similar to the reported value of nona-coordinated Sm (III) complex (around 0.040 ms) [10]. The total quantum yield of 4 G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2 and 4G5/2 → 6H11/2 transitions excited at absorption bands of the ligands (380 nm: π−π⁎ transition) and Sm(III) ion (480 nm: f–f transition) in acetone was found to be 0.36 and 1.4%, respectively. The emission quantum yield excited at ligand absorption of Sm(hfa)3 (phen)2 is larger than those of reported Sm(III) complexes (around 0.16%) [10]. Recently, luminescent lanthanide(III) complex, pyrazolone Eu(III) complex, for EL devices have been also reported [11]. The emission quantum yields excited at absorption bands of the ligands and Eu(III) ion in acetonitrile were reported to be 0.31 and 1.9%, respectively. These emission quantum yields of Sm(hfa)3(phen)2 are on similar order to those of corresponding pyrazolone Eu(III) complex. Generally, the emission quantum yields of Sm(III) complexes are much smaller than those of Eu(III) complexes because of smaller energy gap of Sm(III) ions (Sm(III): 7500 cm− 1, Eu(III): 12500 cm− 1) [1,2]. The excited state of Sm(III) ion having smaller energy gap is quenched by high-vibrational O–H bonds of coordination water, easily [6]. The effective emission quantum yield of Sm(hfa)3 (phen)2 would be due to characteristic ten-coordination structure without water molecules which lead to radiationless transition via vibrational relaxation. Furthermore, luminescent polymer thin film (PMMA) was successfully fabricated by incorporating the Sm(III) complex. From these results, ten coordinated Sm(III) complex having narrow deep-red emission would be regarded as attractive for new luminescent lanthanide(III) complex. 4. Conclusion We synthesized a new Sm(III) complex with ten-coordination structure, for developing luminescent materials having narrow deep-red emission. These emission quantum yields of the Sm (III) complex are on similar order to those of corresponding pyrazolone Eu(III) complex for EL devices. The emission quantum yields of luminescent lanthanide(III) complexes are also affected by vibrational structure of the surrounding media (host matrix). Especially, introduction of low-vibrational fluorinated polymers as a matrices leads to enhancement of the emission quantum yields of the lanthanide(III) complexes [7,12]. Luminescent materials using fluorine polymer containing Sm (hfa)3(phen)2 are desirable for developing applications in novel organic Sm(III) devices such as full-color displays. Acknowledgments
Fig. 3. (a) Emission spectrum of Sm(hfa-H)3 (phen)2 in acetone-d6 (2 × 10− 2 M, excitation at 380 nm). (b) Emission decay profile of Sm(hfa-H)3 (phen)2 in acetone-d6 (2 × 10− 2 M) shown in logarithmic scale.
This work was supported partly by a Grant-in-Aid for Scientific Research on Priority Area A of “Panoscopic
Y. Hasegawa et al. / Thin Solid Films 516 (2008) 2704–2707
Assembling and High Ordered Functions for Rare Earth Materials” from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. References [1] G. Blasse, B.C. Grabmaier, Luminescent Materials, Springer-Verlag, New York, 1994. [2] F. Gan, Laser Materilas, World Scientific, Singapore, 1995, p. 70. [3] M.P.O. Wolbers, F.C.J.M. van Veggel, B.H.M. Snellink-Ruel, J.W. Hofdtraat, F.A.J. Geurts, D.N. Reinhoudt, J. Chem. Soc. Perkin Trans. 2 (1998) 2141. [4] Z. Kin, Y. Hino, H. Kajii, Y. Hasegawa, T. Kawai, Y. Ohmori, Trans. Mater. Res. Soc. Jpn. (in press).
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[5] J. Fang, C. Choy, D. Ma, E. Ou, Thin Solid Films 515 (4) (2006) 2419. [6] Y. Hasegawa, T. Ohkubo, K. Sogabe, Y. Kawamura, Y. Wada, N. Nakashima, S. Yanagida, Angew. Chem. Int. Ed. 39 (2000) 357. [7] Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisa, Y. Kai, S. Yanagida, J. Phys. Chem. A 107 (2003) 1697. [8] R.F. Kubin, A.N. Fletcher, J. Lumin. 27 (1982) 455. [9] D.R. van Staveren, G.A. van Albada, J.G. Haasnoot, H. Kooijman, A.M. M. Lanfredi, P.J. Nieuwenhuizen, A.L. Spek, F. Ugozzoli, T. Weyhermuuller, J. Reedijk, Inorg. Chim. Acta 315 (2001) 163. [10] F.R.G. Silva, O.L. Malta, C. Reinhard, H. Güdel, C. Poguet, J.E. Moser, J.G. Bünzli, J. Phys. Chem. A 106 (2002) 1670. [11] M. Shi, F. Li, T. Yi, D. Zhang, H. Hu, C. Huang, Inorg. Chem. 44 (2005) 8929. [12] Y. Hasegawa, K. Sogabe, Y. Wada, T. Kitamura, N. Nakashima, S. Yanagida, Chem. Lett. (1999) 35.