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Red electroluminescence from a novel europium β-diketone complex with acylpyrazolone ligand
Synthetic Metals 111–112 Ž2000. 445–447 www.elsevier.comrlocatersynmet
Red electroluminescence from a novel europium b-diketone complex with acylpyrazolone ligand Weiguo Zhu a,c , Qing Jiang a , Zhiyun Lu a , Xiaoqiang Wei a , Minggui Xie a,) , Dechun Zou b, Tetsuo Tsutsui b a
b
Department of Chemistry, Sichuan UniÕersity, Chengdu 610064, People’s Republic of China Department of Applied Science for Electronics and Materials, Interdisiplinary Graduate School of Engineering Sciences, Kyushu UniÕersity, Kasuga 6-1, Fukuoka 816-8580, Japan c Department of Chemistry, Xiangtan UniÕersity, Xiangtan 411105, People’s Republic of China
Abstract A novel poly-ligand europium b-diketone complex was prepared, which contains ligand of 1-phenyl-3-methyl-4Ž4-butylbenzoyl.-5pyrazolone ŽHPMBBP.. Its structure is EuŽTTA. 2 ŽPMBBP.Phen. We investigated its PL and EL properties. When it was used as emitting material, the new Eu-complex exhibited intense photoluminescence ŽPL. and electroluminescence ŽEL. at 613 nm in a fabricated three-layer electroluminescent device: ITOrTPDrEuŽTTA. 2 ŽPMBBP.PhenrAlq 3rMg:Ag. The maximum luminance of 16 cdrm2 from the device was obtained at 12.5 V. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Acylpyrazolone; Europium b-diketone; Synthesis; Electroluminescent device
1. Introduction Metal-organic complexes have played an important role in organic electroluminescent devices ŽOELDs. w1x. A green OEL flat panel display, using metal-organic complexes as emitter, was reported in 1997 w2x. Green-emitting and blue-emitting materials have been well investigated. However, red-emitting materials with excellent properties have not been developed successfully w3–8x. To realize full-color organic EL display, it is considered important to develop red-emitting materials with excellent properties. As europium complexes have high fluorescence quantum efficiency, pure luminescent color and good stability, they have been selected as red-emitting materials. Some of these red-emitting materials, such as EuŽTTA. 3Phen, EuŽDBM. 3 Phen and EuŽDBM. 3 bath, have been reported, but they have some disadvantages, such as low luminance, low luminescent efficiency and poor carriertransporting properties. In order to overcome these problems, we designed and prepared a new poly-ligand Eu-complex EuŽTTA. 2ŽPMBBP.Phen, which contains ligand of 1-phenyl-3-me-
)
thyl-4Ž4-butylbenzoyl.-5-pyrazolone ŽHPMBBP . and thenoyltrifluoroacetone ŽHTTA.. When used as emitting material, the new Eu-complex exhibited intense photoluminescence ŽPL. and electroluminescence ŽEL. at 613 nm, and the maximum luminance from the OELD is 16 cdrm2 . It has better film formation, more excellent carrier transporting properties and higher luminance than EuŽTTA. 3 Phen.
2. Experimental HPMBBP was synthesized as literature w9x. EuŽTTA. 2 ŽPMBBP.Phen was prepared as follows: Europium
Corresponding author.
0379-6779r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 3 9 6 - 3
Fig. 1. The chemical structure of EuŽTTA.2ŽPMBBP.Phen.
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W. Zhu et al.r Synthetic Metals 111–112 (2000) 445–447
Fig. 2. The cell structure of the LED.
oxide 0.35 g Ž1 mmol. was dissolved in 3 ml concentrated hydrochloric acid Ž36.5%., then surplus HCl was removed by evaporation, and the residue was diluted with 10 ml water in a flask. The europium chloride solution was added into the mixed ethanol solution of 4,4,4-trifluro-1-Ž2thienyl.-1,3-butandione 0.89 g ŽHTTA, 4 mmol. and 1phenyl-3-methyl-4Ž4-butylbenzoyl.-5-pyrazolone 0.67 g ŽHPMBBP, 2 mmol. in another flask while stirring. The reactant solution was neutralized to pH 6–7 with solution Ž2 N. of NaOH, and heated to 50–608C. After it was stirred for 0.5 h, the ethanol solution of 1.10-phenanthroline 0.36 g Ž2 mmol. was added into the above mixture. The reactant was stirred for 3 h at 50–608C again, and a pale-yellow deposit was obtained. It was filtered and washed with pure water and ethanol until no Cly was found in the washed water, then it recrystallized from ethyl acetate to give EuŽTTA. 2 ŽPMBBP.Phen with yield of 80%; m.p. 195–1978C. Element analysis: C%: 53.12, H%: 3.36, N%: 5.06, Eu%: 13.72; Found: C%: 53.01, H%: 3.32, N%: 5.03, Eu%: 13.56. The chemical structure of EuŽTTA. 2ŽPMBBP.Phen is shown in Fig. 1. The EL devices were fabricated using conventional vacuum vapor deposition in a 5.0 = 10y4 Pa vacuum. The cell structure is shown in Fig. 2, and the emitting area of the device is 2 = 2 mm. The hole-transporting layer ŽHTL., emitting layer ŽEML. and electron-transporting layer ŽETL. are N , N X -diphenyl-N , N X -bis Ž 3-methylphenyl . ,-1,1X bipheny1-4,4X-diamine ŽTPD., EuŽTTA. 2 ŽPMBBP.Phen and tris-8-hydroxyquinolinato aluminum ŽAlq 3 ., respectively.
Fig. 3. PL spectrum of the EuŽTTA.2ŽPMBBP.Phen film Ž10 nm..
Fig. 4. EL spectrum of the ELD with EuŽTTA.2ŽPMBBP.Phen.
The luminance of the EL device was measured with a luminance meter ŽTopcon, BM-8., and EL spectrum was measured with a spectrophotometer ŽPMA-11.. The PL spectrum of EuŽTTA. 2 ŽPMBBP.Phen film Ž10 nm. was measured with a fluorescence spectrophotometer ŽHitachi850.. All the measurements were carried out at room temperature in air. The film deposition rate was about 0.2 nmrs.
3. Results and discussion The PL spectrum of film Ž10 nm. of EuŽTTA. 2ŽPMBBP.Phen and electroluminescence ŽEL. spectrum of the device are shown in Figs. 3 and 4, respectively. The thin film of EuŽTTA. 2 ŽPMBBP.Phen exhibits intense fluorescence at 613 nm with a sharp half linewidth Ž10 nm.. The sharp EL spectrum Žpeak at 613 nm. from the device is almost similar to the PL spectrum of EuŽTTA. 2ŽPMBBP.Phen, indicating that the emission originates from the EML. The luminance–current density and voltage–current density characteristics of the device are shown in Figs. 5
Fig. 5. The luminance–current density characteristics of the LED.
W. Zhu et al.r Synthetic Metals 111–112 (2000) 445–447
447
EuŽTTA. 2 ŽPMBBP.Phen, and decrease the excited energy of PL of EuŽTTA. 2 ŽPMBBP.Phen. On the other hand, ligand HPMBBP contains nitrogen atom in pyrazolone ring, it may improve the carrier-transporting property and film formation in EuŽTTA. 2ŽPMBBP.Phen. Therefore, the device with EuŽTTA. 2ŽPMBBP.Phen as emitter has higher brightness and better film formation than the device with EuŽTTA. 3 Phen as emitter.
4. Conclusions Fig. 6. Current density–voltage characteristics of the LED.
and 6, respectively. Fig. 5 shows that the turn-on voltage of the device is 9 V, and the maximum luminance from the device is 16 cdrm2 at 125 mArcm2 of current density. The maximum luminance of this device is two times as high as that of the device reported using EuŽTTA. 3 Phen as EML. The enhanced luminance and improved film formation are obtained from the device. We suggest that the ligand HPMBBP has a smaller p – p- and p– p-conjugated system, because it has a double bond of carbon and carbon outside pyrazolone ring. Its triplet energy cannot transfer to Eu3q effectively, thus, it does not cause Eu3q to emit light, and EuŽPMBBP. 3 Phen has no fluorescence. The red-emission of EuŽTTA. 2 ŽPMBBP.Phen may stem from an effective energy transfer from the p – p ) triplet energy of anion TTAy to Eu3q. Because of the interaction of electron cloud between ligand HTTA and HPMBBP, the coordinate field of EuŽTTA. 2 ŽPMBBP.Phen complex has been changed. So it is considered that ligand HPMBBP could more effectively transfer ligand HTTA’s triplet energy to europium ion, and EuŽTTA. 2 ŽPMBBP.Phen complex can emit more intense light. The PL spectrum shows that EuŽTTA. 3 Phen complex has a l Exmax of 270 nm, but that of EuŽTTA. 2ŽPMBBP.Phen complex is 348 nm, indicating that ligand HPMBBP could exactly influence the luminescence of
A poly-ligand europium b-diketone with acylpyrazolone has been prepared. The 16 cdrm2 of the maximum luminance and pure red emission from Eu3q peaked at 613 nm have been obtained from an LED with a three-layer structure. The electroluminescence ŽEL. properties indicate that this material can be used as a novel red-emitting material in electroluminescent devices.
Acknowledgements This work was supported by National Natural Science Foundation of China Ž29672025., and the Committee of Science and Technology of Hunan.
References w1x Y. Hamada, IEEE Trans. Electron Devices 44 Ž1997. 1208. w2x C. Hosokawa et al., in: 9th International workshop on inorganic and organic Electroluminescence, 14–17th Sep., Bend, U.S.A., 1998, pp. 151–154, extended abstracts. w3x S. Dirr et al., Jpn. J. Appl. Phys., Part 1 37 Ž1998. 1457. w4x L. Liu et al., Synth. Met. 91 Ž1997. 267. w5x A. Edwards et al., J. Appl. Phys. 82 Ž1997. 1841. w6x D. Chenxia et al., J. Alloys Compd. 265 Ž1998. 81. w7x P. Burrows, R.S. Forrest, E.M. Thompson, PCT Int. Appl. WO 9801011. w8x R.A. Campos et al., J. Appl. Phys. 80 Ž1996. 7144. w9x Z. Weiguo et al., Chin. Chem. Lett. 10 Ž1999. 603.
Red electroluminescence from a novel europium b-diketone complex with acylpyrazolone ligand Weiguo Zhu a,c , Qing Jiang a , Zhiyun Lu a , Xiaoqiang Wei a , Minggui Xie a,) , Dechun Zou b, Tetsuo Tsutsui b a
b
Department of Chemistry, Sichuan UniÕersity, Chengdu 610064, People’s Republic of China Department of Applied Science for Electronics and Materials, Interdisiplinary Graduate School of Engineering Sciences, Kyushu UniÕersity, Kasuga 6-1, Fukuoka 816-8580, Japan c Department of Chemistry, Xiangtan UniÕersity, Xiangtan 411105, People’s Republic of China
Abstract A novel poly-ligand europium b-diketone complex was prepared, which contains ligand of 1-phenyl-3-methyl-4Ž4-butylbenzoyl.-5pyrazolone ŽHPMBBP.. Its structure is EuŽTTA. 2 ŽPMBBP.Phen. We investigated its PL and EL properties. When it was used as emitting material, the new Eu-complex exhibited intense photoluminescence ŽPL. and electroluminescence ŽEL. at 613 nm in a fabricated three-layer electroluminescent device: ITOrTPDrEuŽTTA. 2 ŽPMBBP.PhenrAlq 3rMg:Ag. The maximum luminance of 16 cdrm2 from the device was obtained at 12.5 V. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Acylpyrazolone; Europium b-diketone; Synthesis; Electroluminescent device
1. Introduction Metal-organic complexes have played an important role in organic electroluminescent devices ŽOELDs. w1x. A green OEL flat panel display, using metal-organic complexes as emitter, was reported in 1997 w2x. Green-emitting and blue-emitting materials have been well investigated. However, red-emitting materials with excellent properties have not been developed successfully w3–8x. To realize full-color organic EL display, it is considered important to develop red-emitting materials with excellent properties. As europium complexes have high fluorescence quantum efficiency, pure luminescent color and good stability, they have been selected as red-emitting materials. Some of these red-emitting materials, such as EuŽTTA. 3Phen, EuŽDBM. 3 Phen and EuŽDBM. 3 bath, have been reported, but they have some disadvantages, such as low luminance, low luminescent efficiency and poor carriertransporting properties. In order to overcome these problems, we designed and prepared a new poly-ligand Eu-complex EuŽTTA. 2ŽPMBBP.Phen, which contains ligand of 1-phenyl-3-me-
)
thyl-4Ž4-butylbenzoyl.-5-pyrazolone ŽHPMBBP . and thenoyltrifluoroacetone ŽHTTA.. When used as emitting material, the new Eu-complex exhibited intense photoluminescence ŽPL. and electroluminescence ŽEL. at 613 nm, and the maximum luminance from the OELD is 16 cdrm2 . It has better film formation, more excellent carrier transporting properties and higher luminance than EuŽTTA. 3 Phen.
2. Experimental HPMBBP was synthesized as literature w9x. EuŽTTA. 2 ŽPMBBP.Phen was prepared as follows: Europium
Corresponding author.
0379-6779r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. PII: S 0 3 7 9 - 6 7 7 9 Ž 9 9 . 0 0 3 9 6 - 3
Fig. 1. The chemical structure of EuŽTTA.2ŽPMBBP.Phen.
446
W. Zhu et al.r Synthetic Metals 111–112 (2000) 445–447
Fig. 2. The cell structure of the LED.
oxide 0.35 g Ž1 mmol. was dissolved in 3 ml concentrated hydrochloric acid Ž36.5%., then surplus HCl was removed by evaporation, and the residue was diluted with 10 ml water in a flask. The europium chloride solution was added into the mixed ethanol solution of 4,4,4-trifluro-1-Ž2thienyl.-1,3-butandione 0.89 g ŽHTTA, 4 mmol. and 1phenyl-3-methyl-4Ž4-butylbenzoyl.-5-pyrazolone 0.67 g ŽHPMBBP, 2 mmol. in another flask while stirring. The reactant solution was neutralized to pH 6–7 with solution Ž2 N. of NaOH, and heated to 50–608C. After it was stirred for 0.5 h, the ethanol solution of 1.10-phenanthroline 0.36 g Ž2 mmol. was added into the above mixture. The reactant was stirred for 3 h at 50–608C again, and a pale-yellow deposit was obtained. It was filtered and washed with pure water and ethanol until no Cly was found in the washed water, then it recrystallized from ethyl acetate to give EuŽTTA. 2 ŽPMBBP.Phen with yield of 80%; m.p. 195–1978C. Element analysis: C%: 53.12, H%: 3.36, N%: 5.06, Eu%: 13.72; Found: C%: 53.01, H%: 3.32, N%: 5.03, Eu%: 13.56. The chemical structure of EuŽTTA. 2ŽPMBBP.Phen is shown in Fig. 1. The EL devices were fabricated using conventional vacuum vapor deposition in a 5.0 = 10y4 Pa vacuum. The cell structure is shown in Fig. 2, and the emitting area of the device is 2 = 2 mm. The hole-transporting layer ŽHTL., emitting layer ŽEML. and electron-transporting layer ŽETL. are N , N X -diphenyl-N , N X -bis Ž 3-methylphenyl . ,-1,1X bipheny1-4,4X-diamine ŽTPD., EuŽTTA. 2 ŽPMBBP.Phen and tris-8-hydroxyquinolinato aluminum ŽAlq 3 ., respectively.
Fig. 3. PL spectrum of the EuŽTTA.2ŽPMBBP.Phen film Ž10 nm..
Fig. 4. EL spectrum of the ELD with EuŽTTA.2ŽPMBBP.Phen.
The luminance of the EL device was measured with a luminance meter ŽTopcon, BM-8., and EL spectrum was measured with a spectrophotometer ŽPMA-11.. The PL spectrum of EuŽTTA. 2 ŽPMBBP.Phen film Ž10 nm. was measured with a fluorescence spectrophotometer ŽHitachi850.. All the measurements were carried out at room temperature in air. The film deposition rate was about 0.2 nmrs.
3. Results and discussion The PL spectrum of film Ž10 nm. of EuŽTTA. 2ŽPMBBP.Phen and electroluminescence ŽEL. spectrum of the device are shown in Figs. 3 and 4, respectively. The thin film of EuŽTTA. 2 ŽPMBBP.Phen exhibits intense fluorescence at 613 nm with a sharp half linewidth Ž10 nm.. The sharp EL spectrum Žpeak at 613 nm. from the device is almost similar to the PL spectrum of EuŽTTA. 2ŽPMBBP.Phen, indicating that the emission originates from the EML. The luminance–current density and voltage–current density characteristics of the device are shown in Figs. 5
Fig. 5. The luminance–current density characteristics of the LED.
W. Zhu et al.r Synthetic Metals 111–112 (2000) 445–447
447
EuŽTTA. 2 ŽPMBBP.Phen, and decrease the excited energy of PL of EuŽTTA. 2 ŽPMBBP.Phen. On the other hand, ligand HPMBBP contains nitrogen atom in pyrazolone ring, it may improve the carrier-transporting property and film formation in EuŽTTA. 2ŽPMBBP.Phen. Therefore, the device with EuŽTTA. 2ŽPMBBP.Phen as emitter has higher brightness and better film formation than the device with EuŽTTA. 3 Phen as emitter.
4. Conclusions Fig. 6. Current density–voltage characteristics of the LED.
and 6, respectively. Fig. 5 shows that the turn-on voltage of the device is 9 V, and the maximum luminance from the device is 16 cdrm2 at 125 mArcm2 of current density. The maximum luminance of this device is two times as high as that of the device reported using EuŽTTA. 3 Phen as EML. The enhanced luminance and improved film formation are obtained from the device. We suggest that the ligand HPMBBP has a smaller p – p- and p– p-conjugated system, because it has a double bond of carbon and carbon outside pyrazolone ring. Its triplet energy cannot transfer to Eu3q effectively, thus, it does not cause Eu3q to emit light, and EuŽPMBBP. 3 Phen has no fluorescence. The red-emission of EuŽTTA. 2 ŽPMBBP.Phen may stem from an effective energy transfer from the p – p ) triplet energy of anion TTAy to Eu3q. Because of the interaction of electron cloud between ligand HTTA and HPMBBP, the coordinate field of EuŽTTA. 2 ŽPMBBP.Phen complex has been changed. So it is considered that ligand HPMBBP could more effectively transfer ligand HTTA’s triplet energy to europium ion, and EuŽTTA. 2 ŽPMBBP.Phen complex can emit more intense light. The PL spectrum shows that EuŽTTA. 3 Phen complex has a l Exmax of 270 nm, but that of EuŽTTA. 2ŽPMBBP.Phen complex is 348 nm, indicating that ligand HPMBBP could exactly influence the luminescence of
A poly-ligand europium b-diketone with acylpyrazolone has been prepared. The 16 cdrm2 of the maximum luminance and pure red emission from Eu3q peaked at 613 nm have been obtained from an LED with a three-layer structure. The electroluminescence ŽEL. properties indicate that this material can be used as a novel red-emitting material in electroluminescent devices.
Acknowledgements This work was supported by National Natural Science Foundation of China Ž29672025., and the Committee of Science and Technology of Hunan.
References w1x Y. Hamada, IEEE Trans. Electron Devices 44 Ž1997. 1208. w2x C. Hosokawa et al., in: 9th International workshop on inorganic and organic Electroluminescence, 14–17th Sep., Bend, U.S.A., 1998, pp. 151–154, extended abstracts. w3x S. Dirr et al., Jpn. J. Appl. Phys., Part 1 37 Ž1998. 1457. w4x L. Liu et al., Synth. Met. 91 Ž1997. 267. w5x A. Edwards et al., J. Appl. Phys. 82 Ž1997. 1841. w6x D. Chenxia et al., J. Alloys Compd. 265 Ž1998. 81. w7x P. Burrows, R.S. Forrest, E.M. Thompson, PCT Int. Appl. WO 9801011. w8x R.A. Campos et al., J. Appl. Phys. 80 Ž1996. 7144. w9x Z. Weiguo et al., Chin. Chem. Lett. 10 Ž1999. 603.