- Email: [email protected]
Synthesis and electroluminescent properties of anthracene derivatives containing electron-withdrawing oxide moieties
G Model MRB 7351 No. of Pages 4
Materials Research Bulletin xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
Synthesis and electroluminescent properties of anthracene derivatives containing electron-withdrawing oxide moieties Jhin-yeong Yoon a , Eun Jae Na a , Soo Na Park a , Seok Jae Lee b , Young Kwan Kim b, *, Seung Soo Yoon a, * a b
Department of Chemistry, Sungkyunkwan University, Suwon, 440-746, Republic of Korea Department of Information Display, Hongik University, Seoul, 121-791, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history: Received 5 August 2013 Received in revised form 18 March 2014 Accepted 20 March 2014 Available online xxx
A series of new blue-emitting materials: (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)(phenyl) methanone (1); 9-(naphthalen-2-yl)-10-(4-((diphenyl)phosphine oxide)phenyl)anthracene (2); 9(naphthalen-2-yl)-10-(4-(phenylsulfonyl)phenyl)anthracene (3) were designed and synthesized via Suzuki cross-coupling reaction. Multilayer OLEDs were fabricated in the following sequence: ITO (180 nm)/NPB (50 nm)/blue materials 1–3 (30 nm)/TPBi (15 nm)/Liq (2 nm)/Al (100 nm). All devices showed the efficient blue EL emissions. In particular, the device using 1 as an emitter exhibited efficient blue electroluminescent properties with a maximum luminous, power, external quantum efficiency and CIE coordinates of 0.36 cd/A, 0.90 lm/W, 0.55% at 20 mA/cm2 and (x = 0.16, y = 0.20) at 10.0 V, respectively. ã 2014 Elsevier Ltd. All rights reserved.
Keywords: A. Organic compounds A. Oxides B. Chemical synthesis D. Luminescence
1. Introduction
2. Experimental details
Organic light-emitting devices (OLEDs) have been widely studied in the past two decades for use in flat panel displays and more-efficient lighting products [1]. For the practical applications, three primary color emitters that have high emission efficiency and high color purity are required. However, because of the wide band-gap of blue emitters, blue OLEDs show relatively poorer performance than red and green OLEDs. For this reason, the progress in highly efficient blue-light emitters with good color purity is a great challenge. Up to now, various blue emitters have been developed by many research groups [2–6]. However, the EL performances of blue emitters still need to be improved. In this work, a series of new blue fluorescent material based on 9-naphthylanthracene core unit containing various electronwithdrawing oxide moieties were synthesized and their electroluminescent properties were investigated. The electron-withdrawing oxide moieties in the emitting materials were introduced to tune the HOMO or LUMO energy levels of the emitting materials, and to enhance the EL performances [7–8].
2.1. Material preparation and characterization
* Corresponding authors. Tel.:+ 82 31 290 7071, 2 3142 3750; fax: +82 31 290 7075, 2 3141 8928. E-mail addresses: [email protected] (Y.K. Kim), [email protected] (S.S. Yoon).
The molecular structure and synthetic route of 1–3 compounds are outlined in Scheme 1. General procedure for the Suzuki crosscoupling reaction: the corresponding hetero aryl bromide (1.0 mol), 10-(naphthalen-2-yl)anthracene-9-ylboronic acid (1.2 mol) and Pd(PPh3)4 (0.04 mol) were mixed in a solution of aqueous 2.0 M Na2CO3 (10.0 mol), ethanol and toluene. The mixture was refluxed at 90 C for 2 h. After the reaction had finished, the reaction mixture was extracted with toluene and washed with water. The organic layer was dried with anhydrous MgSO4 and filtered with charcoal. The solution was then evaporated. The crude product was purified by column chromatography with silica gel and subsequent recrystallization from THF/ MeOH and then hot hexane filter. (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl) (phenyl) methanone (1): (yield = 83%). 1H NMR (300 MHz, CDCl3): d [ppm]: 8.10–8.07 (m, 3H), 8.04–7.97(m, 4H), 7.93–7.90(m, 1H), 7.75(t, J = 7.8 Hz, 4H), 7.66–7.63(m, 3H), 7.61(t, J = 1.8 Hz, 1H), 7.59–7.56(m, 4H), 7.40–7.29 (m, 4H). IR(ATR): n [cm1]: 3055, 2954, 2892, 2831,1810,1695,1658, 1601, 1508, 1442, 1395, 1310, 1279, 1176, 1144, 1016, 1023, 960, 931, 905, 847, 822, 796, 762, 699. APCI-MS (m/z): 485 [M+]. 9-(naphthalen-2-yl)-10-(4-((diphenyl)phosphine oxide)phenyl)anthracene (2): (yield = 81%). 1H NMR (300 MHz, CDCl3): d [ppm]: 8.0(d, J = 8.4 Hz, 1H), 8.04–8.01(m, 1H), 7.7(s, 1H), 7.4–7.82 (m, 7H), 7.74(dd, J = 1.2, 7.5 Hz, 2H), 7.66–7.53(m, 13H), 7.3–7.28(m,
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Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
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4H). IR(ATR): n [cm1]: 3051, 281, 2828, 1814, 162, 158, 1502, 143, 135, 1270, 111, 1117, 1022, 65, 35, 06, 823, 72, 756, 68. APCI-MS (m/ z): 581 [M+]. 9-(naphthalen-2-yl)-10-(4-(phenylsulfonyl)phenyl)anthracene (3): (yield = 78%). 1H NMR (300 MHz, CDCl3): d [ppm]: 8.21(d, J = 8.7 Hz, 2H), 8.15(dd, J = 1.5, 8.1 Hz, 2H), 8.08(d, J = 8.4 Hz, 1H), 8.04–8.00(m, 1H), 7.5(s, 1H), 7.2–7.8(m, 1H), 7.73–7.70(m, 2H), 7.67–7.65(m, 3H), 7.62–7.58(m, 4H), 7.56–7.51(m, 3H), 7.36–7.27 (m, 4H). IR(ATR): n [cm1]: 3053, 280, 2831, 1813, 162, 155, 1501, 1443, 137, 1311, 1180, 1154, 1105, 1072, 1021, 68, 36, 88, 844, 81, 76, 768, 744, 715, 687, 664. APCI-MS (m/z): 521 [M+]. 2.2. Device fabrication and characterization
Scheme 1. Structures of blue fluorescent materials 1–3.
All organic materials and metals were deposited under high vacuum (5 106 Torr) using HS-1000 of DOV corp. The OLEDs were fabricated in the following sequence: ITO (180 nm)/4,40 -bis (N-(1-naphthyl)-N-phenyl amino)biphenyl (NPB, HTL) (50 nm)/ blue materials 1–3 (30 nm)/2,20 ,200 -(1,3,5-benzinetriyl)-tris(1-
Fig. 1. (a) UV–vis absorption spectra, PL spectra in dichloromethane and (b) solid-state of blue emitters 1–3.
Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
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Table 1 Photophysical data for the compounds (1 and 3). Material
UV (nm)a
PL, FWHM (nm)a
Solid PL (nm)
Ffb
HOMO (eV)c
LUMO (eV)c
Eg (eV)d
1 2 3
377 376 376
493, 93 425, 55 436, 59
440 436 444
0.32 0.65 0.58
5.88 5.81 5.85
2.86 2.70 2.75
3.02 3.11 3.10
a b c d
Maximum absorption and emission wavelength, measured in CH2Cl2 solution. Kf0 s were determined in a CH2Cl2 solution at 298 K against DPA as a reference (F = 0.90). HOMO energy level was determined by low-energy photoelectron spectrometer (Riken-Keiki, AC-2) and LUMO = HOMO + DE. DE is the band-gap energy estimated from the intersection of the absorption and photoluminescence spectra.
Table 2 EL performance characteristic of the devices (1 and 3). Device
Von (V)a
EL, FWHM (nm)b
L (cd/m2)c
LE (cd/A)d/e
PE (lm/W)d/e
EQE (%)e
CIE (x,y)f
1 2 3
4.2 3.6 3.9
468, 70 458, 77 463, 75
999 556 524
0.57/0.36 0.53/0.25 0.38/0.26
0.94/0.90 0.66/0.66 0.70/0.69
0.55 0.52 0.45
(0.16, 0.20) (0.15, 0.14) (0.16, 0.17)
a b c d e f
Turn-on voltage at 1 cd/m2. Emission maximum and FWHM of EL emission spectra. Maximum values at 10.0 V. Maximum values. At 20 mA/cm2. Commission Internationale d’Énclairage (CIE) coordinates at 10.0 V.
pheny-1-H-benzimidazole) (TPBi, ETL) (15 nm)/lithium quinolate (Liq) (2.0 nm)/Al (100 nm). The current density (J), luminance (L), luminous efficiency (LE), and CIE chromaticity coordinates of the OLEDs were measured with a Keithley 2400, Chroma meter CS1000A. Electroluminance was measured using a Roper Scientific Pro 300i. 3. Results and discussion The UV–vis absorption and photoluminescence (PL) spectra of emitting materials 1–3 in dichloromethane are shown in Fig. 1, and these results are summarized in Table 1. The UV–vis absorption peaks for the blue materials were observed between 358 and 398 nm. The UV–vis absorption spectra of 1–3 show the characteristic vibrational pattern of an isolated anthracene group [9]. In the PL spectra, material 1 showed the longer emission peaks than materials 2 and 3, due to the extended-conjugation through benzophenone moiety. Fig. 1(b) shows PL spectra of compounds 1– 3 in solid state, the maximum emission wavelengths 1–3 showed at 440, 436 and 444 nm, respectively. Compared to solution PL, solid state PL of materials 2 and 3 showed that the red-shifts may be caused by the excimer formation resulting from the overlap of the anthracene units of adjacent molecules. However, the PL spectrum of material 1 in solid film exhibited the blue-shift by 53 nm, in comparison with that in dichloromethane solution. This phenomenon can be explained by the solvent stabilization of the excited state and dipolar interactions between the polar compounds and the polar solvents. Also this observation implies that benzophenone moiety of material 1 prevents the excimerformation. The HOMO/LUMO energy levels of 1–3 were 5.88/2.86, 5.81/2.70 and 5.85/2.75 eV, respectively. Interestingly, all compounds have lower LUMO level than a common blue material, AND (2.50 eV). From the results, it is suggested that the introduction of different electro-withdrawing oxide moieties at the side of anthracene would reduce the LUMO of materials 1–3, which will be beneficial for the injection of electrons [10]. The electroluminescent properties of materials 1–3 are summarized in Table 2. Fig. 2 presents the EL spectra of OLED
devices using materials 1–3. The maximum emission wavelengths of devices 1–3 appeared at 468, 458 and 463 nm, respectively. The CIE x,y coordinates of devices 1–3 were (0.16, 0.20), (0.15, 0.14) and (0.16, 0.17) at 10.0 V, respectively. Notably, the device using material 2 showed the deepest blue emission due to the wide band gap. These observations are well compatible with the trend of PL of materials 1–3 in solution states. Fig. 3 shows the luminance–voltage–current density (L–V–J), luminous efficiencies, power efficiencies and external quantum efficiencies of devices 1–3, respectively. All devices showed the efficient blue emissions and low turn-on voltage no greater than 4.2 V. In particular, device 1 exhibited the highly efficient EL performances; its luminous efficiency (LE), power efficiency (PE), and an external quantum efficiency (EQE) reach 0.36 cd/A, 0.90 lm/ W and 0.55% at 20 mA/cm2, respectively. All devices seem to have similar hole-injection barrier, because HOMO energy levels of materials 1–3 were similar to each other. However, the electron-injection into the emitting-layer of device 1, using material 1, was more effective than the other devices 2 and 3, using material 2 and 3, because of the smaller energy barrier
Fig. 2. EL spectra of blue emitting devices 1–3.
Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
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Fig. 3. (a) Luminance–voltage–current density (L–V–J). (b) Luminous, (c) power and (d) external quantum efficiencies of the devices 1–3 as a function of current density.
between TPBi (2.90 eV) and material 1 (2.86 eV) than material 2 (2.70 eV) and 3 (2.75 eV). This effective electron-injection property of device 1 would lead the improved EL efficiencies.
(H0301-13-1004)supervised by the NIPA (National IT Industry Promotion Agency). References
4. Conclusion We have described three novel blue-emitting materials (1–3) based on naphthylanthracene core with electron-withdrawing oxide moieties. All devices showed the efficient blue EL properties. In particular, (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl) (phenyl) methanone (1) exhibits a highly efficient blue EL emission due to the effective electron-injection property. According to these characteristics, these materials have sufficient potential for OLED applications. Acknowledgment This research was supported by the MSIP (Ministry of Science, ICT & Future Planning), Korea, under the ITRC (Information Technology Research Center) support program NIPA-2013-
[1] C.W. Tang, S.A. Vanslyke, C.H. Chen, Journal of Applied Physics 65 (1989) 3610. [2] K.H. Lee, S.O. Kim, J.N. You, S. Kang, J.Y. Lee, K.S. Yook, S.O. Jeon, J.Y. Lee, S.S. Yoon, Journal of Materials Chemistry 22 (2012) 5145. [3] K.H. Lee, J.K. Park, J.H. Seo, S.W. Park, Y.S. Kim, Y.K. Kim, S.S. Yoon, Journal of Materials Chemistry 21 (2011) 13640. [4] J.K. Park, K.H. Lee, J.S. Park, J.H. Seo, Y.K. Kim, S.S. Yoon, Journal of Nanoscience and Nanotechnology 11 (2011) 4357. [5] J.H. Seo, S.J. Lee, G.W. Hyung, K.H. Lee, J.K. Park, S.S. Yoon, Y.K. Kim, Journal of Nanoscience and Nanotechnology 11 (2011) 5812. [6] K.H. Lee, L.K. Kang, J.Y. Lee, S. Kang, S.O. Jeon, K.S. Yook, J.Y. Lee, S.S. Yoon, Advanced Functional Materials 20 (2010) 1345. [7] Y.J. Su, H.L. Huang, C.L. Li, C.H. Chen, Y. Tao, P.T. Chou, S. Datta, R.S. Liu, Advanced Materials 15 (2003) 884. [8] C.L. Ho, W.Y. Wong, Q. Wang, D. Ma, L. Wang, Z. Lin, Advanced Functional Materials 18 (2008) 928. [9] J. Salbeck, F. Weissortel, N. Yu, J. Baner, H. Bestgen, Synthetic Metals 91 (1997) 209. [10] C.-T. Liao, H.-F. Chen, H.-C. Su, K.-T. Wong, Physical Chemistry Chemical Physics 14 (2012) 9774.
Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
Materials Research Bulletin xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu
Synthesis and electroluminescent properties of anthracene derivatives containing electron-withdrawing oxide moieties Jhin-yeong Yoon a , Eun Jae Na a , Soo Na Park a , Seok Jae Lee b , Young Kwan Kim b, *, Seung Soo Yoon a, * a b
Department of Chemistry, Sungkyunkwan University, Suwon, 440-746, Republic of Korea Department of Information Display, Hongik University, Seoul, 121-791, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Article history: Received 5 August 2013 Received in revised form 18 March 2014 Accepted 20 March 2014 Available online xxx
A series of new blue-emitting materials: (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)(phenyl) methanone (1); 9-(naphthalen-2-yl)-10-(4-((diphenyl)phosphine oxide)phenyl)anthracene (2); 9(naphthalen-2-yl)-10-(4-(phenylsulfonyl)phenyl)anthracene (3) were designed and synthesized via Suzuki cross-coupling reaction. Multilayer OLEDs were fabricated in the following sequence: ITO (180 nm)/NPB (50 nm)/blue materials 1–3 (30 nm)/TPBi (15 nm)/Liq (2 nm)/Al (100 nm). All devices showed the efficient blue EL emissions. In particular, the device using 1 as an emitter exhibited efficient blue electroluminescent properties with a maximum luminous, power, external quantum efficiency and CIE coordinates of 0.36 cd/A, 0.90 lm/W, 0.55% at 20 mA/cm2 and (x = 0.16, y = 0.20) at 10.0 V, respectively. ã 2014 Elsevier Ltd. All rights reserved.
Keywords: A. Organic compounds A. Oxides B. Chemical synthesis D. Luminescence
1. Introduction
2. Experimental details
Organic light-emitting devices (OLEDs) have been widely studied in the past two decades for use in flat panel displays and more-efficient lighting products [1]. For the practical applications, three primary color emitters that have high emission efficiency and high color purity are required. However, because of the wide band-gap of blue emitters, blue OLEDs show relatively poorer performance than red and green OLEDs. For this reason, the progress in highly efficient blue-light emitters with good color purity is a great challenge. Up to now, various blue emitters have been developed by many research groups [2–6]. However, the EL performances of blue emitters still need to be improved. In this work, a series of new blue fluorescent material based on 9-naphthylanthracene core unit containing various electronwithdrawing oxide moieties were synthesized and their electroluminescent properties were investigated. The electron-withdrawing oxide moieties in the emitting materials were introduced to tune the HOMO or LUMO energy levels of the emitting materials, and to enhance the EL performances [7–8].
2.1. Material preparation and characterization
* Corresponding authors. Tel.:+ 82 31 290 7071, 2 3142 3750; fax: +82 31 290 7075, 2 3141 8928. E-mail addresses: [email protected] (Y.K. Kim), [email protected] (S.S. Yoon).
The molecular structure and synthetic route of 1–3 compounds are outlined in Scheme 1. General procedure for the Suzuki crosscoupling reaction: the corresponding hetero aryl bromide (1.0 mol), 10-(naphthalen-2-yl)anthracene-9-ylboronic acid (1.2 mol) and Pd(PPh3)4 (0.04 mol) were mixed in a solution of aqueous 2.0 M Na2CO3 (10.0 mol), ethanol and toluene. The mixture was refluxed at 90 C for 2 h. After the reaction had finished, the reaction mixture was extracted with toluene and washed with water. The organic layer was dried with anhydrous MgSO4 and filtered with charcoal. The solution was then evaporated. The crude product was purified by column chromatography with silica gel and subsequent recrystallization from THF/ MeOH and then hot hexane filter. (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl) (phenyl) methanone (1): (yield = 83%). 1H NMR (300 MHz, CDCl3): d [ppm]: 8.10–8.07 (m, 3H), 8.04–7.97(m, 4H), 7.93–7.90(m, 1H), 7.75(t, J = 7.8 Hz, 4H), 7.66–7.63(m, 3H), 7.61(t, J = 1.8 Hz, 1H), 7.59–7.56(m, 4H), 7.40–7.29 (m, 4H). IR(ATR): n [cm1]: 3055, 2954, 2892, 2831,1810,1695,1658, 1601, 1508, 1442, 1395, 1310, 1279, 1176, 1144, 1016, 1023, 960, 931, 905, 847, 822, 796, 762, 699. APCI-MS (m/z): 485 [M+]. 9-(naphthalen-2-yl)-10-(4-((diphenyl)phosphine oxide)phenyl)anthracene (2): (yield = 81%). 1H NMR (300 MHz, CDCl3): d [ppm]: 8.0(d, J = 8.4 Hz, 1H), 8.04–8.01(m, 1H), 7.7(s, 1H), 7.4–7.82 (m, 7H), 7.74(dd, J = 1.2, 7.5 Hz, 2H), 7.66–7.53(m, 13H), 7.3–7.28(m,
http://dx.doi.org/10.1016/j.materresbull.2014.03.019 0025-5408/ ã 2014 Elsevier Ltd. All rights reserved.
Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
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4H). IR(ATR): n [cm1]: 3051, 281, 2828, 1814, 162, 158, 1502, 143, 135, 1270, 111, 1117, 1022, 65, 35, 06, 823, 72, 756, 68. APCI-MS (m/ z): 581 [M+]. 9-(naphthalen-2-yl)-10-(4-(phenylsulfonyl)phenyl)anthracene (3): (yield = 78%). 1H NMR (300 MHz, CDCl3): d [ppm]: 8.21(d, J = 8.7 Hz, 2H), 8.15(dd, J = 1.5, 8.1 Hz, 2H), 8.08(d, J = 8.4 Hz, 1H), 8.04–8.00(m, 1H), 7.5(s, 1H), 7.2–7.8(m, 1H), 7.73–7.70(m, 2H), 7.67–7.65(m, 3H), 7.62–7.58(m, 4H), 7.56–7.51(m, 3H), 7.36–7.27 (m, 4H). IR(ATR): n [cm1]: 3053, 280, 2831, 1813, 162, 155, 1501, 1443, 137, 1311, 1180, 1154, 1105, 1072, 1021, 68, 36, 88, 844, 81, 76, 768, 744, 715, 687, 664. APCI-MS (m/z): 521 [M+]. 2.2. Device fabrication and characterization
Scheme 1. Structures of blue fluorescent materials 1–3.
All organic materials and metals were deposited under high vacuum (5 106 Torr) using HS-1000 of DOV corp. The OLEDs were fabricated in the following sequence: ITO (180 nm)/4,40 -bis (N-(1-naphthyl)-N-phenyl amino)biphenyl (NPB, HTL) (50 nm)/ blue materials 1–3 (30 nm)/2,20 ,200 -(1,3,5-benzinetriyl)-tris(1-
Fig. 1. (a) UV–vis absorption spectra, PL spectra in dichloromethane and (b) solid-state of blue emitters 1–3.
Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
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Table 1 Photophysical data for the compounds (1 and 3). Material
UV (nm)a
PL, FWHM (nm)a
Solid PL (nm)
Ffb
HOMO (eV)c
LUMO (eV)c
Eg (eV)d
1 2 3
377 376 376
493, 93 425, 55 436, 59
440 436 444
0.32 0.65 0.58
5.88 5.81 5.85
2.86 2.70 2.75
3.02 3.11 3.10
a b c d
Maximum absorption and emission wavelength, measured in CH2Cl2 solution. Kf0 s were determined in a CH2Cl2 solution at 298 K against DPA as a reference (F = 0.90). HOMO energy level was determined by low-energy photoelectron spectrometer (Riken-Keiki, AC-2) and LUMO = HOMO + DE. DE is the band-gap energy estimated from the intersection of the absorption and photoluminescence spectra.
Table 2 EL performance characteristic of the devices (1 and 3). Device
Von (V)a
EL, FWHM (nm)b
L (cd/m2)c
LE (cd/A)d/e
PE (lm/W)d/e
EQE (%)e
CIE (x,y)f
1 2 3
4.2 3.6 3.9
468, 70 458, 77 463, 75
999 556 524
0.57/0.36 0.53/0.25 0.38/0.26
0.94/0.90 0.66/0.66 0.70/0.69
0.55 0.52 0.45
(0.16, 0.20) (0.15, 0.14) (0.16, 0.17)
a b c d e f
Turn-on voltage at 1 cd/m2. Emission maximum and FWHM of EL emission spectra. Maximum values at 10.0 V. Maximum values. At 20 mA/cm2. Commission Internationale d’Énclairage (CIE) coordinates at 10.0 V.
pheny-1-H-benzimidazole) (TPBi, ETL) (15 nm)/lithium quinolate (Liq) (2.0 nm)/Al (100 nm). The current density (J), luminance (L), luminous efficiency (LE), and CIE chromaticity coordinates of the OLEDs were measured with a Keithley 2400, Chroma meter CS1000A. Electroluminance was measured using a Roper Scientific Pro 300i. 3. Results and discussion The UV–vis absorption and photoluminescence (PL) spectra of emitting materials 1–3 in dichloromethane are shown in Fig. 1, and these results are summarized in Table 1. The UV–vis absorption peaks for the blue materials were observed between 358 and 398 nm. The UV–vis absorption spectra of 1–3 show the characteristic vibrational pattern of an isolated anthracene group [9]. In the PL spectra, material 1 showed the longer emission peaks than materials 2 and 3, due to the extended-conjugation through benzophenone moiety. Fig. 1(b) shows PL spectra of compounds 1– 3 in solid state, the maximum emission wavelengths 1–3 showed at 440, 436 and 444 nm, respectively. Compared to solution PL, solid state PL of materials 2 and 3 showed that the red-shifts may be caused by the excimer formation resulting from the overlap of the anthracene units of adjacent molecules. However, the PL spectrum of material 1 in solid film exhibited the blue-shift by 53 nm, in comparison with that in dichloromethane solution. This phenomenon can be explained by the solvent stabilization of the excited state and dipolar interactions between the polar compounds and the polar solvents. Also this observation implies that benzophenone moiety of material 1 prevents the excimerformation. The HOMO/LUMO energy levels of 1–3 were 5.88/2.86, 5.81/2.70 and 5.85/2.75 eV, respectively. Interestingly, all compounds have lower LUMO level than a common blue material, AND (2.50 eV). From the results, it is suggested that the introduction of different electro-withdrawing oxide moieties at the side of anthracene would reduce the LUMO of materials 1–3, which will be beneficial for the injection of electrons [10]. The electroluminescent properties of materials 1–3 are summarized in Table 2. Fig. 2 presents the EL spectra of OLED
devices using materials 1–3. The maximum emission wavelengths of devices 1–3 appeared at 468, 458 and 463 nm, respectively. The CIE x,y coordinates of devices 1–3 were (0.16, 0.20), (0.15, 0.14) and (0.16, 0.17) at 10.0 V, respectively. Notably, the device using material 2 showed the deepest blue emission due to the wide band gap. These observations are well compatible with the trend of PL of materials 1–3 in solution states. Fig. 3 shows the luminance–voltage–current density (L–V–J), luminous efficiencies, power efficiencies and external quantum efficiencies of devices 1–3, respectively. All devices showed the efficient blue emissions and low turn-on voltage no greater than 4.2 V. In particular, device 1 exhibited the highly efficient EL performances; its luminous efficiency (LE), power efficiency (PE), and an external quantum efficiency (EQE) reach 0.36 cd/A, 0.90 lm/ W and 0.55% at 20 mA/cm2, respectively. All devices seem to have similar hole-injection barrier, because HOMO energy levels of materials 1–3 were similar to each other. However, the electron-injection into the emitting-layer of device 1, using material 1, was more effective than the other devices 2 and 3, using material 2 and 3, because of the smaller energy barrier
Fig. 2. EL spectra of blue emitting devices 1–3.
Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019
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Fig. 3. (a) Luminance–voltage–current density (L–V–J). (b) Luminous, (c) power and (d) external quantum efficiencies of the devices 1–3 as a function of current density.
between TPBi (2.90 eV) and material 1 (2.86 eV) than material 2 (2.70 eV) and 3 (2.75 eV). This effective electron-injection property of device 1 would lead the improved EL efficiencies.
(H0301-13-1004)supervised by the NIPA (National IT Industry Promotion Agency). References
4. Conclusion We have described three novel blue-emitting materials (1–3) based on naphthylanthracene core with electron-withdrawing oxide moieties. All devices showed the efficient blue EL properties. In particular, (4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl) (phenyl) methanone (1) exhibits a highly efficient blue EL emission due to the effective electron-injection property. According to these characteristics, these materials have sufficient potential for OLED applications. Acknowledgment This research was supported by the MSIP (Ministry of Science, ICT & Future Planning), Korea, under the ITRC (Information Technology Research Center) support program NIPA-2013-
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Please cite this article in press as: J.- Yoon, et al., Synthesis and electroluminescent properties of anthracene derivatives containing electronwithdrawing oxide moieties, Mater. Res. Bull. (2014), http://dx.doi.org/10.1016/j.materresbull.2014.03.019