Dumbbell-Shaped Spirocyclic Aromatic Hydrocarbon to Control

pubs.acs.org/JPCL

Dumbbell-Shaped Spirocyclic Aromatic Hydrocarbon to Control Intermolecular π-π Stacking Interaction for High-Performance Nondoped Deep-Blue Organic Light-Emitting Devices Ju-Fen Gu,† Guo-Hua Xie,‡ Long Zhang,† Shu-Fen Chen,† Zong-Qiong Lin,† Zhen-Song Zhang,‡ Jian-Feng Zhao,† Ling-Hai Xie,*,† Chao Tang,† Yi Zhao,*,‡ Shi-Yong Liu,‡ and Wei Huang*,† †

Key Laboratory for Organic Electronics & Information Displays (KLOEID) and Institute of Advanced Materials (IAM), Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210046, China, and ‡ State Key Laboratory on Integrated Optoelectronics, College of Electronics Science and Engineering, Jilin University, 2699 Qianjin Street, Changchun 130012, China

ABSTRACT Dumbbell-shaped spirocyclic aromatic hydrocarbons on the basis of molecular modeling exhibit no π-π stacking interaction among chromophores in the molecular packing diagrams. A model compound of 1,6-di(spiro[fluorene-9,90 xanthene]-2-yl)pyrene (DSFXPy) with the pyrene-pyrene distance of up to 10.4 Å has been synthesized for high-performance nondoped deep-blue organic lightemitting devices. The proof-of-concept nondoped OLEDs have been fabricated with the configuration of ITO/MoOx(2 nm)/NPB(30 nm)/DSFXPy(30 nm)/TPBi(40 nm)/ LiF(1 nm)/Al. DSFXPy-based nondoped OLED exhibits a maximum current efficiency of 7.4 cd/A (4.6% at 260 cd m-2) and excellent CIE coordinates (0.16, 0.15) (at 6500 cd m-2), surpassing most reported nondoped deep-blue OLEDs. Dumbbellshaped spirocyclic arenes will be promising candidates for OLEDs. SECTION Electron Transport, Optical and Electronic Devices, Hard Matter

large π-electron delocalization, more favorable for the improvement of quantum efficiency.28,29 Lee et al. reported fluorene-pyrene emitters exhibiting a CE of 6.0 cd A-1 in a nondoped OLED with CIE coordinate of (0.15, 0.19).30 Another pyrene-anthrancene hybrid exhibited a CE of 7.9 cd A-1 with sky-blue (0.15, 0.30).22 Our group also reported pyrene-based blue materials with a diarylfluorene core.31 Although several strategies have been proposed to design nondoped PAH-based blue electroluminescent materials, there are rare candidates with both high CE and excellent CIE coordinates. To improve the color purity of pyrene-based materials, it is necessary to incorporate either large bulky groups32 or multisubstituted rigid moieties33-35 to suppress the aggregates and/or excimers. One reason for the above dilemma is that excessive nonplanar steric hindrance could damage π-electron overlaps and shorten the conjugation length, hindering charge carrier transport and excitons generation, decreasing device efficiencies. Distinguished cruciform spiro-frameworks19,16-40 with spiroconjuction effect offer a compromised platform to resolve the knotty issue owing to their supramolecular steric hindrance (SSH)41 and

S

ince the invention of multilayered organic light-emitting devices (OLEDs) by Tang and VanSlyke,1 organic electroluminescent materials have attracted many industrial and academic interests owing to their potential applications of next-generation flat panel displays and solidstate lighting sources. High-performance blue OLEDs are one of the crucial elements to achieve high quality full-color displays or high color rendering index (CRI) white light.2-6 Up-todate, dramatic improvements of doped blue electrophosphorescent7-12 and electrofluorescent13-18 devices have been achieved by material design, device structural arrangement, and interface engineering. However, the complicated coevaporation techniques require much more precise process control, which may increase the mass production cost. Moreover, troublesome phase separation in doped host-guest systems results in relatively short lifetimes, although some progress continues to be made. Nevertheless, an alternative solution is to develop the more robust nondoped OLEDs.19-21 One kind of promising nondoped blue electroluminescent materials is polycyclic aromatic hydrocarbons (PAHs).22-31 Anthracene-based materials showed excellent deep-blue Commission Internationale de l'Eclairage (CIE) chromaticity coordinates near NTSC standards (0.14, 0.08).24-26 Shu et al. reported anthracene-based electroluminescent materials with a current efficiency (CE) of >5.6 cd/A.27 Pyrene-based materials exhibit high carrier transporting ability owing to

r 2010 American Chemical Society

Received Date: July 28, 2010 Accepted Date: September 10, 2010 Published on Web Date: September 13, 2010

2849

DOI: 10.1021/jz101039d |J. Phys. Chem. Lett. 2010, 1, 2849–2853

pubs.acs.org/JPCL

Scheme 1. Synthetic Procedures for the DSFXPya

a Reaction conditions: (a) phenol, MeSO3H, 150, 48 h. (b) n-BuLi, B(OCH3)3, -78°C; 1,3-propandiol, toluene, reflux. (c) 1,6-dibromopyrene, Pd(PPh3)4, K2CO3, toluene, reflux, 63%.

less reorganization energy.42 In this contribution, we subtly incorporated one-pot synthesized spirofluorenexanthenes (SFXs) into PAHs to create spirocyclic aromatic hydrocarbons (SAHs) with dumbbell-shaped conformation. 1,6-Di(spiro[fluorene-9,90 -xanthene]-2-yl)pyrene (DSFXPy) as a SAHtype model showed both high efficiency with CE of 7.4 cd A-1 and deep-blue emission with CIE coordinate (0.16, 0.15) in nondoped fluorescent OLEDs. Furthermore, DSFXPy is the first example of high-performance SFX-based electroluminescent materials. In our design, the deep-blue electroluminescent DSFXPy synthesized in this work has a 1,6-pyrene core structure endcapped with two bulky SFXs. Dumbbell-shaped conformation of DSFXPy is more favorable for blue-shift deep-blue emission owing to its larger distance of intermolecular pyrenes with respect to monosubstituted systems, avoiding π-π stacking aggregates. Orthogonal SFXs with π-π SSH also facilitate carrier transportation and exciton recombination with respect to other bulky moieties. In addition, laborious spirobifluorenes starting from expensive o-halobiaryls have been replaced with SFXs owing to the latter's convenient one-pot domino route suitable for mass production.43 Synthesis of DSFXPy was outlined in Scheme 1. 2-Bromospiro[fluorene-9,90 -xanthene] was synthesized via tandem protocol of 2-bromofluorenone with overdose phenol under methylsulfonic acid at 150 °C according to our previous work.43 The target DSFXPy was obtained through Suzuki crosscoupling reaction of SFX boronic acid ester with 1,6-dibromopyrene using Pd(PPh3)4 as catalysis with a yield of 63%. The product was confirmed by 1H NMR spectroscopy, mass spectroscopy (MS), and element analysis. DSFXPy shows high decomposition temperature (470 °C) and no obvious glass-transition temperatures (Tg). Photoluminescence (PL) emission peak of DSFXPy was observed at 429 nm in chloroform solution and 444 nm in thin film with a red shift of only 15 nm (Figure 1). The results indicate that 1,6-pyrene endcapped with SFXs effectively suppressed molecular aggregates. Its fluorescence quantum efficiency in solution is ca. 90% with respect to 9,10-diphenylanthranene as the standard reference (Φf = 0.9). Cyclic voltametry (CV) was measured to estimate its HOMO (-5.91 eV), LUMO (-2.36 eV), and bandgap (3.55 eV) from the oxidation potential (1.12 V) and reduce potential (-2.43 V), respectively. To investigate the potential nondoped device applications of DSFXPy, we have fabricated a series of Devices A-C with multilayer configurations (Figure 2). Device A has a configuration of ITO/MoOx(2 nm)/NPB(30 nm)/DSFXPy(30 nm)/ TPBi(40 nm)/LiF(1 nm)/Al. m-MTDATA layer was added in


Figure 1. UV-vis and PL spectra of DSFXPy in dilute chloroform and solid thin film.

Devices B and C. All devices have the same total thickness of organic films (100 nm). In Devices A-C, DSFXPy served as the blue light emitter, a thin-layer MoOx (2 nm) and LiF (1 nm) acted as anode and cathode buffer layers, and m-MTDATA and NPB acted as the hole-injecting and transporting layers, respectively. TPBi was used to serve as the electron-transporting layer and hole/exciton blocking layer. m-MTDATA represents 4,40 ,400 -tris(3-methylphenylphenylamino)-triphenylamine, NPB represents N,N0 -diphenyl-N,N0 -bis(1,10 -biphenyl)-4,40 diamine, and TPBi represents 1,3,5-tris-(N-phenylbenzimidazole-2-yl)-benzene). The EL performances of Devices A-C are summarized in Table 1. Figure 3 compares the luminance (L)-voltage (V)-current density (J) characteristics, CEluminance-power efficiency (PE) characteristics, normalized EL spectra, and external quantum efficiencies of Devices A-C, respectively. Device A exhibits a turn-on voltage of 3.46 V (defined as the onset voltage of the log (J)-V curve, not shown here), and the maximum CE is up to 5.5 cd 3 A-1. The high performances probably contribute to its high PL efficiency and excellent evaporated thin film morphology. Device A shows nearly identical CIE coordinates of (0.17, 0.17 ( 0.01) without color shift over a wide luminance range of 200-5000 cd m-2 (See Figure S-7 of the Supporting Information.) The brightnessindependent EL feature is of great importance for the commercial full-color displays and lighting products. To optimize efficiency further, we inserted m-MTDATA between MoOx and NPB, maintaining the thickness of DSFXPy layer up to 30 nm (Device B) featuring a maximum CE of 7.4 cd/A (at ∼260 cd m-2), PE of 4.1 lm/W (at ∼200 cd m-2), and high external quantum efficiency (EQE) of 4.6% (at ∼260 cd m-2). However, a relatively higher turn-on voltage of 4.06 V with lower current density with respect to that of Device A was observed.

2850


pubs.acs.org/JPCL

Figure 2. Structure diagram of devices A-C and chemical structures of the used materials. Table 1. Comparison of the Performances of Devices A-C EQE (%)c

current efficiency (cd A-1)

power efficiency (lm W-1)

device

Von (V)a

emission peaks / fwhm (nm)b

maximum brightness (cd m-2)

CIEx,y coordinateb

max

5000 (cd cm-2)

max

5000 (cd cm-2)

max

5000 (cd cm-2)

A

3.46

452/75

22500

(0.17, 0.18)

3.7

2.8

5.5

4.1

3.6

1.6

B

4.06

456/75

25100

(0.17, 0.18)

4.6

3.3

7.4

5.2

4.1

1.9

C

3.05

448/73

21600

(0.16, 0.16)

3.6

2.4

5.6

3.6

4.6

1.5

a

Defined as the onset voltage of the log( J)-V curve. b At the brightness of 5000 cd m-2. c EQE: external quantum efficiency.

emitting layer. Therefore, it is necessary to be a thicker emitting layer to increase the exciton generation and recombination rates, and this could also reduce the exciton quenching due to the carriers accumulation at the interfaces. The CIE coordinates of Device C based on DSFXPy is (0.16, 0.16) at the brightness of 5000 cd/m2 with an fwhm of 73 nm. Adeep-blue emission with peak of 448 nm at a high brightness of ∼7000 cd/m2 saturates at the CIE coordinates of (0.16, 0.15) in Device C. This is probably attributed to the main recombination zone shifting from DSFXPy/TPBi interface to NPB/DSFXPy interface. It is worth noting that devices with only m-MTDATA as hole-transporting materials or 4,7-diphenyl-1,10-phenanthroline (Bphen) as electron-transporting layer showed poor performances due to the exciplex formation (not shown here). In summary, a dumbbell-shaped SAH has been synthesized via a concise domino procedure, followed by Suzuki reaction to develop high-performance nondoped blue OLEDs. Voltage-independent deep-blue CIE coordinates (0.17, 0.17 ( 0.01) with a maximum CE of 5.5 cd/A has been achieved in a

The decreased current density is probably attributed to a relatively lower hole mobility of m-MTDATA than that of NPB.44 In some extent, the more balanced carriers in the emitting layer results in the increased efficiencies of Device B (Figure 3b). The CE of Device B turns out to be 5.1 cd/A with the peak emission of 456 nm corresponding to CIE coordinates of (0.17, 0.18) and the full width at half-maximum (fwhm) of 75 nm at the brightness of 5000 cd m-2 (at 8.5 V), which is among the best values ever reported for nondoped deep-blue OLEDs. Device C exhibits a lower turn-on voltage of 3.05 V, with the maximum CE up to 5.6 cd 3 A-1 (at 4.5 V and ∼200 cd m-2). Derived from the J-V characteristics of Device B and C (Figure 3a), DSFXPy exhibits lower hole mobility compared with m-MTDATA. Therefore, Device C exhibits improved power efficiency below 100 cd m-2, attributed to the lower driving voltage. However, the efficiency drops more quickly as the luminance increases because of the narrow emission zone of 10 nm. As compared with Device B, the CE of Device C gradually reduces to 3.6 cd/A at 5000 cd/m2, which indicates a severe imbalance of the carriers in the


2851


pubs.acs.org/JPCL

NNSFC (grants 20704023, 60876010, 60706017, 60977024, 20774043, and 60907047), the Key Project of Chinese Ministry of Education (nos. 104246, 208050, and 707032), and Natural Science Foundation of Jiangsu Province (grants BK2009423, BK2008053, 08KJB510013, BK2008053, SJ209003, and TJ209035).

REFERENCES (1) (2)

(3)

(4)

(5)

(6)

(7)

(8) Figure 3. (a) L-V-J characteristics of Devices A-C. (b) Current efficiency-luminance-power efficiency characteristics of Devices A-C. (c) Normalized EL spectra of Devices A-C. Inset: External quantum efficiency of Devices A-C.

(9)

simplified three-layer structure. By tailoring the holes flow, DSFXPy-based nondoped OLEDs exhibit a maximum CE of 7.4 cd/A (4.6% at 260 cd m-2) and excellent CIE coordinates (0.16, 0.15) (at 6500 cd m-2), surpassing most reported nondoped deep-blue OLEDs. SFXs will be a promising alternative to spirobifluorenes for high-performance organic semiconductors.

(10)

SUPPORTING INFORMATION AVAILABLE Experimental

(11)

details, synthetic procedures, devices structures, EL spectra, and optimized packing diagrams are provided in the Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

(12)

AUTHOR INFORMATION Corresponding Author:

(13)

*To whom correspondence should be addressed. Fax: þ86 25 8586 6999. Tel: þ86 25 8586 6008. E-mail: [email protected] (L.-H.X.); [email protected] (Y.Z.); [email protected] (W.H.).

(14)

ACKNOWLEDGMENT For the financial support for this work, we thank the “973” project (2009CB930600 and 2010CB327701),


2852

Tang, C.; VanSlyke, S. Organic Electroluminescent Diodes. Appl. Phys. Lett. 1987, 51, 913–915. Reineke, S.; Lindner, F.; Schwartz, G.; Seidler, N.; Walzer, K.; Lussem, B.; Leo, K. White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency. Nature 2009, 459, 234– 239. Sun, Y. R.; Giebink, N. C.; Kanno, H.; Ma, B. W.; Thompson, M. E.; Forrest, S. R. Management of Singlet and Triplet Excitons for Efficient White Organic Light-Emitting Devices. Nature 2006, 440, 908–912. Schwartz, G.; Pfeiffer, M.; Reineke, S.; Walzer, K.; Leo, K. Harvesting Triplet Excitons from Fluorescent Blue Emitters in White Organic Light-Emitting Diodes. Adv. Mater. 2007, 19, 3672–3676. Schwartz, G.; Fehse, K.; Pfeiffer, M.; Walzer, K.; Leo, K. Highly Efficient White Organic Light Emitting Diodes Comprising an Interlayer to Separate Fluorescent and Phosphorescent Regions. Appl. Phys. Lett. 2006, 89, 083509. Color Rendering Index (CRI) of State-of-the-Art Broadband Emitters. http://www.hitech-projects.com/euprojects/olla/external%20deliverables/PUBLIC%20OLLA_DEL3.1_Rep_CRI_ Broadband_v3.1.pdf. Holmes, R. J.; D'Andrade, B. W.; Forrest, S. R.; Ren, X.; Li, J.; Thompson, M. E. Efficient, Deep-Blue Organic Electrophosphorescence by Guest Charge Trapping. Appl. Phys. Lett. 2003, 83, 3818–3820. Xiao, L. X.; Su, S. J.; Agata, Y.; Lan, H. L.; Kido, J. Nearly 100% Internal Quantum Efficiency in an Organic Blue-Light Electrophosphorescent Device Using a Weak Electron Transporting Material with a Wide Energy Gap. Adv. Mater. 2009, 21, 1271– 1274. Eom, S.; Zheng, Y.; Wrzesniewski, E.; Lee, J.; Chopra, N.; So, F.; Xue, J. Effect of Electron Injection and Transport Materials on Efficiency of Deep-Blue Phosphorescent Organic LightEmitting Devices. Org. Electron. 2009, 10, 686–691. Jeon, S.; Yook, K.; Joo, C.; Lee, J. High-Efficiency Deep-BluePhosphorescent Organic Light-Emitting Diodes Using a Phosphine Oxide and a Phosphine Sulfide High-Triplet-Energy Host Material with Bipolar Charge-Transport Properties. Adv. Mater. 2010, 22, 1872–1876. Lin, J. J.; Liao, W. S.; Huang, H. J.; Wu, F. I.; Cheng, C. H. A Highly Efficient Host/Dopant Combination for Blue Organic Electrophosphorescence Devices. Adv. Funct. Mater. 2008, 18, 485–491. Chang, C. F.; Cheng, Y. M.; Chi, Y.; Chiu, Y. C.; Lin, C. C.; Lee, G. H.; Chou, P. T.; Chen, C. C.; Chang, C. H.; Wu, C. C. Highly Efficient Blue-Emitting Iridium(III) Carbene Complexes and Phosphorescent OLEDs. Angew. Chem., Int. Ed. 2008, 47, 4542–4545. Lee, M. T.; Chen, H. H.; Liao, C. H.; Tsai, C. H.; Chen, C. H. Stable Styrylamine-Doped Blue Organic Electroluminescent Device Based on 2-Methyl-9,10-di(2-naphthyl)anthracene. Appl. Phys. Lett. 2004, 85, 3301–3303. Lee, M. T.; Liao, C. H.; Tsai, C. H.; Chen, C. H. Highly Efficient, Deep-Blue Doped Organic Light-Emitting Devices. Adv. Mater. 2005, 17, 2493–2497.


pubs.acs.org/JPCL

(15)

(16)

(17)

(18)

(19)

(20)

(21)

(22)

(23)

(24)

(25)

(26)

(27)

(28)

(29)

(30)

Lin, M. F.; Wang, L.; Wong, W. K.; Cheah, K. W.; Tam, H. L.; Lee, M. T.; Chen, C. H. Highly Efficient and Stable Sky Blue Organic Light-Emitting Devices. Appl. Phys. Lett. 2006, 89, 121913. He, F.; Tian, L. L.; Xie, W. J.; Li, M.; Gao, Q.; Hanif, M.; Zhang, Y. F.; Cheng, G.; Yang, B.; Ma, Y. G.; Liu, S. Y.; Shen, J. C. Highly Efficient Blue Organic Light-Emitting Devices Based on Improved Guest/Host Combination. J. Phys. Chem. C 2008, 112, 12024–12029. Wen, S. W.; Lee, M. T.; Chen, C. H. Recent Development of Blue Fluorescent OLED Materials and Devices. Journal of Display Technology 2005, 1, 90–99. Qi, Q. J.; Wu, X. M.; Hua, Y. L.; Hou, Q. C.; Dong, M. S.; Mao, Z. Y.; Yin, B.; Yin, S. G. Enhancement of Performance for Blue Organic Light Emitting Devices Based on Double Emission Layers. Org. Electron. 2010, 11, 503–507. Wei, Y.; Chen, C. Doubly Ortho-Linked cis-4,4-Bis(diarylamino)stilbene/Fluorene Hybrids as Efficient Nondoped, Sky-Blue Fluorescent Materials for Optoelectronic Applications. J. Am. Chem. Soc. 2007, 129, 7478–7479. Lin, S.; Chan, L.; Lee, R.; Yen, M.; Kuo, W.; Chen, C.; Jeng, R. Highly Efficient Carbazole-D-Dimesitylborane Bipolar Fluorophores for Nondoped Blue Organic Light-Emitting Diodes. Adv. Mater. 2008, 20, 3947–3952. Tonzola, C. J.; Kulkarni, A. P.; Gifford, A. P.; Kaminsky, W.; Jenekhe, S. A. Blue-Light-Emitting Oligoquinolines: Synthesis, Properties, and High-Efficiency Blue-Light-Emitting Diodes. Adv. Funct. Mater. 2007, 17, 863–874. Tao, S.; Zhou, Y. C.; Lee, C. S.; Lee, S. T.; Huang, D.; Zhang, X. H. Highly Efficient Nondoped Blue Organic Light-Emitting Diodes Based on Anthracene-Triphenylamine Derivatives. J. Phys. Chem. C 2008, 112, 14603–14606. Tong, Q.; Lai, S.; Chan, M.; Zhou, Y.; Kwong, H.; Lee, C.; Lee, S. Highly Efficient Blue Organic Light-Emitting Device Based on a Nondoped Electroluminescent Material. Chem. Mater. 2008, 20, 6310–6312. Zheng, C. J.; Zhao, W. M.; Wang, Z. Q.; Huang, D.; Ye, J.; Ou, X. M.; Zhang, X. H.; Lee, C. S.; Lee, S. T. Highly Efficient NonDoped Deep-Blue Organic Light-Emitting Diodes Based on Anthracene Derivatives. J. Mater. Chem. 2010, 20, 1560–1566. Shih, P. I.; Chuang, C. Y.; Chien, C. H.; Diau, E. W. G.; Shu, C. F. Highly Efficient Non-Doped Blue-Light-Emitting Diodes Based on an Anthrancene Derivative End-Capped with Tetraphenylethylene Groups. Adv. Funct. Mater. 2007, 17, 3141–3146. Kim, Y. H.; Jeong, H. C.; Kim, S. H.; Yang, K. Y.; Kwon, S. K. High-Purity-Blue and High-Efficiency Electroluminescent Devices Based on Anthracene. Adv. Funct. Mater. 2005, 15, 1799–1805. Wu, C. H.; Chien, C. H.; Hsu, F. M.; Shih, P. I.; Shu, C. F. Efficient Non-Doped Blue-Light-Emitting Diodes Incorporating an Anthracene Derivative End-Capped with Fluorene Groups. J. Mater. Chem. 2009, 19, 1464–1470. Peng, Z. K.; Tao, S. L.; Zhang, X. H.; Tang, J. X.; Lee, C. S.; Lee, S. T. New Fluorene Derivatives for Blue Electroluminescent Devices: Influence of Substituents on Thermal Properties, Photoluminescence, and Electroluminescence. J. Phys. Chem. C 2008, 112, 2165–2169. Tao, S. L.; Peng, Z. K.; Zhang, X. H.; Wang, P. F.; Lee, C. S.; Lee, S. T. Highly Efficient Non-Doped Blue Organic Light-Emitting Diodes Based on Fluorene Derivatives with High Thermal Stability. Adv. Funct. Mater. 2005, 15, 1716–1721. Tao, S.; Lee, C. S.; Lee, S. T.; Zhang, X. H. Efficient Blue and White Organic Light-Emitting Devices Based on a Single Bipolar Emitter. Appl. Phys. Lett. 2007, 91, 013507.


(31)

(32)

(33)

(34)

(35)

(36)

(37)

(38)

(39)

(40)

(41)

(42)

(43)

(44)

2853

Tang, C.; Liu, F.; Xia, Y. J.; Lin, J.; Xie, L. H.; Zhong, G. Y.; Fan, Q. L.; Huang, W. Fluorene-Substituted Pyrenes - Novel Pyrene Derivatives As Emitters in Nondoped Blue OLEDs. Org. Electron. 2006, 7, 155–162. Tao, S. L.; Zhou, Y. C.; Lee, C. S.; Zhang, X. H.; Lee, S. T. HighEfficiency Nondoped Deep-Blue-Emitting Organic Electroluminescent Device. Chem. Mater. 2010, 22, 2138–2141. Moorthy, J.; Natarajan, P.; Venkatakrishnan, P.; Huang, D.; Chow, T. Steric Inhibition of [pi]-Stacking: 1, 3,6,8-Tetraarylpyrenes as Efficient Blue Emitters in Organic Light Emitting Diodes (OLEDs). Org. Lett. 2007, 9, 5215–5218. Wee, K. R.; Ahn, H. C.; Son, H. J.; Han, W. S.; Kim, J. E.; Cho, D. W.; Kang, S. O. Emission Color Tuning and Deep Blue Dopant Materials Based on 1,6-Bis(N-phenyl-p-(R)-phenylamino)pyrene. J. Org. Chem. 2009, 74, 8472–8475. Wang, Z. Q.; Xu, C.; Wang, W. Z.; Fu, W. J.; Niu, L. B.; Ji, B. M. Highly Efficient Undoped Deep-Blue Electroluminescent Device Based on a Novel Pyrene Derivative. Solid-State Electron. 2010, 54, 524–526. Saragi, T.; Spehr, T.; Siebert, A.; Fuhrmann-Lieker, T.; Salbeck, J. Spiro Compounds for Organic Optoelectronics. Chem. Rev. 2007, 107, 1011–1065. Shen, J. Y.; Lee, C. Y.; Huang, T. H.; Lin, J. T.; Tao, Y. T.; Chien, C. H.; Tsai, C. T. High T-g Blue Emitting Materials for Electroluminescent Devices. J. Mater. Chem. 2005, 15, 2455–2463. Shen, W. J.; Dodda, R.; Wu, C. C.; Wu, F. I.; Liu, T. H.; Chen, H. H.; Chen, C. H.; Shu, C. F. Spirobifluorene-Linked Bisanthracene: An Efficient Blue Emitter with Pronounced Thermal Stability. Chem. Mater. 2004, 16, 930–934. Kim, Y. H.; Shin, D. C.; Kim, S. H.; Ko, C. H.; Yu, H. S.; Chae, Y. S.; Kwon, S. K. Novel Blue Emitting Material with High Color Purity. Adv. Mater. 2001, 13, 1690–1693. Cocherel, N.; Poriel, C.; Vignau, L.; Bergamini, J.; RaultBerthelot, J.; DiSpiroXanthene-IndenoFluorene, A New Blue Emitter for Nondoped Organic Light Emitting Diode Applications. Org. Lett. 2010, 12, 452–455. Xie, L. H.; Zhu, R.; Qian, Y.; Liu, R. R.; Chen, S. F.; Lin, J.; Huang, W. Spiro-Functionalized Ligand with Supramolecular Steric Hindrance to Control π-π Interaction in the Iridium Complex for High-Performance Electrophosphorescent Devices. J. Phys. Chem. Lett. 2009, 1, 272–276. Wu, C. C.; Liu, W. G.; Hung, W. Y.; Liu, T. L.; Lin, Y. T.; Lin, H. W.; Wong, K. T.; Chien, Y. Y.; Chen, R. T.; Hung, T. H.; Chao, T. C.; Chen, Y. M. Spiroconjugation-Enhanced Intermolecular Charge Transport. Appl. Phys. Lett. 2005, 87, 052103. Xie, L. H.; Liu, F.; Tang, C.; Hou, X. Y.; Hua, Y. R.; Fan, Q. L.; Huang, W. Unexpected One-Pot Method to Synthesize Spiro[fluorene-9,900 -xanthene] Building Blocks for Blue-LightEmitting Materials. Org. Lett. 2006, 8, 2787–2790. Staudigel, J.; Stossel, M.; Steuber, F.; Simmerer, J. Comparison of Mobility and Hole Current Activation Energy in the Space Charge Trap-Limited Regime in a Starburst Amine. Appl. Phys. Lett. 1999, 75, 217–219.


Dumbbell-Shaped Spirocyclic Aromatic Hydrocarbon to Control

Recommend Documents