Aggregation-Induced Emissions of Fluorenonearylamine Derivatives

Feb 21, 2008 - and Department of Polymer Science and Engineering, College of Chemistry, ... A new kind of fluorenonearylamine derivatives possessing ...
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J. Phys. Chem. C 2008, 112, 3975-3981

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Aggregation-Induced Emissions of Fluorenonearylamine Derivatives: A New Kind of Materials for Nondoped Red Organic Light-Emitting Diodes Yang Liu,† Xutang Tao,*,† Fuzhi Wang,‡ Xiangnan Dang,‡ Dechun Zou,*,‡ Yan Ren,† and Minhua Jiang† State Key Laboratory of Crystal Materials, Shandong UniVersity, Jinan, 250100, People’s Rspublic of China, and Department of Polymer Science and Engineering, College of Chemistry, Peking UniVersity, Beijing 100871, People’s Republic of China ReceiVed: December 13, 2007; In Final Form: January 7, 2008

A new kind of fluorenonearylamine derivatives possessing vagarious red-emitting aggregation-induced emission (AIE) characteristics was reported for the first time. On the basis of theoretical calculations and experimental results, the AIE was found to originate from the unique dimer (excimer) specifically in the aggregates. In the crystals of both compounds, every two molecules are bond together by intermolecular O‚‚‚H or C‚‚‚C bonds to form particular dimers. In virtue of their nice solid-state red fluorescence, nondoped red-light OLEDs based on these AIE-active materials were fabricated. The devices exhibited low turn-on voltages of about 3 V, luminescence of 14135 and 4813 cd m-2, and efficiencies of 1.40 and 0.35 lm W-1 based on the two materials. The results demonstrated that such AIE-active materials are promising candidates for nondoped red emission OLED applications.

Introduction As one of the most prospective applications of OLEDs (organic light-emitting diodes), the development of full-color displays has been strongly dependent on the performances of primary RGB (red, green, and blue) emitters. Compared with green and blue, the development of red-light-emitting materials is far behind in terms of both color purity and efficiency.1 The red emitters, which possess narrow band gaps, usually have strong charge-transfer (CT) character, such as pyran-containing compounds,2 or extended π-conjugation, such as porphyrins.3 Such molecules generally inherit enhanced aggregation propensity due to either attractive dipole-dipole interactions or effective intermolecular π-stackings and result in drastic fluorescence quenching in the solid state.1,4-6 Consequently, the doping method using the aforementioned red dyes integrated with suitable host materials becomes a critical approach for device construction to prevent concentration quenching.1 However, the nondoped emitters are more preferable for the concise fabrication process.4-6 In view of this, as a possible solution to the problem of red OLEDs, the nondoped host red emitters have attracted growing attentions. Chemical engineering on structure modifying is normally adopted. Some examples are D-CN and NPAFN, which possess a pair of antiparallel dipoles,4 the starshaped thieno-[3,4-b]-pyrazine-based molecules and NPAMLI (2,3-bis(N,N-1-naphthylphenylamino)-N-methylmaleimide),5 and the bulky spiro-fused bifluorene-containing PhSPDCV (2-((2(N,N′-diphenylamino)-9,9′-spirofluoren-7-yl)methylene)malononitrile).6 All of these results were accomplished by constructing twist or non-coplanar chemical structures, which are considered to be able to alleviate intermolecular aggregation. Recently, an intriguing phenomenon of aggregation-induced emission (AIE) has turned into a research hot spot. Materials with AIE * To whom correspondence should be addressed. E-mail: txt@ icm.sdu.edu.cn (X.T.). † Shandong University. ‡ Peking University.

characteristics, represented by the siloes (1,1-substituted 2,3,4,5tetraphenylsilole derivatives), were faintly emissive in solutions, but their aggregates or solid states were strongly luminescent.7 Such compounds were regarded as the competitive candidates for practical use as highly emissive materials, and they seem especially ideal for the red emitters. Deserving attention , the tendency of aggregation-induced fluorescence quenching of the red dyes would not exist anymore if the red dyes possessed an AIE property. Whereas most of the discovered AIE materials emitted green or yellow light, red light OLEDs based on AIE materials were still unseen.7 Thus, the AIE materials with redemitting light are deserving of effort and attention, and this is actually the motivation of our research to develop red fluorescence AIE materials for OLEDs applications. Results and Discussion Synthesis. Scheme 1 shows the synthesis routes and molecular structures of the two fluorenonearylamine derivatives, 2-(4-(diphenylamino)phenyl)fluorenone (1DPAFO) and 2,7-bis(4-(diphenylamino)phenyl)fluorenone (2DPAFO). The key synthesis steps of the two compounds are Pd(0)-catalyzed Suzuki coupling reactions.8 All of the starting materials are easily available with low cost. 2-Bromofluorenone and 2,7-dibromofluorenone can be facilely obtained by bromination of fluorenone with NBS,9 and 4-(diphenylamino)phenylboronic acid was prepared from N-(4-bromophenyl)-N-phenylbenzenamine by lithiation with n-butyllithium and boronation with tri-isopropyl borate.10 The yields of the Suzuki coupling reactions can be up to 92 and 81%, respectively. The structures of the product molecules were verified by 1H NMR, 13C NMR, and mass spectral data and confirmed by X-ray crystallographic analysis. Photophysics and Aggregation-Induced Emission (AIE) Properties. Just as with our previously reported fluorenone derivatives,11 the solutions (in CH2Cl2, CHCl3, ethanol, etc.) of 1DPAFO and 2DPAFO were not luminescent, while the separated solids of them were strongly luminescent under the

10.1021/jp7117373 CCC: $40.75 © 2008 American Chemical Society Published on Web 02/21/2008

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SCHEME 1: General Synthetic Routes and Chemical Structures of 1DPAFO and 2DPAFO

Figure 1. Photos of the fluorescence emissions of 1DPAFO (a) and 2DPAFO (b) (20 µM) in ethanol and a water/ethanol mixture (80% volume fractions of water) under UV light (365 nm).

Figure 2. Photos of the solid fluorescence emissions of 1DPAFO (left) and 2DPAFO (right) under UV light (365 nm).

UV lamp (365 nm). Figure 2 shows the solid fluorescence emissions of 1DPAFO and 2DPAFO under the UV light (365 nm). Entirely contrary to common red dyes, the solids of these fluorenonearylamine derivatives exhibited nice orange and red fluorescence. (Also see Figure 1, the photos of the fluorescence of solutions with and without water.) Furthermore, the drops of these compounds’ solutions on the TLC (thin-layer chromatography) plates did not luminesce even after solvent evaporation, which is entirely different from the other AIE materials.7 According to our former report,11 the abnormality was believed to be related to the excimer emission. The fluorescence-off in solutions is due to excimer formation,12 while the fluorescenceon in solid states is due to the unique effectively fluorescent dimer (excimer) specifically in the aggregates. On the TLC plate, the drops of solutions can be regarded as the solid-state solutions; molecules in them are molecular isolated, and in this case, two molecules cannot connect to each other to form a fluorescent excimer. Therefore, the excimer emission cannot be observed; only a dark spot remains on the TLC plate. The AIE feature was also quantitatively characterized by measurement of the photoluminescence (PL) spectra and UVvisible absorption spectra of 1DPAFO and 2DPAFO in ethanol and in a water-ethanol mixture (with the concentration being kept at 20 µM). Figure 1 shows the fluorescence emission pictures of them. A dramatic change of the fluorescence intensity from the nonfluorescent ethanol solutions to the strongly fluorescent suspensions in 80% water/ethanol mixtures can be observed. As shown in Figure 3, for both of the fluorenonearylamine derivatives, the emissions from the pure ethanol solutions were so weak that their PL spectra are virtually flat lines parallel to the abscissa. In contrast, when large amounts of water were added into the solutions, the PLs of the two compounds were switched on. Their PL intensities boosted up about 100 times (See Figure 3). Since water is a nonsolvent of the two

fluorenonearylamine derivatives, the molecules thus should have aggregated into solid particles in the water/ethanol mixture with high water contents. In fact, the systems of 80% water-ethanol “solutions” had become a little turbid. The emissions of the two fluorenone derivatives were apparently induced by aggregation formation, and the compounds were AIE active. In the UV-visible absorption spectra of the two fluorenonearylamine derivatives in pure ethanol and in a water/ethanol mixture, their main absorption bands were located at 300-400 nm. The spectra profiles, both with two absorbance peaks, were similar to each other. In ethanol solution, 1DPAFO showed two peaks at 310 and 345 nm, while the corresponding absorption peaks of 2DPAFO were at 310 and 367 nm; the longer absorption wavelength was attributed to the additional electrondonating group and the enlarged π-conjugated scale of 2DPAFO. In the mixture “solutions” with 80% fractions of water, the absorbance intensities of the two compounds were weaker than those in the pure ethanol. This was also coincident with our previous study on the AIE of the fluorenone derivatives and was explained as the decrease of the “effective concentration” of the solutions.11 The absorption intensity lies on the compound that dissolved in the solvent, and the formation of solid particles lowers the “real” solutions concentration. Level-off tails can be obviously seen in the long-wavelength region of the absorption spectra of both compounds in the water-containing mixtures; this was due to the Mie effect of the compounds’ nanoparticles. The scattering effect of the nanoparticles was responsible for the long-wavelength absorption tail, which did not exist in pure ethanol solutions. The level-off tails and the obvious red shift of the absorption profiles with respect to those in pure ethanol showed the formation of the aggregated nanoparticles. The emissions of the two compounds are correspondent with the characteristics of the excimer emission: (i) a large Stokes shift (∼220 nm) relative to that of the main absorbance; (ii) a featureless emission band (absence of vibronic structure); and (iii) a relative long fluorescence lifetime (about 9 ns).13 This

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Figure 3. PL spectra changes of 1DPAFO (a) and 2DPAFO (b) in pure ethanol and in an 80% water-ethanol mixture. The final concentration was kept unchanged at 20 µM, and the intensity of the PL spectra were recorded under identical measurement conditions.

Figure 4. UV-visible absorption spectra changes of 1DPAFO (a) and 2DPAFO (b) in pure ethanol and in an 80% water-ethanol mixture. The final concentration was kept unchanged at 20 µM, and the intensity of the UV-visible absorption spectra were recorded under identical measurement conditions.

indicates that the emissions of the two compounds’ aggregates come from the excimer emission. Crystal Structure and the Specific Dimer (Excimer)Induced AIE. Generally, excimers are unwanted for their reduction effect on luminescent efficiency. The AIE mechanism of the fluorenone derivatives in our previous study was found to be induced by the specific dimer (excimer). In the crystal structure of 2,7-bis(4-(tert-butylthio)phenyl)fluorenone, every two molecules were bound together by intermolecular hydrogen bonds to form a particular dimer; when excited, the dimer could turn into an excimer without arrangement adjustment, and when the excimer decayed back to the dimer, there were no repulsive interactions either. Therefore, the energy-consuming, nonradiative decay pathways are greatly reduced and thus induce a strongly enhanced excimer luminescence in the solid state.11 In this study, the crystal structures of 1DPAFO and 2DPAFO were determined by using X-ray diffraction and were carefully analyzed. In crystals, the two kinds of molecules adopt a moderate torsional configuration. For 1DPAFO, the dihedral angle between the fluorenone and the 2-linked phenyl rings of the amine is 28.6°. For 2DPAFO, the two dihedral angles between the fluorenone core and the 2,7-linked phenyl rings of amine are not identical; one is 26.8°, and the other is 40.7°. The three substituted aromatic rings attached on the nitrogen atom of the amine show a typical propeller model.

In the crystal packing of the two fluorenone derivatives, intermolecular interactions involving the fluorenonyl groups (CdO) of the molecules were found; both of the compounds’ molecules exist as pairs of dimers in the crystals. As shown in Figure 5, every two molecules in 1DPAFO and 2DPAFO form a dimer; the two molecules in each dimer have the same structure conformation. In 1DPAFO, the two molecules in a dimer pack in a parallel but staggered style. The oxygen atom of one 1DPAFO molecule forms an O‚‚‚H hydrogen bond with a hydrogen atom of the other molecule nearby. The bond length of the two hydrogen bonds between the two molecules in a dimer is 2.57 Å. In 2DPAFO, the two molecules in a dimer are bound by two intermolecular C‚‚‚C bonds. The C atom of the fluorenonyl groups (CdO) of one molecule forms an intermolecular C‚‚‚C bond with a C atom of another molecule nearby with the bond length of 3.38 Å. Each fluorenone plane of the closest 2DPAFO molecules overlaps with the other fluorenone plane; the columns of the dimers align parallel to each other side by side. The appearance of the dimers in the two compounds proves the proposed mechanism of specific dimer (excimer)-induced AIE characteristics. The keto-group-containing compounds, such as fluorenone derivatives, usually possess a CT π-π* state high above the n-π* state.14 At this time, the radiative transition is forbidden according to Kasha’s rule. Therefore, the compounds show very

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Figure 5. The X-ray crystal structures of 1DPAFO and 2DPAFO. The green dashed lines demonstrate the intermolecular O‚‚‚H hydrogen bonds (in 1DPAFO) and the carbonyl C‚‚‚C interactions (in 2DPAFO). In both of the structures of 1DPAFO and 2DPAFO, every two molecules form a dimer. The bottom figures are the packing motifs of the dimers.

Figure 6. The B3LYP/6-31G(d)-calculated highest-occupied (HOMO) (below) and lowest-unoccupied (LUMO) (above) electron molecular orbitals for 1DPAFO and 2DPAFO.

weak or even unseen single-molecule emissions. They are inclined to form excimers when being excited. As shown in Figure 6, the HOMOs and LUMOs of 1DPAFO and 2DPAFO were obtained based on B3LYP/6-31G Gaussian calculations. Notably, comparing with the distribution plots of the HOMOs, the electrons of the compounds’ LUMOs are confined mostly on the fluorenone units, especially on the carbonyl groups (Cd O). This will facilitate the excited molecules to combine with other nearby ground-state molecules by intermolecular charge interactions involving the carbonyl groups (CdO), thus forming the excimers. Moreover, the forbidden relaxation of the singlet excited state would give enough time for the excimer formation. Normally, excimers are notorious for their detrimental effects

in weakeningssometimes even completely quenchingslight emission from organic chromophores because of the great number of nonradiative decay pathways for depopulation of the excited state. This is exactly the reason why these fluorenone derivatives weakly luminesce in solutions. However, in the aggregated solid states, as revealed by the crystal structures, pairs of the molecules are bound together via intermolecular O‚‚‚H or C‚‚‚C bonds to form dimers in the ground state. When the dimers are excited, they could turn into excimers without arrangement changes, and when the excimers decay back to ground-state dimers, no repulsive interactions are involved either. Thus, there is no need to adopt these energy-consuming actions in the process of the excimer formation and decay;

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Figure 7. EL spectra of devices with two kinds of configurations of 1DPAFO (left) and 2DPAFO (right) and the PL spectra of the two compounds in films.

Figure 8. Current density (I)-voltage (V) and luminance (L)-voltage (V) characteristics of the two kinds of devices based on 1DPAFO (left) and 2DPAFO (right).

nonradiative decay pathways are blocked, resulting in strong luminescence in the solid state. Electroluminescent Characteristics. The vagarious AIE property made us believe that such types of materials should be suitable for high-efficiency electroluminescent applications. Several AIE-active dyes previously developed had shown outstanding device performances,7a,15 although none of them had been used for red light OLEDs. In our experiment, 1DPAFO and 2DPAFO were used as light-emitting materials, and red light electroluminescence from AIE-active materials was realized for the first time. The device configuration adopted was ITO/ NPB (40 nm)/1DPAFO or 2DPAFO (30 nm)/BCP (10 nm)/ AlQ (30 nm)/LiF (1 nm)/Al (80 nm) (named configuration A) (NPB ) 4,4′-bis(1-naphthyl-N-phenylamino)biphenyl, acted as hole transport layer; AlQ ) tris(8-hydroxyquinoline)aluminum, acted as electron transport layer; BCP ) 2,9-dimethyl-4,7diphenyl-1,10-phenanthroline, acted as hole-blocking layer). To optimize the device efficiency, TPBI (2,2′,2′′-(1,3,5-benzenetriyl)tris[1-phenylbenzimidazole]), a better electron-transport layer (40 nm), was chosen to replace the BCP/AlQ layers to construct another kind of device, ITO/NPB(40 nm)/1DPAFO or 2DPAFO (30 nm)/TPBI (40 nm)/LiF (1 nm)/Al (80 nm) (named as configuration B, as illustrated in Figure 9). Consistent with their PL spectra in films, the devices based on 1DPAFO showed orange light emissions, while the devices based on 2DPAFO exhibited red emissions with the λem at 610 nm. Figure 7 shows their EL spectra from the devices and the

Figure 9. Luminance efficiency (LE)-current density (I) and power efficiency (PE)-current density (I) characteristics of devices with configuration B based on 1DPAFO and 2DPAFO. Inset: scheme of the device configuration.

PL spectra of thin films. The EL spectra of devices generally resemble their corresponding PL spectra, with a small red shift for 1DPAFO. This suggested that the emissions are entirely generated from the emitting layer. Figure 8 gives the current density (I)-voltage (V)-luminance (L) characteristics of the devices based on the two fluorenone derivatives. All of the

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TABLE 1: Performances of Devices Based on 1DPAFO and 2DPAFO as the Emitters; the Data for the Brightness (L), Luminance Efficiency (ηI), and Power Efficiency (ηL) Maximum Values for Each Device devicea

Uonset/V

1DPAFO/A

3.4 6.25b 3.2 6.3b 3.9 6.7b 3.7 6.9b

1DPAFO/B 2DPAFO/A 2DPAFO/B

Lmax/cd m-2 11073 181b 14135 300b 4777 70b 4813 91b

ηImax/cd A-1

ηLmax/lm W-1

CIE coordinate

λem/nm

0.90 0.87b 1.50 1.37b 0.30 0.29b 0.60 0.52b

0.62 0.44b 1.40 0.70b 0.25 0.14b 0.35 0.25b

(0.534, 0.461)

592

(0.545, 0.451)

591

(0.590, 0.406)

609

(0.594, 0.401)

610

a

Configuration A: ITO/NPB(40 nm)/1DPAFO or 2DPAFO (30 nm)/BCP (10 nm)/AlQ (30 nm)/LiF (1 nm)/Al (80 nm); Configuration B: ITO/ NPB(40 nm)/1DPAFO or 2DPAFO (30 nm)/TPBI (40 nm)/LiF (1 nm)/Al (80 nm). b At the current density of 20 mA/cm-2.

devices showed low turn-on voltages of no more than 3.9 V. The EL brightness (Lmax) can approach 14135 and 4813 cd m-2 for 1DPAFO- and 2DPAFO-based devices, respectively. The performances of devices using TPBI as an electron-transport/ hole-blocking layer were found to be promoted in terms of both efficiency and brightness, which were thanks to a more balanced electron/hole transport. Figure 9 shows the efficiency-current density profiles, and detailed EL data are listed in Table 1. The maximum luminescence efficiency of the devices based on 1DPAFO and 2DPAFO can be up to 1.50 (1.40 lm W-1) and 0.60 cd A-1 (0.35 lm W-1), respectively. Table 1 also lists the device performances at a practical current density of 20 mA/ cm-2 (with the operating bias of about 6V for the four devices); the efficiencies at this current density showed only a small decrease relative to the maxima. The performance of these unoptimized devices is not as good as those of some red-dopantbased devices and some host emitters with the top records.1,5,6,16 However, for red light OLEDs, these preliminary values can at least prove that the AIE-active compounds can be promising candidates for efficient nondoped red-light-emitting materials. The compounds can be facilely synthesized, and further modification of the derivatives chemical structure to get better results could be expected. Conclusion In this study, we reported a new kind of red-emitting fluorenonearylamine derivatives with AIE characteristics which is completely different from the common red fluorescent chromophores. The crystal structures indicated that specific dimers exist in both compounds. The AIE mechanism is attributed to the unique effectively fluorescent dimer (excimer) in the aggregated solid state. In virtue of their nice solid-state red fluorescence, red light OLEDs were fabricated. The devices exhibited encouraging results, demonstrating that such types of AIE-active materials can be promising candidates for red emission OLED applications. Future works on rendering the compound’s chemical structure and optimizing the device configurations would provide more satisfactory results. Experimental Section Materials and Methods. All reagents and starting materials are commercially available and were used as received. Pd(PPh3)4 was purchased from Acros. The melting point was measured on a diamond differential scanning calorimeter under nitrogen atmosphere. 1H NMR and 13C NMR spectra were recorded at 25 °C using a Bruker Avance 400 spectrometer. The electrospray mass spectrum (ES-MS) was recorded on a Finnigan LCQ mass spectrograph, and the concentration of the samples was about 1.0 mmol/mL. Absorption measurements were carried out on a TU-1800 spectrophotometer using a quartz cuvette having a 1 cm path length. Photoluminescence (PL) measurements were

recorded using a Hitachi F-4500 fluorescence spectrophotometer with a 150 W Xe lamp. The excitation wavelengths for PL spectra in ethanol and water/ethanol solutions were 321 nm for 1DPAFO and 322 nm for 2DPAFO; the excitation wavelength for PL spectra for both 1DPAFO and 2DPAFO solid films was 360 nm. The fluorescence lifetime measurement was performed on the Edinburgh FLS920 spectrofluorimeter with a hydrogen flash lamp (pulse duration 1 ns) as the excitation source on the same spectrofluorimeter. Solvents were purified and dried according to standard procedures. OLED devices were fabricated by thermal vacuum deposition at 1.333 × 10-4 Pa. The active area of the device was about 4 mm2. The thickness of the films was measured by a Dektak surface profilometer. Synthesisof2-(4-(Diphenylamino)phenyl)fluorenone(1DPAFO) (Scheme 1). Under an argon atmosphere, to a stirred mixture of 0.39 g (1.5 mmol) of 2-bromofluorenone and 0.46 g (1.6 mmol) of 4-(diphenylamino)phenylboronic acid in 6 mL of THF and 3 mL of 2 M Na2CO3 was added 0.01 g of Pd(PPh3)4. The mixture was heated to 80 °C for 8 h. After cooling, the organic phase was extracted with 50 mL of CH2Cl2, washed with water, dried with Na2SO4, and filtered, and the product was purified by column chromatography (silica gel, petrol ether/ethyl acetate ) 2:1) to give 0.58 g of orange solids (yield 92%); mp 186 °C. 1H NMR (400 MHz, CDCl , ppm) δ: 7.06 (t, 2H, J ) 7.3 Hz), 3 7.14 (m, 6H), 7.28 (m, 5H), 7.52 (m, 5H), 7.68 (m, 2H), 7.88 (d, 1H, J ) 1.2 Hz). 13C NMR (CDCl3, 100.57 MHz, ppm) δ: 120.29, 120.69, 122.40, 123.21, 123.50, 124.38, 124.65, 127.43, 128.87, 129.35, 132.45, 133.37, 134.47, 134.80, 134.91, 141.75, 142.63, 144.43, 147.48, 147.81, 193.98. MS (EI): calcd for C31H21NO, 423.16; found, 423.2. Crystal data for DSFO (C33H32OS2): Mr ) 423.49, monoclinic, space group P2(1)/c, a ) 18.807(5) Å, R ) 90°, b ) 8.584(5) Å, β ) 115.041(5)°, c ) 16.555(5) Å, γ ) 90°, V ) 2421.4(17) Å3, Z ) 4, Fcalcd ) 1.162 Mg/m3, T ) 293 (2) K, crystal size 0.46 × 0.24 × 0.06 mm. Synthesis of 2,7-bis(4-(Diphenylamino)phenyl)fluorenone (2DPAFO). 2DPAFO was prepared according to the same procedure as that of 1DPAFO from 0.606 g (1.8 mmol) of 2,7dibromofluorenone, 1.29 g (4.48 mmol) of 4-(diphenylamino)phenylboronic acid, and 0.02 g of Pd(PPh3)4. Column chromatography (silica gel, petrol ether/ethyl acetate ) 2:1) gave 0.97 g of red solids (yield 81%); mp 255 °C. 1H NMR (400 MHz, CDCl3, ppm) δ: 7.06 (t, 4H, J ) 7.3 Hz), 7.14 (m, 12H), 7.28 (m, 8H), 7.51 (m, 4H), 7.56 (d, 2H, J ) 7.8 Hz), 7.69 (d, 1H, J ) 1.7 Hz), 7.71 (d, 1H, J ) 1.7 Hz), 7.89 (2H, d, d, 1H, J ) 1.5 Hz). 13C NMR (CDCl3, 100.57 MHz, ppm) δ: 120.67, 122.45, 123.23, 123.53, 124.67, 127.43, 129.36, 132.59, 133.42, 135.27, 141.55, 142.64, 147.51, 147.83, 193.99. MS (EI): calcd for C49H34N2O, 666.8; found, 667.8 (M+). Crystal data for DSFO (C33H32OS2): Mr ) 666.78, monoclinic, space group C2/c, a ) 15.8751(8) Å, R ) 90°, b ) 12.3295(7) Å, β )

AIE of Fluorenonearylamine Derivatives 93.705(2)°, c ) 42.907(2) Å, γ ) 90°, V ) 8380.8(8) Å3, Z ) 8, Fcalcd ) 1.057 Mg/m3, T ) 293 (2) K, crystal size 0.39 × 0.17 × 0.12 mm. Acknowledgment. We are grateful for financial support from the National Natural Science Foundation of China (Grant Nos. 50325311, 50590403, 50721002) and 973 programs of the People’s Republic of China (2004CB619002) and also the NSF and 973 programs of the People’s Republic of China (90401028, 50673003). Supporting Information Available: CIF files of 1DPAFO and 2DPAFO. This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) Chen, C.-T. Chem. Mater. 2004, 16, 4389. (2) (a) Tang, C. W.; Van Slyke, S. A.; Chen, C. H. Appl. Phys. Lett. 1989, 65, 3610. (b) Tao, X. T.; Miyata, S.; Sasabe, H.; Zhang, G. J.; Wada, T.; Jiang, M. H. Appl. Phys. Lett. 2001, 78, 279. (c) Zhang, X. H.; Chen, B. J.; Lin, X. Q.; Wong, O. Y.; Lee, C. S.; Kwong, H. L.; Lee, S. T.; Wu, S. K. Chem. Mater. 2001, 13, 1565. (3) (a) Burrows, P. E.; Forrest, S. R.; Sibley, S. P.; Thompson, M. E. Appl. Phys. Lett. 1996, 69, 2959. (b) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151. (c) Kwong, R. C.; Sibley, S.; Dubovoy, T.; Baldo, M.; Forrest, S. R.; Thompson, M. E. Chem. Mater. 1999, 11, 3709. (4) (a) Kim, D. U.; Paik, S. H.; Kim, S.-H.; Tsutsui, T. Synth. Met. 2001, 123, 43. (b) Yeh, H.-C.; Yeh, S.-J.; Chen, C.-T. Chem. Commun. 2003, 2632. (5) (a) Thomas, K. R. J.; Lin, J. T.; Tao, Y.-T.; Chuen, C.-H. AdV. Mater. 2002, 14, 822. (b) Wu, W.-C.; Yeh, H.-C.; Chan, L.-H.; Chen, C.T. AdV. Mater. 2002, 14, 1072. (6) Chiang, C.-L.; Wu, M.-F.; Dai, D.-C.; Wen, Y.-S.; Wang, J.-K.; Chen, C.-T. AdV. Funct. Mater. 2005, 15, 231.

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