Novel host materials for single-component white organic light-emitting
diodes based on 9-naphthylanthracene derivatives†
Lei Wang,
aWai-Yeung Wong,
aMei-Fang Lin,
aWai-Kwok Wong,*
aKok-Wai Cheah,
bHoi-Lam Tam
band Chin H. Chen*
acReceived 14th April 2008, Accepted 10th July 2008
First published as an Advance Article on the web 18th August 2008 DOI: 10.1039/b806183a
A series of 9-naphthylanthracene based dimers and trimers were synthesized and characterized. TGA studies reveal that they are all thermally stable with decomposition temperatures well above 500C. Upon optical excitation, all of these dimers and trimers show intense blue emission in common organic solvents, accompanied by a new peak at long wavelength in the solid state. They exhibit nanosecond transient lifetimes consisting of two decay components, suggesting the formation of excimers. Single-component light-emitting electroluminescent devices based on these robust materials have been fabricated. The device based on 4,40-bis(9-(1-naphthyl)anthracen-10-yl)biphenyl exhibits a maximum luminance efficiency of 7.0 cd A1with CIE coordinates of (0.31, 0.36) and luminance of 1396 cd m2at
6.9 V. The device based on 1,3,5-tris(9-(1-naphthyl)anthracen-10-yl)benzene exhibits a maximum luminance efficiency of 5.78 cd A1with CIE coordinates of (0.33, 0. 43) and luminance of
1156 cd m2at 7.8 V.
Introduction
Since the pioneer work by Tang and VanSlyke on efficient organic light-emitting diodes (OLEDs) based on low-molecular-weight compounds,1significant progress in materials and device
science has led to the realization of full-color OLEDs with improved efficiencies and lifetimes.2White OLEDs are a prime
focus of OLED research due to their advantages of high resolution and possibility for large-scale production. Consider-able achievements in monochromatic efficiency and performance have led to the development of devices with broadband white light emission,3 in which the white light from a single emissive
layer with the formation of electromers,4excimers,5 exciplexes6
and aggregates7was shown to play an important role.
When two aromatic systems are brought into proximity, the propensity for the formation of excimers which are characterized by broad emissive peaks, long lifetimes, and red-shifted emis-sions8is great. It is well known that the formation of excimers
will drastically decrease the photoluminescence (PL) quantum yields of the materials because of the greater number of non-radiative decay pathways for depopulation of the excited state.9
Generally, it is an unwanted effect that often reduces the luminescent efficiency and decreases the emission color purity.
However, the excimer does not always play a negative role in highly luminescent materials, for example, the stable excimer is a main source for single-component white light generation.10
Hou’s group11reported single-component white
electrolumines-cence (EL) with a maximum brightness of 1395 cd m2 and
a current efficiency of 2.07 cd A1in which the blue emission
originated from an isolated molecule and the orange emission from its excimers. Williams et al.12 reported a white organic
light-emitting diode (WOLED) with nearly 100% internal quantum efficiency showing current and power efficiencies of 42.5 cd A1and 29 lm W1, respectively, using a phosphorescent
complex platinum(II) [2-(40,60-difluorophenyl)pyridinato-N,C20
)] (2,4-pentanedionato).
While anthracene is a well-known and important fluorescent material following the initial report in 1963 by Pope et al.13on the
EL emission from its crystal at a voltage of 400 V, its derivatives have been extensively studied as a subject of great importance in chemical physics.14 Recently, anthracene derivatives have been
shown to be excellent candidates for use in efficient blue OLEDs with high device stability.15In some cases, anthracene can also
form excimers.16,17 Ohta and co-workers16 have reported
methylene-linked anthracene and naphthalene molecules and found the methylene chain to play a significant role in the intermolecular excimer formation dynamics and its electric field dependence. It was not until recently that the excimers of aryl-linked dimers and trimers for anthracene derivatives became known and there was a recent preliminary report by us on such a phenomenon based on BUBH-3.18Here, we report a detailed
study on the synthesis and photophysics of a series of 9-naph-thylanthracene based compounds as a new class of host luminescent materials with interesting and potentially useful electroluminescent properties. In a single-component-emitting EL device, some of them can be made to emit white light with
aCentre for Advanced Luminescence Materials, Department of Chemistry,
Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
bCentre for Advanced Luminescence Materials, Department of Physics,
Hong Kong Baptist University, Waterloo Road, Hong Kong, P. R. China
cDisplay Institute, Microelectronics and Information Systems Research
Center, National Chiao Tung University, Hsinchu, Taiwan, 300, Republic of China
† Electronic supplementary information (ESI) available: Definitions; experimental data. CCDC reference numbers 685067. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b806183a
PAPER www.rsc.org/materials | Journal of Materials Chemistry
high device efficiency, therefore they hold great promise in the fabrication of WOLEDs with simple architectures.
Results and discussion
Synthesis and characterizationThe syntheses of compounds 4a–4d are outlined in Scheme 1. A series of anthracene derivatives were synthesized by the Pd-catalyzed Suzuki cross-coupling of the boronic acid of 9-naphthylanthracene and the corresponding aryl bromide. 9-Naphthylanthracene-10-boronic acid was synthesized by means of lithium bromide exchange at low temperature followed by reaction with tris(isopropyl)borate and subsequent acid hydrolysis. In the patent,19 Saitoh et al. have reported the
synthesis of compound 4c using a divergent methodology, which made the isolation of the final product in high purity very complicated and difficult. Also, the authors did not provided any useful characterization, PL or EL data. To simplify the synthesis, we chose to adopt in this paper a convergent methodology as shown in Scheme 1 in which 9-naphthylanthracene-10-boronic acid was first synthesized as the common synthon. It was then reacted with the corresponding aryl bromide to give the product which, owing to its poor solubility, precipitated directly from the reaction mixture, and thus could be obtained in high yield by simple filtration. Further purification was readily accomplished by train sublimation in vacuum (106 Torr). Some of these
compounds (like 4b) are too insoluble in most common organic solvents even at 60C to collect the NMR spectra.
Crystal structure
In order to look at the conformation of these anthracene derivatives, the crystal structure of 4c was determined. As shown in Fig. 1 (left), the molecules of 4c were found to possess a propeller twist topology in the crystal, and the dihedral angles between the central phenyl core and the coordinated anthracene rings are 83.7(1), 61.8(1) and 67.1(1)while the dihedral angles between the 1-naphthyl and anthracene planes are 87.7(1), 68.6(1) and 85.2(1). According to its crystal packing, it is clear that the molecules tend not to aggregate in the ground state. With the additional steric hindrance of the 1-naphthyl ring, it is only possible for the molecules to react with each other by edge-to-edge interaction.
Scheme 1 Synthesis of compounds 4a, 4b, 4c and 4d. Conditions: (a) PdCl2(PPh3)2, toluene, 2 M K2CO3, 1-naphthyl boronic acid; (b) PdCl2(PPh3)2, toluene, 2 M K2CO3, 2-naphthyl boronic acid; (c) hn, NBS, CH2Cl2; (d) n-BuLi, toluene–ether; tris(isopropyl) borate, HCl; (e) 4,40-diiodobiphenyl, Pd(PPh3)4, THF, 2 M K2CO3; (f) Pd(PPh3)4, toluene–EtOH, 2 M Na2CO3.
Fig. 1 A perspective view of the space-filling model of compound 4c and its crystal packing showing two formula units related by an inversion centre at (0.5, 0.5, 0.5). The dichloromethane solvates shown have 0.5 occupancy.
Thermal and electrochemical behavior
The thermal properties of these new compounds were determined by DSC and TGA measurements and the thermal stability data are listed in Table 1. They all possess very high thermal stabilities with decomposition temperatures well above 500C, but exhibit no discernible glass transition temperatures (Tg). Their evapo-rated films exhibit only a broad halo in the X-ray diffraction
patterns (see ESI†) which indicates that they form uniform amorphous films by vacuum deposition. All of the newly synthesized compounds were characterized by cyclic voltam-metry and the data are listed in Table 1. In each case, the anodic scan was performed in CH2Cl2. A reversible oxidation wave was observed at half-wave potentials (E1/2) of 1.25–1.31 V. With the same core, the compounds containing a 2-naphthyl group have lower Eox and smaller energy gaps than the compounds
containing 1-naphthyl groups, which might be attributed to the stronger donor ability of the 2-naphthyl group. The HOMO/ LUMO levels of these compounds, which were calculated from the Eoxand the optical band gap (estimated from the absorption
edge), are listed in Table 1. Photophysical properties
Absorption and PL spectra of compounds 4a–4d in dilute dichloromethane solution and film substrate on quartz are shown in Fig. 2. On irradiation at 376 nm in CH2Cl2, all of the compounds show intense blue fluorescence, with an emission peak centered at 417–430 nm. The PL quantum yields (Vf) of these compounds are listed in Table 1.The absorption bands are centered within the region of 330–400 nm, and they are assigned to the S1 ) S0 transition of the anthracene moiety.16,19 The position of the 0–0 transition to the S1 state remains almost unchanged with changes in the aryl core and peripheral chromophores. In solution, there is a slight red shift in the
Table 1 The optical, photophysical and thermal properties of 4a, 4b, 4c and 4d 4a 4b 4c 4d PL film l/nm 444, 547 457, 513, 544 440, 540 456, 498, 538 PL solution la, max/nma 416, 434 430 414, 432 422, 440 Ffb 0.58 0.50 0.68 0.59 Abs film l/nm 361, 381, 402 364, 384, 405 361, 382, 404 362, 383, 405 Abs solution/ la,max/nma 358, 376, 397 359, 378, 398 359, 378, 399 359, 379, 401 E1/2ox/eV 1.27 1.25 1.31 1.29 HOMO 5.57 5.55 5.61 5.59 LUMO/eV 2.59 2.58 2.61 2.60 Band gap/eV 2.98 2.97 3.00 2.99 Td/C 510 535 542 539 a
The absorption and PL spectra in CH2Cl2.bPL quantum yield relative to quinine sulfate in 1 N H2SO4.
Fig. 2 Photoluminescence (PL) (lex¼ 376 nm) and absorption spectra of compounds 4a, 4b, 4c and 4d in dichloromethane solution and as solid films.
absorption and PL maxima of 4b and 4d as compared to 4a and 4c, respectively, and this is likely due to a decrease in conjugation because of the higher steric hindrance of the 1-naphthyl compared to the 2-naphthyl moiety. Meanwhile, the trimer has a slight blue shift as compared to the corresponding dimer, which may be attributed to p-system distortion because of the propeller twist topology of the trimer.20
The absorption and PL spectra of thin films of 4a–4d are also shown in Fig. 2. The solid-state emission bands of the dimers and trimers are very broad and an additional broad emission at 500– 570 nm tailing to 650 nm is also observed in each case. Compared to the solution PL spectra, the typical peak of anthracene is red-shifted by 25–35 nm (Table 1). These features are usually observed for organic and polymer materials presumably due to intermolecular interactions or exciton hopping in the solid state,21but the appearance of the orange emission is very
inter-esting, which suggests the formation of a new species in the solid film.
In both the solution phase and solid thin film, all of the compounds have similarly structured absorption spectra in the 330–440 nm region. The broad orange emission at around 540 nm may be ascribed to the excimer formation due to the naphthyl-to-naphthyl interactions based on the edge-to-edge model revealed in the X-ray crystallographic analysis. To further explore the photophysics of these new 9-naphthylanthracene derivatives, we obtained PL decay dynamics information. The PL decay dynamics of 4a–4d are exemplified by the PL decay curves and the data are shown in Table 2. All of these compounds in the solid films are rather long-lived in the excited state with the dominant fluorescence lifetimes in the range of 0.28–2.36 ns. Meanwhile, the radiative lifetimes increase as the spectrally selected band shifts toward the long wavelength emission threshold, which suggest the formation of at least one more well-defined excimer. These PL decay dynamics results are also in accordance with the interpretation of the steady-state emission in thin films due to intermolecular excimers.22We also note that the
nanosecond scale of the decay times could rule out the involve-ment of possible triplet excitons and their excimers as a possible source of the long-wavelength emission band.23As a result, it is
reasonable to assign the additional broad orange emission band to singlet excimeric states formed by anthracene derivatives in the solid state.
As shown in Fig. 2, in the solid-state PL spectra of the dimers or trimers, compounds containing a 2-naphthyl group show stronger peaks in the long-wavelength regime than those with the 1-naphthyl moiety. This suggests the peripheral aryl group plays an important role in the formation of excimers, and the 2-naphthyl ring has a smaller steric hindrance than the 1-naph-thyl counterpart and thus is more prone to form the excimer.
Meanwhile, the long wavelength peak of 4c is weaker than that of 4a and it can be explained by the propeller twist topology structure of 4c, which makes the formation of excimers more difficult.
Electroluminescence properties
We explored the performance characteristics of the devices using these compounds as the light-emitting layer in single-layer and triple-layer devices (see Scheme 2). Fig. 3b and Fig. 3d show the EL spectra of 4b and 4d in devices I and II. Compared to their PL spectra, the EL spectra were almost unchanged except for a slight red shift of the emission maximum. But the EL spectra of 4a and 4c show an obvious change in shape compared to their PL spectra with the blue peak decreased and the orange peak increased in intensity, even though their peak position does not change much. This suggests that the EL emission selectively occurs at the excimer sites.24Since compounds 4a and 4c contain
1-naphthyl units which have high steric hindrance, their excimers are not as stable as those of 4b and 4d. When the current density reaches a threshold level, electroluminescence is likely to occur from the emissive site of the excimers. If the current density is near or beyond the threshold, the emission at the excimer will become weaker. As shown in Fig. 3a and 3c, the blue peak plays a more important role in the EL spectra of 4a and 4c as the current density increases from 20 to 200 mA cm2. Comparing
the EL spectra of the single-layer device and the three-layer device of all compounds, no new peaks were observed, and the overall EL pattern of triple-layer device II is similar to that of the single-layer device I, which suggest the long-wavelength EL emissions of these devices should have similar origins (i.e. excimer). This result also rules out the possibility of formation of a species such as an exciplex at the NPB/Host interface (or Alq3/ Host interface) in device II.
The current efficiency versus current density and the current density–voltage characteristics of these compounds in the triple-layer devices (device II) are shown in Fig. 4, and the EL data of the four OLEDs are listed in Table 3. In device II for compound 4a, the emission is close to white with Commission Interna-tionate de’Eclairage (CIEx,y) coordinates of (0.31, 0.36) to (0.29, 0.32) when the drive current increased from 20 to 200 mA cm2
(Fig. 3), which shows a maximum efficiency of 7.0 cd A1and
a brightness of 1396 cd m2at 20 mA cm2. Compound 4c also
emits white light with CIEx,y of (0.33, 0.43) and a maximum efficiency of 5.78 cd A1and brightness of 1156 cd m2at 20 mA
cm2. In contrast, compounds 4b and 4d emit green-yellow and
Table 2 Excited state lifetimes (in ns) of 4a, 4b, 4c and 4d in thin film at different wavelengths Compound 430 nm 460 nm 490 nm 530 nm 550 nm 4a 0.35 0.36 0.38 1.36 2.36 4b 0.34 0.47 0.53 1.02 2.21 4c 0.31 0.45 0.49 1.13 1.61 4d 0.28 0.38 0.42 0.90 1.52
Scheme 2 The structures of devices I and II.
green-blue light respectively, and their color only changes slightly with the current density because their excimers are more stable (Fig. 3). In summary, the 9-naphthylanthracene based trimers and dimers can form excimers in the solid state, and the peripheral groups of anthracene control the stability of the excimer and its associated long-wavelength emission. With the judicious choice of peripheral group and core, these new luminescent materials can be fabricated to emit white light with high current efficiency in a simple device structure.
Fig. 4 (a) Dependence of the current efficiency on the drive current density for 4a–4d based devices II.(b) Current density–voltage (J–V) curves. Fig. 3 Electroluminescence (EL) spectra of (a) 4a, (b) 4b, (c) 4c and (d) 4d based devices I and II.
Table 3 The EL performance of 4a–4d in the triple-layer device II
Current/ mA cm2 Brightness/ cd m2, V Current efficiency/ cd A1 Power efficiency/ lm W1 EQE (%) CIE x,y 4a 20 1396, 6.9 7.0 3.2 2.71 (0.31,0.36) 4b 20 1020, 7.3 5.1 2.04 1.67 (0.28,0.55) 4c 20 1156, 7.8 5.78 2.30 1.96 (0.33,0.43) 4d 20 980, 7.4 4.9 2.07 1.97 (0.19,0.27)
Conclusions
A series of new luminescent materials based on 9-naphthylan-thracene have been prepared via a high-yield convergent synthesis and characterized. All of them possess good thermal stabilities with no detectable glass transitions. They emit deep blue emission in solution, but a new peak at longer wavelength appeared in the solid films. Detailed study of their photophysics shows that the latter peak has nanosecond lifetime with two components in the neat films. The presence of the delayed component is attributed to the formation of excimers. We find the peripheral steric bulky group plays an important role in controlling the stability of the excimer and its associated long-wavelength emission. Single-emitting-component EL devices of theses compound were fabricated. When compounds 4a and 4c were used as hosts, they exhibited bright and efficient white light with good luminance and high current efficiency at a low drive voltage. Since WOLEDs with a single-emitting-component may greatly simplify the fabrication process, the small molecular luminescent materials described in this report are promising for future WOLED displays and lighting applications. Further investigations along this line are currently continuing in our laboratory.
Experimental
Material and methods1-Naphthyl boronic acid, 2-naphthyl boronic acid and 9-bromo-anthracene were used as received from Aldrich. The solvents were used as supplied or purified by the standard techniques. All reactions requiring anhydrous condition were performed in oven-dried glassware under a N2atmosphere using Schlenk flask techniques. The experimental data of the known compounds of 1a, 1b, 2a, 2b are given in the ESI.†1H and13C NMR spectra
were recorded on a JEOLEX 270 spectrometer or a Bruker-AF301 AT 400 MHz spectrometer. The infrared spectra were measured on a Nicolet 670 FT-IR spectrophotometer. Low-resolution mass spectra were obtained on a Finnigan MAT SSQ-710 in FAB (positive) mode. High resolution mass spectrometric measurements were carried out using a Bruker autoflex MALDI-TOF mass spectrometer. Fluorescence spectra were obtained on a Perkin Elmer LS55 Luminescence spectrometer. The differen-tial scanning calorimetry (DSC) analysis was performed under a nitrogen atmosphere on a TA Instruments DSC 2920. Elemental analyses were determined by a Finnigan FLASH 1112 SERIES EA elemental autoanalyzer. To measure the PL quantum yields (Vf), degassed solutions of the compounds in CH2Cl2were prepared. The concentration was adjusted so that the absorbance of the solution would be lower than 0.1. The excitation was performed at the 360 nm, and a solution in 1 N H2SO4 of quinine sulfate, which has Vf ¼ 0.546, was used as a standard.24 Cyclic voltammetric measurements were carried
out in a conventional three electrode cell using a Pt button working electrode of 2 mm in diameter, a platinum wire counter electrode, and a SCE reference electrode on a computer-controlled EG&G Potentiostat/Galvanostat model 283 at room temperature. Reduction CV of all compounds was performed in dichloromethane containing Bu4NPF6(0.1 M) as the supporting electrolyte.
Device fabrication
Prior to the deposition of organic materials, the indium-tin-oxide (ITO)/glass was cleaned with a routine cleaning procedure and pretreated with UV-ozone. Devices were fabricated under a base vacuum of about 106Torr in a thin-film
evapo-ration coater following a published protocol.25 In the device,
2-TNATA (4,40,400 -tris-N-napthyl-N-phenylamino-triphenyl-amine) was used as the hole-injection layer, NPB (N,N00 -bis(1-naphthyl)-N,N0-diphenyl-1,1,10-biphenyl-4,40-diamine) served as hole-transporting layer, and tris(8-hydroxyquinoline)aluminium (Alq3) was used as the electron-transporting layer. The current– voltage–luminance characteristics of the devices were measured with a diode array rapid scan system using a Photo Research PR650 spectrophotometer and a computer-controlled, progra-mmable, direct-current (DC) source.
Single-crystal structure analysis
Diffraction data were collected at 293 K using graphite mono-chromated Mo-Ka radiation (l¼ 0.71073 A˚ ) on a Bruker Axs SMART 1000 CCD diffractometer. The collected frames were processed with the software SAINT+26 and an absorption
correction (SADABS)27was applied to the collected reflections.
The structure was solved by direct methods (SHELXTL)28in
conjunction with standard difference Fourier techniques and subsequently refined by full-matrix least-squares analyses on F2.
Crystallographic data for 4c: C78H48$0.5CH2Cl2, Mr¼ 1027.63, crystal dimensions 0.32 0.25 0.23 mm3, triclinic, space group
P1, Z¼ 2, a ¼ 15.349(1) A˚ , b ¼ 15.706(1) A˚, c ¼ 15.789(1) A˚, a ¼ 66.033(1), b ¼ 61.608(1), g ¼ 62.436(1), U¼ 2882.6(3) A˚3,
rcalcd¼ 1.184 g cm3, F(000)¼ 1074. A total of 13788 reflections were measured in the range 2.54 # q # 25.00 (hkl indices:17 # h # 18,13 # k # 18, 18 # l # 18), 9623 unique reflections. The structure was refined on F2to wR2¼ 0.2973, R1 ¼ 0.1315
(6089 reflections with I > 2s(I), GOF ¼ 0.979 on F2 for 725
refined parameters).† Synthesis
9-(1-Naphthyl)anthracene-10-boronic acid (3a). To a slurry containing (11.52 g, 30 mM) dry 9-(1-naphthyl)-10-bromo-anthracene in 250 mL of dry toluene and 250 mL of dry diethyl ether under nitrogen atmosphere in a 1 L three-necked round flask cooled in a dry ice-acetone bath was added dropwise 16 mL of 2.5 M n-butylithium solution in hexane with stirring within a period of 30 min. Stirring was continued for another 2 h. Tri(isopropyl)borate (40 mM, 1.3 eq) was added over 20 min, then the mixture was equilibrated to room temperature and stirred for an additional 12 h. The mixture was then cooled in a dry ice bath and 100 mL of 2 M HCl and 50 mL of toluene were added . The organic layer was washed with water and dried with Na2SO4, filtered and hexane was added to the concentrated organic layer from which a lot of white solid was precipitated. The solid was dissolved in 100 mL of THF and 10 mL of concentrated HCl and 100 mg of tetra(n-butyl)ammmonium bromide were added. The mixture was stirred overnight at r.t. and the voluminous solid precipitate was isolated by filtration to give 7.6 g of the product as a white solid. Yield 75%.1H NMR
(400 MHz, CDCl3): d 8.96 (s, 2H), 8.17 (d, 1H, J¼ 4.4Hz), 7.09–
8.16 (m, 3H), 7.75–7.77 (m, 1H), 7.47–7.50 (m, 4H), 7.22–7.31 (m, 5H). 6.84–6.86 (m, 1H); IR (KBr, cm1): 3052 (s), 2870, 1559
(s), 1509 (s), 1411 (s), 1313 (s), 1254 (s), 1107 (s), 1047 (s), 949 (s), 761 (s), 655(s); MALDI-TOF-MS m/z calcd for C24H17BO2[M]+, 348.1320; found, 348.1308. 9-(2-Naphthyl)anthracene-10-boronic acid (3b).1H NMR: (400 MHz, CDCl3): 8.17 (d, 2H, J¼ 8.8 Hz), 8.0–8.06 (m, 2H), 7.89– 7.91 (m, 2H), 7.68–7.90 (m, 2H),7.58–7.60 (m, 2H), 7.47–7.53 (m, 3H). 7.3–7.34 (m, 2H). IR (KBr, cm1): 3052 (s), 2975(s), 2877(s), 1599 (s), 1559 (s), 1411 (s), 1316 (s), 1263 (s), 1127 (s), 1046 (s), 946 (s), 821(s), 757 (s), 653 (s). MALDI-TOF-MS m/z calcd for C24H17BO2[M]+, 348.1320; found, 348.1306.
4,40-Bis(9-(1-naphthyl)anthracen-10-yl)biphenyl (4a). A mixture of 9-(1-naphthyl)anthracene-10-boronic acid (9.72 g, 30 mmol), tetrakis(triphenylphosphine)palladium(0) (405 mg, 0.3 mmol), 4,40-di(iodo)biphenyl (6.08 g, 15 mmol), tetrahydro-furan (300 mL), and 2 M K2CO3(100 mL) were heated at 80C with magnetic stirring under nitrogen atmosphere. Some solid began to appear after 2 h and heating was continued overnight. The reaction mixture was cooled to room temperature and the precipitated solid was isolated by filtration, washed with water, then air dried to yield 9.72 g (85%) of the product. 1H NMR
(270 MHz, CDCl3, 50C): d 7.18–7.27 (8H, m), 7.34–7.40 (4H), 7.46–7.51 (m, 6H), 7.59–7.61 (m, 2H), 7.69–7.76 (m, 6H), 7.87– 7.91 (m, 4H), 8.0–8.09 (m, 8H). IR (KBr, cm1): 3035 (s), 1586
(s), 1502 (s), 1437 (s), 1372 (s), 1010 (s), 934 (s), 769 (s), 699 (s); MALDI-TOF-MS m/z calcd for C60H38[M]+, 758.2968; found, 758.2974. Anal. calcd for C60H38: C, 94.95; H, 5.05; Found: C, 94.85; H, 5.15%.
4,40-Bis(9-(2-naphthyl)anthracen-10-yl)biphenyl (4b). The compound was synthesized in a similar way as 4c. Its solubility is very poor. IR (KBr, cm1): 3038 (s), 1627(s), 1598(s), 1586 (s),
1499 (s), 1439 (s), 1393 (s), 1372 (s), 1028 (s), 934 (s), 769 (s); MALDI-TOF-MS m/z calcd for C60H38 [M + 1]+, 759.3046; found, 759.3043. Anal. calcd for C60H38: C, 94.95; H, 5.05; Found: C, 94.83; H, 5.17%.
1,3,5-Tris(9-(1-naphthyl)anthracen-10-yl)benzene (4c). A mixture of 9-(1-naphthyl)anthracene-10-boronic acid (4.5 g, 13 mmol), tetrakis(triphenylphosphine)palladium(0) (405 mg, 0.3 mmol), 1,3,5-tribromobenzene (0.91 g, 2.89 mmol), toluene (200 mL), ethanol (100 mL) and 2 M K2CO3(150 mL) were heated at 100 C for 12 h with magnetic stirring under nitrogen atmo-sphere. The reaction mixture was cooled to room temperature and the precipitated solid was isolated by filtration, washed with water, then recrystallized from dichloromethane–n-hexane to yield 2.5 g (87%) of the product. The yield is calculated according to aryl bromide.1H NMR (400 MHz, CDCl
3) d 8.35 (d, J¼ 8.8 Hz, 6H), 7.98–8.05 (m, 9H), 7.67–7.7 (m, 3H), 7.52– 7.57 (m, 9H), 7.43–7.47 (m, 9H),7.25–7.29 (m, 6H), 7.09–7.19 (m, 6H); 13C NMR (CDCl 3) d 139.57, 136.91, 135.67, 134.46, 134.31, 134.22, 133.91, 133.81, 130.99, 130.29, 129.43, 128.44, 128.38, 127.54, 127.11, 126.83, 126.54, 126.24, 125.83, 125.51; IR (KBr, cm1): 3058 (s), 1586 (s), 1506 (s), 1439 (s), 1363 (s), 1028 (s), 915 (s), 798 (s), 778 (s), 764 (s), 726 (s); MALDI-TOF-MS m/z calcd for C78H48[M]+, 984.3751, found 984.3761.
Anal. calcd for C78H48: C, 95.09; H, 4.91; Found: C, 95.02; H, 4.98%.
1,3,5-Tris(9-(2-naphthyl)anthracen-10-yl)benzene (4d). The compound was synthesized using a similar procedure to that for 4c. Yield 2.28 g (80%). The yield is calculated according to aryl bromide.1H NMR (400 MHz, CDCl 3) d 8.31 (d, J¼ 8.8 Hz, 6H), 7.99–8.07 (m, 6H), 7.89–7.96 (m, 9H), 7.72–7.74 (m, 6H), 7.53– 7.57 (m, 15H), 7.33–7.37 (m, 6H).13C NMR (CDCl 3) d 139.53, 137.57, 136.74, 136.69, 134.28, 133.62, 133.0, 130.46, 130.42, 130.25, 129.76, 128.34, 128.22, 128.13, 127.53, 127.06, 126.67, 126.47, 125.77, 125.41; IR (KBr, cm1): 3054 (s), 1627(s), 1583 (s), 1503 (s), 1437 (s), 1365 (s), 1027 (s), 924 (s), 818, 766(s), 744 (s), 726(s); MALDI-TOF-MS m/z calcd for C78H48[M + 1]+, 985.3748, found 985.3752. Anal. calcd for C78H48: C, 95.09; H, 4.91; Found: C, 95.01; H, 4.99%.
Acknowledgements
This work is supported by the central allocation grant from the Research Grants Council of Hong Kong SAR (GHP/057/05) and Faculty Research Grant (FRG/05-06/II-43) of HKBU.
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