A solution-processable bipolar molecular glass as a host material for
white electrophosphorescent devices
Chen-Han Chien,
aLiang-Rern Kung,
aChen-Hao Wu,
aChing-Fong Shu,*
aSheng-Yuan Chang
band
Yun Chi*
bReceived 11th March 2008, Accepted 16th May 2008
First published as an Advance Article on the web 16th June 2008 DOI: 10.1039/b804192j
A solution-processable bipolar material tBu-OXDTFA comprising an electron-rich triphenylamine core and electron-deficient oxadiazole/fluorene peripheries was synthesized. This dendrimer-like molecule not only possesses a high triplet energy (2.74 eV) but also exhibits excellent film-forming properties upon solution processing. We achieved highly efficient white electrophosphorescent OLEDs (22.3 cd A1, 11.6%) through solution processing, wherein the single white emitting layer was readily formed after spin-coating a solution of blue- and red-phosphor co-dopants containing tBu-OXDTFA as the host matrix.
Introduction
Organic light-emitting diodes (OLEDs) have attracted consid-erable interest because of their potential applications in flat-panel displays and in solid state lighting.1Phosphorescent emitters are considered to be superior to their fluorescent counterparts at improving the efficiency of electroluminescent (EL) devices; because they can harvest both singlet and triplet excitons, their internal quantum efficiencies can reach theoretical levels as high as 100%.2 In phosphorescent OLEDs, the triplet emitters are normally used as emitting guests in a host material to reduce the self-quenching associated with the relatively long excited state lifetimes of triplet emitters and triplet–triplet annihilation;3 consequently, the choice of host materials is of vital importance for the preparation of efficient phosphorescent OLEDs.
Presently, most electroluminescent devices are fabricated using vacuum deposition, which is a complicated and expensive manufacturing process. In contrast, solution processing methods, such as spin-coating and ink-jet printing, are relatively inexpensive and can be utilized for the preparation of large-area displays.4 Most studies have employed solution-processable polymeric host materials, such as poly(9-vinylcarbazole) and polyfluorenes, blended with phosphorescent emitters as the emitting layer (EML).5 Nevertheless, several issues—such as aggregation or phase separation of the phosphor in the macro-molecular matrix and the intrinsic difficulty in purifying the polymeric materials—can hamper the applicability of polymeric hosts.6
In this paper, we report the design and synthesis of a solution-processable, bipolar molecular glass, namely tBu-OXDTFA, for use as a host material in electrophosphorescent devices. As shown in Scheme 1, tBu-OXDTFA comprises a triphenylamine (TPA) core and fluorene/oxadiazole (OXD) peripheries. These individual building blocks each exhibit a high triplet energy
(ET> 2.9 eV)7and are connected through the sp3-hybridized C-9
atoms to effectively interrupt any extended p-conjugation. This structural feature endows tBu-OXDTFA with an adequately high
Scheme 1 Synthesis route to tBu-OXDTFA and chemical structures of Flrpic and Os(fppz).
aDepartment of Applied Chemistry, National Chiao Tung University,
Hsin-Chu, Taiwan 30050
bDepartment of Chemistry, National Tsing Hua University, 300 Hsinchu,
Taiwan
PAPER www.rsc.org/materials | Journal of Materials Chemistry
value of ET for efficient confinement of the triplet excitons
primarily on the guest, blue-emitting phosphors. In addition, the built-in bipolar functionalities, arising from the electron-rich TPA core and electron-deficient OXD pendent units, may facil-itate and balance the hole and electron injection and transport, respectively.8 Moreover, the three-dimensional, rigid, and asymmetric structure of tBu-OXDTFA hinders its close packing and suppresses its crystallizability, leading to an amorphous material exhibiting pronounced thermal stability. We prepared highly efficient white electrophosphorescent OLEDs (22.3 cd A1, 11.6%) through solution processing; the single white EML was formed simply through spin-coating of a solution of blue- and red-phosphor co-dopants containing tBu-OXDTFA as the host matrix.
Results and discussion
SynthesisScheme 1 illustrates the synthesis route followed for the prepa-ration of tBu-OXDTFA. The Grignard reaction of fluorenone with m-tolylmagnesium bromide gave the corresponding alcohol, 9-(m-tolyl)fluoren-9-ol (1), the tolyl group of which was then oxidized using KMnO4in H2O/pyridine to provide the
carbox-ylic acid 2. Subsequent Friedel–Crafts-type substitution of triphenylamine with 2 yielded compound 3. This reaction pro-ceeded through the initial formation of a transitory carbocation from the protonated 9-fluorenol group,9which in turn underwent electrophilic substitution exclusively at the electron-rich para carbon atom of the TPA phenyl group. The formation of the OXD moiety commenced from the acid 3 in a two-step protocol: the acylhydrazide and 3 were coupled under amide bond-forming conditions, followed by cyclodehydration mediated by CBr4and
Ph3P.10Finally, the oxadiazole 5 was subjected to another
Frie-del–Crafts reaction with 9-(4-tert-butylphenyl)-9-fluorenol (6)11 to afford the desired host material tBu-OXDTFA. The structure of tBu-OXDTFA was characterized using 1H and 13C NMR spectroscopy, elemental analysis, and high-resolution mass spectrometry.
Thermal properties
We used thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to investigate the thermal properties of tBu-OXDTFA (Fig. 1). TGA indicated that its 5 and 10%
weight losses occurred at 408 and 426 C, respectively. DSC revealed that tBu-OXDTFA exhibited an extremely high glass transition temperature of 207C with no detectable values of T
c
and Tmat temperatures up to 370C. This observation indicates
the prominent stability of the amorphous glass state of tBu-OXDTFA, which we attribute to the presence of its rigid fluorene and OXD peripheries and its high molecular weight. In addition, the presence of the propeller-like TPA core hinders close packing of tBu-OXDTFA, suppressing its crystallizability.12To investi-gate its morphology, we prepared thin films of tBu-OXDTFA through spin-coating from a chlorobenzene solution onto silicon wafers and imaged them using atomic force microscopy (AFM; Fig. 2). The surface topographies clearly revealed that the spin-coated films exhibited fairly smooth and pinhole-free surface morphologies, with a root-mean-square (RMS) surface rough-ness of 0.306 nm. For a spin-coated, white-emitting tBu-OXDTFA film doubly doped with 14 wt% FIrpic and 0.1 wt% Os(fppz),13we calculated the RMS surface roughness to be 0.359 nm; there was no phase separation or any aggregated domains. These results demonstrate that tBu-OXDTFA is capable of forming amorphous films through solution processing, with organometallic triplet emitters dispersed homogeneously.
Electrochemistry
We employed cyclic voltammetry (CV) to investigate the elec-trochemical behavior of tBu-OXDTFA, using ferrocene as the internal standard. During the anodic scan in CH2Cl2, a reversible
oxidative process occurred at 0.42 V (Eo0), originating from the oxidation of the electron-rich TPA core. Upon the cathodic sweep in THF, we detected a reversible reductive process at 2.60 V (Eo0), attributable to reduction of the peripheral elec-tron-deficient OXD units (Fig. 3). This reversible reductive and oxidative behavior indicates that tBu-OXDTFA can be utilized as both a hole and an electron transporter. Moreover, such pronounced electrochemical stability, which improves the life-time of electroluminescent devices, makes tBu-OXDTFA a desirable host material for use in light-emitting applications.
Photophysical properties
Fig. 4a displays the absorption and PL spectra of tBu-OXDTFA in various organic solvents. In CH2Cl2, the absorption spectrum
Fig. 1 TGA trace of tBu-OXDTFA recorded at a heating rate of 10C
min1. Inset: DSC measurement recorded at a heating rate of 10C min1.
Fig. 2 AFM topographic images (tapping mode) of (a) neat tBu-OXDTFA and (b) tBu-tBu-OXDTFA doped with 14 wt% FIrpic and 0.1 wt% Os(fppz). The films were prepared through spin-coating from chloro-benzene solutions onto silicon wafers.
of tBu-OXDTFA is almost a superimposed image of the absorptions of the fluorene-substituted TPA group and the OXD unit, suggesting that negligible interactions occur between the TPA and OXD moieties in the ground state. Furthermore, in all the solvents studied, the features in the absorption spectra were nearly identical and independent of the solvent polarity, indi-cating that the Franck–Condon excited state of tBu-OXDTFA was subject to a rather small dipolar change with respect to the ground state. In contrast, the PL spectra exhibit a strong dependence on the solvent polarity, with the emission band red-shifting significantly upon increasing the solvent polarity (Fig. 4b). We attribute this phenomenon to a mechanism involving a fast photoinduced electron transfer between the designed donor (TPA)–acceptor (OXD) pairs, leading to a large change in the dipole moment in the excited state; a subsequent solvent relaxation process results in the solvent polarity-depen-dent emission.14 To evaluate the potential of utilizing tBu-OXDTFA as a host material in phosphorescent OLEDs, we measured its phosphorescence spectrum in a frozen 2-methylte-trahydrofuran (2-MeTHF) matrix at 77 K (Fig. 4c). We used the highest-energy 0–0 phosphorescent emission, located at 2.74 eV, to calculate the ETgap of tBu-OXDTFA, giving a value higher
than that reported for the common triplet blue-emitter FIrpic (2.65 eV).15Accordingly, this value of E
Tis sufficiently high to
effectively confine the triplet excitons on the guest and prevent back energy transfer to the host molecules; thus, we expected that tBu-OXDTFA would serve as an appropriate host for short-wavelength dopants, such as FIrpic, as well as long-short-wavelength dopants.16
Electroluminescence properties of OLEDs
To assess the utility of this solution-processable compound as a host material in OLEDs, we fabricated a white light-emitting device having the configuration ITO/PEDOT (35 nm)/EML (60– 80 nm)/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI, 30 nm)/LiF (15 A˚ )/Al (100 nm). The EML—a tBu-OXDTFA film doped with blue-emitting FIrpic (14 wt%) and red-emitting Os(fppz) (0.1 wt%)—was prepared readily through spin-coating from a chlorobenzene solution consisting of the co-dopants and the host material. The TPBI layer was employed as an electron-transporting and hole-blocking layer. As illustrated in Fig. 5, the EL spectrum exhibits dual emissions—with equalized blue and red emission intensities—covering the whole visible region. The Commission Interationale d’Eclairage (CIE) chromaticity coor-dinates of the EL emission at a bias of 11 V were (0.37, 0.39), i.e., in the white light region and close to the equienergy white point. When we increased the driving voltage to 17 V, the CIE coor-dinates of the emission color remained almost constant and the EL spectrum barely changed. Fig. 6a presents the current density–voltage–luminance (I–V–L) curves of the tBu-OXDTFA-based device, which was turned on at 5.9 V (corresponding to 1 cd m2) and had a maximum brightness of 20 280 cd m2. As revealed in Fig. 6b, the maximum external quantum efficiency (max. hext) of this white-emitting device was 11.6% (953 cd m2,
4.27 mA cm2), and the corresponding luminance and power efficiencies were 22.3 cd A1and 5.0 lm W1. Even at brightnesses beyond 10 000 cd m2, 80% of the peak efficiency (9.2%) was sustained, along with a luminescence efficiency of 17.6 cd A1. We attribute this high performance to the presence of both electron-rich TPA and electron-deficient OXD units in tBu-OXDTFA, which may improve and balance charge injection and transport, leading to efficient charge recombination. Moreover, the short triplet excited lifetime of Os(fppz) (ca. 0.7 ms)13assists in this high performance because it prevents undesired T–T and P– T annihilation from occurring under high current densities.3
Fig. 4 (a) UV-Vis absorption and (b) PL spectra of tBu-OXDTFA in various organic solvents. (c) Normalized phosphorescence spectrum (77 K) of tBu-OXDTFA in 2-MeTHF.
Fig. 5 EL spectra of a tBu-OXDTFA-based device co-doped with 14 wt% FIrpic and 0.1 wt% red-emitting Os(fppz), recorded at various driving voltages.
Fig. 3 Cyclic voltammogram of tBu-OXDTFA recorded at a scanning rate of 50 mV s1.
Conclusions
In conclusion, we have synthesized and characterized a bipolar host material, tBu-OXDTFA, containing both hole- and elec-tron-transporting functionalities. This dendrimer-like structure exhibits not only a high triplet energy but also good film-forming properties for solution processing. We achieved highly efficient white electrophosphorescent OLEDs (22.3 cd A1, 11.6%) through solution processing, wherein the single white EML was readily formed after spin-coating a solution containing tBu-OXDTFA and two co-dopants [blue-emitting FIrpic and red-emitting Os(fppz)]. In this paper we demonstrate that utilizing a dendritic small molecule, tBu-OXDTFA, as a host co-doped with organometallic phosphors allows the ready fabrication of white electrophosphorescent OLEDs possessing simple device structures, yet exhibiting high efficiency and luminance.
Experimental
General directions
All chemicals were purchased from Aldrich, TCI, and Acros Organics and used without further purification. Column chro-matography was performed on silica gel (E. Merck Art. 7734 silica gel, 60 particle size, 70–230 mesh ASIM). NMR spectra were recorded on Varian UNITY INOVA 500 MHz, Varian Unity 300 MHz, and Bruker-DRX 300 MHz spectrometers. Chemical shifts are denoted on the scale in ppm, with reference to CDCl3or CD3COCD3. Mass spectra were obtained using JEOL
JMS-HX 110 and SX-102A mass spectrometers. Differential scanning calorimetry (DSC) was performed using a Seiko EXSTAR 6000 DSC unit operated at heating and cooling rates of 10 and 50 C min1, respectively. The glass transition temperatures (Tg) were determined from the second heating scan.
Thermogravimetric analysis (TGA) was undertaken using
a DuPont TGA 2950 instrument. The thermal stabilities of the samples under a nitrogen atmosphere were determined by measuring their weight losses while heating at a rate of 10C min1. UV-Vis spectra were measured using an HP 8453 diode-array spectrophotometer. PL spectra were obtained using a Hitachi F-4500 luminescence spectrometer. The low-tempera-ture phosphorescence spectrum was obtained using a composite spectrometer containing a monochromator (Jobin Yvon, Triax 190) coupled to a liquid nitrogen-cooled charge-coupled device (CCD) detector (Jobin Yvon, CCD-1024 256-open-1LS). Cyclic voltammetry (CV) measurements were performed using a BAS 100 B/W electrochemical analyzer; 0.1 M tetrabuty-lammonium hexafluorophosphate (TBAPF6) was the supporting
electrolyte. The potentials were measured against an Ag/Ag+ (0.01 M AgNO3) reference electrode with ferrocene as the
internal standard. Atomic force microscopy measurements were performed in the tapping mode under ambient conditions using a Digital Nanoscope IIIa instrument.
Device fabrication
PEDOT was spin-coated directly onto indium tin oxide (ITO) glass and dried at 80C for 12 h under vacuum to improve both the hole injection capability and the smoothness of the substrate. The light-emitting layer was spin-coated on top of the PEDOT layer using chlorobenzene as the solvent; the sample was then dried for 3 h at 60C in vacuo. Prior to film casting, the solution was filtered through a Teflon filter (0.45 mm). The TPBI layer, which was used as an electron-transporting layer that would also block holes and confine excitons, was grown through thermal sublimation in a vacuum of 3 106Torr. The cathode was completed through thermal deposition of LiF (15 A˚ )/Al (100 nm). The current– voltage–luminance relationships were measured under ambient conditions using a Keithley 2400 source meter and a Newport 1835C optical meter equipped with an 818 ST silicon photodiode. 9-(m-Tolyl)fluoren-9-ol (1)
3-Bromotoluene (5.0 mL, 41.2 mmol) was added dropwise over 2 min to a stirred mixture of Mg (1.34 g, 54.9 mmol) and dry ether (60 mL) at ambient temperature under nitrogen. The resulting mixture was gently heated for 3 h and then 9-fluorenone (4.95 g, 27.5 mmol) in dry THF (10 mL) was added dropwise over 5 min. The solution was then heated under reflux for 12 h. After cooling, aqueous NH4Cl solution was added and the
mixture was extracted with EtOAc. The organic extracts were washed with water and brine and then dried (MgSO4) The
solvent was removed under reduced pressure and the residue was purified through column chromatography (hexane–EtOAc, 10 : 1) to obtain 1 (7.17 g, 96%).1H NMR (300 MHz, CDCl 3): d 2.27 (s, 3 H), 7.01–7.03 (m, 1 H), 7.13 (dd, J¼ 3.9, 0.9 Hz, 2 H), 7.20– 7.26 (m, 3 H), 7.30–7.37 (m, 4 H), 7.65 (d, J¼ 7.5 Hz, 2 H).13C NMR (75 MHz, CDCl3): d 21.4, 83.4, 119.9, 122.4, 124.6, 125.8, 127.8, 127.9, 128.2, 128.8, 137.6, 139.4, 143.0, 150.4. HRMS (m/z): calcd for C20H16O 272.1201; found, 272.1202.
9-(3-Carboxyphenyl)fluoren-9-ol (2)
KMnO4(61.7 g, 0.31 mol) was added in four portions at intervals
of 12 h to a solution of 1 (7.10 g, 26.1 mmol), pyridine (160 mL),
Fig. 6 (a) Current density–voltage–luminance and (b) luminance efficiency–current density–external quantum efficiency plots of the tBu-OXDTFA-based device.
and water (16 mL) under reflux. After a total period of 48 h, the mixture was filtered and the solids washed with copious hot water. The filtrate was acidified with 12 N HCl and then extracted with EtOAc–Et2O (1 : 1). The organic extracts were
washed with water and brine and then dried (MgSO4). The
solvent was evaporated under reduced pressure and the residue was purified through column chromatography (hexane–Me2CO,
8 : 1) to afford 2 (7.88 g, 75%). 1H NMR (300 MHz, CD3COCD3): d 7.26–7.41 (m, 8 H), 7.61–7.64 (m, 1 H), 7.81 (d, J
¼ 7.5 Hz, 2 H), 7.94 (d, J ¼ 7.5 Hz, 1 H), 8.19 (s, 1 H).13C NMR (75 MHz, CD3COCD3): d 84.3,121.5,126.1,128.1,129.6,129.7,
129.73,130.3,131.5,131.8,141.1,147.0,152.5,168.4. HRMS (m/z): calcd for C20H14O3302.0943; found, 302.0937.
9-(3-Carboxyphenyl)-9-(4-diphenylaminophenyl)fluorene (3) CH3SO3H (40 mL, 660 mmol) was added dropwise under nitrogen
to a solution of 2 (200 mg, 660 mmol) and triphenylamine (240 mg, 990 mmol) in 1,4-dioxane (3 mL) at 100C and then the mixture was heated at that temperature for 1 h. After this period, the reaction mixture was cooled and diluted with CH2Cl2. The
CH2Cl2 solution was washed with saturated NaHCO3(aq) and
brine and then dried (MgSO4). Evaporation of the solvent
fol-lowed by silica gel chromatography (hexane–Me2CO, 3 : 1) gave
3 (250 mg, 70%).1H NMR (300 MHz, CD 3COCD3): d 6.92 (d, J ¼ 8.8 Hz, 2 H), 6.98–7.04 (m, 6 H), 7.13 (d, J ¼ 8.8 Hz, 2 H), 7.22–7.54 (m, 12 H), 7.90–7.94 (m, 4 H). 13C NMR (75 MHz, CD3COCD3): d 65.2, 120.8, 124.6, 124.7, 125.9, 127.7, 129.4, 129.5, 129.6, 130.1, 130.3, 130.5, 130.9, 132.2, 134.2, 140.8, 141.7, 148.2, 148.4, 149.2, 152.4, 168.2. HRMS (m/z): calcd. for C38H27NO2529.2042; found, 529.2047. 9-{3-[N0 -(4-tert-Butylbenzoyl)]-N-benzoylhydrazide}-9-(4-diphenylaminophenyl)fluorene (4)
N-Methylmorphine (0.57 mL, 5.15 mmol) and isobutyl-chloroformate (0.68 mL, 5.15 mmol) were added sequentially under nitrogen to a solution of 3 (2.48 g, 4.68 mmol) in THF (30 mL) at45C; a white suspension formed during the addi-tion of iBuOCOCl. The reacaddi-tion mixture was stirred for 45 min at 45C before 4-tert-butylbenzhydrazide (0.90 g, 4.68 mmol) was added. The resulting mixture was stirred at ambient temperature for an additional 3 h before being filtered through silica gel and washed with EtOAc. The solvent was evaporated under vacuum; column chromatography of the residue (SiO2; hexane–Me2CO, 2
: 1) provided 4 (2.04 g, 62%).1H NMR (300 MHz, CD 3COCD3): d1.35 (s, 9 H), 6.93 (d, J¼ 8.6 Hz, 2 H), 6.99–7.05 (m, 6 H), 7.13 (d, J¼ 8.6 Hz, 2 H), 7.20–7.32 (m, 7 H), 7.36–7.43 (m, 3 H), 7.49– 7.54 (m, 4 H), 7.887.99 (m, 6 H), 9.90 (br, 2 H).13C NMR (75 MHz, CD3COCD3): d 32.1, 36.1, 66.4, 121.9, 124.5, 124.54, 125.8, 126.8, 127.3, 127.7, 128.6, 128.9, 129.3, 129.4, 129.9, 130.4, 130.8, 131.3, 133.0, 134.4, 140.9, 141.5, 148.0, 148.3, 149.0, 152.3, 156.5, 167.5, 167.7. HRMS (m/z): calcd. for C49H41N3O2 703.3199; found, 703.3204. 9-(3-(5-(4-tert-Butylphenyl)-2-oxadiazoyl)phenyl)-9-(4-diphenylaminophenyl)-fluorene (5)
CBr4(66.0 mg, 190 mmol) and Ph3P (52.0 mg, 190 mmol) were
added under nitrogen in a single portion to a solution of 4
(70.0 mg, 90 mmol) in CH2Cl2(5 mL) at ambient temperature.
The mixture was heated under reflux for 6 h; after cooling, evaporation of the solvent and column chromatography of the residue (SiO2; hexane–Me2CO, 3 : 1) afforded 5 (42.4 mg, 62%).
1H NMR (300 MHz, CD 3COCD3): d 1.36 (s, 9 H), 6.91–7.0 (m, 4 H), 7.04–7.09 (m, 6 H), 7.19–7.42 (m, 10 H), 7.46 (d, J¼ 6.0 Hz, 2 H), 7.53 (d, J¼ 6.0 Hz, 2 H), 7.79 (d, J ¼ 6.0 Hz, 2 H), 7.93–7.97 (m, 1 H), 7.99 (d, J¼ 6.0 Hz, 2 H), 8.06 (s, 1 H).13C NMR (75 MHz, CD3COCD3): d 30.1, 35.1, 65.2, 120.8, 121.7, 123.4, 123.5, 124.5, 124.6, 125.4, 126.3, 126.5, 126.9, 128.3, 128.4, 129.3, 129.7, 131.7, 139.5, 140.5, 147.0 148.0, 148.1, 151.0 155.6, 164.4, 164.7. HRMS (m/z): calcd. for C49H39N3O 685.3093; found, 685.3101.
Anal. Calcd: C, 85.81; H, 5.73; N, 6.13. Found: C, 85.77; H, 5.77; N, 6.12%.
Preparation of tBu-OXDTFA
CH3SO3H (30 mL, 520 mmol) was added dropwise under nitrogen
to a mixture of 5 (170 mg, 260 mmol) and 6 (180 mg, 570 mmol) in CH2Cl2 (5 mL) at 50 C and then the resultant mixture was
heated at that temperature for 1 h. Upon cooling, the reaction mixture was diluted with CH2Cl2(20 mL), washed with saturated
NaHCO3solution and water, and then dried (MgSO4).
Evapo-ration of the solvent followed by column chromatography of the residue (SiO2; hexane–Me2CO, 3 : 1) gave tBu-OXDTFA (240
mg, 75%).1H NMR (500 MHz, CD 3COCD3): d 1.21 (s, 18 H), 1.34 (s, 9 H), 6.84–6.86 (m, 6 H), 7.03 (d, J¼ 8.5 Hz, 4 H), 7.06 (d, J¼ 8.5 Hz, 6 H), 7.22–7.25 (m, 8 H), 7.28–7.35 (m, 6 H), 7.38– 7.41 (m, 6 H), 7.44–7.49 (m, 4 H), 7.60 (d, J¼ 8.5 Hz, 2 H), 7.83 (d, J¼ 8.0 Hz, 4 H), 7.89 (d, J ¼ 8.0 Hz, 2 H), 7.95–7.98 (m, 4 H). 13C NMR (75 MHz, CD 3COCD3): d 30.8, 31.1, 34.3, 35.1, 64.2, 65.1, 120.5, 120.8, 121.6, 123.3, 124.0, 124.5, 125.4, 125.5, 126.1, 126.5, 126.8, 127.8, 127.9, 128.0, 128.2, 128.3, 129.1, 129.3, 129.7, 131.8, 139.3, 140.3, 140.4, 140.7, 143.3, 146.0, 146.5, 148.0, 149.4, 150.9, 151.6, 155.5, 164.4, 164.7. HRFAB MS (m/z): calcd. for C95H79N3O 1277.6223; found, 1277.6239. Anal. Calcd: C, 89.24;
H, 6.23; N, 3.29. Found: C, 88.78; H, 6.23; N, 3.37%.
Acknowledgements
This study was supported generously by the National Science Council, Republic of China.
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