angle between two phenyl rings linked to the nitrogen is 11°
for FATPA, while the angle is 54° for triphenylamine.14
These parameters indicate that the fully bridged tripheny-
lamine skeleton forms a more planar configuration compared
to the twisty triphenylamine structure.
transport ability. The LUMO energy level deduced from the
difference between the HOMO level and the optical band
gap is 1.62 eV.
Figure 2 shows the room-temperature absorption, fluores-
cence, and 77 K phosphorescence spectra of FATPA in
As shown in Figure 1, three p-tolyl groups are in axial
positions which act as three “desk-legs” to support the “desk
plane” (cyclic triphenylamine skeleton), while the other three
p-tolyl groups are in equatorial positions which splay out
around the “desk plane”. Such a rigid and sterically bulky
molecular configuration is very beneficial for the thermal
stability,15 as indicated by the high thermal decomposition
temperatures (Td, corresponding to 5% weight loss in the
thermogravimetric analysis) of 399 °C and a rather high
glass-transition temperature (Tg) of 178 °C determined
through differential scanning calorimetry (DSC). This value
is much higher than those of usual host materials, such as
4,4′-bis(9-carbazolyl)-2,2′-biphenyl (CBP, 62 °C) and 1,3-
bis(9-carbazolyl)benzene (mCP, 60 °C).16 As a consequence,
the novel compound can form morphologically stable and
uniform amorphous films, an essential property for OLEDs
upon thermal evaporation.17
The electrochemical property of FATPA is studied by
cyclic voltammetry, and the compound shows a reversible
oxidation process in CH2Cl2 solution. The HOMO energy
level determined from the onset of the oxidation is 5.22 eV
(relative to vacuum energy level), which is almost the same
with that of TPA (5.23 eV).18 This implies that the bridged
TPA derivative retains the low hole-injection and good
Figure 2. Absorption and emission spectra of FATPA in toluene
solution at room temperature and phosphorescence spectrum of
FATPA in toluene at 77 K.
toluene. FATPA exhibits a electronic absorption at 311 nm
and a emission peak at 375 nm. The triplet energy of FATPA
was determined to be 2.78 eV by the highest energy vibronic
subband of the phosphorescence spectra at 77 K. This value
is higher than that of usual host material CBP (2.56 eV),
and it may act as appropriate host material for green, red,
and even light blue phosphorescent emitters.
(3) (a) Adachi, C.; Kwong, R. C.; Djurovich, P.; Adamovich, V.; Baldo,
M. A.; Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett. 2001, 79, 2082.
(b) Holmes, R. J.; Forrest, S. R.; Tung, Y.-J.; Kwong, R. C.; Brown, J. J.;
Garon, S.; Thompson, M. E. Appl. Phys. Lett. 2003, 82, 2422. (c) Tokito,
S.; Iijima, T.; Suzuri, Y.; Kita, H.; Tsuzuki, T.; Sato, F. Appl. Phys. Lett.
2003, 83, 569. (d) Holmes, R. J.; D’Andrade, B. W.; Forrest, S. R.; Ren,
X.; Li, J.; Thompson, M. E. Appl. Phys. Lett. 2003, 83, 3818. (e) Ren, X.;
Li, J.; Holmes, R. J.; Djurovich, P. I.; Forrest, S. R.; Thompson, M. E.
Chem. Mater. 2004, 16, 4743.
To evaluate the performance of FATPA as host material,
the devices are fabricated with a typical structures consisting
of multiple organic layers sandwiched between the bottom
indium tin oxide (ITO) and the top metal cathode (Al). The
device configuration is ITO/MoO3 (10 nm)/NPB (80 nm)/
mCP (5 nm)/FATPA:Ir(ppy)3 (20 nm)/TAZ (40 nm)/LiF (1
nm)/Al (100 nm). 1,4-Bis[(1-naphthylphenyl)amino]biphenyl
(NPB) is used as the hole-transporting material; 1,3-bis(9-
carbazolyl)benzene (mCP) is used to confine excitons to the
emitting layer; 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphe-
nyl)-1,2,4-triazole (TAZ) is utilized as electron-transporting
as well as hole-block material; green-emitter iridium(III) fac-
tris(2-phenylpyridine) (Ir(ppy)3, ET ) 2.42 eV) doped in host
FATPA is used as the emitting layer, with optimized doping
levels of Ir(ppy)3 at 9%; MoO3 and LiF serve as hole- and
electron-injecting layers, respectively. Current-voltage-
luminance (J-V-L) characteristics and current efficiency
and power efficiency versus current density of the device
are shown in Figure 3. The device turns on at a rather low
voltage of 3.3 V. A maximum current efficiency of 83.5 cd/
A, equivalent to an external quantum efficiencies 23.4%, is
(4) Tsai, M.-H.; Lin, H.-W.; Su, H.-C.; Ke, T.-H.; Wu, C.; Fang, F.-C.;
Liao, Y.-Li.; Wong, K.-T.; Wu, C.-I. AdV. Mater. 2006, 18, 1216.
(5) (a) Inomata, H.; Goushi, K.; Masuko, T.; Konno, T.; Imai, T.; Sasabe,
H.; Brown, J. J.; Adachi, C. Chem. Mater. 2004, 16, 1285. (b) Yang, X.;
Mu¨ller, D. C.; Neher, D.; Meerholz, K. AdV. Mater. 2006, 18, 948. (c)
Leung, M.-K.; Yang, C-C.; Lee, J.-H.; Tsai, H.-H.; Lin, C.-F.; Huang, C-Y.;
Su, Y. O.; Chiu, C.-F. Org. Lett. 2007, 9, 235.
(6) Palmer, T. F.; Parmar, S. S. J. Photochem. 1985, 31, 273.
(7) Shih, P.-I.; Chien, C.-H.; Wu, F.-I.; Shu, C.-F. AdV. Funct. Mater.
2007, 17, 3514.
(8) Tao, Y.; Wang, Q.; Yang, C.; Ao, L.; Wang, Q.; Qin, J.; Ma, D.
Chem. Commun. 2009, 77.
(9) Shih, P.-I.; Chiang, C.-L.; Dixit, A. K.; Chen, C.-K.; Yuan, M-C.;
Lee, R.-Y.; Chen, C.-T.; Diau, E. W.-G.; Shu, C-F. Org. Lett. 2006, 8,
2799.
(10) (a) Hellwinkel, D.; Aulmich, G.; Melan, M. Chem. Ber. 1974, 107,
616. (b) Hellwinkel, D.; Schmidt, W. Chem. Ber. 1980, 113, 358.
(11) Fang, Z.; Teo, T.-L.; Cai, L.; Lai, Y.-H.; Samoc, A.; Samoc, M.
Org. Lett. 2009, 11, 1.
(12) Fox, J. L.; Chen, C. H.; Luss, H. R. J. Org. Chem. 1987, 52, 2980.
(13) Field, J. E.; Venkataraman, D. Chem. Mater. 2002, 14, 962.
(14) Sobolev, A. N.; Belsky, V. K.; Romm, I. P.; Chernikova, N. Yu.;
Guryanova, E. N. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1985,
41, 967.
(15) (a) Wong, K. T.; Chi, L. C.; Huang, S. C.; Liao, Y. L.; Liu, Y. H.;
Wang, Y. Org. Lett. 2006, 8, 5029. (b) Wong, K. T.; Chao, T.-C.; Chi,
L. C.; Chu, Y.-Y.; Balaiah, A.; Chiu, S.-F.; Liu, Y-H.; Wang, Y. Org. Lett.
2006, 8, 5033.
(17) Kinoshita, M.; Kita, H.; Shirota, Y. AdV. Funct. Mater. 2002, 12,
(16) Tsai, M. H.; Hong, Y. H.; Chang, C. H.; Su, H. C.; Wu, C. C.;
Matoliukstyte, A.; Simokaitiene, J.; Grigalevicius, S.; Grazulevicius, J. V.;
Hsu, C. P. AdV. Mater. 2007, 19, 862.
780.
(18) This value is evaluated by cyclic voltammetry; see Figure S5
(Supporting Information).
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